JPH06179918A - Production of grain oriented silicon steel sheet with high magnetic flux density - Google Patents

Abstract

PURPOSE:To produce a superior grain oriented silicon steel sheet with high magnetic flux density by incorporating specific amounts of Bi and S into a slab material of specific composition and applying roughing and finish rolling under respectively specified conditions. 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, 0.01-0.06% acid soluble Al, 0.0005-0.013% N, and the balance Fe with inevitable impurities. This material is heated, hot-rolled, and cold-rolled at >=50% draft. Further, decarburizing annealing and finish annealing are done, and nitriding treatment is applied in the course of the above. At this time, 0.002-0.05% Bi and <=0.014% S are incorporated into the slab material. At the time of hot rolling after heating to <=1280 deg.C, plate thickness after roughing is regulated to 25-50mm, and further, finish rolling inlet temp. and outlet temp. are regulated to 900-1150 deg.C and 800-1100 deg.C, respectively. By this method, the grain oriented silicon steel sheet reduced in edge crack of hot rolled plate can be produced.

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. AIM E212 (1958) P7
69/781), 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 to determine what kind of precipitate or grain boundary segregation type element is used to stabilize the secondary recrystallization, and to determine the exact proportion of {110} <001> oriented grains. How to achieve their proper state of presence to enhance. 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 two cold-rolling steps.
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 and a thin product plate are taken to improve iron loss, 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. In other words, the inhibitor required for secondary recrystallization is built in after the completion of decarburization annealing (primary recrystallization) to before the appearance 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, the present inventors have found that, as disclosed in Japanese Patent Application No. 4-240701, by adding Bi to the slab material, secondary recrystallization becomes more stable and a high magnetic flux density can be obtained. On the other hand, there was a tendency that ear cracks in the hot rolled sheet increased. Therefore, a method for producing an excellent grain-oriented electrical steel sheet having not only magnetic properties but also less edge cracking of the hot rolled sheet was studied.

[0009]

As a result of repeated studies to solve the above problems, the present inventors have found that Bi:
0.002-0.05%, S ≦ 0.014%,
In addition, by setting the heating and rolling conditions for hot rolling to be in appropriate ranges, the average edge crack depth of the hot rolled sheet is good at 15 mm or less, secondary recrystallization is stable, and a high magnetic flux density unidirectional electrical steel sheet It was found that

The gist of the present invention is C: 0.025 by weight.
0.10%, Si: 2.5-4.5%, Mn: 0.05
~ 0.45%, acid-soluble Al: 0.01-0.06%,
N: 0.0005 to 0.013% is included, and a slab composed of the balance Fe and unavoidable impurities is used as a raw material, and after heating, hot rolling is performed, and one or more intermediate cold annealing at a final cold rolling reduction of 50% or more is included. A unidirectional electrical steel sheet that has been subjected to cold rolling two or more times, further subjected to decarburization annealing and finish annealing, and has undergone nitriding treatment between the decarburization annealing and the start of secondary recrystallization of the final finish annealing. In the manufacturing method of B, the slab material is B
i: 0.002 to 0.05%, S ≦ 0.014%, and at the time of hot rolling after heating to a temperature of 1280 ° C. or less, the plate thickness after rough rolling is 25 to 50 mm, finish rolling inlet The temperature is 900 to 1150 ° C and the finish rolling outlet temperature is 8
The hot-rolled sheet according to the following definition has an average edge crack depth of 15 mm or less, and is a method for producing a high magnetic flux density unidirectional electrical steel sheet.

Average Ear Crack Depth of Hot Rolled Sheet: Average value of ten ear crack depths from the deepest to the center of the sheet width per 1 m length 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, Bi:
It was found that when 0.002 to 0.05% was contained, fine precipitates before decarburization annealing increased. Therefore, it is presumed that the addition of Bi strengthens the inhibitor at this point, makes the change in the primary recrystallization grain size small and uniform in a wide range of the decarburization annealing temperature, and thus stabilizes the secondary recrystallization. Further, the Bi-added material has a relatively strong inhibitory force, that is, the ability to suppress the growth of the other grains until the {110} <001> oriented grains grow, even if the nitriding treatment is performed after the decarburization annealing. Is considered to be the cause. 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, if it exceeds 0.05%, the edge cracks of the hot-rolled sheet become severe, leading to an increase in cost.

On the other hand, although the magnetic flux density of the product increases with the Bi-added material, in general, when the amount of Bi is large, the edge cracks of the hot-rolled sheet tend to increase. However, even if the amount of Bi is large,
As shown in, the amount of S is reduced and the slab heating temperature is set to 1
The plate thickness after rough rolling is set to 25 to 50 mm and the finish rolling inlet temperature is set to 900 to 11 at 280 ° C. or lower and then hot rolling.
It was found that the occurrence of edge cracks in the hot-rolled sheet can be suppressed by limiting the temperature of 50 ° C and the finish rolling outlet temperature to 800 to 1100 ° C. This is because it is extremely difficult for Bi to form a solid solution in the base iron or to form a compound, and the melting point is less than 300 ° C., so Bi easily aggregates at the grain boundaries and precipitate interfaces, resulting in low strength, and thus at low temperatures. It is considered that the occurrence of edge cracking of the hot-rolled sheet is suppressed by hot-rolling of No. 2 and by reducing the amount of S to reduce Bi agglomeration at the crystal grain boundaries accompanying the precipitate. On the other hand, the reason for setting the lower limit of the plate thickness after rough rolling, the finish rolling inlet temperature and the finish rolling outlet temperature is to suppress the occurrence of edge cracks due to the decrease in deformability accompanying the temperature decrease during rolling, and the finish rolling inlet. The reason for setting the upper limit of the temperature and the finish rolling outlet temperature is to suppress the occurrence of edge cracking due to crystal coarsening and Bi influence due to slab overheating,
Also, the reason for setting the upper limit of the plate thickness after rough rolling is due to the restriction of rolling ability.

[0013]

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 value) 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 the Si content is less than 2.5%, it is difficult to obtain a product having a low iron loss, while the 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. Further, in the Bi-added material of the present invention, as described above, when the amount of S is large, the edge cracking of the hot rolled sheet increases. Therefore, in the present invention, the S content is 0.01
4% or less, preferably 0.010% or less.

Like Se, Se forms a compound with Mn and affects secondary recrystallization, so its content is Se ≦ 0.0.
4%. Al combines with N to form AlN, but in the present invention, it is essential to form (Al, Si) N by nitriding the steel in a subsequent step, that is, after completion of primary recrystallization. A certain amount of free Al is required. Therefore, sol. 0.01 as Al
Add ~ 0.06%.

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 the improvement of magnetic properties. On the other hand, if it exceeds 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. In the steps after hot rolling, in order to obtain the highest magnetic flux density, it is desirable to use a method of cold rolling at a high pressure reduction rate of 80% or more to obtain the final plate thickness after annealing for a short time. However, the hot rolled sheet annealing may be omitted in order to reduce the cost although the magnetic properties are slightly inferior. 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 in wet hydrogen or a mixed atmosphere gas of wet hydrogen and nitrogen. The temperature at this time is slightly different from the optimum value depending on the slab composition and the previous process conditions.
0-900 degreeC is preferable. Next, an annealing separator is applied and finish annealing is performed at high temperature (normally 1100 to 1200 ° C.) 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, an appropriate amount of a compound having a nitriding ability, such as MnN or CrN, is added to the annealing separator, or a gas having a nitriding ability such as NH ₃ is added to the atmosphere gas. As another embodiment of nitriding in the present invention, nitriding is performed in a gas atmosphere having a nitriding ability after soaking during decarburization annealing, or NH provided separately after decarburization annealing.
Nitriding may be performed by passing through a heat treatment furnace having an atmosphere of ₃ or the like, 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.

[0020]

【Example】

Example 1 A slab obtained by casting molten steel containing the steel composition shown in Table 1 was hot-rolled as shown in Table 2 to obtain a hot-rolled sheet having a thickness of 2.0 mm. Next, these hot-rolled sheets were heated at 1050 ° C for 2.5 minutes +
After annealing at 900 ° C for 2 minutes, cooling in hot water at 100 ° C, further pickling, and cold rolling, 0.23 m
It was made m thick. 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.

As shown in Table 2, the obtained product had a small amount of Bi added within the scope of the present invention, a low S material, and a predetermined hot rolling condition, in which the edge crack of the hot rolled sheet was small, Moreover, a product with a high magnetic flux density was obtained.

[0022]

[Table 1]

[0023]

[Table 2]

Example 2 A slab obtained by casting molten steel containing the steel composition shown in Table 3 was hot-rolled as shown in Table 4 to obtain a hot-rolled sheet having a thickness of 2.0 mm. Next, these hot-rolled sheets were heated at 1050 ° C for 2.5 minutes +
After annealing at 900 ° C for 2 minutes, cooling in hot water at 100 ° C, further pickling, and cold rolling, 0.23 m
It was made m thick. 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.

As shown in Table 4, the obtained product had a small amount of Bi addition within the scope of the present invention, a low S material, and a predetermined hot rolling condition, in which the edge crack of the hot rolled sheet was small, Moreover, a product with a high magnetic flux density was obtained.

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

According to the present invention, Bi added, low S material,
Moreover, by setting a predetermined hot rolling condition, it is possible to manufacture a good unidirectional electrical steel sheet with a small edge crack of the hot rolled sheet and a high magnetic flux density.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the average depth of edge cracks in a hot-rolled sheet and the slab heating temperature.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihide Takashima 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technology Development Division

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%,
Acid-soluble Al: 0.01 to 0.06%, N: 0.000
A slab containing 5 to 0.013% and the balance Fe and unavoidable impurities is used as a raw material, and after heating, hot rolling is performed once at a final cold rolling reduction of 50% or more, or at least twice including intermediate annealing. In the manufacturing method of unidirectional electrical steel sheet, cold rolling is performed, decarburization annealing and finish annealing are further performed, and nitriding treatment is performed on the steel sheet after decarburization annealing to the start of secondary recrystallization of final finish annealing. , Bi: 0.002 to the slab material
0.05%, S ≦ 0.014%, and 12
Upon hot rolling after heating to a temperature of 80 ° C. or less, the plate thickness after rough rolling is 25 to 50 mm, the finish rolling inlet temperature is 900 to
1150 ℃ and finish rolling outlet temperature 800 ~ 1100 ℃
The method for producing a high magnetic flux density unidirectional electrical steel sheet according to the following definition, wherein the average edge crack depth of the hot-rolled sheet is 15 mm or less. Average depth of edge cracking of hot-rolled sheet: average value from ten deepest depths of edge cracking to the center of sheet width per 1 m length 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 of the material 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%, acid-soluble Al: 0.01-0.06%,
N: 0.0005 to 0.013%, Bi: 0.002
0.05%, S: ≤ 0.014%, and Sn:
0.01 to 0.10%, Sb: 0.01 to 0.15%,
The method for producing a high magnetic flux density grain-oriented electrical steel sheet according to claim 1, wherein Se ≦ 0.04% and Cu: 0.05 to 1.0% are contained at least one kind.