JP2023125497A - Method for manufacturing grain oriented electrical steel sheet - Google Patents

Abstract

To provide a method for manufacturing a grain oriented electrical steel sheet having a high magnetic flux density, capable of suppressing the formation of defective structure and ear cracking in an end portion in a sheet width direction.SOLUTION: A method for manufacturing a grain oriented electrical steel sheet includes: a hot-rolling step (S1) of setting an accumulative rolling reduction rate in a rough rolling step to less than 75%, setting a rolling reduction rate in the final rolling reduction in the rough rolling step to less than 50%, setting the temperature of a rough bar right after the final rolling reduction to 1,350°C or more, wherein intermediate time t1 from the completion of the final reduction against a back end of the slab in the rough rolling step to the completion of the first reduction against a back end of the rough bar in a finish rolling step is set to 150 seconds or less to satisfy the equation (1):-0.033 t1+44+2000[Bi]≤[Si]/[C]≤-0.033 t1+52+2000[Bi]; and a decarbonization annealing step (S4) of heating a steel sheet at the average temperature-rising rate of 800°C/sec or more until the temperature of the steel sheet reaches 550-800°C.SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing grain-oriented electrical steel sheets.

A grain-oriented electrical steel sheet is a steel sheet that contains approximately 0.5 to 7% Si by mass and has crystal orientations concentrated in the {110}<001> orientation (Goss orientation). Grain-oriented electrical steel sheets are used as soft magnetic materials for core materials in transformers and other electrical equipment. A catastrophic grain growth phenomenon called secondary recrystallization is used to control the crystal orientation of grain-oriented electrical steel sheets.

The method for producing grain-oriented electrical steel sheets is as follows. The slab is heated and hot rolled to produce a hot rolled steel plate. The manufactured hot rolled steel sheet is annealed. Pickle the hot-rolled steel plate if necessary. Cold rolling is performed on the hot rolled steel sheet at a cold rolling rate of 80% or more to produce a cold rolled steel sheet. Decarburization annealing is performed on cold-rolled steel sheets to develop primary recrystallization. Finish annealing is performed on the cold rolled steel sheet after decarburization annealing to develop secondary recrystallization. Through the above steps, a grain-oriented electrical steel sheet is manufactured.

Grain-oriented electrical steel sheets are required to have magnetic properties. Specifically, excellent excitation characteristics and excellent iron loss are required. For example, the magnetic flux density B8 at a magnetic field strength of 800 A/m is used as an index indicating the excitation characteristics. As an index indicating iron loss, iron loss W17/50 when magnetized to 1.7 T at 50 Hz is used.

As a method of increasing the above-mentioned magnetic flux density, it is known to improve the degree of integration in the Goss direction. The improvement in the degree of integration in the Goss orientation depends on the quality of secondary recrystallization during the final annealing process. In order to develop excellent secondary recrystallization, it is important to build in precipitates (inhibitors) before the final annealing step that causes secondary recrystallization to occur. By uniformly dispersing fine inhibitors in the steel sheet, it is possible to suppress the growth of crystal orientations other than the Goss orientation that are inferior in magnetic properties during secondary recrystallization.

When using MnS, MnSe, and AlN as inhibitors in the production of grain-oriented electrical steel sheets, a slab containing coarse MnS, MnSe, and AlN produced in the steelmaking process is heated to 1300°C or higher before hot rolling. , MnS, MnSe and AlN are completely dissolved in solid solution. Then, in the step of annealing a hot-rolled steel sheet produced by hot-rolling a heated slab, precipitation of these inhibitors is controlled and finely dispersed. Thereby, the growth of secondary recrystallization can be controlled.

Methods for controlling the growth of secondary recrystallization are disclosed in JP-A-4-124218 (Patent Document 1), JP-A-6-192736 (Patent Document 2), and JP-A-9-104924 (Patent Document 3). , and proposed in International Publication No. 2013/145784 (Patent Document 4).

Patent Document 1 aims to achieve both refinement of the structure of a hot rolled steel sheet and fine and uniform precipitation of an inhibitor. In Patent Document 1, the final pass of rough rolling in the hot rolling process is performed at a temperature ranging from 1200 to 1250°C from the outermost layer of the steel plate to a depth of 1/5 of the plate thickness, and at a rolling reduction rate of 50% or more. It is characterized by being carried out under certain conditions. However, in the case of Patent Document 1, since the rolling reduction ratio in the final pass of rough rolling is set to 50% or more, coarse MnS , MnSe may precipitate. In this case, secondary recrystallization in the final annealing process tends to become unstable, and as a result, secondary recrystallization occurs where Goss-oriented crystal grains have not grown sufficiently at both ends of the grain-oriented electrical steel sheet in the sheet width direction. Defective areas are more likely to occur. The crystal grains in the defective region of secondary recrystallization are much finer than the crystal grains in the normal region, and are composed of crystal grains different from Goss-oriented grains. Hereinafter, the defective region of secondary recrystallization that occurs at the end of the grain-oriented electrical steel sheet in the sheet width direction will be referred to as a "defective structure."

Similar to Patent Document 1, Patent Document 2 also aims to achieve both refinement of the structure of a hot rolled steel sheet and fine and uniform precipitation of an inhibitor. In Patent Document 2, the end temperature of the final pass of rough rolling in the hot rolling process is set at 1200°C or higher, the time from the end of rough rolling to the exit side of finish rolling is set at 150 seconds or less, and the temperature at the exit side of finish rolling is set at 1000°C or lower. , and is characterized in that the steel sheet is annealed before the final cold rolling to reduce the amount of carbon in the surface layer. However, in Patent Document 2 as well, the exit temperature of the final pass of rough rolling is set to be less than 1300° C. for the purpose of microstructural refinement of the hot rolled steel sheet. Therefore, between the completion of rough rolling and the start of finish rolling, coarse MnS and MnSe may precipitate due to the strain introduced in the rough rolling process. As a result, a defective structure is likely to be generated in the grain-oriented electrical steel sheet.

Similar to Patent Documents 1 and 2, Patent Document 3 also aims to achieve both refinement of the structure of a hot rolled steel sheet and fine and uniform precipitation of an inhibitor. Patent Document 3 is characterized in that the cumulative reduction ratio of the rough rolling is 75% or more, and the rough rolling is completed in a time corresponding to the slab heating temperature. However, in Patent Document 3, the cumulative reduction ratio of rough rolling is set to 75% or more for the purpose of microstructural refinement in a hot rolled steel sheet. Therefore, between the completion of rough rolling and the start of finish rolling, coarse MnS and MnSe may precipitate due to the strain introduced in the rough rolling process. When coarse MnS and MnSe are generated, secondary recrystallization in the finish rolling process becomes unstable. Therefore, defective structures are likely to be generated in grain-oriented electrical steel sheets.

Similar to Patent Documents 1 to 3, Patent Document 4 also aims to achieve both refinement of the structure of a hot rolled steel sheet and fine and uniform precipitation of an inhibitor. In Patent Document 4, the first pass of rough rolling of 30% or more is performed at an α single phase phase out temperature corresponding to the amounts of Si, C, and Ni, and the γ phase is maximized for at least one pass in the finish rolling process. It is characterized by rolling at high temperature. However, in Patent Document 4, in order to perform rolling at a high rolling reduction rate in the rough rolling process for the purpose of microstructural refinement of the hot rolled steel sheet, the rolling process is introduced in the rough rolling process between the completion of rough rolling and the start of finish rolling. There is a possibility that coarse MnS and MnSe will precipitate due to the strain induced. When coarse MnS and MnSe are generated, secondary recrystallization in the finish rolling process becomes unstable. Therefore, defective structures are likely to be generated in grain-oriented electrical steel sheets.

Japanese Unexamined Patent Publication No. 4-124218 Japanese Unexamined Patent Publication No. 6-192736 Japanese Patent Application Publication No. 9-104924 International Publication No. 2013/145784

When a defective structure occurs at the ends of a grain-oriented electrical steel sheet in the sheet width direction, sufficient magnetic properties cannot be obtained at the ends where the defective structure exists. Therefore, it is necessary to cut the end portion of the grain-oriented electrical steel sheet that has a defective structure, resulting in a decrease in product yield. Therefore, it is preferable to suppress the generation of defective structures while maintaining sufficient magnetic properties (magnetic flux density and iron loss) as a grain-oriented electrical steel sheet.

Furthermore, in the hot rolling process, cracks may occur in the width direction of the manufactured hot rolled steel sheet at the ends thereof in the sheet width direction. Hereinafter, cracks that extend in the width direction of a hot rolled steel sheet at the ends in the width direction of the sheet will be referred to as "edge cracks." When edge cracking occurs, it is necessary to cut the edge where the edge cracking occurs, which reduces product yield. Therefore, there is a need for a method for producing grain-oriented electrical steel sheets that can suppress defective structures and edge cracks at the edges in the width direction while maintaining sufficient magnetic properties (magnetic flux density and iron loss) for grain-oriented electrical steel sheets. It is being

An object of the present disclosure is to provide a method for manufacturing a grain-oriented electrical steel sheet that can obtain sufficient magnetic properties and suppress defective structures and edge cracks at the ends in the sheet width direction.

The method for manufacturing a grain-oriented electrical steel sheet according to the present disclosure includes:
The chemical composition is in mass%,
C: 0.060-0.100%,
Si: 3.00-4.00%,
Mn: 0.01 to 0.30%,
S and/or Se: 0.010 to 0.050% in total,
sol. Al: 0.01-0.05%,
N: 0.002-0.015%,
Bi: 0 to 0.0100%,
Sn: 0 to 0.50%,
Cr: 0 to 0.50%,
Cu: 0 to 0.50%, and
A hot rolling process of manufacturing a steel plate by hot rolling a slab with the remainder consisting of Fe and impurities;
a cold rolling step of performing cold rolling one or more times on the steel plate after the hot rolling step;
A final pre-cold rolling annealing step in which the steel plate before the final cold rolling is annealed among the one or more cold rollings;
A decarburization annealing step in which the steel plate after the cold rolling step is heated to a decarburization annealing temperature of 800 to 950° C., and a decarburization annealing is performed in which the steel plate is held at the decarburization annealing temperature;
an annealing separator application step of applying an annealing separator to the surface of the steel plate after the decarburization annealing step;
and a finish annealing step of performing finish annealing on the steel plate coated with the annealing separator,
The hot rolling process includes:
a rough rolling step of performing rough rolling on the slab to produce a rough bar;
a finish rolling step of performing finish rolling on the rough bar to produce the steel plate,
In the rough rolling process,
Performing rolling reduction on the slab multiple times,
The cumulative reduction rate in the rough rolling step is less than 75%,
The rolling reduction ratio in the final rolling of the rough rolling step is less than 50%,
The temperature of the rough bar immediately after the final rolling of the rough rolling step is 1350 ° C. or higher,
When the time from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process is defined as intermediate time t1. , the intermediate time t1 is set to 150 seconds or less, and formula (1) is satisfied;
In the decarburization annealing step,
The steel plate is heated at an average temperature increase rate of 800°C/sec or more until the temperature of the steel plate increases from 550°C to 800°C.
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
Here, the Bi content (mass%) in the chemical composition of the slab is substituted for [Bi] in formula (1), and the Si content (mass%) in the chemical composition of the slab is substituted for [Si]. % by mass), the C content (% by mass) in the chemical composition of the slab is substituted for [C], and the intermediate time t1 (seconds) is substituted for t1. If Bi is not contained, 0 is substituted for [Bi].

The method for manufacturing a grain-oriented electrical steel sheet according to the present disclosure can obtain sufficient magnetic properties and suppress defective structures and edge cracks at the ends in the width direction of the sheet.

FIG. 1 is a diagram showing the relationship between the temperature (°C) of a slab having the chemical composition of this embodiment and the volume fraction of austenite (%). FIG. 2 is a schematic diagram for explaining the occurrence of edge cracks during the hot rolling process. FIG. 3 is a flow diagram showing the manufacturing process of the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. FIG. 4 is a schematic diagram showing a hot rolling equipment line that implements the hot rolling process in FIG. 3. FIG. 5 is a schematic diagram showing a hot rolling equipment line different from FIG. 4. FIG. 6 is a flowchart showing details of the hot rolling process in FIG. 3. FIG. 7 is a schematic diagram showing a cold rolling equipment line that implements the cold rolling process in FIG. 3. FIG. 8 is a schematic diagram showing a heat pattern in the decarburization annealing step in FIG. 3. FIG. 9 is a schematic diagram showing the shape of the sample used in the defective tissue depth measurement test in the example.

The present inventors investigated and studied the cause of coarsening of MnS and MnSe (hereinafter, MnS and MnSe are also referred to as Mn inhibitors). Specifically, the chemical composition is, in mass%, C: 0.060 to 0.100%, Si: 3.00 to 4.00%, Mn: 0.01 to 0.30%, S and/or Se: 0.010 to 0.050% in total, sol. Al: 0.01-0.05%, N: 0.002-0.015%, Bi: 0-0.0100%, Sn: 0-0.50%, Cr: 0-0.50%, Cu : 0 to 0.50%, and the balance is Fe and impurities.When grain-oriented electrical steel sheets are manufactured from slabs, the cause of generation of coarse Mn inhibitors with a long axis length of 1 μm or more in hot rolled steel sheets. We conducted a survey regarding. As a result, the precipitation and growth of Mn inhibitors are affected by the cumulative reduction rate TR in the rough rolling process (condition A), the rolling reduction rate R1 in the final reduction in the rough rolling process (condition B), and the rough rolling process in the hot rolling process. The temperature T1 (condition C) of the rough bar immediately after the final rolling in the rolling process, and the temperature T1 (condition C) for the rear end of the rough bar in the finish rolling process after the final rolling of the slab at the rear end in the rough rolling process is completed. It has been found that four conditions are particularly affected: the time (intermediate time) t1 (condition D) until the first rolling is completed.

Therefore, based on the above findings, attempts were made to manufacture grain-oriented electrical steel sheets by setting conditions A to D to various conditions for the slab having the above chemical composition. As a result, it has been found that by satisfying the following conditions, defective structures at the ends of the grain-oriented electrical steel sheet in the sheet width direction can be significantly suppressed.
(Condition A) Cumulative rolling reduction TR in the rough rolling process: less than 75% (Condition B) Reduction rate R1 in the final rolling of the rough rolling process: less than 50% (Condition C) Immediately after the final rolling of the rough rolling process Temperature T1 of rough bar: 1350°C or higher (Condition D) After the final rolling of the rear end of the slab in the rough rolling process is completed, until the first rolling of the rear end of the rough bar is completed in the finishing rolling process. Time (intermediate time) t1: 150 seconds or less

However, it has been found that when a grain-oriented electrical steel sheet is manufactured by carrying out a hot rolling process that satisfies the above-mentioned conditions A to D, although the defective structure can be significantly suppressed, the magnetic flux density may deteriorate. Therefore, in order to investigate the cause of the deterioration of magnetic flux density, we investigated the microstructure of grain-oriented electrical steel sheets. As a result, a linear defective area (hereinafter referred to as a linear defective area) extending in the rolling direction was generated at the center position of the grain-oriented electrical steel sheet in the sheet width direction. As a result of investigating the cause of this linear defect area, the following reasons were considered.

When the hot rolling process is carried out under conditions that satisfy the above-mentioned conditions A to D, an α-fiber orientation group extending in the rolling direction may develop at the center position of the width of the hot-rolled steel sheet. Here, the α fiber orientation group means a crystal grain group in which the <110> axis of the crystal is along the rolling direction. The α fiber orientation group generated in the hot rolling process is a stable rolling orientation, and remains in the steel sheet after the cold rolling process. This α fiber orientation group deteriorates the primary recrystallized structure and suppresses the selective growth of the Goss orientation during secondary recrystallization in the final annealing process. As a result, it is thought that the α fiber orientation group remains in the grain-oriented electrical steel sheet as a linear defective region, the degree of integration in the Goss orientation decreases, and the magnetic properties (magnetic flux density) deteriorate.

Therefore, the present inventors further investigated a manufacturing method that can suppress the generation and development of the α-fiber orientation group even if the above-mentioned conditions A to D are implemented. As a result, in the decarburization annealing process after the cold rolling process, if the average temperature increase rate RR _550-800 from 550°C to 800°C is made significantly faster than before, it is possible to form α-fiber orientation groups in the hot-rolled steel sheet. It has been found that recrystallization from the α-fiber orientation group can be promoted even when . Specifically, it has been found that excellent magnetic flux density can be obtained by satisfying the following condition F in the decarburization annealing process.
(Condition F) Average temperature increase rate RR in decarburization annealing process _550-800 : 800°C/sec or more

Although the reason for this is not certain, the following reasons may be considered. By increasing the temperature increase rate from 550°C to 800°C in the decarburization annealing process, it is possible to promote recrystallization from the α-fiber orientation group in primary recrystallization, improving the selective growth of the Goss orientation. The number of recrystallized grains such as the Σ9-corresponding orientation ({411}<148>) increases. The Σ9-corresponding oriented grains enhance the selective growth of Goss oriented grains. Therefore, the degree of accumulation of Goss orientation increases in secondary recrystallization, and it is possible to suppress linear defective regions. As a result, it is thought that excellent magnetic properties can be obtained.

The present inventors further investigated the cause of edge cracks occurring in steel sheets during the hot rolling process. As a result, we obtained the following knowledge.

FIG. 1 is a diagram showing the relationship between temperature (° C.) and austenite volume fraction (%) of steel having the above-mentioned chemical composition. When performing a hot working step on a slab having the above-mentioned chemical composition, the slab is first heated to 1300 to 1400°C. At this time, referring to FIG. 1, the microstructure of the slab is almost a single ferrite phase. However, when rough rolling and finish rolling are performed in the hot rolling process, the temperature of the slab gradually decreases. The temperature of the slab at the start of finish rolling, especially the temperature at the end portions, can be about 1200°C. When the temperature of the slab decreases to 1200° C., the austenite in the slab microstructure may increase to as much as 40% by volume. That is, in the finish rolling process, rolling is performed in a two-phase region (ferrite and austenite).

FIG. 2 is a schematic diagram for explaining the occurrence of edge cracks during the hot rolling process. Referring to FIG. 2, during the hot rolling process, the microstructure of the slab transforms from a single phase of ferrite to two phases (ferrite + austenite). The solid solubility of S and Se in austenite is lower than that of S and Se in ferrite. Therefore, when austenite is generated due to transformation accompanying a temperature drop, S and Se in austenite 2 are expelled from the austenite grains to the interface between austenite 2 and ferrite 1, as shown in FIG. As a result, fine Mn inhibitors 3 (MnS and MnSe) are formed at the interface between austenite 2 and ferrite 1. The fine Mn inhibitors 3 formed at the interface between the austenite 2 and the ferrite 1 become a stress concentration source at the interface between the austenite 2 and the ferrite 1, and become the origin of voids 4. It is thought that the generated voids 4 grow and coalesce, leading to ear cracking.

Based on the above findings, the present inventors found that in order to suppress the occurrence of edge cracking, controlling the interface area between ferrite and austenite during finish rolling by controlling the precipitation frequency of fine Mn inhibitors will suppress edge cracking. considered to be effective. Specifically, in order to control the interface area between ferrite and austenite during finish rolling, Si, an element that strongly stabilizes ferrite (ferrite former), is an element that strongly stabilizes austenite (austenite former). By adjusting the ratio to C (=[Si]/[C]) according to the rough rolling conditions that are correlated with the precipitation frequency of fine Mn inhibitors, especially the intermediate time t1 from rough rolling to finish rolling. , we thought that it would be possible to suppress ear cracking.

Furthermore, when the slab contains Bi, the Bi in the slab also increases the frequency of precipitation of fine Mn inhibitors. In other words, Bi is an element that promotes edge cracking. Therefore, it was thought that edge cracking could be further suppressed by adjusting [Si]/[C] according to the Bi content along with the intermediate time t1.

Based on the above findings, the present inventors focused on the Si content, C content, and Bi content of the slab, and the intermediate time t1, and investigated and studied the relationship between the occurrence of edge cracking. As a result, in the hot rolling process, if the following condition E is satisfied, excellent magnetic properties can be obtained, and the formation of defective structures and edge cracks can be suppressed, assuming conditions A to D and F are satisfied. I found out that it is possible.
(Condition E) Formula (1) is satisfied in the hot rolling process.
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
Here, the Bi content (mass%) in the chemical composition of the slab is substituted for [Bi] in formula (1), and the Si content (mass%) in the chemical composition of the slab is substituted for [Si]. , the C content (mass %) in the chemical composition of the slab is substituted for [C], and the intermediate time t1 (seconds) is substituted for t1. If Bi is not contained, 0 is substituted for [Bi].

As described above, the present inventors have found that by implementing a manufacturing process that satisfies conditions A to F using a slab having the above-mentioned chemical composition, excellent magnetic properties can be obtained and defective structures can be suppressed. We have also found that it is possible to produce a grain-oriented electrical steel sheet that can suppress edge cracking.
(Condition A) Cumulative rolling reduction in the rough rolling process: Less than 75% (Condition B) Rolling reduction in the final rolling of the rough rolling process: Less than 50% (Condition C) Rough bar immediately after the final rolling of the rough rolling process Temperature: 1350°C or higher (Condition D) Intermediate time t1 from completion of the final rolling of the rear end of the slab in the rough rolling process to completion of the first rolling of the rear end of the rough bar in the finishing rolling process : 150 seconds or less (Condition E) Formula (1) is satisfied in the hot rolling process.
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
(Condition F) Average temperature increase rate RR in decarburization annealing process _550-800 : 800°C/sec or more

The gist of the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, which was completed based on the above findings, is as follows.

[1]
The chemical composition is in mass%,
C: 0.060-0.100%,
Si: 3.00-4.00%,
Mn: 0.01 to 0.30%,
S and/or Se: 0.010 to 0.050% in total,
sol. Al: 0.01-0.05%,
N: 0.002-0.015%,
Bi: 0 to 0.0100%,
Sn: 0 to 0.50%,
Cr: 0 to 0.50%,
Cu: 0 to 0.50%, and
A hot rolling process of manufacturing a steel plate by hot rolling a slab with the remainder consisting of Fe and impurities;
a cold rolling step of performing cold rolling one or more times on the steel plate after the hot rolling step;
A final pre-cold rolling annealing step in which the steel plate before the final cold rolling is annealed among the one or more cold rollings;
A decarburization annealing step in which the steel plate after the cold rolling step is heated to a decarburization annealing temperature of 800 to 950° C., and a decarburization annealing is performed in which the steel plate is held at the decarburization annealing temperature;
an annealing separator application step of applying an annealing separator to the surface of the steel plate after the decarburization annealing step;
and a finish annealing step of performing finish annealing on the steel plate coated with the annealing separator,
The hot rolling process includes:
a rough rolling step of performing rough rolling on the slab to produce a rough bar;
a finish rolling step of performing finish rolling on the rough bar to produce the steel plate,
In the rough rolling process,
Performing rolling reduction on the slab multiple times,
The cumulative reduction rate in the rough rolling step is less than 75%,
The rolling reduction ratio in the final rolling of the rough rolling step is less than 50%,
The temperature of the rough bar immediately after the final rolling of the rough rolling step is 1350 ° C. or higher,
When the time from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process is defined as intermediate time t1. , the intermediate time t1 is set to 150 seconds or less, and formula (1) is satisfied;
In the decarburization annealing step,
Heating the steel plate at an average temperature increase rate of 800°C/sec or more until the temperature of the steel plate increases from 550°C to 800°C.
A method for manufacturing grain-oriented electrical steel sheets.
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
Here, the Bi content (mass%) in the chemical composition of the slab is substituted for [Bi] in formula (1), and the Si content (mass%) in the chemical composition of the slab is substituted for [Si]. % by mass), the C content (% by mass) in the chemical composition of the slab is substituted for [C], and the intermediate time t1 (seconds) is substituted for t1. If Bi is not contained, 0 is substituted for [Bi].

[2]
The method for producing a grain-oriented electrical steel sheet according to [1],
The chemical composition of the slab is
Bi: 0.0001-0.0100%,
containing,
A method for manufacturing grain-oriented electrical steel sheets.

[3]
The method for producing a grain-oriented electrical steel sheet according to [1] or [2],
The chemical composition of the slab is
Sn: 0.01-0.50%,
Cr: 0.01 to 0.50%, and
Cu: 0.01 to 0.50%,
Containing one or more selected from the group consisting of
A method for manufacturing grain-oriented electrical steel sheets.

Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be described in detail. In addition, in this specification, % regarding the content of an element means mass % unless otherwise specified.

[Manufacturing process flow]
FIG. 3 is a flow diagram of a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. Referring to FIG. 3, this manufacturing method includes a hot rolling process (S1) in which a slab is hot rolled to produce a steel plate, and a steel plate (hot rolled steel plate) after the hot rolling process. A cold rolling process (S2) in which cold rolling is performed one or more times (S20), and a steel plate before the final cold rolling (S20) of one or more cold rolling (S20). A final pre-cold rolling annealing step (S3) in which annealing is performed on the steel sheet, and a decarburization annealing step (S4) in which decarburization annealing is performed on the steel plate (cold rolled steel sheet) after the cold rolling step (S2). , an annealing separator application step (S5) in which an annealing separator is applied to the surface of the steel sheet after the decarburization annealing step (S4), and a finish annealing step in which finish annealing is performed on the steel sheet coated with the annealing separator. (S6). Each step S1 to S6 will be explained below.

[Hot rolling process (S1)]
In the hot rolling step (S1), a prepared slab is hot rolled to produce a steel plate. The chemical composition of the slab contains the following elements:

[Essential elements in the chemical composition of the slab]
C: 0.060-0.100%
Carbon (C) is effective in controlling the structure during the manufacturing process until the decarburization annealing process is completed. If the C content is less than 0.060%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the C content exceeds 0.100%, the contents of other elements are within the range of this embodiment, and decarburization will be insufficient even if the decarburization annealing process described below is performed, resulting in magnetic aging. will happen. In this case, sufficient iron loss characteristics cannot be obtained.
Therefore, the C content is 0.060-0.100%.
The lower limit of the C content is preferably 0.065%, more preferably 0.070%. A preferable upper limit of the C content is 0.090%, more preferably 0.080%.

Si: 3.00-4.00%
Silicon (Si) increases the resistivity of grain-oriented electrical steel sheets and reduces eddy current loss among iron losses. If the Si content is less than 3.00%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the Si content exceeds 4.00%, the cold workability of the steel will decrease even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Si content is 3.00-4.00%.
The lower limit of the Si content is preferably 3.10%, more preferably 3.20%, and still more preferably 3.30%.
A preferable upper limit of the Si content is 3.90%, more preferably 3.80%, and still more preferably 3.70%.

Mn: 0.01-0.30%
Manganese (Mn) increases the resistivity of grain-oriented electrical steel sheets and reduces core loss. Mn further improves hot workability and suppresses the occurrence of cracks during hot rolling. Mn further combines with S and/or Se to form fine MnS and/or fine MnSe in the hot rolling process. Fine MnS and fine MnSe become precipitation nuclei of fine AlN used as an inhibitor. Therefore, if a large amount of fine MnS and fine MnSe are precipitated in the hot rolling process, a sufficient amount of fine AlN can be obtained in the final pre-cold rolling annealing process. If the Mn content is less than 0.01%, the above effects cannot be sufficiently obtained.
On the other hand, if the Mn content exceeds 0.30%, the magnetic flux density of the grain-oriented electrical steel sheet will decrease even if the contents of other elements are within the range of this embodiment.
Therefore, the Mn content is 0.01-0.30%.
The lower limit of the Mn content is preferably 0.02%, more preferably 0.03%.
A preferable upper limit of the Mn content is 0.20%, more preferably 0.15%.

S and/or Se: 0.010 to 0.050% in total
Sulfur (S) and selenium (Se) combine with Mn during the hot rolling process to form the above-mentioned fine MnS and/or fine MnSe. As described above, fine MnS and fine MnSe serve as precipitation nuclei of fine AlN used as an inhibitor. Therefore, in the hot rolling process, if the amount of fine MnS and fine MnSe precipitated is large, a sufficient amount of fine AlN can be obtained. If the total content of S and/or Se is less than 0.010%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment.
On the other hand, if the total content of S and/or Se exceeds 0.050%, even if the content of other elements is within the range of this embodiment, MnS and/or MnSe will be present in the steel sheet after the final annealing process. may remain. In this case, the magnetic properties deteriorate.
Therefore, the total content of S and/or Se is 0.010 to 0.050%.
A preferable lower limit of the total content of S and/or Se is 0.012%, more preferably 0.014%.
A preferable upper limit of the total content of S and/or Se is 0.040%, more preferably 0.030%.

sol. Al: 0.01~0.05%
During the manufacturing process of grain-oriented electrical steel sheets, aluminum (Al) combines with N to form AlN and functions as an inhibitor. sol. If the Al content is less than 0.01%, even if the contents of other elements are within the range of this embodiment, a sufficient amount of AlN to function as an inhibitor cannot be obtained.
On the other hand, sol. If the Al content exceeds 0.05%, even if the contents of other elements are within the ranges of this embodiment, the function as an inhibitor will be excessive and good secondary recrystallization will not occur.
Therefore, sol. Al content is 0.01-0.05%.
sol. A preferable lower limit of the Al content is 0.02%. sol. A preferable upper limit of the Al content is 0.04.
In addition, in this specification, sol. Al content means the content of acid-soluble Al.

N: 0.002-0.015%
During the manufacturing process of grain-oriented electrical steel sheets, nitrogen (N) combines with Al to form AlN and functions as an inhibitor. In order to reduce the N content to less than 0.002%, excessive refining is required in the steel manufacturing process, which increases manufacturing costs. Therefore, the lower limit of N content is 0.002%.
On the other hand, if the N content in the steel material exceeds 0.015%, even if the content of other elements is within the range of this embodiment, many blisters (holes) are likely to be generated in the steel sheet during cold rolling. Become.
Therefore, the N content is 0.002-0.015%.
The lower limit of the N content is preferably 0.004%, more preferably 0.006%. A preferable upper limit of the N content is 0.012%, more preferably 0.010%.

The remainder of the chemical composition of the slab according to this embodiment consists of Fe and impurities. Here, impurities are those that are mixed in from ores as raw materials, scraps, or the manufacturing environment when industrially manufacturing slabs, which are the raw materials for grain-oriented electrical steel sheets. It means what is permissible within a range that does not adversely affect the grain-oriented electrical steel sheet manufactured by the manufacturing method.

[Arbitrary elements in the chemical composition of the slab]
The chemical composition of the slab described above may contain one or more selected from the group consisting of Bi, Sn, Cr, and Cu in place of a part of Fe.

Bi: 0~0.0100%
Bismuth (Bi) is an optional element and may not be included. That is, the Bi content may be 0%.
When included, Bi stabilizes MnS and MnSe, enhancing their function as inhibitors. If even a small amount of Bi is contained, the above effects can be obtained to some extent.
However, if the Bi content exceeds 0.0100%, the adhesion of the primary coating formed on the steel sheet will decrease even if the contents of other elements are within the ranges of this embodiment. If the Bi content exceeds 0.0100%, edge cracking becomes even more likely to occur.
Therefore, the Bi content is 0 to 0.0100%.
The preferable lower limit of the Bi content in order to more effectively obtain the above effects is 0.0001%, more preferably 0.0003%, still more preferably 0.0005%, and even more preferably 0.0007%. and more preferably 0.0010%.
A preferable upper limit of the Bi content is 0.0070%, more preferably 0.0050%, and even more preferably 0.0040%.

Sn: 0-0.50%
Tin (Sn) is an optional element and may not be included. That is, the Sn content may be 0%.
When contained, Sn increases the density of the oxide layer produced during the decarburization annealing process. As a result, the properties of the primary coating produced using this oxide layer during the final annealing process are also improved. Furthermore, Sn improves the magnetic properties of the grain-oriented electrical steel sheet by stabilizing the formation of the oxide layer and the primary coating, thereby suppressing variations in the magnetic properties. Furthermore, Sn is a grain boundary segregation element and stabilizes secondary recrystallization. If even a small amount of Sn is contained, the above effects can be obtained to some extent.
However, if the Sn content exceeds 0.50%, the surface of the steel sheet becomes difficult to oxidize, and the formation of the primary film may become insufficient.
Therefore, the Sn content is 0 to 0.50%.
The preferable lower limit of the Sn content in order to more effectively obtain the above effects is 0.01%, and more preferably 0.02%.
A preferable upper limit of the Sn content is 0.30%, more preferably 0.20%.

Cr: 0-0.50%
Chromium (Cr) is an optional element and may not be included. That is, the Cr content may be 0%.
When contained, Cr improves the properties of the oxide layer produced during the decarburization annealing process, and also improves the properties of the primary coating produced using this oxide layer during the final annealing process. Furthermore, Cr improves the magnetic properties of the grain-oriented electrical steel sheet by stabilizing the formation of the oxide layer and the primary coating, thereby suppressing variations in the magnetic properties. If even a small amount of Cr is contained, the above effects can be obtained to some extent.
However, if the Cr content exceeds 0.50%, the formation of the primary film may become unstable even if the contents of other elements are within the range of this embodiment.
Therefore, the Cr content is between 0 and 0.50%.
A preferable lower limit of the Cr content in order to more effectively obtain the above effects is 0.01%, more preferably 0.02%.
The upper limit of the Cr content is preferably 0.20%, more preferably 0.15%.

Cu: 0-0.50%
Copper (Cu) is an optional element and may not be included. That is, the Cu content may be 0%.
When contained, Cu promotes the precipitation of fine MnS that becomes AlN generation nuclei in the hot rolling process. If even a small amount of Cu is contained, the above effects can be obtained to some extent.
However, if the Cu content exceeds 0.50%, CuS precipitates may precipitate and remain even after final annealing even if the contents of other elements are within the range of this embodiment. arise. If CuS precipitates remain in the steel, the magnetic properties of the grain-oriented electrical steel sheet will deteriorate.
Therefore, the Cu content is 0-0.50%.
The lower limit of the Cu content is preferably 0.01%, more preferably 0.03%, and still more preferably 0.05% in order to more effectively obtain the above effects.
A preferable upper limit of the Cu content is 0.40%, more preferably 0.30%.

[Method for producing a slab having the above chemical composition]
An example of a method for manufacturing a slab having the above chemical composition is as follows. Molten steel having the above chemical composition is manufactured (molten). Slabs are manufactured by continuous casting using molten steel.

[Hot rolling process using the above slab]
The prepared slab having the chemical composition described above is hot rolled using a hot rolling mill to produce a steel plate (hot rolled steel plate). In this embodiment, the hot rolling process is an important process. Details will be explained below.

FIG. 4 is a schematic diagram showing a hot rolling equipment line including a row of hot rolling mills that performs a hot rolling process. Referring to FIG. 4, the hot rolling equipment line 1 includes a rough rolling mill RM and a finishing rolling mill FM in order from upstream to downstream. The rough rolling mill RM and the finishing rolling mill FM are arranged on the pass line PL. Here, the pass line PL means a virtual line through which the slab (and the steel plate during hot rolling) passes.

The rough rolling mill RM includes one rough rolling stand RMS arranged on the pass line PL or a plurality of rough rolling stands RMS arranged in a line on the pass line PL. In FIG. 4, the rough rolling mill RM includes one rough rolling stand RMS. However, as shown in FIG. 5, the rough rolling mill RM may include a plurality of rough rolling stands RMS ₁ to RMS _m (m is a natural number of 2 or more). Each rough rolling stand RMS includes a plurality of work rolls arranged one above the other. When there is one rough rolling stand RMS in the rough rolling mill RM, the rough rolling stand RMS is a reverse type rolling mill. When a plurality of rough rolling stands RMS in the rough rolling mill RM are arranged, the rough rolling stands RMS may be of a reverse type or a tandem type.

The finish rolling mill FM includes a plurality of finish rolling stands FMS ₁ to FMS _n (n is a natural number of 2 or more) arranged in a line on the pass line PL. Among the plurality of finishing rolling stands FMS ₁ to FMS _n , the finishing rolling stand FMS ₁ is arranged at the most upstream of the hot rolling equipment line 1, and the finishing rolling stand FMS _n is arranged at the most downstream of the hot rolling equipment line 1. Ru. Each finishing rolling stand FMS includes a plurality of work rolls arranged one above the other. Finish rolling mill FM including a plurality of finish rolling stands FMS ₁ to FMS _n is of a tandem type.

FIG. 6 is a flowchart showing details of the hot rolling step (S1) shown in FIG. 3. Referring to FIG. 6, the hot rolling process (S1) includes a heating process (S11), a rough rolling process (S12) using a rough rolling mill RM, and a finishing rolling process (S13) using a finishing rolling machine FM. ). Each step will be explained below.

[Heating step (S11)]
In the heating step (S11), the slab is heated. For example, the slab is placed in a well-known heating furnace or a well-known soaking furnace and heated. The preferred heating temperature for the slab is 1300-1400°C. A preferable lower limit of the heating temperature is 1320°C.

[Rough rolling process (S12)]
In the rough rolling step (S12), the heated slab is rough rolled to produce a rough bar. Here, rough rolling means hot rolling a slab using a rough rolling mill RM. The rough bar means a steel plate after completion of rough rolling and before start of finish rolling. In the rough rolling process, a rough rolling mill RM is used to apply rolling to the slab multiple times to produce a rough bar. Here, when a rolling reduction is applied to the slab when it passes through one rough rolling stand RMS, it means that one rolling reduction is applied. In the case of reverse rolling, one rolling reduction is applied to the slab as it passes through the rough rolling stand RMS from upstream to downstream. Also, when the slab passes through the same rough rolling stand RMS from downstream to upstream, one rolling reduction is applied to the slab. Note that when the slab passes through the rough rolling stand RMS, there are cases where no reduction is applied to the slab.

As described above, in the rough rolling step, the slab is subjected to multiple rolling reductions to produce a rough bar. At this time, the cumulative rolling reduction TR in the rough rolling step, the rolling reduction R1 in the final rolling, and the temperature T1 of the rough bar immediately after the final rolling are as follows.
(Condition A) Cumulative rolling reduction TR in the rough rolling process: less than 75% (Condition B) Reduction rate R1 in the final rolling of the rough rolling process: less than 50% (Condition C) Immediately after the final rolling of the rough rolling process Rough bar temperature T1: 1350℃ or more

[(Condition A) Regarding the cumulative reduction rate TR in the rough rolling process]
In this embodiment, the cumulative rolling reduction ratio TR in the rough rolling process is less than 75%. If the cumulative reduction ratio TR in the rough rolling process is 75% or more, excessive strain will be accumulated in the rough bar. Excessive strain induces precipitation of MnS and/or MnSe. If the cumulative rolling reduction ratio TR is 75% or more, excessive strain has been introduced into the rough bar. Therefore, after the completion of the rough rolling process and until the rear end of the rough bar receives the first rolling in the finish rolling process, in other words, the rough rolling stand RMS where the rear end of the slab is undergoing the final rolling is After passing through and before the rear end of the rough bar passes through the first finishing rolling stand FMS ₁ , MnS and/or MnSe precipitates, grows and coarsens.

If the cumulative reduction ratio TR in the rough rolling step is less than 75%, it is possible to suppress excessive strain from being accumulated in the rough bar. Therefore, on the premise that conditions B, C and condition D described below are satisfied, it is possible to suppress the generation of coarse MnS and/or MnSe in the rough bar after the rough rolling process. A preferable upper limit of the cumulative reduction ratio TR in the rough rolling step is 74%, more preferably 73%, still more preferably 72%, and still more preferably 71%. The lower limit of the cumulative rolling reduction TR in the rough rolling process is not particularly limited, but is, for example, 55%, more preferably 60%.

[(Condition B) Regarding the rolling reduction ratio R1 in the final rolling of the rough rolling process]
In this embodiment, the rolling reduction ratio R1 in the final rolling of the rough rolling process is less than 50%. Here, the rolling reduction ratio R1 in the final rolling is defined as follows.
Reduction rate R1 at final reduction = (1-thickness of rough bar/thickness of slab before final reduction) x 100

The plate thickness of the slab before the final rolling is, for example, when rolling is performed m times (m is a natural number of 2 or more) to produce a rough bar in the rough rolling process, the thickness of the slab before the final rolling is completed. The thickness of the subsequent slab corresponds to the "thickness of the slab before final rolling."

Also when the final rolling reduction R1 is 50% or more, excessive strain is accumulated in the rough bar. As mentioned above, excessive strain induces precipitation of MnS and/or MnSe. Therefore, if the rolling reduction ratio R1 in the final rolling is 50% or more, the period after the completion of the rough rolling process and until the rear end of the rough bar receives the first rolling in the finish rolling process, that is, the slab MnS and/or MnSe precipitates between the time when the rear end of the rough bar passes through the rough rolling stand RMS 1, which is performing the final rolling, and the time when the rear end of the rough bar passes through the first finishing rolling stand FMS ₁ . It grows and becomes coarser.

If the reduction ratio R1 at the final reduction in the rough rolling step is less than 50%, it is possible to suppress excessive strain from being accumulated in the rough bar. Therefore, on the premise that conditions A, C, and D are satisfied, generation of coarse MnS and/or MnSe in the rough bar after the rough rolling process can be suppressed. The preferable upper limit of the rolling reduction ratio R1 in the final rolling of the rough rolling process is 49%, more preferably 48%, still more preferably 47%, still more preferably 46%, still more preferably 45%. It is. The lower limit of the rolling reduction R1 in the final rolling of the rough rolling process is not particularly limited, but is, for example, 20%, more preferably 25%.

[(Condition C) Regarding the temperature T1 of the rough bar immediately after the final rolling of the rough rolling process]
In this embodiment, the temperature T1 of the rough bar immediately after the final rolling of the rough rolling step is 1350° C. or higher. Here, "the temperature of the rough bar immediately after the final rolling of the rough rolling process" means the temperature of the rough bar immediately after the rough rolling is completed, and more specifically, it refers to the rear end of the slab (the temperature of the rough bar immediately after the final rolling of the rough rolling process). The temperature at the center of the width and center of the thickness of the rough bar in the longitudinal direction from the tip to the rear end of the rough bar, immediately after the rough bar (corresponding to the rear end) passes through the rough rolling stand RMS where the final rolling is performed. means the average value of Hereinafter, the temperature at the center position of the plate width and the center position of the plate thickness of the rough bar will be simply referred to as the "plate thickness center temperature." The temperature at the center of the plate thickness of the rough bar may be measured by inserting a thermocouple at the center position of the plate width and the center position of the plate thickness of the rough bar. The plate thickness center temperature of the rough bar may be determined by heat transfer calculation from the surface temperature of the steel plate measured with a thermometer installed on the exit side of the rough rolling stand RMS that performs the final reduction in the rough rolling process. The thermometer is, for example, a radiation thermometer.

If the temperature T1 of the rough bar immediately after the final rolling in the rough rolling process is less than 1350°C, the temperature T1 after the rough rolling process is completed and before the rear end of the rough bar receives the first rolling in the finish rolling process. During this time, the temperature of the rough bar is reduced to a temperature range that promotes the formation of MnS and MnSe. In this case, MnS and MnSe precipitate, grow, and coarsen before the first reduction of the finish rolling process is applied over the entire length of the rough bar.

If the temperature T1 of the rough bar immediately after the final rolling in the rough rolling process is 1350°C or higher, the temperature T1 after the rough rolling process is completed and before the rear end of the rough bar receives the first rolling in the finish rolling process. During this time, the temperature of the rough bar can be prevented from decreasing to a temperature range that promotes the production of MnS and MnSe. Therefore, on the premise that conditions A, B, and D are satisfied, precipitation of MnS and MnSe can be suppressed before the first reduction in the finish rolling step is applied over the entire length of the rough bar. A preferable lower limit of the temperature T1 of the rough bar immediately after the final rolling of the rough rolling step is 1355°C, more preferably 1360°C, and still more preferably 1370°C. A preferable upper limit of the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step is 1400°C.

[Finish rolling process (S13)]
In the finish rolling step (S13), finish rolling is performed on the rough bar produced in the rough rolling step (S12) to produce a steel plate (hot rolled steel plate). Here, finish rolling means hot rolling a rough bar using a finish rolling mill FM. In the finish rolling process, a plurality of tandem finish rolling stands FMS ₁ to FMS _n arranged in a row on the pass line PL are used to apply rolling to the rough bar multiple times to produce a hot rolled steel sheet. . In the finishing rolling process, the rough bar passes through each finishing rolling stand FMS from upstream to downstream of each finishing rolling stand FMS, and when the rough bar passes through each finishing rolling stand FMS, the workpiece of each finishing rolling stand FMS Receives pressure from the roll. Note that among the plurality of finish rolling stands FMS, there may be a finish rolling stand FMS that does not apply rolling.

As described above, in finish rolling (S13), the rough bar is rolled down multiple times to produce a steel plate (hot rolled steel plate). Here, the time t1 from the completion of the final rolling of the rear end of the slab in the rough rolling process (S12) to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process (S13), that is, , the time t1 from when the rear end (bottom) of the slab passes through the rough rolling stand RMS that performs the final rolling until the rear end (bottom) of the rough bar passes through the first finishing rolling stand FMS ₁ . , defined as "intermediate time" t1. At this time, the intermediate time t1 is made to satisfy the following conditions D and E.
(Condition D) Intermediate time t1: 150 seconds or less (Condition E) -0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
Here, the Bi content (mass%) in the chemical composition of the slab is substituted for [Bi] in formula (1), and the Si content (mass%) in the chemical composition of the slab is substituted for [Si]. The C content (mass %) in the chemical composition of the slab is substituted for [C], and the intermediate time t1 (seconds) is substituted for t1. If Bi is not contained, 0 is substituted for [Bi].

[(Condition D) Regarding intermediate time t1]
If the intermediate time t1 exceeds 150 seconds, even if the rough rolling process satisfies conditions A to C, the temperature of the rough bar will fall to a temperature range that promotes the formation of Mn inhibitor during the intermediate time t1. Therefore, Mn inhibitors (MnS, MnSe) precipitate in the coarse bars during the intermediate time t1, and they grow and become coarse.

If the intermediate time t1 is 150 seconds or less, on the premise that the rough rolling process satisfies conditions A to C, the entire length of the rough bar is rolled before the temperature of the rough bar decreases to the temperature range that promotes the formation of Mn inhibitor. , finish rolling can be started. In this case, the production of Mn inhibitor during the intermediate time t1 can be suppressed. As a result, coarse Mn inhibitors with a major axis length of 1 μm or more can be suppressed in the steel plate after finish rolling (hot rolled steel plate), and coarse Mn inhibitors with a major axis length of less than 1 μm can be suppressed in the steel plate (hot rolled steel plate). fine Mn inhibitors can be dispersed. A preferable upper limit of the intermediate time t1 is 145 seconds, more preferably 140 seconds, still more preferably 135 seconds, still more preferably 130 seconds, and still more preferably 125 seconds. It is preferable that the intermediate time t1 be as short as possible. The lower limit of the intermediate time t1 is not particularly limited. The lower limit of the intermediate time t1 may be 0 seconds, 1 second, or 3 seconds.

[(Condition E) Regarding formula (1)]
The intermediate time t1 further satisfies equation (1).
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
Here, the Bi content (mass%) in the chemical composition of the slab is substituted for [Bi] in formula (1), and the Si content (mass%) in the chemical composition of the slab is substituted for [Si]. The C content (mass %) in the chemical composition of the slab is substituted for [C], and the intermediate time t1 (seconds) is substituted for t1. If Bi is not contained, 0 is substituted for [Bi].

As mentioned above, in the slab having the chemical composition of this embodiment, if a large number of fine Mn inhibitors precipitate at the interface between ferrite and austenite, cracks are likely to occur at the interface between ferrite and austenite, and as a result, edge cracks occur. Likely to happen. Therefore, in order to suppress the occurrence of edge cracking, it is effective to control the phase interface between ferrite and austenite in accordance with the frequency of precipitation of fine Mn inhibitors. Specifically, it is effective to suppress the transformation from ferrite to austenite as much as possible during hot rolling. Among the elements in the chemical composition of the slab, Si is a strong ferrite former and C is a strong austenite former. Therefore, increasing [Si]/[C] makes it easier to suppress the interface area between ferrite and austenite during hot rolling. On the other hand, although Bi can stabilize secondary recrystallization and improve magnetic properties even if the Si content is increased, it has the characteristic that it promotes the formation of fine Mn inhibitors during hot rolling. In other words, the Bi content is correlated with the frequency of precipitation of fine Mn inhibitors. Furthermore, the intermediate time t1 from rough rolling to finish rolling is also correlated with the frequency of precipitation of fine Mn inhibitors. Therefore, by adjusting [Si]/[C] according to the Bi content and the intermediate time t1, the occurrence of edge cracking can be sufficiently suppressed. Specifically, in the manufacturing method of this embodiment, formula (1) is satisfied in the hot rolling process.
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)

Define F1=-0.033t1+44+2000[Bi]. If [Si]/[C] is less than F1, the phase interface between ferrite and austenite on which fine Mn inhibitors are precipitated increases in the finish rolling process, and voids are likely to occur. As a result, ear cracks are more likely to occur.

Define F2=-0.033t1+52+2000[Bi]. If [Si]/[C] exceeds F2, although the occurrence of edge cracking can be suppressed, secondary recrystallization is not stabilized. In this case, the magnetic properties deteriorate.

If [Si]/[C] is greater than or equal to F1 and less than or equal to F2, that is, if [Si]/[C] satisfies formula (1), then other conditions A to D and F are satisfied. Assuming this, it is possible to obtain excellent magnetic properties and to suppress defective structures and edge cracks. A preferable lower limit of [Si]/[C] is -0.033t1+45+2000[Bi], more preferably -0.033t1+46+2000[Bi]. The preferable upper limit of [Si]/[C] is -0.033t1+51+2000[Bi], and more preferably -0.033t1+50+2000[Bi].

Note that F1, [Si]/[C], and F2 are all values up to the third decimal place. That is, F1, [Si]/[C], and F2 are values up to the third decimal place obtained by rounding off the fourth decimal place.

A hot rolled steel plate is manufactured by the above hot rolling process (S1). In the method for producing a grain-oriented electrical steel sheet according to the present embodiment, by performing hot rolling that satisfies all conditions A to E in the hot rolling process, fine inhibitors (MnS, MnSe ).

[Cold rolling process (S2)]
In the cold rolling step (S2), the manufactured hot rolled steel sheet is cold rolled one or more times. FIG. 7 is a schematic diagram showing a cold rolling equipment line that performs a cold rolling process. Referring to FIG. 7, the cold rolling equipment line 2 includes, from upstream to downstream, a payoff reel (unwinding device) 21, a cold rolling mill CM, and a tension reel (winding device) 22. The payoff reel 21 unwinds the steel plate (hot-rolled steel plate or cold-rolled steel plate) ST that is being wound up. The tension reel 22 winds up the cold rolled steel plate ST. The cold rolling mill CM cold-rolls the rewound steel plate (hot-rolled steel plate or cold-rolled steel plate). In FIG. 7, the cold rolling mill CM includes a plurality of cold rolling stands CMS ₁ to CMS _j (j is a natural number of 2 or more) arranged in a line from upstream to downstream. Each cold rolling stand CMS includes a pair of horizontally extending work rolls. In FIG. 7, the cold rolling mill CM is a tandem continuous rolling mill equipped with a plurality of cold rolling stands CMS ₁ to CMS _j . However, the cold rolling mill CM may be a reverse rolling mill including one cold rolling stand CMS.

In this specification, "carrying out one cold rolling" means cold rolling to a desired final thickness by rolling multiple times including one or more reciprocations using a reverse cold rolling mill CM. A steel plate is formed into a steel plate, or from a plurality of cold rolling stands CMS ₁ to CMS _j arranged in a row from the first rolling stand CMS ₁ to the last rolling stand CMS _j by using a tandem cold rolling mill CM. This refers to rolling a cold-rolled steel sheet to a desired final thickness by passing it through the cold-rolled steel sheet. In addition, after performing cold rolling, in the case where intermediate annealing and/or pickling, etc., are carried out on a separate line, and further cold rolling is performed to obtain a cold rolled steel sheet with the desired final thickness. , corresponds to "carrying out two cold rolling operations". When rolling is performed multiple times without intervening intermediate annealing, it corresponds to "performing cold rolling once."

As described above, in the cold rolling process of this embodiment, cold rolling may be performed once or cold rolling may be performed multiple times. When cold rolling is performed only once, the hot-rolled steel sheet rewound by the payoff reel 21 is passed once through the cold rolling mill CM to apply a rolling reduction to form a cold-rolled steel sheet. On the other hand, when performing cold rolling multiple times, the steel plate (hot-rolled steel plate or cold-rolled steel plate) rewound by the payoff reel 21 is passed through the cold rolling mill CM once to apply a reduction, and the tension reel 22 After that, the rolled steel plate is rewound again by the payoff reel 21, passed through the cold rolling mill CM once to apply a rolling reduction, and then wound again by the tension reel.

In the cold rolling process, when cold rolling is performed multiple times, intermediate annealing is performed after cold rolling, and then the next cold rolling is performed. Known conditions may be used for the intermediate annealing treatment performed between cold rolling and the next cold rolling. The annealing temperature in the intermediate annealing treatment is, for example, 900 to 1200°C, and the holding time at the annealing temperature is 30 to 180 seconds. After the intermediate annealing treatment reduces the strain introduced into the steel plate in the previous cold rolling (softens the steel plate), the next cold rolling is performed.

In addition, in the cold rolling process, as described above, only one cold rolling may be performed.

The cumulative reduction rate in cold rolling performed once or in multiple times is not particularly limited. A preferable cumulative reduction rate in the cold rolling step (S2) is 80 to 95%. Here, the cumulative rolling reduction rate (%) in the cold rolling process (S2) is defined as follows.
Cold rolling ratio (%) = (100 - thickness of steel plate after last cold rolling / thickness of steel plate before start of first cold rolling) x 100

In addition, in a cold rolling process, when implementing only one cold rolling, the said cold rolling rate is the cold rolling rate in only one cold rolling. A steel plate manufactured by a cold rolling process is wound into a coil shape.

[Annealing step before final cold rolling (S3)]
In the annealing step (S3) before final cold rolling, the steel sheet before the final cold rolling (S20) of one or more cold rolling steps (S20) in the cold rolling step (S2) is annealed. Perform processing. In the final pre-cold rolling annealing step (S3), two-stage heat treatment (first heat treatment, second heat treatment) is performed. First, primary heat treatment is performed. In the primary heat treatment, the steel plate is heated to the primary heat treatment temperature. The primary heat treatment temperature is 1000 to 1200°C. After heating the steel plate to the primary heat treatment temperature, the secondary heat treatment is performed. In the secondary heat treatment, the steel plate is lowered from the primary heat treatment temperature to the secondary heat treatment temperature and held at the secondary heat treatment temperature. The secondary heat treatment temperature is 850 to 950°C. The holding time at the secondary heat treatment temperature is 30 to 180 seconds. By performing the above final pre-cold annealing treatment, AlN can be finely dispersed throughout the width direction of the steel sheet.

[Decarburization annealing process (S4)]
In the decarburization annealing step (S4), the steel plate (cold rolled steel sheet) after the cold rolling step (S2) is subjected to decarburization annealing to cause primary recrystallization to occur.

FIG. 8 is a schematic diagram showing a heat pattern in the decarburization annealing step (S4). Referring to FIG. 8, the decarburization annealing step (S4) includes a temperature raising step (S41), a decarburization step (S42), and a cooling step (S43). In the temperature raising step (S41), the steel plate is heated to a decarburization annealing temperature Ta. In the decarburization step (S42), the steel plate is held at a decarburization annealing temperature Ta to carry out decarburization annealing to cause primary recrystallization to occur. In the cooling step (S43), the steel plate after the decarburization step (S42) is cooled by a well-known method. In this embodiment, in the temperature raising step (S41), the temperature raising rate in the temperature range from 550 to 800°C, which corresponds to the recrystallization temperature range of the steel plate, is significantly increased. This promotes recrystallization of the α-fiber orientation group developed at the center position of the sheet width of the steel sheet in the hot rolling process (S1), and suppresses the remaining α-fiber orientation group. As a result, it is possible to suppress the occurrence of a linear defective region extending in the rolling direction, which is caused by the remaining α-fiber orientation group at the width center position of the grain-oriented electrical steel sheet. As a result, it is possible to suppress deterioration of the magnetic properties of the grain-oriented electrical steel sheet due to the linear defect area. The details of each step will be explained below.

[Temperature raising step (S41)]
In the temperature raising step, first, the steel plate after the cold rolling step (S2) is charged into a heat treatment furnace. In the heat treatment furnace for decarburization annealing in this embodiment, the temperature of the cold rolled steel sheet is raised to the decarburization annealing temperature Ta, for example, by high frequency induction heating. The temperature raising step satisfies the following condition F.
(Condition F) Average heating rate RR _550-800 : 800°C/sec or more

[(Condition F) Regarding average heating rate RR _550-800 ]
In the heating process, the average heating rate during which the temperature of the steel plate increases from 550°C to 800°C is defined as average heating rate RR _550-800 (°C/sec). If the average heating rate RR _550-800 is less than 800° C./sec, the strain energy that serves as the driving force for recrystallization will be released before recrystallization starts. In this case, recrystallization from the α-fiber orientation group extending in the rolling direction at the width center position of the steel sheet is not promoted, and the α-fiber orientation group remains. As a result, a linear defective region extending in the rolling direction is formed in the grain-oriented electrical steel sheet. In this case, the magnetic properties of the grain-oriented electrical steel sheet deteriorate.

If the average temperature increase rate RR _550-800 is 800° C./sec or more, release of strain energy is suppressed until recrystallization starts. Therefore, recrystallization from the α-fiber orientation group is promoted, and the remaining α-fiber orientation group can be suppressed. As a result, the formation of linear defective regions in the grain-oriented electrical steel sheet can be suppressed, and excellent magnetic properties can be obtained.

Note that the upper limit of the average temperature increase rate RR _550-800 is not particularly limited. However, even if the average heating rate RR _550-800 is higher than 2400° C./sec, the above effect is saturated. Therefore, the upper limit of the average heating rate RR _550-800 is 2400° C./sec.

The lower limit of the average temperature increase rate RR _550-800 is preferably 850°C/sec, more preferably 860°C/sec, even more preferably 880°C/sec, and still more preferably 900°C/sec. A preferable upper limit of the average heating rate RR _550-800 is 2300°C/sec, more preferably 2200°C/sec, and even more preferably 2100°C/sec.

The average heating rate RR _550-800 is measured by the following method. A plurality of thermometers are installed in the heat treatment furnace to measure the surface temperature of the steel plate. The plurality of thermometers are arranged from upstream to downstream of the heat treatment furnace. An average temperature increase rate RR _550-800 is determined based on the temperature of the steel plate measured by a thermometer and the time taken for the steel plate temperature to rise from 550°C to 800°C. The average temperature increase rate RR _550-800 may be determined by attaching a thermocouple to a sample steel plate and actually measuring the change in temperature over time.

[Decarburization step (S42)]
In the decarburization step (S42) in the decarburization annealing step (S4), the steel plate after the temperature raising step (S41) is held at the decarburization annealing temperature Ta, and decarburization annealing is performed. This causes the steel plate to undergo primary recrystallization. The atmosphere during the decarburization step may be a well-known atmosphere, such as a wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. By performing decarburization annealing, carbon in the steel sheet is removed from the steel sheet, and primary recrystallization occurs. The manufacturing conditions in the decarburization step (S42) are as follows.

Decarburization annealing temperature Ta: 800-950℃
As described above, the decarburization annealing temperature Ta corresponds to the furnace temperature of the heat treatment furnace that performs the decarburization annealing, and corresponds to the temperature of the steel sheet during the decarburization annealing. If the decarburization annealing temperature Ta is less than 800°C, the crystal grains of the steel sheet after primary recrystallization are too small. In this case, secondary recrystallization does not occur sufficiently in the final annealing step (S6). On the other hand, if the decarburization annealing temperature Ta exceeds 950°C, the crystal grains of the steel sheet after primary recrystallization are too large. Also in this case, secondary recrystallization does not occur sufficiently in the final annealing step (S6). If the decarburization annealing temperature Ta is 800 to 950° C., the crystal grains of the steel sheet after primary recrystallization will have an appropriate size, and secondary recrystallization will sufficiently occur in the final annealing step (S6).

Note that the holding time at the decarburization annealing temperature Ta in the decarburization step (S42) is not particularly limited. The holding time at the decarburization annealing temperature Ta is, for example, 15 to 150 seconds.

[Cooling process (S43)]
In the cooling step (S43), the steel plate after the decarburization step (S42) is cooled to room temperature by a well-known method. The cooling method may be air cooling or water cooling. Preferably, the steel plate after the decarburization step is allowed to cool. Through the above steps, in the decarburization annealing step (S4), the steel plate is subjected to decarburization annealing treatment.

By performing the above decarburization annealing step (S4), it is possible to promote recrystallization from the α fiber orientation group generated in the steel sheet during the hot rolling process, and to suppress the remaining α fiber orientation group. I can do it. Therefore, in the final annealing step (S6), Goss-oriented grains can be grown, and the formation of linear defective regions extending in the rolling direction due to α-fiber orientation groups in the grain-oriented electrical steel sheet is suppressed. can do.

[Annealing separator application step (S5)]
An annealing separator application step (S5) is performed on the steel plate after the decarburization annealing step (S6). In the annealing separator application step (S5), an annealing separator is applied to the surface of the steel plate. Specifically, an aqueous slurry containing an annealing separator is applied to the surface of the steel plate. The aqueous slurry is prepared by adding water to the annealing separation agent and stirring the mixture. The annealing separator contains magnesium oxide (MgO). Preferably, MgO is the main component of the annealing separator. Here, "main component" means that the MgO content in the annealing separator is 60.0% or more in mass %. The annealing separator may contain known additives in addition to MgO.

In the annealing separator application step (S5), an aqueous slurry annealing separator is applied onto the surface of the steel plate. A steel plate whose surface is coated with an annealing separator is wound up into a coil. After forming the steel plate into a coil shape, a final annealing step (S6) is performed.

Incidentally, after applying an aqueous slurry annealing separator on the surface of the steel plate and forming the steel plate into a coil shape, a baking treatment may be performed before performing the final annealing step (S6). In the baking process, a coiled steel plate is placed in a furnace maintained at 400 to 1000°C and held there (baking process). This dries the annealing separator applied to the surface of the steel plate. The holding time is, for example, 10 to 90 seconds.

The final annealing step (S6) may be performed on the coiled steel plate coated with the annealing separator without performing the baking process.

[Final annealing process (S6)]
After the annealing separator application step (S5), the steel plate is subjected to a final annealing step (S6) to cause secondary recrystallization. The final annealing step (S6) is performed using a heat treatment furnace. For example, the manufacturing conditions in the final annealing step (S6) are as follows. Note that the atmosphere in the furnace during final annealing is a well-known atmosphere.

Finish annealing temperature: 1150-1250℃
Holding time at final annealing temperature: 5 to 30 hours If the final annealing temperature is less than 1150°C, sufficient secondary recrystallization will not occur, and purification to remove precipitates used in secondary recrystallization will not be sufficient. isn't it. Therefore, the magnetic properties of the produced grain-oriented electrical steel sheet become low. On the other hand, even if the final annealing temperature exceeds 1250° C., the effect on secondary recrystallization and purification is low, and problems such as deformation of the steel sheet occur. If the finishing temperature is 1150 to 1250°C, sufficient secondary recrystallization will occur and the magnetic properties will improve, provided that the holding time is appropriate. Furthermore, a primary film containing forsterite is formed soundly on the surface of the steel sheet.

In the manufacturing method of this embodiment, in the hot rolling step (S1), fine Mn inhibitors (MnS and MnSe) having a major axis length of less than 1 μm are finely dispersed in the steel sheet. Therefore, these fine Mn inhibitors and fine AlN inhibitors generated in the final pre-cold rolling annealing step (S3) stabilize secondary recrystallization in the final annealing step (S5). As a result, it is possible to suppress the occurrence of a defective structure due to secondary recrystallization at both ends of the grain-oriented electrical steel sheet in the sheet width direction.

In the manufacturing method of this embodiment, by implementing conditions A to E in the hot rolling step (S1), priority is given to miniaturization of the Mn inhibitor. Therefore, an α fiber orientation group extending in the rolling direction may be generated at the center position of the width of the hot rolled steel sheet after the hot rolling step (S2). However, in the decarburization annealing step (S4), by setting the average temperature increase rate RR _550-800 in the temperature range from 550°C to 800°C to 800°C/sec or more (condition F) , suppresses the release of strain energy in the steel sheet before starting recrystallization, and promotes recrystallization from the α fiber orientation group. Thereby, in the grain-oriented electrical steel sheet, it is possible to suppress the remaining linear defective region due to the α-fiber orientation group, and excellent magnetic properties can be obtained.

In addition, in the final annealing step (S6), each element in the chemical composition of the steel sheet is removed to some extent from the steel sheet. In particular, S, Al, N, etc. that function as inhibitors are largely removed. Furthermore, a primary coating containing forsterite is formed on the surface of the grain-oriented electrical steel sheet after the final annealing step (S6).

[Secondary film formation process]
In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, a well-known secondary film forming step may be further performed after the final annealing step (S6), if necessary. In the secondary film forming step, a well-known insulating coating agent mainly containing colloidal silica and phosphate is applied to the surface (on the primary film) of the grain-oriented electrical steel sheet after cooling in the final annealing step (S6). , perform baking. This forms a secondary coating, which is a well-known tensile insulating coating, on the primary coating.

[Magnetic domain refining process]
The grain-oriented electrical steel sheet according to the present embodiment may further be subjected to a magnetic domain refining process after the final annealing process (S6) or the secondary coating forming process, if necessary. In the magnetic domain refining process, the surface of the grain-oriented electrical steel sheet is irradiated with a laser beam that has a magnetic domain refining effect, or grooves are formed on the surface. In this case, a grain-oriented electrical steel sheet with even better magnetic properties can be produced.

As described above, in the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, a hot rolled steel sheet is manufactured under conditions that satisfy conditions A to E in the hot rolling step (S1), and in the decarburization annealing step (S4). , Decarburization annealing is performed under conditions that satisfy condition F. As a result, sufficient magnetic properties can be obtained in the manufactured grain-oriented electrical steel sheet, and defective structures and edge cracks can be suppressed at the ends in the width direction of the sheet.

In addition, in the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, if any of conditions A to D is not satisfied, not only a defective structure occurs, but also magnetic properties (magnetic flux density and/or iron loss) may also decrease. Further, in condition E, if [Si]/[C] is too low, not only edge cracking occurs but also iron loss may decrease.

Hereinafter, aspects of the present invention will be specifically explained with reference to Examples. These Examples are examples for confirming the effects of the method for manufacturing grain-oriented electrical steel sheets of the present embodiment, and do not limit the present invention.

In Example 1, a grain-oriented electrical steel sheet was manufactured by changing the chemical composition of a slab consisting of only essential elements. The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 1 were prepared.

The "-" in the element content in Table 1 indicates that the corresponding element content is 0% when rounded to the specified significant figure (number to the lowest digit) in the above embodiment. means. For example, the Bi content defined in this embodiment is defined as a numerical value to the fourth decimal place. Therefore, test number 1 in Table 1 means that the measured Bi content was 0% when rounded to the fifth decimal place. Further, the Sn content specified in this embodiment is specified as a numerical value to the second decimal place. Therefore, test number 1 in Table 1 means that the measured Sn content was 0% when rounded to the second decimal place.
Note that rounding means rounding down if the digit (fraction) below the specified minimum digit is less than 5, and rounding up if it is 5 or more.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate). In any test number, the cumulative rolling reduction TR in the rough rolling process was 73%, and the rolling reduction R1 in the final rolling of the rough rolling process was 48%. Further, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in both cases.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 800° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1200°C, and the holding time at the final annealing temperature was 20 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
[Magnetic property evaluation test]
As a magnetic property evaluation test, magnetic flux density B8 and iron loss W17/50 were measured. Specifically, the magnetic flux density B of the grain-oriented electrical steel sheet of each test number was evaluated in accordance with JIS C2556 (2015). Samples were taken from the grain-oriented electrical steel sheets of each test number. A magnetic field of 800 A/m was applied to the collected sample, and the magnetic flux density B8 (T) was measured. Furthermore, using the sample, the iron loss W17/50 when magnetized to 1.7 T at 50 Hz was measured. Table 1 shows the obtained magnetic flux density B8 and iron loss W17/50. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it. Note that when the magnetic flux density B8 was less than 1.900T, the measurement of the iron loss W17/50 was not performed.

[Ear crack confirmation test]
The presence or absence of edge cracking at both ends of the steel plate in the width direction of the steel plate was confirmed using the steel plate after the hot rolling process in the manufacturing process of each test number. If an edge crack was present, the length of the edge crack in the board width direction was measured. If even one edge crack with a length in the board width direction exceeding 20 mm was confirmed, it was determined that an edge crack had occurred ("x" in Table 1). On the other hand, if no edge cracks exceeding 20 mm in length in the board width direction were observed, it was determined that no edge cracks occurred ("○" in Table 1).

[Bad tissue depth measurement test]
FIG. 9 is a diagram showing the sample shape used in the defective tissue depth measurement test. Referring to FIG. 9, the plate width of the grain-oriented electrical steel sheet of each test number was defined as W. A sample of 100 mm in the rolling direction RD and W mm in the sheet width direction TD was taken from the grain-oriented electrical steel sheet of each test number. The primary coating and secondary coating were removed from the collected sample using the following method. A grain-oriented electrical steel sheet was immersed for 7 minutes in a sodium hydroxide aqueous solution containing 40% by mass of NaOH and 60% by mass of H ₂ O at 80 to 90°C. After dipping, the grain-oriented electrical steel sheet was washed with water. After washing with water, it was dried with a hot air blower for a little less than 1 minute. Through the above treatment, a grain-oriented electrical steel sheet from which the secondary coating was removed (that is, a base steel sheet with a primary coating) was produced. Furthermore, the grain-oriented electrical steel sheet from which the secondary coating had been removed was immersed in hydrochloric acid at 80 to 90° C. for 5 to 30 seconds to remove the primary coating from the base steel sheet. The base steel plate from which the primary coating had been removed was washed with water, and then dried with a warm air blower for a little less than 1 minute. By the above method, a sample was prepared in which the primary coating and the secondary coating were removed and the rolled surface (surface) was etched.

As shown in FIG. 9, in the sample after etching, when defective tissue IA is generated at both ends of TD in the board width direction, the crystal grain size of defective tissue IA is larger than the crystal grain size of normal tissue NA. is also much smaller. Therefore, the defective tissue IA can be easily identified visually. Therefore, the etched sample was visually checked to identify the presence or absence of defective tissue IA at both ends. If the defective tissue IA is generated at the left end in the sheet width direction TD in FIG. 9, the maximum length of the defective tissue IA in the sheet width direction TD is determined as the defective tissue depth WL (mm). It was defined as Furthermore, if a defective tissue IA occurs at the right end in the sheet width direction TD in FIG. 9, the maximum length of the defective tissue IA in the sheet width direction TD is defined as the defective tissue depth WR (mm). It was defined as The larger value of the defective structure depths WL and WR was defined as the defective structure depth WO (mm) in the grain-oriented electrical steel sheet of that test number. When the defective tissue depth WO was 5 mm or more, it was determined that a defective tissue had occurred ("x" in Table 1). On the other hand, when the defective tissue depth WO was less than 5 mm, it was determined that no defective tissue was observed ("○" in Table 1).

In addition, in the steel plate having the test number in which an edge crack occurred in the above-mentioned edge crack confirmation test, the edge of the steel plate was trimmed and the edge was cut before the annealing step before final cold rolling. Therefore, the depth of the defective structure from the edge of the plate width was not measured ("-" is written in the "5mm or more defective structure" column in Table 1). Furthermore, in test numbers in which [Si]/[C] exceeded the upper limit of formula (1) (that is, exceeded F2), secondary recrystallization was poor over the entire width of the plate. Therefore, the depth of the defective structure from the edge of the plate width was not measured ("-" is written in the "5mm or more defective structure" column in Table 1). The test results are shown in Table 1.

[Test results]
The test results obtained are shown in Table 1. Referring to Table 1, in test numbers 2, 5, 6, 9, 11, 12, 15, 16, 19 and 20, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process. was appropriate. Therefore, no edge cracking occurred and no defective structure was observed in any of the test numbers. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 1, 3, 4, 8, 14, and 18, the [Si]/[C] value was less than the lower limit (=F1) of formula (1). As a result, ear cracking was confirmed.

In test numbers 7, 10, 13, 17, and 21, the [Si]/[C] value exceeded the upper limit (=F2) of formula (1). As a result, the magnetic flux density B8 was less than 1.900T, and the magnetic properties were poor.

In Example 2, a grain-oriented electrical steel sheet was manufactured by changing the chemical composition of the slab. The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 2 were prepared.

Similar to Table 1, "-" in Table 2 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate). In any test number, the cumulative rolling reduction TR in the rough rolling process was 73%, and the rolling reduction R1 in the final rolling of the rough rolling process was 48%. Further, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in both cases.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 800° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1200°C, and the holding time at the final annealing temperature was 20 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 2. Referring to Table 2, in all test numbers 1 to 7, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

In Example 3, a grain-oriented electrical steel sheet was manufactured by changing the chemical composition of the slab and changing the average temperature increase rate RR of Condition F of _550-800 . The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 3 were prepared.

Similar to Table 1, "-" in Table 3 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above-mentioned embodiment in the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate). In any test number, the cumulative rolling reduction TR in the rough rolling process was 73%, and the rolling reduction R1 in the final rolling of the rough rolling process was 48%. Further, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in both cases.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was as shown in Table 4.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1200°C, and the holding time at the final annealing temperature was 20 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it. Note that when the magnetic flux density B8 was less than 1.900T, the measurement of the iron loss W17/50 was not performed.

[Test results]
The test results obtained are shown in Table 4. Referring to Table 4, in all test numbers 3, 4, 7, 8, and 11 to 27, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, no defective tissue was observed in any of the test numbers, and no edge cracking occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 1, 2, 5, 6, 9, and 10, the average temperature increase rate RR _550-800 was too slow. Therefore, as a result, the magnetic flux density B8 was less than 1.900 T, and the magnetic properties were poor. In addition, in test numbers 1, 2, 5, 6, 9, and 10, the magnetic flux density B8 was a very inferior value, and secondary recrystallization was poor over the entire board width. Therefore, the depth of the defective structure from the edge of the plate width was not measured ("-" is written in the column "5mm or more defective structure" in Table 4).

In Example 4, the cumulative reduction ratio TR (condition A) in the rough rolling process in the hot rolling process was changed to determine the presence or absence of edge cracking, the presence or absence of defective structure, and the magnetic properties (magnetic flux density B8 and iron loss W17/50) were measured. Specifically, slabs having the chemical composition shown in Table 5 were prepared.

Similar to Table 1, "-" in Table 5 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

In each test number, the cumulative rolling reduction ratio TR in the rough rolling process was as shown in Table 6. Furthermore, in all test numbers, the rolling reduction ratio R1 at the final rolling in the rough rolling step was 46%. Furthermore, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in any test number.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 6. Referring to Table 6, in all test numbers 1 to 9, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 10 to 15, the cumulative reduction ratio TR of rough rolling was too high. As a result, the depth of the defective structure was 5 mm or more, and the defective structure was excessively generated at both ends in the sheet width direction TD.

In Example 5, the rolling reduction ratio R (condition B) at the final rolling in the rough rolling process in the hot rolling process was changed to determine the presence or absence of edge cracking, the presence or absence of defective structure, and the magnetic properties. (Magnetic flux density B8 and iron loss W17/50) were measured. Specifically, slabs having the chemical composition shown in Table 7 were prepared.

Similar to Table 1, "-" in Table 7 indicates 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above-mentioned embodiment in the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

In all test numbers, the cumulative reduction ratio TR in the rough rolling step was 73%. Further, in each test number, the rolling reduction ratio R1 at the final rolling in the rough rolling step was as shown in Table 8. Furthermore, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in any test number.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 8. Referring to Table 8, in all test numbers 1 to 6, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 7 to 12, the rolling reduction ratio at the final rolling in the rough rolling process was too high. As a result, the depth of the defective structure was 5 mm or more, and the defective structure was excessively generated at both ends in the sheet width direction TD.

In Example 6, the temperature of the rough bar immediately after the final rolling in the rough rolling process in the hot rolling process (condition C) was changed to determine the presence or absence of defective structure, the presence or absence of edge cracking, and the magnetic properties (magnetic flux Density B8 and iron loss W17/50) were measured. Specifically, slabs having the chemical composition shown in Table 9 were prepared.

Similarly to Table 1, "-" in Table 9 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above-mentioned embodiment in the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

In each test number, the temperature T1 of the rough bar immediately after the final rolling of the rough rolling process was as shown in Table 10. Furthermore, in all test numbers, the cumulative rolling reduction TR in the rough rolling step was 73%, and the rolling reduction R1 in the final rolling in the rough rolling step was 48%. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in any test number.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 10. Referring to Table 10, in all test numbers 7 to 12, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 1 to 6, the temperature T1 of the rough bar immediately after the final rolling of the rough rolling process was too low. As a result, the depth of the defective structure was 5 mm or more, and the defective structure was excessively generated at both ends in the sheet width direction TD.

In Example 7, the time from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process (intermediate Time) t1 (condition D) was varied to measure the occurrence of ear cracks, the occurrence of defective tissue, and the magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 11 were prepared.

Similar to Table 1, "-" in Table 11 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

For each test number, the time (intermediate time) t1 from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process is shown in the table. It was as shown in 11. Furthermore, in all test numbers, the cumulative rolling reduction TR in the rough rolling step was 73%, and the rolling reduction R1 in the final rolling in the rough rolling step was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 11. In all test numbers 2 to 6, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, no defective tissue was observed in any of the test numbers, and no edge cracking occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test number 1, the [Si]/[C] value was less than the lower limit (=F1) of formula (1). As a result, an edge crack of more than 20 mm occurred.

In test numbers 7, 8, and 10, after the final rolling of the rear end of the slab in the rough rolling process in the hot rolling process was completed, until the first rolling of the rear end of the rough bar was completed in the finish rolling process. The intermediate time t1 was too long. As a result, the defective structure depth WO was 5 mm or more, and defective structures were excessively generated at both ends in the sheet width direction TD.

In test numbers 9, 11, and 12, the [Si]/[C] value exceeded the upper limit (=F2) of formula (1). As a result, the magnetic flux density B8 was less than 1.900T, and the magnetic properties were poor.

In Example 8, a grain-oriented electrical steel sheet was manufactured by changing the chemical composition of a slab consisting of essential elements and Bi. The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 12 were prepared.

Similar to Table 1, "-" in Table 12 means 0% when rounding off to the specified significant figures (numbers to the lowest digit) in the above-mentioned embodiment in the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate). In any test number, the cumulative rolling reduction TR in the rough rolling process was 73%, and the rolling reduction R1 in the final rolling of the rough rolling process was 48%. Further, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in both cases.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 800° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1200°C, and the holding time at the final annealing temperature was 20 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
[Magnetic property evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it. Note that when the magnetic flux density B8 was less than 1.900T, the measurement of the iron loss W17/50 was not performed.

[Test results]
The test results obtained are shown in Table 12. Referring to Table 12, in test numbers 3, 5, 6, 8 to 14, 16, 17, 19 and 20, the chemical composition of the slab was appropriate and conditions A to F during the manufacturing process were appropriate. Met. Therefore, in any of the test numbers, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.906 T or more, and the iron loss W17/50 was 0.727 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 1, 2, 4, and 7, the [Si]/[C] value was less than the lower limit (=F1) of formula (1). As a result, ear cracking was confirmed.

In test numbers 15, 18, and 21, the [Si]/[C] value exceeded the upper limit (=F2) of formula (1). As a result, the magnetic flux density B8 was less than 1.900T, and the magnetic properties were poor.

In Example 9, a grain-oriented electrical steel sheet was manufactured by changing the chemical composition of a slab consisting of essential elements and Bi. The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 13 were prepared.

Similar to Table 1, "-" in Table 13 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate). In any test number, the cumulative rolling reduction TR in the rough rolling process was 73%, and the rolling reduction R1 in the final rolling of the rough rolling process was 48%. Further, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in both cases.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 800° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1200°C, and the holding time at the final annealing temperature was 20 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it. Note that when the magnetic flux density B8 was less than 1.900T, the measurement of the iron loss W17/50 was not performed.

[Test results]
The test results obtained are shown in Table 13. Referring to Table 13, in test numbers 1 to 3, 7 to 9, 13 to 15, and 20 to 22, the chemical composition of the slab was appropriate and conditions A to F during the manufacturing process were appropriate. Ta. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 4 to 6, 10 to 12, 16 to 18, 23 and 24, the [Si]/[C] value was less than the lower limit (=F1) of formula (1). As a result, ear cracking was confirmed.

In test number 19, the [Si]/[C] value exceeded the upper limit (=F2) of formula (1). As a result, the magnetic flux density B8 was less than 1.900T, and the magnetic properties were poor. In addition, in test number 19, the magnetic flux density B8 was a very inferior value, and secondary recrystallization was poor over the entire board width. Therefore, the depth of the defective structure from the edge of the plate width was not measured ("-" is written in the column "5mm or more defective structure" in Table 13).

In Example 10, grain-oriented electrical steel sheets were manufactured by changing the chemical composition of the slab containing essential elements and Bi, and by changing the average temperature increase rate RR of Condition F, RR _550-800 . The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 14 were prepared.

Similar to Table 1, "-" in Table 14 means 0% when rounding off to the specified significant figures (values to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate). In any test number, the cumulative rolling reduction TR in the rough rolling process was 73%, and the rolling reduction R1 in the final rolling of the rough rolling process was 48%. Further, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in both cases.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was as shown in Table 15.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1200°C, and the holding time at the final annealing temperature was 20 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it. Note that when the magnetic flux density B8 was less than 1.900T, the measurement of the iron loss W17/50 was not performed.

[Test results]
The test results obtained are shown in Table 15. Referring to Table 15, in test numbers 3, 4, 7, 8, and 11 to 25, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 1, 2, 5, 6, 9, and 10, the average temperature increase rate RR _550-800 was too slow. Therefore, as a result, the magnetic flux density B8 was less than 1.900 T, and the magnetic properties were poor. In addition, in test numbers 1, 2, 5, 6, 9, and 10, the magnetic flux density B8 was a very inferior value, and secondary recrystallization was poor over the entire board width. Therefore, the depth of the defective structure from the edge of the plate width was not measured ("-" is written in the column "5mm or more defective structure" in Table 15).

In Example 11, the cumulative reduction ratio TR (condition A) in the rough rolling process in the hot rolling process was changed to determine the occurrence of edge cracks, the occurrence of defective structures, and the magnetic properties (magnetic flux density B8). and iron loss W17/50) were measured. Specifically, slabs having the chemical composition shown in Table 16 were prepared.

Similar to Table 1, "-" in Table 16 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

In each test number, the cumulative rolling reduction ratio TR in the rough rolling step was as shown in Table 17. Furthermore, in all test numbers, the rolling reduction ratio R1 at the final rolling in the rough rolling step was 46%. Furthermore, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in any test number.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film forming process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 17. Referring to Table 17, in test numbers 1 to 15, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 16 to 25, the cumulative reduction ratio TR of rough rolling was too high. As a result, the defective structure depth WO was 5 mm or more, and defective structures were excessively generated at both ends in the sheet width direction TD.

In Example 12, the rolling reduction ratio R (condition B) at the final rolling in the rough rolling process in the hot rolling process was changed to determine whether or not edge cracking occurred, the presence or absence of defective structure, and the magnetic properties. (Magnetic flux density B8 and iron loss W17/50) were measured. Specifically, slabs having the chemical composition shown in Table 18 were prepared.

Similar to Table 1, "-" in Table 18 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

In all test numbers, the cumulative reduction ratio TR in the rough rolling process was 73%. Further, in each test number, the rolling reduction ratio R1 at the final rolling in the rough rolling step was as shown in Table 19. Furthermore, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in any test number.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 19. Referring to Table 19, in test numbers 1 to 6, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 7 to 12, the rolling reduction ratio at the final rolling in the rough rolling process was too high. As a result, the depth of the defective structure was 5 mm or more, and the defective structure was excessively generated at both ends in the sheet width direction TD.

In Example 13, the temperature of the rough bar immediately after the final rolling in the rough rolling process in the hot rolling process (condition C) was changed to determine the occurrence of edge cracks, the occurrence of defective structure, and the magnetic properties. (Magnetic flux density B8 and iron loss W17/50) were measured. Specifically, slabs having the chemical composition shown in Table 20 were prepared.

Similar to Table 1, "-" in Table 20 indicates 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above embodiment for the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

In each test number, the temperature T1 of the rough bar immediately after the final rolling of the rough rolling process was as shown in Table 21. Furthermore, in all test numbers, the cumulative rolling reduction TR in the rough rolling step was 73%, and the rolling reduction R1 in the final rolling in the rough rolling step was 48%. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in any test number.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 21. Referring to Table 21, in all test numbers 7 to 12, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 1 to 6, the temperature T1 of the rough bar immediately after the final rolling of the rough rolling process was too low. As a result, the depth of the defective structure was 5 mm or more, and the defective structure was excessively generated at both ends in the sheet width direction TD.

In Example 14, the time from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process (intermediate Time) t1 (condition D) was varied to measure the occurrence of ear cracks, the occurrence of defective tissue, and the magnetic properties (magnetic flux density B8 and iron loss W17/50). Specifically, slabs having the chemical composition shown in Table 22 were prepared.

Similar to Table 1, "-" in Table 22 means 0% when rounding off the fraction to the specified significant figure (number to the lowest digit) in the above-mentioned embodiment in the corresponding element content. It means that.

The above slab was heated to 1370°C in a heating furnace. A hot rolling process was performed on the heated slab to produce a steel plate (hot rolled steel plate).

For each test number, the intermediate time t1 from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process is shown in Table 22. That's right. Furthermore, in all test numbers, the cumulative rolling reduction TR in the rough rolling step was 73%, and the rolling reduction R1 in the final rolling of the rough rolling step was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final rolling in the rough rolling step was 1350°C. After the rough rolling process, a finish rolling process was performed to produce a steel plate with a thickness of 2.3 mm.

The steel plate manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing step before final cold rolling, primary heat treatment and secondary heat treatment were performed. In the first heat treatment, the steel plate was heated to 1120°C to recrystallize it. After the first heat treatment, a second heat treatment was performed. Specifically, in the secondary heat treatment, the steel plate was annealed at an annealing temperature of 900° C. and a holding time at the annealing temperature of 30 seconds.

The steel plate after the annealing step before final cold rolling was cold rolled once (final cold rolling) to produce a cold rolled steel plate with a thickness of 0.22 mm. A decarburization annealing process was performed on the cold rolled steel sheet after the cold rolling process. In the decarburization annealing step, the decarburization annealing temperature Ta was 800° C., and the holding time at the decarburization annealing temperature was 120 seconds. Furthermore, the average temperature increase rate RR _550-800 from 550° C. to 800° C. in the temperature increasing step of the decarburization annealing step was 1000° C./sec.

A sintering separation agent (aqueous slurry) containing MgO as a main component was applied to the surface of the steel sheet after decarburization and annealing, and then wound into a coil. Finish annealing was performed on the steel plate wound into a coil shape. The final annealing temperature was 1150°C, and the holding time at the final annealing temperature was 10 hours. The steel plate after finish annealing was allowed to cool.

A secondary film formation process was performed on the steel plate after the final annealing process. In the secondary coating forming step, an insulating coating agent mainly containing colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after the final annealing step, and then baking was performed. The baking temperature was 900° C., and the holding time at the baking temperature was 30 seconds. As a result, a secondary coating, which was a tension-applying insulating coating, was formed on the primary coating. After forming the secondary coating, a magnetic domain refining process was performed. Specifically, the steel plate surface was irradiated with a laser beam under the same conditions for each test number to perform magnetic domain refining treatment. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
A magnetic property evaluation test was conducted on the grain-oriented electrical steel sheets of each test number in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17/50 were measured. Furthermore, in the same manner as in Example 1, an ear crack confirmation test and a defective tissue depth measurement test were conducted. In this example, if the magnetic flux density B8 is 1.900T or more, it is determined that high magnetic flux density has been obtained, and if the iron loss W17/50 is 0.770 W/kg or less, excellent iron loss is determined. I decided that I got it.

[Test results]
The test results obtained are shown in Table 22. In test numbers 2 to 10, the chemical composition of the slab was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in any test number, no edge cracking or defective tissue occurred. Furthermore, the magnetic flux density B8 was as high as 1.900 T or more, and the iron loss W17/50 was 0.770 W/kg or less, indicating excellent magnetic properties.

On the other hand, in test numbers 11 to 18, after the final rolling down of the rear end of the slab in the rough rolling process in the hot rolling process was completed, until the first rolling of the rear end of the rough bar was completed in the finishing rolling process. The intermediate time t1 was too long. As a result, the depth of the defective structure was 5 mm or more, and the defective structure was excessively generated at both ends in the sheet width direction TD.

Further, in test number 1, although the intermediate time t1 was 150 seconds or less, the [Si]/[C] value was less than the lower limit (=F1) of formula (1). As a result, ear cracking was confirmed.

The embodiments of the present invention have been described above. However, the embodiments described above are merely examples for implementing the present invention. Therefore, the present invention is not limited to the embodiments described above, and can be implemented by appropriately modifying the embodiments described above without departing from the spirit thereof.

Claims (3)

The chemical composition is in mass%,
C: 0.060-0.100%,
Si: 3.00-4.00%,
Mn: 0.01 to 0.30%,
S and/or Se: 0.010 to 0.050% in total,
sol. Al: 0.01-0.05%,
N: 0.002-0.015%,
Bi: 0 to 0.0100%,
Sn: 0 to 0.50%,
Cr: 0 to 0.50%,
Cu: 0 to 0.50%, and
A hot rolling process of manufacturing a steel plate by hot rolling a slab with the remainder consisting of Fe and impurities;
a cold rolling step of performing cold rolling one or more times on the steel plate after the hot rolling step;
A final pre-cold rolling annealing step in which the steel plate before the final cold rolling is annealed among the one or more cold rollings;
A decarburization annealing step in which the steel plate after the cold rolling step is heated to a decarburization annealing temperature of 800 to 950° C., and a decarburization annealing is performed in which the steel plate is held at the decarburization annealing temperature;
an annealing separator application step of applying an annealing separator to the surface of the steel plate after the decarburization annealing step;
and a finish annealing step of performing finish annealing on the steel plate coated with the annealing separator,
The hot rolling process includes:
a rough rolling step of performing rough rolling on the slab to produce a rough bar;
a finish rolling step of performing finish rolling on the rough bar to produce the steel plate,
In the rough rolling process,
Performing rolling reduction on the slab multiple times,
The cumulative reduction rate in the rough rolling step is less than 75%,
The rolling reduction ratio in the final rolling of the rough rolling step is less than 50%,
The temperature of the rough bar immediately after the final rolling of the rough rolling step is 1350 ° C. or higher,
When the time from the completion of the final rolling of the rear end of the slab in the rough rolling process to the completion of the first rolling of the rear end of the rough bar in the finishing rolling process is defined as intermediate time t1. , the intermediate time t1 is set to 150 seconds or less, and formula (1) is satisfied;
In the decarburization annealing step,
Heating the steel plate at an average temperature increase rate of 800°C/sec or more until the temperature of the steel plate increases from 550°C to 800°C.
A method for manufacturing grain-oriented electrical steel sheets.
-0.033t1+44+2000[Bi]≦[Si]/[C]≦-0.033t1+52+2000[Bi] (1)
Here, the Bi content (mass%) in the chemical composition of the slab is substituted for [Bi] in formula (1), and the Si content (mass%) in the chemical composition of the slab is substituted for [Si]. % by mass), the C content (% by mass) in the chemical composition of the slab is substituted for [C], and the intermediate time t1 (seconds) is substituted for t1. If Bi is not contained, 0 is substituted for [Bi]. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1, comprising:
The chemical composition of the slab is
Bi: 0.0001-0.0100%,
containing,
A method for manufacturing grain-oriented electrical steel sheets. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1 or 2, comprising:
The chemical composition of the slab is
Sn: 0.01-0.50%,
Cr: 0.01 to 0.50%, and
Cu: 0.01 to 0.50%,
Containing one or more selected from the group consisting of
A method for manufacturing grain-oriented electrical steel sheets.

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