JP2009235574A - Method for producing grain-oriented electrical steel sheet having extremely high magnetic flux density - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably producing a grain-oriented electrical steel sheet having extremely high magnetic flux density in an industrial scale. <P>SOLUTION: The method for producing the grain-oriented electrical steel sheet uses as material a slab composed of 0.02-0.10% C, 2.5-4.5% Si, 0.01-0.15% Mn, 0.001-0.050% S, 0.01-0.05% acid-soluble Al, 0.002-0.015% N, 0.0005-0.1000% Te. The method includes a series of processes: hot-rolling the above slab then applying a hot-rolled sheet annealing to the hot-rolled steel sheet; obtaining cold-rolled steel sheet by applying cold-rolling one time or two or more times with a process annealing interposed therebetween; then applying decarburization-annealing to the cold-rolled steel sheet and coating the cold-rolled steel sheet with an annealing separator; then applying finish-annealing to the steel sheet. In the method, just before the decarburization annealing or in the temperature raising process for decarburization annealing, the heating treatment to the temperature of ≥800°C at ≥50°C/sec heating speed, is performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for stably producing a grain-oriented electrical steel sheet having a remarkably high magnetic flux density on an industrial scale.

  The grain-oriented electrical steel sheet is a steel sheet containing about 2 to 5% Si and highly accumulating the crystal grain orientation of the product in the {110} <001> orientation, and is mainly used for stationary inductors such as transformers. Used as iron core material. Control of crystal orientation in the production of such grain-oriented electrical steel sheets is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization.

  As a method for controlling this secondary recrystallization, a fine precipitate called an inhibitor is completely dissolved at the time of heating the steel slab before hot rolling, and then finely precipitated in hot rolling and subsequent annealing steps. There is. In this method, MnS and AlN as exemplified in Patent Document 1 are used as inhibitors, rolling at a rolling reduction exceeding 80% in the final cold rolling step, and MnS and MnSe as exemplified in Patent Document 2 are performed. A method of carrying out the cold rolling step twice using the above as an inhibitor has been practiced industrially. In this method, the steel slab before hot rolling is heated at a high temperature of 1280 ° C. or higher in order to completely dissolve the precipitate.

  Further, as another method for controlling secondary recrystallization, as exemplified in Patent Documents 3 and 4, heating of the steel slab before hot rolling is performed at a temperature lower than 1280 ° C., and nitriding after cold rolling is performed. A method of using AlN formed by treatment as an inhibitor has been industrially implemented.

In the production of the grain-oriented electrical steel sheet as described above, many developments have been made to obtain a steel sheet having superior magnetic properties. However, as the demand for energy saving increases in recent years, the iron loss has been further reduced. Is required.
There are various methods for reducing the iron loss of the grain-oriented electrical steel sheet, but it is effective to increase the magnetic flux density and reduce the hysteresis loss as shown in Patent Document 1 described above.

In order to improve the magnetic flux density of the grain-oriented electrical steel sheet, it is necessary to highly accumulate the crystal grain orientation of the product plate in the {110} <001> orientation. There is a method using an auxiliary additive element that is considered to be strengthened.
Patent Documents 5 to 7 disclose methods using Te as such an additive element.

However, according to the inventor's study, when Te is added, fine grains based on secondary recrystallization defects are likely to occur even when manufactured using any of the above-described manufacturing methods, and stable over the entire coil length. It was found that a steel plate with a high magnetic flux density could not be obtained.
Moreover, when Te is added, the steel plate macro grain structure after secondary recrystallization becomes a unique shape extending in the rolling direction. Under industrial production conditions, finish annealing in which secondary recrystallization occurs is performed in a coil shape, so if the macro grains become too large in the rolling direction, the deviation angle of the crystal orientation becomes large based on the coil set, resulting in iron loss. It was also found that deteriorated.

Japanese Patent Publication No. 40-15644 Japanese Patent Publication No. 51-13469 Japanese Examined Patent Publication No. 62-45285 Japanese Patent Laid-Open No. 2-77525 Japanese Patent Laid-Open No. 06-184640 Japanese Patent Laid-Open No. 06-207220 Japanese Patent Laid-Open No. 10-273727

  Therefore, the present invention provides a method for producing a grain-oriented electrical steel sheet having a significantly increased magnetic flux density by adding Te, stably on an industrial scale, and suppressing deterioration of iron loss. Let it be an issue.

  The gist of the present invention for solving the above problems is as follows.

  (1) By mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, S: 0.001 to 0.050% Slab containing acid-soluble Al: 0.01 to 0.05%, N: 0.002 to 0.015%, Te: 0.0005 to 0.1000%, the balance Fe and unavoidable impurities, After heating to 1280 ° C. or higher and performing hot rolling, it is subjected to hot rolled sheet annealing, and after performing cold rolling of two times or more sandwiching one cold rolling or intermediate annealing to make a cold rolled steel sheet, In the manufacturing method for grain-oriented electrical steel sheets, which consists of a series of steps in which decarburization annealing is performed and an annealing separator containing MgO as a main component is applied to the steel sheet surface and then finish annealing is performed, immediately before decarburization annealing or decarburization annealing. Heating to 800 ° C or higher at a heating rate of 50 ° C / sec or higher Significantly the manufacturing method of the magnetic flux density is high oriented electrical steel sheet, which comprises carrying out.

  (2) By mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, S and Se in total: 0.001 -0.050%, acid-soluble Al: 0.010-0.050%, N: 0.002-0.015%, Te: 0.0005-0.1000%, the balance Fe and inevitable impurities The slab made of is heated to 1280 ° C. or higher, hot-rolled, then subjected to hot-rolled sheet annealing, and cold-rolled by performing two or more cold rollings with one cold rolling or intermediate annealing. After making a steel plate, decarburization annealing is performed, and decarburization annealing is performed in a method for producing a grain-oriented electrical steel sheet consisting of a series of steps in which an annealing separator containing MgO as a main component is applied to the steel plate surface and then finish annealing is performed. Immediately before or at a heating rate of decarburization annealing at a heating rate of 50 ° C / sec or higher at 800 ° C Significantly the manufacturing method of the magnetic flux density is high oriented electrical steel sheet, which comprises carrying out the process of heating to the temperature.

(3) By mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.05 to 0.50%, S alone or S and Se in total In: 0.02% or less, acid-soluble Al: 0.010 to 0.050%, N: 0.001 to 0.015%, Te: 0.0005 to 0.1000%, balance Fe and inevitable A slab made of a general impurity is heated below 1280 ° C., hot-rolled, then subjected to hot-rolled sheet annealing, and subjected to one or more cold rolling or two or more cold rolling sandwiching intermediate annealing. In the manufacturing method of grain-oriented electrical steel sheet, which consists of a series of steps in which after cold-rolled steel sheet, decarburization annealing and nitridation annealing are performed, and an annealing separator containing MgO as a main component is applied to the steel sheet surface and then finish annealing is performed. More than 50 ℃ / sec immediately before decarburization annealing or in the temperature raising process of decarburization annealing Significantly the manufacturing method of the magnetic flux density is high oriented electrical steel sheet, which comprises carrying out the process of heating at a heat rate to 800 ° C. or higher.
(4) The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the slab further contains Bi: 0.0005 to 0.1000%.
(5) A grain-oriented electrical steel sheet produced by the method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the shape of the steel sheet crystal grains in the product plate is a shape ratio C = {(rolling If the average value of (direction length) / (length in the plate width direction)} is Cave, then Cave> 2, and if the average value of rolling direction length D is Dave, Dave ≦ 150 mm. Directional electrical steel sheet with high magnetic flux density.

  According to the present invention, a grain-oriented electrical steel sheet having a remarkably high magnetic flux density can be stably produced on an industrial scale. Therefore, the present invention can satisfy the increasing demand for high-quality grain-oriented electrical steel sheets accompanying an increase in the amount of power generation around the world while meeting the recent demand for energy saving, and the effect is enormous.

It is a figure for demonstrating the influence of the temperature increase rate of decarburization annealing with respect to the magnetic flux density of a product plate, and the fine grain generation | occurrence | production area ratio.

  Hereinafter, embodiments of the present invention will be described in detail.

  The steel sheet to which Te is added has a secondary recrystallization start temperature shifted to a high temperature side, which is considered to cause the secondary recrystallization to become unstable. Moreover, the steel plate macro grain structure after the secondary recrystallization has a unique shape extending in the rolling direction, and depending on the shape, it is considered to cause iron loss deterioration based on the coil set. Therefore, the present inventors have made the structure after decarburization annealing easy to develop secondary recrystallization, thereby ensuring the effect of addition of Te, and making the grain-oriented electrical steel sheet with extremely high magnetic flux density iron loss. The following experiment was conducted to establish a technique for stable production while suppressing deterioration.

  In a vacuum melting furnace, in mass%, C: 0.08%, Si: 3.23%, Mn: 0.08%, S: 0.025%, acid-soluble Al: 0.03%, N: 0.00. A slab containing 008% and composed of the balance Fe and unavoidable impurities (without Te) and a slab with a composition added with Te: 0.013% (with Te) were prepared at 1300 ° C. Hot rolling was performed after annealing for 1 hour.

The obtained hot-rolled sheet was annealed at 1100 ° C. for 120 seconds, pickled, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm. This cold-rolled sheet was decarburized and annealed at 850 ° C. in wet hydrogen for 150 seconds. In the decarburization annealing, the heating rate up to 800 ° C. was changed in the range of 25 ° C./sec to 1000 ° C./sec.
An annealing separator containing MgO as a main component was applied to the steel sheet surface after decarburization annealing with a water slurry, and then finish annealing was performed at 1150 ° C. for 20 hours. In the test for observing the macro grain structure of the steel sheet after the finish annealing, the actual coil was simulated to give a curvature with a radius of curvature of 500 mm, and then the finish annealing was performed.

The steel plate after the finish annealing was washed with water, then sheared to a single plate magnetic measurement size, and an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied and baked to prepare a sample.
After measuring the magnetic flux density B8 value of the obtained sample (the magnetic flux density value when a magnetic field of 800 A / m is applied at 50 Hz), the sample coating is removed and fine particles with a particle size of less than 2 mm are generated. The area ratio of the area | region (secondary recrystallization defect part) which is carrying out was measured.

In FIG. 1, the relationship of the magnetic flux density with respect to the temperature increase rate at the time of decarburization annealing, and the fine grain generation | occurrence | production area ratio in the case of using a slab (Te entering) are shown.
As shown in the figure, when the slab added with Te is used, the magnetic flux density of the obtained steel plate is greatly improved as compared with the case where the slag not added with Te is used. In particular, in the temperature raising process of decarburization annealing, in the process of heating to a temperature of 800 ° C. or higher at a heating rate of 50 ° C./sec or higher, even though the slab heating temperature is 1300 ° C., B8 A good magnetic flux density of 1.960 T or more is obtained.

  In addition, in the range where the temperature rising rate was 50 ° C./sec or more, the fine grain generation area ratio was 1% or less, and secondary recrystallization appeared stably over the entire sample, but the temperature rising rate was 25 At ° C / sec, the fine grain generation area ratio was 5%, and the occurrence of secondary recrystallization was unstable.

  From these facts, generation of fine grains due to secondary recrystallization failure under the conditions of adding Te and heating to a temperature of 800 ° C. or higher at a heating rate of 50 ° C./sec or higher in the temperature raising process of decarburization annealing. Is 1% or less, B8> 1.960T or more, and it has been found that good characteristics can be obtained.

  In addition, as a result of the structure observation, the steel grain macro grain structure after the finish annealing has an average value of the grain length in the rolling direction of 150 mm or less in the range where the rate of temperature rise is 50 ° C./sec or more. No iron loss deterioration was observed. When the heating rate was 25 ° C./sec, the average value of the grain length in the rolling direction was 183 mm, and iron loss deterioration accompanying the coil set was observed.

  From these, in the condition of adding Te and heating to a temperature of 800 ° C. or higher at a heating rate of 50 ° C./sec or more in the temperature raising process of decarburization annealing, the average value of the grain length in the rolling direction is It was found that all of them were 150 mm or less, and good characteristics were obtained.

  As described above, the present inventors perform a treatment of adding Te and heating to a temperature of 800 ° C. or higher at a heating rate of 50 ° C./sec or more immediately before decarburization annealing or in the temperature raising process of decarburization annealing. As a result, a new technique for realizing a remarkably high magnetic flux density and low iron loss over the entire length and width was newly found, and the present invention was completed based on this knowledge.

Hereinafter, embodiments of the present invention will be described in detail.
As described above, the manufacturing method of industrially oriented grain-oriented electrical steel sheets is as follows. (1) The slab before hot rolling is heated at 1280 ° C. or higher depending on whether the inhibitor is formed before cold rolling. In some cases, (2) heating may be performed at less than 1280 ° C.
In the present invention, the effect of addition of Te is mainly intended to be fully expressed in secondary recrystallization, so it is not particularly affected by the difference in the manufacturing method until finish annealing, and any manufacturing method is adopted. It may be.
Therefore, first, each manufacturing method will be described, and then the heat treatment immediately before decarburization annealing or in the temperature rising process of decarburization annealing will be described.

The production method (1) will be described.
In this production method, by mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, S alone, or S and Se In total: 0.001 to 0.050%, acid-soluble Al: 0.01 to 0.05%, N: 0.002 to 0.015%, the balance Fe and steel consisting of inevitable impurities are used as a basis . In the present invention, the steel further contains Te: 0.0005 to 0.1000% alone, or Te: 0.0005 to 0.1000% and Bi: 0.0005 to 0.1000% simultaneously.

  The reason why the steel composition is selected as described above is as follows. Hereinafter, the content of the element may be simply expressed as%, but% means mass%.

C has various roles, but if it is less than 0.02% by mass, the crystal grain size at the time of slab heating becomes too large and the iron loss of the product deteriorates. On the other hand, if it exceeds 0.10% by mass, decarburization annealing after cold rolling requires not only a long time, but is not economical, and decarburization tends to be incomplete. This is not preferable because it causes a magnetic defect called magnetic aging.
For this reason, the lower limit of the C content is 0.02%, and the upper limit is 0.10%. A more appropriate range within this range is 0.05 to 0.09%.

  Si is an extremely effective element for increasing the electrical resistance of steel and reducing the eddy current loss that constitutes a part of the iron loss. The mass% ranges from 2.5% to 4.5%. Must be controlled. If it is less than 2.5%, eddy current loss of the product cannot be suppressed, and if it exceeds 4.5%, workability deteriorates, which is not preferable.

  Mn is an important element for forming MnS and / or MnSe, which is an inhibitor that influences secondary recrystallization, and it is necessary to control Mn in a range of 0.01% to 0.15%. If it is less than 0.01%, the absolute amount of MnS and MnSe necessary for causing secondary recrystallization is insufficient, which is not preferable. On the other hand, if it exceeds 0.15%, not only the solid solution during slab heating becomes difficult, but also the precipitation size tends to become coarse, and the optimum size distribution as an inhibitor is impaired.

  S is an important element that forms an inhibitor with Mn described above, and its content needs to be controlled in the range of 0.001% to 0.05%. If it deviates from the above range, a sufficient inhibitor effect cannot be obtained.

  Se is an important element that forms an inhibitor with Mn as described above, and may be contained together with S. When it contains, it is necessary to control to 0.001% or more and 0.05% or less of the total amount with S. If it deviates from the above range, a sufficient inhibitor effect cannot be obtained.

  Acid-soluble Al is a main inhibitor constituting element for producing a high magnetic flux density grain-oriented electrical steel sheet and needs to be controlled in a range of 0.01% to 0.05% by mass. If it is less than 0.01%, the quantity is insufficient, and the inhibitor strength is insufficient. On the other hand, if it exceeds 0.05%, AlN precipitated as an inhibitor becomes coarse, and as a result, the inhibitor strength is lowered, which is not preferable.

  N is an important element that forms the above-described acid-soluble Al and AlN, and is required to be controlled in a range of 0.002% to 0.015% by mass. If it deviates from the above range, a sufficient inhibitor effect cannot be obtained.

Te is an element effective for strengthening the inhibitor and improving the magnetic flux density of the steel sheet. In order to obtain the effect, it is necessary to control the addition amount in the range of 0.0005 to 0.10%. If it is less than 0.0005%, a sufficient effect cannot be obtained, and if it exceeds 0.10%, the rollability deteriorates, which is not preferable.
Bi is further added to Te to further improve the magnetic flux density. In order to obtain the effect, it is necessary to control the addition amount in the range of 0.0005 to 0.10%. If it is less than 0.0005%, a sufficient effect cannot be obtained, and if it exceeds 0.10%, the rollability is deteriorated.

  In addition, Sn, Sb, Cu, Ag, As, Mo, Cr, P, Ni, B, Pb, V, Ge, Ti, and Bi are used as elements for stabilizing secondary recrystallization. In addition, it is useful to contain 0.0005 to 1.0% by mass in total. If the amount of these elements is less than 0.0005%, the effect of stabilizing the secondary recrystallization is not sufficient, and if it exceeds 1.0%, the effect is saturated. Is limited to 1.0%.

  The molten steel for producing grain-oriented electrical steel sheets with the components adjusted as described above is cast by a normal method. There is no particular limitation on the casting method. Next, slab heat treatment is performed, and the lower limit of the heating temperature is set to 1280 ° C. in order to completely dissolve the inhibitor. If it is less than 1280 degreeC, inhibitor components, such as MnS, MnSe, and AlN, cannot fully be made into solution. The upper limit is not particularly defined, but is preferably 1450 ° C. or less from the viewpoint of equipment protection.

  The slab heated as described above becomes a hot-rolled sheet by subsequent hot rolling. The thickness of the hot-rolled sheet is not particularly specified, but is usually 1.8 to 3.5 mm because it is related to the cold rolling rate described later. This hot-rolled sheet is cold-rolled after being annealed for a short time. The annealing is performed in a temperature range of 750 to 1200 ° C. for 30 seconds to 10 minutes, and is effective for enhancing the magnetic properties of the product.

Cold rolling is performed once or divided into two or more times with intermediate annealing in between. One cold rolling means that one or a plurality of rollings are performed without including an annealing process in which the plate temperature exceeds 600 ° C. At that time, it is preferable for the magnetic properties to perform annealing at about 300 ° C. or less during rolling.
When cold rolling is divided into two or more times, intermediate annealing is performed during cold rolling. The intermediate annealing is preferably performed in a temperature range of 750 to 1200 ° C. for 30 seconds to 10 minutes.

When the cold rolling is performed once, the full width characteristics of the product are likely to be unstable, and when the cold rolling is performed twice or more, the product characteristics are stabilized but the ultimate magnetic flux density tends to be low. For this reason, the number of cold rolling is appropriately selected in consideration of the desired characteristic level and cost of the product.
In any case, the final cold rolling reduction is preferably in the range of 80 to 95%.

Subsequently, the cold-rolled steel sheet is decarburized and annealed at a temperature of 900 ° C. or lower in a wet atmosphere containing hydrogen nitrogen, and C is reduced to 20 ppm or lower, which is essential for product characteristics. In the present invention, as described later, the heating rate is controlled in the temperature raising process of decarburization annealing.
Thereafter, a powder mainly composed of MgO is applied and coiled. Then, batch-type finish annealing is performed on the wound coil, and then unwinding, removing the powder, applying a slurry liquid mainly composed of aluminum phosphate and colloidal silica, and baking are performed. Complete the product.

  The finish annealing is a step of secondary recrystallization of {110} <001> oriented grains, and is extremely important for improving the magnetic flux density of the steel sheet. Usually, after secondary recrystallization is developed in the process of raising the temperature to 1100 to 1200 ° C. in a nitrogen-hydrogen mixed atmosphere, switching to a hydrogen atmosphere and annealing for about 20 hours at an annealing temperature of 1100 to 1200 ° C. By carrying out the process, N, S, Se, etc. are diffused and removed out of the steel sheet to improve the magnetic properties of the product plate.

  The annealing atmosphere in the finish annealing is preferably a mixed atmosphere of nitrogen and hydrogen as described above from the viewpoint of product characteristics and productivity. Increasing the nitrogen partial pressure tends to stabilize secondary recrystallization, and decreasing the nitrogen partial pressure provides high magnetic flux density characteristics but tends to destabilize secondary recrystallization.

  Note that the steel sheet added with Te tends to have a high secondary recrystallization temperature, and the temperature increase rate on the high temperature side in the temperature increasing process may be a slow rate of 20 ° C./h or less. It is effective for stabilization. In addition, it is also effective to perform retention annealing in the middle of the temperature rise for the purpose of reducing the moisture contained in the MgO powder and improving the adhesion of the glass coating in the product to the steel plate.

Next, the production method (2) will be described.
In this production method, by mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.05 to 0.50%, S alone, or S and Se. Total: 0.02% or less, acid-soluble Al: 0.010 to 0.050%, N: 0.001 to 0.015%, based on steel consisting of the balance Fe and unavoidable impurities, Similarly, steel further containing Te: 0.0005 to 0.1000% is used.

  In this manufacturing method, since (Al, Si) N is used as an inhibitor, MnS is not particularly required as an inhibitor. Therefore, the contents of Mn, S and Se are selected for the following reasons. About other components, it is the same as that of the case of the manufacturing method of (1).

Mn is contained in the range of 0.05% or more and 0.5% or less for the purpose of increasing the specific resistance and reducing iron loss and for the purpose of preventing the occurrence of cracks in hot rolling. . If the addition amount is less than 0.05%, these objects cannot be achieved. On the other hand, if it exceeds 0.5%, the magnetic flux density of the product is lowered, which is not preferable.
Since S and Se adversely affect the magnetic properties, the total amount is 0.02% or less.

From the molten steel for producing grain-oriented electrical steel sheets, the components of which are adjusted as described above, the slab is cast by a normal method and heat-treated before hot rolling. The heating temperature at that time is sufficient to be less than 1280 ° C.
Thereafter, in the same manner as the production method (1), hot rolling and cold rolling are performed. The steel sheet after cold rolling is subjected to decarburization annealing in a humid atmosphere in order to remove C contained in the steel, and then finish annealing.

In this manufacturing method, in order to form (Al, Si) N as an inhibitor, a process of increasing nitrogen in the steel sheet between cold rolling and finish annealing is performed. The treatment for increasing nitrogen is performed by nitridation annealing in an atmosphere containing a gas having nitriding ability such as ammonia.
The time of this nitridation annealing may be between cold rolling and finish annealing, and may be performed either before or after decarburization annealing. Moreover, the same effect is acquired even if it performs decarburization annealing and nitridation annealing simultaneously.

  As described above, the steel sheets cold-rolled in accordance with the respective production methods are subsequently decarburized and finish-annealed as described above. Improving the magnetic flux density and stabilizing secondary recrystallization by heating to 800 ° C or higher at a heating rate of 50 ° C / sec or higher immediately before the carbon annealing or in the temperature raising process of decarburization annealing. obtain. Moreover, the effect which suppresses iron loss deterioration is acquired by shortening the rolling direction length of the steel plate macro grain structure after finish annealing.

  The heat treatment for heating to a temperature of 800 ° C. or higher at a heating rate of 50 ° C./sec or higher may be performed separately from the decarburization annealing immediately before the decarburization annealing. It may also be implemented.

  The steel sheet to which Te is added has a secondary recrystallization start temperature shifted to a high temperature side, and it is considered that secondary recrystallization becomes unstable due to this, but in the present invention, the above heat treatment is performed. The structure after decarburization annealing is made into a structure in which secondary recrystallization is easy to develop.

  Moreover, the steel plate macro structure after the finish annealing of the steel plate to which Te has been added has a unique shape extending in the rolling direction. The reason for such a stretched macrostructure is not clear, but the steel sheet orientation integration degree is remarkably high and the magnetic properties are good. However, in industrial production conditions, finish annealing in which secondary recrystallization occurs is performed in a coil shape, and the steel sheet is bent in the rolling direction. For this reason, if the grain size becomes too large in the rolling direction, the deviation angle of the crystal orientation becomes large based on the coil set, and the iron loss deteriorates.

In the present invention, the heat treatment as described above is performed, and the structure after decarburization annealing is made into a structure in which secondary recrystallization is likely to occur, so that the steel plate macro grains after finish annealing are shaped to satisfy the following conditions. Suppresses the deterioration of iron loss.
That is, regarding the steel plate crystal grains after the finish annealing, the average value of the shape ratio C = {(length in the rolling direction) / (length in the plate width direction)} is Cave, and the average value of the maximum length D in the rolling direction is Dave. In this case, average shape ratio: Cave> 2, and maximum length in rolling direction: Dave ≦ 150 mm.
Here, the average shape ratio: Cave> 2 is because when Cave is 2 or less, the deviation angle of crystal orientation becomes large even if Dave ≦ 150 mm.

  The temperature range that controls the heating rate is at least 800 ° C. If it is less than 800 degreeC, the effect which controls a heating rate is not enough. The lower limit of the heating rate is 50 ° C./sec. If it is slower than this, a good magnetic flux density cannot be obtained, and secondary recrystallization failure tends to occur.

  A higher heating rate is preferable because the effect of improving the magnetic flux density and the occurrence of secondary recrystallization failure are suppressed, and the production stability is further increased. In particular, a heating rate exceeding 300 ° C./sec is preferable. The upper limit of the heating rate is not particularly limited, but a heating rate of about 2000 ° C./sec is sufficient.

  The method for controlling the heating rate is not particularly limited, and an existing heating means is appropriately employed depending on the heating rate. For example, when heat treatment is performed at a rate of 100 ° C / sec or higher in the temperature raising process of decarburization annealing, induction heating, electric heating, etc. are performed before the decarburization annealing equipment using a conventional radiant tube or elema using normal radiant heat. It is also possible to implement by incorporating the electric heating device.

Hereinafter, the feasibility and effects of the present invention will be further described using examples.
The conditions used in the examples are a condition example for the confirmation, and the present invention is not limited to this condition example.

Example 1
A steel slab containing the components shown in Table 1 and the balance being inevitable impurities and Fe was produced in a laboratory vacuum melting furnace. This slab was subjected to hot rolling after annealing at 1300 ° C. and 1350 ° C. for 1 hour. The obtained hot-rolled sheet was annealed at 1100 ° C. for 120 seconds, pickled, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm. Then, this cold-rolled sheet was subjected to decarburization annealing at 850 ° C. in wet hydrogen for 150 seconds. At that time, the heating rate up to 800 ° C. in the temperature raising process of the decarburization annealing was changed in the range of 10 to 1000 ° C./sec as shown in Table 2.

  Next, an annealing separator mainly composed of MgO is applied to the steel sheet after decarburization annealing in a water slurry, and heated at 750 ° C. or higher at an average temperature increase rate of 20 ° C./h for 20 hours at a maximum reached temperature of 1150 ° C. for 20 hours. The finish annealing was performed. The obtained steel sheet was washed with water, then sheared to a size for single-plate magnetism measurement, an insulating film mainly composed of aluminum phosphate and colloidal silica was applied and baked, and a magnetic flux density B8 value was measured. Thereafter, the coating was removed, and the area ratio of the secondary recrystallization failure portion was measured.

  Here, B8 is a magnetic flux density value when a magnetic field of 800 A / m is applied at 50 Hz. Moreover, the secondary recrystallization defect part was defined as the area | region of a fine grain whose particle size is less than 2 mm. The same applies to the following embodiments.

Evaluation was performed on 10 test pieces, and at any slab heating temperature, the maximum B8: B8max ≧ 1.960T, the area ratio of secondary recrystallization failure portion: A ≦ 1%, and the average B8: B8ave ≧ 1.950T. Were judged as good.
Note that both slab heating temperatures were set because the slab after heating always has a low temperature depending on the location, so if the required magnetic characteristics cannot be obtained at a lower slab heating temperature, the product coil This is because good magnetic properties cannot be obtained stably over the entire length.

  The results are shown in Table 2. The slab heating temperature satisfying the good judgment at both 1300 ° C. and 1350 ° C. uses Te-containing slab B, and the heating rate up to 800 ° C. in the temperature raising process of decarburization annealing is 50 ° C./sec or more. Range. In particular, when the heating rate was 100 ° C./sec or higher, B8ave ≧ 1.955 T or higher, which was even better. Furthermore, in the range where the heating rate exceeded 300 ° C./sec, B8ave ≧ 1.960T or more, which was very good.

(Example 2)
A steel slab containing the components shown in Table 3 and the balance consisting of inevitable impurities and Fe was produced in a laboratory vacuum melting furnace. This slab was subjected to hot rolling after annealing at 1350 ° C. and 1400 ° C. for 1 hour. The obtained hot-rolled sheet was annealed at 1000 ° C. for 100 seconds, pickled, and then cold-rolled to obtain a steel sheet having a thickness of 1.7 mm. This steel sheet was subjected to an intermediate annealing at 1050 ° C. for 100 seconds and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm. Further, this cold-rolled sheet was decarburized and annealed at 850 ° C. in wet hydrogen for 150 seconds. At that time, the heating rate up to 800 ° C. in the temperature raising process of decarburization annealing was changed in the range of 10 to 1000 ° C./sec as shown in Table 4.

Next, an annealing separator mainly composed of MgO is applied to the steel sheet after decarburization annealing in a water slurry, and heated at 750 ° C. or higher at an average temperature increase rate of 20 ° C./h for 20 hours at a maximum reached temperature of 1150 ° C. for 20 hours. The finish annealing was performed. The obtained steel sheet was washed with water, then sheared to a size for single-plate magnetism measurement, an insulating film mainly composed of aluminum phosphate and colloidal silica was applied and baked, and a magnetic flux density B8 value was measured. Thereafter, the coating was removed, and the area ratio of the secondary recrystallization failure portion was measured.
The measurement results were evaluated in the same manner as in Example 1 for 10 test pieces.

  The results are shown in Table 4. The slab heating temperature satisfying the good judgment at both 1350 ° C. and 1400 ° C. uses the slab D containing Te, and the heating rate up to 800 ° C. in the temperature raising process of decarburization annealing is 50 ° C./sec. It was the above range. In particular, when the heating rate was 100 ° C./sec or higher, B8ave ≧ 1.955 T or higher, which was even better. Further, in the range where the heating rate exceeded 300 ° C./sec, B8ave ≧ 1.960T or more, which was very good.

(Example 3)
A steel slab containing the components shown in Table 5 and the balance being inevitable impurities and Fe was produced in a laboratory vacuum melting furnace. This slab was annealed at 1150 ° C. for 1 hour and then hot-rolled. The obtained hot-rolled sheet was annealed at 1100 ° C. for 100 seconds, pickled, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm. Further, this cold-rolled sheet was subjected to decarburization annealing at 800 ° C. and 850 ° C. for 150 seconds in wet hydrogen. Nitriding annealing was performed after decarburization annealing or simultaneously with decarburization annealing. At that time, the heating rate up to 800 ° C. in the temperature raising process of decarburization annealing was changed in the range of 10 to 1000 ° C./sec as shown in Table 4.

Next, an annealing separator mainly composed of MgO is applied to the steel sheet after decarburization annealing in a water slurry, and heated at 750 ° C. or higher at an average temperature increase rate of 20 ° C./h for 20 hours at a maximum reached temperature of 1150 ° C. for 20 hours. The finish annealing was performed. The obtained steel sheet was washed with water, then sheared to a size for single-plate magnetism measurement, an insulating film mainly composed of aluminum phosphate and colloidal silica was applied and baked, and a magnetic flux density B8 value was measured. Thereafter, the coating was removed, and the area ratio of the secondary recrystallization failure portion was measured.
The measurement results were evaluated in the same manner as in Example 1 for 10 test pieces.

  The results are shown in Tables 6 and 7. What satisfy | fills favorable determination in both decarburization annealing temperature of 800 degreeC and 850 degreeC uses the slab F containing Te, and the heating rate to 800 degreeC in the temperature rising process of decarburization annealing is 50 degreeC / It was in the range of sec or more. In particular, when the heating rate was 100 ° C./sec or higher, B8ave ≧ 1.955 T or higher, which was even better. Furthermore, in the range where the heating rate exceeded 300 ° C./sec, B8ave ≧ 1.960T or more, which was very good.

Example 4
A steel slab containing the components shown in Table 8 with the balance being inevitable impurities and Fe was prepared in a laboratory vacuum melting furnace. This slab was subjected to hot rolling after annealing at 1300 ° C. and 1350 ° C. for 1 hour. The obtained hot-rolled sheet was annealed at 1100 ° C. for 120 seconds, pickled, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm. Then, this cold-rolled sheet was subjected to decarburization annealing at 850 ° C. in wet hydrogen for 150 seconds. At that time, the heating rate up to 800 ° C. in the temperature raising process of the decarburization annealing was changed in the range of 10 to 1000 ° C./sec as shown in Table 9.

Next, an annealing separator mainly composed of MgO is applied to the steel sheet after decarburization annealing in a water slurry, and heated at 750 ° C. or higher at an average temperature increase rate of 20 ° C./h for 20 hours at a maximum reached temperature of 1150 ° C. for 20 hours. The finish annealing was performed. The obtained steel sheet was washed with water, then sheared to a size for single-plate magnetism measurement, an insulating film mainly composed of aluminum phosphate and colloidal silica was applied and baked, and a magnetic flux density B8 value was measured. Thereafter, the coating was removed, and the area ratio of the secondary recrystallization failure portion was measured.
Evaluation was performed on 10 test pieces. In this example, the maximum B8: B8max ≧ 1.965T, the area ratio of secondary recrystallization failure portion: A ≦ 1%, and the average B8: B8ave ≧ 1.955T. The case of ◎ was determined to be even better at any slab heating temperature.

  The results are shown in Table 9. When the slab H containing Te and Bi was used, the magnetic flux density was improved at any heating rate than when the slab G containing only Te was used. Moreover, what satisfy | filled the further favorable determination in any of slab heating temperature 1300 degreeC and 1350 degreeC was the range where a heating rate exceeded 300 degreeC / sec in the case of using slab G containing only Te. However, when the slab H containing Te and Bi was used, the heating rate was in the range of 50 ° C./sec or more.

(Example 5)
A steel slab containing the components shown in Table 10 and the balance being inevitable impurities and Fe was produced in a laboratory vacuum melting furnace. The slab was annealed at 1350 ° C. for 1 hour and then hot-rolled. The obtained hot-rolled sheet was annealed at 1100 ° C. for 120 seconds, pickled, and then cold-rolled to obtain a cold-rolled sheet having a thickness of 0.23 mm. Then, this cold-rolled sheet was subjected to decarburization annealing at 850 ° C. in wet hydrogen for 150 seconds. At that time, the heating rate up to 800 ° C. in the temperature raising process of decarburization annealing was changed in the range of 10 to 1000 ° C./sec as shown in Table 11.

Next, an annealing separator containing MgO as a main component is applied to the steel sheet after decarburization annealing with a water slurry, and a curvature with a radius of curvature of 500 mm is imparted for the purpose of providing a coil set, and then an average heating rate of 750 ° C. or higher. Heat annealing was performed at 20 ° C./h, and a final annealing for 20 hours was performed at a maximum temperature of 1150 ° C. The obtained steel sheet was washed with water, then sheared to a size for single-plate magnetism measurement, an insulating film mainly composed of aluminum phosphate and colloidal silica was applied and baked, and a magnetic flux density B8 value was measured. Thereafter, the coating was removed, and the area ratio of the secondary recrystallization failure portion was measured. Further, the length in the rolling direction and the length in the sheet width direction are measured for the shape of the steel plate macro grain, and the average value Cave and the length in the rolling direction of the shape ratio C = {(length in the rolling direction) / (length in the sheet width direction)} The average value of D was measured for Dave.
Evaluation was performed on 10 test pieces, the maximum B8: B8max ≧ 1.960T, the area ratio of the secondary recrystallization failure portion: A ≦ 1%, the average B8: B8ave ≧ 1.950T, and the shape ratio average: Cave > 2 and average length in the rolling direction: those having Dave ≦ 150 mm were determined to be good, and those having Dave ≦ 100 mm were determined to be even better.

  The results are shown in Table 11. What satisfy | filled favorable determination used the slab J containing Te and Bi, and the heating rate to 800 degreeC in the temperature rising process of decarburization annealing was the range of 50 degree-C / sec or more. In particular, in the range where the heating rate exceeds 300 ° C./sec, Dave <100 mm, which is even better.

  Since the grain-oriented electrical steel sheet having a remarkably high magnetic flux density can be stably produced on an industrial scale, the present invention has a great industrial applicability.

Claims (5)

In mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, S: 0.001 to 0.050%, acid-soluble A slab containing Al: 0.01 to 0.05%, N: 0.002 to 0.015%, Te: 0.0005 to 0.1000%, and the balance Fe and unavoidable impurities is 1280 ° C or higher. After performing hot rolling, hot-rolled sheet annealing is performed, and cold rolling steel sheet is subjected to cold rolling of two or more times with one cold rolling or intermediate annealing, followed by decarburization annealing. In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of applying a finish annealing after applying an annealing separator mainly composed of MgO to the steel sheet surface,
Production of grain-oriented electrical steel sheet having a remarkably high magnetic flux density characterized by performing a treatment immediately before decarburization annealing or in a temperature raising process of decarburization annealing at a heating rate of 50 ° C / sec or higher to a temperature of 800 ° C or higher. Method. In mass%, C: 0.02-0.10%, Si: 2.5-4.5%, Mn: 0.01-0.15%, S and Se in total: 0.001-0. A slab containing 050%, acid-soluble Al: 0.010 to 0.050%, N: 0.002 to 0.015%, Te: 0.0005 to 0.1000%, the balance being Fe and inevitable impurities The steel sheet is heated to 1280 ° C. or higher, hot-rolled, then subjected to hot-rolled sheet annealing, and cold-rolled steel sheet is obtained by performing one or more cold rolling or two or more cold-rolling sandwiches intermediate annealing. Then, in the method for producing a grain-oriented electrical steel sheet comprising a series of steps in which decarburization annealing is performed and finish annealing is performed after applying an annealing separator mainly composed of MgO to the steel sheet surface.
Production of grain-oriented electrical steel sheet having a remarkably high magnetic flux density characterized by performing a treatment immediately before decarburization annealing or in a temperature raising process of decarburization annealing at a heating rate of 50 ° C / sec or higher to a temperature of 800 ° C or higher. Method. In mass%, C: 0.02 to 0.10%, Si: 2.5 to 4.5%, Mn: 0.05 to 0.50%, S alone or S and Se in total: 0 0.02% or less, acid-soluble Al: 0.010 to 0.050%, N: 0.001 to 0.015%, Te: 0.0005 to 0.1000%, from the balance Fe and inevitable impurities The resulting slab is heated at less than 1280 ° C., hot-rolled, then subjected to hot-rolled sheet annealing, and subjected to one or more cold rollings or two or more cold rollings sandwiching the intermediate annealing to cold-rolled steel sheet After the decarburization annealing and nitridation annealing, in the manufacturing method of the grain-oriented electrical steel sheet consisting of a series of steps of applying a finishing annealing after applying an annealing separator mainly composed of MgO to the steel sheet surface,
Production of grain-oriented electrical steel sheet having a remarkably high magnetic flux density characterized by performing a treatment immediately before decarburization annealing or in a temperature raising process of decarburization annealing at a heating rate of 50 ° C / sec or higher to a temperature of 800 ° C or higher. Method.   The said slab contains Bi: 0.0005 to 0.1000% further, The manufacturing method of the grain-oriented electrical steel sheet with remarkably high magnetic flux density in any one of Claims 1-3 characterized by the above-mentioned.   A grain-oriented electrical steel sheet produced by the method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the shape of the steel sheet crystal grains in the product sheet is a shape ratio C = {(length in the rolling direction). ) / (Length in the plate width direction)} is Cave> 2 where Cave is the average value, and Dave ≦ 150 mm where the average value in the rolling direction length D is Dave. Highly oriented electrical steel sheet.

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