JP3352904B2 - Manufacturing method of non-oriented electrical steel sheet - Google Patents

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 a core of a motor or a small transformer 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 manufactured by increasing the electrical resistance by increasing Si and Al in order to improve iron loss, and by improving the impurities, ie, S, N,
Efforts have been made to purify 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, especially in winter, the production obstacles such as cracking at a place where bending deformation of the steel sheet after hot-rolled sheet annealing is applied and breakage by a cold-rolled Sendzimir mill were very important problems. 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 at 0 to 1 time in a bending test using a bending tester (radius of a part where bending is attached: 5 mm) using 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% A hot-rolled steel sheet continuously annealed to a hot-rolled steel sheet including the balance of Fe and unavoidable impurities to have a crystal grain size of 100 μm or more, and then cooled. In the method for producing a non-oriented electrical steel sheet having a grain size of 100 to 300 μm by performing rolling and recrystallization annealing, the thickness of the hot rolled sheet is set to 0.8 to 2.0 mm, A method for producing a non-oriented electrical steel sheet, wherein a cooling rate of annealing is 1 to 40 ° C./sec.

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 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 C content is limited to 0.003% or less is that if the C content exceeds this, there is a problem in magnetic aging.

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 Al content is less than 0.1%, the 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 a hot rolled sheet, and is required to be 0.07% or more. If the amount 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 to deteriorate iron loss, and there is a problem of addition cost.
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 decreases, and at the same time, magnetic wall properties are hindered by deteriorating the magnetic properties and must be avoided.

The amount of N is limited to 0.003% or less. 0.
In 003% ultra is because blister-like surface defects called blisters occur. The O content is 0.004% or less. O forms oxides and deteriorates iron loss.
04% or less. In addition to the above elements, Sn, Ni, Cu, Sb, and Cr which are known to improve magnetic properties
The effect of the present invention is not impaired even if such is added.

Next, the processing conditions of the present invention will be described.
The slab heating for hot rolling is not particularly limited, but the temperature is preferably low and preferably 950 to 1200 ° C. for the purpose of preventing fine precipitates. 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 if it is thinner, but if it 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 the inside, inside, outside, or 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 the 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, and 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. Temperature annealing, a high temperature of about conventional 900 to 1,250 ° C. are employed, in particular 100 ～300Myuemu grain size
Need to be controlled. As is known, the grain size is 150
Iron loss becomes better with increasing to about μm.
If it exceeds 50 μm, the iron loss hardly decreases and tends to increase slightly. Therefore, if the thickness is less than 100 μm, the 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. Further, in order to prevent the deterioration of the high magnetic field iron loss due to the 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 prepared by vacuum melting, hot-rolled at a heating temperature of 1000 ° C., and hot-rolled sheets having the thickness shown in Table 1 were obtained.

[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 effect of slow cooling (40 ° C./second or less) in hot-rolled sheet annealing. It is clear that even if the hot-rolled sheet is made thin, it is rapidly cooled by hot-rolled sheet annealing, or if the hot-rolled sheet is thick even if the hot-rolled sheet annealing is gradually cooled, it is not a brittle measure.
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 rate 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 excellent in magnetic properties and free from embrittlement was obtained.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 8/12 C22C 38/00 303 C22C 38/06 H01F 1/16

Claims (1)

(57) [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% A hot-rolled steel sheet continuously annealed to a hot-rolled steel sheet comprising the balance of Fe and unavoidable impurities to have a crystal grain size of 100 μm or more. Then, cold rolling is performed, and the recrystallization annealing is performed to produce a non-oriented electrical steel sheet having a crystal grain size of 100 to 300 μm, and the thickness of the hot rolled sheet is set to 0.8 to 2.0 mm. A method for producing a non-oriented electrical steel sheet, wherein the cooling rate of the hot-rolled sheet annealing is 1 to 40 ° C./sec.