JPH08311597A - Production of ultrahigh performance silicon steel, and its intermediate product, and ultrahigh performance silicon steel product - Google Patents

Abstract

PURPOSE: To easily and stably produce an ultrahigh silicon steel excellent in magnetic properties but difficult to manufacture. CONSTITUTION: A powder mixture is prepared by mixing powdery Fe and Si, containing inevitable impurities, in the proportion where the amount of Si becomes <=7% by weight. This powder mixture is filled into a vessel composed of easily cold-workable metallic material and having a thin layer, facilitating the separation of the powder from the vessel, on the internal surface, in the position between the powder and the vessel. Then, the powder is subjected, together with the vessel, to cold rolling, to cold forging, or to cold drawing. In this method, the draft of the powder layer is regulated to >=70% by reduction of area, and further, annealing is done in the course of or after cold rolling. By this procedure, the ultrahigh silicon steel excellent in soft-magnetic properties can be produced, and also the intermediate product before the annealing and the final product can be produced. By this method, the ultrahigh performance silicon steel sheet having extremely high silicon content, without causing brittle crack, brittle fracture, etc., can be easily produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ultra-high performance electromagnetic steel, its intermediate products and ultra-high performance electromagnetic products.

[0002]

2. Description of the Related Art Since steel containing Si has a larger specific electric resistance than ordinary steel, eddy current generation in AC magnetization is reduced and magnetic energy loss is reduced. Therefore, it has been used as an iron core for rotating machines, generators, and transformers. Although the magnetic properties are improved as the Si content is increased, the steel becomes brittle with the Si content, and Si is produced as an industrial product premised on a process including rolling, particularly cold rolling.
The content naturally had an upper limit. Therefore, the Si content of the commercially available silicon steel sheet by the method of general steelmaking, hot rolling, cold rolling, and annealing has been set to about 4% as the upper limit.

On the other hand, it is known that when the Si content reaches about 6.5%, the magnetostriction becomes extremely small and the magnetic characteristics are remarkably improved accordingly. In addition, M. Goertz
According to the research of, the single crystal of 6.5% Si steel is
When magnetized in the 0> direction, the maximum magnetic permeability is 3800000.
It has been shown to reach (electrostatic unit) (J. App.
l. Phys ,; vol. 22, no. 7, p964
(1951)), which is the largest soft magnetic material known so far.

While it is known that 6.5% Si steel has these advantages, steel containing a large amount of Si is brittle as described above, and is rolled for finishing into a steel plate or the like, and formed for practical use. Since it was difficult to process, it was not easy to put it on the market as a practical material.

Several techniques for producing such ultra-high performance electromagnetic steel have been proposed so far. For example, JP-A-62-227032 discloses a method of rolling steel having a low Si content, introducing a gas containing Si into the atmosphere during annealing after rolling, and increasing the Si content by siliconizing. Has been done. However, this method requires siliconizing heat treatment in a special atmosphere in order to diffuse and infiltrate Si into the steel from the gas phase through the surface of the steel sheet, which results in high equipment cost and operating cost, and further to the final product. Since it becomes a low-ductility alloy containing about 6.5% Si before forming, it has a high cost technology for forming.

[0006] Further, Japanese Patent Laid-Open No. 63-227717 discloses a method in which strain is left in steel during hot working prior to cold working to facilitate cold working. In cold rolling, unless the steel sheet is kept at a temperature higher than room temperature, stable production without ear cracking and other cattle production becomes difficult, and it is difficult to realize sufficient productivity and low cost. As described above, steel containing a large amount of Si is widely known for its superiority in properties, but it is difficult to put it into practical use due to the difficulty in manufacturing, and the actual production amount is actually small.

[0007]

DISCLOSURE OF THE INVENTION The present invention easily and stably manufactures an ultra-high-performance electromagnetic steel sheet having excellent soft magnetic properties and small magnetostriction, which is extremely difficult to manufacture and form, and is capable of producing a rotor, a generator, It was made for the purpose of providing a material that greatly contributes to the improvement of the electromagnetic characteristics of a transformer or the like.

[0008]

[Means for Solving the Problems] A steel ingot obtained by casting or the like as in the prior art is not used as a starting material for production, but powder is used as a starting material to avoid cracking of steel which is a barrier to production in the conventional method. Therefore, a method of forming a molded body from powder was considered. Adhesiveness between the powders is insufficient and it is difficult to perform sufficient molding simply by compacting, and the compact is sealed in a container and cold rolled or cold forged or cold drawn. It is necessary to further press-bond the powders together.

In the case of cold rolling, if the green compact is directly subjected to rolling, the shape cannot be maintained. Therefore, the powder was packed in a steel pipe, sealed, and cold-rolled together with the pipe. As an example, the powder was mixed and rolled so that the weight ratio of Si was 6.5%, and rolled by about 70%. As a result, it was possible to obtain a molded product having ductility by itself.

If the inner surface of the pipe is pickled to increase its activity so that the metal surface comes into direct contact with the powder, the pipe and the molded body are pressed after rolling and the molded body cannot be separated. , Did not meet the purpose of the present invention. Rather, it has been discovered that if a slight amount of oxide film or dirt adheres to the inner surface of the pipe, the molded product can be peeled off easily.

On the other hand, when cold forging was carried out using the die shown in FIG. 1, ductility appeared in the molded product itself in this case also when the number of times of processing was several tens. It was suggested that it is possible to manufacture the target ultra-high performance electromagnetic steel by such a method, but at the time of this compact, the magnetic properties were extremely poor and it was not the expected product. I understand.

When the structure of this molded article was examined by X-ray diffraction, two types of diffraction lines, which were classified as bcc-Fe and Si, appeared. That is, it was found that this compact, although mixed with Fe and Si, was not in an alloy state. It is considered that this is the reason why good magnetic properties could not be obtained. By further sintering the compact in hydrogen or high vacuum, Si is alloyed with Fe and diffused to form a homogeneous silicon-iron alloy. That is, silicon steel was obtained.

As a result, when the molded body obtained by cold rolling was annealed at a temperature of 1100 ° C. or higher for about 1 hour, a good soft magnetic material having a coercive force of 25 A / m or less could be obtained for the first time. Note that FIG. 2 shows the relationship between the sintering temperature and the relative density. As shown in FIG. 2, it was revealed that the relative density becomes 95% or more at the sintering temperature of 1100 ° C. or more.

Further, the powder was packed in a steel pipe at a compounding ratio such that the amount of Si was 8.0% by weight, and the same cold rolling was performed. However, this time, no matter how much the rolling rate was increased, the toughness and ductility did not appear in the molded body, and in particular, when the rolling rate exceeded 70%, the molded body became a powder shape that was destroyed. . When this powder was examined by X-ray diffraction to investigate the cause, no Si diffraction line appeared, and only a diffraction line corresponding to bcc-Fe appeared.

Since it has been confirmed that Si is contained as a component, this means that Fe and Si are alloyed. The inventors have conducted various investigations such as tissue observation to explain this phenomenon, and as a result, they have concluded that the following may occur.

That is, since Si is brittle and Fe is rich in ductility,
When the Si content is about 6.5%, the Si powder is not processed so much, and instead Fe is processed intensively and S
It comes to cover i powder. Then, even in the subsequent rolling, the Si powder only moves and is not processed, and Fe does not change to S.
It acts like an adhesive that binds i and is processed while maintaining ductility.

When the amount of Si reaches about 8.0%, there is not enough Fe to cover the Si powder, and the Si powders come into contact with each other and are crushed. As a result, so-called mechanical alloying occurs in which Si is finely pulverized and absorbed in Fe to form an alloy, and the resulting molded article loses ductility and is poor in workability, which is an extremely defective intermediate product. In fact, a photograph of the metallographic structure of the two during processing is shown in FIG. 3 (cross-sectional structure of the sample before sintering), where the 6.5% Si material is separated from the Si grains, while the 8.0% Si -F
e It can be seen that the molding pauses are already in the same phase.

On the basis of the results of such investigations, it was investigated to what extent the phenomenon found by the inventors could be applied. As a result, a compact having toughness and ductility was obtained up to a Si content of 7%. It was found that a molded product could not be obtained if the amount was exceeded. This molded product is an intermediate product, but since it has toughness and ductility by itself, it is also possible to obtain a product by, for example, chipping based on this product, remolding it to manufacture a profile, and then sintering it. Is.

From the above, the skeleton of the present invention is a metal which can be easily cold worked by mixing powdery Fe and Si containing unavoidable impurities in a ratio such that the Si content is 7% or less by weight. Filling a container made of material, and having a thin layer on the inner surface of the container to facilitate the separation of the powder, characterized by peeling and removing the container corresponding portion after cold rolling or other cold working together with the container, A method for producing an ultra-high-performance electromagnetic steel having excellent soft magnetic characteristics and small magnetostriction, and characterized in that after cold working, a container-corresponding portion is peeled off and annealed at a temperature of 1100 ° C. or higher. And a method for producing an ultra-high-performance electromagnetic steel having a small magnetostriction, an intermediate product of the above powder having excellent workability in which Si is mixed in the Fe base, and Si diffused in the Fe base in the manufacturing method. Ultra-high performance electricity with excellent soft magnetic properties It is a product.

The present invention will be described in detail below. If the Si compounding ratio of the pre-molding powder exceeds 7%, a mechanical alloying phenomenon occurs, and a molded product rich in toughness and ductility cannot be obtained, so it is set to 7% or less. No lower limit is set, but 3.8
%, The cold rolling of the steel ingot obtained by casting becomes easy, so that the industrial merit of the present invention becomes small.

When the cold working is cold rolling, it is necessary to pack and seal it in a container such as a pipe or a box because the shape being processed cannot be maintained only by compacting. At this time, the material of the container must be not only rollable, but also strong enough to suppress the metal flow of the powder.

Further, since the inner surface of the container is not pressed against the powder, it is necessary to have an extremely thin non-metal layer. This may be a naturally-occurring oxide layer, various inorganic powders mixed in, or bond treatment, plating treatment, lubricating oil, dirt, and the like. In the case of cold forging, the die may replace the container in some cases.

The annealing temperature of the obtained molded body is as shown in FIGS.
If the temperature is lower than 1100 ° C, the material does not have a sufficient strength and does not form a shape as a material, and the soft magnetic properties are not exhibited. It is considered that if the temperature is lower than 1100 ° C, alloying of Si and Fe does not sufficiently occur.

In the method of the present invention, part of Fe is M
The fact that the total content of elemental components such as n, Al, Ni, Cr, Co, Nb, V, Ti, and Cu is 1% or less does not impair the toughness and ductility of the formed body, and the magnetic properties of high Si steels. Therefore, it does not impair the essence of the present invention.

[0025]

EXAMPLE Fe and Si powders having a purity of 99.9% and an average particle size of 40 μm were mixed and mixed sufficiently so that Si was 6.5% by weight, and a steel pipe having an inner diameter of 25 mm and a length of 150 mm was prepared. And then seal both ends of the pipe by welding,
A 2 hi cold rolling machine with a roll diameter of 300 mm was used for rolling with a rolling force of 20 t / pass to a thickness of 0.5 mm in 15 passes. After rolling, when the edge of the rolled material was cut off, the steel portion of the original pipe became a foil and could be peeled off very easily from the molded body.

The obtained molded article containing Si was rich in toughness and ductility, and could sufficiently withstand processing such as shearing and punching. The density of the compact was about 90% of 6.5% Si steel. After that, this molded body is punched out to obtain 31 mm × 3
When processed into a size of 50 mm and annealed in hydrogen at 1300 ° C. for 1 hour, the density was 1.1 times that of the compact, and the dimensions were 30 mm × 320 mm.

When the magnetic characteristics of this sample were measured, the coercive force was 19.1 A / m, the maximum magnetic permeability was 54000 (electrostatic unit) in DC Epstein measurement, and the magnetostriction was at the detection level by the method of attaching a strain gauge to the sample. It was below. The hardness after annealing was 370 Hv as measured by 50 kg Vickers hardness. Also, the crystal grain size is about 40 μm, which is shown in FIG. 5 (6.5%).
It was found that there is no different phase as shown in (Cross section structure of silicon steel) and alloying is completely performed.

As a comparative material, although Si powder was blended so as to have a weight of 7.2%, an attempt was made by the same process, but there were minute cracks inside the steel at the stage of the intermediate formed body. However, punching was impossible. Then, this was processed into 31 mm x 350 mm by electric discharge machining, and
Although annealing was performed at 00 ° C for 1 hr, cracks in the steel sheet could not be completely removed.

As a result, the coercive force was 150 A / m and the maximum magnetic permeability was about 2500 (electrostatic unit), and only very poor properties were obtained. An attempt was made to manufacture 6.5% Si steel by a vapor phase method, but it was difficult to punch the sample when measuring the magnetic properties, and an Epstein sample was prepared by electric discharge machining. The characteristics at this time are that the coercive force is 25.3 A / m,
The maximum magnetic permeability was 45,000 (electrostatic unit), which was inferior to the material of the present invention. In addition, in FIG. 6, the present invention material, the comparative material of 7.2% Si material, 6.5% Si material by the vapor phase method,
The end face shape at the time of punching is shown. It can be seen that the inventive material is processed linearly, whereas the comparative materials are all notched. From the above, it was demonstrated that the ultra-high performance electromagnetic steel produced by the method of the present invention is superior to other methods in workability such as punchability, magnetic characteristics, and surface appearance.

[0030]

According to the present invention, an ultra-high performance electromagnetic steel sheet containing an extremely large amount of silicon can be easily manufactured without cracking or breaking due to brittleness.

[Brief description of drawings]

1A and 1B are explanatory views of a die used for cold forging, and FIGS. 1C and 1D are cold forging cycles.

2A and 2B are graphs showing the relationship between the relative density of a 6.5% Si material compact, the sintering temperature, and the strength.

FIGS. 3 (a) and 3 (b) are electron micrographs showing the metal structure of a molded intermediate of Si6.5% material and 8.0% material.

4 (a) and 4 (b) are graphs showing the relationship between the annealing temperature of the compact and the magnetic characteristics.

5 (a), (b) and (c) are electron micrographs showing the metal structure of the final product.

6 (a), (b) and (c) are explanatory views showing the processing states of the material of the present invention and the comparative material.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenichi Ichige 7-3-1 Hongo, Bunkyo-ku, Tokyo, Faculty of Engineering, University of Tokyo (72) Inventor Hiroaki Masui 20-1 Shintomi, Futtsu Shin Nippon Steel Co., Ltd. Within the development headquarters

Claims (4)

[Claims] 1. A powdery Fe containing inevitable impurities,
Si is mixed at a ratio such that the amount of Si is 7% or less by weight,
Fill a container made of metal material that can be easily cold worked,
A method for producing an ultra-high-performance electromagnetic steel, characterized in that it has a thin layer on the inner surface of the container for facilitating separation from the powder, and the container-equivalent portion is peeled off after cold rolling or other cold working together with the container. 2. The method for producing an ultra-high performance electromagnetic steel according to claim 1, wherein after cold working, a portion corresponding to the container is peeled off and then annealed at a temperature of 1100 ° C. or higher. 3. The powdery intermediate product according to claim 1, wherein Si is mixed in the Fe base. 4. The ultra-high performance electromagnetic product according to claim 2, which has excellent soft magnetic characteristics in which Si is diffused in the Fe base.