JPH1161259A - Manufacture of nonoriented silicon steel sheet with low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of a non-oriented silicon steel sheet reduced in iron loss after finish annealing. SOLUTION: A steel, having a composition consisting of, by weight, <=0.005% C, <=4.5% Si, 0.05-1.0% Mn, <=0.1% P, <=0.005% (including 0%) N, <=1.0% Al, <=0.001% (including 0%) S, and the balance essentially Fe, is hot-rolled, pickled, subjected to hot rolled plate annealing in an atmospheric gas of <=20% partial pressure of nitrogen, successively cold-rolled to prescribed sheet thickness, and then annealed continuously.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a non-oriented electrical steel sheet having a low iron loss and used for electric equipment and the like.

[0002]

2. Description of the Related Art In recent years, electromagnetic steel sheets having lower iron loss have been demanded from the viewpoint of energy saving of electric equipment. In order to reduce the iron loss, it is effective to increase the crystal grain size.
% Of medium- and high-grade non-oriented electrical steel sheets, increase the finish annealing temperature to about 1000 ° C, lower the line speed during annealing, and increase the annealing time to increase the grain size. I have.

In order to improve the grain growth during the finish annealing, it is effective to reduce the amount of inclusions and precipitates in the steel sheet. For this reason, attempts have been made to render the inclusions and precipitates harmless, and particularly in high-grade materials, attempts have been made to reduce the S content from the viewpoint of preventing precipitation of MnS.

[0004] For example, Japanese Patent Publication No. 56-22931 discloses that in steel containing 2.5% to 3.5% of Si and 0.3% to 1.0% of Al, S:
There is disclosed a technique for reducing iron loss by reducing the content of iron to 50 ppm or less and O: 25 ppm or less.

In Japanese Patent Publication No. 2-50190,
Si: 2.5-3.5%, Al: 0.25-1.0% steel: S: 15p
There is disclosed a technique for reducing iron loss by setting the pm or less, O: 20 ppm or less, and N: 25 ppm or less.

Further, Japanese Patent Application Laid-Open No. 5-140647 discloses that, in a steel containing 2.0% to 4.0% of Si and 0.10% to 2.0% of Al, S: 30 ppm or less and Ti, Zr, Nb, and V each being 50 ppm or less. Techniques for reducing iron loss have been disclosed.

[0007]

However, in each of these techniques, the total amount of Si and Al is 3 to 3.
The iron loss value of a high-grade steel sheet with about 5% and S content of 10 ppm or less is about W _15/50 = 2.4 W / Kg (sheet thickness 0.5 mm), and a lower iron loss than this has been achieved. There is no present.

[0008] The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a method for producing a non-oriented electrical steel sheet having a lower iron loss after finish annealing.

[0009]

The gist of the present invention is that S is 1
Based on the new finding that the reason why the iron loss does not decrease even when controlled to a very small amount of 0 ppm or less is that a remarkable nitrided layer is formed in the surface region during annealing of the hot-rolled sheet in the minute amount S region, By reducing the nitrogen partial pressure during annealing, the formation of nitrides is suppressed, and iron loss is reduced.

[0010] That is, the above-mentioned problem is expressed by:
%, P: 0.2% or less, N: 0.005% or less (including 0), Si: 4.5% or less, Mn: 0.05 to 1.0%, Al: 1.0% or less, S: 0.001% (including 0) The steel whose balance is substantially Fe or less is hot-rolled and pickled, then hot-rolled in an atmosphere gas having a nitrogen partial pressure of 20% or less, and then cooled to a predetermined thickness. It is solved by a method of performing continuous annealing after cold rolling.

Here, "the balance is substantially Fe" means that those containing other trace elements fall within the scope of the right within a range not to impair the features of the present invention. In the following description, all percentages indicating the composition of steel mean weight%,
ppm also means ppm by weight.

(History leading to the invention, and reasons for limiting S content and nitrogen partial pressure) Hereinafter, the background leading to the present invention will be described in detail.

First, in order to investigate the effect of S on iron loss, C: 0.0025%, Si: 2.85%, Mn: 0.20%, P: 0.
01%, Al: 0.31%, N: 0.0021%, S amount is tr.
The steel changed in the range of pm was melted in a laboratory, hot-rolled, and then pickled. Subsequently, the hot-rolled sheet is subjected to hot-rolled sheet annealing at 830 ° C. for 3 hours in an atmosphere of 75% H ₂ -25% N ₂ , and thereafter, a sheet thickness of 0.5 mm
Cold rolling to 900 ° C × 1m in 25% H ₂ -75% N ₂ atmosphere
Finish annealing between in was performed.

FIG. 1 shows the relationship between the S content of the sample thus obtained and the iron loss W _15/50 (marked by x). here,
The magnetic measurement was performed by the 25 cm Epstein method.

FIG. 1 shows that a significant reduction in iron loss can be achieved when S is set to 10 ppm or less. This is because grain growth was improved by reducing the amount of S. From the above, in the present invention, S is set to 10 ppm or less, more preferably, 5 ppm or less.

However, if S is 10 ppm or less,
Iron loss has been reduced moderately.
It cannot be less than W / Kg.

The present inventors have considered that the reason why the reduction of iron loss is inhibited by an extremely low S material having S of 10 ppm or less may be due to unknown factors other than MnS. Was used to observe the structure. As a result, in the region of S> 10 ppm, the nitrided layer was slight, while in the region of S ≦ 10 ppm, a remarkable nitrided layer was recognized.

Although the mechanism of accelerating the nitridation reaction accompanying the reduction of the amount of S has not been sufficiently elucidated, the present inventors think as follows. That is, S is easily concentrated on the surface and the grain boundaries and has a relatively high diffusion rate, so that S is segregated on the surface in the initial process of hot-rolled sheet annealing. As a result, even when the nitrogen partial pressure in hot-rolled sheet annealing is high, S segregated on the surface serves as a barrier for the nitrogen adsorption reaction. In principle, the lower limit of S for becoming a barrier for the nitrogen adsorption reaction is an extremely small amount sufficient to cover the surface, and the range of S> 10 ppm found experimentally is sufficient. Corresponding to this. On the other hand, in the region where S ≦ 10 ppm, the effect of suppressing nitrogen adsorption by S is reduced, and it is considered that nitriding is more likely to occur than in the region where S> 10 ppm.

The present inventors have considered that the nitrided layer in the surface layer is mainly formed during hot-rolled sheet annealing, and may hinder the growth of crystal grains during the final annealing to suppress the reduction in iron loss. Based on this idea, we conducted various studies focusing on the gas atmosphere during hot-rolled sheet annealing to suppress the adsorption of nitrogen during hot-rolled sheet annealing. Pressure 20
% Or less was found to significantly improve iron loss after finish annealing.

FIG. 1 shows the results of annealing the hot-rolled sheet in 95% hydrogen on the same samples from which the data indicated by the crosses in FIG. 1 were obtained. In the region where S exceeds 10 ppm, the iron loss hardly changes, but when S ≦ 10 ppm, the iron loss is reduced by about 0.15 W / Kg. In the case of a small amount of S, the effect of improving the iron loss is remarkably recognized. When the structure of these samples was observed with an optical microscope, almost no nitrided layer was observed. That is, in this case, it is considered that the nitriding during the annealing of the hot-rolled sheet was slight, so that the growth of crystal grains during the final annealing was not hindered and the iron loss was reduced.

Next, in order to investigate the relationship between the nitrogen partial pressure during hot-rolled sheet annealing and iron loss during finish annealing, C: 0.0028%, Si:
2.65%, Mn: 0.20%, P: 0.02%, Al: 0.30%, S: 0.
0006%, N: 0.0019% steel was melted in a laboratory, hot rolled,
Pickling was performed. Continuously, the nitrogen partial pressure was 0-
830 ℃ × 3h in an atmosphere gas consisting of 50% and the balance being hydrogen
The hot-rolled sheet was subjected to r annealing, then cold-rolled to a sheet thickness of 0.5 mm, and subjected to finish annealing at 900 ° C. for 1 minute in a 25% H ₂ -75% N ₂ atmosphere.

FIG. 2 shows the relationship between the nitrogen partial pressure during hot-rolled sheet annealing and iron loss after finish annealing. FIG. 2 shows that the iron loss decreases due to the reduction in the nitrogen partial pressure, and sharply decreases until the nitrogen partial pressure becomes 20%. 0.15W especially when nitrogen partial pressure is 10% or less
A remarkable improvement effect of about / Kg was observed.

This is presumably because when the nitrogen partial pressure decreases, the amount of free nitrogen that contributes to the nitriding of the hot-rolled sheet decreases. In fact, when observing the structure of these finish annealing materials,
When the amount of nitrogen in the atmosphere gas is 20% or less, the nitrided layer on the steel sheet surface decreases, and when the partial pressure is 10% or less, it becomes almost unrecognizable with an optical microscope.

From the above, in the present invention, the nitrogen partial pressure during annealing of a hot-rolled sheet is set to 20% or less, preferably 10% or less. The remainder of the atmospheric gas may be any gas that does not oxidize the steel sheet surface, and may be, for example, hydrogen gas or an inert gas such as argon or helium.

(Reasons for Limiting Other Components) Next, reasons for limiting other components will be described. C: C is 0.005% or less because of the problem of magnetic aging. Si: Si is an element effective for increasing the specific resistance of the steel sheet. However, if it exceeds 4.5%, the magnetic flux density decreases with a decrease in the saturation magnetic flux density, so the upper limit is set to 4.5%. Mn: Mn is used to prevent red hot brittleness during hot rolling.
0.05% or more is necessary, but if it is 1.0% or more, the magnetic flux density is reduced. P: P is an element necessary for improving the punching property of the steel sheet, but if added in excess of 0.1%, the steel sheet becomes brittle, so that the content is set to 0.1% or less. N: N is set to 0.005% or less to increase the amount of AlN and increase iron loss when the content of N is large. Al: Al, like Si, is an element effective for increasing the specific resistance. However, if it exceeds 1.0%, the magnetic flux density decreases with a decrease in the saturation magnetic flux density, so the upper limit is set to 1.0%. If the content is less than 0.1%, the lower limit is set to 0.1% because AlN becomes finer and the grain growth is reduced.

[0026]

EXAMPLES The steels shown in Table 1 were cast into a given component after being degassed after being blown in a converter,
After the slab was heated at 1200 ° C. for 1 hour, hot rolling was performed to a thickness of 2.0 mm. The hot rolling finishing temperature was 800 ° C. The winding temperature was 550 ° C., and the hot rolled sheet was annealed under the conditions shown in Table 1. Next, the hot-rolled sheet was pickled, cold-rolled to a sheet thickness of 0.5 mm, and then annealed under the finish annealing conditions shown in Table 1.

The magnetic measurement was performed using a 25 cm Epstein test piece. Table 1 also shows the magnetic properties of each steel sheet after the finish annealing.

[0028]

[Table 1]

From this, it can be seen that when the S content and the hot-rolled sheet annealing conditions are controlled within the range of the present invention, a steel sheet having extremely low iron loss after finish annealing can be obtained.

On the other hand, the steel sheets No. 6 and No. 14 have a nitrogen partial pressure in the hot-rolled sheet annealing atmosphere which is out of the range of the present invention. Iron loss is high. Further, the steel sheets of No. 7 and No. 15 have higher iron loss than the steel sheets manufactured by the method of the present invention because the range of S is out of the range of the present invention.

[0031]

As described above, in the present invention, C: 0.005% or less, Si: 4.5% or less, Mn:
Steel containing 0.05 to 1.0%, P: 0.1% or less, N: 0.005% or less (including 0), Al: 1.0% or less, S: 0.001% or less (including 0), and the balance being substantially Fe Is subjected to hot rolling and pickling, then subjected to hot rolled sheet annealing in an atmosphere gas having a nitrogen partial pressure of 20% or less, and subsequently cold rolled to a predetermined sheet thickness, and then subjected to continuous annealing. Therefore, a steel sheet with low iron loss after magnetic annealing can be obtained. This steel sheet is suitable for being widely used for applications requiring low iron loss such as electric materials.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the amount of S and magnetic properties (iron loss) after finish annealing.

FIG. 2 is a diagram showing a relationship between a nitrogen partial pressure in a hot-rolled sheet annealing atmosphere gas and magnetic properties (iron loss) after finish annealing.

Claims (1)

[Claims] 1. In weight%, C: 0.005% or less, Si: 4.5%
Mn: 0.05 to 1.0%, P: 0.1% or less, N: 0.005%
Or less (including 0), Al: 1.0% or less, S: 0.001%
In the following (including 0), the steel whose balance is substantially Fe is hot-rolled, pickled, and then subjected to hot-rolled sheet annealing in an atmosphere gas having a nitrogen partial pressure of 20% or less. A method for producing a non-oriented electrical steel sheet having a low iron loss, wherein the steel sheet is subjected to continuous annealing after cold rolling to a sheet thickness of 1 mm.