JPH07278675A - 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 purging 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 hot rolled, and then, cold rolled. This cold-rolled steel sheet is primary re-crystalfization annealed in common with the decarburization. The steel sheet is nitrided to form and increase the nitride as the inhibitor. One or more kinds of At, Ti, V, Nb, Zr, Ta and Cr is preferably used as the element to form the nitride contained in the steel sheet. Then, the separation agent for annealing is coated on this decarburization annealed steel sheet to perform the finish annealing. The atmospheric gas for the finish annealing is the nitrogen gas or the mixed gas containing nitrogen during the secondary re-crystallization annealing, and the partial pressure of nitrogen is controlled to be reduced continuously or step by step, and the purifying annealing is performed in the hydrogen atmosphere. This constitution controls the formation of the nitride, stabilizes the secondary re-crystallization, and obtains the grain-oriented silicon steel sheet with high magnetic flux density.

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 an ancillary substance for precipitate-type inhibitors. This inhibitor is {11
It has a function of suppressing the growth of crystal grains other than 0} <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.K. 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 AlN disclosed in Japanese Examined Patent Publication No. 40-15644 by Taguchi and Sakakura.
The third cold rolling method using + MnS, the third technology is the second cold rolling method using MnS (or MnSe) + Sb disclosed in Japanese Patent Publication No. 51-13469, and the fourth technology is The technology of is by Komatsu et al.
This is a one-time cold rolling method using (Al, Si) N disclosed in JP-A-2-45285.

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, in the method of forming fine precipitates by these methods, the inhibitor strength fluctuates significantly unless the amount of the inhibitor constituent element of the steel component is adjusted and the heat history is strictly controlled. Then each coil,
Further, secondary recrystallization failure or magnetic failure that occurs in each coil portion has not been completely eliminated. 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 present inventors have conducted investigations to solve the above-mentioned problems, and rather than strictly controlling the incorporation of the inhibitor, a certain amount or more of the inhibitor is formed and the inhibitor It is concluded that controlling change behavior is effective. An experiment was conducted based on these results, and nitride was used as a specific condition, and final annealing was separated into secondary recrystallization annealing and purification annealing. It was found that the secondary recrystallization can be stabilized by controlling the nitrogen partial pressure of
The details will be described. By weight, Si: 3.3%, Mn: 0.
14%, C: 0.05%, S: 0.007%, N: 0.
008% Acid-soluble Al: 0.025-0.045%
After heating the silicon steel slab of
Hot rolled to 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. After that, the amount of nitrogen is reduced to 0.0 by ammonia nitriding.
The inhibitor was strengthened by increasing it to 2 to 0.1%. After applying an annealing separator to this decarburized annealed plate, finish annealing was performed.

The finish annealing was performed under two conditions. (A)
The temperature is raised to 1070 ° C at 30 ° C / hr and 20 at 1070 ° C.
Secondary recrystallization annealing was carried out for holding for a time. The atmosphere gas for this secondary recrystallization annealing was N ₂ gas up to 1070 ° C.
After maintaining at 70 ° C., the gas was switched to H ₂ gas by 5% in 1 hour. Then, the temperature was raised to 1200 ° C. in H ₂ gas and
Purification annealing was performed while holding the time. (B) The temperature was raised to 1200 ° C. at a heating rate of 30 ° C./hr in N ₂ atmosphere gas, and H
It switched to ₂ gas and performed annealing for 20 hours. The magnetic properties of these samples are shown in FIG.

From FIG. 1, it can be seen that in the annealing cycle (A), a high magnetic flux product can be obtained in a wide range for both Al and N which are the inhibitor constituent elements in the steel. Therefore, it is possible to stabilize the secondary recrystallization by separating the finish annealing into the secondary recrystallization annealing and the purification annealing and controlling the change behavior of the nitride in the secondary recrystallization annealing by the nitrogen partial pressure of the atmospheric gas. I confirmed that I can do it.

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 blisters are generated.
% Is the upper limit. In order to suppress the primary recrystallized grain growth as an inhibitor, nitriding is performed after the primary recrystallization to 0.01
It is necessary to keep the percentage above. Sn, Sb, Bi, Se, P which are grain boundary segregation elements as inhibitor constituent elements
b, S, etc. may be supplementarily added.

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. At this time, the point of the present invention is to stabilize the secondary recrystallization by controlling the change of the nitride as the inhibitor by continuously or stepwise decreasing the nitrogen partial pressure of the atmospheric gas. This nitrogen partial pressure control of atmospheric gas is disclosed in Japanese Patent Application Laid-Open No. 2-258929 for unidirectional electrical steel sheets and Japanese Patent Application Laid-Open No. 2-141531 for bidirectional electrical steel sheets. It may be controlled in the secondary recrystallization temperature range. After the secondary recrystallization is completed, 1100 is performed with 100% hydrogen to purify the nitride.
Anneal at a temperature of ℃ or more. 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: 0.1%, C: 0.0
5%, S: 0.005%, Ti: 0.02-0.1%,
A silicon steel slab of N: 0.008% was heated at 1150 ° C. and then hot-rolled to a plate thickness of 2.0 mm. 1100 this hot rolled sheet
After annealing at 0 ° C for 2 minutes, the product was cold rolled to a final plate thickness of 0.23 mm.
This cold rolled sheet was annealed at 830 ° C. for 90 seconds in a wet gas for decarburization to carry out primary recrystallization. After that, the inhibitor was strengthened by nitriding by annealing in an atmosphere gas containing ammonia.

This decarburized annealed plate was coated with an annealing separating agent containing alumina as a main component and then subjected to finish annealing. Finish annealing is the following two conditions. (A) Up to 1050 ° C., the temperature was raised in an atmosphere gas of N ₂ : 2 atm, and the temperature was raised to 2 at 1050 ° C.
After holding for 0 hour, N ₂ was replaced with Ar at 0.1 atmosphere every hour to carry out secondary recrystallization. Then, the atmosphere gas was switched to H ₂ and annealing was performed at 1200 ° C. for 20 hours. (B) N
₂ : 90% + H ₂ : 10% to 1200 ° C.
₂ : switched to 100% and annealed for 20 hours. The magnetic properties of the obtained product are shown in Table 1. It can be seen that by the annealing cycle (A), the secondary recrystallization is stabilized over a wide range and a product with high magnetic flux density can be obtained.

[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 hot-rolled silicon steel sheet having N: 0.008% and Sn: 0.05% and a thickness of 1.8 mm was pickled and cold-rolled to 1.4 mm. Then 1
After annealing at 100 ° C. for 2 minutes, it was cold rolled to a final plate thickness of 0.14 mm. This cold-rolled sheet also serves as decarburizer in a humid atmosphere gas.
It was annealed at 0 ° C. for primary recrystallization. Then, the amount of nitrogen was increased to 0.025% by ammonia nitriding to strengthen the inhibitor.

Alumina was applied to these steel sheets as an annealing separator, and then finish annealing was applied. Finish annealing is 11
The temperature was raised up to 00 ° C. in an atmosphere gas of N ₂ : 1.5 atm, and kept at 1100 ° C. for 20 hours. During this 20-hour holding at 1100 ° C., N ₂ was continuously switched to Ar for secondary recrystallization. Then, the atmosphere gas was switched to H ₂ and purification annealing was performed at 1200 ° C. for 20 hours. The magnetic characteristics (magnetic flux density: B ₈ (T)) of the obtained product are 1.955T.
Met.

Example 3 By weight, Si: 3.3%, Mn: 0.14%, C: 0.
05%, S: 0.007%, acid-soluble Al: 0.028
~ 0.045%, N: 0.008% silicon steel slab 1
After heating at 150 ° C., it was hot rolled to a plate thickness of 2.0 mm. This hot-rolled sheet was annealed at 1100 ° C. for 2 minutes, then subjected to cross cold rolling with a rolling reduction of 50% in the hot rolling direction and then a rolling reduction of 50% in the orthogonal direction, and cold rolled 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 reduced to 0.
Increased to 019% to potentiate the inhibitor.

After applying an annealing separator to the decarburized annealed plate, finish annealing was performed. The finish annealing is performed under the same two conditions (A) and (B) as in Example 1. The magnetic properties of the obtained product are shown in Table 2. A according to the annealing cycle (A) of the present invention
It can be seen that secondary recrystallization is stable over a wide range of the amount: 0.028 to 0.045%, and a product having a high magnetic flux density can be obtained.

[0023]

[Table 2]

[0024]

According to the present invention, a grain-oriented electrical steel sheet having a high magnetic flux density can be stably manufactured in a wide range of inhibitor constituent elements by controlling the inhibitor during finish annealing by an atmospheric gas.

[Brief description of drawings]

FIG. 1 is a table showing the stability of secondary recrystallization by the secondary recrystallization annealing cycle of finish annealing (relationship between the amount of acid-soluble Al in steel and the magnetic properties of products (magnetic flux density: B ₈ )).

Claims (3)

[Claims] 1. Containing 0.8 to 6.8% Si by weight,
In the method for producing a grain-oriented silicon steel sheet using a nitride as an inhibitor, the atmosphere gas at each stage of the secondary recrystallization annealing and the purification annealing in finish annealing is (1) nitrogen or nitrogen is contained in the secondary recrystallization annealing. A method for producing a high magnetic flux density grain-oriented electrical steel sheet, characterized in that a mixed gas is used and the partial pressure of nitrogen is controlled continuously or stepwise to reduce the pressure. (2) A hydrogen atmosphere is used in the purification annealing. 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.