JP2574607B2 - Method for producing grain-oriented silicon steel sheet with excellent coating properties without iron loss deterioration due to strain relief annealing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet which is suitable for use in applications such as iron cores of transformers and other electric equipment, and more particularly to a steel sheet having good coating properties and capable of reducing iron loss due to strain relief annealing. An object of the present invention is to propose a method for advantageously producing a low-oriented silicon steel sheet.

[0002]

2. Description of the Related Art The properties required of a grain-oriented silicon steel sheet include not only good magnetic properties as the steel sheet itself,
In order to ensure good insulation between the steel sheets stacked in the iron core processing, there are coating properties such as insulation properties on the steel sheet surface coating and peel resistance during processing. In order to improve the film properties of such a steel sheet, it is important to improve the adhesion of the forsterite film generated during finish annealing.

[0003] With respect to the improvement of forsterite coating, many techniques have been disclosed in which an annealing separator applied to the surface of a steel sheet prior to finish annealing contains a Ti compound such as TiO ₂ in addition to MgO as a main component. For example, in Japanese Patent Publication No. 51-12451, a Ti compound is contained in an amount of 2 to 40 with respect to 100 parts by weight of a Mg compound.
By blending so that it becomes part by weight,
JP-29409 discloses that 2 parts per 100 parts of heavy low activity fine MgO
It is disclosed that the uniformity and adhesion of the forsterite film are improved by mixing TiO2 parts by weight of TiO ₂ . Further JP 50-145315, Japanese, technology to eliminate the black dot deposits consisting of Ti compound by the TiO ₂ used in the annealing separator and the fine particle, JP 54-12892
No. 8 discloses a method of strengthening the tension of a forsterite film by adding MgO to TiO ₂ and SiO ₂ , and further a boron compound.
_The technology has been developed to improve iron loss by compounding ₂ , antimony sulfate and manganese nitride or ferromanganese nitride.

[0004] The technique of including a Ti compound in the annealing separator is a powerful method for obtaining excellent film properties, but as described in Japanese Patent Application Laid-Open No. 2-93021, the technique of distorting a Ti compound is disclosed. There is a serious problem that iron loss is deteriorated by removing annealing.

[0005] Here, about half of transformer cores using a grain-oriented silicon steel sheet are small core-type cores called wound cores. This wound core is subjected to mechanical external force in the deformation process during the production and produces distortion, resulting in deterioration of magnetic properties. Therefore, in order to recover the distortion due to this processing, strain relief annealing is usually performed at around 800 ° C. It is inevitable to do it. However, when a Ti compound is contained in the annealing separator as described above, carbides of Ti, or selenides and sulfides of Ti are preferentially precipitated in the portion of the surface layer of the base iron into which the processing strain has been introduced by strain relief annealing. However, it is known that core loss deteriorates because the movement of the domain wall is partially prevented. Therefore, it has been desired that the material steel sheet for the wound core has a small deterioration of iron loss even when subjected to strain relief annealing.

To address the problem that the inclusion of a Ti compound in the annealing separator deteriorates iron loss after strain relief annealing, Japanese Patent Application Laid-Open No. 2-93021 discloses a method in which the carbon content after finish annealing is reduced to 0.0015 wt. % By precipitation
A solution to reduce Ti carbides is proposed. However, this technology is difficult in actual operation to suppress the absorption of carbon dioxide into MgO.
Since it is impossible in principle to reduce precipitates such as sulfides and selenides of Ti, iron loss deterioration during strain relief annealing cannot be completely suppressed.

[0007]

SUMMARY OF THE INVENTION The present invention solves the problem that iron loss deteriorates after strain relief annealing when a Ti compound is contained in the annealing separator. An object of the present invention is to propose a method for producing a silicon steel sheet having good film properties without loss and deterioration.

[0008]

Means for Solving the Problems The present inventors have repeated various experiments and studies on measures to prevent deterioration of iron loss due to strain relief annealing even when an annealing separator containing a Ti compound is used. As a result, by setting the initial stage of the purification annealing in which a film is formed on the surface of the steel sheet to a nitrogen-containing atmosphere, it is possible to advantageously suppress the precipitation of carbides of Ti or selenides of Ti or sulfides on the surface layer of the steel sheet. It has been found that iron loss deterioration can be advantageously prevented. The present invention is based on the above findings.

That is, the present invention is directed to a grain-oriented silicon steel sheet which is subjected to a secondary recrystallization annealing and then a purification annealing after applying an annealing separator containing MgO as a main component on the surface of the silicon steel sheet after the decarburizing annealing. In the production method of the above, a Ti oxide or a Ti compound which becomes a Ti oxide by heating is added to the annealing separator by MgO: 10
0 to 40 parts by weight of TiO _{2 based on} 0 parts by weight, and purification annealing in the range of 1150 to 1250 ° C.
From the beginning, at least until a time t (min) given by the following formula, in a non-oxidizing atmosphere with a nitrogen concentration of 10 vol% or more, and then in a hydrogen atmosphere with a nitrogen concentration of less than 3 vol%, the Ti content in the base iron Reduced to 30 ppm or less,
This is a method for producing a grain-oriented silicon steel sheet having excellent film properties without iron loss deterioration due to strain relief annealing. Description t (min) = 668 -19.1 x +0.171 x ² -4.42 x 10 ^-4 x ³ where x: nitrogen concentration in atmosphere (vol%)

An experiment which led to the present invention will be described below. C: 0.078 wt% (hereinafter simply indicated as%), Si: 3.3%, Mn: 0.0
83%, Se: 0.025%, Al: 0.020%, N: 0.0089%, Sb: 0.0
A silicon steel material containing 25% and 0.09% of Cu and substantially having a balance of Fe was heated at 1420 ° C. for 20 minutes, and then subjected to hot rolling to finish to a sheet thickness of 2.2 mm. Subsequently, hot-rolled sheet annealing was performed at 1000 ° C. for 30 seconds, and a sheet thickness of 1.5 mm was obtained by cold rolling.
After intermediate annealing at 00 ° C. for 2 minutes, the steel sheet was rapidly cooled at 30 ° C./second, and further finished by cold rolling to a final sheet thickness of 0.22 mm.

Thereafter, decarburizing annealing is performed at 840 ° C. for 2 minutes in a humid hydrogen atmosphere, and then TiO ₂ is added to 100 parts by weight of MgO.
Is added to the surface of the steel sheet by 10% by weight, and the secondary recrystallization annealing is performed at a rate of 20 ° C / sec to 1150 ° C in a mixed atmosphere of 25vol% nitrogen and 75vol% hydrogen. And then perform purification annealing at 1180 ° C from the beginning of the purification annealing.
Various times up to 60 minutes for nitrogen 75 vol%, hydrogen 25 vol%
And the remaining 5 hours in hydrogen. After this purification annealing, an insulating coating mainly composed of magnesium phosphate was applied.

The product sheet thus obtained is subjected to strain relief annealing at 800 ° C. for 3 hours, and iron loss before and after the strain relief annealing (W _17/50 )
Were compared. Furthermore, the Ti content inside the base steel of the product plate was determined by wet analysis.

FIG. 1 summarizes the experimental data, and FIG. 1 shows the effect of the purification annealing time on the iron loss change before and after the strain relief annealing in a mixed atmosphere of 75 vol% nitrogen and 25 vol% hydrogen, and FIG. Fig. 3 shows the effect of the time of purification annealing in the mixed atmosphere of 75 vol% nitrogen and 25 vol% hydrogen on the amount of Ti in the product sheet iron. The relationship with the amount of change in iron loss before and after annealing is shown.

From the results of these experiments (FIGS. 1 to 3), if the amount of Ti in the product sheet iron is 30 ppm or less, the amount of deterioration of iron loss due to strain relief annealing can be reduced to less than 0.02 W / kg, and If the annealing time is 30 minutes or more in a mixed atmosphere of 75 vol% nitrogen and 25 vol% hydrogen in the first half of annealing, the amount of Ti in
It was clarified that it can be reduced to below ppm.

Based on the above results, furthermore, various changes in the nitrogen concentration in the atmosphere in the first half of the purification annealing are performed to minimize the amount of Ti in the atmosphere necessary for reducing the Ti content in the product sheet iron to 30 ppm or less. I checked about time. FIG. 4 shows the results in relation to the nitrogen concentration and the required holding time.

[0016] From this figure, the required retention time t (min) in relation to the nitrogen concentration x in the atmosphere (vol%), t ^{(min) = 668 -19.1x + 0.171 x 2} -4.42 × 10 - It was found to be represented as ⁴ × ³ . As described above, the necessary holding time is 30 minutes when the nitrogen partial pressure is 75% or more, but requires 5 hours when the nitrogen partial pressure is about 25%. Based on these experimental results, the present invention has been achieved.

[0017]

The reason why the present invention can prevent iron loss deterioration due to strain relief annealing is not always clear, but the inventors consider as follows. That is, the Ti compound contained in the annealing separator has a role of reacting with SiO ₂ in a form mixed with MgO to form a black base coat. However, the remaining portion of Ti used for forming the film is diffused by the high temperature due to the purification annealing and moves into the base iron.
Thus, due to the presence of Ti in the base steel, C,
In the part where the processing strain is introduced by combining with Se or N, Ti carbide or selenide or nitride is preferentially precipitated after strain relief annealing to cause magnetic deterioration. In contrast, in the present invention, by introducing nitrogen in the first half of the purification annealing, the remaining Ti combines with nitrogen inside the coating and is fixed as TiN in the coating, so It is considered that diffusion is suppressed, and as a result, precipitation of carbides, selenides or nitrides of Ti is suppressed, and deterioration of iron loss can be prevented.

Regarding the component composition of the silicon steel material which is the object of the present invention, those having a range usually used as a grain-oriented silicon steel sheet can be used. For example, C: 0.02
Preferred is a composition containing 0.1 to 0.10%, Si: 2.0 to 4.0%, Mn: 0.02 to 0.20%, and containing at least one of S and Se alone or in a total amount of 0.010 to 0.040%. In addition, if necessary, Al: 0.010 to 0.065%, N: 0.0010 to 0.01
50%, Sb: 0.01 to 0.20%, Cu: 0.02 to 0.20%, Mo: 0.01
-0.05%, Sn: 0.02-0.20%, Ge: 0.01-0.30%, Ni:
0.02 to 0.20%.

If C is less than 0.02%, a good primary recrystallized structure cannot be obtained, and if it exceeds 0.10%, decarburization becomes poor and the magnetic properties deteriorate, so that C is preferably about 0.03 to 0.10%. Si
Is a necessary component to increase the electrical resistance of the product and reduce the eddy current loss. If it is less than 2.0%, the crystal orientation is impaired by α-γ transformation during final finish annealing, and if it exceeds 4.0%, Since there is a problem in cold rolling, the content is preferably about 2.0 to 4.0%. Mn, Se and S function as inhibitors. If the amount of Mn is less than 0.02% or the amount of S or Se alone or the total amount is less than 0.010%, the inhibitor function is insufficient, and the amount of Mn exceeds 0.20%. Alternatively, if S or Se alone or in total exceeds 0.040%, the temperature required for the slab heating temperature is too high to be practical, so that Mn is 0.02 to 0.20%,
S or Se is preferably used alone or in a total amount of 0.010 to 0.040%.

In addition, AlN known as an inhibitor component can be used, and in order to obtain good iron loss, Al is preferably in the range of 0.010 to 0.065%, and N is preferably in the range of 0.0010 to 0.0150%. If the amount exceeds this, the AlN becomes coarse and loses its suppressing power. If the amount is less than this, the amount of AlN is insufficient.

In order to further improve the magnetic flux density, Sb, Cu
Can be reduced. If Sb exceeds 0.20%, the decarburization property deteriorates, and if it is less than 0.01%, there is no effect.
0.01-0.20% is preferred. If the content of Cu exceeds 0.20%, the pickling property deteriorates, and if it is less than 0.01%, there is no effect.
% Is preferred.

Mo can be added to improve the surface properties. If it exceeds 0.05%, the decarburization property deteriorates, and if it is less than 0.01%, there is no effect, so 0.01 to 0.05% is preferable.

In order to improve iron loss, Sn, Ge and Ni can be added. If the content of Sn exceeds 0.30%, a good primary recrystallized structure cannot be obtained, and if it is less than 0.01%, there is no effect.
01-0.30% is preferred. If Ge exceeds 0.30%, a good primary recrystallized structure cannot be obtained, and if it is less than 0.01%, there is no effect, so 0.01 to 0.30% is preferable. If the Ni content exceeds 0.20%, the hot strength decreases, and if it is less than 0.01%, there is no effect.
20% is preferred.

In the production of a grain-oriented silicon steel sheet, which is the object of the present invention, molten steel obtained by a conventional steelmaking method is cast by a continuous casting method or an ingot-forming method, and if necessary, is subjected to slab rolling. A slab is obtained by sandwiching the process, followed by hot rolling and, if necessary, hot-rolled sheet annealing, and then cold rolling of the final sheet thickness by one or two or more cold-rolling steps of intermediate annealing. Get the board.

After decarburizing annealing after the final cold rolling, an annealing separator is applied to the surface of the steel sheet. At this time, Ti oxide or a Ti compound which becomes Ti oxide by heating as an annealing separator is used.
It is important that MgO be contained in the range of 1.0 to 40 parts by weight in terms of TiO _{2 with} respect to 100 parts by weight. Examples of Ti oxides or Ti compounds that become Ti oxides by heating include TiO ₂ ,
TiO ₃ .H ₂ O, TiO. (OH) ₂ , Ti (OH) _{4 and the} like. If the amount of the Ti oxide in the annealing separator or the Ti compound which becomes a Ti oxide by heating is less than 1.0 part by weight with respect to 100 parts by weight of MgO in terms of TiO ₂ , the effect of improving the film properties is poor, and 40 parts by weight. If it exceeds, the brittleness suddenly worsens,
1.0 to 40 parts by weight.

Next, a secondary recrystallization annealing is performed, followed by a purification annealing in a temperature range of 1150 to 1250 ° C. from the beginning until at least a time t (min) given by the following formula, the nitrogen concentration is 10 vol%.
In the above non-oxidizing atmosphere, then nitrogen concentration 3 vol%
It is performed in a hydrogen atmosphere of less than. Serial ^{t = 668 -19.1x + 0.171 x 2} -4.42 × 10 -4 x 3 temperature purification annealing here is less than 1150 ° C. When Se to S
Etc. are insufficiently removed and the magnetic properties deteriorate, while 1250
If the temperature exceeds 100 ° C, the hot strength decreases, the coil shape deteriorates, and winding cannot be performed.
Set to 50 ° C. Nitrogen concentration in the first half atmosphere of purification annealing is 10 v
If the concentration is less than ol%, Ti will penetrate into the base iron and iron loss will be degraded by strain relief annealing, so the nitrogen concentration is preferably higher,
At least 10 vol%. The remaining atmosphere components may be non-oxidizing in order to form TiN preferentially, and include a hydrogen atmosphere and an inert gas atmosphere. The time for annealing at such a nitrogen concentration of 10 vol% or more depends on the nitrogen concentration in the atmosphere, and is not less than the time t (min) shown in the above equation in relation to the nitrogen concentration x (vol%). .
If this time is less than t (minutes), Ti penetrates into the base iron, and iron loss deteriorates due to strain relief annealing. If the nitrogen concentration in the latter half of the purification annealing is 3 vol% or more, nitrogen remains in the base iron after annealing and the magnetic properties deteriorate rather, so the nitrogen concentration in the latter half is less than 3 vol%.

Thereafter, an insulating coating, preferably an insulating coating for imparting tension, is applied to obtain a product.

[0028]

【Example】

Example 1 C: 0.044%, Si: 3.23%, Mn: 0.075%, Se: 0.021
%, Sb: 0.026%, and the balance substantially consisting of Fe was heated at 1420 ° C. for 30 minutes, and then hot-rolled to obtain a hot-rolled sheet having a sheet thickness of 2.0 mm. Next, after annealing at 1000 ° C. for 1 minute, the sheet was cold-rolled to a sheet thickness of 0.60 mm.
After intermediate annealing for 2 minutes, cold rolling was performed to finish to a final thickness of 0.20 mm. Next, decarburization annealing is performed at 820 ° C. for 2 minutes to obtain 100 parts by weight of MgO as shown in Table 1.
After applying the annealing separator containing TiO ₂ to the steel sheet surface,
Secondary recrystallization annealing was performed in a nitrogen atmosphere at 850 ° C. for 50 hours. Subsequently, purification annealing was performed at 1200 ° C. in the atmosphere and time shown in Table 1. After the purification annealing, an insulating coating composed of colloidal SiO ₂ , magnesium phosphate and chromic anhydride was applied. Thereafter, the steel sheet was plastically worked into a toroidal shape, stretched linearly, and then subjected to strain relief annealing at 800 ° C. for 3 hours. Table 1 also shows the iron loss after the coating and after the strain relief annealing.

[0029]

[Table 1]

Example 2 C: 0.071%, Si: 3.34%, Mn: 0.069%, S: 0.021
%, Al: 0.025%, N: 0.0083%, Cu: 0.12%, Sb: 0.2%
A silicon steel slab containing 029% and substantially the balance of Fe is heated at 1430 ° C. for 30 minutes and then subjected to hot rolling to obtain a sheet thickness of 2.
A 2 mm hot rolled sheet was used. Next, after hot-rolled sheet annealing at 1000 ° C for 1 minute, cold-rolled to a sheet thickness of 1.5 mm, intermediate annealing at 1100 ° C for 2 minutes, and cooling at a rate of 30 ° C / sec,
Cold rolling was performed to obtain a final thickness of 0.23 mm. Then 8
After decarburizing annealing at 20 ° C for 2 minutes, an annealing separator containing TiO ₂ containing 100 parts by weight of MgO and containing TiO ₂ as shown in Table 2 was applied to the surface of the steel sheet, and then nitrogen at 850 ° C for 20 hours. This was kept in an atmosphere and subsequently subjected to secondary recrystallization annealing in which the temperature was raised to 1150 ° C. at a rate of 12 ° C./h in an atmosphere of 75 vol% of hydrogen and 25 vol% of nitrogen. Subsequently, the atmosphere and time shown in Table 2 were used for 1200
Purification annealing was performed at ℃. After the purification annealing, an insulating coating composed of colloidal SiO ₂ , magnesium phosphate and chromic anhydride was applied. Thereafter, the steel sheet was plastically worked into a toroidal shape, stretched linearly, and then subjected to strain relief annealing at 800 ° C. for 3 hours. Table 2 also shows the iron loss after coating and after strain relief annealing.

[0031]

[Table 2]

Example 3 Silicon steel slabs having various component compositions shown in Table 3 were prepared.

[0033]

[Table 3]

After heating these silicon steel slabs at 1430 ° C. for 30 minutes, they were subjected to hot rolling to obtain hot-rolled sheets having a thickness of 2.2 mm. After hot-rolled sheet annealing at 1000 ° C for 1 minute, cold-rolling to 1.5mm thickness, intermediate annealing at 1100 ° C for 2 minutes, cold-rolling to final thickness of 0.23mm Finished.
Next, decarburizing annealing was performed at 820 ° C for 2 minutes, and an annealing separator containing 10 parts by weight of TiO ₂ per 100 parts by weight of MgO was applied, and then kept at 850 ° C for 20 hours in a nitrogen atmosphere. Subsequently, secondary recrystallization annealing in which the temperature was raised to 1150 ° C. at a rate of 12 ° C./h in an atmosphere of 75 vol% of hydrogen and 25 vol% of nitrogen was performed. Next, the first 5 hours consisted of 50 vol% hydrogen and 50 v nitrogen.
ol% atmosphere, the last 5 hours in a hydrogen atmosphere 1200
Purification annealing was performed at an annealing temperature of ° C. After the purification annealing, an insulating coating composed of colloidal SiO ₂ , magnesium phosphate and chromic anhydride was applied. Thereafter, the steel sheet was plastically worked into a toroidal shape, stretched linearly, and then subjected to strain relief annealing at 800 ° C. for 3 hours. Table 3 also shows the iron loss difference between after coating and after strain relief annealing.

[0035]

According to the method for manufacturing a grain-oriented silicon steel sheet of the present invention, a Ti oxide or a Ti compound which becomes a Ti oxide by heating is used as an annealing separator in the form of TiO _{2 in} terms of TiO _{2 with} respect to 100 parts by weight of MgO.
0 to 40 parts by weight and purification annealing of 1150 to
In the range of 1250 ° C., initially at least the following formula t ^{(min) = 668 -19.1x + 0.171 x 2} -4.42 × 10 -4 x 3 ( here x: the concentration of nitrogen in the atmosphere (vol%)) is given by Until the time t (min), in a non-oxidizing atmosphere with a nitrogen concentration of 10 vol% or more, and then in a hydrogen atmosphere with a nitrogen concentration of less than 3 vol%, the Ti content in the base iron is reduced to 30 ppm or less. No iron loss deterioration due to strain relief annealing,
A silicon steel sheet having good coating characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the time of purification annealing in a nitrogen-containing atmosphere on the amount of change in iron loss before and after strain relief annealing.

FIG. 2 is a graph showing the effect of the time of purification annealing in a nitrogen-containing atmosphere on the amount of Ti in a product sheet iron.

FIG. 3 is a graph showing the relationship between the amount of Ti in a product sheet metal and the amount of change in iron loss before and after strain relief annealing.

FIG. 4 is a graph showing the effect of the nitrogen concentration in the first half of the purification annealing on the required holding time.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masataka Yamada 2-88 Wakihama Kaigandori, Chuo-ku, Kobe City, Hyogo Prefecture Inside the Hanshin Works of Kawasaki Steel Corporation (72) Inventor Tetsuya Oishi 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (Without address) Kawasaki Steel Corporation Mizushima Works (72) Inventor Shigeru Yoshida 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture Kawasaki Steel Corporation Mizushima Works (72) Inventor Hiroshi Shimizu Kurashiki, Okayama Prefecture 1-chome Kawasaki-dori, Mizushima-shi (without address) Kawasaki Steel Corporation Mizushima Works

Claims (1)

(57) [Claims] [1] MgO on the surface of a silicon steel sheet after decarburizing annealing.
In the method for producing a grain-oriented silicon steel sheet, which is subjected to a secondary recrystallization annealing and then a purification annealing after applying an annealing separating agent containing as a main component, a Ti oxide or a Ti oxide by heating is applied to the annealing separating agent. Ti compound was converted to TiO _{2 by} 1.100 parts by weight of MgO: 1.
0 to 40 parts by weight, and purifying annealing.
In the range of 1150 to 1250 ° C., from the beginning, in a non-oxidizing atmosphere having a nitrogen concentration of 10 vol% or more, at least until a time t (minute) given by the following formula, and then in a hydrogen atmosphere having a nitrogen concentration of less than 3 vol% reducing Ti content in the row have a base steel to 30ppm or less
A method for producing a grain-oriented silicon steel sheet having excellent coating properties without iron loss deterioration due to strain relief annealing. Description t (min) = 668 -19.1 x +0.171 x ² -4.42 x 10 ^-4 x ³ where x: nitrogen concentration in atmosphere (vol%)