JPH06179917A - Production of grain oriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PURPOSE:To produce a grain oriented silicon steel sheet with high magnetic flux density by incorporating specific percentage of Bi into a slab material of specific composition, applying cooling from a specific soaking temp. at hot rolled plate annealing at specific cooling velocity, and specifying average crystalline grain size after decarburizing annealing. CONSTITUTION:The slab material has a composition consisting of, by weight, 0.025-0.10% C, 2.5-4.5% Si, 0.05-0.45% Mn, <=0.014% (S+0.4O5Se), 0.01-0.06% acid soluble Al, 0.0005-0.013% N, and the balance Fe with inevitable impurities. This slab is heated to <=1280 deg.C, hot-rolled, and cold-rolled at >=50% final cold rolling draft. Further, decarburizing annealing and finish annealing are executed, and nitriding treatment is applied in the interime. At this time, Bi is incorporated into the slab material by 0.002-0.05%, and further, cooling velocity through the region between the soaking temp. at hot rolled plate annealing, 900-1200 deg.C, and 750-900 deg.C is regulated to (0.3 to 50) deg.C/sec and also average crystalline grain size after decarburizing annealing is regulated to 13-28mum. By this method, secondary recrystallization can be stabilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has an S content of 2.5 to 4.5%.
The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet having a high magnetic flux density including i.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are used as iron core materials for electrical equipment such as transformers, and must have good magnetic excitation characteristics and iron loss characteristics. Moreover, in recent years, the market demand for low iron loss materials with particularly low energy loss has been increasing. A steel sheet with a high magnetic flux density has a low iron loss and a small iron core, which is an extremely important development target. This unidirectional electrical steel sheet having a high magnetic flux density is obtained by finish-annealing a steel sheet having a final thickness from a hot-rolled sheet by appropriate cold rolling and annealing to produce primary recrystallized grains having a {110} <001> orientation. It is obtained by so-called secondary recrystallization in which selective growth is performed.

The secondary recrystallization is carried out by fine precipitates such as MnS, AlN, MnSe and Cu _{2 in} the steel sheet before the secondary recrystallization.
This is achieved by the presence of S, BN, (Al, Si) N, etc., or the presence of grain boundary segregation type elements such as Sn, Sb. These precipitates and grain boundary segregation type elements are described in J. B. May and Turnbull (Tran
s. Met. Soc. Aime 212 (1958) P
769/781), the function of suppressing the growth of primary recrystallized grains other than the {110} <001> orientation and selectively growing the {110} <001> oriented grains in the finish annealing step. To have. Such a grain growth suppressing effect is generally called an inhibitor effect. Therefore, the priority issue of research and development in this field is any kind of precipitate,
Or to stabilize secondary recrystallization by using grain boundary segregation type elements, and how to achieve the proper existence state of accurate {110} <001> oriented grains in order to increase their existence rate. is there. In particular, recently, the method using one kind of precipitate has a limitation in controlling the altitude of the {110} <001> orientation. Therefore, by clarifying the advantages and disadvantages of each precipitate, some precipitates can be organically separated. In combination with the above, development of a technology capable of producing a product having a higher magnetic flux density in a stable manner and at a low cost is in progress.

At present, there are three kinds of typical industrially produced grain-oriented electrical steel sheets, each of which has advantages and disadvantages. The first technology is M. F. Lit
It is a process by a two-time cold rolling process using MnS disclosed in Japanese Patent Publication No. 30-3651 by Tmann,
The obtained secondary recrystallized grains grow stably, but a high magnetic flux density cannot be obtained. The second technique is Taguchi et al.
This is a process in which the final cold rolling using AlN + MnS disclosed in 0-15644 is performed at a high pressure reduction rate of 80% or more, and a high magnetic flux density can be obtained, but strict control of manufacturing conditions is required in industrial production. To be done. The third technique is a process for producing silicon steel containing MnS (and / or MnSe) + Sb, which is disclosed in Japanese Patent Publication No. 51-13469, by a double cold rolling process.
Although a relatively high magnetic flux density can be obtained, the production cost is high because harmful and expensive elements such as Sb and Se are used and the double cold rolling method is used.

Further, the above three types of technology have the following problems in common. That is, in any of the above techniques, the slab heating temperature prior to hot rolling as a technique for finely and uniformly controlling precipitates is 1260 ° C. or higher in the first technique, and JP-A-48-51852 in the second technique. As shown, it depends on the amount of Si in the material, but it is 1350 ° C. in the case of 3% Si, and 1230 ° C. or higher in the third technique as shown in JP-A-51-20716. Coarsely existing precipitates are once solid-dissolved by making the temperature extremely high such as 1320 ° C., and then precipitated during the subsequent hot rolling or heat treatment. Raising the slab heating temperature lowers the production efficiency due to the increase in energy used during heating, the decrease in yield due to the generation of slag, and the increase in the repair frequency of the heating furnace.
As disclosed in Japanese Patent No. 41526, there is a problem that a continuous casting slab cannot be used because a linear secondary recrystallization defect occurs. However, what is more important than such a problem in terms of cost is that if a large amount of Si is used to improve iron loss and a product plate thickness is thinned, the occurrence of this linear secondary recrystallization defect increases, Technology based on the high-temperature slab heating method has no hope for improving iron loss in the future.

On the other hand, in the technique disclosed in Japanese Patent Publication No. 61-60896, by reducing S in the steel, secondary recrystallization is extremely stable, and a high Si thin product is made possible. However, this technique has a problem in the stability of the magnetic flux density in factory production on a mass production scale.
Although an improved technique disclosed in Japanese Patent Publication No.-40315 has been proposed, it has not been solved completely until now.

[0007]

As described above, the manufacturing method currently industrialized is to incorporate the inhibitor required for secondary recrystallization in the step before cold rolling. On the other hand, the present invention is a manufacturing method based on the same technical idea as JP-A-62-40315. That is, the inhibitor required for secondary recrystallization is built in after the completion of decarburization annealing (primary recrystallization) to before the manifestation of secondary recrystallization in finish annealing. Functions as an inhibitor (Al,
Si) N is formed. As the means for injecting N into the steel, the invasion of N from the atmospheric gas in the finish annealing temperature rising process is used as proposed in the prior art, or after the decarburization annealing or after the decarburization annealing is completed. Stripping is performed on a continuous line using an atmosphere gas such as NH ₃ which serves as a nitriding source.

By the way, even if a suitable inhibitor is formed by the above method, good secondary recrystallization having a high magnetic flux density cannot be obtained unless the state of the primary recrystallization structure during nitriding is appropriate. However, in the conventional molten steel composition,
If hot rolling is performed after heating to a temperature of 1280 ° C or less, which is a feature of this method, the precipitates become too coarse and hardly function as an inhibitor. It is necessary to strictly control the decarburization annealing conditions to control the crystal structure. There is. Therefore, as disclosed in Japanese Patent Application No. 4-240701, the present inventors have found that by adding Bi to the slab material, secondary recrystallization is more stable and a high magnetic flux density can be obtained. Then, a method for manufacturing an excellent grain-oriented electrical steel sheet, which can obtain more stable high magnetic flux density characteristics, was examined.

[0009]

As a result of repeated studies to solve the above problems, the present inventors have found that Bi:
By containing 0.002 to 0.05% and adjusting the cooling rate of hot-rolled sheet annealing and the crystal grain size after decarburization annealing within an appropriate range, the secondary re-annealing of the final finish annealing is performed after decarburization annealing. It has been found that secondary recrystallization is more stable and a high magnetic flux density unidirectional electrical steel sheet can be obtained by nitriding the steel sheet before the start of crystallization.

The gist of the present invention is C: 0.025 by weight.
0.10%, Si: 2.5-4.5%, Mn: 0.05
~ 0.45%, S + 0.405Se≤0.014%, acid-soluble Al: 0.01-0.06%, N: 0.0005
A slab containing 0.013% to 0.013% of balance Fe and unavoidable impurities is used as a raw material, heated to a temperature of 1280 ° C. or lower, then hot-rolled, and subjected to one-time or intermediate annealing with a final cold rolling reduction of 50% or more. Includes two or more cold rollings, including decarburization annealing and finish annealing, and performs nitriding treatment on the steel sheet between the decarburization annealing and the start of secondary recrystallization in the final finishing annealing. In the method for producing a steel sheet, the slab material is made to contain Bi: 0.002 to 0.05%, and the soaking temperature of hot-rolled sheet annealing: 900 to 1200 ° C to 750 to 750.
A method for producing a high magnetic flux density unidirectional electrical steel sheet, characterized in that the cooling rate up to 900 ° C. is 0.3 to 50 ° C./sec, and the average grain size after decarburization annealing is 13 to 28 μm. .

The present invention will be described in detail below. First, the effect of adding Bi, which is a feature of the present invention, will be described. The present inventors have made various studies in order to solve the above problems in the production of grain-oriented electrical steel sheets. As a result, it was found that when Bi: 0.002 to 0.05% was contained in the slab material having the above components, fine precipitates before decarburization annealing increased. Therefore, the addition of Bi strengthens the inhibitor at this point, and the average primary recrystallized grain size after decarburization annealing is 13 to 2
Minimized to 8 μm and the standard deviation σ _N according to the following definition
Is estimated to be 0.6 to 0.2.

[0012]

[Equation 1]

By this sizing, {110} <001>
The oriented grains easily grow, and the Bi-added material is relatively an inhibitor, that is, {110} even if it is nitrided after decarburization annealing.
The force that suppresses the growth of grains in the other position until the <001> oriented grains grow is strong, and this is considered to be one of the reasons for good secondary recrystallization and obtaining a high magnetic flux density. Therefore, the cross-sectional grain size was measured by an image analysis method. With the Bi-added material, the relationship between the average primary recrystallization grain size after decarburization annealing and the product magnetic flux density was as shown in FIG. From the above, it is considered that the addition of Bi is more effective for a thin / extra-low iron loss material that requires a stronger inhibitor because secondary recrystallization is unstable. The reason for limiting the amount of Bi is that when it is less than 0.002%, the effect of strengthening the inhibitor, that is, stabilizing secondary recrystallization is not achieved. On the other hand, 0.05
If it exceeds%, the ear cracks of the hot-rolled sheet become severe, leading to higher costs. In addition, as shown in FIG. 2, the Bi-added material has a soaking temperature for hot-rolled sheet annealing: 900 to 1200 ° C. to 750 to 90 ° C.
A high magnetic flux density material can be obtained at a cooling rate up to 0 ° C of 0.3 to 50 ° C / sec, preferably 1 to 20 ° C / sec. It is presumed that this is because when the cooling rate is in the above range, the precipitation-dispersed phase is proper for obtaining good secondary recrystallization, that is, the inhibitor strength.

[0014]

The reason why the steel composition and manufacturing conditions are limited as described above in the present invention will be described in detail. When the content of C is less than 0.025%, the secondary recrystallization becomes unstable, and the magnetic flux density (B
₍₈ values) is low, less than 1.80T. On the other hand, C
If the content of Al exceeds 0.10% and becomes too large, the decarburization annealing time becomes long and the productivity is significantly impaired.

When Si content is less than 2.5%, it is difficult to obtain a product with low iron loss, while Si content is 4.5%.
If the amount exceeds the above range, cracks and fractures occur during manufacturing such as cold rolling, and stable industrial production becomes impossible.
One of the characteristics of the component system of the starting material of the present invention is that S is 0.014% or less, preferably 0.010% or less. A conventionally known technique, for example, Japanese Patent Publication No. 40-156
In the technique disclosed in Japanese Patent Publication No. 44-44 or Japanese Patent Publication No. 47-25250, S was essential as an element for forming MnS, which is one of the precipitates necessary for causing secondary recrystallization. . In the above-mentioned known technology, there is a content range in which S exerts the most effect, and it has been defined as an amount capable of forming a solid solution of MnS in the heating step of the slab performed prior to hot rolling. However, in the present invention using (Al, Si) N as the inhibitor, Mn
S is not particularly required. Rather, increasing MnS is not preferable in terms of magnetic properties. Therefore, in the present invention,
S content is 0.014% or less, preferably 0.010
% Or less.

Like Se, Se forms a compound with Mn and affects secondary recrystallization, so its content is S + 0.
405Se ≦ 0.014%. Al combines with N to form AlN, but in the present invention, by nitriding the steel in a later step, that is, after completion of primary recrystallization (Al,
Since it is essential to form Si) N, free Al is required to have a certain amount or more. Therefore, sol.
0.01-0.06% is added as Al.

If the content of Mn is too small, the secondary recrystallization becomes unstable, while if it is too large, it becomes difficult to obtain a product having a high magnetic flux density. The proper content is 0.05-0.
45%. If N is less than 0.0005%, the development of secondary recrystallized grains becomes poor. On the other hand, if it exceeds 0.013%, blister of the steel sheet called blister occurs.

If Sn is less than 0.01%, it has no effect on improving the magnetic properties, while if over 0.10%, it suppresses nitriding and deteriorates the development of secondary recrystallized grains. As Sb, 0.01 to 0.15% is suitable as an inhibitor effect. Similarly, Cu has an inhibitor effect of 0.05 to 1.0.
% Is appropriate. Regarding the slab heating temperature, the secondary recrystallization is carried out even in the high temperature slab heating in which the inhibitor is dissolved, and in the low temperature slab heating similar to that of ordinary steel. However, since the edge cracking of the hot-rolled sheet can be suppressed and naturally the low-temperature slab heating with a small amount of heat energy is advantageous, 1280 ° C. or less at which no slag is generated is desirable.

In the steps after hot rolling, in order to obtain the highest magnetic flux density, it is desirable that the final sheet thickness is obtained by cold rolling at a high pressure reduction rate of 80% or more after short-time annealing. In addition, in order to reduce the crystal grains of the final product, it is possible to perform the process including intermediate annealing. Next, decarburization annealing is performed at 800 to 900 ° C. for an appropriate time in wet hydrogen or a mixed atmosphere gas of wet hydrogen and nitrogen so as to obtain the crystal structure.

Next, an annealing separator is applied, and the high temperature (usually 11
(00 to 1200 ° C.) Finish annealing is performed for a long time. The most preferable embodiment of the nitriding of the present invention is nitriding in the temperature rising process of finish annealing, which makes it possible to build an inhibitor necessary for secondary recrystallization. To achieve this, a compound with nitriding capacity in the annealing separator,
For example, MnN, CrN or the like is added in an appropriate amount, or a gas having a nitriding ability such as NH ₃ is added to the atmosphere gas. Note that, as another embodiment of nitriding in the present invention, a nitriding is performed in a gas atmosphere having a nitriding ability after soaking during decarburization annealing, or a heat treatment furnace having an atmosphere such as NH ₃ separately provided after decarburization annealing is used. Nitrogen may be passed and passed, or a combination of the above means may be used.

After the completion of secondary recrystallization, purification annealing is performed in a hydrogen atmosphere. Next, examples of the present invention will be described. Example 1 A slab obtained by casting molten steel containing the component composition of steel shown in Table 1 was heated at 1150 ° C. and then hot rolled to obtain a hot rolled sheet having a thickness of 2.0 mm.

Next, these hot-rolled sheets were heated at 1050 ° C. × 2.
After annealing for 5 minutes + 900 ° C. × 2 minutes, it was cooled in 100 ° C. hot water, further pickled, and then cold-rolled.
It was 23 mm thick. Next, this cold rolled sheet was decarburized and annealed in a wet hydrogen and nitrogen atmosphere at different temperatures and times to obtain a steel sheet having a crystal grain size as shown in Table 2. Then, nitriding treatment was performed at 750 ° C. for 30 seconds in an atmosphere of hydrogen and nitrogen containing 1% of ammonia so that the amount of nitrogen in the steel sheet was 200 ppm. Furthermore M
After applying the gO powder, high temperature annealing was performed in a hydrogen gas atmosphere at 1200 ° C. for 20 hours.

The product thus obtained was, as shown in Table 2, Bi
Secondary recrystallization was stable with the additive material and the average grain size after decarburization annealing was within the range of the present invention, and good magnetic characteristics were obtained.

[0024]

[Table 1]

[0025]

[Table 2]

Example 2 A slab obtained by casting molten steel containing the steel composition shown in Table 3 was heated at 1150 ° C. and then hot rolled to obtain a hot rolled sheet having a thickness of 2.0 mm. Then these hot-rolled sheets were heated at 1050 ° C ×
2.5 minutes + 900 ℃ × 2 minutes annealing, and 1050
After changing the cooling rate between 0 ° C and 900 ° C as shown in Table 4, after cooling in hot water at 100 ° C and further pickling,
Cold rolling was performed to a thickness of 0.23 mm. Next, this cold rolled sheet was decarburized and annealed in an atmosphere of wet hydrogen and nitrogen for 90 seconds at 830 ° C. Then, nitriding treatment was performed at 750 ° C. for 30 seconds in an atmosphere of hydrogen and nitrogen containing 1% of ammonia so that the amount of nitrogen in the steel sheet was 200 ppm. After applying MgO powder, high temperature annealing was performed in a hydrogen gas atmosphere at 1200 ° C. for 20 hours.

The product thus obtained was, as shown in Table 4, Bi
The secondary recrystallization was stable and good magnetic properties were obtained when the additive was used and the cooling rate condition of the hot-rolled sheet annealing was within the range of the present invention.

[0028]

[Table 3]

[0029]

[Table 4]

[0030]

According to the present invention, the secondary recrystallization is stabilized and the magnetic flux density is stabilized by adjusting the cooling rate of hot-rolled sheet annealing and the crystal grain size after decarburization annealing with the Bi-added material. It is possible to manufacture a high-oriented electrical steel sheet.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between magnetic property B ₁₀ and average grain size after decarburization annealing.

FIG. 2 is a graph showing the relationship between the magnetic property B ₁₀ and the cooling rate of hot-rolled sheet annealing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihide Takashima 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd. Technology Development Division (72) Inventor Yoshio Nakamura 20-1 Shintomi, Futtsu-shi, Chiba Made by Shinnihon Iron & Steel Co., Ltd.

Claims (3)

[Claims] 1. C: 0.025 to 0.10% by weight, S
i: 2.5 to 4.5%, Mn: 0.05 to 0.45%,
S + 0.405Se ≦ 0.014%, acid-soluble Al:
0.01-0.06%, N: 0.0005-0.013
%, With the balance Fe and unavoidable impurities as the raw material, heated to a temperature of 1280 ° C. or lower, then hot-rolled, once at a final cold rolling reduction of 50% or more, or twice at least including intermediate annealing. Cold rolling of steel sheet, decarburization annealing and finish annealing, and nitriding treatment of steel sheet between decarburization annealing and start of secondary recrystallization of final finishing annealing. In the slab material, Bi: 0.
002-0.05%, and the soaking temperature of hot-rolled sheet annealing: The cooling rate from 900-1200 ° C to 750-900 ° C was 0.3-50 ° C / sec, and the average after decarburization annealing A method for producing a high magnetic flux density unidirectional electrical steel sheet, which has a crystal grain size of 13 to 28 μm. 2. The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein the final cold rolling reduction is 80% or more. 3. A molten steel component, by weight, C: 0.025 to.
0.10%, Si: 2.5-4.5%, Mn: 0.05
~ 0.45%, S + 0.405Se≤0.014%, acid-soluble Al: 0.01-0.06%, N: 0.0005
-0.013% Bi: 0.002-0.05%, Sn: 0.01-0.10%, Sb: 0.01-
0.15% and Cu: 0.05-1.0% of at least 1 sort (s) are contained, The manufacturing method of the high magnetic flux density grain-oriented electrical steel sheet of Claim 1 characterized by the above-mentioned.