JPH07278674A - Manufacture of grain-oriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PURPOSE:To manufacture the grain-oriented silicon steel sheet excellent in the magnetic property in an industrially stable manner by respectively prescribing the atmospheric gases for the secondary re-crystallization annealing and the purifying annealing in the finish annealing of the grain-oriented silicon steel sheet containing Si of a specific amount. CONSTITUTION:The grain-oriented silicon steel sheet containing 0.8-6.8wt.% Si is primary re-crystallization annealed in common with the decarburization in the wet gas after the cold rolling. The steel sheet is nitrided to increase the nitrogen content to reinforce the nitride as the inhibitor. One or more kinds of Al, Ti, V, Nb, Zr, Ta and Cr is preferably used as the element to form the nitride contained in the grain- oriented silicon steel sheet. Then, the separation agent for annealing is coated on this steel sheet to perform the finish annealing. The partial pressure of nitrogen in the atmospheric gas for the finish annealing is >=1 atm during the secondary re- crystallization annealing, the nitride is further reinforced to stabilize the high magnetic flux density, and 100% hydrogen gas is realized in the purifying annealing to purify the nitride. The grain-oriented silicon steel sheet with high magnetic flux density is obtained through the specific treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is mainly used as an iron core for transformers and other electric devices, etc. {110} <00
1> or {100} <001> orientation integration is highly developed and it relates to a method for producing a so-called grain-oriented electrical steel sheet (unidirectional or bidirectional).

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets have a Miller index of {11.
0.8% to 6.8% of Si, which is composed of crystal grains accumulated in the 0} <001> or {100} <001> orientation.
It is a steel plate containing (usually about 3%). This steel plate is required to have excellent magnetic excitation properties and iron loss properties. In order to satisfy the required characteristics, it is important to make the orientation of crystal grains highly aligned, and normally, the magnetic flux density (B) when the integration degree is excited by a magnetic field of 800 A / m
₈ values). The crystal orientation control to the {110} <001> or {100} <001> orientation is achieved by utilizing a catastrophic grain growth phenomenon called secondary recrystallization. In order to control the secondary recrystallization, it is essential to adjust the primary recrystallization structure before the secondary recrystallization and to adjust the fine precipitates or grain boundary segregation type elements called inhibitors.

Until now, MnS (JE May
& D. Turnbull: Trans. Met. Soc. AIME212 (1958) p76
9), AlN (Taguchi, Sakakura: Japanese Patent Publication No. 40-15644), (Al, Si) N (Komatsu et al., Japanese Patent Publication No. 62-45)
No. 285) is effective.
As the grain boundary segregation type element, Saito has Pb, Sb, Nb,
Show that Ag, Te, etc. are effective (Journal of Japan Institute of Metals)
27 (1963) p186, p191), but it is industrially used only as a supplement of a precipitate-type inhibitor. This inhibitor is {1 in the primary recrystallization structure.
It has a function of suppressing the growth of crystal grains other than the 10} <001> or {100} <001> oriented grains and preferentially growing these orientations.

The conditions necessary for these precipitates to function as an inhibitor are considered as follows. (1) Before the secondary recrystallization, the amount of fine precipitates becomes sufficient to suppress the grain growth of primary recrystallized grains. (2) No sudden thermal change occurs during the secondary recrystallization annealing. At present, there are four typical methods for producing a grain-oriented electrical steel sheet. The first technique is M. F. The double cold rolling method using MnS disclosed in Littmann et al. In Japanese Examined Patent Publication No. 30-3651, and the second technique is Al disclosed in Japanese Examined Patent Publication No. 40-15644 by Taguchi and Sakakura.
The one-time cold rolling method using N + MnS, the third technique is the two-time cold rolling method using MnS (or MnSe) + Sb disclosed in Japanese Patent Publication No. 51-13469, and the fourth technique is The technique of (Al, Si) N disclosed in Japanese Patent Publication No. 62-45285 by Komatsu et al.
The one-time cold rolling method using.

There are two types of typical bidirectional electrical steel sheet manufacturing methods. The first technology is Japanese Patent Publication No. 35-26
According to the cross cold rolling method using AlN + MnS disclosed in Japanese Patent Application Laid-Open No. 57-57, the second method is JP-A-2-14153.
This is based on the cross cold rolling method using (Al, Si) N disclosed in Japanese Patent Publication No. From the viewpoint of inhibitors, these techniques are classified into (1) high-temperature slab heating in the hot rolling step and (2) precipitating a precipitate by nitriding.

[0006]

However, the fine precipitates formed by these methods greatly change depending on the coil site until the secondary recrystallization occurs during the actual finish annealing, and the secondary recrystallization occurs. The defect or magnetic defect has not been completely resolved. An object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet that avoids such problems and is industrially stable and has excellent magnetic properties.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted studies for solving the above problems, and have concluded that it is important to suppress the deterioration of the inhibitor during finish annealing. Experiments were conducted based on these results, and as a specific condition, a nitride was used as an inhibitor, and by increasing the nitrogen partial pressure of the atmosphere gas at the time of finish annealing to 1 atm or more, the inhibitor and the secondary recrystallization were It was found that it can be stabilized.

The details will be described below. By weight, Si:
3.3%, Mn: 0.14%, C: 0.05%, S:
0.007%, acid-soluble Al: 0.028%, N: 0.
A 008% silicon steel slab was heated at 1150 ° C. and then hot-rolled to a plate thickness of 1.6 mm. The hot rolled sheet was annealed at 1100 ° C. for 2 minutes and then cold rolled to a final sheet thickness of 0.15 mm. This cold-rolled sheet was annealed at 830 ° C. for 70 seconds in wet gas for decarburization to perform primary recrystallization. Then, the amount of nitrogen was increased to 0.02% by ammonia nitriding to strengthen the inhibitor. After applying an annealing separator to this decarburized annealed plate, finish annealing was performed.

In the finish annealing, the temperature was raised to 1100 ° C. at 20 ° C./hr, and the temperature was maintained at 1100 ° C. for 15 hours for secondary recrystallization. The atmosphere gas for this secondary recrystallization annealing is (1) N ₂ + H
₂ mixed gas, N _{2 in} 1 atm: 0 to 100%, or
(2) N ₂ gas: Performed at 1 to 2 atm to investigate the influence of nitrogen partial pressure. Then, H _2: 100% in switching 1200 ℃
Then, a purification annealing was performed for 20 hours. The magnetic properties of these samples are shown in FIG.

From these results, it is understood that the variation of the magnetic flux density (B ₈ ) is reduced by setting the nitrogen partial pressure to 1 atm or more, and a product having a high magnetic flux density can be stably manufactured. This is probably because the nitride basically decomposes when the nitrogen partial pressure is low, and the nitrogen permeability varies due to the dispersion of the oxide film at the interface, resulting in different stability of the nitride. To be It is considered that such variations in the inhibitor amount during the finish annealing make the secondary recrystallization unstable.

Embodiments will be described below. As a basic manufacturing method, for example, JP-B-40-15644 may be applied as the unidirectional electrical steel sheet, and JP-B-62-45285 may be applied as the bidirectional electrical steel sheet. Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.8%, the material is likely to crack during cold rolling, which necessitates warm rolling. The upper limit is set to 6.8% at which the effect of improving the magnetic characteristics is rapidly diminished. On the other hand, if the amount of Si is reduced, α → γ transformation occurs during finish annealing, and the crystal orientation is impaired. Therefore, the lower limit is 0.8%, which does not substantially affect the crystal orientation.

As the nitride-forming element, Al, Ti, V,
Nb, Zr, Ta and Cr are effective. It is effective to add two or more of these elements in combination. In particular, Al is an effective element that combines with N to function as an inhibitor as AlN or (Al, Si) N. If N is added in an amount of 0.01% or more at the time of steel making, voids in the steel sheet called blister are generated, so 0.01% is made the upper limit. In order to suppress the growth of primary recrystallized grains as an inhibitor, it is necessary to nitride the primary recrystallized grains to 0.01% or more. Sn, Sb, Bi, Se, Pb, S, which are grain boundary segregation elements, may be supplementarily added as an inhibitor constituent element.

The molten steel having the above components is formed into a hot-rolled sheet by a usual process, or the molten steel is continuously cast into a ribbon. The hot-rolled sheet or the continuously cast ribbon is immediately or cold-rolled after annealing for a short time. The above annealing is 750
The annealing is performed in a temperature range of ~ 1200 ° C for 30 seconds to 30 minutes, and this annealing is effective for enhancing the magnetic properties of the product. It is advisable to decide whether to accept or reject the product considering the characteristic level and cost of the desired product.

In the cold rolling, a final cold rolling compression ratio of 80% or more for unidirectional electrical steel sheets, and 40-80% and 30-70% cross cold rolling for bidirectional electrical steel sheets. You can give it. The material after cold rolling is subjected to primary recrystallization annealing in a temperature range of 750 to 900 ° C. in which removal of carbon contained in steel is combined. This primary recrystallization annealed plate is subjected to a nitriding treatment to form a nitride as an inhibitor. The method of this nitriding treatment is not particularly limited, and there is a method of annealing in an atmosphere gas having a nitriding ability such as ammonia, or a method of performing it during finish annealing. Quantitatively, 0.005% or more, preferably, the total nitrogen content should be equal to or more than the nitride equivalent in the steel.

An annealing separator is applied to these primary recrystallization annealed plates and finish annealing is applied. Japanese Unexamined Patent Publication No. 2-258929 discloses a grain-oriented electrical steel sheet in finish annealing.
Further, with respect to the bi-directional electrical steel sheet, JP-A-2-14153
It is effective to control the secondary recrystallization temperature as disclosed in JP-A-1. At this time, the point of the present invention is to stabilize the inhibitor nitride by the nitrogen partial pressure of the atmospheric gas. As this atmosphere gas, nitrogen alone or a mixed gas of hydrogen and an inert gas such as argon may be used. This nitrogen partial pressure control may be performed in the temperature range where the change of the nitride occurs. After the completion of the secondary recrystallization, annealing is performed at a temperature of 1100 ° C. or higher with 100% hydrogen in order to purify the nitride. After finish annealing, tension coating treatment may be performed, and if necessary, magnetic domain subdivision treatment such as laser irradiation may be performed.

[0016]

【Example】

Example 1 By weight, Si: 3.3%, Mn: 0.14%, C: 0.
05%, S: 0.007%, acid-soluble Al: 0.028
%, N: 0.008% of a silicon steel slab was heated at 1150 ° C. and then hot-rolled to a plate thickness of 1.6 mm. This hot rolled sheet 11
After annealing at 00 ° C. for 2 minutes, it was cold-rolled to a final plate thickness of 0.15 mm. The cold-rolled sheet was decarburized in wet gas at 830 ° C for 7
It was annealed for 0 seconds and primary recrystallized. After that, the amount of nitrogen was increased to 0.016 to 0.039% by ammonia nitriding to strengthen the inhibitor.

After the annealing separator was applied to the decarburized annealed plate, finish annealing was performed. For finish annealing, the temperature is raised to 1000 ° C. at 50 ° C./hr, and 5 ° C./1000 to 1100 ° C.
Secondary heating was performed by gradually heating at hr. Atmosphere gas is N ₂ :
It is 1.5 atm. Then, the atmosphere gas was switched to H ₂ and purification annealing was performed at 1200 ° C. for 20 hours. The magnetic properties of the obtained product are shown in Table 1. Nitriding amount 0.016 to 0.0
The magnetic flux density B ₈ is highly stable in a wide range of 39%.

[0018]

[Table 1]

Example 2 By weight, Si: 3.3%, Mn: 0.1%, C: 0.0
5%, S: 0.007%, acid-soluble Al: 0.03%,
A 1.8 mm thick silicon steel hot-rolled steel sheet having N: 0.008% and Sn: 0.05% was pickled and cold-rolled to 1.4 mm. Then 11
After annealing at 00 ° C for 2 minutes, the product was cold-rolled to a final plate thickness of 0.14 mm. This cold rolled sheet is also used for decarburization in a humid atmosphere gas 820
It was annealed at ℃ and recrystallized. Then, the amount of nitrogen was increased to 0.025% by ammonia nitriding to strengthen the inhibitor.

After applying an annealing separator to these steel sheets,
Finish annealing was applied. The finish annealing is (1) N ₂ : 2 atm and (2) N ₂ : 15% + H ₂ : 8 up to 1050 ° C.
The temperature was raised in an atmosphere gas of 5% and the temperature was kept at 1050 ° C. for 20 hours for secondary recrystallization. Then, the atmosphere gas was switched to H ₂ and annealing was performed at 1200 ° C. for 20 hours. After subjecting these samples to tension coating, laser irradiation was performed to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 2. By increasing the nitrogen partial pressure during secondary recrystallization, a product with high magnetic flux density and low iron loss could be manufactured.

[0021]

[Table 2]

Example 3 A hot rolled steel sheet having a thickness of 2.0 mm shown in Table 3 was heated at 1120 ° C. for 2 hours.
After annealing for a minute, it was cold rolled to a final plate thickness of 0.23 mm. This cold-rolled sheet was annealed at 830 ° C. in a humid atmosphere gas to perform primary recrystallization. After that, the amount of nitrogen is reduced to 0.0 by ammonia nitriding.
The inhibitor was strengthened by increasing it to 2 to 0.04%. An annealing separator was applied to this sample and finish annealing was performed. Finish annealing up to 1200 ° C in nitrogen gas at 1.3 atm 15 ° C
The temperature was raised at a heating rate of / hr for secondary recrystallization. Then 1
The hydrogen gas was switched to atmospheric pressure and purified annealing was performed at 1200 ° C. for 20 hours. Table 4 shows the magnetic properties of the obtained product. It can be seen that the secondary recrystallization is stabilized and the magnetic flux density B ₈ is increased by adding the nitride forming elements Ti and V.

[0023]

[Table 3]

[0024]

[Table 4]

Example 4 By weight, Si: 3.3%, Mn: 0.14%, C: 0.
05%, S: 0.007%, acid-soluble Al: 0.028
%, N: 0.008% of a silicon steel slab was heated at 1150 ° C. and then hot rolled to a plate thickness of 2.0 mm. This hot rolled sheet 11
After annealing at 00 ° C for 2 minutes, the rolling reduction is 50% in the hot rolling direction,
Next, cross cold rolling with a reduction rate of 50% was performed in the orthogonal direction to a final plate thickness of 0.25 mm. This cold-rolled sheet was annealed at 810 ° C. for 90 seconds in a wet gas for decarburization to carry out primary recrystallization.
Then, the amount of nitrogen was increased to 0.018% by ammonia nitriding to strengthen the inhibitor.

After the annealing separator was applied to this decarburized annealed plate, finish annealing was performed. The finish annealing was performed by raising the temperature to 1050 ° C. and annealing at 1050 ° C. for 20 hours for secondary recrystallization. The atmosphere gas is N ₂ : 1.5 atm. Then, the atmosphere gas was switched to H ₂ and purification annealing was performed at 1200 ° C. for 20 hours. Table 5 shows the magnetic properties of the obtained products. Also in the case of a grain-oriented electrical steel sheet, a product having a high magnetic flux density was obtained by the method of the present invention.

[0027]

[Table 5]

[0028]

Industrial Applicability According to the present invention, it is possible to stabilize an inhibitor during finish annealing and to stably produce a grain-oriented electrical steel sheet having a high magnetic flux density on an industrial scale.

[Brief description of drawings]

FIG. 1 is a table showing the relationship between the nitrogen partial pressure during secondary recrystallization annealing of finish annealing and the magnetic characteristics (magnetic flux density: B ₈ ) of a product.

Claims (3)

[Claims] 1. A method for producing a grain-oriented silicon steel sheet containing Si: 0.8 to 6.8% by weight and using a nitride as an inhibitor, wherein each step of secondary recrystallization annealing and purification annealing in finish annealing. Of the atmosphere gas of (1) in the secondary recrystallization annealing, the nitrogen partial pressure should be 1 atm or more. (2) In the purification annealing, 100% hydrogen gas was used. Production method. 2. A nitride forming element such as Al, Ti,
The method according to claim 1, wherein one or more of V, Nb, Zr, Ta and Cr are used. 3. The method according to claim 1, wherein the nitriding treatment is performed after the primary recrystallization annealing.