JPH11286753A - Silicon steel sheet stable and low in residual magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon steel sheet capable of obtaining stable, low residual magnetic flux density. SOLUTION: This silicon steel sheet has a stable and low residual magnetic flux density and has a compsn. contg., by weight, 0.001 to 0.02% C, 0.05 to 0.5% Mn, 0.01 to 0.01% P, 0.001 to 0.02% S, 0.001 to 0.06% sol.Al, 0.0001 to 0.01% N and Si by <=7% on the average, and in the concn. gradient of Si in the sheet thickness direction, the Si concn. in the surface layer is higher than the Si concn. in the sheet center part, the difference between the maximum and the minimum in the Si concn. is regulated to <=0.5 wt.%, and the average grain size is regulated to >=50 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer, a reactor, and a transformer (CT) in which an inrush current due to magnetic bias becomes a problem.
The present invention relates to a silicon steel sheet having a low residual magnetic flux density used as an iron core of a motor or a motor.

[0002]

2. Description of the Related Art Research has been conducted on silicon steel sheets used for iron cores of transformers, motors and the like in order to increase magnetic flux density and reduce iron loss, and materials having a large squareness ratio have been developed. As a result, the residual magnetic flux density increases, and in the case of a device such as a transformer, various problems occur due to the magnetic polarization. The present inventors have found that it is effective to form a Si concentration gradient in the thickness direction to reduce the residual magnetic flux density, which is a cause of magnetic bias, and disclosed it in Japanese Patent Application Laid-Open No. 9-184051. The present inventors have conducted further studies on the material disclosed in Japanese Patent Application Laid-Open No. 9-184051, and as a result, in order to stably obtain a low residual magnetic flux density, it is only necessary to define the Si concentration gradient. I found that it was not always enough.

The formation of a Si concentration gradient in the thickness direction is disclosed in JP-A-62-227033-227036 and JP-A-4-24.
No. 6,157,157. However, its purpose is to improve the production efficiency of 6.5% silicon steel sheet manufactured by the siliconizing method (CVD method), reduce iron loss and improve workability. No mention is made of the low residual magnetic flux density characteristics targeted by the present invention.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to solve the problems of the prior art and to obtain silicon having a low residual magnetic flux density stably. It is to provide a steel plate.

[0005]

That is, the present invention provides: (1) 0.001 wt% ≦ C ≦ 0.02 wt%;
05wt% ≦ Mn ≦ 0.5wt%, 0.001wt% ≦
P ≦ 0.01 wt%, 0.001 wt% ≦ S ≦ 0.02
wt%, 0.001wt% ≦ sol.Al ≦ 0.06wt%,
0.0001 wt% ≦ N ≦ 0.01 wt%, and Si
Steel sheet containing on average 7 wt% or less, having a Si concentration gradient in the thickness direction, the Si concentration in the surface layer being higher than the Si concentration in the center of the plate, and the difference between the maximum and the minimum of the Si concentration being 0.1%.
A silicon steel sheet having a stable and low residual magnetic flux density, characterized by being at least 5 wt% and having an average crystal grain size of at least 50 μm. (2) The silicon steel sheet according to (1), wherein the difference between the maximum and minimum of the Si concentration is 0.7 wt% or more, and the residual magnetic flux density is stable and low.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. As described above, the present inventors have investigated the cause of the fact that the residual magnetic flux density does not sufficiently decrease even if a predetermined Si concentration distribution is formed. As a result, when the average crystal grain size is small, the coercive force increases. The inventors have found that the residual magnetic flux density increases, and have completed the present invention.

The reasons for limiting the composition of the present invention, the reasons for limiting the concentration gradient, the reasons for limiting the concentration difference, and the reasons for limiting the average crystal grain size will now be described. 0.001 wt% ≦ C ≦ 0.02 wt%, when C is contained in a large amount, magnetic aging is caused, and the upper limit is set to 0.02 to reduce the particle size due to precipitation of carbide.
wt%. The lower limit is 0.001 wt% as a limit that can be economically removed.

0.05 wt% ≦ Mn ≦ 0.5 wt%, if Mn is contained in a large amount, the upper limit is 0.5 wt% to make the steel sheet brittle and to reduce the grain size by precipitation of MnS. However, if it is too low, the lower limit is set to 0.05 wt% because breakage and surface flaws are induced in the hot rolling process.

[0009] 0.001 wt% ≦ P ≦ 0.01 wt%, P is a preferable element from the viewpoint of magnetic properties. However, when P is contained in a large amount, the workability of the steel sheet is deteriorated, so that 0.01 w
t% is the upper limit. The lower limit is 0.001 wt% as a limit that can be economically removed.

[0010] 0.001 wt% ≦ S ≦ 0.02 wt%, S deteriorates workability, and it is necessary to set the upper limit to 0.02 wt% in order to reduce the particle size by precipitation of MnS, and it is economically removed. As a possible limit, the lower limit is 0.001 wt%.

[0011] 0.001wt% ≦ sol.Al ≦ 0.06wt%, sol.Al also impairs workability, and the upper limit is made 0.06wt% in order to reduce the particle size by precipitation of AlN. Further, the lower limit is 0.001 wt% from the necessity as a deoxidizing agent.
And

0.0001 wt% ≦ N ≦ 0.01 wt% When N is contained in a large amount, the upper limit needs to be 0.01 wt% in order to form a nitride and reduce the particle diameter. Further, it is impossible to set the content to 0.0001 wt% or less due to the limit of steelmaking technology, so this is set as the lower limit.

Average Si concentration: 7 wt% or less. If the average Si concentration exceeds 7 wt%, the workability is rapidly deteriorated.

Difference between maximum and minimum Si concentration: 0.5 wt%
The difference between the maximum and the minimum of the Si concentration is necessary to secure low residual magnetic flux density characteristics. To reduce the residual magnetic flux density to about 0.5 T or less, the difference between the maximum and the minimum of the Si concentration is 0.5 wt%. Or more, preferably 0.7 wt% or more.

Incidentally, Ti, Nb, V, which form carbides,
It is desirable that Mo, Cr, etc. be as low as possible. Average crystal grain size: 50 μm or more In order to stably maintain the residual magnetic flux density at 0.5 T or less, the average crystal grain size is set to 50 μm or more. Average grain size is 50μ
If it is less than m, it cannot be stabilized to 0.5T or less.

The present inventors have investigated the relationship between the average crystal grain size and the residual magnetic flux density. FIG. 1 shows that the average Si concentration is 4.0 w
4 shows the relationship between the grain size and the residual magnetic flux density of a steel sheet having a Si concentration difference of 2.5 wt% at t%. When the particle size is 50 μm or less, the value of the residual magnetic flux density varies greatly, and it can be seen that a sufficiently low residual magnetic flux density cannot be achieved.

The average crystal grain size varies depending on the heat treatment temperature, time, precipitates in steel, and the like.
These manufacturing conditions are adjusted so as to be as described above. Those skilled in the art can easily adjust these manufacturing conditions.

The material having a concentration gradient of Si of the present invention is obtained by chemical vapor deposition (CVD, siliconizing), physical vapor deposition (P).
It can be manufactured by various methods such as a VD) method, a cladding technique, and a plating technique. Here, one example of the manufacturing method by the CVD method will be described. First, a cold rolled coil of, for example, 3 wt% silicon steel is manufactured by a normal steel plate manufacturing process.
The coil is subjected to a CVD process to obtain a steel sheet having a Si concentration gradient. That is, it is heated to 1100 ° C. or more in a non-oxidizing atmosphere to react with the SiCl ₄ gas and to form a high concentration S
An i-layer is formed. Subsequently, a diffusion treatment is performed to diffuse a required amount of Si into the inside of the steel sheet to produce a steel sheet of the present invention having a target average Si amount and a concentration gradient. The temperature or time of the CVD or diffusion treatment is selected so that the necessary Si concentration distribution and the average crystal grain size become 50 μm or more.

There are several possible embodiments of the concentration gradient of Si for realizing a low residual magnetic flux density. As a typical example, FIG. 2 shows a schematic diagram of the Si concentration distribution in the cross section of the plate thickness. Any of these can be manufactured as desired by controlling the manufacturing conditions. In general, the Si concentration distribution is symmetrical with respect to the center of the plate thickness, but need not be symmetrical. A low residual magnetic flux density can be obtained when these distributions are present and the difference between the highest and lowest Si concentrations is 0.5 wt% or more.

In the present invention, the average Si means the average value of the Si concentration with respect to the total thickness, and is a value obtained by performing chemical analysis with the product thickness. The highest and lowest Si concentrations are values determined from a Si concentration profile obtained by EPMA analysis of the entire plate thickness. The element concentration is a value in a product, and the residual magnetic flux density is a value after a DC excitation of 1.2 T.

[0021]

EXAMPLE The thickness of the composition shown in Table 1 (except for Si, the composition at the time of becoming a product; Si is the composition before the CVD process) is 0.0.
Steel sheets of 5-0.5 mm were manufactured by the usual steel making process. This is subjected to CVD treatment to obtain various average crystal grain sizes, Si
Steel sheets with average concentration and concentration distribution were produced. A plurality of steel sheets under each condition were manufactured, and the maximum residual magnetic flux density under each condition is shown in Table 2. From these results, it is understood that the steel sheet of the present invention has stable and low residual magnetic flux density characteristics.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

According to the present invention, since the average crystal grain size is determined together with the Si concentration gradient, a remarkable effect of stably obtaining a silicon steel sheet having a desired low residual magnetic flux density is exhibited.

[Brief description of the drawings]

Fig. 1 Average Si concentration is 4.0wt%, Si concentration difference is 2.5wt%
The figure which shows the relationship between the average crystal grain size of the steel plate of FIG.

FIGS. 2A to 2F are schematic diagrams of Si concentration distribution in a cross section of a plate thickness.

Continuation of the front page (72) Inventor Katsushi Kasai 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (2)

[Claims] 1. 0.001 wt% ≦ C ≦ 0.02 wt
%, 0.05 wt% ≦ Mn ≦ 0.5 wt%, 0.001
wt% ≦ P ≦ 0.01wt%, 0.001wt% ≦ S ≦
0.02 wt%, 0.001 wt% ≦ sol.Al ≦ 0.06
wt%, 0.0001wt% ≦ N ≦ 0.01wt%,
A silicon steel sheet containing 7 wt% or less of Si on average, having a Si concentration gradient in the thickness direction, the Si concentration in the surface layer being higher than the Si concentration in the center of the plate, and the difference between the maximum and the minimum of the Si concentration being 0. 0.5 wt% or more and the average crystal grain size is 50 μm
A silicon steel sheet having a stable and low residual magnetic flux density. 2. The difference between the maximum and minimum Si concentration is 0.7 wt.
%, Wherein the residual magnetic flux density is stable and low according to claim 1.