JP2023155059A - Production method of grain-oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a method for producing a grain-oriented electromagnetic steel sheet for obtaining a high magnetic flux density and suppressing dispersion of the magnetic flux density.SOLUTION: In a production method of a grain-oriented electromagnetic steel sheet of an embodiment, a cold rolling step includes a tandem rolling step and a reverse rolling step. In the tandem rolling step, an average diameter D1 of a plurality of work rolls used in a plurality of passes is set to 200 mm or more, and a cumulative reduction ratio CR1 is set to 30-87%. In the reverse rolling step, an average diameter D2 of the plurality of work rolls used in the plurality of passes is set to 100 mm or less, and a cumulative reduction ratio CR2 is set to 24-86%. In a decarburization annealing step, an average heating rate HR in the range of 550-750°C of the cold-rolled steel sheet is 100°C/sec or more.SELECTED DRAWING: Figure 1

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 in which the crystal orientation is concentrated in the {110}<001> direction (Goss direction). Grain-oriented electrical steel sheets are used as soft magnetic materials for core materials in transformers and other electrical equipment.

A method for manufacturing grain-oriented electrical steel sheets is, for example, as follows. The slab is heated and hot rolled to produce a hot rolled steel plate. The manufactured hot rolled steel sheet is annealed. Cold rolling is performed on the hot rolled steel sheet 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.

As mentioned above, since grain-oriented electrical steel sheets are used as core materials, they are required to have high magnetic properties. Specifically, it is desired to improve the magnetic flux density B8 when the magnetic field strength is 800 A/m.

Improving the degree of integration in the Goss direction is known as a method for increasing magnetic flux density. In order to increase the degree of integration in the Goss orientation, finishing annealing is usually performed at a high temperature and for a long time. During final annealing, Goss-oriented grains with excellent magnetic properties grow to a size on the order of centimeters (secondary recrystallization) while eating away at surrounding crystal grains in other orientations. Due to such coarsening of the Goss-oriented grains, the crystal orientation becomes uniform, and the degree of accumulation in the Goss orientation increases.

As the grains in the Goss orientation become coarser, the degree of accumulation in the Goss orientation increases. As a result, the magnetic flux density also increases. However, coarsening of Goss-oriented grains causes variations in magnetic flux density. Specifically, in the above manufacturing method, a coiled steel plate is charged into a heat treatment furnace and finish annealed. In this case, secondary recrystallization occurs in a state where a certain curvature is imparted to the steel plate. Therefore, when a coiled steel plate is unwound into a flat state, continuous deviations in crystal orientation occur depending on the curvature of the coil. Due to this deviation in crystal orientation, the crystal orientation of the crystal grains may deviate from the Goss orientation. In this case, the magnetic flux density decreases. Such deviations in crystal orientation cause variations in magnetic flux density.
Means for increasing the degree of accumulation in the Goss direction are disclosed in JP-A-6-049543 (Patent Document 1), JP-A-7-62436 (Patent Document 2), JP-A-10-280040 (Patent Document 3), and This is proposed in Japanese Unexamined Patent Publication No. 2003-096520 (Patent Document 4).
In these documents, rapid heating is performed in the temperature raising process of the annealing treatment to induce primary recrystallization. By rapid heating, Goss-oriented grains, which serve as nuclei for secondary recrystallization, are enriched in the primary recrystallized structure.

Japanese Patent Application Publication No. 6-049543 Japanese Patent Application Publication No. 7-62436 Japanese Patent Application Publication No. 10-280040 JP2003-096520A

It is true that the manufacturing methods described in Patent Documents 1 to 4 can enrich fine Goss-oriented grains, which serve as nuclei for secondary recrystallization, in the primary recrystallized structure, thereby increasing the degree of accumulation in the Goss orientation. can be increased. However, if Goss-oriented grains become excessively coarse during secondary recrystallization, the above-mentioned deviation in crystal orientation will occur. Therefore, variations may occur in the magnetic flux density between the outermost circumferential portion and the innermost circumferential portion of the coiled grain-oriented electromagnetic steel sheet.

An object of the present disclosure is to provide a method for manufacturing a grain-oriented electrical steel sheet that can obtain high magnetic flux density and suppress variations in magnetic flux density.

A method for manufacturing a grain-oriented electrical steel sheet according to the present disclosure includes the following steps.

The chemical composition is in mass%,
C: 0.01-0.20%,
Si: 2.0 to 4.5%,
Mn: 0.01 to 0.30%,
S: 0.01-0.05%,
sol. Al: 0.01-0.05%,
N: 0.01-0.02%,
Cr: 0.00-0.50%,
Sn: 0.00-0.30%,
Sb: 0.00 to 0.30%,
Ni: 0.00 to 0.50%,
Mo: 0.00-0.20%,
P: 0.00-0.15%,
Cu: 0.00-0.50%,
Se: 0.00-0.03%,
V: 0.00 to 0.15%, and
Bi: 0.0000-0.0100%,
A hot rolling step of producing a hot rolled steel plate by hot rolling a slab containing Fe and the remainder consisting of Fe and impurities;
a hot-rolled plate annealing step of annealing the hot-rolled steel plate;
A cold rolling step of manufacturing a cold rolled steel sheet by cold rolling the hot rolled steel sheet after the hot rolled sheet annealing step at a cumulative reduction rate CR0 of 90% or more;
a decarburization annealing step of performing decarburization annealing on the cold rolled steel sheet to produce a decarburization annealed steel sheet;
A finish annealing step of applying an annealing separator to the decarburized annealed steel plate, and performing finish annealing on the decarburized annealed steel plate coated with the annealing separator to produce a finish annealed steel plate;
An insulating film forming step of applying an insulating film forming liquid to the finish annealed steel plate, and performing heat treatment on the finish annealed steel plate coated with the insulating film forming liquid to form an insulating film on the finish annealed steel plate. and,
The cold rolling process includes:
A tandem rolling step of manufacturing an intermediate steel plate by continuously rolling the hot-rolled steel plate in a plurality of passes using a tandem rolling mill including a plurality of rolling stands arranged in a row;
A reverse rolling step of manufacturing the cold rolled steel sheet by performing reverse rolling for a plurality of passes on the intermediate steel sheet that has not been heat treated after the tandem rolling step using a multi-high rolling mill. ,
In the tandem rolling process,
The average diameter D1 of the plurality of work rolls used in the plurality of passes is 200 mm or more,
The cumulative reduction rate CR1 is set to 30 to 87%,
In the reverse rolling process,
The average diameter D2 of the plurality of work rolls used in the plurality of passes is 100 mm or less,
The cumulative reduction rate CR2 is set to 24 to 86%,
In the decarburization annealing step,
The average temperature increase rate HR in the temperature range of 550°C to 750°C of the cold rolled steel sheet is 100°C/second or more,
A method for producing grain-oriented electrical steel sheets.

The method for manufacturing a grain-oriented electrical steel sheet according to the present disclosure can produce a grain-oriented electrical steel sheet that can obtain high magnetic flux density and suppress variations in magnetic flux density.

FIG. 1 is a flow diagram of a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. FIG. 2 is a schematic diagram of a tandem rolling mill. FIG. 3 is a schematic diagram of a multi-high rolling mill used in the reverse rolling process.

The present inventors believed that in order to obtain a high magnetic flux density and suppress variations in the magnetic flux density, it is effective to suppress excessive coarsening of Goss-oriented grains after secondary recrystallization. Therefore, the chemical composition is C: 0.01-0.20%, Si: 2.0-4.5%, Mn: 0.01-0.30%, S: 0.01-0.05%, sol. Al: 0.01 to 0.05%, N: 0.01 to 0.02%, Cr: 0.00 to 0.50%, Sn: 0.00 to 0.30%, Sb: 0.00 to 0.30%, Ni: 0.00-0.50%, Mo: 0.00-0.20%, P: 0.00-0.15%, Cu: 0.00-0.50%, Se : 0.00 to 0.03%, V: 0.00 to 0.15%, and Bi: 0.0000 to 0.0100%, with the balance consisting of Fe and impurities. The magnetic flux density and the variation in magnetic flux density between the outer circumferential portion and the inner circumferential portion of the coil were investigated when a magnetic steel sheet was manufactured.

First, rapid heating was performed in the decarburization annealing process where primary recrystallization occurs. As a result, if the heating rate HR from 550°C to 750°C is 100°C/sec or more, a sufficient amount of fine Goss-oriented grains will be generated in the primary recrystallized structure, and secondary recrystallization will occur. It was found that the degree of accumulation in the Goss orientation increases during crystallization.

However, by simply performing rapid heating during the decarburization annealing process, although it was possible to increase the degree of accumulation in the Goss orientation during secondary recrystallization, it was not possible to sufficiently suppress the coarsening of the Goss orientation grains. Therefore, it has not been possible to sufficiently suppress variations in magnetic flux density.

Therefore, the present inventors investigated a method for suppressing Goss-oriented crystal grains during secondary recrystallization. As a result, we obtained the following knowledge.

The present inventors focused on the cold rolling process. In the cold rolling step during the manufacturing process of grain-oriented electrical steel sheets, reverse rolling using a multi-high rolling mill is often employed in order to increase the rolling reduction. In a multi-high rolling mill, a pair of work rolls is supported by a plurality of backup rolls in order to apply a high reduction to a steel plate to be rolled. The diameter of the pair of work rolls can be made small, and the deflection of the rolls can be reduced as much as possible. This achieves a high rolling reduction ratio.

However, when cold rolling is performed using work rolls with a small diameter, a large amount of shear strain is introduced into the surface layer of the steel sheet. When a large amount of shear strain is introduced, an α-fiber orientation group, which is one of the stable orientation groups during cold rolling, develops in the steel sheet surface layer. Crystal orientation grains that undergo primary recrystallization from the α-fiber orientation group tend to become coarse. Therefore, when a large number of Goss-oriented grains are generated in primary recrystallization, the number of Goss-oriented grains that become the nucleus of secondary recrystallization decreases during the grain growth process immediately before the appearance of secondary recrystallization in the final annealing process. The next recrystallized grains tend to become coarser. As a result, in a grain-oriented electrical steel sheet that is finish annealed in a coiled state, variations in magnetic flux density tend to occur.

Therefore, the present inventor thought that if the introduction of shear strain in the cold rolling process could be reduced, coarsening of Goss-oriented grains during secondary recrystallization could be suppressed. If the introduction of shear strain is suppressed in the cold rolling process, the γ fiber orientation group tends to remain in the cold rolled steel sheet instead of the α fiber orientation group. The γ fiber orientation group generates a {111} recrystallization group during primary recrystallization. The {111} recrystallized group has a low driving force for grain growth and is difficult to coarsen. Therefore, when a large number of Goss-oriented grains are generated in the primary recrystallization, the Goss-oriented grains that become the nuclei of the secondary recrystallization are difficult to decrease in the grain growth process immediately before the appearance of secondary recrystallization in the final annealing step. Therefore, a large number of nuclei (Goss-oriented grains) undergo secondary recrystallization, and grain growth of each secondary recrystallized grain is suppressed. As a result, in a grain-oriented electrical steel sheet that is finish annealed in a coiled state, variations in magnetic flux density tend to occur.

Based on the above considerations, the present inventors investigated the cold rolling process. As a result, if a tandem rolling process and a reverse rolling process are carried out in the cold rolling process, and the conditions specified below are met in each process, a high hourly density can be obtained in a coiled grain-oriented electrical steel sheet. It has also been found that variations in magnetic flux density can be suppressed.

The method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, which was completed based on the above knowledge, includes the following steps.

[1]
The chemical composition is in mass%,
C: 0.01-0.20%,
Si: 2.0 to 4.5%,
Mn: 0.01 to 0.30%,
S: 0.01-0.05%,
sol. Al: 0.01-0.05%,
N: 0.01-0.02%,
Cr: 0.00-0.50%,
Sn: 0.00-0.30%,
Sb: 0.00 to 0.30%,
Ni: 0.00 to 0.50%,
Mo: 0.00-0.20%,
P: 0.00-0.15%,
Cu: 0.00-0.50%,
Se: 0.00-0.03%,
V: 0.00 to 0.15%, and
Bi: 0.0000-0.0100%,
A hot rolling step of producing a hot rolled steel plate by hot rolling a slab containing Fe and the remainder consisting of Fe and impurities;
a hot-rolled plate annealing step of annealing the hot-rolled steel plate;
A cold rolling step of manufacturing a cold rolled steel sheet by cold rolling the hot rolled steel sheet after the hot rolled sheet annealing step at a cumulative reduction rate CR0 of 90% or more;
a decarburization annealing step of performing decarburization annealing on the cold rolled steel sheet to produce a decarburization annealed steel sheet;
A finish annealing step of applying an annealing separator to the decarburized annealed steel plate, and performing finish annealing on the decarburized annealed steel plate coated with the annealing separator to produce a finish annealed steel plate;
An insulating film forming step of applying an insulating film forming liquid to the finish annealed steel plate, and performing heat treatment on the finish annealed steel plate coated with the insulating film forming liquid to form an insulating film on the finish annealed steel plate. and,
The cold rolling process includes:
A tandem rolling step of manufacturing an intermediate steel plate by continuously rolling the hot-rolled steel plate in a plurality of passes using a tandem rolling mill including a plurality of rolling stands arranged in a row;
A reverse rolling step of manufacturing the cold rolled steel sheet by performing reverse rolling for a plurality of passes on the intermediate steel sheet that has not been heat treated after the tandem rolling step using a multi-high rolling mill. ,
In the tandem rolling process,
The average diameter D1 of the plurality of work rolls used in the plurality of passes is 200 mm or more,
The cumulative reduction rate CR1 is set to 30 to 87%,
In the reverse rolling process,
The average diameter D2 of the plurality of work rolls used in the plurality of passes is 100 mm or less,
The cumulative reduction rate CR2 is set to 24 to 86%,
In the decarburization annealing step,
The average temperature increase rate HR in the temperature range of 550°C to 750°C of the cold rolled steel sheet is 100°C/second or more,
A method for manufacturing grain-oriented electrical steel sheets.

[2]
The method for producing a grain-oriented electrical steel sheet according to [1],
The slab is
Cr: 0.01-0.50%,
Sn: 0.01-0.30%,
Sb: 0.01 to 0.30%,
Ni: 0.01-0.50%,
Mo: 0.01-0.20%,
P: 0.01-0.15%,
Cu: 0.01 to 0.50%,
Se: 0.01-0.03%,
V: 0.01 to 0.15%, and
Bi: 0.0001-0.0100%,
Containing one or more elements 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. 1 is a flow diagram of a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. Referring to FIG. 1, the present manufacturing method includes the following steps S1 to S6.
・Hot rolling process S1
・Hot rolled plate annealing process S2
・Cold rolling process S3
・Decarburization annealing process S4
・Final annealing process S5
・Insulating film formation step S6

The cold rolling step S3 further includes the following two steps.
・Tandem rolling process S31
・Reverse rolling process S32

The manufacturing method of this embodiment is characterized in that the following manufacturing conditions are satisfied in the cold rolling step S3 (tandem rolling step S31, reverse rolling step S32) and decarburization annealing step S4.
(Conditions for tandem rolling process S31)
Condition 1: Continuous rolling with a plurality of passes is performed using a tandem rolling mill.
Condition 2: The average diameter D1 of the work roll is 200 mm or more.
Condition 3: Cumulative rolling reduction rate CR1 is 30 to 87%.
(Conditions for reverse rolling process S32)
Condition 4: Reverse rolling is performed in a plurality of passes using a multi-high rolling mill.
Condition 5: An intermediate steel plate that has not been subjected to heat treatment after the tandem rolling process is to be rolled.
Condition 6: The average diameter D2 of the work roll is 100 mm or less.
Condition 7: Cumulative rolling reduction rate CR2 is 24 to 86%.
(Overall conditions of cold rolling process S3)
Condition 8: The cumulative rolling reduction CR0 in the entire cold rolling step S3 is 90% or more.
(Conditions in decarburization annealing step S4)
Condition 9: The average temperature increase rate HR in the range of 550°C to 750°C is 100°C/sec or more.
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: 0.01-0.20%
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 0.01%, 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 0.20%, 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 0.01-0.20%.
The preferable lower limit of the C content is 0.02%, more preferably 0.05%, and still more preferably 0.07%.
A preferable upper limit of the C content is 0.18%, more preferably 0.16%, and still more preferably 0.14%.

Si: 2.0-4.5%
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 2.0%, 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 4.5%, the cold workability of the steel decreases even if the contents of other elements are within the ranges of this embodiment.
Therefore, the Si content is between 2.0 and 4.5%.
The lower limit of the Si content is preferably 2.2%, more preferably 2.5%, and still more preferably 2.8%.
A preferable upper limit of the Si content is 4.3%, more preferably 4.0%, and still more preferably 3.7%.

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 to form fine MnS in the hot rolling process. The fine MnS becomes a precipitation nucleus of fine AlN used as an inhibitor. Therefore, if the amount of fine MnS precipitated is large in the hot rolling process, a sufficient amount of fine AlN can be obtained in the hot rolled sheet 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: 0.01~0.05%
Sulfur (S) combines with Mn during the hot rolling process to form the above-mentioned fine MnS. As described above, fine MnS becomes a precipitation nucleus of fine AlN used as an inhibitor. Therefore, in the hot rolling process, if the amount of fine MnS precipitated is large, a sufficient amount of fine AlN can be obtained. If the S content is less than 0.01%, 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 S content exceeds 0.05%, MnS may remain in the steel sheet after the final annealing process even if the contents of other elements are within the range of this embodiment. In this case, the magnetic properties of the grain-oriented electrical steel sheet deteriorate.
Therefore, the S content is 0.01-0.05%.
The preferable lower limit of the S content is 0.02%. A preferable upper limit of the S content is 0.04%.

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: 0.01-0.02%
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 0.01%, excessive refining is required in the steel manufacturing process, which increases manufacturing costs. Therefore, the lower limit of N content is 0.01%.
On the other hand, if the N content in the steel material exceeds 0.02%, even if the content of other elements is within the range of this embodiment, many blisters (vacancies) are likely to be generated in the steel sheet during cold rolling. Become.
Therefore, the N content is 0.01-0.02%.

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 above-mentioned slab further includes, in place of a portion of Fe,
Cr: 0.00-0.50%,
Sn: 0.00-0.30%,
Sb: 0.00 to 0.30%,
Ni: 0.00 to 0.50%,
Mo: 0.00-0.20%,
P: 0.00-0.15%,
Cu: 0.00-0.50%,
Se: 0.00-0.03%,
V: 0.00 to 0.15%, and
Bi: 0.0000-0.0100%,
It may contain one or more elements selected from the group consisting of.

[Group 1: Cr, Sn and Sb]
Cr, Sn, and Sb all enhance the magnetic properties of the grain-oriented electrical steel sheet and reduce variations in the magnetic properties. Cr, Sn and Sb will be explained below.

Cr: 0.00~0.50%
Chromium (Cr) is an optional element and may not be included. That is, the Cr content may be 0.00%.
When included, Cr improves the properties of the oxide layer produced during the decarburization annealing process. In this case, the properties of the primary coating produced using this oxide layer during the final annealing step are improved. 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 0.00-0.50%.
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 0.40%, more preferably 0.30%, even more preferably 0.20%, and still more preferably 0.15%.

Sn: 0.00-0.30%,
Tin (Sn) is an optional element and may not be included. That is, the Sn content may be 0.00%.
When included, Sn improves the properties of the oxide layer produced during the decarburization annealing process. In this case, the properties of the primary coating produced using this oxide layer during the final annealing step are 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. If even a small amount of Sn is contained, the above effects can be obtained to some extent.
However, if the Sn content exceeds 0.30%, 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 0.00 to 0.30%.
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 0.25%, more preferably 0.20%.

Sb: 0.00~0.30%
Antimony (Sb) is an optional element and may not be included. That is, the Sb content may be 0.00%.
When included, Sb improves the properties of the oxide layer produced during the decarburization annealing process. In this case, the properties of the primary coating produced using this oxide layer during the final annealing step are improved. Furthermore, Sb 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 Sb is contained, the above effects can be obtained to some extent.
However, if the Sb content exceeds 0.30%, the surface of the steel sheet becomes difficult to oxidize, and the formation of the primary film may become insufficient.
Therefore, the Sb content is 0.00-0.30%.
The preferable lower limit of the Sb content in order to more effectively obtain the above effects is 0.01%, and more preferably 0.02%.
A preferable upper limit of the Sb content is 0.25%, more preferably 0.20%.

[Second group: Ni, Mo and P]
Ni, Mo, and P all reduce core loss of grain-oriented electrical steel sheets. Hereinafter, Ni, Mo and P will be explained.

Ni: 0.00~0.50%
Nickel (Ni) is an optional element and may not be included. That is, the Ni content may be 0.00%.
When contained, Ni homogenizes the hot rolled structure and improves the primary recrystallization texture. As a result, Ni reduces iron loss in grain-oriented electrical steel sheets (final products). If even a small amount of Ni is contained, the above effects can be obtained to some extent.
However, if the Ni content exceeds 0.50%, secondary recrystallization may become unstable even if the contents of other elements are within the range of this embodiment.
Therefore, the Ni content is 0.00-0.50%.
The preferable lower limit of the Ni content in order to more effectively obtain the above effects is 0.01%, and more preferably 0.02%.
A preferable upper limit of the Ni content is 0.45%, more preferably 0.40%, and still more preferably 0.35%.

Mo: 0.00~0.20%
Molybdenum (Mo) is an optional element and may not be included. That is, the Mo content may be 0.00%.
When contained, Mo increases the electrical resistance of the grain-oriented electrical steel sheet and reduces core loss. If even a small amount of Mo is contained, the above effects can be obtained to some extent.
However, if the Mo content exceeds 0.20%, the workability of the steel sheet will decrease even if the contents of other elements are within the range of this embodiment.
Therefore, the Mo content is 0.00-0.20%.
The lower limit of the Mo content is preferably 0.01%, more preferably 0.02%, and still more preferably 0.05% in order to more effectively obtain the above effects.
A preferable upper limit of the Mo content is 0.18%, more preferably 0.15%, and still more preferably 0.13%.

P: 0.00-0.15%
Phosphorus (P) is an optional element and may not be included. That is, the P content may be 0.00%.
When contained, P improves the primary recrystallization texture of the grain-oriented electrical steel sheet and reduces the core loss of the grain-oriented electrical steel sheet (final product). If even a small amount of P is contained, the above effects can be obtained to some extent.
However, if the P content exceeds 0.15%, the workability of the steel sheet will decrease even if the contents of other elements are within the range of this embodiment.
Therefore, the P content is 0.00-0.15%.
A preferable lower limit of the P content in order to more effectively obtain the above effects is 0.01%, more preferably 0.02%, and still more preferably 0.03%.
A preferable upper limit of the P content is 0.13%, more preferably 0.11%, and still more preferably 0.09%.

[Group 3: Cu, Se, V and Bi]
Cu, Se, V, and Bi all promote the production of inhibitors or function as inhibitors. Hereinafter, Cu, Se, V, and Bi will be explained.

Cu: 0.00-0.50%
Copper (Cu) is an optional element and may not be included. That is, the Cu content may be 0.00%.
When contained, Cu promotes the precipitation of fine MnS, which becomes the nucleus of AlN that functions as an inhibitor, 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 0.00-0.50%.
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%.

Se: 0.00~0.03%
Selenium (Se) is an optional element and may not be included. That is, the Se content may be 0.00%.
When contained, it combines with Mn during the hot rolling process to form fine MnSe. The fine MnSe becomes precipitation nuclei of fine AlN that functions as an inhibitor. Therefore, the formation of fine AlN is promoted in the hot rolling process. If even a small amount of Se is contained, the above effects can be obtained to some extent.
However, if the Se content exceeds 0.03%, MnSe may remain in the steel sheet after the final annealing process even if the contents of other elements are within the range of this embodiment. In this case, the magnetic properties of the grain-oriented electrical steel sheet deteriorate.
Therefore, the Se content is 0.00-0.03%.
The preferable lower limit of the Se content in order to more effectively obtain the above effects is 0.01%. A preferable upper limit of Se content is 0.02%.

V: 0.00~0.15%
Vanadium (V) is an optional element and may not be included. That is, the V content may be 0.00%.
When contained, it binds to C or N and functions as an inhibitor. If even a small amount of V is contained, the above effects can be obtained to some extent.
However, if the V content exceeds 0.15%, V inhibitors may remain in the steel sheet after the final annealing process even if the contents of other elements are within the range of this embodiment. In this case, the magnetic properties of the grain-oriented electrical steel sheet deteriorate.
Therefore, the V content is 0.00-0.15%.
A preferable lower limit of the V content in order to more effectively obtain the above effects is 0.01%, more preferably 0.02%, and still more preferably 0.03%.
A preferable upper limit of the V content is 0.13%, more preferably 0.11%, and still more preferably 0.09%.

Bi:0.0000~0.0100%
Bismuth (Bi) is an optional element and may not be included. That is, the Bi content may be 0.0000%.
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 0.0000 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%.

[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 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). Specifically, the hot rolling step S1 includes the following steps.
・Heating process S11
・Rough rolling process S12
・Finish rolling process S13

[Heating step S11]
In the heating step, 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 1100 to 1450°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 well-known rough rolling mill. The rough bar means a steel plate after completion of rough rolling and before start of finish rolling. In the rough rolling step, a rough rolling mill is used to apply a plurality of passes to the slab to produce a rough bar.

[Finish rolling process S13]
In the finish rolling step S13, the rough bar produced in the rough rolling step S12 is subjected to well-known finish rolling to produce a hot rolled steel plate. Here, finish rolling means hot rolling a rough bar using a well-known finish rolling mill. In the finish rolling step S13, a continuous rolling mill consisting of a plurality of tandem finish rolling stands arranged in a line on a pass line is used to apply a plurality of passes to the rough bar to perform hot rolling. Manufactures steel plates.

[Hot rolled plate annealing process S2]
In the hot rolled sheet annealing step S2, an annealing treatment is performed on the hot rolled steel sheet manufactured in the hot rolling step S1. By performing the hot-rolled sheet annealing step S2, recrystallization occurs in the steel sheet structure, and the magnetic properties are improved.

In the hot-rolled plate annealing step S2, it is sufficient to carry out well-known hot-rolled plate annealing. The method of heating the hot-rolled steel sheet in hot-rolled sheet annealing is not particularly limited, and any known heating method may be employed. The hot rolled sheet annealing temperature is, for example, 900 to 1200°C. The holding time at the hot rolled sheet annealing temperature is, for example, 10 to 300 seconds. In addition, when hot-rolled sheet annealing process S2 is implemented, you may implement pickling treatment with respect to a hot-rolled steel plate after hot-rolled sheet annealing process S2 and before cold rolling process S3.

[Cold rolling process S3]
In the cold rolling step S3, the manufactured hot rolled steel sheet is cold rolled to manufacture a cold rolled steel sheet. As mentioned above, the cold rolling step S3 includes the following two steps.
・Tandem rolling process S31
・Reverse rolling process S32
Each step S31 and S32 will be explained below.

[Tandem rolling process S31]
In the tandem rolling step S31, cold rolling is performed using a tandem rolling mill.
FIG. 2 is a schematic diagram of a tandem rolling mill. Referring to FIG. 2, the tandem rolling mill CM is arranged between a payoff reel (unwinding device) 11 and a tension reel (winding device) 12 from upstream to downstream.

The payoff reel 11 unwinds the hot-rolled steel sheet ST0. The tension reel 12 winds up the intermediate steel plate ST1 produced by the tandem rolling mill CM.
The tandem rolling mill CM performs continuous rolling of a plurality of passes on the rewound hot rolled steel sheet ST to manufacture an intermediate steel sheet ST1.

The tandem rolling mill CM includes a plurality of 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 rolling stand CMS includes a pair of horizontally extending work rolls WR1. The pair of work rolls WR1 come into contact with the hot-rolled steel sheet to be cold-rolled, and cold-roll the hot-rolled steel sheet. The rolling stand CMS may include a plurality of backup rolls BR1. Backup roll BR1 supports work roll WR1 and suppresses deflection of work roll WR1 during rolling.

In continuous rolling using a tandem rolling mill CM, rolling down a hot rolled steel sheet at each rolling stand CMS when passing through each rolling stand CMS is referred to as "one pass" rolling. Continuous rolling means rolling in multiple passes using a tandem rolling mill CM. Note that it is not necessary to roll down the hot rolled steel sheet in all the rolling stands CMS in the tandem rolling mill CM. For example, when six rolling stands CMS ₁ to CMS ₆ are arranged in a tandem rolling mill CM, and when a hot rolled steel plate is passed through rolling stand CMS ₆ without being rolled, five passes of continuous rolling are performed. This means that this has been carried out.

[Reverse rolling process S32]
FIG. 3 is a schematic diagram of a multi-high rolling mill used in the reverse rolling process S32. Referring to FIG. 3, in the reverse rolling step S32, a multi-stage rolling mill SM is used to perform reverse rolling for a plurality of passes on the intermediate steel sheet ST1 after the tandem rolling step S31, thereby forming a cold rolled steel sheet ST2. Manufacture.

The multi-high rolling mill is, for example, a Sendzimir rolling mill. The multi-high rolling mill SM includes a pair of work rolls WR2 and a plurality of backup rolls BR2. In the multi-high rolling mill SM, the deflection of the work roll WR2 is suppressed as much as possible by supporting the pair of work rolls WR2 with a plurality of backup rolls BR2. This makes it possible to achieve a high reduction.

Here, when the intermediate steel plate ST1 is subjected to a rolling reduction when the intermediate steel plate ST1 passes through the multi-stage rolling mill SM, it means that one pass of rolling has been performed. In the case of reverse rolling, rolling is performed when intermediate steel plate ST1 moves from upstream to downstream, and rolling is also performed when intermediate steel plate ST1 moves from downstream to upstream. More specifically, when the intermediate steel plate ST1 passes through the multi-stage rolling mill SM from upstream to downstream, one pass of rolling is applied to the intermediate steel plate ST1. Also, when the intermediate steel plate ST1 passes through the same multi-stage rolling mill SM from downstream to upstream, one pass of rolling is applied to the intermediate steel plate ST1. That is, when rolling is performed in a reciprocating manner, rolling is performed in two passes on the intermediate steel plate ST1. Note that when the intermediate steel plate ST1 passes through the multi-stage rolling mill SM, there are cases where no rolling is applied to the intermediate steel plate ST1.

In the cold rolling step S3, the above tandem rolling step S31 and reverse rolling step S32 are performed to manufacture a cold rolled steel sheet.

[Manufacturing conditions in cold rolling process S3]
In the cold rolling process S3, the following conditions 1 to 8 are satisfied.
(Conditions for tandem rolling process S31)
Condition 1: Continuous rolling with a plurality of passes is performed using a tandem rolling mill CM.
Condition 2: The average diameter D1 of the work roll WR1 is 200 mm or more.
Condition 3: Cumulative rolling reduction rate CR1 is 30 to 87%.
(Conditions for reverse rolling process S32)
Condition 4: Reverse rolling is performed in a plurality of passes using a multi-high rolling mill SM.
Condition 5: An intermediate steel plate that has not been subjected to heat treatment after the tandem rolling process is to be rolled.
Condition 6: The average diameter D2 of the work roll WR2 is 100 mm or less.
Condition 7: Cumulative rolling reduction rate CR2 is 24 to 86%.
(Overall conditions of cold rolling process S3)
Condition 8: The cumulative rolling reduction CR0 in the entire cold rolling step S3 is 90% or more.
Conditions 1 to 8 will be explained below.

[Conditions of tandem rolling process S31]
[About condition 1]
In the tandem rolling process S31, continuous rolling is performed in a plurality of passes using the tandem rolling mill CM described above to manufacture the intermediate steel plate ST1. As mentioned above, in tandem rolling, rolling can be performed using rolls with a larger roll diameter than in reverse rolling. Therefore, compared to reverse rolling, shear strain imparted to the steel sheet can be suppressed. As a result, the size of Goss-oriented crystal grains can be suppressed as much as possible in the final annealing step. Therefore, in the grain-oriented electrical steel sheet, not only can a sufficient magnetic flux density be obtained, but also the difference between the magnetic flux density at the outermost circumferential portion and the magnetic flux density at the innermost circumferential portion of the coil of the grain-oriented electromagnetic steel sheet can be reduced. In other words, variations in magnetic flux density of the grain-oriented electrical steel sheet can be suppressed.

[About condition 2]
In tandem rolling, the average diameter D1 of the plurality of work rolls used in each pass is 200 mm or more. In a multi-stage rolling mill (Sendzimir rolling mill) used in the reverse rolling process described below, the diameter of the work roll is kept to 100 mm or less in order to suppress deflection of the work roll, and the work roll is supported by a plurality of backup rolls. In a multi-high rolling mill, high pressure is exerted by a combination of such a pair of work rolls and a plurality of backup rolls that support the work rolls. However, since the diameter of the work rolls is small, rolling using a Sendzimir rolling mill results in large shear strain imparted to the steel sheet being rolled.

As described above, when the applied shear strain is large, α-fiber orientation groups develop in the surface layer of the cold-rolled steel sheet. When the α-fiber orientation group develops, the number of Goss-oriented grains that become the nucleus of secondary recrystallization decreases due to grain growth just before the onset of secondary recrystallization. Therefore, the secondary recrystallized grains become coarse. As a result, the magnetic properties of the grain-oriented electrical steel sheet become low or vary.

In this embodiment, tandem rolling is adopted as part of the cold rolling, and the average diameter D1 of the plurality of work rolls used in each pass is set to 200 mm or more. In this case, the amount of shear strain imparted to the surface layer of the steel sheet during cold rolling can be reduced. In this case, during cold rolling, the γ fiber orientation group is more stable than the α fiber orientation group. Therefore, in the surface layer of the cold-rolled steel sheet, the α-fiber orientation group is suppressed, and the γ-fiber orientation group remains. The γ fiber orientation group produces {111} recrystallized grains when primary recrystallization occurs. In the final annealing step, the {111} recrystallized grains suppress the erosion of Goss-oriented grains by other crystal grains before secondary recrystallization occurs. Therefore, the degree of integration in the Goss orientation after secondary recrystallization can be increased. As a result, the magnetic properties of the grain-oriented electrical steel sheet can be improved, and variations in the magnetic properties can also be suppressed.

The average diameter D1 is an arithmetic mean value of the diameters (mm) of each of the plurality of pairs of work rolls used in each pass.

The lower limit of the average diameter D1 is preferably 250 mm, more preferably 300 mm, even more preferably 325 mm, and still more preferably 350 mm.
A preferable upper limit of the average diameter D1 is 1000 mm, more preferably 900 mm, still more preferably 800 mm, still more preferably 700 mm, and still more preferably 650 mm.

[About condition 3]
The cumulative rolling reduction ratio CR1 in the tandem rolling process is set to 30 to 87%. Here, the cumulative rolling reduction rate CR1 (%) is defined by the following equation (1).
CR1 = (Thickness of hot rolled steel plate before tandem rolling process - Thickness of intermediate steel plate after tandem rolling process) / Thickness of hot rolled steel plate before tandem rolling process x 100 (1)

If the cumulative rolling reduction ratio CR1 is less than 30%, the rolling reduction in the tandem rolling process is insufficient. In this case, the amount of reduction in the reverse rolling process increases. Therefore, the amount of shear strain imparted to the cold rolled steel sheet becomes excessively large. Therefore, the degree of accumulation of Goss orientation after secondary recrystallization becomes low. As a result, the magnetic properties of the grain-oriented electrical steel sheet deteriorate.
On the other hand, if the cumulative rolling reduction ratio CR1 exceeds 87%, the amount of rolling reduction in the reverse rolling process is too small. In this case, the amount of shear strain imparted to the cold rolled steel sheet becomes too small. If the shear strain is too small, non-uniform deformation regions called shear bands, which are the origin of primary recrystallization of Goss orientation, will be reduced. Therefore, secondary recrystallization nuclei (Goss oriented grains) decrease. As a result, variations in the magnetic properties of grain-oriented electrical steel sheets occur.
Therefore, the cumulative rolling reduction rate CR1 is set to 30 to 87%.
A preferable lower limit of the cumulative rolling reduction ratio CR1 is 35%, more preferably 40%, and still more preferably 45%.
A preferable upper limit of the cumulative rolling reduction ratio CR1 is 85%, more preferably 80%, and still more preferably 75%.

[Conditions for reverse rolling process S32]
[About condition 4]
In the reverse rolling step S32, using the multi-high rolling mill SM, reverse rolling is performed for a plurality of passes on the intermediate steel sheet ST1, which has not been heat treated after the tandem rolling step S31, to produce a cold rolled steel sheet. In reverse rolling using a multi-high rolling mill SM, a higher rolling reduction can be applied to a steel sheet than in tandem rolling. Therefore, the cold rolled steel sheet can be made thinner.

[About condition 5]
The object to be rolled in the reverse rolling process S32 is an intermediate steel plate that has not been subjected to heat treatment after the tandem rolling process S31. That is, in the reverse rolling process S32, the intermediate steel plate, which is the tandem-rolled material, is to be rolled. Here, "heat treatment" means a treatment in which a steel plate is heated to a temperature of 500° C. or higher and/or maintained for a predetermined period of time. The heat treatment is, for example, annealing.

When heat treatment such as annealing is performed on the intermediate steel plate ST1 manufactured by the tandem rolling process S31, recovery and recrystallization within the intermediate steel plate ST1 progresses, and the total strain introduced by cold rolling is reduced. In this case, even if the cumulative reduction rate CR0 after the reverse rolling step S32 is 90% or more, the magnetic properties of the grain-oriented electrical steel sheet deteriorate. This is because when heat treatment is performed on the intermediate steel plate ST1, the strain decreases as described above, and as a result, the primary recrystallization texture in the center layer of the steel plate deteriorates. Specifically, the steel sheet center layer inherits the α fiber orientation group formed in the hot rolling process S1. Even after the reverse rolling process S32, the α-fiber orientation group in the center layer of the steel sheet is significantly developed compared to the surface layer of the steel sheet. In order to promote recrystallization of this α-fiber orientation group, a cumulative reduction rate CR0 of 90% or more is required.

When heat treatment such as annealing is performed on the intermediate steel plate ST1, even if the cumulative reduction rate CR0 is 90% or more, recrystallization of the α-fiber orientation group in the center layer of the steel plate cannot be promoted. If the recrystallization of the α-fiber orientation group in the center layer of the steel sheet is not sufficiently promoted, the {411}<148> recrystallization orientation decreases in the center layer of the steel sheet. The {411}<148> recrystallization orientation has a Σ9 correspondence relationship with the Goss orientation, and promotes secondary recrystallization of the Goss orientation.

[About condition 6]
In reverse rolling using a multi-high rolling mill, the average diameter D2 of the plurality of work rolls WR2 used in each pass is set to 100 mm or less. If the average diameter D2 exceeds 100 mm, a sufficient rolling reduction cannot be applied to the intermediate steel plate ST1 to be reverse rolled. In this case, sufficient shear strain cannot be applied to the intermediate steel plate ST1.
If the average diameter D2 is 100 mm or less, sufficient shear strain can be applied to the intermediate steel plate ST1 to be reverse rolled in each pass. As a result, it is possible to sufficiently form a shear zone which becomes the origin of primary recrystallization of the Goss orientation, and a sufficient amount of Goss oriented grains are generated in the decarburization annealing step S4.

When performing reverse rolling using one multi-high rolling mill SM, the average diameter D1 is the arithmetic mean value of the diameters (mm) of each of the pair of work rolls used in each pass. When reverse rolling is performed using a plurality of multi-high rolling mills SM, the average diameter D2 is an arithmetic mean value of the diameters (mm) of each of a plurality of pairs of work rolls used in each pass.

A preferable upper limit of the average diameter D2 is 95 mm, more preferably 90 mm, and still more preferably 85 mm.
The lower limit of the average diameter D2 is not particularly limited. The preferable lower limit of the average diameter D2 is 50 mm, more preferably 55 mm, and still more preferably 60 mm.

[About condition 7]
The cumulative rolling reduction ratio CR2 in the reverse rolling step S32 is set to 24 to 86%. Here, the cumulative rolling reduction rate CR2 (%) is defined by the following equation (2).
CR2 = (Thickness of intermediate steel plate before reverse rolling process - Thickness of cold rolled steel plate after reverse rolling process) / Thickness of intermediate steel plate before reverse rolling process x 100 (2)

If the cumulative rolling reduction ratio CR2 is less than 24%, the rolling reduction in the reverse rolling process is insufficient. In this case, there is a shortage of shear bands that serve as the origin of the primary recrystallization of the Goss orientation, and a sufficient number of Goss oriented grain nuclei generated by the primary recrystallization are not generated in the subsequent decarburization annealing step S4. Therefore, the degree of accumulation of Goss orientation after secondary recrystallization becomes low. As a result, the magnetic properties of the grain-oriented electrical steel sheet deteriorate.
On the other hand, if the cumulative rolling reduction ratio CR2 exceeds 86%, the applied shear strain increases and α fiber orientation groups develop in the surface layer of the cold rolled steel sheet. When the α-fiber orientation group develops, in the final annealing step S5, the number of Goss-oriented grains that become the nucleus of secondary recrystallization decreases due to grain growth just before the appearance of secondary recrystallization. Therefore, the secondary recrystallized grains become coarse. As a result, the magnetic properties of the grain-oriented electrical steel sheet become low or vary.
Therefore, the cumulative rolling reduction rate CR2 is set to 24 to 86%.

A preferable lower limit of the cumulative rolling reduction rate CR2 is 30%, more preferably 35%, and still more preferably 40%.
A preferable upper limit of the cumulative rolling reduction ratio CR2 is 80%, more preferably 75%, and still more preferably 70%.

[About condition 8]
The cumulative rolling reduction ratio CR0 in the entire cold rolling process S3 (tandem rolling process S31 and reverse rolling process S32) is set to 90% or more. Here, the cumulative rolling reduction rate CR0 (%) is defined by the following equation (3).
CR0 = (Thickness of hot rolled steel plate before tandem rolling process - Thickness of cold rolled steel plate after reverse rolling process) / Thickness of hot rolled steel plate before tandem rolling process x 100 (3)

If the cumulative rolling reduction ratio CR0 is less than 90%, the rolling reduction in the cold rolling process is insufficient. In this case, the total amount of strain accumulated in the cold-rolled steel sheet is small, and the magnetic properties of the grain-oriented electrical steel sheet deteriorate. This is because if the cumulative rolling reduction ratio CR0 is less than 85%, the total amount of strain accumulated in the cold rolled steel sheet is too small, and as a result, the primary recrystallization texture in the center layer of the steel sheet deteriorates. Specifically, the center layer of the steel sheet inherits the α-fiber orientation group formed in the hot rolling process. Therefore, even after the reverse rolling step S32, the α-fiber orientation group in the center layer of the steel sheet is significantly developed compared to the surface layer of the steel sheet. In order to promote recrystallization of this α-fiber orientation group, a cumulative reduction rate CR0 of 90% or more is required.

When heat treatment such as annealing is performed on the intermediate steel plate ST1, even if the cumulative reduction rate CR0 is 90% or more, recrystallization of the α-fiber orientation group in the center layer of the steel plate cannot be promoted. If the recrystallization of the α-fiber orientation group in the center layer of the steel sheet cannot be promoted, the {411}<148> recrystallization orientation will decrease in the center layer of the steel sheet. This {411}<148> recrystallization orientation has a Σ9 correspondence relationship with the Goss orientation, and has the role of promoting secondary recrystallization of the Goss orientation.
Therefore, the cumulative rolling reduction rate CR0 is set to 90% or more.

A preferable lower limit of the cumulative rolling reduction ratio CR0 is 91%, more preferably 92%, and still more preferably 93%.
A preferable upper limit of the cumulative rolling reduction ratio CR0 is 97%, more preferably 95%.

In the cold rolling step S3, tandem rolling and reverse rolling are performed so as to satisfy the above-mentioned conditions 1 to 8 to produce a cold rolled steel sheet in which the amount of shear strain in the surface layer of the steel sheet is controlled. By performing post-processing using this cold-rolled steel sheet, it is possible to manufacture a grain-oriented electrical steel sheet in which variations in magnetic flux density are suppressed.

[Decarburization annealing step S4]
In the decarburization annealing step S4, decarburization annealing is performed on the cold rolled steel sheet after the cold rolling step S3 to cause primary recrystallization to occur.

The decarburization annealing step S4 includes the following steps.
・Temperature raising step S41
・Decarburization step S42
・Cooling process S43

In the temperature raising step S41, the steel plate is heated to an arbitrary temperature (achieved temperature) from 750°C to 950°C. In the decarburization step S42, the steel plate is held at a decarburization annealing temperature of 750° C. to 950° C. to carry out decarburization annealing, thereby causing primary recrystallization to occur. In the cooling step S43, the steel plate after the decarburization step S42 is cooled by a well-known method. Note that the attained temperature and the decarburization annealing temperature may be the same temperature, or the attained temperature may be higher than the decarburization annealing temperature.

In the present embodiment, in the temperature increasing step S41, the average temperature increasing rate HR in the temperature range of 550° C. to 750° C., which corresponds to the recrystallization temperature range of the steel plate, is significantly increased. This promotes recrystallization of the Goss orientation. Thereby, the degree of integration in the Goss orientation after secondary recrystallization can be increased. As a result, the magnetic properties of the grain-oriented electrical steel sheet can be improved, and variations in the magnetic properties can also be suppressed.

The details of each step will be explained below.

[Temperature raising step S41]
In the temperature raising step S41, first, the cold rolled steel sheet after the cold rolling step (S3) is charged into a heat treatment furnace. In the heat treatment furnace for decarburization annealing in this embodiment, a cold rolled steel sheet is heated to an arbitrary temperature of 750° C. to 950° C., for example, by high frequency induction heating or electrical heating. The temperature raising step S41 satisfies the following condition 9.
Condition 9: Average heating rate HR in the range of 550°C to 750°C: 100°C/sec or more

[About condition 9]
In the temperature increase step S41, the average temperature increase rate in the temperature range of 550° C. to 750° C. of the cold rolled steel sheet is defined as the average temperature increase rate HR (° C./sec).

As mentioned above, strain is accumulated in cold-rolled steel sheets. If the average heating rate HR is less than 100° C./sec, the strain energy that serves as the driving force for recrystallization will be released before recrystallization starts. In this case, a sufficient amount of Goss-oriented grains cannot be generated in the cold-rolled steel sheet after primary recrystallization (that is, the cold-rolled steel sheet after the decarburization annealing step).

If the average temperature increase rate HR is 100° C./second or more, primary recrystallization occurs in a state where strain energy is sufficiently accumulated in the cold rolled steel sheet. Therefore, a sufficient amount of Goss-oriented grains can be generated in the cold-rolled steel sheet after primary recrystallization. Therefore, in the final annealing step S5, which is a subsequent step, many Goss-oriented grains remain when secondary recrystallization occurs. Therefore, the degree of integration in the Goss orientation after secondary recrystallization can be increased. As a result, the magnetic properties of the grain-oriented electrical steel sheet can be improved, and variations in the magnetic properties can also be suppressed.

Note that the upper limit of the average temperature increase rate HR is not particularly limited. However, even if the average heating rate HR is higher than 2000° C./sec, the above effect is saturated. Therefore, the upper limit of the average heating rate HR is 2000°C/sec.

The preferable lower limit of the average heating rate HR is 150°C/sec, more preferably 200°C/sec, even more preferably 300°C/sec, even more preferably 400°C/sec, and even more preferably 500°C/sec. C/sec, more preferably 600 C/sec, even more preferably 700 C/sec, still more preferably 800 C/sec, even more preferably 900 C/sec.

The average temperature increase rate HR 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. The average temperature increase rate HR is determined based on the temperature of the steel plate measured by the thermometer and the time taken for the steel plate temperature to rise from 550°C to 750°C.

[Decarburization step S42]
In the decarburization step S42, the cold rolled steel sheet after the temperature raising step S41 is held at the decarburization annealing temperature Ta, and decarburization annealing is performed. This causes the cold rolled steel sheet 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 decarburization annealing temperature Ta and the holding time at the decarburization annealing temperature Ta are not particularly limited. The decarburization annealing temperature Ta is, for example, 800 to 950°C. 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 cold rolled steel sheet after the decarburization step S42 is cooled to room temperature by a well-known method to obtain a decarburized annealed steel sheet. The cooling method may be air cooling or water cooling. Preferably, the cold rolled steel sheet after the decarburization step S42 is allowed to cool. In the decarburization annealing step (S4), a decarburization annealing steel plate is manufactured through the above steps.

[Final annealing step S5]
In the finish annealing step S5, an annealing separator is applied to the decarburized annealed steel plate, and finish annealing is performed on the decarburized annealed steel plate coated with the annealing separator to produce a finish annealed steel plate.
The final annealing step S5 includes the following steps.
・Annealing separator application step S51
・Annealing process S52
Each step will be explained below.

[Annealing separator application step S51]
In the annealing separator application step S51, an annealing separator is applied to the decarburized annealed steel plate. Specifically, an aqueous slurry containing an annealing separator is applied to a decarburized annealed 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 S51, an aqueous slurry annealing separator is applied onto the surface of the decarburized annealed steel sheet. 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, an annealing step S52 is performed.

[Annealing step S52]
The steel plate after the annealing separator application step S51 is subjected to an annealing step S52 to cause secondary recrystallization. The final annealing step (S5) is carried out by charging the coiled steel plate into a heat treatment furnace. For example, the manufacturing conditions in the annealing step S52 are as follows. Note that the atmosphere in the furnace in the annealing step S52 is a well-known atmosphere.

Finish annealing temperature: 1000-1300℃
Holding time at final annealing temperature: 5 to 60 hours If the final annealing temperature is less than 1000°C, sufficient secondary recrystallization will not occur, and purification to remove precipitates used for 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 1300° C., the effect on secondary recrystallization and purification is low, and problems such as deformation of the steel plate occur. If the final annealing temperature is 1000 to 1300°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 on the surface of the steel plate.
Through the above manufacturing process, a final annealing steel plate is manufactured in the final annealing step S5.

In addition, each element of the chemical composition of the steel plate is removed from the steel plate to some extent by the final annealing step S5. 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 S5.

[Insulating film forming step S6]
In the insulating film forming step S6, an insulating film forming liquid is applied to the finish annealed steel plate, and the finish annealed steel plate coated with the insulating film forming liquid is heat treated to form an insulating film on the finish annealed steel plate.

Specifically, a well-known insulating film forming liquid mainly containing colloidal silica and phosphate is applied to the surface (on the primary coating) of the finish annealed steel sheet. Then, baking is performed on the finish annealed steel plate coated with the insulating film forming liquid. As a result, a well-known insulating film is formed on the primary film.

[Other arbitrary steps]
[Nitriding process]
The method for manufacturing grain-oriented electrical steel sheet 1 according to the present embodiment may further include a nitriding step after the decarburization annealing step and before the finish annealing step, if necessary. The nitriding process may be carried out under known conditions. For example, preferable nitriding conditions are as follows.
Nitriding temperature: 700-850℃
Atmosphere inside the nitriding furnace (nitriding atmosphere): An atmosphere containing gases with nitriding ability such as hydrogen, nitrogen, and ammonia.

If the nitriding temperature is 700° C. or higher or 850° C. or lower, nitrogen tends to penetrate into the steel sheet during the nitriding process. If the nitriding treatment is performed within this temperature range, a preferable amount of nitrogen can be ensured inside the steel sheet. Therefore, fine AlN is preferably formed in the steel sheet before secondary recrystallization. As a result, secondary recrystallization preferably occurs during final annealing. Note that the time for holding the steel plate at the nitriding temperature is not particularly limited, but is, for example, 10 to 60 seconds.

[Magnetic domain refining process]
The grain-oriented electrical steel sheet according to the present embodiment may further be subjected to a magnetic domain refining treatment step after the final annealing step S5 or the insulation film forming step S6, 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.

[Summary of manufacturing process]
As described above, in the manufacturing method of the present embodiment, by satisfying Conditions 1 to 8 in the cold rolling step S3, the development of the α-fiber orientation group in the surface layer of the steel sheet in the cold-rolled steel sheet is suppressed, and the γ-fiber orientation is Leave a sufficient amount of the group remaining. Then, the cold-rolled steel sheet is subjected to a decarburization annealing step S4 that satisfies Condition 9. As a result, in the decarburization annealing step S4, a sufficient amount of {111} recrystallization groups as well as a sufficient amount of fine Goss-oriented grains are generated in the steel sheet surface layer of the decarburized annealed steel sheet after primary recrystallization has occurred.

In the final annealing step S5, the {111} recrystallization group suppresses grains other than the fine Goss orientation grains from becoming coarser before secondary recrystallization occurs. Therefore, it is possible to suppress other crystal grains from becoming coarse and eating away at the Goss-oriented grains. As a result, a sufficient amount of Goss-oriented grains undergo secondary recrystallization, and the degree of accumulation of Goss-oriented grains can be increased. As a result, the magnetic flux density of the grain-oriented electrical steel sheet can be increased.

Furthermore, since a sufficient amount of Goss-oriented grains undergo secondary recrystallization, it is possible to suppress the secondary recrystallized grains (Goss-oriented grains) from increasing in diameter. By suppressing the grain size of the Goss-oriented grains after secondary recrystallization, the texture of the coiled steel sheet can be improved by reducing the variation from the Goss orientation, specifically, the <100> grains parallel to the rolling direction of each grain. It is possible to suppress deviation from the direction. Therefore, it is possible to suppress variations in magnetic flux density between a portion near the outer periphery and a portion near the inner periphery of the coiled grain-oriented electrical steel sheet.

In addition, in the manufacturing method of this embodiment, even if the in-process time, which is the period from hot-rolled sheet annealing step S2 to cold rolling step S3, becomes long, the grain-oriented electrical steel sheet to be manufactured can be sufficiently A high magnetic flux density can be obtained, and variations in magnetic flux density between a portion near the outer periphery and a portion near the inner periphery of the grain-oriented electrical steel sheet can be suppressed. In addition, as in the case where the in-process time becomes long, even if annealing treatment is performed to suppress the occurrence of brittle cracks in the cold rolling process S3, the grain-oriented electrical steel sheet to be manufactured may A sufficiently high magnetic flux density can be obtained, and variations in magnetic flux density between a portion near the outer periphery and a portion near the inner periphery of the grain-oriented electrical steel sheet can be suppressed.

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 Conditions 1 to 9 in the manufacturing process described above.

Specifically, the chemical composition is C: 0.08%, Si: 3.3%, Mn: 0.08%, S: 0.02%, sol. A slab containing 0.03% Al and 0.01% N, with the balance being Fe and impurities was prepared.

Hot rolling step S1 was performed on the slabs of each test number shown in Tables 1-1 and 1-2. Specifically, the slabs of each test number were heated to 1340°C in a heating furnace. The heated slab was hot rolled to produce a hot rolled steel plate with a thickness of 1.8 to 3.5 mm.

The hot rolled steel sheet after the hot rolling process was subjected to a hot rolled sheet annealing step S2 at a hot rolled sheet annealing temperature of 900 to 1200° C. and a holding time of 10 to 300 seconds. After the hot rolled sheet annealing step S2, a cold rolling step S3 was performed to produce a cold rolled steel sheet having a thickness of 0.22 mm. Specifically, after implementing the 1st cold rolling process, the 2nd cold rolling process was implemented. Conditions 1 to 9 were as shown in Tables 1-1 and 1-2.

Specifically, "reverse" in the "condition 1" column of the "first cold rolling process" column in Table 1-1 means that a reverse rolling process was performed as the first cold rolling process. . "Tandem" means that a tandem rolling process was performed as the first cold rolling process.

In the "Condition 2" column of the "First Cold Rolling Step" column in Table 1-1, the average diameter D1 (mm) of the work rolls used in each pass is listed. In "Condition 3" in the "First Cold Rolling Step" column in Table 1-1, the cumulative rolling reduction CR1 (%) in the first cold rolling step is listed.

"Reverse" in the "Condition 4" column of the "Second Cold Rolling Step" column in Table 1-1 means that a reverse rolling step was performed as the second cold rolling step. "Tandem" means that a tandem rolling process was performed as the second cold rolling process. "-" means that the second cold rolling step was not performed.

The "Condition 5" column in the "Second Cold Rolling Step" column in Table 1-1 indicates whether or not the cold rolled steel sheet to be rolled has been heat treated. "None" means that a cold-rolled steel sheet that has not been annealed and is an as-rolled material is subjected to rolling in the second cold rolling step. “Present” means that the annealed cold-rolled steel sheet was subjected to rolling in the second cold-rolling step. In addition, during annealing, the cold rolled steel plate was held at 1100° C. for 80 seconds.

In the "Condition 6" column of the "Second Cold Rolling Step" column in Table 1-1, the average diameter D2 (mm) of the work rolls used in each pass is listed. In "Condition 7" in the "Second cold rolling process" column in Table 1-1, the cumulative rolling reduction ratio CR2 (%) in the second cold rolling process is listed.

In the "Condition 8" column in Table 1-1, the cumulative rolling reduction rate CR0 (%) of the entire cold rolling step S3 is listed.

A decarburization annealing step S4 was performed on the cold rolled steel sheet after the cold rolling step S3. Specifically, after the temperature was raised to a final temperature of 870°C, the decarburization annealing temperature was held at 830°C for 80 seconds. Thereafter, the cold-rolled steel sheet was allowed to cool to room temperature to obtain a decarburized annealed steel sheet. In addition, during temperature increase, the average temperature increase rate HR from 550 ° C to 750 ° C was as described in the "Condition 9" column of "Decarburization annealing step 4" in Table 1-2. .

An annealing separator containing MgO as a main component was applied to the surface of a decarburized annealed steel sheet. Thereafter, the decarburized annealed steel plate coated with the annealing separator was wound into a coil. Hereinafter, the coiled steel plate will also be simply referred to as a "coil." The radius of curvature of the inner circumference of the coil was 250 mm, and the radius of curvature of the outer circumference of the coil was 850 mm.

Finish annealing was performed on the coil to produce a finish annealed steel plate. The final annealing temperature in the final annealing was 1100°C to 1200°C, and the holding time at the final annealing temperature was 5 to 30 hours.

An insulation film forming step S6 was performed on the steel plate after the final annealing step S5. Specifically, an insulating film forming liquid mainly containing colloidal silica and phosphate was applied to the surface of the finish annealed steel plate of each test number. Thereafter, the finish annealed steel plate coated with the insulating film forming liquid was baked under the same conditions to form an insulating film on the primary film. Through the above manufacturing process, coil-shaped grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
Of the grain-oriented electrical steel sheets produced for each test number, test pieces were taken from the innermost and outermost parts of the coil during final annealing. The size of the test piece was 60 mm x 300 mm x plate thickness. Hereinafter, the test piece at the innermost circumference of the coil will be referred to as the "inner circumference test piece," and the test piece at the outermost circumference of the coil will be referred to as the "outer circumference test piece."

The magnetic flux density B8 of the inner circumference test piece and the outer circumference test piece was determined in accordance with JIS C2556:2015. Furthermore, the magnetic flux density difference ΔB was determined using the following equation.
ΔB=Magnetic flux density of the outer circumference test piece B8−Magnetic flux density of the inner circumference test piece B8

[Evaluation results]
The obtained magnetic flux density B8 is shown in Table 1-2.
In test numbers 3-6, 8-16, 18-23, 25-33, 42 and 43, conditions 1-9 were appropriate. Therefore, the magnetic flux density B8 was 1.911T or more in both the inner circumference test piece and the outer circumference test piece. Furthermore, ΔB was 0.006T or less, and there was little variation in magnetic flux density.

On the other hand, in test number 1, the second cold rolling step was not performed. Therefore, the magnetic flux density B8 of the inner circumference test piece and the outer circumference test piece was low. Furthermore, ΔB exceeded 0.006T, and the variation in magnetic flux density was large.

In test number 2, condition 2 was not satisfied. Therefore, the magnetic flux density B8 of the inner circumference test piece and the outer circumference test piece was low. Furthermore, ΔB was 0.006T or more, and the variation in magnetic flux density was large.

In test numbers 7 and 24, condition 8 was not satisfied. Therefore, the degree of accumulation in the Goss direction was low. As a result, the magnetic flux density B8 of both the inner circumference test piece and the outer circumference test piece was low.

In test number 17, the lower limit of condition 3 was not satisfied. Condition 7 exceeded the upper limit. Therefore, the magnetic flux density B8 of the inner circumference test piece and the outer circumference test piece was low. Furthermore, ΔB exceeded 0.006T, and the variation in magnetic flux density was large.

In test number 34, the upper limit of condition 3 was not satisfied. Therefore, condition 7 was less than the lower limit. Therefore, the degree of accumulation in the Goss direction was low. As a result, the magnetic flux density B8 of both the inner circumference test piece and the outer circumference test piece was low. Furthermore, ΔB exceeded 0.006T, and the variation in magnetic flux density was large.

In test numbers 35 to 39, heat-treated intermediate steel plates were rolled in the reverse rolling process. Therefore, the degree of accumulation in the Goss direction was low. As a result, the magnetic flux density B8 of both the inner circumference test piece and the outer circumference test piece was low, and ΔB exceeded 0.006T in some cases.

Condition 9 was not satisfied in test numbers 40 and 41. Therefore, the degree of accumulation in the Goss direction was low. As a result, the magnetic flux density B8 of both the inner circumference test piece and the outer circumference test piece was low. Furthermore, ΔB exceeded 0.006T, and the variation in magnetic flux density was large.

In Example 2, grain-oriented electrical steel sheets were manufactured using slabs having various chemical compositions. Specifically, slabs having chemical compositions shown in Tables 2-1 and 2-2 were prepared.

The "-" in the element content in Table 2-1 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. For example, the Cr content specified in this embodiment is specified as a numerical value to the second decimal place. Therefore, test number 1 in Table 2-1 means that the measured Cr content was 0% when rounded to the second 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 2-1 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.

Hot rolling step S1 was performed on the slabs of each test number listed in Tables 2-1 and 2-2. Specifically, the slabs of each test number were heated to 1340°C in a heating furnace. The heated slab was hot rolled to produce a hot rolled steel plate with a thickness of 2.3 mm.

The hot rolled steel sheet after the hot rolling process was subjected to a hot rolled sheet annealing step S2 at a hot rolled sheet annealing temperature of 900 to 1200° C. and a holding time of 10 to 300 seconds.

After the hot rolled sheet annealing step S2, a cold rolling step S3 was performed to produce a cold rolled steel sheet having a thickness of 0.22 mm. Specifically, first, a tandem rolling process S31 was performed on a hot rolled steel plate to produce an intermediate steel plate. In the tandem rolling process, rolling was performed in 5 passes. The average diameter D1 of the work rolls in tandem rolling was 500 mm, and the cumulative rolling reduction CR1 was 60%. A reverse rolling process was carried out without applying heat treatment to the intermediate steel plate. In the reverse rolling process, three passes of rolling were performed. The average diameter of the work rolls in the reverse rolling process was 70 mm, and the cumulative rolling reduction CR2 was 76%. The cumulative rolling reduction ratio CR0 of the entire cold rolling process S3 was 90%.

A decarburization annealing step S4 was performed on the cold rolled steel sheet after the cold rolling step S3. Specifically, after raising the temperature to a final temperature of 850°C, it was held at a decarburization annealing temperature of 830°C for 80 seconds. Thereafter, the cold-rolled steel sheet was allowed to cool to room temperature to obtain a decarburized annealed steel sheet. Note that during temperature increase, the average temperature increase rate HR from 550°C to 750°C was 1300°C/sec.

An annealing separator containing MgO as a main component was applied to the surface of a decarburized annealed steel sheet. Thereafter, the decarburized annealed steel plate coated with the annealing separator was wound into a coil. Hereinafter, the coiled steel plate will also be simply referred to as a "coil." The curvature reflection of the inner circumference of the coil was 250 mm, and the radius of curvature of the outer circumference of the coil was 850 mm.

Finish annealing was performed on the coil to produce a finish annealed steel plate. The final annealing temperature in the final annealing was 1100°C to 1200°C, and the holding time at the final annealing temperature was 5 to 30 hours.

An insulation film forming step S6 was performed on the steel plate after the final annealing step S5. Specifically, an insulating film forming liquid mainly containing colloidal silica and phosphate was applied to the surface of the finish annealed steel plate of each test number. Thereafter, the finish annealed steel plate coated with the insulating film forming liquid was baked under the same conditions to form an insulating film on the primary film. Through the above manufacturing process, coil-shaped grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
As in Example 1, an inner circumference test piece and an outer circumference test piece were taken from the coiled grain-oriented electrical steel sheets of each test number. Then, the magnetic flux density B8 of the inner circumference test piece and the outer circumference test piece was determined in accordance with JIS C2556:2015. Furthermore, the magnetic flux density difference ΔB was determined.

[Test results]
The evaluation results are shown in Table 2-2.
In any of the grain-oriented electrical steel sheets of test numbers 1 to 15, the chemical composition of the slab was appropriate. Furthermore, conditions 1 to 9 during the manufacturing process were also appropriate. Therefore, the magnetic flux density B8 was 1.911T or more in both the inner circumference test piece and the outer circumference test piece. Furthermore, ΔB was 0.006T or less, and there was little variation in magnetic flux density.

In Example 3, the influence of the period (in-process time) from the completion of the hot-rolled plate annealing step S2 to the implementation of the cold rolling step S3, and the annealing temperature when the annealing treatment is performed before the cold rolling step S3 We investigated the impact of

Specifically, the chemical composition is C: 0.08%, Si: 3.4%, Mn: 0.08%, S: 0.02%, sol. A slab containing 0.03% Al and 0.01% N, with the balance being Fe and impurities was prepared.

Hot rolling step S1 was performed on the slabs with each test number shown in Table 3-1 and Table 3-2. Specifically, the slabs of each test number were heated to 1340°C in a heating furnace. The heated slab was hot rolled to produce a hot rolled steel plate with a thickness of 2.3 mm.

The hot rolled steel sheet after the hot rolling process was subjected to a hot rolled sheet annealing step S2 at a hot rolled sheet annealing temperature of 900 to 1200° C. and a holding time of 10 to 300 seconds.

After the hot rolled sheet annealing step S2, the hot rolled steel sheets were placed in an indoor yard for the number of days shown in Table 3-2. After the number of work days had passed, the hot rolled steel sheets with test numbers 7 to 14 were annealed (heat treated) at the annealing temperature (°C) listed in Table 3-2 immediately before performing cold rolling step S3. . Note that in test numbers 1 to 6, the hot rolled steel sheets were not annealed.
Thereafter, cold rolling step S3 was performed on the hot rolled steel plates of test numbers 1 to 14 to produce cold rolled steel plates with a plate thickness of 0.19 mm. Specifically, after implementing the 1st cold rolling process, the 2nd cold rolling process was implemented. Conditions 1 to 4, Condition 6, and Condition 7 were as shown in Table 3-1.
Specifically, "reverse" in the "condition 1" column of the "first cold rolling process" column in Table 3-1 means that a reverse rolling process was performed as the first cold rolling process. . "Tandem" means that a tandem rolling process was performed as the first cold rolling process.

In the "Condition 2" column of the "First Cold Rolling Step" column in Table 3-1, the average diameter D1 (mm) of the work rolls used in each pass is listed. In "Condition 3" in the "First Cold Rolling Step" column in Table 3-1, the cumulative rolling reduction CR1 (%) in the first cold rolling step is listed.

"Reverse" in the "Condition 4" column of the "Second cold rolling process" column in Table 3-1 means that a reverse rolling process was performed as the second cold rolling process. "-" means that the second cold rolling step was not performed.

In the "Condition 6" column of the "Second Cold Rolling Step" column in Table 3-1, the average diameter D2 (mm) of the work rolls used in each pass is listed. In "Condition 7" in the "Second cold rolling process" column in Table 3-1, the cumulative rolling reduction ratio CR2 (%) in the second cold rolling process is listed. In the "Condition 8" column in Table 3-1, the cumulative rolling reduction rate CR0 (%) of the entire cold rolling step S3 is listed.

Regarding condition 5, in any test number, the intermediate steel plate that had not been subjected to heat treatment was subjected to rolling in the second cold rolling step. Note that when Condition 1 was reverse rolling, three passes of rolling were performed. When Condition 1 was tandem rolling, 5 passes of rolling were performed.

A decarburization annealing step S4 was performed on the cold rolled steel sheet after the cold rolling step S3. Specifically, after raising the temperature to a final temperature of 850°C, it was held at a decarburization annealing temperature of 830°C for 80 seconds. Thereafter, the cold-rolled steel sheet was allowed to cool to room temperature to obtain a decarburized annealed steel sheet. Note that during heating, the average temperature increase rate HR (condition 9) from 550°C to 750°C was 1300°C/sec.

An annealing separator containing MgO as a main component was applied to the surface of a decarburized annealed steel sheet. Thereafter, the decarburized annealed steel plate coated with the annealing separator was wound into a coil. Hereinafter, the coiled steel plate will also be simply referred to as a "coil." The curvature reflection of the inner circumference of the coil was 250 mm, and the radius of curvature of the outer circumference of the coil was 850 mm.

Finish annealing was performed on the coil to produce a finish annealed steel plate. The final annealing temperature in the final annealing was 1100°C to 1200°C, and the holding time at the final annealing temperature was 5 to 30 hours.

An insulation film forming step S6 was performed on the steel plate after the final annealing step S5. Specifically, an insulating film forming liquid mainly containing colloidal silica and phosphate was applied to the surface of the finish annealed steel plate of each test number. Thereafter, the finish annealed steel plate coated with the insulating film forming liquid was baked under the same conditions to form an insulating film on the primary film. Through the above manufacturing process, coil-shaped grain-oriented electrical steel sheets of each test number were manufactured.

[Evaluation test]
As in Example 1, an inner circumference test piece and an outer circumference test piece were taken from the coiled grain-oriented electrical steel sheets of each test number. Then, the magnetic flux density B8 of the inner circumference test piece and the outer circumference test piece was determined in accordance with JIS C2556:2015. Furthermore, the magnetic flux density difference ΔB was determined.

[Test results]
The evaluation results are shown in Table 3-2.

In test numbers 1 to 3 and 7 to 10, conditions 1 to 9 were appropriate. Therefore, even if the processing time was one day or more, and even if annealing was performed before the first cold rolling step, excellent magnetic flux density B8 was obtained on both the inner and outer circumferences of the coil.

On the other hand, in test numbers 4 to 6 and 11 to 14, the conventional cold rolling process was performed. Therefore, when the processing time was one day or more, the magnetic flux density B8 was low at both the inner and outer circumferences of the coil. Further, even when annealing was performed before the first cold rolling step, the magnetic flux density B8 was low at both the inner and outer circumferences of the coil. Furthermore, ΔB exceeded 0.006T, and the variation in magnetic flux density was large.

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 (2)

The chemical composition is in mass%,
C: 0.01-0.20%,
Si: 2.0 to 4.5%,
Mn: 0.01 to 0.30%,
S: 0.01-0.05%,
sol. Al: 0.01-0.05%,
N: 0.01-0.02%,
Cr: 0.00-0.50%,
Sn: 0.00-0.30%,
Sb: 0.00 to 0.30%,
Ni: 0.00 to 0.50%,
Mo: 0.00-0.20%,
P: 0.00-0.15%,
Cu: 0.00-0.50%,
Se: 0.00-0.03%,
V: 0.00 to 0.15%, and
Bi: 0.0000-0.0100%,
A hot rolling step of producing a hot rolled steel plate by hot rolling a slab containing Fe and the remainder consisting of Fe and impurities;
a hot-rolled plate annealing step of annealing the hot-rolled steel plate;
A cold rolling step of manufacturing a cold rolled steel sheet by cold rolling the hot rolled steel sheet after the hot rolled sheet annealing step at a cumulative reduction rate CR0 of 90% or more;
a decarburization annealing step of performing decarburization annealing on the cold rolled steel sheet to produce a decarburization annealed steel sheet;
A finish annealing step of applying an annealing separator to the decarburized annealed steel plate, and performing finish annealing on the decarburized annealed steel plate coated with the annealing separator to produce a finish annealed steel plate;
An insulating film forming step of applying an insulating film forming liquid to the finish annealed steel plate, and performing heat treatment on the finish annealed steel plate coated with the insulating film forming liquid to form an insulating film on the finish annealed steel plate. and,
The cold rolling process includes:
A tandem rolling step of manufacturing an intermediate steel plate by continuously rolling the hot-rolled steel plate in a plurality of passes using a tandem rolling mill including a plurality of rolling stands arranged in a row;
A reverse rolling step of manufacturing the cold rolled steel sheet by performing reverse rolling for a plurality of passes on the intermediate steel sheet that has not been heat treated after the tandem rolling step using a multi-high rolling mill. ,
In the tandem rolling process,
The average diameter D1 of the plurality of work rolls used in the plurality of passes is 200 mm or more,
The cumulative reduction rate CR1 is set to 30 to 87%,
In the reverse rolling process,
The average diameter D2 of the plurality of work rolls used in the plurality of passes is 100 mm or less,
The cumulative reduction rate CR2 is set to 24 to 86%,
In the decarburization annealing step,
The average temperature increase rate HR in the temperature range of 550°C to 750°C of the cold rolled steel sheet is 100°C/second or more,
A method for manufacturing grain-oriented electrical steel sheets. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1, comprising:
The slab is
Cr: 0.01-0.50%,
Sn: 0.01-0.30%,
Sb: 0.01 to 0.30%,
Ni: 0.01-0.50%,
Mo: 0.01-0.20%,
P: 0.01-0.15%,
Cu: 0.01 to 0.50%,
Se: 0.01-0.03%,
V: 0.01 to 0.15%, and
Bi: 0.0001-0.0100%,
Containing one or more elements selected from the group consisting of
A method for manufacturing grain-oriented electrical steel sheets.

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