JPH10251754A - Manufacture of nonoriented silicon steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of a nonoriented silicon steel sheet free from embrittlement problem and excellent in magnetic properties. SOLUTION: Hot rolled plate continuous annealing is applied to a hot rolled steel plate having a composition consisting of, by weight, <=0.003% C, 2.5-4.5% Si, 0.1-2% Al, 0.07-3% Mn, <=0.05% P, <=0.002% S, <=0.003% N, <=0.004% O, and the balance inevitable components to regulate crystalline grain size to >=100μm. Subsequently, cold rolling is applied to the plate and also recrystallization annealing is performed to regulate crystalline grain size to 100-300μm, by which the nonoriented silicon steel sheet can be manufactured. At this time, the thickness of the hot rolled plate and the cooling rate at hot rolled plate annealing is are regulated to 0.8-2.0mm and (1 to 40) deg.C/sec, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the production of high grade non-oriented electrical steel sheets. That is, the present invention provides a method for producing a non-oriented electrical steel sheet having excellent magnetic properties, particularly excellent iron loss, used for motors and small transformer cores in the electric industry.

[0002]

2. Description of the Related Art From the viewpoint of the global environment, the harmful effects of recent energy-intensive civilization have been regarded as a problem. For this reason, in the field of electrical equipment in which non-oriented electrical steel sheets are used, further reduction in power consumption is demanded for motors for cooling and heating equipment, main motors for electric vehicles, and large motors for generators. I have.

[0003] Conventionally, non-oriented electrical steel sheets have been produced by increasing the electrical resistance by increasing Si and Al for the purpose of improving iron loss, and improving the impurities, ie, S, N,
Efforts have been made to increase the purity of molten steel by minimizing O, Ti, Nb, V and the like. In addition, the crystal grain size of the product is about 150 μm (for example, M. Shiozaki & Y. Kurosaki:
J. Mater. Eng., 11 (1989) 37), high-temperature finish annealing was performed. Further, the crystal grain size before cold rolling is coarsened, and in the recrystallization annealing after cold rolling, the hard magnetization axis <111
> High-temperature annealing of hot-rolled sheets, which is a technique for reducing the orientation grain (for example, Mitsunobu Abe et al .: Journal of the Japan Institute of Metals, 44 (1980) 84), has been adopted. Further, the product thickness is often as thin as 0.2 to 0.5 mm.

[0004] Although these technologies are combined for production, the problems at the production site are the brittleness of the steel sheet due to the large amount of Si + Al and the coarsened grain size of the hot-rolled sheet. That is, particularly in winter and the like, there is a very important problem of production failure such as cracking at a place where bending deformation of the steel sheet after hot-rolled sheet annealing is applied, and breaking at a cold-rolled Sendzimir mill. However, to date no effective solution has been provided.

[0005] The brittle fracture trouble at this factory is as follows.
It has been empirically known that it corresponds to cracking in 0 to 1 time in a bending test using a bending tester (radius of a part to which bending is applied) with a small test piece cut out from the original plate.

[0006]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention provides a method for producing a high-grade non-oriented electrical steel sheet having excellent iron loss while solving the problem of brittleness.

[0007]

That is, the gist of the present invention is as follows. By weight%, C ≦ 0.003%, Si: 2.5-4.5%, Al: 0.1-2%, Mn: 0.07-3%, P ≦ 0.05%, S ≦ 0 0.002%, N ≦ 0.003%, O ≦ 0.004% The hot-rolled steel sheet containing the remaining unavoidable components is subjected to continuous hot-rolling annealing to reduce the crystal grain size to 100 μm or more.
Perform cold rolling and recrystallization annealing to reduce the crystal grain size to 100-
In the method for producing a non-oriented electrical steel sheet having a thickness of 300 μm, the thickness of the hot-rolled sheet is 0.8 to 2.0 mm, and the cooling rate of the hot-rolled sheet annealing is 1 to 40 ° C./sec. Manufacturing method of non-oriented electrical steel sheet.

The points of the present invention are the following three points.
The first point is that when the thickness of the hot rolled sheet is small, cracks are small. Secondly, cracking is small if the steel sheet is gradually cooled by hot-rolled sheet annealing. Third
In addition, it has been discovered that a combination of a thin hot-rolled sheet and slow cooling of hot-rolled sheet annealing significantly improves the ductility after hot-rolled sheet annealing. By this technique, it was possible to completely prevent crack breakage in an annealing line after hot-rolled sheet annealing in a factory or crack breakage occurring in the first or second pass of cold rolling.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The reason why the amount of C is limited to less than 0.005% is that the amount of C
This is because there is a problem with magnetic aging in the amount.

The amount of Si is limited to 2.5 to 4.5%. S
It is known that as the amount of i increases, the iron loss decreases.
The reason for the limitation is that if the amount of Si is less than 2.5%, the brittleness aimed at by the present invention hardly causes a problem, and the iron loss is unsatisfactory. The use of a steel sheet causes brittleness of the steel sheet and must be avoided.

The amount of Al is limited to 0.1 to 2%. Al also reduces iron loss, but if the amount of Al is less than 0.1%, iron loss is unsatisfactory, and if it exceeds 2%, there is a problem of addition cost, so avoid it. The Mn content is set to 0.07 to 3%. Mn is effective in preventing red-hot brittleness in hot rolling and improving the edge roughness of the hot-rolled sheet, and is required to be 0.07% or more. Further, if it is too large, there is a problem of cost increase.

P is set to 0.05% or less. If P is increased, the number of <111> -oriented grains increases and iron loss is deteriorated, and there is a problem of addition cost. Therefore, the content of P is limited to 0.05% or less.
The amount of S is set to 0.002% or less. If the S content exceeds 0.002%, sulfides such as MnS increase and the crystal grain size of the hot-rolled sheet becomes small, and at the same time, the magnetic wall properties of the product are hindered and the magnetic properties are deteriorated.

The amount of N is limited to 0.003% or less. 0.
If the content is 003% or more, blister-like surface defects called blisters are generated. The amount of O is 0.004% or less. O forms oxides and deteriorates iron loss.
004% or less. In addition to the above elements, Sn, Ni, Cu, Sb, C
Addition of r and the like does not impair the effects of the present invention.

Next, the processing conditions of the present invention will be described.
The slab heating for hot rolling is not particularly limited, but is preferably at a low temperature of 950 to 1200 ° C. for the purpose of preventing fine precipitates, and then normal hot rolling is performed. Limit to 8 to 2.0 mm. The hot rolled sheet thickness can avoid brittleness of the steel sheet when it is thin. However, when the thickness is less than 0.8 mm, the finishing temperature during hot rolling is significantly reduced and the power for reduction is insufficient, so that it is industrially difficult. If it exceeds 0.0 mm, the steel sheet must be avoided because the steel sheet becomes significantly embrittled.

Next, continuous annealing of the hot-rolled sheet is performed. There are long-time batch annealing and short-time continuous annealing in the annealing of hot-rolled sheets, but in batch annealing, the temperature tends to be uneven in, inside, outside, or in the width direction of the coil, and the magnetic variation and the cold-rolled shape are poor. Not possible due to problems. The cooling rate after continuous annealing is important and is limited to 1 to 40 ° C / sec. The slower the cold speed,
The above-mentioned special interaction with the thin hot rolled sheet has an effect on brittleness, but if it is less than 1 ° C./sec, it takes too much time for cooling, so that the equipment of the cooling zone becomes long and is not industrial. Also, 4
If it exceeds 0 ° C./sec, embrittlement of the steel sheet becomes a problem. This cooling rate is an average cooling rate from the cooling start temperature (soaking temperature) to 100 ° C. In addition, it is necessary to control the crystal grain size after hot-rolled sheet annealing, and it is necessary to control the crystal grain size to 100 μm or more. As is well known, the larger the crystal grain size after annealing the hot-rolled sheet is, the better the magnetic properties are, and if it is less than 100 μm, the magnetic properties are unsatisfactory.

Before or after the hot-rolled sheet annealing, pickling is performed, and then cold rolling is performed. Cold rolling is performed by ordinary reversing or tandem.At this time, as before, the heat retention or heating before cold rolling is effective for brittleness countermeasures.In that sense, the heat retained in the coil after hot rolled sheet annealing is used. It is also advantageous to cold roll immediately.

After cold rolling, it is degreased and subjected to ordinary continuous annealing. As the annealing temperature, a conventional high temperature of about 900 to 1250 ° C. is adopted, and it is particularly necessary to control the crystal grain size to 70 to 300 μm. As is known, the crystal grain size is 150μ.
m, the iron loss becomes better.
When the thickness exceeds 0 μm, the iron loss hardly decreases, but slightly increases. For this reason, if it is less than 70 μm, iron loss is unsatisfactory and must be avoided. On the other hand, if the thickness exceeds 300 μm, annealing at a high temperature for a long time is indispensable. In order to prevent deterioration of high magnetic field iron loss due to surface oxidation of the steel sheet by this annealing, a reducing atmosphere is preferable as disclosed in JP-A-56-16623. After this annealing, a mixture of an organic material and an inorganic material or an inorganic insulating film is applied and baked.

[0018]

Embodiments of the present invention will be described below. Steel ingots containing various components were produced by vacuum melting, and hot-rolled at a heating temperature of 1000 ° C. to obtain hot-rolled sheets having the thickness shown in Table 1.

[0019]

[Table 1]

The temperature of the hot rolled sheet was changed to the temperature shown in Table 2, and a soaking treatment was performed in nitrogen gas for 30 seconds, and the cooling rate was changed as shown in Table 2. 30mm width x 300mm from this steel plate
A long test piece was cut out and JIS C 2550 (1975)
The bending times were measured in accordance with the bending test method of (year). The number of n was 5, and the minimum number was shown in the table. Then, after pickling, after cold rolling to a thickness of 0.35 mm,
It was degreased and annealed. The annealing temperature was changed, soaking was performed for 20 seconds, and the crystal grain size was controlled in 100% hydrogen. The obtained iron loss was measured and averaged for L and C using an 80 mm square SST sample.

[0021]

[Table 2]

As shown in Tables 1 and 2, when the thickness of the hot-rolled sheet exceeds 2.0 mm, there is no slow cooling effect in the hot-rolled sheet annealing, and zero or one bending occurs. On the other hand, when the hot rolled sheet is 2.0
It can be seen that when the thickness is reduced to not more than mm, the number of times of repeated bending is remarkably improved by multiplying with the slow cooling (40 ° C./sec or less) effect in the hot-rolled sheet annealing. It is also clear that brittle measures are not taken if the hot rolled sheet is thinned but rapidly cooled by hot rolled sheet annealing, or if the hot rolled sheet is thickened even if the hot rolled sheet annealing is gradually cooled.
Further, when the component composition is out of the range of the present invention, deterioration of iron loss is large. The reason why the thinner the hot rolled sheet is, the better the iron loss is, probably because the effect of improving the texture due to the effect of the cold rolling reduction is seen.

[0023]

As described above, by controlling the components, hot rolling conditions and hot rolling sheet annealing conditions, a non-oriented electrical steel sheet having excellent magnetic properties and no problem of embrittlement was obtained.

Claims (1)

[Claims] 1. Weight%, C ≦ 0.003%, Si: 2.5-4.5%, Al: 0.1-2%, Mn: 0.07-3%, P ≦ 0.05 %, S ≦ 0.002%, N ≦ 0.003%, O ≦ 0.004% The hot-rolled steel sheet containing the remaining unavoidable components is subjected to continuous hot-rolled sheet annealing to reduce the crystal grain size to 100 μm or more. And then
Perform cold rolling and recrystallization annealing to reduce the crystal grain size to 100-
In the method for producing a non-oriented electrical steel sheet having a thickness of 300 μm, the thickness of the hot-rolled sheet is 0.8 to 2.0 mm, and the cooling rate of the hot-rolled sheet annealing is 1 to 40 ° C./sec. Manufacturing method of non-oriented electrical steel sheet.