JP3438282B2 - Method of manufacturing oriented silicon steel sheet with high magnetic flux density - Google Patents

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 silicon steel sheet, and particularly to a method capable of producing a steel sheet having a high magnetic flux density.

[0002]

2. Description of the Related Art Grain-oriented silicon steel sheets are used for transformers and iron cores for generators, and have magnetic characteristics as a magnetic flux density (indicated by a value B ₈ at a magnetic field strength of 800 A / m). High and low iron loss (indicated by the alternating iron loss value W _17/50 at 50 Hz at a maximum magnetic flux density of 1.7 T) is required.

Various efforts have been made so far to reduce the iron loss of this material. (1) thin the plate thickness of the steel sheet, (2) increase the Si content, (3) increase the grain size of the final product. As a result of improvements such as making it smaller, W _17/50 is 0.90 as the iron loss value of _{0.23 mm} thickness.
Materials with low iron loss such as W / kg are now available. However, it is not easy to reduce iron loss more than the current situation. That is, when the plate thickness of the steel sheet is made thinner than the current one, the secondary recrystallization defect described later is caused and the iron loss is deteriorated. Further, if the Si content is increased, cold rolling becomes difficult. Further, if the method of reducing the crystal grain size metallurgically is also made smaller than the current average grain size of 4 to 8 mm, secondary recrystallization becomes defective and iron loss deteriorates.

However, in recent years, a so-called magnetic domain refining technique of locally introducing strain or forming grooves on the surface of a steel sheet has made it possible to significantly improve iron loss. That is, the above
In the case of a material that has an iron loss value of W17 _{/ 50} of 0.90 W / kg, it is possible to reduce the iron loss to 0.80 W / kg by introducing an appropriate local strain on the surface of the steel sheet with a plasma jet etc. became. In order to obtain a material with excellent iron loss by such a method, unlike the conventional method, it is not necessary to reduce the crystal grain size of the final product, and to exclusively reduce the plate thickness, increase the Si content, and increase the magnetic flux density. Depends on raising. Where Si
Since it is difficult to increase the content further,
The improvement of iron loss characteristics depends on the solution of the technical problem of how to improve the magnetic flux density of a material having a thin plate thickness.

In order to improve the magnetic flux density of grain-oriented silicon steel sheet, the crystal grain orientation of the product should be (110) [00
1] It is necessary to highly integrate the azimuth, so-called Goth azimuth. The Goss-oriented crystal grains are obtained by a secondary recrystallization phenomenon caused by final finish annealing. And
In order to cause this secondary recrystallization, (110) [00
1] Suppressor (inhibitor) for suppressing the growth of crystal grains in other orientations in order to suppress the growth of crystal grains in other orientations, that is, so-called selective growth, by growing only crystal grains close to the orientation is necessary. That is, the inhibitor forms a precipitate-dispersed phase in the steel and exerts a function of suppressing grain growth.

As such an inhibitor, the one having the strongest inhibitory action has a strong selective growth effect and a material having a high magnetic flux density can be obtained. Therefore, many studies have been conducted so far, but the most effective one is obtained. The material was AlN. That is, as disclosed in Japanese Patent Publication No. 46-23820, a steel sheet containing Al is subjected to a quenching treatment by annealing before final cold rolling, and the final cold rolling reduction is 80 to 95%. Therefore, in Example 5, B having a thickness of 0.35 mm
A material with a high magnetic flux density of ₁₀ is 1.981 T (about 1.95 T for B ₈ ) is obtained.

However, when the above method is applied to a thin steel sheet, there arises a problem that a high magnetic flux density cannot be obtained. That is, it becomes a nucleus of secondary recrystallized grains (110).
Grains in the [001] orientation do not exist uniformly in the plate thickness direction but exist near the surface layer of the plate thickness. However, when the plate thickness becomes thin, the atmosphere during final finishing annealing And the secondary recrystallization becomes unstable. This is because Al existing in the surface layer of the steel sheet
This is because N is decomposed and disappeared due to the oxidation of the steel sheet surface, and the suppressing force is weakened. In this way, the surface layer of the steel sheet originally has a region where the suppressing force is weak. However, when the plate thickness becomes thin, it becomes a nucleus of secondary recrystallized grains during the final annealing (110). ) The location where the grains of the [001] orientation are present is close to or included in the region where the suppressing force is weak, resulting in secondary recrystallization failure.

In the case of a conventional silicon steel sheet using AlN as an inhibitor, which has a small thickness, the above-mentioned Japanese Patent Publication No.
In Example 6 of Japanese Patent Laid-Open No. 6-23820, B ₁₀ : 1.930 T (B ₈ of about 1.91 by a cold rolling twice method with a plate thickness of 0.228 mm.
However, this is not a satisfactory high magnetic flux density.

Further, in Japanese Patent Publication No. 63-11406, Sn and Cu are added to the steel, and the cold rolling once method is used for 0.15 to 0.25.
Techniques for producing mm-oriented grain-oriented silicon steel sheets are disclosed. Here, Sn has the effect of stabilizing secondary recrystallization,
Cu is needed to counteract the deleterious effects on the coating due to the addition of Sn. However, even with this technology, the magnetic flux density is 1.92T at B ₁₀ (about ₈ at B ₈
It is 1.90T), and it cannot be said that it is still sufficiently effective.

The reason is that when the thickness of the steel plate is reduced,
There is a phenomenon that the inhibitor of the surface layer of the steel sheet is affected by the atmosphere of the final finish annealing, and the suppression force decreases, and the nucleation region of secondary recrystallization approaches the region of the steel plate surface layer affected by the reduction of the suppression force. This is because, with respect to such a problem that is included, it is not effective means to increase the restraining force of the entire steel sheet or to improve the structure after the first cold rolling.

On the other hand, the inventors have proposed a technique of adding Sb to the steel as a method of strengthening the suppressing force of the surface layer of the steel sheet of the Al-containing grain-oriented silicon steel. That is, it is a technology for producing a high magnetic flux density material by suppressing the oxidation of the steel sheet surface during the final finish annealing by the surface segregation effect of Sb to suppress the division and disappearance of the inhibitor.
Proposed in Japanese Patent No. 319. However, even with this technique, it has not been possible to sufficiently suppress the decrease in the suppressing force, and the improvement of the magnetic flux density of the thin grain-oriented silicon steel sheet has not been sufficient.

[0012] As a result of investigating the reason, in the grain-oriented silicon steel sheet containing AL and Sb, the denitrification phenomenon of the surface layer portion was caused by the intermediate annealing, which is the cause of the decrease in the surface layer suppression force. It was found that there was such a problem, and as a countermeasure against this, a technique of applying a nitriding accelerator before intermediate annealing to compensate the denitrification amount was proposed in JP-A-4-173923. However, even with this technique, it is not always sufficient to suppress the reduction of the suppression force of the steel sheet surface layer portion, and it is difficult to stably obtain a high magnetic flux density material in the thin grain-oriented silicon steel sheet.

Apart from these techniques, a method of nitriding the steel sheet surface layer portion has long been known as a method for strengthening the restraining force of the steel sheet surface portion. For example, Japanese Patent Application Laid-Open No. 49-6455 discloses a technique of nitriding after a decarburization annealing step in the production of a grain-oriented silicon steel sheet containing Al.

Further, Japanese Examined Patent Publication No. 50-19489 discloses a process for producing a grain-oriented silicon steel sheet containing Al in a nitriding atmosphere at 600 to 1200 ° C. in a step before final cold rolling.
A technique is disclosed in which a nitriding treatment with a nitriding increase amount of 0.005 to 0.075% is performed on a surface layer portion of a steel sheet which is converted into a final thickness ratio and leaves a region of 0.10 mm or more in a central portion of the steel sheet. However, the magnetic flux density obtained by this technique is at most B _10: a 1.93 T (approximately in the B ₈ 1.91 T), no material having a high magnetic flux density is obtained.

[0015]

As described above, when the thickness of the steel sheet becomes thin, the secondary recrystallization occurs in a region where the inhibitor in the surface layer of the steel sheet is affected by the final finishing annealing atmosphere and the inhibitory power is reduced. With respect to the problem that the nuclei of No. 1 are included, it has been impossible to increase the restraining force of the entire steel sheet or to improve the structure after the first cold rolling. Moreover, although the technique of incorporating Sb into steel and utilizing the surface segregation effect has achieved some results, it is still not sufficient. Further, the technique of increasing the suppression force of the surface layer of the steel sheet by nitriding in the intermediate step often has a problem of inducing secondary recrystallization of grains having poor orientation.

The present invention advantageously solves the problem of the reduction of the suppression force of the steel sheet surface layer portion in the final finish annealing described above. By adding a device to the steel containing Sb, the suppression of the suppression force can be improved. It is an object of the present invention to propose a manufacturing method capable of suppressing a decrease and obtaining a grain-oriented silicon steel sheet having a high magnetic flux density.

[0017]

The gist of the present invention is as follows. (1) C: 0.02 to 0.09 wt%, Si: 2.5 to 5.0 wt%, Mn:
0.02 to 0.3 wt%, Al: 0.01 to 0.04 wt%, Sb: 0.005 to 0.
060 wt% and N: 0.0055 to 0.0095 wt% , balance Fe
And silicon steel slab consisting of unavoidable impurities and hot rolling, once the reduction ratio of cold rolling to a final thickness of 80 to 95
% , And cold rolling is performed once or twice before the first rolling to achieve the final plate thickness, followed by decarburizing annealing and further applying an annealing separator. in the final finishing method for producing oriented silicon steel sheet consisting of a series of manufacturing step of performing annealing after, 1, final thickness
Annealing performed before the first cold rolling is divided into a first stage and a second stage. In the first stage, at a temperature in the range of 750 to 850 ℃, 30 ~
It is a soaking for 90 seconds or a gradual heat for staying in the temperature range of 700-900 ° C for 30-90 seconds, and the annealing atmosphere is 0.1-10% NH ₃
And containing 20 to 80% of H ₂ and performing a nitriding heat treatment with a dew point of 20 to 60 ° C. and the balance of N ₂ balance.
Then, in an atmosphere where the NH ₃ concentration was regulated to less than 0.1%,
Performing a recrystallization heat treatment for soaking for 30 to 90 seconds at 1050 to 1200 ° C and increasing the N content after the decarburization annealing step,
A method for manufacturing a grain-oriented silicon steel sheet having a high magnetic flux density, which is characterized by a combination of suppressing to 10 wt ppm or less. (2) In the above (1), the silicon steel slab further contains one or two of S and Se in a total amount of 0.005 to 0.040 wt%.
A method for producing a grain-oriented silicon steel sheet having a high magnetic flux density, which is characterized by containing. (3) In the above (1) or (2), the silicon steel slab further contains one or more of Cu, Sn, P, Bi, As, B, Ge, V, Nb and Cr. Cu, Sn and Cr
Respectively 0.03 to 0.30 wt%, Bi 0.005 to 0.020 wt%,
P, Ge, V, Nb and As are each 0.005 to 0.030 wt.
% And B are contained in the range of 0.0005 to 0.0020 wt%, a method for producing a grain-oriented silicon steel sheet having a high magnetic flux density.

The experiments that motivated the completion of the present invention will be described in detail below. C: 0.078%, Si:
3.31%, Mn: 0.068%, P: 0.006%, S: 0.005%,
Al: 0.024%, Se: 0.019%, Sb: 0.026% and N: 0.
The steel slab containing 14% was heated at 1420 ° C. for 15 minutes soaking, and then hot-rolled to form a 1.9 mm hot-rolled sheet. The hot rolled sheet was annealed at 1000 ° C for 60 seconds, then pickled,
The 1.20 mm intermediate rolled plate was obtained by the first cold rolling. The intermediate rolled plate was degreased and then divided into 9 to form coils a to i.

Next, the coil a is composed of NH ₃ : 2% H ₂ : 75%,
40se at 800 ℃ under dew point of 35 ℃ and balance of N ₂ balance.
After performing the nitriding treatment of c, the temperature was raised to 1100 ° C., annealed in an atmosphere of H ₂ for 60 seconds, and then rapidly cooled at 40 ° C./sec with a mist.

Of the remaining 8 coils (b to i), coil b
_{Is, NH 3: 25%, H} 2: 75%, a high nitriding atmosphere than in the coil a such residual N ₂ balance at dew point 35 ° C., 800
After nitriding at 40 ° C for 40 seconds, raise the temperature to 1100 ° C and
After annealing in H ₂ atmosphere for sec, mist 40 ℃ / sec
Was quenched. These 2 coils of a and b were then cold-rolled for the second time to a final plate thickness of 0.18 mm, and then dew point 60 ° C, H ₂ : 55%, N ₂ balance in a wet hydrogen atmosphere at 850 ° C.
Decarburization annealing was performed for 2 hours.

The remaining 7 coils (c to i) are H ₂ : 75%, dew point 35 ° C., and the balance is 800 ° C. for 40 sec in an N ₂ balanced atmosphere.
Then, the sample was annealed in H ₂ at 1100 ° C. for 60 seconds, and then rapidly cooled with mist at 40 ° C./sec.

After that, in the coil c, NH ₃ : 2%, H ₂ :
75%, dew point 35 ° C, balance 800 ° C in N ₂ balanced atmosphere
Then, nitriding treatment was performed for 40 seconds. Also, the coil d has N
Nitrogen treatment was performed for 40 seconds at 800 ° C in an atmosphere of H ₃ : 25%, H ₂ : 75%, dew point of 35 ° C and the balance of N ₂ balance. These coils c and d were then subjected to a second cold rolling to obtain a final plate thickness of 0.18 mm, and then deheated at 850 ° C. for 2 minutes in a wet hydrogen atmosphere with a dew point of 60 ° C., H ₂ 55% and N ₂ balance. It was subjected to charcoal annealing.

The remaining 5 coils (e to i) were successively cold-rolled a second time to a final plate thickness of 0.18 mm. After cold rolling, the coil _{e, NH 3: 0.3%,} H 2: 75%, dew point 35
Nitriding treatment was performed at 800 ° C for 40 seconds in an atmosphere of balance N _{2 at} ℃. Further, in the coil f, NH ₃ : 4.0%,
H ₂ : 75%, dew point 35 ° C, balance N ₂ balanced atmosphere,
Nitriding was performed at 800 ° C for 40 seconds. The coils of e and f were further subjected to decarburization annealing at 850 ° C. for 2 minutes in a wet hydrogen atmosphere having a dew point of 60 ° C., H ₂ : 55%, and N ₂ balance.

For the remaining three coils (coils g, h, i),
Dew point 60 ℃, H ₂ : 55%, N ₂ balance in wet hydrogen atmosphere, 85
Decarburization annealing was performed at 0 ° C for 2 minutes. Of these, coil g
Furthermore the _{NH 3: 0.3%, H 2} : 75%, in an atmosphere of residual at 35 ° C. dew point is N ₂ balance, subjected to nitriding treatment 40sec at 800 ° C., the coil h NH _3: 4.0%, H ₂ : 75%, dew point 35 ° C
The rest was subjected to nitriding treatment at 800 ℃ for 40 seconds in N ₂ balanced atmosphere.

With respect to these coils, the N contents after the intermediate annealing and after the decarburizing annealing are shown as follows: Coil a: (N content after the intermediate annealing 86 ppm, N content after the decarburizing annealing 87 ppm)
Similarly, coil b: (125, 127), coil C: (87, 88), coil d: (130, 133), coil e:
(74, 87), coil f: (75, 119), coil g: (7
5, 88), coil h: (75, 127), coil i: (74, 7)
It was 5).

Each of the decarburized and annealed coils a to i
Then, an annealing separator containing MgO as a main component containing 5% of TiO ₂ and 3% of Sr (OH) ₂ · 8H ₂ O is applied, and then wound into a coil and heated in an H ₂ atmosphere at 840 ° C. Hold for 40 hours, then 15 ℃
/ To speed raised to 1200 ° C. in the _{hr H 2: 25%, N} 2: 2 primary recrystallization annealing in a 75% atmosphere, consisting of purification annealing at successive 1200 ° C., in an H ₂ atmosphere for 5 hours Final finish annealing was performed. The obtained magnetic characteristics are shown in Table 1 for each coil.
Shown in.

[0027]

[Table 1]

As shown in Table 1, in the intermediate annealing, among the coils a to d which were subjected to the nitriding treatment, the coil a having a smaller nitriding amount had an extremely high magnetic flux density. On the other hand, the magnetic flux density of the coil b, which has a large amount of nitriding, is low at the level of 1.8 T.
The coil also has a low magnetic flux density of 1.8 T level. Also,
Even in coils with a small amount of nitriding, the final cold-rolled sheet and decarburized and annealed sheet were subjected to nitriding treatment at e, f, g, and h coils, where the magnetic flux density was 1.8 T level in general, and no nitriding Lower than 1.913 T for coil i.

As described above, according to the present experiment, when the nitriding treatment is performed after the intermediate annealing, the magnetic flux density is deteriorated, and even before the intermediate annealing, the magnetic flux density is decreased when the nitriding amount is large. I found out that As a result of investigating the cause of this, when the amount of nitriding is large or when nitriding is performed after the intermediate annealing, Si ₃ N ₄ or FeN is formed in the surface layer of the steel sheet by the nitriding treatment, and as a result, the suppressing force is weak. I found out that. In other words, according to the research conducted by the inventors, when Si ₃ N ₄ or FeN remains in the surface layer of the steel sheet, the suppression force of the surface layer of the steel sheet is weakened conversely and the temperature of secondary recrystallization sharply decreases. It was newly found that although the stability of the secondary recrystallization is increased, the grains having inferior orientation are secondary recrystallized and hence the magnetic flux density is lowered.

Based on this finding, the present invention provides the above-mentioned Japanese Patent Publication No.
Unlike the large amount of nitriding technology such as 245 ppm (Example 1) and 213 ppm (Example 2) described in Japanese Patent Publication No. 0-19489, the nitriding amount is set to about 1 in the first step in order to avoid the adverse effect of the decrease in magnetic flux density. By performing nitriding treatment within the range of 3 to 20 ppm, and by performing high-temperature recrystallization heat treatment as the second stage intermediate annealing, FeN and Si ₃ N ₄ generated during this nitriding treatment are decomposed and converted to AlN. The idea was to obtain a high magnetic flux density. From this, it was also found that after the intermediate annealing, it was necessary to suppress the nitriding phenomenon as much as possible, and to suppress the increase of the N content to 10 ppm or less.

The range of appropriate conditions for the nitriding treatment in the present invention was determined as follows by various experiments. That is, the temperature range is 750 to 850 ° C.
At a temperature lower than 750 ° C, it took a long time to obtain a predetermined amount of nitriding, which was not practical. If it exceeds 850 ° C, the amount of nitriding tends to be excessive, and even if it is an appropriate amount, nitrogen penetrates to the central portion of the plate thickness of the steel sheet, and the purpose of this invention of strengthening the restraining force of the steel sheet surface layer part is lost. On the contrary, the magnetic flux density is lowered. A soaking time of 30 to 90 seconds was appropriate. Further, not only the case where the temperature is maintained at a constant temperature but also the case where the nitriding is performed in the temperature rising process has the same effect. In this case, the temperature range may be 700 to 900 ° C, which is rather wide, and the rate of temperature rise is effectively 2.0 to 5.0 ° C / sec.

The atmosphere during the nitriding treatment is 0.1-10%.
The NH ₃ concentration of was appropriate. If the NH ₃ concentration is less than 0.1%, the nitriding amount is not sufficient, and if it exceeds 10%, the nitriding amount becomes excessive and the magnetic flux density deteriorates. Also, during processing, H ₂ is 20 ~
The inclusion of 80% was necessary for stabilizing the nitriding treatment. When H ₂ was less than 20%, the amount of nitriding varied greatly, and when H ₂ was more than 80%, nitriding tended to be difficult. Furthermore, the inventor has newly found that increasing the dew point of the atmosphere during the treatment is effective for enhancing the nitriding treatment. The exact reason for this is unknown, but it is considered that the surface oxidation and decarburization form a pure Fe phase on the surface, which facilitates the generation of FeN. For this purpose it was necessary to adjust the dew point to 20-60 ° C.

Next, in the second stage of the intermediate annealing, it can be said that one of the main purposes is to decompose and diffuse FeN and Si ₃ N ₄ produced by nitriding to convert the whole amount into useful AlN. To this end, in the second stage, NH ₃ in the atmosphere
Was found to be present at no more than 0.1%. That is, if NH ₃ is present in excess of 0.1%, the nitriding reaction proceeds at high temperature and harmful FeN and Si ₃ N ₄ are present. In this regard, the Japanese Examined Japanese Patent Publication Sho-50-19
The nitriding treatment in Japanese Patent No. 489 is high temperature, and in this sense, it cannot be said that it is appropriate from the viewpoint of the technique of the present invention. Also, these FeN and Si ₃ N ₄ are decomposed and diffused to form AlN.
1050 to 1200 as temperature for annealing for conversion to
Soaking for 20 to 90 seconds was required at ℃.

Since there is no high-temperature heat treatment step capable of sufficiently converting FeN or Si ₃ N ₄ to AlN after the nitriding step by annealing before the final high pressure cold rolling, nitriding is performed after the annealing step. When the treatment is carried out, the magnetic flux density is deteriorated due to an adverse effect as is clear from the above experiment. Therefore, it was found that it is necessary to suppress nitriding after the decarburization annealing step as much as possible, and it is necessary to suppress the nitriding amount to 10 ppm or less.

[0035]

First, the components of the grain-oriented silicon steel slab which is the material of the present invention will be described. C: 0.02 to 0.09% C is 0.02 in order to improve the hot rolled structure by utilizing the γ transformation.
% Or more is required. On the other hand, if it exceeds 0.09%, decarburization becomes poor, so the range is 0.02 to 0.09%. Si: 2.5 to 5.0% Si is required to be 2.5% or more in order to increase electric resistance and improve iron loss. On the other hand, if it exceeds 5.0%, embrittlement is severe and cold rolling becomes difficult, so the range is 2.5 to 5.0%.

Al: 0.01 to 0.04% Al is a main inhibitor essential for obtaining the high magnetic flux density of the present invention, and is a basic component for AlN precipitation.
%, The amount of precipitation of AlN is insufficient. Conversely, if it exceeds 0.04%, the precipitation of AlN becomes coarse and the suppressing power deteriorates.
The range is up to 0.04%. N: 0.0055 to 0.0095% N is also a basic component for precipitation of AlN, which is an essential main inhibitor for obtaining the high magnetic flux density of the present invention, and
If it is less than 0055%, the precipitation amount of AlN is insufficient, and if it exceeds 0.0095%, it is gasified during heating of the steel slab and causes troubles such as blistering. Therefore, the range is set to 0.0055 to 0.0095%.

Sb: 0.005 to 0.060% Sb is a component necessary for suppressing the oxidation and nitriding of the surface layer of the steel sheet and strengthening the suppressing power of the surface layer of the steel sheet during final annealing, and is also effective for reinforcing the inhibitor effect. is there.
0.005% or more is required for this effect, but 0.06%
If it exceeds 0%, the embrittlement of the steel sheet will be severe, so 0.00
The range is 5 to 0.060%.

Mn: 0.02 to 0.3% Mn is useful for preventing cracks during hot rolling, and is also useful as an inhibitor-forming component when using a secondary inhibitor such as MnS or MnSe. For that, 0.02
% Or more is required. However, if it exceeds 0.3%, these MnS
Since it becomes difficult to dissolve MnSe and MnSe by heating the slab, the range is 0.02 to 0.3% . C mentioned above,
Si, Al, N, Sb and Mn are essential components in the present invention, but S, Se and the like may be contained in addition to them.

S and Se are bound to Mn to bind to Mn which is a secondary inhibitor.
It is a useful component because it precipitates S and MnSe. In order to bring about this effect, 0.005% or more is necessary. On the other hand, if it exceeds 0.040%, coarsening of the precipitates causes deterioration of magnetic properties, so 0.005 to 0.040% is preferable.

Furthermore, it goes without saying that Cu, Sn, P, Bi, As, B, Ge, V, Nb, Cr and the like, which are known as inhibitor reinforcing components, may be contained. For this purpose, Cu, Sn, and Cr are 0.03 to 0.30% and Bi is 0.005 to 0.020.
%, P, Ge, V, Nb, As 0.005 to 0.030%, B 0.00
The content of 05 to 0.0020% is preferable. In addition, Mo is added to prevent cracking in hot rolling peculiar to silicon steel.
It is also possible to contain 5 to 0.020%.

Next, the manufacturing method according to the present invention will be described. The silicon steel slab containing the above components is slab-heated by a conventional method and then hot-rolled. The coil of hot rolling is made into the final steel plate thickness by the cold rolling process. In this cold rolling process, the cold rolling one time method in which the final plate thickness is obtained by one cold rolling There are two types: a cold rolling twice method in which the final plate thickness is obtained by performing two cold rolling processes with annealing. Compared to the cold-rolling once-rolling method, the cold-rolling twice-rolling method causes harmful destruction of the hot-rolled structure, which is advantageous in terms of magnetic properties, but disadvantageous in cost. Both the cold rolling once method and the cold rolling twice method are the steps to be covered by the present invention.

In the case of the one-time cold rolling method, hot-rolled sheet annealing is always performed. This corresponds to the annealing performed before the cold rolling under the final high pressure according to the present invention.

On the other hand, in the case of the cold-rolling twice method, hot-rolled sheet annealing is not essential and may be performed as needed. That is, hot-rolled sheet annealing is performed for recrystallization and size adjustment of carbides in order to improve the hot-rolled structure, and when the conditions of hot rolling in the cold rolling two-time method are sufficiently controlled, Such an anneal is not always necessary. Further, it is also possible to perform annealing for adjusting only carbides without performing hot-rolled sheet annealing. Generally, the hot-rolled sheet annealing conditions are 900-1200 ° C and 30-
120 sec. Annealing for adjusting the carbide is performed at a lower temperature for a shorter time. In the cold-rolling double rolling method, the first cold rolling is performed by adding the working strain and the purpose of adjusting the intermediate plate thickness to make the reduction ratio of the second high-pressure cold rolling appropriate. The purpose is to accelerate the recrystallization in the intermediate annealing by opening the. To achieve these objectives, a reduction of 10% or more is sufficient. Further, in order to prevent cracking of the steel sheet during rolling, warm rolling may be performed in the temperature range of 50 to 300 ° C.

The coil that has been subjected to the first cold rolling is degreased and then subjected to intermediate annealing. This corresponds to the annealing performed before the cold rolling under the final high pressure according to the present invention. That is, the hot rolling sheet annealing in the cold rolling once method and the annealing performed before the cold rolling under the final high pressure, which is the intermediate annealing in the cold rolling twice method, are divided into two stages in the present invention. In the first stage, nitriding heat treatment is performed under predetermined conditions, and the second
At the stage, the recrystallization heat treatment is performed under predetermined conditions. The first and second heat treatments are
Although it is possible to perform each heat treatment independently, it is more efficient to perform the heat treatment in only one heat cycle.

The annealing performed before the cold rolling under the final high pressure will be described in detail below. The first stage of annealing is for performing a nitriding treatment, and is carried out by soaking for 30 to 90 seconds at 750 to 850 ° C or gradual heat treatment for staying in the temperature range of 700 to 900 ° C for 30 to 90 seconds. In the case of soaking that is maintained at such a constant temperature, it is not practical at a temperature lower than 750 ° C because it takes time to obtain a predetermined nitriding amount.
At a temperature higher than 0 ° C, the nitriding amount is likely to be excessive, and even if the nitriding amount is suppressed to an appropriate amount, nitrogen penetrates to the central portion of the plate thickness of the steel sheet. The purpose is not achieved. Soaking time is also 30 seconds
If it is shorter than the above, the specified amount of nitriding cannot be obtained, while 90 seconds
If the length is longer than that, nitriding is excessively performed, which causes a decrease in magnetic flux density.

The nitriding treatment in the slow heating process is basically the same as the case of maintaining a constant temperature, but the temperature range is 700 to 90.
It becomes a slightly wide range of 0 ° C. The effective residence time is 30 to 90 seconds. In other words, if it exceeds 90 seconds, the nitriding process takes too long and is not practical.
If it is less than this, a sufficient amount of nitriding cannot be obtained.

NH ₃ is used as an atmosphere for performing the nitriding treatment. When the concentration of NH ₃ is less than 0.1%, the nitriding amount is not sufficient, and when it exceeds 10%, the nitriding amount becomes excessive and the nitriding amount is also increased in the second stage heat treatment described later.
The conversion to AlN is not sufficient and the magnetic flux density deteriorates. Therefore, the proper value for the NH ₃ concentration should be in the range of 0.1 to 10%.

Further, it is necessary to mix H ₂ in the atmosphere. H ₂ is necessary because it has a function of controlling the amount of nitriding of the steel sheet due to the following reaction.

[Chemical 1] For this purpose, H ₂ concentration of 20% or more is necessary,
If it exceeds 80%, the nitriding reaction itself tends to be suppressed, so the H ₂ concentration is set to 20-80%.

Further, as the atmosphere of the nitriding treatment,
One of the features of the present invention is that water vapor is mixed therein. By increasing the dew point of the atmosphere, the nitriding speed increases dramatically and the processing time can be shortened. At the same time, the generated nitride is easily converted into AlN in the second stage heat treatment, which is useful for improving the magnetic flux density. Achieves the desired effect. For this purpose, the dew point of the atmosphere is required to be 20 ° C or higher. On the other hand, when the dew point exceeds 60 ° C, surface oxidation becomes severe and the disappearance of the inhibitor in the surface layer progresses. It is necessary to set the temperature within the range of to 60 ° C.
The balance gas may be a neutral gas such as Ar, but N ₂ gas is cheap and most suitable.

Next, regarding the second stage heat treatment performed after the nitriding heat treatment, the purpose is to obtain FeN of the surface layer formed in the first stage and
Dissociation and solid solution of Si ₃ N ₄ nitride are converted to useful AlN by diffusion, and recrystallization of steel sheet crystal composition.

For these purposes, a temperature of 1050
The range is to 1200 ℃. FeN and Si ₃ N ₄ below 1050 ℃
The conversion of nitrides such as etc. to AlN is not sufficiently performed. Further, when the temperature is 1200 ° C. or higher, the recrystallized grains become coarse and the secondary recrystallization becomes difficult. Therefore, the heat treatment temperature of the second stage is limited to the range of 1050 to 1200 ° C. If the soaking time is less than 30 sec, the above-mentioned various nitrides are not sufficiently converted into AlN. On the other hand, if the soaking time is more than 90 sec, the recrystallized grains become coarse and secondary recrystallization becomes difficult. Therefore, the soaking time should be in the range of 30 to 90 seconds.

Next, the annealing atmosphere in this second stage may be any of oxidizing, reducing and neutral, but it is necessary to use a non-nitriding atmosphere in which the NH ₃ concentration is suppressed to less than 0.1%. That is, when the NH ₃ concentration is 0.1% or more, FeN or NiN produced by nitriding even in the second stage intermediate annealing is generated.
Si ₃ N ₄ remains on the surface of the steel sheet, and as a result the magnetic flux density of the product decreases. Therefore, it is necessary to keep the NH ₃ concentration in the atmosphere below 0.1%. In order to satisfy this requirement, the nitriding treatment in the first stage and the recrystallization heat treatment in the second stage are performed in separate steps, or when the treatments are performed in the same step, a partition wall for preventing atmospheric gas mixture is provided in the annealing furnace. It is preferable to perform processing such as providing.

As for the cooling after the heat treatment in the second step, it is necessary to rapidly cool it to 500 ° C., as is well known. This is necessary for controlling the precipitation state of carbides in the steel, and more preferably, the size and dispersion of the carbides can be controlled more strictly by slow cooling at 500 ° C or lower or maintaining the temperature at low temperature. It will be possible.

The coil which has been heat-treated before the cold rolling under the final high pressure is subjected to pickling, washing or grinding, if necessary, and then subjected to the final cold rolling. The final cold rolling is
As is well known, it is necessary to apply a high pressure with a reduction rate of 80 to 95%, and if it deviates from this range, the magnetic flux density will decrease on either side.

In the cold rolling, as is well known, during the rolling, the aging treatment is performed only once in a short time, the aging treatment is performed many times between passes (pass aging treatment), or 100 to 300.
It is also possible to carry out rolling at a high temperature of ° C (warm rolling) to improve the magnetic properties.

The coil after the final cold rolling is subjected to decarburization annealing after degreasing. Decarburization annealing is performed in a known wet hydrogen atmosphere at 750
It is carried out at ~ 900 ℃ and 60 ~ 180 sec. In the present invention, in each process after the nitriding heat process, N in steel is
It is necessary to suppress the increase of the content as much as possible, and the increase amount of the N content after the decarburization annealing step is specified to be 10 ppm or less. If it exceeds 10ppm, Fe is
N and Si ₃ N ₄ are generated, and the magnetic flux density of the product is lowered because the suppression force is weakened. Therefore, it is necessary to suppress the increase in N content after the decarburization annealing step to 10 ppm or less.

The coil after decarburization annealing is coated with an annealing separating agent, and then wound into a coil and subjected to final annealing. The final finish annealing may be performed by a known method, in particular,
Since Sb is contained in this invention, 800 to 87
Treatment at a constant temperature of 0 ° C for 10 to 80 hours is effective for improving the magnetic properties.

After the final annealing, the coil is made into a product by removing the remaining annealing separator and then applying an insulating coating if it is necessary to increase the insulation resistance and performing flattening annealing. Further, the product can be applied with a plasma domain, laser or electron beam irradiation, or magnetic domain subdivision technology such as groove formation, which is consistent with the object of the present invention.

[0059]

EXAMPLES Next, the preferred range of the present invention will be described based on examples. First, steel ingot symbols A to S having the composition shown in Table 2 were prepared.

[0060]

[Table 2]

Example 1 A slab having a steel ingot symbol A shown in Table 2 was heated at 1420 ° C. for 15 minutes.
After soaking for 1 minute, a 1.8 mm hot rolled coil was prepared according to a conventional method. The hot-rolled coil was annealed at 1000 ° C. for 60 seconds and then hot-rolled at 120 ° C. to obtain a coil having an intermediate thickness of 1.20 mm, and then split into 28. Each split coil was subjected to intermediate annealing in which nitriding heat treatment and recrystallization heat treatment were performed under the conditions shown in Table 3. The cooling of the intermediate annealing was performed with a mist under all conditions, and was cooled to 500 ° C. at a cooling rate of 40 ° C./sec, after which the mist was cut and gradually cooled.

After cleaning the coils after the intermediate annealing,
The second cold rolling was carried out at a temperature of 150 ° C. to give a final strip thickness of 0.18 mm. After that, degreasing and decarburization annealing at 850 ° C for 2 minutes in wet hydrogen were performed, and MgO containing 5% TiO ₂ and 1% SrSO ₄ was applied as an annealing separator, and wound into a coil. After that, hold at 840 ° C for 40 hours in Ar followed by
The temperature rising process of 15 ° C / hr was performed under 2 atmosphere of N ₂ 25% and H ₂ 75%.
A final finish anneal consisting of a secondary recrystallization anneal and a refining anneal in H ₂ at 1200 ° C. for 10 hours was performed. The coil after the final finish annealing was subjected to flattening annealing at 800 ° C. for 1 minute after applying a tension coating after removing the unreacted separating agent. The magnetic properties of the steel sheet after the flattening annealing were measured and are also shown in Table 3. Next, each coil was irradiated with a plasma jet (PJ) on the surface in a direction perpendicular to the rolling direction at a pitch of 7.5 mm to perform magnetic domain subdivision processing. The iron loss value after PJ irradiation is also shown in Table 3.

[0063]

[Table 3]

As shown in Table 3, for the invention examples subjected to the intermediate annealing conditions satisfying the present invention, thin grain oriented silicon steel sheets having extremely high magnetic flux density were obtained.

Example 2 A slab having a steel ingot symbol B shown in Table 2 was heated at 1430 ° C. for 15 minutes.
After soaking for a minute, a hot rolled coil of 2.0 mm was obtained by hot rolling according to a conventional method. This hot-rolled coil was annealed at 950 ° C. for 70 seconds and then hot-rolled at 150 ° C. to obtain a coil having an intermediate thickness of 1.30 mm and then divided into 10. Nitriding heat treatment was performed on each split coil from the temperature of 700 to 900 ℃.
After nitriding with NH ₃ by slow annealing for sec,
The temperature is raised to 00 ° C and the atmosphere of N ₂ 25% and H ₂ 75% (residual NH
The amount of ₃ was less than 0.05% in each case) and the recrystallization annealing was performed for 60 seconds, and it was rapidly cooled by mist to 80 ° C at a cooling rate of 40 ° C / sec. The atmosphere during the nitriding treatment is
H ₂ : 55%, dew point 40 ℃, NH ₃ concentration 0%, 0.01%, 0.05%, 0.1%, 0.5%, 2.0%, depending on each split coil
The contents were changed to 5.0%, 10%, 15% and 25%, and the balance was balanced with H ₂ gas.

After the nitriding heat treatment, each coil was pickled, and then the second cold rolling was performed at 200 ° C. The coil was wound in each pass and subjected to an aging treatment to obtain a final plate thickness of 0.20 mm. afterwards,
Degreasing and decarburization annealing in wet hydrogen at 850 ℃ for 2 minutes,
Applying MgO with 7% TiO ₂ as an annealing separator,
After winding into a coil, holding in H ₂ at 850 ℃ for 25 hours and the subsequent heating process at 15 ℃ / hr were performed secondary recrystallization in an atmosphere of N ₂ 25% and H ₂ 75%. A final finish anneal consisting of an anneal and a refining anneal in H ₂ at 1200 ° C. for 10 hours was performed. After the final finish annealing, the unreacted separating agent was removed from the coil, a tension coating was applied, and a flattening annealing was performed at 820 ° C. for 1 minute. The magnetic characteristics after the flattening annealing are shown in Table 4 and FIG.
Further, each coil was irradiated with a plasma jet (PJ) at a pitch of 7.5 mm to perform magnetic domain subdivision processing. The results of measuring the iron loss after the magnetic domain subdivision are also shown in Table 4.

[0067]

[Table 4]

As is clear from Tables 4 and 1, the invention examples which were subjected to the nitriding treatment and the recrystallization treatment with the NH ₃ concentration satisfying the present invention produced thin grain oriented silicon steel sheets having extremely high magnetic flux density. There is.

Example 3 A slab of steel ingot symbol C shown in Table 2 was heated at 1410 ° C. for 20
After soaking for a minute, a hot rolled coil of 2.0 mm was formed by a conventional hot rolling. The hot rolled coil was pickled to an intermediate thickness of 1.30 mm, and then subjected to nitriding heat treatment from 700 ℃ to 900 ℃, and annealed by annealing for 40 seconds with NH ₃ 3%, H ₂ 75
%, Dew point 40 ° C., nitriding in an atmosphere of balance N ₂ balance, cooling, and recrystallization annealing at 1050 ° C. for 60 seconds again N ₂ 3
Performed in an atmosphere of 0% and 70% H ₂ and 350
After quenching at 45 ℃ / sec to ℃, hold at 330 ℃ for 25 seconds,
Water cooled. After the nitriding, each coil was pickled, and then the second cold rolling was performed at a temperature of 180 ° C. to obtain a final plate thickness of 0.20 mm, and then the coil was divided into five coils. After that, each coil was degreased and decarburized and annealed in wet hydrogen at 840 ° C for 2 minutes to obtain 7%
Coating a MgO addition of TiO ₂ as an annealing separator, then wound into a coil, but the annealing for 25 hours at 850 ° C. were carried out in N _2, NH this time, in N ₂ to split coil ₃ for each 0
%, 0.05%, 0.1%, 0.3% and 1.0% were mixed and decarburized and annealed. The N content in the steel after decarburization annealing is 0 for each.
The increase was ppm, 3 ppm, 5 ppm, 12 ppm and 25 ppm. After the final annealing, each coil was subjected to a tension coating after removing the unreacted separating agent and subjected to a flattening annealing at 820 ° C. for 1 minute. Table 5 shows the magnetic characteristics after the flattening annealing. Each coil was irradiated with a pulsed laser at a pitch of 5 mm to subdivide the magnetic domain and measure the iron loss. The iron loss value after the pulse laser irradiation is also shown in Table 5.

[0070]

[Table 5]

As shown in Table 5, in decarburization annealing
The magnetic flux density of the steel sheet nitrided above 10 ppm is drastically reduced, whereas in the steel sheet with a nitriding amount of 10 ppm or less specified in this invention, a thin grain oriented silicon steel sheet with an extremely high magnetic flux density is obtained. There is.

Example 4 The slabs of symbols D to S shown in Table 2 were heated to 1420 ° C.
After soaking for 1 minute, a hot rolled coil of 1.8 mm was obtained by hot rolling. However, the slab with the steel ingot symbol H was soaked at 1230 ° C. for 60 minutes and then used as a 1.8 mm hot rolled coil. Each hot-rolled coil was annealed by hot-rolled sheet and then hot-rolled at 120 ° C for 1.20
After forming a coil having an intermediate thickness of mm, it was subjected to intermediate annealing. The intermediate annealing is performed by nitriding heat treatment at 800 ° C for 40 seconds, NH ₃ 4
%, H ₂ 55%, dew point 45 ° C, and the balance after nitriding in an atmosphere of N ₂ balance, H ₂ 80%, dew point 15 ° C, NH ₃ 0.03
%, Heating up to 1100 ° C under an atmosphere of balance N ₂ and
After recrystallization annealing at 00 ℃ for 60sec, 350 ℃ with mist
It was rapidly cooled at 35 ° C / sec until it was kept at 330 ° C for 20 sec and cooled with water.

After the intermediate annealing, each coil was pickled, and then the second cold rolling was performed at a temperature of 180 ° C. At that time, each coil was wound up in each rolling pass and subjected to an aging treatment to obtain 0.18 mm. The final plate thickness was used. After that, degreasing and decarburization annealing at 850 ° C for 2 minutes in wet hydrogen, and applying MgO with 5% TiO ₂ and 1% Sr (OH) ₂ · 8H ₂ O as an annealing separator, After winding into a coil, N ₂ atmosphere up to 850 ℃, N ₂ 20%, H ₂ 80% up to 850 to 1150 ℃, H ₂ atmosphere up to 1150 to 1200 ℃, heating rate 15 to 20 ℃ heating at 1200 / hr for 10 hours at 1200 ℃
Purification annealing was performed in an H ₂ atmosphere. Then, after removing the unreacted separating agent, each coil is coated with tension coating to 800
Flattening annealing was performed at 1 ° C. for 1 minute. Table 6 shows the magnetic characteristics after the flattening annealing. Next, each coil was irradiated with a plasma jet (PJ) at a pitch of 7.5 mm, subjected to magnetic domain subdivision processing, and iron loss was measured. The iron loss value after the plasma jet irradiation is also shown in Table 6.

[0074]

[Table 6]

Example 5 Each of the slabs indicated by the symbols A, B and C shown in Table 2 was heated 1410
After soaking at ℃ for 20 minutes, hot rolling was performed to obtain 1.8 mm hot rolled coil. When performing hot-rolled sheet annealing on each hot-rolled coil, first, as nitriding heat treatment, the temperature is raised from 700 ° C to 900 ° C for 60 seconds while containing 5% of NH ₃ , 60% of H ₂ and 45% of dew point. The balance of N ₂ balance is maintained at ℃, followed by recrystallization annealing at 1150 ℃ for 60 seconds in an atmosphere of NH ₃ less than 0.1%, followed by rapid cooling at 40 ℃ / sec using mist. And

Then, each coil was pickled to remove the scale and then cold-rolled once at a temperature of 180 ° C. to 0.22 mm.
The final thickness of After that, degreasing and 850 in wet hydrogen
Decarburization annealing at ℃ for 2 minutes, 5% TiO ₂ and 1% SrSO ₄
MgO with added is applied as an annealing separator, wound into a coil, and kept in N ₂ at 850 ℃ for 40 hours, then N ₂ 2
5%, H ₂ 75% of the atmosphere until 1200 ℃ 12 ℃ / hr of heating rate heating to secondary recrystallization annealing, further 1200 ° C. for 10 hours H ₂
After performing the final finishing annealing which was held in the inside, the furnace was cooled.

After removing the unreacted separating agent from each coil, a tension coating was applied and flattening annealing was performed at 800 ° C. for 1 minute. Table 7 shows the magnetic characteristics after the flattening annealing. Each coil has a plasma jet (PJ) of 7.5.
The magnetic domain was subdivided by irradiation with mm pitch. The iron loss value after the magnetic domain subdivision treatment is also shown in Table 7.

[0078]

[Table 7]

[0079]

As described above, according to the present invention, it is possible to produce a grain-oriented silicon steel sheet having excellent magnetic properties, which can maintain the normal grain growth suppressing force of the steel sheet surface despite the reduction of the steel sheet thickness. To enable.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an NH ₃ concentration in a nitriding heat treatment and a magnetic flux density after secondary recrystallization annealing.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-125446 (JP, A) JP-A-4-168222 (JP, A) JP-A-2-259019 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 C22C 38/00-38/60 H01F 1/16-1/18

Claims (3)

(57) [Claims] 1. C: 0.02 to 0.09 wt%, Si: 2.5 to 5.0 wt%
%, Mn: 0.02 to 0.3 wt%, Al: 0.01 to 0.04 wt %, Sb: 0.
Contains 005 to 0.060 wt% and N: 0.0055 to 0.0095 wt%
Then, a silicon steel slab consisting of the balance Fe and unavoidable impurities is hot-rolled to a final thickness of one cold-rolling reduction ratio of 80 to 95%.
And one cold rolling before and after the first rolling to achieve the final plate thickness, followed by decarburization annealing, and then applying an annealing separator. In the method for producing a grain-oriented silicon steel sheet comprising a series of production steps for subjecting the sheet to final finishing annealing, the annealing performed before one cold rolling to obtain the final sheet thickness is divided into a first stage and a second stage, In the first stage, 30 to 90 seconds at a temperature in the range of 750 to 850 ℃
Or soaking in the temperature range of 700 to 900 ° C for 30 to 90 seconds, the annealing atmosphere contains 0.1 to 10% of NH _3, and contains 20 to 80% of H ₂ , and the dew point of 20 to The balance is N ₂ at 60 ° C
A balanced nitriding heat treatment is performed, and in the second step, subsequently, a recrystallization heat treatment is performed in which the NH ₃ concentration is regulated to less than 0.1% at a temperature of 1050 to 1200 ° C for 30 to 90 seconds, and decarburization is performed. A method for manufacturing a grain-oriented silicon steel sheet having a high magnetic flux density, characterized by the combination of suppressing the increase of N content after the annealing step to 10 wtppm or less. 2. The silicon steel slab according to claim 1,
Furthermore, one or two of S and Se in total 0.005 to 0.040 wt%
A method for producing a grain-oriented silicon steel sheet having a high magnetic flux density, which is characterized by containing. 3. The silicon steel slab according to claim 1 or 2, wherein the silicon steel slab further comprises Cu, Sn, P, Bi, As, B, Ge, V, Nb and Cr. , Sn and Cr are each 0.03-0.30 wt%, Bi is 0.005-0.020 wt%, P, Ge, V, Nb and As are each 0.005-0.030 wt%.
%, B is contained in the range of 0.0005 to 0.0020 wt%, a method for producing a grain-oriented silicon steel sheet having a high magnetic flux density.