JPH1192890A - Nonoriented silicon steel sheet low in core loss and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce core loss in a steel sheet by allowing it to have a specified compsn. contg. Si, Mn, Al, S, and the balance substantial Fe and regulating the content of nitride in a region at a specified distance from the surface of the steel sheet after finish annealing to a specified value or below. SOLUTION: This steel sheet contains, by weight, <=4.0% Si, 0.05 to 1.0% Mn, 0.1 to 1.0% Al and <=0.001% S. Then, the content of nitride in a region within 30 μm from the surface of the steel sheet after finish annealing is regulated to <=300 ppm. As for S as the contained element, in the case it is regulated to 0.001%, namely, to >=10 ppm, its remarkable core loss resistance can be attained, but, even if it is furthermore reduced, reduction in the core loss is made mild, and the core loss can not be regulated to <=2.4 W/kg. This is because a nitriding layer remarkably formed in the region of S<=10 ppm disturbs the growth of the crystal grains in the surface layer part to suppress reduction in the core loss. Therefore, the nitriding layer in the surface layer part of the steel sheet is removed by pickling after finish annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet having low iron loss and suitable as an electrical material used for electrical equipment.

[0002]

2. Description of the Related Art In recent years, electromagnetic steel sheets with lower iron loss have been required from the viewpoint of energy saving of electrical equipment. In order to reduce the iron loss, it is effective to increase the crystal grain size.
For medium- and high-grade non-oriented electrical steel sheets of up to about 3%, coarsening of crystal grains can be achieved by increasing the finish annealing temperature to about 1000 ° C, reducing the line speed during annealing, and lengthening the annealing time. I'm trying.

In order to improve the grain growth during 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 a technique for reducing iron loss by reducing S: 50 ppm or less and O: 25 ppm or less in a steel of Si: 2.5 to 3.5% and Al: 0.3 to 1.0%. Is disclosed.

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 any of these techniques, the iron loss value of a high-grade steel sheet having an S content of 10 ppm or less is about W _15/50 = 2.4 W / kg (sheet thickness 0.5
mm), and no further low iron loss has been achieved. To put it simply, it seems that reducing the amount of S reduces the amount of MnS in the steel, which facilitates the growth of crystal grains, and thus the iron loss seems to decrease more and more. However, in reality, the decrease in iron loss due to the decrease in the amount of S is saturated when the amount of S is about 10 ppm, and the iron loss value as described above is the limit.

The present invention has been made in view of such circumstances, and has as its object to provide an electromagnetic steel sheet with low iron loss.

[0009]

The gist of the present invention is that S is 10
The iron loss does not decrease even if it is controlled to a trace amount of ppm or less.
Based on the new finding that a remarkable nitride layer is formed in the surface region in the trace S region, the amount of nitride on the steel sheet surface after the finish annealing is suppressed to a predetermined range, so that the iron loss is low. The purpose is to obtain a conductive electrical steel sheet.

[0010] That is, the problem is that Si: 4.0% by weight.
% Or less, Mn: 0.05 to 1.0%, Al: 0.1 to 1.0%, S: 0.001
% Or less (including 0), and the balance is substantially Fe, and the amount of nitride in a region within 30 μm from the surface of the steel sheet after finish annealing is 300 ppm or less. The problem is solved by a non-oriented electrical steel sheet having a low value.

Further, the non-oriented electrical steel sheet having a low iron loss is characterized in that the steel sheet of the above-mentioned component is pickled after finish annealing to reduce the nitride content in a region within 30 μm from the surface of the steel sheet after finish annealing to 300 ppm or less. Adjustment (claim 2) enables easy manufacture.

Here, "the balance is substantially Fe" means:
This means that those containing trace elements other than the inevitable impurities are within the scope of the right within a range not to impair the effects of the present invention.
In the following description, all the percentages indicating the components of steel mean weight%, and ppm also means weight ppm.

(Circumstances leading to the invention and the reasons for limiting the amounts of S and nitrides) The present inventors investigated the effect of S on iron loss, so that C: 0.0025%, Si: 2.75%, and Mn: 0.20% , P: 0.
010%, Al: 0.31%, N: 0.0018%, and the S amount is tr.
The steel changed in the ppm range 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.
cold rolled to 900 mm in a 10% H ₂ -90% N ₂ atmosphere.
Finish annealing was performed for 2 minutes. FIG. 1 shows the relationship between the S content of the sample thus obtained and the iron loss W _15/50 (marked by X in FIG. 1). Here, the magnetic measurement was performed by a 25 cm Epstein method.

FIG. 1 shows that a significant reduction in iron loss (W _15/50 = 2.5 W / kg) is achieved when S is set to 10 ppm or less.
It can be seen that there is a critical point around 10 ppm. This is because grain growth was improved by reducing the amount of S. For this reason, in the present invention, the range of S is limited to 10 ppm or less, preferably 5 ppm or less.

However, when the S content is 10 ppm or less, the iron loss decreases gradually, and even if the S content is tr.
Iron loss cannot be less than 2.4 W / kg.

The present inventors consider that the reason why the reduction of iron loss is inhibited by the extremely low S material of S = 10 ppm or less may be due to unknown factors other than MnS. went. As a result, a remarkable nitride layer was recognized on the surface layer of the steel sheet in the region of S ≦ 10 ppm. On the other hand, S> 10pp
In the region of m, the nitrided layer was slight. This nitrided layer is considered to have been generated during hot rolled sheet annealing and finish annealing performed in a nitriding atmosphere.

The cause of the acceleration of the nitridation reaction accompanying the reduction of the amount of S is considered as follows. That is, since S is an element easily concentrated on the surface and the grain boundaries, S> 10 pp
In the region of m, S is concentrated on the surface of the steel sheet to suppress adsorption of nitrogen from the atmosphere to the surface layer of the steel sheet during hot-rolled sheet annealing and finish annealing. For this reason, a nitrided layer is not generated, or is generated very little. On the other hand, in the region where S ≦ 10 ppm, the effect of suppressing the adsorption of nitrogen by S is reduced, so that a nitride layer is formed on the surface layer of the steel sheet.

The inventors of the present invention have found that the nitrided layer which is remarkably generated in the region of S ≦ 10 ppm hinders the growth of crystal grains on the surface layer of the steel sheet,
We thought that the reduction of iron loss might be suppressed.

Based on the above idea, the present inventors,
It was considered that if the nitride layer in the surface layer of the steel sheet could be controlled within a predetermined range, the iron loss of the extremely low S material would be further reduced.

Therefore, the same material as the sample indicated by the symbol x in FIG. 1 was used, and the sample which was similarly subjected to finish annealing was subjected to pickling treatment to completely remove the surface nitrided layer. It was measured. The result is shown by a circle in FIG.

Focusing on the iron loss reduction effect of the pickling treatment, in the region of S> 10 ppm, the iron loss by the pickling treatment is 0.02%.
The iron loss is reduced by about 0.20 W / kg by the pickling treatment in the region of S ≦ 10 ppm, and the iron loss reduction effect by the pickling treatment is small when the amount of S is small. Prominently observed.

From the above, it has been found that, unlike the case of the magnetic steel sheet having a high S, the iron loss is significantly reduced in the ultra-low S magnetic steel sheet by reducing the nitrided layer in the steel sheet surface portion.

Next, in order to investigate the relationship between the amount of nitride in the surface layer of the steel sheet and the iron loss, C: 0.0020%, Si: 2.75%, Mn: 0.
20%, P: 0.012%, Al: 0.30%, S: 0.0003%, N:
The steel of 0.0017% was melted in a laboratory, pickled after hot rolling. Subsequently, the hot rolled sheet was subjected to 83% H ₂ -25% N ₂ atmosphere.
Hot rolled sheet annealing at 0 ° C x 3hrs, then a sheet thickness of 0.50 ~ 0.5
And cold rolled to 5 mm, 930 ° C. × in 10% H ₂ -90% N ₂ atmosphere
Finish annealing was performed for 2 minutes.

Thereafter, a steel sheet was produced in which the amount of nitride on the surface layer of the steel sheet was changed by changing the pickling time variously, and the magnetic properties were measured by the 25 cm Epstein method. Here, the plate thickness after the pickling treatment was all adjusted to be 0.5 mm.

FIG. 2 shows that 30 μm from the surface of the steel sheet after the pickling treatment.
_Shows the relationship between the amount of nitride and W _{15/50 in} the region within. In this steel type, the nitrides were AlN, Si ₃ N ₄ , and TiN. Attention was paid to the range of 30 μm from the surface of the steel plate because 80 to 90% of the nitride exists in this range, and the amount of nitride is extremely small at a depth greater than that, so This is because it was considered that it was sufficient to evaluate the amount of nitride in the range of 30 μm.

FIG. 2 shows that when the nitride content at the surface layer portion of the steel sheet of 30 μm is 300 ppm or less, the iron loss decreases, and W _15/50 = 2.25 W
/ Kg is achieved.

From the above, in the present invention, the amount of nitride in a region within 30 μm from the steel sheet surface is limited to 300 ppm or less.

(Reasons for Limiting Other Components) Next, the reasons for limiting other components will be described. Si: Si is an effective element for increasing the specific resistance of the steel sheet. However, if it exceeds 4.0%, the magnetic flux density decreases with a decrease in the saturation magnetic flux density, so the upper limit is set to 4.0%. Mn: Mn is 0.1% to prevent red hot brittleness during hot rolling.
It is required to be not less than 05%, but if it is not less than 1.0%, the magnetic flux density is reduced. Al: Al is an element effective for increasing the specific resistance, like Si, but 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%. Also,
If it is less than 0.1%, the lower limit is set to 0.1% because AlN becomes finer and the grain growth is reduced.

(Manufacturing method) In the present invention, as long as the amount of S and the nitride in the surface layer portion of the steel sheet are within a predetermined range, the manufacturing method may be an ordinary method of manufacturing a non-oriented electrical steel sheet. That is, the molten steel blown in the converter is degassed to adjust to a predetermined component, and then casting and hot rolling are performed. The finish annealing temperature and the winding temperature at the time of hot rolling do not need to be particularly specified, and may be a temperature in a range where a normal non-oriented electrical steel sheet is manufactured. In addition, hot-rolled sheet annealing after hot-rolling may be performed, but is not essential. Next, final cold-rolling or cold-rolling two or more times with intermediate annealing to obtain a predetermined sheet thickness is performed, followed by final annealing.

The method for controlling the amount of nitride in the surface layer of the steel sheet within a predetermined range does not need to be particularly defined. For example, the method is achieved by removing the nitride layer in the surface layer of the steel sheet by pickling after finish annealing.

[0031]

EXAMPLES The steels shown in Table 1 were cast into a given component after being degassed after being blown in a converter,
After heating at a slab heating temperature of 1160 ° C. for 1 hour, hot rolling was performed to a sheet thickness of 2.0 mm. Finishing temperature during hot rolling is 750
° C, the winding temperature was 610 ° C, and hot-rolled sheet annealing at 830 ° C for 180 minutes was performed. Next, the hot-rolled sheet is pickled and then
Cold rolling was performed to 0.50 to 0.55 mm, and finish annealing at 920 ° C. × 2 min was performed.

After the finish annealing, pickling was performed, and the amount of nitride in the surface layer of the steel sheet was changed by variously changing the pickling time. Then, the amount of nitride in a range of 30 μm from the steel sheet surface was measured. The nitride was AlN.

The magnetic measurement was performed using a 25 cm Epstein test piece ((L + C) / 2). The amount of nitride in the range of 30 μm from the steel sheet surface of each steel sheet and the magnetic properties (iron loss W
_15/50 and magnetic flux density B ₅₀ ) are also shown in Table 1.

[0034]

[Table 1]

As can be seen from Table 1, the steel of the present invention, N
o-No. 3 steel loss W after finish annealing
_15/50 is very low.

On the other hand, in the steel sheets No. 4 and No. 5, since the S content is larger than the range of the present invention, the iron loss W _15/50 is extremely high.

Further, in the steel sheets No. 6 and No. 7, since the amount of nitride in the range of 30 μm from the steel sheet surface is larger than the range of the present invention, the iron loss W _15/50 is high.

[0038] The steel sheet No. 8 has a higher content of Si than the range of the present invention, so that the iron loss _{W15 / 50} is low, but the magnetic flux density _B50 is low.

[0039] No.9 of steel sheet, so the Mn content is larger than the range of the present invention, the magnetic flux density B ₅₀ is low.

Since the steel sheet No. 10 has a higher Al content than the range of the present invention, the iron loss W _15/50 is low, but the magnetic flux density B ₅₀ is low.

[0041]

As described above, according to the present invention, the weight%
With Si: 4.0% or less, Mn: 0.05-1.0%, Al: 0.1-1.0%,
S: contains 0.001% or less (including 0), the balance is substantially Fe, and 30 μm from the surface of the steel sheet after finish annealing
Since the non-oriented electrical steel sheet has a nitride content of 300 ppm or less in the region within, the iron loss after magnetic annealing is low.

Further, the amount of nitride in a region within 30 μm from the surface of the steel sheet after the finish annealing is reduced by pickling after the finish annealing.
When the content is adjusted to 0 ppm or less, a non-oriented electrical steel sheet having a low iron loss can be easily manufactured.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a relationship between an amount of nitride in a region 30 μm from a steel sheet surface and magnetic properties after finish annealing.

Claims (2)

[Claims] (1) Si: 4.0% or less by weight%, Mn: 0.05 to 1.0
%, Al: 0.1 to 1.0%, S: 0.001% or less (including 0), the balance being substantially Fe, and the amount of nitride in a region within 30 μm from the surface of the steel sheet after finish annealing. Is 300ppm
Non-oriented electrical steel sheet with low iron loss, characterized by the following. 2. Si: 4.0% or less by weight%, Mn: 0.05 to 1.0% by weight
%, Al: 0.1 to 1.0%, S: 0.001% or less (including 0), the balance being substantially Fe, a method for producing a non-oriented electrical steel sheet having a low iron loss, and after finish annealing By pickling,
A method for producing a non-oriented electrical steel sheet having a low iron loss, wherein a nitride amount in a region within 30 μm from a surface of a steel sheet after finish annealing is adjusted to 300 ppm or less.