JPH11229097A - Nonoriented silicon steel sheet reduced in core loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably provide a nonoriented silicon steel sheet reduced in core loss. SOLUTION: This steel sheet has a composition consisting of, by weight, <=0.005% C, <=4.0% Si, 0.05-1.0% Mn, <=0.2% P, <=0.005% (including 0%) N, 0.1-1.0% Al, <=0.001% (including 0%) S, at least either of Sb and Sn in an amount satisfying Sb+Sn/2=0.001 to 0.05%, <=0.005% (including 0%) Ti, and the balance essentially Fe.

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 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 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 an object of the present invention is to provide an electromagnetic steel sheet having a stable and 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 a new finding that a remarkable nitride layer is formed in the surface region in the trace S region, at least one of Sb and Sn is contained in 0.001 to 0.05% by Sb + Sn / 2,
By limiting the Ti content to 0.005% or less, the formation of nitrides is suppressed and iron loss is reduced.

[0010] That is, the above-mentioned problem is expressed by:
005% or less, Si: 4.0% or less, Mn: 0.05 to 1.0%, P: 0.2
%, N: 0.005% or less (including 0), Al: 0.1 to 1.0
%, S: 0.001% or less (including 0), at least one of Sb and Sn is 0.001 to 0.05% by Sb + Sn / 2, Ti: 0.005% or less (including 0), and the balance is substantially Fe The problem is solved by a non-oriented electrical steel sheet having low iron loss.

The amount of Sb + Sn / 2 is adjusted to 0.001 to
By setting the content to 0.005%, iron loss can be significantly reduced.

Here, "the balance is substantially Fe" means:
This means that those containing inevitable impurities and other trace elements fall within the scope of the right as long as the functions and effects of the present invention are not lost. 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 S, Sb, Sn) The present inventors investigated the effect of S on iron loss, so that C: 0.0025%, Si: 2.85%, Mn: 0.20% , P: 0.01
0%, Al: 0.31%, N: 0.0021%, and the S amount is tr.
The steel changed in the range of m was melted in a laboratory in a vacuum, hot-rolled, and then pickled. 75% H ₂ -25
% N subjected to hot band annealing of 830 ° C. × 3 hr at ₂ atmosphere, then cold rolled to a thickness of 0.5 mm, subjected to finish annealing between 900 ° C. × 1min at 25% H ₂ -75% N ₂ atmosphere Was. 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 when S is set to 10 ppm or less, a significant reduction in iron loss is achieved, and there is a critical point near S = 10 ppm. This is because grain growth was improved by reducing the amount of S. From this, in the present invention, S
Is limited to 10 ppm or less.

However, when the amount of S is 10 ppm or less, the iron loss decreases gradually, and even if the amount of S 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 nitrided layer was observed in 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.

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 suppresses adsorption of nitrogen from the atmosphere to the surface layer of the steel sheet, so that no nitrided layer is formed. 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 present inventors have thought that the nitride layer generated in the surface layer region may hinder the growth of crystal grains and suppress the reduction of iron loss. Based on this idea, the inventors of the present invention have proposed an element that suppresses the adsorption of nitrogen by containing elements other than S, thereby suppressing the formation of a nitrided layer and promoting the growth of crystal grains to reduce iron loss. Based on the idea of reducing Sb, various studies were conducted on such elements, and as a result, it was found that Sb was effective.

FIG. 1 shows the results of a test conducted under the same conditions with respect to a sample containing 40 ppm of Sb in the components of the sample indicated by the symbol x. Focusing on the iron loss reduction effect of Sb, in the region of S> 10 ppm, iron loss is reduced only by about 0.02 to 0.04 W / kg due to Sb content, but S ≦ 10 ppm
In the region, the iron loss is reduced by about 0.2 W / kg, and the effect of reducing iron loss by Sb is remarkably observed when the amount of S is small. In this sample, no nitrided layer was observed regardless of the S content. From this, it is considered that Sb was concentrated in the surface layer of the steel sheet to suppress adsorption of nitrogen, and as a result, growth of crystal grains was not hindered, so that iron loss was reduced.

Next, in order to investigate the optimum Sb content,
C: 0.0026%, Si: 2.70%, Mn: 0.20%, P: 0.020
%, Al: 0.30%, S: 0.0004%, N: 0.0020%, Sb
The steel whose amount was changed from tr. To 700 ppm was melted in a laboratory in a vacuum, hot-rolled, and then pickled. Continue to add 75%
Subjected to hot rolled sheet annealing of H _2% -25% N ₂ atmosphere 830 ° C. × 3 hr, then cold rolled to a thickness of 0.5mm, 25% H ₂ -75%
Finish annealing was performed at 900 ° C. × 1 min in a N ₂ atmosphere. FIG.
The following shows the relationship between the Sb content and the iron loss W _15/50 .

FIG. 2 shows that iron loss is reduced in the region where the Sb content is 10 ppm or more, and W which cannot be obtained with the conventional magnetic steel sheet.
It can be seen that _15/50 = 2.25 to 2.35 W / kg is achieved.
However, when Sb is further added and Sb> 50 ppm, the iron loss increases again. However,
Even if it increases, at least the Sb content up to 700 ppm, W _15/50 = 2.2 which cannot be obtained with the conventional electrical steel sheet
5 to 2.35 W / kg has been achieved.

In order to investigate the cause of the increase in iron loss in the region where Sb> 50 ppm, the structure was observed with an optical microscope. As a result, although the surface layer fine grain structure was not recognized, the average crystal grain size was slightly smaller. Although the cause is not clear, it is considered that since Sb is an element that is easily segregated at the grain boundary, the grain growth property is reduced by the grain boundary drag effect of Sb.

As described above, in the present invention, Sb is
It is limited to 10 ppm or more, and is limited to 500 ppm or less for economic reasons. However, for the above-mentioned reason, it is more preferable that Sb be 50 ppm or less. Further, it is desirable that the content be 20 ppm or more and 40 ppm or less.

The inventors have studied whether the same effect can be obtained by the addition of another element, and conducted a test focusing on the effect of Sn. First, in order to investigate the effect of S on iron loss, as in the above test, C: 0.0020%, Si:
2.85%, Mn: 0.18%, P: 0.01%, Al: 0.30%, N: 0.
0018%, Ti: 0.0020%, and steel in which the S content was changed in the range of tr. To 15 ppm was melted in a vacuum 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 25% H ₂ -75% N ₂ atmosphere
Finish annealing was performed for 1 min. FIG. 3 shows the relationship between the S content of the sample thus obtained and the iron loss W _15/50 (marked by x in FIG. 3). Here, the magnetic measurement was performed by a 25 cm Epstein method.

FIG. 3 also shows that when S is set to 10 ppm or less, a significant reduction in iron loss is achieved. When there is a critical point near S = 10 ppm and when the amount of S is 10 ppm or less, the reduction in iron loss does not increase. It is confirmed that the iron loss cannot be reduced to 2.4 W / kg or less even if the amount of S is tr.

FIG. 3 shows the results of a test conducted under the same conditions on a sample in which 60 ppm of Sn was added to the components of the sample indicated by the symbol x, and the result is indicated by the symbol ○. Focusing on the iron loss reduction effect of Sn, in the region of S> 10 ppm, the iron loss is reduced only by about 0.02 to 0.04 W / kg due to the inclusion of Sn, but S ≦ 10 ppm
In the region of the above, it is reduced by about 0.2 W / kg, and when the amount of S is small, the effect of reducing iron loss of Sn is remarkably recognized. In this sample, no nitrided layer was observed regardless of the S content. From this, it is considered that Sn was concentrated in the surface layer portion of the steel sheet to suppress adsorption of nitrogen, and as a result, growth of crystal grains was not hindered, so that iron loss was reduced.

Next, in order to investigate the optimum Sn content,
C: 0.0025%, Si: 2.72%, Mn: 0.20%, P: 0.020
%, Al: 0.30%, S: 0.0002%, N: 0.0020%, Ti: 0.
A steel having a Sn content of 0010% and varied in the range of tr. To 1400 ppm was melted in a laboratory, hot-rolled, and then pickled. Subsequently, the hot-rolled sheet is annealed at 830 ° C. for 3 hours in a 75% H ₂ -25% N ₂ atmosphere, and then cold-rolled to a sheet thickness of 0.5 mm,
Finish annealing was performed at 900 ° C. for 1 minute in an H ₂ -75% N ₂ atmosphere. FIG. 4 shows the relationship between the Sn amount and the iron loss _{W15 / 50} .

FIG. 4 shows that iron loss is reduced in the region where the Sn content is 20 ppm or more, and W which cannot be obtained with the conventional magnetic steel sheet.
It can be seen that _15/50 = 2.25 to 2.35 W / kg is achieved.
However, when Sn is further added and Sn> 100 ppm, the iron loss increases again. However, even if it increases, at least the Sn amount up to 1400 ppm cannot be obtained with the conventional magnetic steel sheet.
_15/50 = 2.25 to 2.35 W / kg has been achieved.

In order to investigate the cause of the increase in iron loss in the region where Sn> 100 ppm, the structure was observed with an optical microscope.
As a result, although the surface layer fine grain structure was not recognized, the average crystal grain size was slightly smaller. Although the cause is not clear, since Sn is an element that easily segregates at the grain boundary, Sn
It is considered that the grain growth was reduced due to the grain boundary drag effect. Also in this sample, no nitrided layer was observed regardless of the amount of S. This is considered to be because Sn concentrated in the surface layer of the steel sheet and suppressed the adsorption of nitrogen.

As described above, in the present invention, Sn is
Limit to 20 ppm or more, and limit to 1000 ppm or less for economic reasons. However, for the reasons described above, it is more preferable to set the upper limit of Sn to 100 ppm. Further, the content is preferably 40 ppm or more and 80 ppm or less.

The difference between the effects of Sn and Sb on iron loss can be understood as follows. That is, since Sn has a segregation coefficient smaller than that of Sb, an amount about twice as large as that of Sb is required to suppress nitriding due to surface segregation. Therefore, Sn is 20
Addition of ppm or more will reduce iron loss. On the other hand, the addition amount at which iron loss starts to increase due to the drag effect due to the grain boundary segregation of Sn is also about twice as large as the segregation coefficient of Sn is smaller than that of Sb.

As described above, the mechanism by which Sb and Sn suppress nitriding is the same. For this reason, even when Sb and Sn are added simultaneously, the same nitriding suppression effect can be obtained.
However, in order for Sn to exhibit the same effect as Sb, 2
A double addition amount is required.

Therefore, in the present invention, Sb and Sn are treated collectively, and at least one of them is expressed as (Sb + Sn / 2).
It was decided to limit the content to 001-0.05%. It is more preferable to limit (Sb + Sn / 2) to 0.001 to 0.005%.

(Reason for Limiting Ti) Next, in order to investigate the production stability of the present steel type, C: 0.0025%, Si: 2.85%, Mn: 0.2%.
20%, P: 0.01%, Al: 0.31%, N: 0.0021%, S: 0.
0003%, Sb: 40 ppm steel was melted by a 10-charge actual machine, hot rolled, and then pickled. Continue to add 75%
Hot rolled sheet annealing at 830 ° C for 3 hours in an H ₂ -25% N ₂ atmosphere, and then cold rolling to a sheet thickness of 0.5mm, 25% H ₂ -75%
Finish annealing was performed at 900 ° C. × 1 min in a N ₂ atmosphere. As a result, it was found that iron loss varied greatly from 2.2 to 2.6 W / kg.

In order to investigate the cause, a thin film was prepared from the sample after the finish annealing, and TEM observation was performed. As a result, fine precipitates were not observed in the sample with low iron loss, but about 50 nm of TiN was observed in the sample with high iron loss. From this, it became clear that the cause of the variation in iron loss was due to the precipitation of fine TiN.

In order to investigate the effect of Ti on the grain growth, C: 0.0015%, Si: 2.87%, Mn: 0.20%,
P: 0.01%, Al: 0.31%, N: 0.0021%, S: 0.0003
%, Sb: 40 ppm, and steels with variously changed Ti contents were vacuum-melted in a laboratory, hot-rolled, and then pickled. Subsequently, the hot-rolled sheet was annealed at 830 ° C. for 3 hours in a 75% H ₂ -25% N ₂ atmosphere, and then cold-rolled to a sheet thickness of 0.5 mm.
Finish annealing was performed at 900 ° C. × 1 min in a% H ₂ -75% N ₂ atmosphere.

FIG. 5 shows the relationship between the Ti content of the sample thus obtained and the iron loss W _15/50 after the finish annealing. FIG. 5 shows that when the Ti content is 50 ppm or less, the iron loss W _15/50 is 2.35 W / kg or less, and a low iron loss can be stably obtained. From the above, in the present invention, the Ti content is limited to 50 ppm or less. It is more preferable that the content be 20 ppm or less.

(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 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 at least 05%, but if it is at least 1.0%, the magnetic flux density will be reduced. P: P is an element necessary for improving the punching property of the steel sheet, but if added in excess of 0.2%, the steel sheet will be embrittled, so that the content is set to 0.2% or less.

N: N is set to 0.005% or less in order to increase the amount of AlN and increase iron loss when the content of N is large. 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, S, Sb +
As long as predetermined components including Sn / 2 and Ti are within a predetermined range, the production method may be a normal method for producing 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.

[0041]

[Example] By degassing after blowing in a steel converter, the components were adjusted to predetermined components shown in Table 1 (the component values in Table 1 are% by weight) and cast, and the slab was heated at 1200 ° C for 1 hour. After that, hot rolling was performed to a sheet thickness of 2.0 mm. Hot rolling finishing temperature is 800
° C. The winding temperature was 550 ° C., and after hot rolling, the sheet was annealed under the conditions shown in Table 1. The atmosphere for hot-rolled sheet annealing is 75
% H ₂ -25% N ₂ . Next, the hot-rolled sheet is pickled and then cold-rolled to a sheet thickness of 0.5 mm, and 25% H ₂ -75% N ₂
Annealing was performed in the atmosphere under the finish annealing conditions shown in Table 1. The magnetic measurement was performed using a 25 cm Epstein test piece ((L
+ C) / 2). Table 1 also shows the magnetic properties (iron loss W _15/50 and magnetic flux density B ₅₀ ) of each steel sheet.

As can be seen from Table 1, No. 1 to No. 13
In the steel of the present invention, compared to the comparative steel, iron loss W _15/50
And the magnetic flux density _B50 is high.

On the other hand, the steel sheet No. 14 has an S content higher than the range of the present invention, a Sb + Sn / 2 content lower than the range of the present invention, and a Ti content higher than the range of the present invention, Loss W
The value of _15/50 is very high. The steel sheet No. 15 also has a very high value of iron loss _{W15 / 50} because the Sb + Sn / 2 content is lower than the range of the present invention and the Ti content is higher than the range of the present invention. The steel sheet of No. 16 has a high iron loss W _15/50 since the Ti content exceeds the range of the present invention. In the steel sheet No. 17, since the Sb + Sn / 2 content was higher than the range of the present invention, the value of the iron loss _{W15 / 50} was slightly higher.

Since the C content exceeds the range of the present invention, the steel sheet No. 18 not only has a high iron loss but also has a problem of magnetic aging. In the No. 19 steel sheet, since the Si content exceeds the range of the present invention, the iron loss W _15/50 is low, but the magnetic flux density B ₅₀ is low. No.20
Since the steel sheet has a Mn content beyond the scope of the present invention,
Iron loss W _15/50 is higher. The steel sheet No. 21 has an extremely high iron loss W _15/50 because the Al content is below the range of the present invention. Since the steel content of No. 22 has an Al content beyond the range of the present invention, the iron loss W _15/50 is low, but the magnetic flux density B ₅₀ is low. No.23 steel plate
Since the N content exceeds the range of the present invention, the iron loss W
_15/50 is higher.

[0045]

[Table 1]

[0046]

As described above, in the present invention, the components of the non-oriented electrical steel sheet are expressed in terms of% by weight as C: 0.005.
%, Si: 4.0% or less, Mn: 0.05-1.0%, P: 0.2%
Hereinafter, N: 0.005% or less (including 0), Al: 0.1 to 1.0
%, S: 0.001% or less (including 0), at least one of Sb and Sn is 0.001 to 0.05% by Sb + Sn / 2, Ti: 0.005% or less (including 0), and the balance is substantially Fe Therefore, a non-oriented electrical steel sheet having a small iron loss and a high magnetic flux density can be stably obtained.

The non-oriented electrical steel sheet according to the present invention is suitable for being widely used as an electric material which is required to have low iron loss, such as a motor or a transformer core.

[Brief description of the drawings]

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

FIG. 2 is a graph showing the relationship between the amount of Sb and magnetic properties (iron loss) after finish annealing.

FIG. 3 is a diagram showing a relationship between S and magnetic properties (iron loss) after finish annealing.

FIG. 4 is a diagram showing the relationship between the amount of Sn and magnetic properties (iron loss) after finish annealing.

FIG. 5 is a graph showing the relationship between the amount of Ti and magnetic properties (iron loss) after finish annealing.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Yasushi Tanaka, Inventor: 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Atsushi Chino, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor Katsumi Yamada 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Hideki Matsuoka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor Noritaka Takahashi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (1)

[Claims] 1. C: 0.005% or less, Si: 4.0% by weight%
Mn: 0.05 to 1.0%, P: 0.2% or less, N: 0.005%
Or less (including 0), Al: 0.1 to 1.0%, S: 0.001% or less (including 0), at least one of Sb and Sn is 0.0 by Sb + Sn / 2.
Non-oriented electrical steel sheet with low iron loss, containing 01-0.05%, Ti: 0.005% or less (including 0), and the balance being substantially Fe.