JPH11124628A - Production of grain oriented silicon steel sheet of which product sheet is thick - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good magnetism even in the case of a low carbon content in a steel sheet by using a grain oriented silicon steel sheet stock having a specified compsn. and specifying the draft in the final stand in hot rolling, the final cold rolling ratio, the temp. in the hot rolling and the product sheet thickness. SOLUTION: A slab contg., by weight, 0.010 to 0.040% C, 2.5 to 4.0% Si, 0.020 to 0.040% acid soluble Al, 0.005 to 0.010% N, one or more kinds of S and Se by 0.005 to 0.015%, 0.05 to 0.8% Mn, and the balance Fe is heated at <1,280 deg.C, is subjected to hot rolling, is subjected to hot rolled sheet annealing, is subjected to descaling, is thereafter subjected to cold rolling for one time and is subjected to decarburizing annealing, subsequently, the strip is subjected to nitriding treatment in a gaseous mixture of H2 , N2 and NH3 in a running state, is thereafter coated with an MgO series separation agent for annealing and is subjected to final finish annealing, where the product thickness (t: mm) is regulated to 0.30 to 0.65 mm, and the upper limit of the range of the final cold rolling ratio Rc(%) is limited by the inequality I and the lower limit by the inequalities II to V (R: the draft in the final stand in the hot rolling).

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 A grain-oriented electrical steel sheet is mainly used as an iron core material of transformers and other electric devices, and has excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. Required for reduced energy loss. As a characteristic value representing the excitation characteristics, magnetic flux density B ₈ in the strength of 800A / m of the magnetic field standardized by JIS it is normally used. Further, as the characteristic value indicating the energy loss, the energy loss (iron loss) W _17/50 per kg of the steel sheet when magnetized at a frequency of 50 Hz to 1.7 Tesla (T) is also JI.
Standardized by S.

[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-rolled sheet stage, and it is necessary to set the heating temperature of the steel ingot (slab) to 1350 ° C. or more during actual hot rolling.

[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 while the strip is running (JP-A-2-77525, JP-A-1-82400, JP-A-3-180).
460, JP-A-1-317592) have been proposed.

A method of controlling the primary recrystallized grain size at an intermediate stage from the completion of the primary recrystallization at the time of decarburizing annealing to the completion of the secondary recrystallization at the time of final finishing annealing (Japanese Patent Laid-Open No. 3-294425).
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. Therefore, 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 grain-oriented electrical steel sheet, it has been essential in the prior art to contain carbon to some extent at the steel making stage. The purpose of containing carbon is high temperature (135
In the case of slab heating at a temperature of 0 ° C. or more, there are prevention of abnormal grain growth at the time of slab heating, securing of a transformed phase for adjusting texture of primary recrystallization, securing of solid solution amount of inhibitor, and the like.
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 slab at a temperature lower than 1280 ° C. as in the present invention, it is required to contain carbon to some extent for the above-mentioned purpose. In this case, C needs to exceed 0.040%.

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 decarburization 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 stipulates conditions during hot rolling when hot-rolled sheet annealing of a thick grain-oriented electrical steel sheet is not performed.
Of course, a thick grain-oriented electrical steel sheet 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 adjustment of the inhibitor is performed only in the hot rolling step, and the stability of the magnetic properties and the reduction of iron loss are performed. There was a limit to improvement.

[0009]

As described above, the production of a grain-oriented electrical steel sheet necessarily involves a decarburization step. Therefore, in the case of a thick material (0.30 mm or more), the carbon before the decarburization annealing is used. It is important to reduce the content as much as possible to improve the 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. If the oxide layer on the surface becomes extremely thick, defects occur in the primary film (film containing forsterite as a main component) 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 grain-oriented electrical steel sheet having good magnetic properties as well as iron loss among magnetic properties 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 running a strip after decarburizing annealing, a reduction ratio of a final stand of hot rolling, a final cold rolling It has been found that by setting the rate, the temperature at the time of hot rolling and the product sheet thickness appropriately, it is possible to produce a unidirectional magnetic steel sheet having good magnetism even if the carbon content is lower than before.

The gist is as follows. (1) C: 0.010-0.040%, Si: 2.5 by weight ratio
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
Slab consisting of Fe and inevitable impurities is heated at a temperature of less than 1280 ° C., and hot-rolled.
Hot-rolled sheet annealing is performed, after the subsequent deskelting, one cold rolling is performed, and after decarburizing annealing, the strip is allowed to run, then nitriding is performed in a mixed gas of hydrogen, nitrogen, and ammonia, and then MgO is mainly used. In a method for producing a grain-oriented electrical steel sheet in which an annealing separator as a component is applied and subjected to final finish annealing, the product thickness (t: mm) is set to 0.30 mm ≦ t ≦ 0.
The upper and lower limits of the range of the final cold rolling reduction: R _C (%) are defined by the following formula.

Upper limit: R _C ≦ (300-50t) / 3 (%) Lower limit: When 5 ≦ R _H ≦ 15% in relation to the reduction ratio R _H (%) of the final stand of hot rolling, R _C ≧ − 75t / 3 + 92.5 (%) 15 <R when _{H ≦ 30% R C ≧ -100t} / 3 + 92.5 (%) 30 < when _{R H ≦ 45% R C ≧} -125t / 3 + 92.5 (%) 45 <R _H ≦ 60% When R _C ≧ −150 t / 3 + 92.5 (%), a method for producing a unidirectional magnetic steel sheet having a large product sheet thickness is provided. Regarding the temperature at the time of cold rolling, the finishing inlet temperature is 950 to 1150 ° C, the finishing outlet temperature is 800 to 1050 ° C, and the winding temperature is 50.
0 to 650 ° C., which is a method for producing a unidirectional magnetic steel sheet having a large product sheet thickness.

[0016]

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 phase. In the present invention, the rolling reduction and the cold rolling reduction of the final stand in hot rolling are specified 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%. This relationship is shown in FIGS.
FIG. 1 shows the relationship among the C content, the cold rolling reduction, and the magnetic flux density when the rolling reduction of the final stand of the hot rolling is 40%, the product thickness is 0.50 mm, and Si% = 3.0%. . FIG.
Is: cold rolling reduction 87%, product thickness 0.50mm, Si% =
The relationship between the C content at 3.0%, the rolling reduction of the final stand in hot rolling, and the magnetic flux density is shown.

Next, the reason for limiting the plate thickness will be described. When the product sheet thickness is less than 0.30 mm, even if the C content is 0.040% or more, if the C content is 0.070% or less, decarburization to carbon of 30 ppm or less is not rate-limiting in decarburization annealing, and the surface oxide layer The formation is rate-limiting and there is little merit of low carbon. For this reason, the plate thickness is set to 0.30 mm or more. If the plate thickness is less than 0.30 mm, and if the amount of carbon is small, the primary recrystallization texture is not made sufficiently appropriate, the degree of deterioration of the inhibitor (mainly AlN) during the secondary recrystallization annealing is increased, which is favorable. No Goss-oriented grains can be obtained. Of course, it is possible to control the atmosphere during the secondary recrystallization to suppress the decomposition of the inhibitor and obtain good Goss orientation grains.
In this case, many defects occur in the primary film containing forsterite as a main component, and the yield is significantly reduced.

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 secondary recrystallization in a good Goss orientation.

Next, the final rolling reduction in cold rolling will be described. In the first place, in order to obtain good magnetic properties (secondary recrystallization texture having a good Goss orientation) in the production of a grain-oriented electrical steel sheet, it is necessary to optimize the primary recrystallization texture after decarburization annealing and Inhibitor strength must be ensured. 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, 12
It has been found that in the slab heating method at less than 80 ° C., the degree of optimizing the primary recrystallization texture may be small.
This degree of optimization is quantitatively based on the corresponding grain boundary theory of the original group (for example, Japanese Patent Publication No. Hei 7-26155, Journal of the Japan Institute of Metals No. 59,
No. 9 (1995) 917-924). That is, Goss orientation grains ({110} <011>) and Σ
Good Goss if 9 corresponding orientation grains exist even in a small amount and the value is the largest (strong) in the distribution of all 方位 9 orientation relationships
The 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 controlled arbitrarily 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. Of these, the cold rolling reduction is an important factor, but the texture before cold rolling is also important. 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 rolling reduction in the final rolling in hot rolling.

The above findings will be described in detail based on experimental results. % By weight, C: 0.025 to 0.038%, S
i: 2.80 to 3.25%, Al: 0.026 to 0.0
29%, N: After heating the slab of the component based on 0.0070-0.0085% at 1100 ° C-1200 ° C,
The hot rolling was performed by a normal method, but the rolling reduction ( _RH ) of the final finishing stand at that time was 8 to 15%, 18 to 30%, 33
~ 45%, 48 ~ 60%, thickness: 1.0 ~ 12.0
mm. In this case, the finishing inlet temperature is 975-10
75 ° C, the finish outlet temperature was 850 to 975 ° C, and the winding temperature was 540 to 580 ° C. Thereafter, hot-rolled sheet annealing is performed at 1120 ° C. for 2 minutes, and after pickling, 180 to 220 ° C.
At least 2 passes of warm rolling at a thickness of 0.20 to 0.20
It was rolled to 0.70 mm. Thereafter, at 820 to 860 ° C., in an atmosphere gas of N ₂ : 25% and H ₂ : 75%, a dew point of 6
Decarburization primary recrystallization was performed at 2 ° C. for 70 seconds to 150 seconds.
Thereafter, strip nitriding treatment was performed so that the total nitrogen content was 195 to 210 ppm, an annealing separator containing MgO as a main component was applied, and finish annealing was performed. This finish annealing is 9
The temperature was raised from 00 to 1200 ° C. at 10 to 20 ° C./hr, and the atmosphere was N ₂ : 25% and H ₂ : 75%. Then 1
H ₂ : 100% purification annealing was performed at 200 ° C. for 20 hours. Thereafter, application of a commonly used tension coating and smoothing treatment were performed. The results of the magnetic properties of the grain-oriented electrical steel sheet manufactured through these steps are shown in FIGS.

The mark ◎ indicates B8 ≧ 1.91T, and the mark １1.8.
6 ≦ B8 <1.91T, Δ indicates B8 <1.86T. Although there are ◎ marks outside the range of the present invention, in this case, the product was manufactured by the conventional technique without satisfying the range of the present invention (the range of the product thickness). That is, when the thickness is thin, the decarburization annealing time is short, and the decarburization reaction is not rate-determining. When the thickness is larger than the range of the present invention, the decarburization time is unusually long, which is not suitable for an industrial production base.

In the present invention, the final cold rolling reduction: R _C
(%) Is related to the thickness and the rolling reduction R _H (%) of the final stand of hot rolling, and the upper and lower limits are defined by the following equations. _{Limit: R C ≦ (300-50t) /} 3 (%) lower: When 5 ≦ R _H ≦ 15% in relation to the reduction rate of the final stand of the hot rolling _{R H (%) R C ≧} -75t / 3 + 92 0.5 (%) 15 <R _H ≦ 30% _RC ≧ −100t / 3 + 92.5 (%) 30 <R _H ≦ 45% _RC ≧ −125t / 3 + 92.5 (%) 45 <R _{When H} ≦ 60%, R _C ≧ −150 t / 3 + 92.5 (%) When the above conditions are satisfied and the final cold rolling ratio is out of the lower limit, the secondary recrystallization is good, but the magnetism, especially B8, is not good. Inferior.

Although the upper limit of the final cold rolling rate also depends on the reduction rate of the final stand of hot rolling in principle, annealing is performed before final cold rolling such as hot rolling sheet annealing as in the present invention. And its dependencies are significantly reduced. Next, the reason for defining the rolling reduction of the final stand in hot rolling will be described. Japanese Patent Application 2-2
74811 and the like define the cumulative rolling reduction of the last three stands, but in actual hot rolling, the time between stands before the last stand is shorter than the time between the last stand and winding, and the The effect is small and the final stand draft has the greatest effect on recrystallization.

The reason why the reduction rate of the final stand is set to 60% or less is that in actual hot rolling, a reduction of more than this is not practical considering the capacity (mill power) of the hot rolling mill. Further, the reason why the lower limit is set to 5% is that a reduction ratio lower than this is not practical. The lower the product rolling thickness, the lower the lower limit of cold rolling reduction. That is, the reason why the lower limit is widened is that the degree of deterioration of the inhibitor in the secondary recrystallization region is small, that is, the degree of deterioration is slower than the deterioration time, and the preferential growth of the Goss orientation is likely to occur.

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 1075 ° C. and the finishing outlet temperature is 85, based on the precipitation behavior of AlN.
0 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. If it exceeds 40%,
The brittleness makes it difficult to treat the steel sheet at room temperature such as cold rolling. S and Se are 0.015% or less, preferably 0.1% or less.
013% or less. A one-way electromagnetic device manufactured by manufacturing a hot-rolled sheet at a slab heating temperature of 1280 ° C. or lower, 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 the content is less than 0.005%, primary recrystallized grains may grow due to unavoidable fluctuation factors in the operation of hot rolling (temperature difference on and between skids, fluctuation of hot rolling temperature due to acceleration of rolling speed, etc.). Locational fluctuations easily occur, and products cannot be manufactured industrially stably.

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, sol. 0.020 or more as Al
Add 0.040%. If the content of Mn is too small, secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. The appropriate content is 0.
05 to 0.8%. Preferably, 0.070-0.0.
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, this effect is small and the cost of steelmaking increases, so the lower limit is made 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 controlling the precipitation of sulfides such as n-S is enhanced. Furthermore, when Sn and Sb are added in a large amount, there is a tendency that oxidation during decarburization annealing is hardly performed and primary recrystallized grains grow hardly. For this reason, the decarburization annealing temperature is set to 820 to 84
It has to be raised by about 20 ° C. from 0 ° 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, when Sb or Sn is less than 0.02%, the secondary recrystallized grains do not become too 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.

[0032] Cr is added in order to secure an oxygen amount after decarburizing 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. If Cu is less than 0.03%, the effect is small. On the other hand, when the content exceeds 0.5%, the precipitate of Cu-S becomes coarse, and the effect is reduced. Further, during hot rolling, the frequency of occurrence of so-called "Cu scab" flaws 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 the cost is high. Cr and N
The addition of i further improves the effect of the present invention, and may be added only in an amount 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 Gos
The s orientation is small, and according to the corresponding grain boundary theory, the particle size of the final product tends to be large and iron loss tends to be inferior. An effective means for securing the amount of Goss orientation grains in the primary 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.

[0034]

Next, examples of the present invention will be described. After producing a steel ingot having the components shown in Table 1 by a usual method and heating the slab at 1100 to 1150 ° C, the finishing inlet temperature was set to 975 to 1125 ° C,
The rolling reduction of the final stand is 10 to 55%, the finishing outlet temperature is 825 to 1025 ° C, and the winding temperature is 525 to 6
Finished to a thickness of 1.4 to 6.5 mm by hot rolling at 25 ° C.

Thereafter, hot-rolled sheet annealing was performed at 1120 ° C. × 2 minutes, and after pickling, cold rolling was performed at a temperature of 180 to 220 ° C. and a minimum of two passes at a temperature of 0.22 to 0.60 mm. Thereafter, decarburization primary recrystallization annealing was performed at 820 to 840 ° C. in an atmosphere gas of N ₂ : 25% and H ₂ : 75% at a dew point of 62 ° C. for 70 seconds to 150 seconds. Thereafter, the total nitrogen content is reduced to 1
Strip nitriding to 95-210 ppm
An annealing separator containing gO as a main component was applied, and finish annealing was performed. This finish annealing raises the temperature at 10 to 20 ° C./hour,
_{Atmosphere, N 2: 25%, H} 2: it was 75%.

Thereafter, H ₂ : 10 at 1200 ° C. for 20 hours.
A 0% purification annealing 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 1 together with the hot rolling conditions, sheet thickness, and cold rolling conditions.

[0037]

[Table 1]

[0038]

As described above, in the conventional method for manufacturing a grain-oriented electrical steel sheet, it is necessary to contain a somewhat large amount of C in order to secure the transformation phase. In the case of production, decarburization took time and increased costs. On the other hand, in the present invention, even when the product sheet thickness is as thick as 0.30 mm to 0.65 mm, the cold rolling reduction determined by the relationship between the sheet thickness and the rolling reduction of the final stand of hot rolling is specified. When the thickness falls within the range, it is possible to manufacture a thick unidirectional magnetic steel sheet having excellent magnetic properties.

[Brief description of the drawings]

FIG. 1 shows the C content, the cold rolling reduction (R _C ), and the magnetic flux density when the rolling reduction of the final stand of hot rolling is 40%, the product plate thickness is 0.50 mm, and Si% = 3.0%. The figure which shows a relationship.

Fig. 2 Cold rolling reduction 87%, product thickness 0.50mm, Si
The figure which shows the relationship between the C content at the time of% = 3.0%, the rolling reduction ( _RH ) of the final stand of hot rolling, and magnetic flux density.

FIG. 3 shows a reduction ratio (R _H ) of the final stand of hot rolling of 8
The figure which shows the relationship between the product thickness (t: mm) and the final cold rolling reduction ( _RC :%) in the case of -15%.

FIG. 4 shows a reduction ratio (R _H ) of the final stand of hot rolling of 1
The figure which shows the relationship between the product thickness (t: mm) and the final cold rolling reduction ( _RC :%) in the case of 8-30%.

FIG. 5: Reduction ratio (R _H ) of the final stand of hot rolling is 3
The figure which shows the relationship between the product thickness (t: mm) and the final cold rolling reduction ( _RC :%) in the case of 3-45%.

FIG. 6: The reduction ratio (R _H ) of the final stand of hot rolling is 4
The figure which shows the relationship between the product thickness (t: mm) and the final cold rolling reduction ( _RC :%) in the case of 8-60%.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Katsuro Kuroki 59 Nippon Steel Plant Design Co., Ltd.

Claims (2)

[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 0.8%, 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 deskelling, one cold rolling is performed, and after decarburizing annealing, hydrogen and nitrogen are allowed to run in a strip. 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 product thickness (t: mm) is set to 0. .30mm ≦ t ≦ 0.65
mm and the range of the final cold rolling ratio: R _C (%) is the upper limit: R _C ≦ (300-50t) / 3 (%) The lower limit: The relationship of the reduction ratio R _H (%) of the final stand of hot rolling When 5 ≦ _RH ≦ 15%, _RC ≧ −75t / 3 + 92.5 (%) When 15 < _RH ≦ 30%, _RC ≧ −100t / 3 + 92.5 (%) 30 < _RH ≦ 45% When R _C ≧ −125 t / 3 + 92.5 (%) When 45 <R _H ≦ 60%, R _C ≧ −150 t / 3 + 92.5 (%). Manufacturing method of electrical steel sheet. 2. 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.