JPH0617202A - Composite silicon steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a silicon steel sheet in which the difficulties such as problem in strength, brittle fracture, fracture elongation in a conventional 6.5% silicon steel sheet are dissolved and which has high strength and high toughness and furthermore low core loss as well as iron magnetostriction. CONSTITUTION:By using a nonoriented silicon steel sheet contg., by weight, about 3 to 3.5% silicon as a base metal 11, a silicon thin film 12 is stuck and formed on the surface and back of the base metal 11, thereafter relevant silicon is diffused into the base metal 11 by a heat diffusing means and a diffusion layer 13 having such a concn. gradient that the silicon concn. on the topmost surface is regulated to about 6.5%, and the silicon concn. is continuously reduced in the direction toward the inner part is formed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has a silicon content of about 3%.
To a 3.5% non-oriented normal non-oriented silicon steel sheet as a base material, and a composite silicon steel sheet in which a thin surface layer containing approximately 6.5% silicon is formed on both sides of the steel sheet and a method for producing the same. Is.

[0002]

2. Description of the Related Art Magnetic materials are used as materials for various energy conversion devices and information conversion devices. Among them, silicon steel sheets are used as a typical magnetic material because of their versatility. This silicon steel sheet is composed of an alloy of iron and silicon, and in particular, the addition of silicon improves the electrical resistance and improves the AC magnetic characteristics. Generally, silicon is added up to 3.5%.

On the other hand, in order to enhance the high frequency characteristics and the magnetostriction characteristics, it is effective to increase the amount of silicon added. Particularly, the silicon steel sheet with the amount of silicon added of 6.5% has almost zero magnetostriction. It is also known to have excellent high frequency magnetic properties. However, in the conventional silicon steel sheet, if 3.5% or more of silicon is added, the steel becomes brittle and cold rolling becomes impossible, so that a 6.5% silicon steel sheet has not been realized.

However, in recent years, improvements in the rolling method and the chemical vapor deposition method (CVD method) have enabled the mass production of silicon steel sheets containing approximately 6.5% silicon.

In the case of the above rolling method, 6.5% S in the steelmaking process
The steel whose composition has been adjusted to i is made into a slab in the ingot-making and slab-breaking steps, is made into a hot-rolled coil by a continuous hot rolling mill, and is made into a product by sheet rolling. However, it could not be conventionally rolled by 6.5.
% As the technology for rolling silicon steel, optimization of the crystal structure of the hot-rolled sheet and innovation of rolling processing technology for brittle materials are required.

On the other hand, the chemical vapor deposition method is a method in which a steel sheet is rolled in a low Si state which is rich in workability, and Si is added after rolling, and it is obtained by steelmaking, casting, hot rolling and thin sheet rolling. Simplify a low Si content CVD material in a CVD line
The content is set to 6.5%. This CVD line consists of a CVD zone for siliconizing by reacting a high temperature steel plate with a Si compound gas, and a soaking zone that uniformly diffuses Si in the surface layer in the plate thickness direction. Becomes These techniques enable the production of silicon steel sheets containing approximately 6.5% silicon (for each of the above methods,
For example, “High-performance magnetic thin steel sheet”, NKK Technical Report No. 125
Pp. 58-63, 1989).

Further, by applying an annealing treatment after rolling,
Low iron loss and low magnetostriction are achieved. As a result, a steel sheet having excellent magnetic properties such as iron loss of about 1/2, magnetic permeability of about 9 times, and magnetostriction of about 1/10 was obtained compared to ordinary non-oriented silicon steel sheet, and tensile strength was also about It is 1.6 times (about 2.8 times when not annealed).

[0008]

However, in the case of such a conventional method for producing a 6.5% silicon steel sheet, although the magnetic properties are enhanced, it breaks due to a composite crack such as "crack" or "cleavage". May exhibit brittle fracture surface,
For example, there has been a problem that it is difficult to adopt it as a high strength member such as a rotor of a high speed electric motor.

That is, in the case of silicon steel in which 6.5% of silicon is added to the entire width of the steel plate, that is, the whole steel plate by the above-mentioned CVD method, the strongly work-rolled structure disappears due to recrystallization during annealing, As shown in FIGS. 3 and 4, the average grain size r of the crystals 2 constituting the silicon steel sheet 1 is about 0.7 to 1.1 m.
A coarse crystal grain structure of m is obtained. Therefore, although the strength in static tension is high, a brittle fracture surface is formed in which a composite crack due to a mixed mode of cracks at the grain boundaries z and cleavage cracks in the grains is united to present a brittle fracture surface, and the elongation at fracture is nondirectional silicon. It is extremely small, 1/10 of the steel plate. Therefore, when such a 6.5% silicon steel sheet is used as a high-strength member, its large notch sensitivity is a major bottleneck in structural design.

Further, at the present time, in order to avoid the generation of minute cracks during the cutting process as much as possible, it is unavoidable to adopt the electric discharge machining method in place of the means such as punching, and the cutting process cost is higher than that of the ordinary die-cutting process. Has the drawback that it becomes expensive.

Therefore, the present invention is 6.5% of the conventional one.
It is an object of the present invention to solve the problems of a silicon steel sheet and to obtain a silicon steel sheet having high strength and high toughness, and also having low iron loss and iron magnetostriction.

[0012]

In order to achieve the above object, the present invention firstly provides, according to claim 1, a non-oriented silicon steel sheet in which iron is added with silicon in an amount of about 3% to 3.5%. The silicon concentration of the outermost surface of the base material is about 6.5%, and the silicon concentration has a concentration gradient such that the silicon concentration continuously decreases toward the base material. The structure is a composite silicon steel sheet having a diffusion layer.

Further, according to claim 2, the silicon content is about 3% to
A non-oriented silicon steel sheet containing 3.5% is used as a base material, a silicon thin film is adhered and formed on the front and back surfaces of the base material, and then silicon is diffused in the base material by a heat diffusion means to obtain the silicon on the outermost surface. Provided is a method for producing a composite silicon steel sheet which forms a silicon diffusion layer having a concentration gradient such that the concentration is about 6.5% and the silicon concentration continuously decreases toward the inside.

[0014]

According to the composite silicon steel sheet and the manufacturing method thereof, the base material of the obtained silicon steel sheet has a low Si content and a large deformability as compared with the Si diffusion layer, and the base material with respect to the Si diffusion layer. Since the elongation at break and the intragranular fracture property are high, by sandwiching such a base material inside the Si diffusion layer, the toughness is improved and the notch susceptibility is decreased as compared with the usual 6.5% silicon steel sheet.

Therefore, punching of silicon steel sheet is possible, cutting cost is reduced, and strength is high even when used for a member such as a rotor core of a high-speed electric motor which is required to endure high centrifugal force. It is possible to improve reliability in terms of aspect.

Further, since the Si diffusion layer having a high Si content has a higher hardness and rigidity than the base material portion, the deformation of the base material is restrained to improve the strength and the rigidity, and the iron loss is reduced. Eddy current loss on the surface of the steel sheet can be reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the composite silicon steel sheet and its manufacturing method according to the present invention will be described below with reference to the drawings.

Reference numeral 11 shown in FIG. 1 (A) is a base material made of an alloy of iron and silicon. The base material 11 has an electric resistance obtained by adding about 3% to 3.5% of silicon to iron. And is composed of a non-oriented silicon steel sheet whose surface is not coated with an insulating film.

The front surface and the back surface of the base material 11 are subjected to a surface treatment such as a well-known chemical vapor deposition means (CVD method) or physical vapor deposition means (PVD method), and the silicon thin film 1 is processed.
Form 2.

Next, the base material 11 is held at a high temperature in vacuum to form the Si diffusion layer 13 on the front surface and the back surface of the base material 11 as shown in FIG. 1 (B). This Si diffusion layer 1
No. 3 has a Si concentration of about 6.5% at the outermost surface, and is formed with a concentration gradient such that the Si concentration decreases toward the inside. FIG. 2 is a graph showing the distribution of the Si content in the AA cross section of FIG. 1B. In this example, the Si concentration of the outermost surface portion of the Si diffusion layer 13 is about 6.5%.
However, the Si content gradually decreases toward the inside, and the Si concentration in the base material 11 continuously changes from 3% to 3.5%.

Next, if necessary, an insulating coating is applied to the surface to complete the composite silicon steel sheet according to the present invention.

The above-mentioned base material 11 is characterized in that it has a lower Si than the Si diffusion layer 13 and has a large deformability. For example, the base material 11 is about 6.5% silicon steel sheet. It has a tenfold elongation at break and intragranular fracture characteristics. By sandwiching such a base material 11 inside the Si diffusion layer 13, it is possible to improve the toughness although the tensile strength and the iron loss characteristics are slightly lowered as compared with the 6.5% silicon steel sheet.
Therefore, the presently known 6.5% silicon steel sheet can be punched, which is difficult to carry out, and the cutting cost can be reduced.

Further, since the toughness of the steel sheet is improved and the notch sensitivity is lowered, it is possible to use the conventional 6. when used for a member required to withstand a high centrifugal force such as a rotor core of a high speed electric motor.
The reliability in terms of strength can be improved as compared with a 5% silicon steel sheet.

On the other hand, the Si diffusion layer 13 having a high Si content
Has greater hardness and rigidity than the base material 11 part,
The deformation of the base material 11 can be restrained, and when viewed from the side of the base material 11, the iron loss phenomenon, particularly the eddy current loss reducing effect on the surface of the steel sheet, and the strength and rigidity of the steel sheet can be improved.

[0025]

As described in detail above, according to the composite silicon steel sheet and the method for manufacturing the same according to the present invention, the obtained silicon steel sheet has a toughness higher than that of a usual 6.5% silicon steel sheet. It is possible to improve notch sensitivity and reduce notch sensitivity, and brittle fracture surfaces due to complex cracks such as “cracking” and “cleavage” do not occur, and it withstands high centrifugal force like the rotor core of high-speed motors in particular. Even when it is used for a member that is required to have high reliability, the reliability in strength can be improved.

Further, even when the silicon steel sheet is processed, ordinary punching can be performed instead of conventional electric discharge machining.
The cutting cost can be reduced, and since the Si diffusion layer having a high Si content has a higher hardness and rigidity than the base material portion, the deformation of the base material is restrained and the strength and rigidity of the base material are restrained. In addition to the improvement, it is effective in reducing iron loss and reducing eddy current loss on the surface of the steel sheet.

[Brief description of drawings]

1 (A) and 1 (B) are cross-sectional views of a main part for schematically explaining a method for manufacturing a composite silicon steel sheet according to the present embodiment.

FIG. 2 is a graph showing a Si content distribution in a cross section taken along the line AA of FIG.

FIG. 3 is a plan view showing an average grain size and a crystal grain structure of crystals constituting a conventional silicon steel sheet in which 6.5% of silicon is added to the entire steel sheet.

FIG. 4 is a cross-sectional view of essential parts of the silicon steel sheet shown in FIG.

[Explanation of reference numerals] 11 ... Base material (non-oriented silicon steel plate) 12 ... Silicon thin film 13 ... Si diffusion layer

Claims (3)

[Claims] 1. A non-oriented silicon steel plate containing iron in which silicon is added in an amount of about 3% to 3.5% is used as a base material, and the silicon concentration of the outermost surface portion of the base material is about 6.5. %, A composite silicon steel sheet having a silicon diffusion layer having a concentration gradient in which the silicon concentration continuously decreases toward the inside of the base material. 2. A non-oriented silicon steel sheet containing silicon in an amount of about 3% to 3.5% is used as a base material, and after a silicon thin film is adhered and formed on the front and back surfaces of the base material, the silicon is removed by a heat diffusion means. Forming a silicon diffusion layer that has a concentration gradient such that the outermost surface has a silicon concentration of about 6.5% and the silicon concentration continuously decreases toward the inside, by diffusion. Manufacturing method of silicon steel sheet. 3. A surface treatment method such as a chemical vapor deposition means (CVD method) or a physical vapor deposition means (PVD method) is adopted as a method of depositing the silicon thin film.
A method for producing the composite silicon steel sheet described.