JP3073598B2 - Manufacturing method of grain-oriented electrical steel sheet with high magnetic flux density - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably producing a grain-oriented electrical steel sheet having a high magnetic flux density.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet has an easy axis of <10 in an iron-based alloy having a crystal structure of a body-centered cubic lattice.
0> The steel plates are all aligned in the same direction. A general steel plate obtained industrially is a polycrystalline body, and the direction of crystal grains varies depending on each grain. A grain-oriented electrical steel sheet is one in which the orientation of the crystal grains is aligned with the (110) <001> direction called the Goss orientation in the rolling direction by using rolling and recrystallization. The recrystallization used here is a so-called secondary recrystallization, in which crystal grains grow extremely large as compared with a normal steel sheet. Its size ranges from a few millimeters to a few centimeters. In general, ferromagnetic metals having a crystal structure have different magnetization characteristics depending on the direction of the crystal axis.
The <100> axis is the best. Therefore, the grain-oriented electrical steel sheet has extremely excellent magnetization characteristics in the rolling direction. Further, since the crystal grains are large and the axis of easy magnetization is only in the rolling direction, all the domain walls which are boundaries that separate the directions of magnetization are block-type 180 ° domain walls. The magnetization properties of the steel sheet as a whole are determined by the speed of domain wall movement,
Since the 180 ° domain wall is easy to move, the grain-oriented electrical steel sheet becomes a steel sheet having excellent magnetization characteristics. Excellent magnetizing properties mean that energy loss is small in the magnetizing process.

When the direction of magnetization of a steel sheet changes due to an external magnetizing force, an eddy current flows in the steel sheet according to the law of magnetic induction so as to cancel the change in magnetization, and the change in magnetization is prevented. I do. The same applies to the movement of the domain wall, and a small eddy current is generated around the domain wall. Joule heat generated by the eddy current causes energy loss in the magnetization process of the steel sheet. This loss is called eddy current loss. Since the eddy current loss is proportional to the moving speed of the domain wall, for example, when an electromagnetic steel sheet is used for a high-frequency transformer or the like, it is particularly required that the eddy current loss be small. The eddy current loss can be reduced by increasing the electric resistance of the steel sheet. For that purpose, 2 to 4 % of Si is added to the electromagnetic steel sheet.

[0004] The electrical steel sheet has a good magnetizing property,
It has been widely used as a soft magnetic material for applications under AC magnetization, such as transformer cores and motor cores. When an electromagnetic steel sheet is AC-magnetized as a soft magnetic material, energy loss appears as heat. To reduce energy loss, increase the electrical resistance of the steel sheet, align the Goss orientation grains obtained in the secondary recrystallization more sharply, and stably generate the secondary recrystallization. Is required.

[0005] In order to stably generate secondary recrystallization, it is necessary to ensure that the texture is ideal and the crystal grain size is appropriate and uniform at the time of primary recrystallization that occurs prior to secondary recrystallization. It is necessary to be. The primary recrystallization texture is adjusted by hot rolling, cold rolling and annealing. At this time, it is desirable that a small number of goss grains and a large amount of (111) <112> orientation grains eroded when the goss grains grow are present.

[0006] The primary recrystallized grain size is determined by the annealing temperature and an inhibitor such as AlN or MnS which functions to suppress grain growth. Also, like (100) grains,
Grains in which recrystallization is likely to occur on the spot or crystal grains before deformation are large have a large crystal grain size after primary recrystallization.

When a slab is heated at a high temperature of 1250 ° C. or more to manufacture an electromagnetic steel sheet, some of the crystal grains in the slab may be coarsened to several centimeters. Secondary recrystallization often becomes unstable due to spatial non-uniformity in the recrystallization behavior. This has been partially solved by inventions such as (Each Path Aging),
The fundamental problem was the casting structure, which was the raw material, and no measures were taken from that point, which was insufficient.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the cast structure and provides a more stable secondary recrystallization process.

[0009]

The slab heating at 1250 ° C. or more causes the slab crystal grains to become coarse, but the degree depends on the casting structure, and the equiaxed crystal grows preferentially as compared with the columnar crystal. Large crystal grains have a large crystal grain size even after recrystallization after hot rolling and cold rolling. During secondary recrystallization, the smaller the crystal grain size is, the more likely it is to be eroded, and the presence of large primary recrystallized grains is disadvantageous for the progress of secondary recrystallization.

It is known that secondary recrystallized grains are generated on the surface side of a steel sheet. This is the effect of the texture. In hot rolling, since the surface side undergoes shear deformation, the texture is mainly the (110) plane.
When this is cold rolled and primary recrystallized, a large amount of (11
1) A slight Goss orientation is generated as <112>. This is an ideal texture for secondary recrystallization. On the other hand, the central portion is not different from the ordinary cold-rolled texture even in hot rolling, and thus has a texture in which both the (111) plane and the (100) plane are present. Therefore, the surface side in texture is advantageous for secondary recrystallization.

When nuclei of secondary recrystallized grains are generated on the surface side,
The crystal grains grow in the thickness direction until they penetrate the plate. Since the central portion of the plate thickness is not so advantageous in terms of texture, the grain size affects the grain growth. That is, crystal grains having a small particle size are preferentially eroded. Therefore, if coarse crystal grains are present at the center of the plate thickness eroded by the nucleus of the secondary recrystallization, the progress of the secondary recrystallization is hindered.

The first aspect of the present invention is as follows. By weight ratio, C: 0.01 to 0.2%, Si: 2 to 4%, acid-soluble Al: 0.010 to 0.060%, N: 0.003
0 to 0.0130%, S: 0.01 to 0.06%, M
n: 0.080 to 0.45%, electromagnetic steel slab consisting of balance Fe and unavoidable impurities is heated to a temperature range of 1250 ° C. or higher, then hot-rolled, and subjected to cold rolling, decarburization and primary recrystallization. the method of manufacturing a grain-oriented electrical steel sheet annealing alms, annealing finishing after applying an annealing separating agent for, AlN及
And MnS function as an inhibitor, and a starting material is a continuous cast slab having at least one slab surface with at least 40% of a columnar crystal region in a thickness direction. Manufacturing method. Here, the case where the columnar crystal region of the present invention is 40% or more,
The case of less than 40% of the conventional method is compared. The equiaxed crystal ratio, which is the ratio to the thickness of the equiaxed crystal region at the center of the slab, can be controlled by the temperature of the tundish molten steel regardless of the presence or absence of electromagnetic stirring as shown in FIG.

[0013] In the present invention, the central layer of the slab is columnar.
Or a crystal, or a relatively particle small equiaxed crystal, thus cold-rolled, the primary recrystallized grains after annealing is small. In contrast,
The center layer of the conventional slab is equiaxed with relatively large grains, and the primary recrystallized grains after cold rolling and annealing are relatively large. Therefore, the present invention is more advantageous for secondary recrystallization.

As described above, since the nuclei of the secondary recrystallization are generated near the surface of the plate and the secondary recrystallized grains penetrate the plate, the columnar crystal region is present on at least one of the surfaces of the plate. It is considered that the ratio should be higher than the ratio. Therefore, if the equiaxed crystal ratio is the same, if the equiaxed crystal is shifted from the center of the slab by a curved continuous casting machine, the position of the equiaxed crystal becomes closer to the surface layer which is advantageous in terms of texture. This is more advantageous for the next recrystallization. Columnar crystals favor secondary recrystallization
The ratio of the band, as seen in the examples, a small <br/> Kutomo 40% on one side (conditions A, B).

[0015]

EXAMPLES Table 1 shows the state of secondary recrystallization when the secondary recrystallization step is processed using a silicon steel slab produced by using a curved continuous caster as a starting material. After the cast slab was heated under the conditions shown in Table 1,
Hot rolling was performed to a predetermined thickness, annealing was performed at 1120 ° C., and cold rolling was performed. Cold rolling was performed once or twice with intermediate annealing. The rolling ratio of the first cold rolling at this time is shown in the table. All three types of continuously cast slabs have the same composition, and the equiaxed crystal ratio was changed by changing the tundish temperature during casting according to FIG.

In this case, it is a curved continuous casting machine, and the equiaxed crystal is present at a position shifted downward from the center of the slab. Regarding the billet material used in this example, the ratio (%) of the upper columnar crystal, equiaxed crystal, and lower columnar crystal was A: 70/10/20 and B, respectively, using the symbols in the table. : 40/30 /
30, C: 30/50/20. In the examples, those using materials A and B as starting materials correspond to the present invention.

The state of the secondary recrystallization was represented by a linear fine grain generation rate. When the slab heating temperature is high and the crystal grain size of the slab is as large as about 30 mm, the rolled recrystallized texture is not properly formed in that portion, and the slab becomes linear fine grains. The lower the linear fine grain generation rate, the better the secondary recrystallization is performed, which means that the effect of the present invention is exhibited.

[0018]

[Table 1]

[0019]

According to the present invention, in the production of a grain-oriented electrical steel sheet by heating a slab at 1250 ° C. or more, secondary recrystallization is more favorably generated, and a more stable production than before can be attained.

[Brief description of the drawings]

FIG. 1 shows a slab created by a continuous casting method.
It is a chart which shows the ratio of a tundish molten steel temperature and an equiaxed crystal.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Munihiro Tsuchida Inventor 1-1, Tobata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works (56) References JP-A-4-17617 (JP, A) Japanese Patent Publication No. 50-37009 (JP, B2) Japanese Patent Publication No. 54-27820 (JP, B2)

Claims (4)

(57) [Claims] 1. C: 0.01 to 0.2%, Si: 2 to 4%, acid-soluble Al: 0.010 to 0.060%, N: 0.0030 to 0.0130% by weight , S: 0.01 to 0.06%, Mn: 0.080 to 0.45%, An electromagnetic steel slab consisting of the balance Fe and unavoidable impurities,
A method for producing a unidirectional electrical steel sheet which is heated to a temperature range of 1250 ° C. or higher, then hot-rolled, cold-rolled, decarburized and subjected to annealing for primary recrystallization, coated with an annealing separator, and finish-annealed. In the above, AlN and MnS as inhibitors
A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density, wherein a starting material is a continuous cast slab having at least one slab surface having at least 40% columnar crystal regions in a thickness direction. 2. A continuous cast slab having at least one slab surface having at least 40% columnar regions in the thickness direction is produced by a horizontal continuous cast method, or in a non-vertical portion of a curved continuous cast process. 2. The method according to claim 1, wherein the solidification is completed, and the equiaxed crystal is displaced to one side from the center in the thickness direction. 3. A weight ratio of C: 0.01 to 0.2%, Si: 2 to 4%, acid-soluble Al: 0.010 to 0.060%, N: 0.0030 to 0.0130% , S: 0.01 to 0.06%, Mn: 0.080 to 0.45%, An electromagnetic steel slab consisting of the balance Fe and unavoidable impurities,
A method for producing a unidirectional electrical steel sheet which is heated to a temperature range of 1250 ° C. or higher, then hot-rolled, cold-rolled, decarburized and subjected to annealing for primary recrystallization, coated with an annealing separator, and finish-annealed. In the above, AlN and MnS as inhibitors
A continuous cast slab having at least one slab surface with at least 40% columnar crystal area in the thickness direction is used as a starting material, and cold rolling is performed only once, or final rolling reduction is 85% or more. A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density. 4. A continuous cast slab having at least one slab surface with at least 40% of columnar areas in the thickness direction is produced by a horizontal continuous cast method, or in a non-vertical portion in a curved continuous cast process. 4. The method according to claim 3, wherein the solidification is completed, and the equiaxed crystal is displaced to one side from the center in the thickness direction.