JPH05295438A - Production of grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To obtain the steel sheet for an iron core for electrical equipment by specifying the Al/Si value in a steel with a specific composition, the grain size between decarburizing annealing and the initiation of finish annealing, and nitriding treatment at the initiation of secondary recrystallization at the final finish annealing after hot rolling, respectively. CONSTITUTION:A slab of a steel having a composition consisting of, by weight, 0.025-0.075% C, 3.4-5.0% Si, 0.015-0.080% acid-soluble Al, 0.0030-0.013% N, <=0.014% of (S+0.405Se), 0.05-0.8% Mn, and the balance iron is heated at <1280 deg.C and hot-rolled. Successively, hot rolled plate annealing is done and the resulting plate is subjected to one or more cold rollings including the final cold rolling at >=80% draft and also including, if necessary, process annealing between the cold rolling stages, and the resulting sheet is subjected to decarburizing annealing and final finish annealing, by that the nonoriented silicon steel sheet can be obtained. In this method, the ratio between acid-soluble Al and Si contents is regulated so that it satisfies Al(%)/Si(%)>=0.0080, and also the average grain size of primary recrystallized grains in the course between the completion of decarburizing annealing and the initiation of final finish annealing is regulated to 18-35mu. Further, nitriding treatment for allowing the steel sheet to absorb >=0.0010% nitrogen is done before secondary recrystallization is initiated in the final finish annealing.

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 electrical 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 as a numerical value indicating the excitation characteristic.
A magnetic flux density B _{8 at} / m is usually used. In addition, as a numerical value representing the iron loss characteristic, the iron loss W per 1 kg when magnetized to 1.7 Tesler (T) at a frequency of 50 Hz.
I am using _17/50 . 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 is manufactured by causing secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} axis on the steel sheet surface and <001> axis in the rolling direction. Has been done. 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 present technology, it is indispensable to appropriately control the size, morphology and dispersion state of 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.

1) A high temperature slab heating furnace dedicated to 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, but this means that the amount of MnS effective as an inhibitor should be reduced at the same time, or no MnS should be used at all. However, this inevitably causes destabilization of secondary recrystallization. Therefore, in order to realize low temperature slab heating, it is necessary to strengthen the inhibitor in some form by a precipitate 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 conceivable. Known techniques include, for example, the following.

In Japanese Patent Publication No. 54-24685, A
The slab heating temperature is adjusted to 1050 to 1350 ° C. by including grain boundary segregation elements such as s, Bi, Sn and Sb in the steel.
In Japanese Patent Laid-Open No. 52-24116, in addition to Al, Zr, Ti, B, Nb, Ta,
A method of 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 in JP-A-57-158322, the Mn content is lowered, Low temperature slab heating is performed by setting the Mn / S ratio to 2.5 or less, and further Cu
Discloses a technique for stabilizing the secondary recrystallization by adding. On the other hand, a technique in which improvement is added from the metal structure side in combination with reinforcement of these inhibitors is also disclosed. That is, in JP-A-57-89433, elements such as S, Se, Sb, Bi, Pb, Sn, and B are added in addition to Mn, and the columnar crystal ratio of the slab and the secondary cold rolling reduction are combined with this. As a result, low temperature slab heating of 1100 to 1250 ° C is realized. Further, JP-A-59-190324
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a technique in which an inhibitor is mainly composed of Al and B and nitrogen in addition to S or Se, and pulse annealing is performed during primary recrystallization annealing after cold rolling to stabilize secondary recrystallization. Disclosure. 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.

[0006] First, in JP-A-59-56522, Mn is 0.08 to 0.45% and S is 0.00.
A technique has been disclosed that enables low temperature slab heating by making the content 7% 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.

[0007]

Although the method by low temperature slab heating is originally intended to reduce the manufacturing cost,
As a matter of course, unless it is a technique that stably obtains good magnetic characteristics, industrialization cannot be achieved. Therefore, the present inventors have conducted research to improve the iron loss characteristics by increasing the amount of Si, but the target characteristics could not be obtained because the secondary recrystallization orientation control is difficult.

As a result of extensive research aimed at overcoming such a situation, it has been recognized that control of precipitates during secondary recrystallization is important.

[0009]

The subject matter of the present invention is as follows. (1) C: 0.025 to 0.075% by weight, Si:
3.4-5.0%, acid-soluble Al: 0.015-0.0
80%, N: 0.0030 to 0.0130%, S + 0.
405 Se: 0.014% or less, Mn: 0.05-0.
A slab containing 8% and the balance consisting of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, and if necessary, hot-rolled sheet is annealed, and then rolled at a reduction ratio of 8
In a method for producing a unidirectional electrical steel sheet, which comprises 0% or more of final cold rolling, performs one or more cold rollings with intermediate annealing if necessary, and then performs decarburization annealing and final finishing annealing.
Content of acid-soluble Al and Si in units of weight% Al
(%) And Si (%), Al and Si are controlled within the following ranges, and Al (%) / Si (%) ≥ 0.0080 Primary after completion of decarburization annealing until start of final finishing annealing The average grain size of the recrystallized grains is set to 18 to 35 μm, and the steel sheet is subjected to a nitriding treatment for absorbing 0.0010% by weight or more of nitrogen between the hot rolling and the start of secondary recrystallization in the final finish annealing. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties.

(2) 0.01 to 0.15% by weight of S
The method for producing a grain-oriented electrical steel sheet with excellent magnetic properties according to item 1, wherein n is contained in the slab. (3) Excellent magnetic properties according to the above 1 or 2, wherein the nitrogen partial pressure in the annealing atmosphere is 30% or more in the range of 900 to 1150 ° C. in the temperature of the steel sheet in the temperature rising process of final finish annealing. Method for manufacturing unidirectional electrical steel sheet.

[0011]

The function of the grain-oriented electrical steel sheet of 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
A final cold rolling of 0% or more is included, and if necessary, one or more cold rollings with intermediate annealing, decarburization annealing, and final finishing annealing are sequentially performed.

The present inventors have found two problems in the case of increasing the amount of Si.
A wide range of secondary recrystallization orientation control from various viewpoints
Research showed that the ratio of the amount of Al to the amount of Si is an important factor.
I found that. Below is a detailed description based on the experimental results.
It Figure 1 shows the ratio of the amount of Si to the amount of Al (Al / Si) and the magnetic characteristics.
Indicates a sexual relationship. Here, the amount of acid-soluble Al is
It is written as (%). In this case, C: 0.045 ~
0.067% by weight, Si: 3.4 to 4.7% by weight, acid
Soluble Al: 0.018 to 0.061% by weight, N: 0.0
073-0.0092% by weight, Mn: 0.14% by weight,
S: 0.006 to 0.008 wt%, balance Fe
And a 40 mm thick slab consisting of inevitable impurities 11
After heating at 50 ° C. for 1 hour, it was hot rolled to a thickness of 2.3 mm. Or
Keep the hot-rolled sheet at 1100 ° C for 30 seconds and then 90
After performing hot-rolled sheet annealing in which it is held at 0 ° C for 30 seconds and rapidly cooled,
Cold rolled to 0.22 mm, then 9 to 810-850 ° C
Decarburization annealing for 0 seconds (annealing atmosphere N₂: 25%, H
₂: 75%, D.I. P. = 60 ° C), then 750 ° C
Annealing for 30 seconds (annealing atmosphere N₂: 25%, H
₂: 75%, D.I. P. NH in an annealing atmosphere at <0 ° C)
₃Gas was mixed in and the steel sheet was made to absorb nitrogen. At this time
The amount of nitriding (the amount of nitrogen increase) is 0.0081 to 0.0127 weight
%Met. Then, the average crystal grain size of such a steel plate is
When measured using a microscope and an image analyzer, 21 to 2
It was 9 μm (equivalent circle diameter). MgO on such steel
Applying the annealing separator as the main component, N₂: 25%,
H₂: 1200 at 15 ° C / hr in 75% annealing atmosphere
Temperature is raised to ℃, H at 1200 ℃ for 20 hours₂Hold in
Final finish annealing was performed. As is clear from FIG.
Good magnetic flux density (B₈/
B_S≧ 0.95) (B_S: Saturation magnetic flux density)
It

Based on the results shown in FIG. 1, the present inventors have examined means for further improving the magnetic characteristics. FIG. 2 shows the relationship between the nitrogen partial pressure (P _N2 (%)) in the annealing atmosphere and the magnetic properties between 900 and 1150 ° C. in the temperature rising process of the final finish annealing. In this case, C: 0.054 wt%, Si: 3.51 wt%, acid-soluble Al: 0.034 wt%, N: 0.008
40% by weight, containing 6% by weight, Mn: 0.14% by weight, S: 0.007% by weight, the balance being Fe and inevitable impurities.
The mm-thick slab was subjected to steps from hot rolling to nitriding under the conditions described in FIG. In this case, the nitriding amount is 0.011
It was 5% by weight, and the average grain size of the steel sheet after this nitriding treatment was 23 μm (equivalent circle diameter). Mg on such steel sheet
An annealing separator containing O as a main component was applied, the temperature was raised to 1200 ° C. at 15 ° C./hr, and a final finish annealing was carried out at 1200 ° C. for 20 hours in H ₂ . During the temperature rising process of this final finish annealing, it was treated in an annealing atmosphere of N ₂ : 25% and H ₂ : 75% up to 900 ° C., and various partial pressure ratios of N ₂ and H ₂ were varied from 900 ° C. to 1200 ° C. Treated under conditions. As is clear from FIG. 2, P between 900 and 1150 ° C.
If _N2 (%) is more than 30%, good magnetic properties comprising B ₈ ≧ 1.94T is obtained.

The mechanism of the effect of improving the magnetic flux density shown in FIGS. 1 and 2 is not necessarily clear, but the present inventors speculate as follows. In the case of the material of the present invention, the main inhibitor for causing the secondary recrystallization is AlN, but when the amount of Si in the steel increases, AlN becomes unstable and (Al, Si) N or Si ₃ N ₄ Is likely to stabilize. As in the present invention, when the steel sheet is subjected to nitriding treatment after the hot rolling and before the start of secondary recrystallization in the final finish annealing, nitrogen is concentrated near the surface of the steel sheet after nitriding, and Si ₃ N ₄ etc. The base nitride precipitates. Then, during the temperature increase of the final finish annealing, the nitride such as Si ₃ N ₄ is decomposed and the nitrogen amount in the entire plate thickness is made uniform,
Stable AlN precipitation occurs. Increasing the amount of Si as in the present invention affects such changes in the nitride. That is, as the amount of Si increases, Si such as Si ₃ N ₄
The base nitride is stabilized, and it becomes difficult for the nitrogen content in the plate thickness direction and the nitride to become uniform as described above, and AlN hardly precipitates. When secondary recrystallization starts in such a state that the precipitates are non-uniform in the plate thickness direction and the proportion of nitrides such as Si ₃ N ₄ is large, Si-based nitrides such as Si ₃ N ₄ decompose at high temperature. The secondary recrystallization progresses in a state where the inhibitor strength is low due to reasons such as being easy to do and lacking nitride in the central portion of the plate thickness. In the state where the inhibitor strength is low, the dependence of the grain boundary movement on the grain boundary character is low, and the oriented grains dispersed from the Goss orientation with a low grain boundary density corresponding to Σ9 are likely to undergo secondary recrystallization. As a result, the secondary recrystallization orientation Gos
s The degree of integration is reduced and the magnetic flux density is reduced. Since this phenomenon is caused by the influence of the Si amount on the nitride, the Al amount increases as the Si amount increases.
The action to stabilize N (Fig. 1) and the action to increase P _N2 in the secondary recrystallization temperature region during the temperature rise of final finish annealing to suppress the decomposition of nitride (Fig. 2) are as follows. It is presumed that it has become a means for solving the problem of secondary recrystallization orientation control associated with higher Si.

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. When C is less than 0.025% by weight (hereinafter simply referred to as%), the secondary recrystallization becomes unstable, and even when the secondary recrystallization is performed, B ₈ > 1.80 (T)
Since it is difficult to obtain, it was set to 0.025% or more. On the other hand, if C is too much, 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. If it is less than 3.4%, 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. Al is 0.01% as acid-soluble Al so as to secure AlN necessary for stabilizing the secondary recrystallization.
5% or more is required. If the acid-soluble Al exceeds 0.080%, the AlN of the hot-rolled sheet becomes unsuitable and the secondary recrystallization becomes unstable, so the content was made 0.080% or less.

In order to obtain good magnetic characteristics,
Al (%) / Si (%) needs to be 0.0080 or more. By setting this range, excellent magnetic characteristics as shown in FIG. 1 can be obtained, so the above range was defined. The upper limit of this value is not particularly specified, but Al (%)
From the upper limit of Si and the lower limit of Si (%), Al (%) / Si
The upper limit of (%) is necessarily 0.0235.

N is 0.00 in the ordinary steelmaking work.
Since it is difficult to make it less than 30% and it is not economically preferable, it is set to 0.0030% or more, while 0.01
When it exceeds 30%, "blister on the steel plate surface" called blister occurs, so the content was made 0.0130% or less. Mn
Even if S and MnSe are present in the steel, it is possible to improve the magnetic properties by properly selecting the conditions of the manufacturing process. However, if S and Se are high, secondary recrystallization defective portions called linear fine grains tend to occur, and in order to prevent the generation of this secondary recrystallization defective portion, (S + 0.4
05Se) ≦ 0.014% is desirable. If S or Se exceeds the above value, the probability of occurrence of defective secondary recrystallization is increased no matter how the manufacturing conditions are changed, which is not preferable. Further, the time required for purification in the final finish annealing is too long, which is not preferable, and it is meaningless to increase S or Se unnecessarily from such a viewpoint.

The lower limit of Mn is 0.05%. 0.0
If it is less than 5%, the shape (flatness) of the hot-rolled sheet obtained by hot rolling, especially the side edge of the strip becomes corrugated,
Since Mn decreases the yield, Mn is defined as 0.05% or more. On the other hand, if the Mn content exceeds 0.8%, the magnetic flux density of the product will be reduced, which is not preferable. Therefore, the upper limit of the amount of Mn is set to 0.8%.

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.

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. This hot-rolled sheet is subjected to hot-rolled sheet annealing if necessary, and then rolled at a reduction ratio of 80.
% Or more final cold rolling and, if necessary, one or more cold rollings with intermediate annealing. The rolling reduction of the final cold rolling is set to 80% or more because the rolling reduction is within the above range.
In the decarburizing plate, sharp {110} <001> oriented grains,
Corresponding grains ({111} <112>) that are easily eclipsed by silkworms
This is because an appropriate amount of oriented grains, etc.) can be obtained, which is preferable for increasing the magnetic flux density.

After cold 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 to 18 to 35 μm after the completion of decarburization annealing and before the start of final finish annealing. If the average particle size is less than 18 μm, it becomes difficult to control the secondary recrystallization orientation, and if it exceeds 35 μm, the 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 method of nitriding is not particularly limited, and it is a method of mixing NH ₃ gas into the annealing atmosphere after decarburization annealing to perform nitriding, a method of using plasma, a nitride is added to an annealing separating agent, and a 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, 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,
10 ppm or more is necessary.

Further, it is more preferable to set the nitrogen partial pressure of the annealing atmosphere to 30% or more when the temperature of the steel sheet in the temperature rising process of the final annealing is in the range of 900 to 1150 ° C. in order to obtain excellent magnetic properties. .. The annealing atmosphere in the temperature range of less than 900 ° C. is not specified. Secondary recrystallization is usually 9
Since it occurs at 00 to 1150 ° C., it is sufficient to control the annealing atmosphere in this temperature range. The temperature rise is usually 1100-
It is carried out up to 1250 ° C., and usually the secondary recrystallization is completed during the temperature rise, and the isothermal holding for purification is started. The isothermal holding subsequent to this temperature rise is usually carried out for 5 to 50 hours, but this isothermal holding is usually carried out in an annealing atmosphere in which H ₂ gas or H ₂ gas is the main. For secondary recrystallization, for example, 1000 to 1
When the temperature is kept constant at 100 ° C. and then the temperature is further raised to start the constant temperature maintenance for purification, the temperature range up to the purification is understood as the temperature raising process. The upper limit of P _{N2 in} the temperature rising process of 900 to 1150 ° C. is not particularly specified, and 10
Permissible up to 0%.

[0025]

EXAMPLES Examples will be described below. Example 1 C: 0.056% by weight, Si: 3.58% by weight, Mn:
0.14% by weight, S: 0.005% by weight, acid-soluble A
1: 0.020% by weight, 0.031% by weight, 0.
Three types of 40 mm thick slabs containing 036 wt% and N: 0.0078 wt% and the balance Fe and unavoidable impurities were heated at a temperature of 1150 ° C., and then hot rolling was started at 1050 ° C. for 6 passes. Was hot-rolled into a hot-rolled sheet having a thickness of 2.3 mm.

This hot-rolled sheet was annealed at 1120 ° C. for 30 seconds and at 900 ° C. for 30 seconds to quench it, and then cold-rolled to a thickness of 0.22 mm at a reduction rate of about 90.4%. As a plate, decarburization annealing was performed at 830 ° 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. In this case, the nitriding amount (nitrogen increase amount) is 0.0110 to 0.013.
It was 2% by weight, and the average grain size (circle equivalent diameter) of the steel sheet after this nitriding treatment was 22 to 25 μm. An annealing separator containing MgO as a main component is applied to the steel sheet after the nitriding treatment, the temperature is raised to 1200 ° C. at 15 ° C./hr, and the temperature is set to 1 in H _2.
A final finish annealing was carried out at 200 ° C. for 20 hours. Up to 900 ° C. during the temperature rising process of this final finish annealing, N ₂ : 2
5%, H _2: treated in 75% of the annealing atmosphere, 900 ° C.
From 1 to 1200 ° C, (a) N ₂ : 15%, H ₂ : 8
5%, (b) N ₂ : 25%, H ₂ : 75%, (c)
N ₂ : 50%, H ₂ : 50%, (d) N ₂ : 90%, H
₂ : Processed under 4 levels of 10%.

Table 1 shows the relationship between process conditions and magnetic properties.
As is clear from Table 1, in the case of the Al amount of, which is the condition of the present invention, good magnetic properties of B ₈ ≧ 1.92 T are obtained, and further, the annealing atmosphere condition of the final finish annealing in the present invention is obtained. Under the conditions of (c) and (d), B ₈ ≧ 1.94
A particularly good magnetic property of T was obtained.

[0028]

[Table 1]

Example 2 C: 0.058% by weight, Si: 3.51% by weight, Mn:
0.14% by weight, S: 0.006% by weight, acid-soluble A
1: 0.021% by weight, 0.034% by weight, N:
0.0082 wt%, Sn: 0.05 wt%,
2 types of 40mm consisting of balance Fe and unavoidable impurities
After heating the thick slab at a temperature of 1150 ° C., it was hot rolled into a hot rolled sheet having a thickness of 2.3 mm.

This hot-rolled sheet was annealed at 1120 ° C. for 30 seconds and at 900 ° C. for 30 seconds to quench it, and then cold-rolled to a thickness of 0.22 mm at a rolling reduction of about 90.4%. As a plate, decarburization annealing was performed at 835 ° 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. In this case, the nitriding amount (nitrogen increase amount) is 0.0114 to 0.012.
It was 1% by weight, and the average crystal grain size (equivalent circle diameter) of the steel sheet after this nitriding treatment was 23 to 24 μm. An annealing separator containing MgO as a main component is applied to the steel sheet after the nitriding treatment, the temperature is raised to 1200 ° C. at 10 ° C./hr, and the temperature is set to 1 in H _2.
A final finish annealing was carried out at 200 ° C. for 20 hours. Up to 850 ° C. in the temperature rising process of this final finish annealing, N ₂ : 1
Treated in 5%, H ₂ : 85% annealing atmosphere, 850 ° C
From 1 to 1200 ° C, (a) N ₂ : 15%, H ₂ : 8
5%, (b) N ₂ : 90%, H ₂ : 10%.

Table 2 shows the relationship between process conditions and magnetic properties.
As is clear from Table 2, in the case of the amount of Al which is the experimental condition of the present invention, good magnetic properties of B ₈ ≧ 1.93T are obtained, and further, the annealing atmosphere condition of the final finish annealing in the present invention is the condition. In the case of the condition (b), particularly good magnetic characteristics of B ₈ ≧ 1.95 T were obtained.

[0032]

[Table 2]

Example 3 C: 0.060% by weight, Si: 4.01% by weight, Mn:
0.14% by weight, S: 0.007% by weight, acid-soluble A
1: 0.039% by weight, N: 0.0086% by weight, S
n: 0.003% by weight, 0.07% by weight, 0.2
Three 40 mm-thick slabs containing 0% by weight and the balance of Fe and unavoidable impurities were heated at a temperature of 1150 ° C., and then hot-rolled to a 2.3 mm-thick hot-rolled sheet. In this case, Al (%) / Si (%) = 0.0097.

The hot-rolled sheet was annealed at 1100 ° C. for 30 seconds and at 900 ° C. for 30 seconds for rapid cooling, and then 0.22 mm thick cold-rolled at a reduction rate of about 90.4%. As a plate, decarburization annealing was performed at 830 ° 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. In this case, the nitriding amount (nitrogen increasing amount) is 0.0078 to 0.012.
It was 9% by weight, and the average crystal grain size (circle equivalent diameter) of the steel sheet after this nitriding treatment was 21 to 26 μm. An annealing separator having MgO as a main component is applied to the steel sheet after the nitriding treatment, and the steel sheet is annealed in an annealing atmosphere of N ₂ : 25% and H ₂ : 75%.
Heat up to 00 ° C at 15 ° C / hr, 1200 ° C in H ₂
Was subjected to final finishing annealing for 20 hours.

Table 3 shows the relationship between process conditions and magnetic properties.
All the conditions of this experiment are included in the conditions of the present invention, and B ₈
≧ 1.92 T, good magnetic properties are obtained, and in the case where the Sn content range of the present invention is satisfied, B ₈ ≧
Particularly good magnetic characteristics of 1.95 T were obtained.

[0036]

[Table 3]

Example 4 C: 0.059% by weight, Si: 3.75% by weight, Mn:
0.14% by weight, S: 0.005% by weight, acid-soluble A
1: 0.039% by weight, N: 0.0088% by weight, S
A 40 mm thick slab containing n: 0.06% by weight and consisting of the balance Fe and unavoidable impurities was heated at a temperature of 1150 ° C. and then hot rolled to obtain a hot rolled sheet having a thickness of 1.8 mm. In this case, Al (%) / Si (%) = 0.0104.

After cold rolling the hot-rolled sheet to 1.4 mm, 1
Hold at 120 ° C for 30 seconds, then at 900 ° C for 30 seconds
It is annealed for cooling, and then rolled at a reduction rate of about 89.6% to 0.1.
A cold-rolled sheet with a thickness of 45 mm is kept at 830 ° C for 70 seconds.
Charcoal anneal and then hold at 750 ° C for 30 seconds
NH in the blunt₃Gas is mixed into the annealing atmosphere and the steel sheet is nitrided.
Reasoned. In this case, the nitriding amount (nitrogen increasing amount) is 0.01
41 to 0.0152% by weight, the steel after this nitriding treatment
The average crystal grain size (circle equivalent diameter) of the plate is 23 to 25 μm.
It was. After the nitriding treatment, the steel sheet containing MgO as a main component is fired.
Apply a blunt separator and raise the temperature to 1200 ° C at 15 ° C / hr.
And H₂Final baking at 1200 ° C for 20 hours
Blunted. During the temperature rising process of this final finish annealing,
Then N ₂: 25%, H₂: Treated in 75% annealing atmosphere
(A) N from 900 ° C to 1200 ° C₂: 2
5%, H₂: 75%, (b) N₂: 75%, H₂: 25
%, (C) N₂: 90%, H₂: 10% 3 level article
Processed in case.

Table 4 shows the relationship between process conditions and magnetic properties.
All the experimental conditions are within the conditions of the present invention, and B ₈
Good magnetic characteristics of ≧ 1.92 T were obtained. Further, in the case of the conditions (b) and (c) of the final finish annealing of the present invention, B ₈ ≧ 1.94T, which is a better magnetic property, was obtained.

[0040]

[Table 4]

[0041]

As described above, according to the present invention, A
Controlling the value of 1 / Si, and further controlling the average grain size of primary recrystallized grains between the completion of decarburization annealing and the start of final finish annealing, and the start of secondary recrystallization of final finish annealing after hot rolling. Nitriding treatment during this, more preferably, Sn addition, by controlling the nitrogen partial pressure of the annealing atmosphere in the temperature rising process of final finishing annealing, it is possible to stably produce a unidirectional electrical steel sheet having excellent magnetic properties. Since it can be done, its industrial significance is extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the Al / Si range and magnetic characteristics.

FIG. 2 is a graph showing the relationship between nitrogen partial pressure and magnetic characteristics in the temperature rising process of final finish annealing.

Front page continuation (72) Inventor Hiroaki Masui 1-1 Tobahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Co., Ltd. Yawata Works (72) Inventor Yoshio Nakamura 20-1 Shintomi, Futtsu-shi, Chiba Japan Steel Engineering Co., Ltd.

Claims (3)

[Claims] 1. C: 0.025 to 0.075% by weight,
Si: 3.4-5.0%, acid-soluble Al: 0.015-
0.080%, N: 0.0030 to 0.0130%, S
+0.405 Se: 0.014% or less, Mn: 0.05
A slab containing 0.8 to 0.8% of which the balance is Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, and subsequently hot-rolled sheet annealed if necessary, and then a reduction rate of 80%. In the method for producing a unidirectional electrical steel sheet by performing cold rolling one or more times with intermediate annealing if necessary including the above final cold rolling, and then performing decarburizing annealing and final finishing annealing, acid-soluble Al, When the content of Si is defined as Al (%) and Si (%) with weight% as a unit, the Al and Si are controlled within the following range, and Al (%) / Si (%) ≧ 0.0080 decarburization After the completion of annealing, the average grain size of the primary recrystallized grains until the start of the final finish annealing is set to 18 to 35 μm, and after the hot rolling, before the start of the secondary recrystallization of the final finish annealing, 0.0010% by weight or more of the steel sheet is added. Magnetism characterized by nitriding treatment to absorb nitrogen A method for producing a grain-oriented electrical steel sheet having excellent characteristics. 2. The method for producing a grain-oriented electrical steel sheet with excellent magnetic properties according to claim 1, wherein 0.01 to 0.15% by weight of Sn is contained in the slab. 3. The magnetic material according to claim 1, wherein the nitrogen partial pressure in the annealing atmosphere is 30% 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. A method for producing a grain-oriented electrical steel sheet having excellent characteristics.