JPH11256289A - Silicon steel sheet reduced in high frequency iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon steel sheet reduced in high frequency iron loss and suitable for iron core for transformer, reactor, motor, etc. SOLUTION: The steel sheet has a composition containing, by weight, <=0.02% C, 0.05-0.5% Mn, <=0.01% P, <=0.02% S, 0.001-0.06% sol.Al, and <=0.01 N. In this steel sheet, a part having 5-8 wt.% Si concentration comprises >=10% of sheet thickness from respective surface and rear surface layers of the steel sheet in a direction of depth of sheet thickness, and further, Si concentration in the vicinity of the center of sheet thickness is made to 2.2 to 3.5 wt.%. By this method, the silicon steel sheet low in high frequency iron loss can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon steel sheet having a low high-frequency iron loss suitable for use in iron cores of transformers, reactors, motors and the like.

[0002]

2. Description of the Related Art It is generally known that the iron loss of a silicon steel plate rapidly increases as the excitation frequency increases. On the other hand, in recent years, the driving frequency of transformers, reactors, motors, and the like, in which silicon steel sheets are widely used, has been increasing year by year in order to reduce the size and increase the efficiency of the iron core.

[0003] With the increase in the driving frequency, the number of cases in which a rise in the temperature of these iron cores and a decrease in efficiency due to iron loss of the silicon steel plate become a problem are increasing. For these reasons, it has become necessary to reduce high-frequency iron loss of silicon steel sheets.

Conventionally, there are two methods of reducing the high-frequency iron loss of silicon steel sheets: a method of reducing the high-frequency iron loss by increasing the Si content and increasing the specific resistance, and a method of reducing the eddy current loss by reducing the thickness of the sheet. A method of reducing high-frequency iron loss by suppressing it has been adopted.

[0005]

However, among the above-mentioned prior arts, the method of increasing the Si content significantly lowers the workability of the silicon steel sheet, so that the productivity of the silicon steel sheet itself is lowered. There is a problem that the cost of processing the iron core also increases.

The method of reducing the thickness of the sheet also has a problem that the thinner the sheet, the higher the manufacturing cost of the steel sheet itself, and the more the number of laminated iron cores, resulting in an increase in the manufacturing cost of the iron core.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silicon steel sheet having low high-frequency iron loss, which is suitable for use in iron cores of transformers, reactors, motors, and the like.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the surface Si concentration of a steel sheet in a silicon steel sheet and the depth in the thickness direction of the region having the Si concentration It has been found that by defining the content in a specific range, the iron loss of the silicon steel sheet, particularly the high-frequency iron loss, can be significantly reduced.

The present invention has been completed on the basis of these findings. First, C ≦ 0.02 wt. %,
0.05 wt. % ≦ Mn ≦ 0.5 wt. %, P ≦ 0.0
1 wt. %, S ≦ 0.02 wt. %, 0.001 wt.
% ≦ soI. Al ≦ 0.06 wt. %, N ≦ 0.01.
wt%, and the Si concentration is 5 to 8 wt. % Is 10% or more of the sheet thickness in the thickness direction from the upper and lower surfaces of the steel sheet, and the Si concentration near the center of the sheet thickness is 2.2 to 3.%.
5 wt. %, Provided is a silicon steel sheet having a low high-frequency iron loss.

Second, in the silicon steel sheet, the Si concentration is 5 to 8 wt. % Is substantially 15 to 25% of the sheet thickness in the thickness direction from the upper and lower surface layers of the steel sheet.

Third, in the first silicon steel sheet, S
i concentration is substantially 6.5 wt. % Is 10% or more of the sheet thickness in the thickness direction from the upper and lower surface layers of the steel sheet.

Fourth, in the third silicon steel sheet, S
i concentration is substantially 6.5 wt. The present invention provides a silicon steel sheet having a low high-frequency iron loss, characterized in that the percentage is 15 to 25% of the sheet thickness in the thickness direction from the upper and lower surfaces of the steel sheet.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The silicon steel sheet according to the present invention basically has a Si concentration of 5 to 8 wt. % Portion is 10% or more of the thickness in the thickness direction from the upper and lower surfaces of the steel sheet,
And the Si concentration near the center of the sheet thickness is 2 to 3.5 wt. %.

FIG. 1 shows a case where the Si concentration is 5 wt. 5 is a diagram showing a relationship between a depth ratio dep (%) of a portion equal to or more than% and iron loss W1 / 10k (iron loss value at a frequency of 10 kHz and a magnetic flux density of 1 kGauss). FIG. However, here, as shown in FIG. % Is the depth and the plate thickness is t
, The Si concentration from the surface layer is 5 wt. % Is defined as depth (%) = (a / t) × 100.

Incidentally, the Si concentration is E
It is the result of having analyzed with PMA (electron probe microanalyzer). In addition, here, 3 wt. % Si steel sheet
Silicon carbide in an atmosphere of SiCl _{4 at}
Samples in which various Si concentration distributions were formed by performing a diffusion treatment in an N ₂ atmosphere at 0 ° C. were used.

FIG. 1 shows that the surface layer has a Si concentration of 5 wt. %
It can be seen that when the depth ratio of the above portion is 10% or more, more preferably 15 to 25%, the iron loss is significantly reduced. The iron loss at this time was 6.5 wt. % Si up to about 30% lower. Note that the upper limit of the Si concentration in the high Si concentration portion of the steel sheet surface layer is not particularly limited from the viewpoint of iron loss characteristics, but the Si concentration is 8 wt. %, The workability of the steel sheet is significantly reduced. %.

If a transformation point is present in a phase diagram, the particles are refined by passing through the transformation point due to heat treatment, and the magnetic properties are significantly impaired.
Therefore, the lower limit of the Si concentration in the low Si portion at the center of the plate thickness is 2.2 wt. %.

As described above, materials having a high surface layer Si concentration and a low Si thickness center portion are disclosed in Japanese Patent No. 2541383, JP-A-6-17202 and JP-A-9-184051.
No. 6,086,045. However, Patent 254138
No. was 6.5 wt. %, A silicon steel sheet having a high surface Si concentration obtained as a result of shortening the diffusion processing time in order to increase the productivity in order to increase productivity has a core loss of 6.5 wt. % Silicon steel sheet. Also, Japanese Patent Application Laid-Open No. 6-17202 discloses that 6.5% by weight of only the surface layer is used to improve the workability of a 6.5% silicon steel sheet. % Si
The iron loss was 6.5 wt. It is said that it deteriorates as compared with the% silicon steel sheet. Further, Japanese Patent Application Laid-Open No. 9-18405
No. 1 discloses a high surface layer Si to reduce the residual magnetic flux density.
A steel plate is proposed, and the purpose is different from the present invention. Regarding the iron loss at 50 Hz, a material having a high surface layer Si has a low iron loss. However, it is generally considered that the iron loss is generally governed by the total amount of Si when the frequency increases, and it is said that a material having a low Si amount at the center of the sheet thickness has poor iron loss characteristics.

The present invention is based on the first finding that a material having a low high-frequency iron loss can be obtained by overturning such common sense and forming a specific Si concentration distribution.

The method of forming the high Si concentration portion on the surface layer of the steel sheet may be CVD, PVD or any other method, and is not particularly limited, but the base material before forming the Si concentration distribution may be formed from the viewpoint of productivity. It is preferable to manufacture by a rolling method suitable for mass production. Therefore, the Si content of the base material is 3.5 wt. % Is preferably the upper limit. Therefore, in the silicon steel sheet of the present invention, the upper limit of the Si concentration in the low Si portion at the center of the thickness is 3.5 wt. %
And

FIG. 3 shows that when the Si concentration distribution is formed in the thickness direction, the Si concentration is substantially 6.5 W from the surface layer.
t. FIG. 9 is a diagram showing a relationship between a depth ratio (%) of a portion which is% and an iron loss W1 / 10k. However, here, as shown in FIG. 4, the Si concentration was 6.0 to 7.0 wt. % When the depth is b and the plate thickness is t, the Si concentration from the surface layer is substantially 6.5 wt. Dep (%) =
(B / t) × 100.

In addition, here, 3 wt. % Si steel sheet is subjected to a siliconizing treatment in a SiCl ₄ atmosphere at 1150 ° C.
Samples in which various Si concentration distributions were formed by performing a diffusion treatment in a N ₂ atmosphere at a temperature of ° C were used.

As shown in FIG. 3, the Si yield from the surface layer is substantially 6.5 wt. It can be seen that the iron loss is significantly reduced when the depth ratio of the portion which is% is 10% or more, more preferably 15 to 25%. Further, comparing FIG. 1 with FIG. 3, the concentration of the high Si portion of the surface layer is substantially 6.5 wt. %, The iron loss can be further reduced.

The effect of the present invention does not depend on the thickness of the silicon steel sheet, and the iron loss can be significantly reduced by setting the thickness within the range specified in the present invention regardless of the thickness.

Next, the reasons for limiting elements other than Si will be described. If C is contained in a large amount, it causes magnetic aging, so the upper limit is 0.02 wt. %. Although the lower limit is not particularly specified, 0.001 wt. % Is preferable.

If Mn is contained in a large amount, the steel sheet becomes brittle, so the upper limit is 0.5 wt. %. However, if the content is too low, breakage and surface flaws are induced in the hot rolling step, so the lower limit is 0.05 wt. %.

P is a preferable element from the viewpoint of magnetic properties. However, if P is contained in a large amount, the workability of the steel sheet is deteriorated. %. The lower limit is not particularly defined, but from the viewpoint of economical removal, 0.0
01 wt. % Is preferable.

Since S deteriorates workability, its upper limit is 0.02 wt. %. Although the lower limit is not particularly defined, it is 0.001 from the viewpoint of economical removal.
wt. % Is preferable.

Sol. A1 also impairs processability, so its upper limit is 0.06 wt. %. On the other hand, the lower limit is 0.001 wt. %.

If N is contained in a large amount, it forms nitrides and deteriorates magnetic properties.
%. The lower limit is not specified, but
With the current steelmaking technology, 0.0001 wt. % Is effectively the lower limit.

[0031]

Embodiments of the present invention will be described below. (Example 1) A steel sheet having a composition of Table 1 and having a thickness of 0.2 mm was prepared by a rolling method, subjected to a siliconizing treatment in a SiCl ₄ atmosphere at 1200 ° C, and then in a N ₂ atmosphere at 1200 ° C. Diffusion treatment was performed to produce silicon steel sheets having various Si concentration distributions. The Si concentration distribution is E
The analysis was performed with a PMA (electron probe microanalyzer). The amounts of the elements other than Si hardly changed before and after the siliconizing and diffusion treatment.

[0032]

[Table 1]

From the steel sheet produced in this way, the outer diameter 31
mm, a ring sample with an inner diameter of 19 mm
The alternating current magnetic characteristics at kHz and a magnetic flux density of 0.1 T were measured. FIG. 1 shows that a Si concentration of 5 wt. FIG. 9 is a diagram showing a relationship between a depth ratio dep (%) of a portion which is equal to or more than% and an iron loss W1 / 10k. However, here, as shown in FIG. %, The thickness a and the thickness t are 5 wt. % Is defined as dep (%) = (a / t) × 100.

As shown in FIG. 1, the Si concentration from the surface layer was 5 wt. %
It was confirmed that when the depth ratio of the above portion was 10% or more, more preferably 15 to 25%, the iron loss was significantly reduced.

[0035]

Example 2 A steel sheet having a composition of Table 1 and having a thickness of 0.2 mm was prepared by a rolling method, subjected to a siliconizing treatment in a SiCl ₄ atmosphere at 1150 ° C., and then diffused in a N ₂ atmosphere at 1150 ° C. The treatment was performed to produce silicon steel sheets having various Si concentration distributions. Si concentration distribution is EP
Analyzed by MA. The amounts of the elements other than Si hardly changed before and after the siliconizing and diffusion treatment.

From the steel sheet produced in this way, the outer diameter 31
mm, a ring sample with an inner diameter of 19 mm
The alternating current magnetic characteristics at kHz and a magnetic flux density of 0.1 T were measured. FIG. 3 shows that the Si concentration is substantially 6.5 wt.
FIG. 9 is a diagram showing a relationship between a depth ratio (%) of a portion which is% and an iron loss W1 / 10k. However, here, as shown in FIG. 4, the Si concentration was 6.0 to 7.0 wt. B is the depth to be%.
Assuming that the plate thickness is t, the Si concentration from the surface layer is substantially 6.
5 wt. Dep (%) = (b)
/ T) × 100.

FIG. 3 shows that the Si concentration from the surface layer is substantially 6.5 wt. It has been confirmed that when the depth ratio of the portion which is% is 10% or more, more preferably 15 to 25%, the iron loss is remarkably reduced.

Further, comparing FIG. 1 with FIG. 3, it was confirmed that the iron loss can be further reduced by limiting the concentration of the high Si portion of the surface layer to substantially 6.5 wt%.

[0039]

As described above, according to the present invention,
A silicon steel sheet with extremely low high-frequency iron loss can be obtained without impairing workability and without reducing the sheet thickness.

[Brief description of the drawings]

FIG. 1 shows a case where a Si concentration is 5 wt. The figure which shows the relationship between the depth ratio dep (%) of the part which is more than% and iron loss W1 / 10k.

FIG. 2 is a view for explaining the definition of a depth ratio dep (%) in FIG. 1;

FIG. 3 shows that the Si concentration is substantially 6.5 wt. The figure which shows the relationship between the depth ratio (%) of the part which is%, and iron loss W1 / 10k.

FIG. 4 is a view for explaining the definition of a depth ratio dep (%) in FIG. 3;

Claims (4)

[Claims] 1. The method according to claim 1, wherein C ≦ 0.02 wt. %, 0.05 wt.
% ≦ Mn ≦ 0.5 wt. %, P ≦ 0.01 wt. %, S
≦ 0.02 wt. %, 0.001 wt. % ≦ soI. A
l ≦ 0.06 wt. %, N ≦ 0.01. wt%,
When the Si concentration is 5 to 8 wt. % Is 10% or more of the sheet thickness in the thickness direction from the upper and lower surfaces of the steel sheet, and the Si concentration near the center of the sheet thickness is 2.2 to 3.5 wt. % Silicon steel sheet having a low high-frequency iron loss. 2. An Si concentration of 5 to 8 wt. % Portion is substantially 1% of the sheet thickness in the thickness direction from the upper and lower surfaces of the steel sheet.
The silicon steel sheet having a low high-frequency iron loss according to claim 1, wherein the content is 5 to 25%. 3. The method according to claim 1, wherein the Si concentration is substantially 6.5 wt. 2. The silicon steel sheet having a low high-frequency iron loss according to claim 1, wherein the percentage of the steel sheet is 10% or more of the sheet thickness in the thickness direction from the upper and lower surfaces of the steel sheet. 4. The method according to claim 1, wherein the Si concentration is substantially 6.5 wt. 4. The silicon steel sheet having a low high-frequency iron loss according to claim 3, wherein the percentage of the steel sheet is 15 to 25% of the sheet thickness in the thickness direction from the upper and lower surfaces of the steel sheet.