JPH11323437A - Production of thick grain-oriented silicon steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a grain-oriented silicon steel plate(GO) with low carbon content, inexpensive in the production cost, thick in the product plate thickness and excellent in magnetic properties. SOLUTION: This is the method for producing a GO in which a slab contg. 0.01 to 0.04% C, 2.5 to 4.0% Si, 0.020 to 0.040% acid soluble Al, 0.005 to 0.010% N, at least one kind of S and Se by 0.005 to 0.0150, 0.05 to 0.8% Mn, and the balance Fe with inevitable impurities is heated at <1280 deg.C, is subjected to hot rolling, is subjected to hot rolled sheet annealing and descaling, is subjected to cold rolling for one time, is subjected to decarburizing annealing, is thereafter subjected to nitriding treatment in a gaseous mixture of hydrogen, nitrogen and ammonia in a state in which the strip is run, is then applied with a separation agent for annealing essentially consisting of MgO and is subjected to final finish annealing. The relation between the final total draft (Hf: true strain) in the hot rolling and the final cold rolling ratio (Cr: true strain) lies in -0.25Hf+2.6<=Cr<=-0.25Hf+3.6 and 2.709<=Hf<=3.912.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thick grain-oriented electrical steel sheet used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional electromagnetic ropes are mainly used as iron core materials for transformers and other electric equipment, and have excellent magnetic properties such as excitation characteristics and iron loss characteristics. Required for reduction of energy loss. As a characteristic value representing the excitation characteristic, a magnetic flux density B8 at a magnetic field strength of 800 A / m is standardized by JIS and is usually used. As the characteristic value representing the energy one loss, energy loss (core loss) W _{17/5 0} per steel 1kg upon magnetization at a frequency 50Hz to 1.7 Tesla (T) also J
Standardized by IS.

[0003] The magnetic flux density is the largest controlling factor of iron loss. Generally, the higher (larger) the magnetic flux density, the better the iron loss characteristics. In general, as the magnetic flux density increases, the size of the secondary recrystallized grains increases, and iron loss may deteriorate. In this case, as already widely known, by controlling the magnetic domain, the iron loss can be improved irrespective of the grain size of the secondary recrystallization.

[0004] This unidirectional electrical steel sheet has a so-called goss structure having a {110} axis on the steel sheet surface and a <001> axis in the rolling direction caused by secondary recrystallization in the final finish annealing step. In order to obtain good magnetic properties, it is necessary that <001>, which is the axis of easy magnetization, be highly aligned in the rolling direction. The manufacturing technology of such high magnetic flux density unidirectional magnetic steel sheet has been developed for a long time, and in Japan, a method using MnS or AlN as a so-called inhibitor (Japanese Patent Laid-Open No. 40-1).
5644), a method using MnS, MnSe, Sb, and the like (Japanese Patent Application Laid-Open No. 51-13469). In these cases, complete solid solution of the inhibitor is required in the hot rolling process, and it is necessary to set the heating temperature of the steel ingot (slab) to 1350 ° C. or more during actual hot pressing.

[0005] This high temperature heating has a number of disadvantages and disadvantages. For this reason, attempts have been made to lower the heating temperature of the steel ingot (slab) during hot rolling. JP-A-59-56522 discloses one of them. A number of inventions have been made as a development of this technology, and a method of performing nitridation in the process of increasing the temperature from decarburizing annealing to final finish annealing to form inhibitors (Japanese Patent Application Laid-Open Nos. 62-45285 and 60-179855). ), And a method of performing a nitriding treatment using a mixed gas of hydrogen, nitrogen, and ammonia under a condition in which the strip is run (Terakai 2-77525, JP-A-1-82400, JP-A-3-82400). 180
460, JP-A-6-317592) have been proposed.

Further, a method of controlling primary recrystallized grains in an intermediate stage after completion of primary recrystallization at the time of decarburization annealing and before completion of secondary recrystallization at the time of final finish annealing (JP-A-9-294425)
JP, JP-A-2-96275, JP-A-2-59
020, JP-A-1-82393) have also been proposed. By the way, the grain-oriented electrical steel sheets are mainly used by being laminated as an iron core of a transformer. In particular, in the case of a large-sized power transformer, the work of laminating the iron cores is performed manually, and thus the workability (productivity) is improved as the thickness of the unidirectional magnetic steel sheet is increased. For this reason, there has been a strong demand for the production of a unidirectional magnetic steel sheet which is thick (for example, more than 0.40 mm) and has excellent magnetic properties. However, in the production of the unidirectional electromagnetic steel slope, it has been essential in the prior art to contain carbon to some extent at the steelmaking stage. The nature of carbon inclusion is high temperature (11
In the case of slab heating at a temperature of 50 ° C. or more), 1) prevention of abnormal grain growth during slab heating, 2) securing of transformed phase for adjusting texture of primary recrystallization, 3) securing of solid solution amount of inhibitor, etc. is there. In this case, the C amount was required to be 0.060% or more under the condition that the slab was manufactured with continuous casting. Further, even in the case of performing the nitriding treatment in a state where the strip is run by heating the slap at a temperature lower than 1230 ° C. as in the present invention, it is required to contain carbon to some extent for the purposes 1) and 2). In this case, C is 0.040
It is necessary to exceed%.

On the other hand, if carbon is present in the final product of the grain-oriented electrical steel sheet in an amount of 30 ppm or more, magnetic aging occurs and the commercial value is lost. Therefore, the carbon content is forcibly reduced to 30 ppm or less in the decarburizing annealing step. In this case, if the sheet thickness is large, decarburization takes time, productivity is significantly reduced, and the cost is high. For this reason, the product thickness of the grain-oriented electrical steel sheet is currently specified by JIS or the like with a maximum of 0.35 mm. As a method for reducing the carbon content, as an alternative to the above method, a method of once making a crystal grain called pre-rolling (breakdown) before hot rolling and heating is adopted.
However, also in this case, the cost is inevitably increased. Therefore, there is a limit to the reduction in C.

Further, Japanese Patent Application Laid-Open Nos. Hei 4-323 and Hei 4-
Japanese Patent Application Laid-Open No. 324-324 specifies the conditions at the time of hot rolling in the case where a hot unidirectional magnetic steel sheet is not hot-rolled. Of course, thick unidirectional steel sheets can also be manufactured by this method. In this case, only the primary recrystallization texture is modified in the production of the grain-oriented electrical steel sheet, but the inhibitor is adjusted only in the hot rolling step, and the stability of magnetic properties and iron loss There was a limit to the improvement of

[0009]

As described above, in the production of a grain-oriented electrical steel sheet, a decarburization step is inevitably present. Therefore, in the case of a thick material (thickness of 0.30 mm or more), decarburization annealing is performed. It is important to reduce the previous carbon building capacity as much as possible to improve its productivity. The present invention provides a method for reducing the carbon content in order to secure magnetic properties and reduce the load in such decarburizing annealing.

[0010] As is well known, the decarburizing annealing process of the grain-oriented electrical steel sheet is performed continuously and has the following three functions. That is, (1) primary recrystallization, (2) decarburization,
(3) The three functions of the formation of the surface oxide layer. These three
Careful operation is required for the two functions to work well. When the product thickness is large as in the present invention, it has been difficult to make both (2) and (3) economically compatible.

That is, when the plate thickness is large, the time required for decarburization becomes longer (approximately, the decarburization time becomes longer in proportion to the square of the thickness). On the other hand, if the steel sheet is retained for a long time in a decarburizing atmosphere (oxidizing atmosphere), the oxidized layer on the surface becomes thicker, the decarburizing property is reduced, and it is very difficult to reduce the residual carbon to 30 ppm or less. Also, when the oxide layer on the surface becomes extremely thick, 2
Defects occur in the primary film (film mainly composed of forsterite) after the secondary recrystallization annealing, and the commercial value is significantly reduced. For this reason, it is necessary to reduce the carbon content before decarburization annealing.

Further, what is required is to produce a thick unidirectional electrical steel sheet having good magnetic properties, not only magnetic flux density but also iron loss, by using a material having a low carbon content.

[0013]

Means for Solving the Problems The present inventors diligently studied the above problems, and found that the slab heating temperature was 128 ° C.
In a method for producing a grain-oriented electrical steel sheet whose main technology is to perform nitriding treatment at a temperature of less than 0 ° C. and in which the strip is run after decarburizing annealing, the total reduction ratio of the hot rolling finish and the final cold rolling It has been found that by defining the relationship of the ratio, it is possible to produce a grain-oriented electrical steel sheet having good magnetism even if the carbon content is lower than before.

The gist is as follows. By weight ratio, C: 0.010 to 0.040%, Si: 2.5 to
4.0%, acid-soluble Al: 0.020 to 0.040%,
N: 0.005 to 0.010%, at least one of S and Se is 0.005 to 0.015%, Mn: 0.05 to
A slab consisting of 0.8%, the balance being Fe and unavoidable impurities, is heated at a temperature of less than 1280 ° C., hot-rolled, hot-rolled sheet annealing is performed, and after the subsequent deskering, one cold rolling is performed. Unidirectional electrical steel sheet that is subjected to nitriding in a mixed gas of hydrogen, nitrogen, and ammonia while the strip is running after decarburizing annealing, and then applying an annealing separator containing MgO as a main component and performing final finish annealing In the manufacturing method, the relationship between the finish draft in hot rolling (Hf: true strain) and the final cold rolling rate (Cr: true strain) is -0.25Hf + 2.6 ≦ Cr ≦ −0.25Hf + 3.
6 2.709 ≦ Hf ≦ 3.912, which is a method for producing a unidirectional magnetic steel sheet having a large product plate thickness, wherein the product plate thickness is 0.30 m
m to 0.65 mm, and the finishing inlet temperature of the hot rolling is 950 to 1150 ° C and the finishing outlet temperature is 80
This is a method for manufacturing a grain-oriented electrical steel sheet having a thick product thickness of 0 to 1050 ° C and a winding temperature of 500 to 650 ° C.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the reason for limiting the range of the content of carbon (C) in the present invention will be described. As described above, in the production of a grain-oriented electrical steel sheet, the inclusion of C to some extent is essential. In the present invention, the objectives are 1) the presence of a transformed phase for adjusting the texture of the primary recrystallization, and 2) ensuring the solid solution amount of the inhibitor in the γ layer. In the present invention, the total rolling reduction and the cold rolling reduction of the finishing stand in hot rolling are defined in order to obtain good magnetic properties in a range smaller than the conventional C content. However, 0.01% or more of C is required for the presence of the transformation phases 1) and 2). Further, from the viewpoint of magnetic properties, even if the upper limit is contained up to 0.10% of carbon, no problem occurs. However, when the product sheet thickness is relatively thick as in the present invention, the decarburization time in the decarburization annealing becomes extremely long, which is not suitable for industrial production. Therefore, the upper limit is 0.0
4%.

A description will be given below based on experimental results. FIG.
Is the total rolling reduction (true strain) of the hot rolling finishing stand,
The relationship between the final cold rolling rate (true strain) and the magnetism (B ₈ ) is shown. The conditions in this case are as follows. C: 0.035-0.
038%, Si: 2.9-3.10%, acid-soluble Al:
0.026 to 0.028%, N: 0.0078 to 0.0
83%, S is 0.0065 to 0.0075%, Mn:
A slab consisting of 0.08 to 0.1.1%, the balance being Fe and unavoidable impurities, was heated at a temperature of 1140 to 1160 ° C and hot rolled. Thereafter, a hot-rolled sheet is annealed at 1120 ° C. for 120 seconds, and then cooled at a rate of 30 ° C./second. After deskelling, one cold rolling is performed at 180 to 230 ° C. for 2 minutes or more for 2 passes. After degreasing, 830-
After decarburizing annealing at 850 ° C. for 90 to 200 seconds, nitriding in a mixed gas of hydrogen, nitrogen, and ammonia after running the strip so that the total amount of nitrogen becomes 0.019 to 0.022% after nitriding. After treatment, an annealing separator containing MgO as a main component is applied, and N ₂ = 25% and H ₂ = 75%
Under an atmosphere of 650 ° C. to 120 ° C. at 10 to 20 ° C./hour.
The temperature was raised to 0 ° C., and then H
Purification annealing was performed at ₂ = 100%. Thereafter, application of a commonly used insulating tension coating and smoothing treatment were performed.
In this case, the coarse bar thickness (ti: the thickness of the finished entrance) is 3
0, 50, 70, 90, 110 and 130 mm, and the finish outlet thickness (to: hot rolled steel strip thickness) is 1.6, 2.0,
The final product thickness was set to 2.4, 3.0, 4.0, 5.0, 6.0 mm and 0.35 mm. As shown in FIG.
Final cold-rolling rate (true strain): Cr is greatly affected by the final cold-rolling total rolling rate (true strain): Hf. From the experimental results, the range in which B ₈ achieves 1.86 (T) or more is expressed as a formula. , −
0.25Hf + 2.6 ≦ Cr ≦ −0.25Hf + 3.6
It can be found that Hf is 2.70.
It is determined from the experimental results that 9 ≦ Hf ≦ 3.912, and the range determined by each of the above-described equations is 0.
Even in the case of 30 to 0.65 mm, B ₈ ≧ 1.86 or more can be surely achieved.

Next, the final rolling reduction in cold rolling will be described. In the first place, in order to obtain good magnetic properties (secondary recrystallized texture having a good directionality of Goss orientation) in the production of a grain-oriented electrical steel sheet, the primary recrystallized texture after decarburization annealing must be optimized. In addition, it is necessary to secure the inhibitor strength. Conventionally, in order to optimize the primary recrystallization texture in the production of a grain-oriented electrical steel sheet, a certain degree of transformation phase has been required during the final cold rolling after hot rolling. For this purpose, carbon is contained. However, 1
It has been found that in the slab heating method at a temperature lower than 280 ° C., the degree of optimization of the primary recrystallization texture may be small. This degree of optimization is quantitatively determined by the corresponding group boundary theory of the original group (for example, Japanese Patent Publication No. 1-255155, Journal of the Japan Institute of Metals No. 59).
No. 9 (1995) 917-924). That is, Goss orientation grains ({110} <001>)
And a small amount of # 9 corresponding orientation grains exist and their values are all $ 9
The largest (strong) and good Go in the distribution of the orientation relationship
The ss orientation undergoes secondary recrystallization. However, the stability and sharpness of the expression of the Goss orientation depend on the inhibitor strength.

In the method according to the present invention, it has been found that since the inhibitor strength can be arbitrarily controlled as strip nitriding, only good Goss orientation grains can be selectively expressed. Methods for maximizing the Σ9 value for this Goss orientation grain in the entire distribution mainly include a texture before cold rolling, a grain size, and a cold rolling rate. Factors that greatly affect the primary recrystallization texture are the overall finish rolling reduction in hot rolling and the final cold rolling reduction. The present inventors have found that the cold rolling reduction can be reduced by optimizing the texture before cold rolling. It is well known that the texture before cold rolling is greatly affected by components and hot rolling conditions. An important element of the present invention is that, based on the above principle, it has been found that the cold rolling reduction can be reduced by defining the finished total draft in hot rolling.

Next, the reason for limiting the plate thickness will be described. 0.040% when the product thickness is less than 0.30mm
If it is not more than 0.070%, decarburization to carbon of 30 ppm or less is not rate-limiting in decarburization annealing, and the formation of a surface oxide layer is rate-limiting. For this reason, the plate thickness is set to 0.30 mm or more. If the sheet thickness is less than 0.30 mm, and if the amount of carbon is small, the primary recrystallization texture is not adequately adjusted, the degree of deterioration of the inhibitor (mainly AlN) during the secondary recrystallization annealing is increased, and good results are obtained. Goss orientation grains cannot be obtained. of course,
It is possible to control the atmosphere at the time of secondary recrystallization to suppress the decomposition of the inhibitor and obtain good Goss orientation grains. Retention significantly decreases.

On the other hand, the upper limit of the sheet thickness of 0.65 mm is that if the sheet thickness is more than this, the C content must be less than 0.010% in order to secure productivity. C
If the content is less than 0.010%, it is difficult to favorably form a primary film containing forsterite as a main component and to stabilize the secondary recrystallization in a good Goss orientation.

Next, the temperature during hot rolling will be described. In the present invention, the heating temperature of the slab is lower than 1280 ° C,
Therefore, most of so-called inhibitors such as AlN are precipitated. In order to further carry out this precipitation, the finish inlet temperature is set to 950 to 1150 ° C., and the finish outlet temperature is set to 80
It is necessary to set the winding temperature to 0 to 1050 ° C and the winding temperature to 500 to 650 ° C. Preferably, the finishing inlet temperature is 975 to 1
015 ° C, the finishing temperature is 850 to 975 ° C, and the winding temperature is 525 to 600 ° C.

Next, the reasons for limiting the component composition of the magnetic steel slab used as the starting material in the present invention are as follows.
C was set to 0.010 to 0.040%. 0.010%
If it is less than the above, it is described above. On the other hand, if it exceeds 0.040%, the productivity in the decarburization step is remarkably impaired, deviating from the object of the present invention.

If the content of Si is less than 2.5%, good iron loss cannot be obtained. On the other hand, if it exceeds 4.0%, it becomes difficult to treat the steel sheet at room temperature such as cold rolling due to brittleness. S and Se are 0.015% or less, preferably 0.013% or less. A unidirectional electromagnetic device manufactured by manufacturing a hot-rolled sheet at a slab heating temperature of 1280 ° C. or less, and then manufacturing an inhibitor after a decarburizing annealing step by strip nitriding after hot-rolled sheet annealing and cold rolling. This is because, in a steel sheet, a large amount of S and Se hinders the growth of primary recrystallized grains and is harmful. If it is less than 0.005%, due to unavoidable fluctuation factors in the operation in hot rolling (difference in temperature history on and between skids, fluctuation of hot rolling temperature due to acceleration of rolling speed, etc.),
Locational fluctuations are likely to occur in the grain growth of the primary recrystallized grains, and a product cannot be manufactured stably industrially.

Al combines with N to form AlN,
In the present invention, since it is essential to form (Al, Si) N by nitriding the steel after the post-process, ie, after the completion of the primary recrystallization, a certain amount of free Al is required. Therefore, 0.020-
Add 0.040%. If the content of Mn is too small, the secondary recrystallization becomes unstable, while if it is too large, the defect rate of the primary coating (a so-called glass coating containing forsterite as a main component) increases. The appropriate content is 0.05-
0.8%. Preferably, it is 0.070 to 0.3%.

If N is less than 0.005%, the development of secondary recrystallized grains becomes worse. On the other hand, if it exceeds 0.010%, blisters of the steel plate called blisters are generated. It has been reported that P improves the primary recrystallization texture. At a low P, the effect is small and the cost is increased in terms of steelmaking cost. Therefore, the lower limit is set to 0.02%. With respect to the upper limit, if it exceeds 0.30%, P segregates at the grain boundary and brittle fracture is likely to occur, and industrial production becomes difficult. Preferably it is 0.30% or less.

Sn and Sb are, as conventionally known,
The primary recrystallization texture has the effect of increasing the grain size of the {110} <001> orientation and has the effect of uniformly depositing sulfide. Therefore, in the present invention, Cu-S, M
The effect of uniformly controlling the precipitation of sulfide such as nS is enhanced. Furthermore, when Sn and Sb are added in a large amount, oxidation during decarburization annealing is difficult to occur, and the secondary recrystallized grains tend to grow apart. For this reason, the decarburization annealing temperature is set to 820 to
It has to be raised by about 20 ° C. from 840 ° C. This is a direction that facilitates the formation of the primary coating of the grain-oriented electrical steel sheet. In addition, since the secondary recrystallized grain size is reduced by adding Sb and Sn, iron loss (particularly, low magnetic field iron loss) is improved as compared with no addition. On the other hand, if Sb or Sn is 0.02
%, The secondary recrystallized grains are not so small. On the other hand, when Sb or Sn exceeds 0.30%, nitriding treatment after decarburizing annealing becomes difficult, which is not suitable for industrial production.

Cr is added in order to secure an oxygen amount after decarburization annealing necessary for forming a forsterite film.
If it is less than 0.02%, the amount of oxygen becomes extremely small. On the other hand, if it exceeds 0.30%, the amount of oxygen increases extremely, and good forsterite cannot be formed. Also, the magnetic flux density decreases. When Cu is less than 0.03%, the effect of improving the magnetic properties is small. On the other hand, if it exceeds 0.5%, the size of the Cu-S precipitate becomes coarse and the effect is reduced. In addition, the frequency of occurrence of so-called “Cu scabs” during hot rolling sharply increases. Preferably, it is 0.05 to 0.10%.

If the content of Ni is less than 0.03%, the effect is small, and if it exceeds 0.3%, the effect is obtained as shown in JP-A-5-306410, but it is expensive. Cr and N
The addition of i further improves the effect of the present expression, and may be added in an amount that is commensurate with cost. Next, the necessity of hot-rolled sheet annealing will be described. As described above, JP-A-4-323 and JP-A-4-324 specify the hot-rolling conditions when hot-rolled sheet annealing is not performed. In this case, hot rolling is substituted for hot rolled sheet annealing. However, in this case, the primary recrystallization texture is Go
The ss orientation is small, and according to the corresponding grain boundary theory, the particle size of the final product tends to be large and the iron loss tends to be inferior. An effective means for securing the amount of Goss-oriented grains in the next recrystallization texture, reducing the grain size of the final product, and improving iron loss is to perform hot-rolled sheet annealing. In fact, in both of the above-mentioned patent publications, there is a description that the magnetic flux density is improved, but there is no description about the iron loss improvement.

[0029]

Next, examples of the present invention will be described. After producing a steel ingot of the components shown in Table 1 by a usual method and heating the slab at 1100 to 1175 ° C, the finishing inlet temperature was set to 975 to 1125 ° C,
Total rolling reduction in finish rolling is 1.764 to 4.0 in true strain.
30 and hot rolling at a finishing outlet temperature of 825 to 1025C and a winding temperature of 525 to 625C.
Finished to 6-6.0 mm.

Thereafter, hot-rolled sheet annealing was performed at 1120 ° C. for 2 minutes, and after pickling, cold rolling was performed at a minimum of two passes at 180 to 220 ° C. to 0.22 to 0.65 mm.
Then, at 820-850 ° C., N ₂ : 25%, H ₂ : 75 in order to make the primary recrystallization average particle size 22-22 μm.
The decarburization primary recrystallization annealing was carried out at a dew point of 62 ° C. for 70 seconds to 150 seconds in an atmosphere gas of 50%. Thereafter, strip nitriding treatment was carried out to a total nitrogen content of 195 to 210 ppm, and an annealing separator containing MgO as a main component was applied, followed by finish annealing. In this finish annealing, the temperature was raised at 10 to 20 ° C./hour, and the atmosphere was N ₂ : 25% and H ₂ : 75%.

Thereafter, H ₂ : 1 at 1200 ° C. for 20 hours.
A purification annealing of 00% was performed. Thereafter, application of a commonly used tension coating and smoothing treatment were performed. The magnetic properties obtained in the examples of the present invention are shown in Table 2 together with the hot rolling conditions, sheet thickness, and cold rolling conditions. All of the methods according to the present invention show good magnetic properties.

[Table 1]

[Table 2]

[0032]

As described above, according to the present invention, the relationship between the total rolling reduction (Hf: true strain) and the final cold-rolling rate (Cr: true strain) in hot rolling is determined in a specific range obtained by an empirical formula. The C content can be reduced even when the product sheet thickness is as large as 0.30 to 0.65 mm by operating at, and the product cost of the grain-oriented electrical steel sheet can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the total draft (Hf: true strain), the final cold-rolling rate (Cr: true strain), and the magnetic flux density (B ₈ ) of a hot rolling finishing stand.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Katsuro Kuroki, Nippon Steel Plant Design Co., Ltd., 46-46 Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture 1. Inside Nippon Steel Corporation Yawata Works

Claims (3)

[Claims] 1. A weight ratio of C: 0.010 to 0.040%, Si: 2.5 to 4.0%, acid-soluble Al: 0.020 to 0.040%, N: 0.005 to 0.010%, at least one of S and Se is 0.005 to 0.015
%, Mn: 0.05 to 0.3%, the balance being 128 slabs composed of Fe and inevitable impurities.
After heating at a temperature of less than 0 ° C., hot rolling is performed, hot-rolled sheet annealing is performed, and then after deskering, one cold rolling is performed, and after decarburizing and sintering, hydrogen and nitrogen are allowed to run under stripping conditions. In a method for producing a grain-oriented electrical steel sheet in which a nitriding treatment is performed in a mixed gas of ammonia and then an annealing separator containing MgO as a main component is applied and final finish annealing is performed, the final total draft in hot rolling ( Hf: true strain) and the final cold-rolling rate (Cr: true strain) are: -0.25Hf + 2.6 ≦ Cr ≦ −0.25Hf + 3.
6. A method for producing a grain-oriented electrical steel sheet having a large product sheet thickness, wherein 2.709 ≦ Hf ≦ 3.912. 2. The product thickness is 0.30 mm to 0.65.
2. The method according to claim 1, wherein the thickness of the product is 0.1 mm. 3. The finishing inlet temperature of hot rolling is set to 950-1.
The method for producing a unidirectional magnetic steel sheet having a thick product sheet according to claim 1, wherein the finishing temperature is 150 ° C, the finishing outlet temperature is 800 to 1050 ° C, and the winding temperature is 500 to 650 ° C.