JPH09143558A - Production of semi-process nonoriented silicon steel sheet excellent in isotropic magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technology for producing a nonoriented silicon steel sheet having excellent isotropic magnetic properties by a skinpass rolling method. SOLUTION: Molten steel contg., by weight, <=0.01% C, <=4% Si, <=2% Al, <=1.5% Mn, <=0.3% P, <=0.02% S and <=0.005% N, and the balance Fe with inevitable components is subjected to continuous casting to form into a slab, which is subjected to hot rolling, and after that, the stages of pickling, intensive reduction cold rolling, annealing and skinpass rolling at 2 to 15% draft, the roughness of the steel sheet after the cold rolling is regulated to Ra: 0.7 to 3.0μm and the roughness of the steel sheet after the skinpass rolling is regulated to Ra: <=0.6μm. Furthermore, after the hot rolling, hot rolled sheet annealing is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-oriented electrical steel sheet, and more particularly to a non-oriented electrical steel sheet having excellent isotropic magnetic properties used for a motor in the electric industry field. is there.

[0002]

2. Description of the Related Art Magnetization of a motor core is applied in a random direction within a plane of a steel sheet. Therefore, the magnetic characteristics are 3
Uniform magnetic properties are required in each of the 60 ° directions. In particular, for stepping motors, motors for industrial robots, disk drive motors, etc., which require uniformity of rotational torque for each angle and accuracy of stop position of rotation, uniform and isotropic magnetic properties within the steel plate surface are important.

Generally, as a process for producing a non-oriented electrical steel sheet in the field of motor cores, a hot-rolled sheet is cold-rolled once and
There are many so-called one-time cold rolling methods in which a final product is obtained by performing continuous annealing once. However, when lower iron loss is required, skin pass rolling is performed in the final step of this one-time cold rolling method, and crystals are obtained by magnetic annealing (typically about 750 ° C x 2 hr) by the customer. A process of coarsening the particle size is adopted. The present invention relates to this skin-pass process method, and is a technical field called a semi-process non-oriented electrical steel sheet because it is premised on annealing by a customer.

In this field, several techniques have been disclosed in the past in order to improve iron loss and magnetic flux density. For example, there is Japanese Patent Laid-Open No. 53-109815 which proposes improvement of magnetic permeability of steel sheet vertical and horizontal by refining molten steel by Si deoxidation and controlling roughness of skin pass rolling. Specifically, deoxidation of steel is performed with Si, and a shot blast roll is used for skin pass rolling, and the surface of the steel sheet is 40
The first method for improving the magnetic permeability between the vertical and the horizontal stitches in the step of giving a roughness of μ-in, rms or more. Further, it is a second method for drastically improving the magnetic permeability in the warp direction by carrying out skin pass rolling with a smooth roll so that the surface roughness of the final product becomes 15 μ-in, rms or less.

Certainly, with this method, it was possible to improve the magnetic permeability of each of the vertical and horizontal eyes. However, in the first method, since the surface roughness of the product is large, the volume of the core becomes large at the time of stacking, and the effective magnetic flux density of the core decreases, which is a problem of so-called space factor. Also, the second
According to the method (1), excellent magnetic properties were obtained with respect to the vertical grain, but there was a defect that the magnetic characteristic deteriorated in the direction of about 70 ° from the cross stitch or the rolling direction.

According to Japanese Patent Laid-Open No. 63-263313, bright roll rolling is performed in the first half of the second cold rolling, and dull roll rolling with a reduction rate of 1-5% is performed in the latter half of the cold rolling. A method of manufacturing a magnetic electrical steel sheet is presented. Although magnetic properties can be expected with this method, there were problems of roll replacement cost during skin pass rolling and deterioration of product space factor.

Japanese Unexamined Patent Publication (Kokai) No. 53-31515 discloses a method of obtaining isotropic magnetic properties by annealing in the γ region. However, in this method, since internal strain due to transformation is introduced, even if the subsequent annealing is performed, a satisfactory iron loss cannot be obtained.

[0008]

SUMMARY OF THE INVENTION In view of the above points, the present invention provides a non-oriented electrical steel sheet manufacturing technique having not only excellent isotropic magnetic properties in the skin pass rolling method but also an excellent space factor. It is a thing.

[0009]

That is, the present invention provides (1)
% By weight, C ≦ 0.01%, Si ≦ 4%, Al ≦ 2%,
Mn ≦ 1.5%, P ≦ 0.3%, S ≦ 0.02%, N ≦
0.005%, molten steel containing the balance Fe and unavoidable components is continuously cast into a slab, and after hot rolling,
When carrying out the steps of pickling, cold rolling under strong reduction, annealing, and skin pass rolling with a reduction rate of 2-15%, the steel sheet roughness after cold rolling is Ra: 0.7-3.0 μm, and the roughness after skin pass rolling. Ra: 0.6 μm or less is a method for producing a semi-process non-oriented electrical steel sheet having excellent isotropic magnetic properties, wherein (2) hot rolling is followed by hot rolling sheet annealing. It is a method for producing a semi-process non-oriented electrical steel sheet having excellent isotropic magnetic properties as described in the above item (1).

The present invention has three points. One is to roughen the steel plate after cold rolling under high pressure, then insert annealing,
To improve the texture of the steel sheet by reducing the roughness of the steel sheet by skin pass rolling. The second point is to improve the space factor when stacking by making the surface of the final product smooth. The third point is that this method is industrially sufficient and stable production is possible.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the present invention will be described below. The amount of C is limited to 0.01% or less. This is because if the amount of C exceeds this amount, the time required for decarburization in decarburization annealing becomes long and the productivity falls. There is a problem of magnetic aging unless the C content of the product is 0.005% or less.
The amount of Si is 4% or less. Si is necessary in order to reduce iron loss, but if it is too much, it causes embrittlement, which causes troubles at breaks in the sheet passing line and punching into the motor core.
Since this limit is 4%, the lower limit of the amount of Si is set to 4%.

The Al content is 2% or less. Al is effective in reducing iron loss, but due to the problem of addition cost, it is made 2% or less. The amount of Mn is 1.5% or less. As a countermeasure for ear rust in hot rolling, the precipitate FeS is suppressed to suppress MnS.
In order to achieve this, Mn is necessary, but if it is too large, there is a problem of addition cost, so it is made 1.5% or less.

The amount of P is limited to 0.3% or less. P is useful for reducing the burrs and sagging at the time of punching into the motor core at the customer, but if it is too large, it segregates in the steel plate center layer and causes problems such as cracking, so it is made 0.3% or less. The amount of N shall be 0.005% or less. If the amount of N is large, blister defects on the surface of the steel plate called blister occur,
It is limited to 0.005% or less. The amount of S shall be 0.02% or less. Since S forms a sulfide and deteriorates iron loss, the S content is preferably small and is limited to 0.02% or less.

As other components, known Cu, Cr, Sn, Ni, B may be used for further improving the texture of the product. The content is Cu: 0.02-0.
2%, Sn: 0.01-0.35%, Cr: 0.04-
0.2%, Ni: 0.01-0.3%, B: 0.000
5-0.01% is preferable. There is no problem even if two or more of these are added in combination.

The molten steel containing these component compositions is made into a slab by ordinary continuous casting. Hot rolling is carried out by a conventional method to obtain a usual hot rolled coil having a thickness of 1.0 to 3.0 mm. The hot rolled coil may or may not be annealed. When annealed, the magnetic flux density is improved especially in each angle direction. However, the cost of annealing is high.

Then, after pickling, cold rolling under high pressure is performed. The surface roughness of the steel sheet after this cold rolling under high pressure must be controlled. The surface roughness is a center line average roughness Ra of 0.7 μm or more and 3.0 μm or less. If the surface becomes rough after cold rolling under high pressure, the isotropic magnetic characteristics of the present invention can be obtained.
When the thickness is 0.7 μm, there is a large difference in magnetic characteristics between the rolling direction and the other directions, which is impossible. In general, the rolling dull roll for roughening the surface of the steel sheet is worn and smoothened as the number of rolled betons increases. For this reason, if the surface of the steel sheet is to be Ra> 3.0 μm, the number of times the roll has to be dulled by shot projection or the like in order to avoid smooth rolling, and this must be avoided in terms of cost. As a method for obtaining the steel plate roughness of the present invention, for example, in the case of tandem rolling, only the rolling in the final stand may be dull rolls, or all the stands may be dull rolls, and the important point is skin pass. That is, the surface of the steel sheet before rolling is rough. Subsequent annealing is usually 600-1000 ° for several seconds.
Perform soaking for a few minutes. The atmosphere is conventional H ₂ and N
_Although it is a mixed air flow of ₂ , decarburization is performed by blowing H ₂ O as needed.

Next, skin pass rolling is performed. The rolling reduction at this time is limited to 2-15%. If the content is out of the range of 2% or more and 5% or less, the crystal grain size does not become coarse after the magnetic annealing by the customer and the iron loss becomes poor, so avoid it. A smooth roll is used for the skin pass rolling, and the surface roughness of the steel sheet after the skin pass needs to be Ra of 0.6 μm or less. Ra0.6
If it exceeds μm, the excellent space factor of the present invention cannot be obtained and the magnetic characteristics of the motor core become unsatisfactory, so avoid it. Magnetic annealing after skin pass is usually 700-800 ℃ for 2h
r Only soaking is required.

[0018]

EXAMPLES Examples will be described in detail below. [Example-1] 0.002% C, 1.5% S by weight
i, 0.5% Mn, 0.03% P, 0.2% Al, 0.
A continuously cast slab containing 001% S and 0.002% N was heated to 1150 ° C. to produce a hot rolled sheet having a thickness of 2.5 mm. This was pickled, and the cold rolled sheet was rolled with rolls having various roll roughnesses to obtain the steel sheet roughness shown in Table 1. The plate thickness was 0.535 mm. Then, after degreasing, the intermediate annealing was soaked in a 20% H ₂ + 80% N ₂ atmosphere at 800 ° C. for 30 seconds, and then skin-pass cold rolled to 0.5 mm. The skin pass roll roughness at this time was also variously changed to obtain the steel plate roughness shown in Table 1.

The steel sheet was sheared to a width of 30 mm and a length of 60 mm. The longitudinal direction at this time is 0 ° with the rolling direction, 22.5
There are 5 types, °, 45 °, 67.5 °, 90 °, 75
After soaking at 0 ° C. for 2 hours in an N ₂ atmosphere, the magnetic properties of the samples in each angle direction were measured. Table 1 shows the maximum and minimum magnetic properties and the difference between the two. The space factor was measured according to JIS C 2550 (1987) by producing 16 Epstein samples each.

[0020]

[Table 1]

Experiment No. Since (4) to (9) are within the scope of the present invention, isotropic magnetic characteristics are obtained and a high space factor is secured. Experiment No. In (1) to (3), the steel sheet roughness after strong cold rolling, that is, before skin pass rolling is too small to be outside the range of the present invention, and therefore isotropic magnetic characteristics cannot be obtained. Experiment No. (10)-(12) are not within the scope of the present invention because the steel sheet roughness after skin pass is too large and the space factor deteriorates. The directions with the best magnetic properties were all in the rolling direction (0 °), and the directions with the worst were 45 ° or 67.5 ° with the rolling direction.

[Example-2] 0.005% C by weight,
0.3% Si, 0.2% Mn, 0.10% P, 0.00
A continuous casting slab containing 5% Al, 0.001% S, 0.002% N is heated to 1100 ° C to obtain a thickness of 2.5 mm.
Was manufactured. A part of these is hot-rolled sheet annealed at 800 ° C. for 1 minute, then pickled and subjected to strong cold rolling with a dull roll to obtain a steel plate roughness of Ra 1.1 μm constant, and the plate thickness is shown in Table 2. The following skin pass roll reduction rate was adjusted as much as possible. Then, after degreasing, intermediate annealing is performed with 40% H ₂ + 60%
0.5 mm after soaking at 700 ℃ for 30 seconds in N ₂ atmosphere
Cold rolled until skin pass. The skin pass roll roughness at this time was variously changed to obtain the steel plate roughness shown in Table 1.

This steel plate was sheared to a width of 30 mm and a length of 60 mm. The longitudinal direction at this time is 0 ° with the rolling direction, 22.5
750 in 5 types: °, 45 °, 67.5 °, 90 °
After soaking at ℃ × 2 hours in N ₂ atmosphere, the magnetic properties of the samples in each angle direction were measured. Table 1 shows the maximum and minimum magnetic properties and the difference between them.

[0024]

[Table 2]

The skin pass reduction ratio of the example of the present invention is 2-15%.
Experiment No. (2)-(4) show excellent iron loss, but other experiment Nos. (1), (5),
Regarding (6), the iron loss is deteriorated. Moreover, the experiment No. which performed the hot rolled sheet annealing. In (7) to (10), the magnetic flux density is particularly improved as compared with the case where the hot rolled sheet is not annealed, but the iron loss is not satisfied unless the skin pass reduction ratio is within the range of the present invention. The directions with the best magnetic properties were all in the rolling direction (0 °), and the directions with the worst were 45 ° or 67.5 ° with the rolling direction.

[0026]

INDUSTRIAL APPLICABILITY As described above, by controlling the roughness in the cold rolling of the strong cold rolling and the skin pass rolling, the semi-process non-directional electromagnetic having an isotropic magnetic property and an excellent space factor at the same time. A steel plate was obtained.

Claims (2)

[Claims] 1. By weight%, C ≦ 0.01%, Si ≦ 4%, Al ≦ 2%, Mn ≦ 1.5%, P ≦ 0.3%, S ≦ 0.02%, N ≦ 0 0.005%, the molten steel containing the balance Fe and unavoidable components is continuously cast into a slab, hot-rolled, then pickled, cold-rolled under strong reduction, annealed, and subjected to skin-pass rolling with a reduction rate of 2-15%. In carrying out the process, the isotropic magnetic property is characterized in that the steel sheet roughness after cold rolling is Ra: 0.7-3.0 μm and the steel sheet roughness after skin pass rolling is Ra: 0.6 μm or less. Of excellent semi-processed non-oriented electrical steel sheet. 2. The method for producing a semi-process non-oriented electrical steel sheet having excellent isotropic magnetic properties according to claim 1, wherein hot-rolled sheet annealing is carried out after hot rolling.