JPH06306473A - Production of grain-oriented magnetic steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To improve magnetic properties such as excitation properties, core loss properties or the like in a steel sheet by subjecting a cold rolled magnetic steel sheet to decarburizing treatment, thereafter subjecting it to nitriding treatment under specified conditions and then producing secondary recrystallization by final finish annealing by continuous annealing. CONSTITUTION:A slab contg., by weight, <=0.075% C, 2.2 to 5.0% Si, <=0.0050% N, <=0.0050% S and 0.005 to 0.060% Al, and the balance Fe is heated at <1280 deg.C and is subjected to hot rolling. Next, cold rolling contg. cold rolling at >=80% draft and including, at need, process annealing is executed for one or more times. Next, it is subjected to decarburizmng annealing, is thereafter subjected to nitriding treatment at 600 to 1000 deg.C so as to regulate the amt. of nitrogen to be increased into >=0.0005% and is successively subjected to final finish annealing for producing secondary recrystallization by continuous annealing, by which the grain-oriented silicon steel sheet excellent in magnetic properties can be obtd.

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 grain-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional magnetic steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. As a numerical value showing the excitation characteristic, the strength of a normal magnetic field is 8
A magnetic flux density B _{8 at} 00 A / m is used. In addition, as a numerical value showing the iron loss characteristic, the iron loss per kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is W _17/50.
Are using. The magnetic flux density is the most dominant factor of the iron loss characteristics, and generally speaking, the higher the magnetic flux density, the better the iron loss characteristics. Generally, when the magnetic flux density is increased, the secondary recrystallized grains become large, which may result in poor iron loss characteristics. On the other hand, by controlling the magnetic domains, the iron loss characteristics can be improved regardless of the grain size of the secondary recrystallized grains.

This unidirectional electrical steel sheet undergoes secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and <001> axis in the rolling direction. Being manufactured. In order to obtain good magnetic properties, it is necessary to align <001>, which is the easy axis of magnetization, in the rolling direction.

A typical technique for producing such a high magnetic flux density unidirectional electrical steel sheet is Japanese Patent Publication No. 40-15644.
There is a method described in JP-B No. 51-13469. In the former, MnS and AlN are used as main inhibitors, and in the latter, MnS, MnSe, Sb, etc. are used. Therefore, in the current technology, it is essential to appropriately control the size, morphology and dispersion state of the precipitates that function as these inhibitors.

As for MnS, in the present process, after the MnS is completely solid-soluted at the time of heating the slab before hot rolling,
The method of precipitation during hot rolling is adopted. A temperature of about 1400 ° C. is necessary to completely form a solid solution of the required amount of MnS for secondary recrystallization. This is higher than the slab heating temperature of ordinary steel by 200 ° C. or more, and this high-temperature slab heating treatment has the following disadvantages. 1) A high temperature slab heating furnace exclusively for grain oriented electrical steel is required. 2) The energy intensity of the heating furnace is high. 3) The amount of molten scale increases, and the adverse effect on operation is large, as seen in so-called shaving.

In order to avoid such a problem, the slab heating temperature should be lowered to the level of ordinary steel.
This means that at the same time, the amount of MnS effective as an inhibitor is reduced or not used at all, and inevitably results in destabilization of secondary recrystallization. Therefore, in order to realize low-temperature slab heating, it is necessary to strengthen the inhibitor in some form with precipitates other than MnS to sufficiently suppress normal grain growth during finish annealing.

As such inhibitors, sulfides, nitrides, oxides, grain boundary precipitation elements, and the like are considered, and known techniques include, for example, the following. That is, in Japanese Examined Patent Publication No. 54-24685, As, Bi,
A method of controlling the slab heating temperature in the range of 1050 to 1350 ° C. by including grain boundary segregation elements such as Sn and Sb in the steel is disclosed. JP-A-52-24116 discloses Al, Zr, Ti, B, Nb, Ta, V, Cr, M
It discloses a method for controlling the slab heating temperature in the range of 1100 to 1260 ° C. by containing a nitride-forming element such as o. Further, in JP-A-57-158322, M
A technique is disclosed in which the n content is reduced and the Mn / S ratio is set to 2.5 or less to perform low temperature slab heating, and further Cu is added to stabilize secondary recrystallization.

Techniques have also been disclosed in which improvements are made from the metallographic side in combination with the reinforcement of these inhibitors. That is, in JP-A-57-89433, S, in addition to Mn,
Elements such as Se, Sb, Bi, Pb, Sn, and B are added, and the columnar crystal ratio of the slab and the secondary cold rolling reduction are combined to realize low-temperature slab heating at 1100 to 1250 ° C. Further, in JP-A-59-190324, an inhibitor is composed mainly of Al and B and nitrogen in addition to S or Se, and secondary annealing is performed by performing pulse annealing at the time of primary recrystallization annealing after cold rolling. The technology to stabilize is released.

As described above, in order to realize the low temperature slab heating in the production of grain-oriented electrical steel sheet, great efforts have been made so far. Furthermore, JP-A-59-5652
Japanese Patent Publication No. 2 discloses a technique that enables low temperature slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less. By this method, the problem of defective linear secondary recrystallization of the product due to coarsening of the slab crystal grains during heating of the high temperature slab was solved.

[0010]

Although the method using low temperature slab heating is originally intended to reduce the manufacturing cost, it cannot be industrialized unless it is a technique that can stably obtain good magnetic characteristics. The present inventors, for the industrialization of low-temperature slab heating, average grain size control of primary recrystallization before final finish annealing, after hot rolling, to perform nitriding treatment on the steel sheet before the start of secondary recrystallization of final annealing. We have built technology centered on. On the other hand, the final finish annealing of the unidirectional electrical steel sheet is usually performed by forming the steel sheet into a coil shape of about 5 to 20 tons, and the secondary recrystallization that occurs between 900 and 1200 ° C. in this final finish annealing is It occurs in a bent state. After the final finish annealing, the steel sheet is subjected to strain relief annealing and coating to become a product. This product is used in the form of a flat plate, but when it is recrystallized in a curved state, it is in a flat state when it has the same orientation within the secondary recrystallized grains (particle size: 1 to 50 mm). In the product), azimuth dispersion occurs around the TD axis in the grain due to geometrical reasons.

This azimuth dispersion is, of course, {1
The azimuth dispersion is from the 10} <001> azimuth, which causes a decrease in the magnetic flux density. Secondary recrystallization in the bent state of the steel sheet causes a decrease in magnetic flux density, but this is because the maximum temperature is 1100 to 1300 ° C because the impurities must be purified in the final annealing. 50 hours
This is because it takes about 300 hours to perform annealing in a box shape in Box. An object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet which causes secondary recrystallization in the form of a flat plate, performs final finishing annealing by continuous annealing, and has good magnetic properties.

[0012]

The gist of the present invention is as follows. (1) C: 0.075% or less by weight, Si: 2.2
5.0%, N: 0.0050% or less, S: 0.0050
% Or less, Al: 0.005 to 0.060%, with the balance 1280 slabs consisting of Fe and unavoidable impurities.
Heating at a temperature of less than ℃, hot rolling, including final cold rolling with a rolling reduction of 80% or more, if necessary, one or more cold rolling with intermediate annealing sandwiched, then decarburization annealing, final finish annealing In the method for producing a grain-oriented electrical steel sheet by applying the method, following decarburization annealing, the steel sheet is subjected to a nitriding treatment of 0.0005% or more with a nitrogen increase amount in a temperature range of 600 to 1000 ° C, and then 1
By continuous annealing in the temperature range of 000 to 1300 ° C,
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises performing final finishing annealing that causes secondary recrystallization.

(2) In the above (1), Sb, Sn,
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises using a slab containing 0.005 to 1.00% by weight of one or more Ps, respectively. (3) In the above (1) or (2), after the final finishing annealing that causes secondary recrystallization, 1100 to 13
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises subjecting impurities to purification annealing in an atmosphere gas having a hydrogen partial pressure of 25% or more in a temperature range of 00 ° C.

[0014]

The unidirectional electrical steel sheet targeted by the present invention is
Molten steel obtained by the conventional steelmaking method is cast by continuous casting method or ingot making method, and if necessary, the slab is sandwiched to form a slab, followed by hot rolling into a hot rolled sheet, and then reduction. It is manufactured by including a final cold rolling of a rate of 80% or more, performing one or more cold rollings with an intermediate annealing as needed, and then sequentially performing decarburization annealing and final finishing annealing.

The present inventors have conducted a detailed study on a method for making the magnetic characteristics favorable by carrying out final finishing annealing by continuous annealing which causes secondary recrystallization in the form of a flat plate. And as a measure, the amount of N and S in the slab is extremely reduced, decarburization annealing is followed by nitriding treatment, and continuous annealing is performed at a high temperature. It has been found that it is effective to contain and to carry out purification annealing after the above continuous annealing.

These points will be described in detail below.
Originally, secondary recrystallization is a phenomenon in which the grain boundary character dependence of grain boundary migration is emphasized by using impurities. Therefore, Journal of the Japan Institute of Metals, Vol. 55, No. 6 (1991) P630-638.
As described in (1), the higher the inhibitor strength (Zener factor (proportional precipitate body integration rate / precipitate size)) during the progress of secondary recrystallization, the more the {110} of the secondary recrystallization oriented grains.
<001> High degree of integration. In order to increase the inhibitor strength, usually, a method of increasing the amount of precipitates or making the precipitate size finer is used. Increasing the amount of precipitates lengthens the time required to purify impurities after secondary recrystallization,
Since the required temperature becomes high, it is unsuitable for performing final finishing annealing by short-time continuous annealing.

On the other hand, the method of making the precipitation size finer is suitable for continuous temperature increase in a short time, as compared with the method of increasing the amount. However, this method is also subject to volume limitations. Therefore, the third method studied by the present inventors is the use of grain boundary precipitation of precipitates and grain boundary segregation. Below, it demonstrates in detail based on an experimental result.

C = 0.054% by weight (hereinafter abbreviated as%),
Si = 3.20%, acid-soluble Al = 0.020%, N =
0.0015%, S = 0.017%, balance F
A 40 mm slab consisting of e and inevitable impurities was prepared. Then, after soaking at a temperature of 1150 ° C. for 60 minutes, hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm.

The hot-rolled sheet was annealed at 1100 ° C. for 10 seconds, at 900 ° C. for 30 seconds, air-cooled to 700 ° C., and then rapidly cooled. Then, about 90% strong reduction rolling was performed to obtain a cold rolled sheet having a final sheet thickness of 0.220 mm. The cold-rolled sheet was subjected to decarburization annealing at 810 ° C for 90 seconds, and then subjected to the following three types of treatments. 750
During annealing at 30 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere to cause the steel sheet to absorb nitrogen. The N of the steel sheet after this nitriding treatment was 0.0052%. N ₂ : 90
%, H ₂ : 10% in an annealing atmosphere, 800 ° C. × 1 hr
Annealing (soaking) was performed. The N of the steel sheet after this annealing is
It was 0.0049%. No treatment was done.

After these treatments, the steel sheet is subjected to final finishing annealing at 1150 ° C. for 5 minutes (soaking) under two conditions: (a) flat plate shape, and (b) fixing the steel sheet to a curved surface having an inner diameter of 600 mm. Thereafter, strain relief annealing and tension coating at 850 ° C. × 4 hr (uniform heating) were applied. The N content of the steel sheet after the stress relief annealing was 0.0037% under the condition, 0.0033% under the condition, and 0.0009% under the condition.
Table 1 shows the magnetic characteristics under these conditions.

[0021]

[Table 1]

As is clear from Table 1, nitriding treatment was performed,
In addition, a flat plate that has been subjected to secondary recrystallization exhibits good magnetic properties. The present inventors consider the mechanism of the phenomenon shown in Table 1 as follows. In order to cause secondary recrystallization, some inhibitors that emphasize the dependence of grain boundary migration on grain boundary character are necessary. The material of the present invention uses a slab having an extremely small amount of N and S as a starting material, and in order to sufficiently bring out the inhibitor effect, it is necessary to reinforce the inhibitor which is effective in a small amount.

Therefore, the nitriding treatment according to the present invention is considered to be effective. This is because 750 ° C or 8 as in the present invention
In nitriding at a temperature of 00 ° C. or the like, grain boundary diffusion of N is more prominent than intragranular diffusion, so that precipitation of nitride mainly occurs at grain boundary.
This means that an inhibitor that suppresses grain boundary migration is selectively arranged at grain boundaries, and secondary recrystallization is performed by continuous annealing for a short time as in the present invention, and in a technique that does not particularly take a purification time, It is considered to be extremely effective.

Further, in the case of the present technology, since secondary recrystallization occurs in a flat plate shape, {110} <001> when made into a product.
The azimuth dispersion around the TD axis from the azimuth does not occur, and as a result, the magnetic flux density can be kept high. Next, the reasons for limiting the constituent features of the present invention will be described.

First, the reasons for limiting the slab components and the slab heating temperature will be described in detail. If the amount of C is too large, the decarburization annealing time becomes long and it is not economical, so the content was made 0.075% or less. If Si exceeds 5.0%, cracking during cold rolling becomes significant, so the content of Si is set to 5.0% or less. On the other hand, if it is less than 2.2%, the specific resistance of the material is too low, and the low iron loss required for the transformer core material cannot be obtained. It is preferably 3.0% or more.

The amount of N was set to 0.0050% or less. This is because, as in the present invention, when the final finish annealing is performed in a short time, purification cannot be performed so much, so reducing the N content of the slab leads to reduction of iron loss. The lower limit of the amount of N is not particularly limited, but N in the steelmaking stage
Of 0.0001% or less is industrially difficult.

The S content was set to 0.0050% or less. This is also because when the final finish annealing is performed in a short time as in the present invention, purification cannot be performed so much, and thus reducing the S content of the slab leads to a reduction in iron loss. The lower limit of the amount of N is not particularly limited, but it is industrially difficult to make S 0.0001% or less in the steelmaking stage.

Al is AlN or (A
1, Si) N to ensure that the acid-soluble Al is 0.1.
005% or more is required. Acid soluble Al 0.060
If it exceeds 0.1%, the decomposition of the nitride is less likely to occur in the final finish annealing for a short time, so purification is difficult to occur even in a small amount, which is not preferable in terms of iron loss characteristics.

Further, it is preferable that 0.005 to 1.00% of each of Sb, Sn, and P is contained in an amount of 0.005 to 1.00% in order to improve magnetic properties. Sb, Sn, and P are grain boundary segregation elements and have an effect of suppressing grain growth. By adding these elements, secondary recrystallization can be performed even if the amount of nitriding after decarburization annealing is reduced. This means that a good secondary recrystallized structure can be obtained with a small amount of N after the final annealing in a short time, which is advantageous in terms of iron loss characteristics. Addition of less than 0.01% of Sb, Sn, and P is not sufficient for suppressing grain boundary migration, and if more than 1.00%,
It is not preferable because it adversely affects brittleness. In addition, Cu, Cr, Ni, which are known as inhibitor constituent elements,
There is no problem in containing a small amount of B, Nb, etc.

The slab heating temperature was limited to less than 1280 ° C. for the purpose of cost reduction in the same manner as ordinary steel. It is preferably 1200 ° C or lower. The heated slab is subsequently hot rolled to form a hot rolled plate. The hot rolling method is not particularly limited, but the hot rolling finish temperature is set to 850 to 1050 ° C., and the cumulative rolling reduction of the hot rolling finish pass is set to 40% or more. It is more preferable in terms of reducing the local variation of the above and improving the magnetism.

This hot-rolled sheet is then subjected to one or more cold-rollings including a final cold-rolling with a rolling reduction of 80% or more, with intermediate annealing sandwiched as necessary. The reduction ratio of the final cold rolling is set to 80% or more because the reduction ratio is set in the above range because the sharpened {110} <001> oriented grains in the decarburized plate and the corresponding oriented grains ( This is because an appropriate amount of {111} <112> oriented grains, etc. can be obtained, which is preferable in increasing the magnetic flux density.

After the hot rolling, although not particularly limited, it is more preferable to perform hot rolled sheet annealing at 850 to 1250 ° C. in order to stabilize the magnetic characteristics at a high level. The heat treatment in this temperature range has the effect of reducing the spatial nonuniformity of the AlN hot rolled sheet. The steel sheet after the final cold rolling is subjected to decarburization annealing and final finishing annealing by a usual method to obtain a final product. Although not particularly limited here, it is more preferable to control the average particle size of the primary recrystallized grains to 18 to 35 μm after the completion of decarburization annealing and before the start of final finish annealing. The reason is that it is easy to obtain a good magnetic flux density in this range of the average particle size, and the change of the magnetic flux density due to the particle size variation is small.

Then, after decarburization annealing, 600 to 1
The amount of nitrogen added to the steel plate in the temperature range of 000 ° C is 0.0005
%, The nitriding treatment is specified to be carried out. As in the present invention, reinforcement of the inhibitor by nitriding is effective for causing secondary recrystallization by using a steel having a very small N and S slab. This is because when the treatment is performed in the temperature range of 600 to 1000 ° C., grain boundary precipitation mainly occurs and the efficiency as an inhibitor is high with the same nitriding amount. If the amount of nitrogen increase is less than 0.0005%, this inhibitory effect is not sufficient, which is not preferable.

The upper limit value is not particularly limited, but is 0.3.
Nitriding of 000% or more is not preferable because when a final finish annealing is performed in a short time as in the present invention, a large amount of nitride remains in the product and iron loss characteristics deteriorate. Further, the reason for defining the nitriding temperature will be described. If the temperature is lower than 600 ° C, the nitriding treatment takes too long, which is not preferable, and if it exceeds 1000 ° C, the ratio of grain boundary precipitation is lowered, which is not preferable.

The method of nitriding is not particularly limited, and after decarburizing and annealing, a method of nitriding by subsequently mixing NH ₃ gas in an annealing atmosphere, a method of using plasma, a method of applying nitride to the surface of a steel sheet and annealing. And the method of annealing in an atmosphere containing N ₂ .

Next, it is an object of the present invention that the final finishing annealing that causes secondary recrystallization is performed by continuous annealing in the temperature range of 1000 to 1300 ° C., which is a necessary condition of the present invention. . It is difficult to cover the entire steel sheet with secondary recrystallized grains in a short time below 1000 ° C,
If it exceeds 1300 ° C, the decomposition of the inhibitor occurs remarkably, and as a result, the {110} <00
1> It is not preferable because it is difficult to keep the degree of integration high.

The annealing time is not particularly limited, but it takes a long time when the temperature is low. However, it is not industrially preferable to take 10 hours or more, and it is desirable to complete the process within 10 minutes. After this final finish annealing, impurities such as N amount of 0.0
When 050% or more remains, 1100 to 1300 ° C
It is more preferable to carry out purification annealing of impurities in an atmosphere gas having a hydrogen partial pressure of 25% or more in the temperature range of 1) from the viewpoint of improving iron loss characteristics.

If it is less than 1100 ° C., it takes too much time for purification, and if it exceeds 1300 ° C., it is not preferable because the cost of annealing equipment increases. If the hydrogen partial pressure in the atmosphere gas is less than 25%, purification takes too much time, which is not preferable. The upper limit of the hydrogen partial pressure is not particularly specified, and generally, the higher the hydrogen partial pressure, the easier the purification. Gas other than hydrogen gas may be N ₂ , Ar or the like.

[0039]

【Example】

Example 1 C = 0.051%, Si = 3.28%, acid-soluble Al =
0.018%, N = 0.0012%, S = 0.007
%, With the balance being Fe and unavoidable impurities 40
Created a mm slab. And 60 at a temperature of 1150 ° C
After soaking and soaking, the hot-rolled sheet was 2.3 mm thick. The hot-rolled sheet was held at 1100 ° C. for 10 seconds, then at 900 ° C. for 30 seconds, and then subjected to hot-rolled sheet annealing for rapid cooling. Then, about 88% strong reduction rolling is performed to obtain a final plate thickness of 0.285.
mm cold rolled sheet.

This cold-rolled sheet was subjected to decarburizing annealing at 810 ° C. for 90 seconds, and then subjected to the following three types of treatments.
During annealing at 750 ° C for 30 seconds, N in the annealing atmosphere
Nitrogen absorption was caused to the steel sheet is mixed with H ₃ gas. The N of the steel sheet after this nitriding treatment was 0.0045%. N
800 ° C in an annealing atmosphere of ₂ : 75% and H ₂ : 25%
Annealing was performed for x 1 hr (soaking). N of the steel sheet after this annealing
Was 0.0043%. No treatment was done.

The steel sheets after these treatments are subjected to final finishing annealing at 1180 ° C. for 5 minutes (soaking) under the two conditions of (a) flat plate shape, and (b) fixing the steel sheet to a curved surface having an inner diameter of 500 mm. Thereafter, strain relief annealing and tension coating at 850 ° C. × 4 hr (uniform heating) were applied. The N content of the steel sheet after the stress relief annealing was 0.0030% under the condition, 0.0028% under the condition, and 0.0006% under the condition.
Table 2 shows the magnetic characteristics under these conditions.

[0042]

[Table 2]

As is clear from Table 2, nitriding treatment was performed,
In addition, a plate (corresponding to continuous annealing) that has been subjected to secondary recrystallization exhibits good magnetic properties.

Example 2 C = 0.050%, Si = 3.25%, acid-soluble Al =
0.017%, N = 0.0013%, S = 0.0010
%, Sb = 0.10% added, Sn =
0.15% addition, P = 0.10% addition, Sb = 0.
05% addition, Sn = 0.06% addition, Sn = 0.07
% Addition, P = 0.05% addition, Sb = 0.05% addition, P = 0.07% addition, Sb = 0.07% addition, S
A 40 mm slab consisting of n = 0.07% addition, P = 0.07% addition, no addition, balance Fe and unavoidable impurities was prepared. Then, after soaking at a temperature of 1150 ° C. for 60 minutes, hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm.

The hot-rolled sheet was annealed at 1100 ° C. for 10 seconds, at 900 ° C. for 30 seconds, air-cooled to 700 ° C., and then rapidly cooled. Then, about 90% strong reduction rolling was performed to obtain a rolled sheet having a final sheet thickness of 0.220 mm. The cold-rolled sheet was subjected to decarburizing annealing at 810 ° C. for 90 seconds, and then, at the time of annealing at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere to cause nitrogen absorption in the steel sheet.

In this nitriding treatment, the amount of NH ₃ gas was adjusted, and the amount of N after nitriding was set to (a) 0.
0031% and (b) 0.0045% with respect to the components. After that, the steel sheet was subjected to final finishing annealing at 1150 ° C. for 5 minutes (soaking) in a flat plate shape, and then subjected to strain relief annealing and tension coating. The N content of the steel sheet after the strain relief annealing is 0.0015 to 0.0020 under the condition (a).
%, 0.0031 to 0.0037% under the condition of (b). Table 3 shows the magnetic characteristics under these conditions. As is clear from Table 3, iron loss characteristics are particularly good when one or more of Sb, Sn and P are added and the amount of nitriding is reduced.

[0047]

[Table 3]

Example 3 After the final finishing annealing was performed under the conditions of Example 2, H ₂ 100 was added.
% Annealing was performed at 1200 ° C. for 5 hours (soaking). Then, strain relief annealing and tension coating were applied. The N content in the steel after this strain relief annealing was 0.0001 to 0.0007% under any of the conditions. Table 4 shows the magnetic characteristics under these conditions. Tables 3 and 4
As is clear from the comparison of, the iron loss characteristics are improved by performing the purification annealing.

[0049]

[Table 4]

Example 4 C = 0.051%, Si = 3.25%, acid-soluble Al =
0.021%, N = 0.0010%, S = 0.007
%, Sn = 0.15% addition, no Sn addition, a 40 mm slab consisting of balance Fe and inevitable impurities was prepared. Then, after soaking at a temperature of 1150 ° C. for 60 minutes, hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm.

Without hot-rolled sheet annealing, the hot-rolled sheet was subjected to strong reduction rolling of about 88% to obtain a final sheet thickness of 0.285.
mm cold rolled sheet. This cold-rolled sheet was subjected to decarburizing annealing at 815 ° C. for 120 seconds, and then, at the time of annealing at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere to cause nitrogen absorption in the steel sheet. The N of the steel sheet after this nitriding treatment was 0.0032%.

Next, this steel sheet was subjected to final finish annealing at 1150 ° C. for 5 minutes (soaking), and then 850 ° C. for 4 hours.
The strain relief annealing (uniform heating) and tension coating were applied.
The N content of the steel sheet after the stress relief annealing was 0.0023.
Was 0.0026%. Table 5 shows the magnetic characteristics under these conditions.

[0053]

[Table 5]

[0054]

Industrial Applicability According to the present invention, a product having a silicon steel material in which the amount of N and S in the slab is extremely reduced is obtained, and a final finish annealing is performed for a short time by performing a slight amount of nitriding after decarburization annealing. In addition, the addition of Sb, Sn, and P can reduce the amount of nitriding to improve the iron loss characteristics, and the additional annealing for purification improves the iron loss characteristics. The effect is extremely large.

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[Procedure amendment]

[Submission date] July 25, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

These points will be described in detail below.
Originally, secondary recrystallization is a phenomenon in which the grain boundary character dependence of grain boundary migration is emphasized by using impurities. Therefore, Journal of the Japan Institute of Metals, Vol. 55, No. 6 (1991) P630-638.
As described in (1), the higher the inhibitor strength (Zener factor ( constant × precipitate integral fraction / precipitate size)) during the progress of secondary recrystallization, the {110} of the secondary recrystallization oriented grains.
<001> High degree of integration. In order to increase the inhibitor strength, usually, a method of increasing the amount of precipitates or making the precipitate size finer is used. Increasing the amount of precipitates lengthens the time required to purify impurities after secondary recrystallization,
Since the required temperature becomes high, it is unsuitable for performing final finishing annealing by short-time continuous annealing.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

On the other hand, the method of making the precipitation size finer is suitable for continuous annealing in a shorter time than the method of increasing the amount. However, this method is also subject to volume limitations. Therefore, the third method studied by the present inventors is the use of grain boundary precipitation of precipitates and grain boundary segregation. Below, it demonstrates in detail based on an experimental result.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

The S content was set to 0.0050% or less. This is also because when the final finish annealing is performed in a short time as in the present invention, purification cannot be performed so much, and thus reducing the S content of the slab leads to a reduction in iron loss. The lower limit of the amount of S is not particularly limited, but it is industrially difficult to set S to 0.0001% or less in the steelmaking stage.

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Claims (3)

[Claims] 1. C: 0.075% or less by weight ratio, Si: 2.2 to 5.0%, N: 0.0050% or less, S: 0.0050% or less, Al: 0.005 to 0 0.060% 128 slabs with the balance being Fe and unavoidable impurities
Heating at a temperature below 0 ° C, hot rolling, including final cold rolling with a rolling reduction of 80% or more, if necessary, one or more cold rollings with intermediate annealing sandwiched, then decarburizing annealing, final annealing In the method of producing a unidirectional electrical steel sheet by applying the above method, following decarburization annealing, the steel sheet is subjected to a nitriding treatment of 0.0005% or more with a nitrogen increase amount in a temperature range of 600 to 1000 ° C., and then,
A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which comprises performing final finishing annealing that causes secondary recrystallization by continuous annealing in a temperature range of 1000 to 1300 ° C. 2. A unidirectional excellent magnetic property according to claim 1, wherein a slab containing 0.005 to 1.00% by weight of one or more of Sb, Sn and P is used. For manufacturing high-performance electrical steel sheet. 3. Purification annealing of impurities is carried out in an atmosphere gas having a hydrogen partial pressure of 25% or more in a temperature range of 1100 to 1300 ° C., following the final finishing annealing that causes secondary recrystallization. The method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1.