JPH06306474A - Production of grain-oriented magnetic steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To stably impart good magnetic properties to a steel sheet by subjecting a magnetic steel sheet in which the relationship among the content of Mn, S and Si is specified to nitriding treatment under specified conditions after the completion of decarburization and next executing final finish annealing in a specified atmosphere. CONSTITUTION:The compsn. of steel is constituted of, by weight, 0.025 to 0.075% C, 2.2 to 5.0% Si, 0.015 to 0.080% acid soluble Al, <=0.0130% N, S+0.405Se; >=0.0020% and <=0.03% Mn, and the balance Fe with inevitable impurities. Furthermore, Mn/(S+0.405Se)<=3 is satisfied. This steel slab is heated to <1280 deg.C, is subjected to hot rolling and is subjected to hot annealing according to necessity. Next, it is subjected to cold rolling and decarburizing annealing to regulate the average grain size of primarily recrystallized grains into 18 to 35mum. Then >=0.0010% nitrogen is absorbed into the steel sheet by nitriding treatment. In succession, final finish annealing in which the partial pressure of nitrogen in the annealing atmosphere is regulated to 1% is executed in the steel sheet temp. range of 900 to 1150 deg.C to generate secondary recrystallization.

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. The magnetic field strength is 800A /
The magnetic flux density B _{8 at} m is usually used. As the numerical value showing the iron loss characteristic, the iron loss W _17/50 per 1 kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz is used. 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 highly align <001>, which is the easy magnetization axis, in the rolling direction. Typical methods for producing such a high magnetic flux density unidirectional electrical steel sheet are methods described in Japanese Patent Publication No. 40-15644 by Satoru Taguchi et al. And Japanese Patent Publication No. 51-13469 by Takuichi Imanaka. . MnS and AlN are used in the former and Mn are used in the latter.
S, MnSe, Sb, etc. are used as main inhibitors. Therefore, in the current technology, it is essential to properly control the size, morphology and dispersion state of the precipitates that function as these inhibitors. Regarding MnS, in the present process, a method is used in which MnS is once completely solid-soluted during slab heating before hot rolling and then precipitated during hot rolling.

A temperature of about 1400 ° C. is required to completely dissolve 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. That is, 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 can be seen in so-called shaving.

In order to avoid such problems, the slab heating temperature should be lowered to the level of ordinary steel.
This means that at the same time the amount of MnS that is effective as an inhibitor is reduced or not used at all,
Inevitably, it causes destabilization of secondary recrystallization. Therefore, in order to realize low-temperature slab heating, some form of MnS
It is necessary to strengthen the inhibitor with precipitates other than those mentioned above to sufficiently suppress normal grain growth during finish annealing. As such inhibitors, sulfides, nitrides, oxides, grain boundary precipitation elements, and the like are conceivable. Known techniques include, for example, the following.

Japanese Patent Publication No. 54-24685 discloses A
By including grain boundary segregation elements such as s, Bi, Sn, and Sb in the steel, the slab heating temperature is increased to 1050 to 1350 ° C.
The method for controlling the range is disclosed in JP-A-52-24116.
In addition to Al, Zr, Ti. B, Nb, Ta,
A method for controlling the slab heating temperature in the range of 1100 to 1260 ° C. by containing a nitride-forming element such as V, Cr, or Mo is disclosed, and JP-A-57-158322 discloses that the Mn content is lowered. , Mn / S ratio is 2.5 or less to perform low temperature slab heating, and further C
A technique for stabilizing secondary recrystallization by adding u is disclosed.

On the other hand, a technique has also been disclosed in which improvements are made from the metal structure side in combination with the reinforcement of these inhibitors. That is, in JP-A-57-89433, Mn
In addition to the above, elements such as S, Se, Sb, Bi, Pb, Sn and B are added, and by combining this with the columnar crystal ratio of the slab and the secondary cold rolling reduction ratio, low temperature slab heating at 1100 to 1250 ° C is achieved. Has been realized. Further, JP-A-59-190
In Japanese Patent No. 324, Al and B are added in addition to S or Se.
By configuring an inhibitor mainly composed of nitrogen and nitrogen, and subjecting this to pulse annealing at the time of primary recrystallization annealing after cold rolling,
Techniques for stabilizing secondary recrystallization are disclosed. Thus, in order to realize low temperature slab heating in the production of grain-oriented electrical steel sheets, great efforts have been made so far.

By the way, Japanese Patent Application Laid-Open No. 59-56522 discloses a technique for enabling low temperature slab heating by setting Mn to 0.08 to 0.45% and S to 0.007% or less. However, this technique has solved the problem of the occurrence of defective linear secondary recrystallization of the product due to the coarsening of the slab crystal grains during heating of the high temperature slab.

[0009]

Although the method by low temperature slab heating is originally intended to reduce the manufacturing cost, it is needless to say that it cannot be industrialized unless it is a technique for stably obtaining good magnetic characteristics. . Therefore, the present inventors have constructed a technique based on primary recrystallization grain size control and nitriding. Then, research has been advanced to further improve the iron loss characteristics, but in the process, it has been recognized that the Mn amount greatly affects the magnetic characteristics when the S and Se amounts are extremely low.

[0010]

The subject matter of the present invention is as follows. (1) C: 0.025 to 0.075% by weight, Si:
2.2-5.0%, acid-soluble Al: 0.015-0.0
80%, N: 0.0130% or less, S + 0.405S
e: 0.0020% or less, Mn: 0.03% or less, and the balance is 12 slabs containing Fe and unavoidable impurities.
It is heated at a temperature of less than 80 ° C., hot-rolled, subsequently hot-rolled sheet is annealed if necessary, and then includes final cold rolling with a reduction rate of 80% or more, and if necessary, an intermediate annealing is performed once or more. In the method of producing a grain-oriented electrical steel sheet by performing cold rolling, decarburization annealing, and final finishing annealing, Mn / (S + 0.405Se) ≧ 3 in the slab, and after decarburizing annealing, final finishing annealing The average grain size of the primary recrystallized grains until the start is set to 18 to 35 μm, and the nitriding treatment is performed after the hot rolling and before the start of the secondary recrystallization of the final finish annealing so that the steel sheet absorbs 0.0010 wt% or more of nitrogen. And the temperature of the steel sheet in the temperature rising process of final finishing annealing is in the range of 900 to 1150 ° C., the nitrogen partial pressure in the annealing atmosphere is 1% or more, and the unidirectional electrical steel sheet has excellent magnetic properties. Manufacturing method. (2) The slab contains 0.01 to 0.15% by weight of Sn in the slab. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the above item (1).

[0011]

The unidirectional electrical steel sheet targeted by the present invention is
Molten steel obtained by a conventional steelmaking method is cast by a continuous casting method or an ingot making method, and if necessary, a slab may be sandwiched between slabs, followed by hot rolling to a hot rolled sheet, and then this The hot-rolled sheet is annealed if necessary, and then the rolling reduction is 8
It is manufactured by including 0% or more of final cold rolling, and if necessary, performing one or more cold rollings with intermediate annealing, decarburizing annealing, and final finishing annealing in this order.

The present inventor has conducted various studies on the component design when S and Se are extremely lowered, and as a result, the magnetic characteristic is M.
A new finding was obtained that the amount of n has a great influence. The details will be described below based on the experimental results.

FIG. 1 shows the relationship between the amount of Mn and the magnetic characteristics. In this case, C: 0.054% by weight (hereinafter abbreviated as%), S
i: 3.26%, acid-soluble Al: 0.030%, N:
0.0083%, Mn: 0.01 to 0.12%, S:
A 40 mm thick slab of silicon steel containing 0.0004% and the balance Fe and unavoidable impurities was heated at 1150 ° C. for 1 hour and then hot rolled to a thickness of 2.3 mm. 1 on the obtained hot-rolled sheet
After hot-rolled sheet annealing in which the temperature is kept at 100 ° C for 30 seconds and then kept at 900 ° C for 30 seconds to be rapidly cooled, cold-rolled to 0.220 mm, and then held at 835 ° C for 150 seconds for decarburization annealing (annealing atmosphere N ₂ : 25%, H ₂ : 75%, DP =
62 ° C.), and then annealing at 750 ° C. for 30 seconds (annealing atmosphere N ₂ : 25%, H ₂ : 75%, DP <
NH ₃ gas was mixed into the annealing atmosphere at 0 ° C. to cause the steel sheet to absorb nitrogen.

In this case, the nitriding amount (nitrogen increasing amount) is 0.012.
It was 5 to 0.0140%, and the average crystal grain size of the steel sheet after this nitriding treatment was 22 to 25 μm (equivalent circle diameter).
An annealing separator having MgO as a main component is applied to this steel plate,
The temperature is raised to 1200 ° C at a rate of 15 ° C / hr and is increased to 1200 ° C for 20
A final finish anneal of holding in time H ₂ was applied. N ₂ : 25%, H up to 900 ° C. in the temperature rising process of this final finish annealing
₂ : Treated in 75% annealing atmosphere, 900 ℃ to 12
Up to 00 ° C., the annealing was performed under the conditions of an annealing atmosphere of N ₂ : 50% and H ₂ : 50%.

As is clear from FIG. 1, the amount of Mn: 0.0
When it was 3% or less, extremely good magnetic properties were obtained.

Although the mechanism of the effect of improving the magnetic flux density shown in FIG. 1 is not always clear, the present inventors presume as follows. When S and Se are extremely small as in the present invention, most of the added Mn amount becomes solid solution Mn. The present inventors have found that the primary recrystallization texture is M
It has been found that the amount of n has an influence, and specifically, Mn.
The primary recrystallization texture tended to become randomized as the amount increased.

In particular, {110} which is the secondary recrystallization orientation.
{111} having a Σ9 corresponding bearing relationship with <001>
The degree of integration in the primary recrystallization texture of <112> is Mn.
It tended to decrease with increasing amount. Therefore, as the amount of Mn increases, the {110} <001> of the secondary recrystallization orientation increases.
It is considered that the degree of integration is reduced, and as a result, the magnetic flux density of the product is reduced. Therefore, it is considered that reducing the amount of Mn has the effect of improving the magnetic flux density of the product.

Next, the reasons for limiting the constituent features of the present invention will be described. First, the reasons for limiting the components of the slab and the slab heating temperature will be described in detail. If C is less than 0.025%, the secondary recrystallization becomes unstable, and even if the secondary recrystallization is performed, it is difficult to obtain B ₈ > 1.80 (T).
% And above. On the other hand, if the amount of C is too large, the decarburization annealing time becomes long and it is not economical.

If Si exceeds 5.0%, cracking during cold rolling becomes significant, so the content was made 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, which is the object of the present invention, cannot be obtained. In order to secure AlN or (Al, Si) N necessary for stabilizing secondary recrystallization, 0.015% or more is required as acid-soluble Al. If the acid-soluble Al exceeds 0.080%, the AlN of the hot-rolled sheet becomes inappropriate and the secondary recrystallization becomes unstable.
Below.

When N exceeds 0.0130%, "blister on the steel plate surface" called blister occurs, so the content of N is set to 0.0130% or less. Regarding S + 0.405Se, when the Mn content is as low as 0.03% or less as in the present invention, MnS and MnSe are solid-dissolved during slab heating and fine precipitation occurs after hot rolling. If the amount of finely precipitated MnS and MnSe is too large, the growth of primary recrystallized grains during decarburization annealing is suppressed and it becomes difficult to control the primary recrystallized grain size. In the present invention, in order to solve this problem, S + 0.
405Se ≦ 0.0020%. If it exceeds 0.0020%, it is difficult to control the primary recrystallized grain size, which is not preferable. The lower limit value is not particularly limited, but S +
It is industrially difficult to reduce 0.405Se to 0.0001% or less.

The upper limit of Mn is 0.03%. This is because, as is clear from FIG. 1, the magnetic characteristics are extremely good when Mn ≦ 0.03%. The lower limit of Mn is not particularly limited, but it is industrially difficult to reduce the amount of Mn to 0.0001% or less. In addition, Mn / (S + 0.405S
e) ≧ 3. This is for reducing S and Se in a solid solution state and reducing cracks during hot rolling and the like. Mn /
Although the upper limit of (S + 0.405Se) is not particularly limited,
The upper limit of Mn is 0.03%, and S + 0.405Se
Since the lower limit value that can be industrially lowered is 0.0001%, Mn / (S + 0.405Se) is substantially 3
It will be around 00.

It is more preferable to add 0.01 to 0.15% of Sn in order to stabilize the magnetic properties at a high level by increasing the inhibitor strength in the secondary recrystallization. 0.
If it is less than 01%, this effect is not sufficient, and if it exceeds 0.15%, nitriding treatment becomes difficult, which is not preferable. In addition, Sb, Ti, Zr, B, which are known as inhibitor constituent elements
It is possible to add i, Nb, etc. Further, it is permissible to add P, Cr or the like for the reason of increasing the electric resistance of the product.

The slab heating temperature is 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. This hot-rolled sheet is subjected to hot-rolled sheet annealing at 800 to 1200 ° C., if necessary, and then includes final cold rolling with a rolling reduction of 80% or more and, if necessary, one or more cold rollings with intermediate annealing. Give. The reduction ratio of the final cold rolling was set to 80% or more because the reduction ratio in the above range makes the sharp decarburizing plate {11.
This is because it is possible to obtain an appropriate amount of 0} <001> oriented grains and the corresponding oriented grains ({111} <112> oriented grains and the like) that are easily eroded by silkworms, which is preferable in increasing the magnetic flux density.

After rolling, the steel sheet is sequentially subjected to decarburizing annealing, applying an annealing separator, and finishing annealing to obtain a final product. Here, in order to obtain good magnetic properties, it is necessary to control the average grain size of the primary recrystallized grains from the completion of decarburization annealing to the start of final finish annealing to 18 to 35 μm. Average particle size is 18μ
If it is less than m, it becomes difficult to control the secondary recrystallization orientation, and it becomes 35 μm.
If it exceeds the above value, secondary recrystallization becomes unstable, which is not preferable.

Further, it is defined that the steel sheet is subjected to the nitriding treatment after the hot rolling and before the start of the secondary recrystallization of the final finish annealing, in the process which is premised on the low temperature slab heating as in the present invention. This is because the inhibitor strength required for recrystallization tends to be insufficient. The nitriding method is not particularly limited, and a method of mixing NH ₃ gas in an annealing atmosphere after decarburization annealing to perform nitriding, a method of using plasma, adding a nitride to an annealing separator and adding a nitride to the final finishing annealing is performed. Any method may be used, such as a method of absorbing nitrogen formed by decomposition of nitrides in the temperature into the steel sheet or a method of nitriding the steel sheet by increasing the N ₂ partial pressure in the atmosphere of the final annealing. For the amount of nitriding,
10ppm or more is necessary.

Further, the nitrogen partial pressure in the annealing atmosphere must be 1% or more when the temperature of the steel sheet in the temperature rising process of final finish annealing is in the range of 900 to 1150 ° C. Secondary recrystallization occurs in the range of 900 to 1150 ° C., and it is possible to increase the inhibitor strength at this time by increasing the {110} of the secondary recrystallized grains.
It is effective in increasing the <001> orientation integration. For this, the nitrogen partial pressure in the annealing atmosphere is set to 1% or more, AlN,
It is necessary to suppress decomposition of nitrides in steel such as (Al, Si) N. The upper limit of the nitrogen partial pressure is not limited. Up to 100% is acceptable.

The annealing atmosphere in the temperature range of less than 900 ° C. is not specified. Since the secondary recrystallization usually occurs at 900 to 1150 ° C., it is sufficient to control the annealing atmosphere in this temperature range. The temperature is usually raised to 1100 to 1250 ° C. During the temperature rise, secondary recrystallization is usually completed, and the isothermal holding for purification is started. The constant temperature maintenance following this temperature rise is usually 5
It is carried out for about 50 hours, but this constant temperature holding is usually carried out in an annealing atmosphere in which H ₂ gas or H ₂ gas is mainly used. For secondary recrystallization, if the temperature is kept constant at, for example, 1000 to 1100 ° C., and then the temperature is further raised to start the constant temperature maintenance for purification, the temperature range until the start of purification is understood to be the temperature raising process. .

[0028]

【Example】

Example 1 C: 0.059%, Si: 3.35%, S: 0.001
0%, acid-soluble Al: 0.029%, N: 0.0083
%, Mn content: 0.25%, 0.14%,
Three types of 40 mm thick slabs consisting of 0.02%, balance Fe and unavoidable impurities were heated at a temperature of 1150 ° C. and then rolled to obtain a hot rolled sheet having a thickness of 1.8 mm. This hot-rolled sheet was annealed at 1120 ° C. for 30 seconds and 900 ° C. for 30 seconds to be rapidly cooled, and then rolled at a reduction rate of about 90.
A 6% 0.170 mm thick cold rolled sheet was decarburized and held at 840 ° C for 90 seconds, and then NH ₃ gas was mixed into the annealing atmosphere during annealing at 750 ° C for 30 seconds.
The steel sheet was nitrided.

In this case, the nitriding amount (nitrogen increasing amount) is 0.01
It was 35 to 0.0144%, and the average crystal grain size (circle equivalent diameter) of the steel sheet after this nitriding treatment was 22 to 24 μm. An annealing separator containing MgO as a main component is applied to the steel sheet after the nitriding treatment, and the temperature is raised to 1200 ° C. at 15 ° C./hr,
A final finish anneal was held in H ₂ at 1200 ° C. for 20 hours. Up to 900 ° C. in the temperature rising process of this final finish annealing, it was treated in an annealing atmosphere of N ₂ : 20%, H ₂ : 80%, and from 900 ° C. to 1200 ° C., N ₂ : 75%, H _2
The treatment was performed under the condition of ₂ : 25%. Table 1 shows the relationship between process conditions and magnetic properties. As is clear from Table 1, good magnetic properties are obtained under the conditions of the present invention.

[0030]

[Table 1]

Example 2 C: 0.058%, Si: 3.50%, Mn: 0.01
5%, S: 0.0006%, acid-soluble Al: 0.034
%, N: 0.0082%, Sn: 0.002%,
Three types of 40 mm thick slabs containing 0.06% and 0.27% with the balance Fe and unavoidable impurities are 115
After heating at a temperature of 0 ° C., hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm. The hot rolled sheet was held at 1120 ° C for 30 seconds,
Hot-rolled sheet is annealed by holding it at 00 ° C for 30 seconds and rapidly cooling it, then making a cold-rolled sheet with a thickness of 0.220 mm at a reduction rate of about 90%.
Decarburization annealing is performed by holding at 30 ° C for 90 seconds, and then 7
During annealing at 50 ° C. for 30 seconds, NH ₃ gas was mixed into the annealing atmosphere and the steel sheet was nitrided.

In this case, the nitriding amount (nitrogen increasing amount) is 0.01
The average crystal grain size (circle equivalent diameter) of the steel sheet after the nitriding treatment was 24 to 26 μm. An annealing separator containing MgO as a main component is applied to the steel sheet after the nitriding treatment, and the temperature is raised to 1200 ° C. at 15 ° C./hr,
A final finish anneal was held in H ₂ at 1200 ° C. for 20 hours. The temperature rising process of this final finish annealing is N ₂ : 25%,
H _2: were treated in 75 percent of the annealing atmosphere. Table 2 shows the relationship between process conditions and magnetic properties. As is clear from Table 2,
The conditions of this experiment are all the conditions of the present invention, and good magnetic characteristics are obtained. In particular, when the Sn content satisfies the conditions of the present invention, extremely good magnetic characteristics are obtained.

[0033]

[Table 2]

Example 3 C: 0.058%, Si: 3.48%, Mn: 0.01
0%, S: 0.0005%, acid-soluble Al: 0.035
%, N: 0.0088%, Sn: 0.001%,
Two 40 mm thick slabs containing 0.04% and the balance Fe and unavoidable impurities were heated at a temperature of 1150 ° C. and then hot rolled to obtain a hot rolled sheet having a thickness of 1.8 mm. After cold rolling this hot rolled sheet to 1.4 mm, it was annealed by holding it at 1120 ° C. for 30 seconds and then at 900 ° C. for 30 seconds to quench it, and then rolling it at a reduction rate of about 89.6% to a thickness of 0.145 mm. As a cold-rolled sheet, decarburization annealing was performed at 825 ° C. for 90 seconds, and then NH ₃ gas was mixed into the annealing atmosphere during annealing at 750 ° C. for 30 seconds to perform nitriding treatment on the steel sheet.

In this case, the nitriding amount (nitrogen increasing amount) is 0.01
It was 34 to 0.0148%, and the average crystal grain size (equivalent circle diameter) of the steel sheet after this nitriding treatment was 24 to 25 μm. An annealing separator having MgO as a main component is applied to the steel sheet after the nitriding treatment, and the temperature is raised to 1200 ° C. at 10 ° C./hr,
A final finish anneal was held in H ₂ at 1200 ° C. for 20 hours. Up to 900 ° C. in the temperature rising process of this final finish annealing, it was treated in an annealing atmosphere of N ₂ : 20%, H ₂ : 80%, and from 900 ° C. to 1200 ° C., N ₂ : 75%, H _2
The treatment was performed under the condition of ₂ : 25%. Table 3 shows the relationship between process conditions and magnetic properties. All of the experimental conditions were within the conditions of the present invention, and good magnetic characteristics were obtained. Further, when the Sn condition of the present invention is satisfied, better magnetic properties are obtained.

[0036]

[Table 3]

Example 4 C: 0.040%, Si: 2.80%, S: 0.000
3%, acid-soluble Al: 0.035%, N: 0.0088
%, Mn content: 0.28%, 0.12%,
Three types of 40 mm thick slabs consisting of 0.01%, balance Fe and unavoidable impurities were heated at a temperature of 1150 ° C., and then hot rolled to a hot rolled sheet having a thickness of 2.3 mm. This hot-rolled sheet was not subjected to hot-rolled sheet annealing and was rolled at a reduction rate of about 85% to 0.1%.
A cold-rolled sheet having a thickness of 335 mm was subjected to decarburization annealing at 840 ° C. for 90 seconds, and then NH ₃ gas was mixed into the annealing atmosphere during annealing at 750 ° C. for 30 seconds to subject the steel sheet to nitriding treatment. did.

In this case, the nitriding amount (nitrogen increasing amount) is 0.01
It was 49 to 0.0162%, and the average crystal grain size (circle equivalent diameter) of the steel sheet after this nitriding treatment was 21 to 23 μm. An annealing separator containing MgO as a main component is applied to the steel sheet after the nitriding treatment, and the temperature is raised to 1200 ° C. at 15 ° C./hr,
A final finish anneal was held in H ₂ at 1200 ° C. for 20 hours. Up to 900 ° C. in the temperature rising process of the final finish annealing, the annealing is performed in an annealing atmosphere of N ₂ : 20% and H ₂ : 80%, and from 900 ° C. to 1200 ° C., N ₂ : 50%, H _2
2 : Treated under the condition of 50%. Table 4 shows the relationship between process conditions and magnetic properties. As is clear from Table 4, in the case of the conditions of the present invention, good magnetic properties are obtained without performing hot-rolled sheet annealing.

[0039]

[Table 4]

[0040]

According to the present invention, the amounts of S and Se are extremely reduced, the amount of Mn is controlled to a predetermined amount or less, and the average grain size of primary recrystallized grains after the completion of decarburization annealing and before the start of final finishing annealing. By controlling the diameter, nitriding treatment after hot rolling until the start of secondary recrystallization of final finishing annealing, and controlling the nitrogen partial pressure of the annealing atmosphere during the temperature rising process of final finishing annealing, excellent magnetic properties Stable production of unidirectional electrical steel sheet, and S
Since the addition of n makes it possible to stably produce a grain-oriented electrical steel sheet having more excellent magnetic properties, the industrial significance of these techniques is extremely great.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of Mn and the magnetic flux density.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 25, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

The upper limit of Mn is 0.03%. This is because, as is clear from FIG. 1, the magnetic characteristics are extremely good when Mn ≦ 0.03%. The lower limit of Mn is not particularly limited, but it is industrially difficult to reduce the amount of Mn to 0.0001% or less. In addition, Mn / (S + 0.405S
e) ≧ 3. This is for reducing S and Se in a solid solution state and reducing cracks during hot rolling and the like. Mn /
Although the upper limit of (S + 0.405Se) is not particularly limited,
The upper limit of Mn is 0.03%, and S + 0.405Se
Since the lower limit value that can be industrially lowered is 0.0001%, the upper limit value of Mn / (S + 0.405Se) is substantially about 300.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location H01F 1/16 B (72) Inventor Biao Kono No. 1 Tobata-cho, Tobata-ku, Kitakyushu Inside the Yawata Works,

Claims (2)

[Claims] 1. By weight ratio, C: 0.025 to 0.075%, Si: 2.2 to 5.0%, acid-soluble Al: 0.015 to 0.080%, N: 0.0130% or less. , S + 0.405Se: 0.0020% or less, Mn: 0.03% or less 1280 slab with the balance Fe and unavoidable impurities
Heating at a temperature of less than ℃, hot-rolling, hot-rolled sheet annealing if necessary, and then final cold rolling with a rolling reduction of 80% or more, and if necessary, one or more cold-rolling steps with intermediate annealing. In the method of producing a grain-oriented electrical steel sheet by performing deferring, decarburization annealing, and final finishing annealing in the slab,
Mn / (S + 0.405Se) ≧ 3, after decarburization annealing is completed, the average grain size of primary recrystallized grains until the start of final finishing annealing is 18 to 35 μm, and after hot rolling, secondary recrystallization of final finishing annealing is started. In the meantime, the steel sheet is subjected to a nitriding treatment to absorb 0.0010% by weight or more of nitrogen, and the nitrogen partial pressure of the annealing atmosphere is adjusted in the range of 900 to 1150 ° C. in the temperature of the steel sheet in the temperature rising process of final annealing. 1% or more, The manufacturing method of the grain-oriented electrical steel sheet excellent in the magnetic characteristic characterized by the above-mentioned. 2. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein 0.01 to 0.15% by weight of Sn is contained in the slab.