JPH05258935A - Low iron loss unidirectional electromagnetic steel plate and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To device the title manufacturing method of low iron loss unidirectional electromagnetic steel plate without deteriorating the magnetic characteristics even in annealing step for removing strain may be performed. CONSTITUTION:Within the title directional electromagnetic steel plate, fine crystalline particles in diameter not exceeding 1/5 of the plate thickness are linearly juxtaposed in the direction at an angle of 30-90 deg. to the rolling direction 0-80mum deep from the surface of an underneath iron. A linear trench of a depth of less than 80mum is formed on the surface of the steel plate before performing the finishing annealing step and after coating the surface with an anneal releasing agent, the finishing annealing step is performed to form fine crystalline particles. Thus, the magnetic region is finely sectioned by the existing fine crystalline particles so as to reduce the iron loss. Furthermore, the deterioration of the magnetic flux density and the space factor can be minimized by introducing the minimum requisite fine crystalline particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low iron loss grain-oriented electrical steel sheet in which magnetic properties do not deteriorate even when strain relief annealing is performed, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, grain oriented electrical steel sheets have been required to reduce iron loss from the viewpoint of energy saving. As a method for reducing iron loss, a method of subdividing a magnetic domain by laser irradiation has already been disclosed in Japanese Patent Publication No. 58-26405. The reduction in iron loss by this method is due to the strain introduced by the laser. Therefore, it can be used as a transformer for a laminated iron core, but cannot be used as an iron core for a wound iron transformer that requires strain relief annealing.

As a technique for subdividing a magnetic domain, a technique for forming a groove on the surface of a silicon steel sheet is disclosed in Japanese Patent Publication No. 50-35679.
JP-A-59-28525 and JP-A-59-1975.
It is disclosed in Japanese Patent Laid-Open No. 20 and Japanese Patent Laid-Open No. 61-117218 and Japanese Patent Laid-Open No. 61-117284, and is a well-known technique. However, since these techniques subdivide the 180 ° magnetic domains while eliminating subdomains generated by the generation of free magnetic poles in the groove space by applying tension, they are methods that can withstand strain relief annealing, respectively. However, the magnetic flux density (B ₈ value) is significantly deteriorated, the mechanical characteristics are deteriorated, and the space factor is significantly deteriorated depending on the method of forming the groove.

Further, as a means for producing magnetic domain refinement, Japanese Patent Application Laid-Open No. 56-130454 proposes a method of producing fine primary recrystallized grains in the surface layer of secondary recrystallized grains. JP-A-59-208911 discloses a method of introducing artificial grain boundaries by locally heat-treating a steel sheet after secondary recrystallization annealing and annealing at a temperature of 800 ° C. or higher. Japanese Patent Application Laid-Open No. 61-117218 and Japanese Patent Application Laid-Open No. 62-67114 disclose a method of introducing recrystallized grains by heat treatment after forming a recess by pressing. According to these methods, the magnetic properties do not deteriorate even when strain relief annealing is performed, and the deterioration of B ₈ and space factor is less than that of the groove forming method.

[0005]

DISCLOSURE OF THE INVENTION The present invention utilizes a film formed from decarburization annealing to finish annealing in order to further improve the decrease in space factor due to the concave portions necessarily formed on the surface in the conventional method. and introducing the fine grains while keeping the flatness of the surface, B _8, less deterioration of the space factor, and to provide excellent low iron loss grain-oriented electrical steel sheet and a manufacturing method for coating adhesion With the goal.

[0006]

The gist of the present invention is to reduce the grain size of fine crystal grains to 5 to 40 μm in order to minimize the deterioration of B _8. It is to linearly align at a position of 0 to 80 μm from the iron surface in the direction of an angle of 30 to 90 ° with the rolling direction.

Here, the meaning that the crystal grains exist at a position of 0 μm from the surface of the base metal means that the crystal grains are in contact with the recesses intentionally introduced slightly deeper than the recesses of the unevenness due to the surface roughness of the base metal. The meaning that the crystal grain exists at a position of 80 μm means that the position of the crystal grain boundary closest to the steel plate surface is 80 μm from the position where the irregularities on the surface of the base steel are averaged. The linear shape may be linear, dotted or broken.

Although the effect of reducing iron loss by fine crystal grains is well known, how to introduce the fine crystal grains B _{8 is} sufficient to reduce iron loss while suppressing deterioration of space factor to a minimum. It was unclear whether the effect could be obtained. The present inventors, in addition to the conventional method of introducing a crystal grain by giving a strain to the steel sheet after secondary recrystallization, during secondary recrystallization annealing, it is eaten by the secondary recrystallized grain having a large grain size and disappears. The detailed formation mechanism of the fine crystal grains which never existed was investigated. As a result, the oxide film formed on the grain-oriented electrical steel sheet surface during finish annealing after the application of the annealing separator intentionally has roots deeply embedded in the base iron, thereby forming fine crystals around the roots of the oxide film. It has been found that it is possible to leave grains. According to the present invention, it becomes possible to control the position, size and distribution of fine crystal grains by controlling the depth and distribution of the roots of the oxide film. At the same time, the coating adhesion is improved, and the surface flatness is superior to the surface strain introduction method. A technique for forming grooves in a steel sheet in the step before secondary recrystallization annealing is disclosed in Japanese Patent Laid-Open No. 59-59-
As disclosed in Japanese Patent Laid-Open No. 197520, this technique aims at promoting purification during finish annealing by forming grooves, which is different from the idea of the introduction of fine crystal grains of the present invention.

Hereinafter, the present invention will be specifically described with reference to an embodiment. Fig. 1 shows the deterioration of the size and magnetic flux density (B ₈ ) of the fine crystal grains introduced when a groove having a depth of 5 µm was formed on the surface of a decarburized plate having a plate thickness of 0.23 mm in the direction perpendicular to the rolling direction. It is a figure which shows the cost and the improvement cost of iron loss. The distance between the grooves was 5 mm. From this figure, it can be seen that B ₈ decreases as the particle size increases and that the particle size of 40 to 50 μm is sufficient as an allowance for improving iron loss. However, it is considered that the thinner the plate thickness, the smaller the required grain size, and the thicker the plate grain, the larger the required grain size. Therefore, from the viewpoint of improving iron loss and suppressing B ₈ deterioration, In the invention, the grain size is set to be ⅕ or less of the plate thickness.
The crystal grain size in FIG. 1 is the average grain size of fine crystal grains observed by plate cross-section optical microscope observation.

FIG. 2 shows the groove depth, the magnetic flux density (B ₈ ) deterioration margin, and the iron loss improvement margin. Under any of the conditions, fine crystal grains were introduced into the bottom of the groove, but if the groove depth becomes too deep, iron loss tends to deteriorate rather than improve. Therefore, the groove depth of the present invention is 80 μm.
It was set to m or less. FIG. 3 is a diagram showing an angle between a groove forming direction and a rolling direction and an improvement margin of iron loss. The angle with the rolling direction is 3
It can be seen that an improvement in iron loss can be seen at 0 ° or more.

Although the present invention uses the hot-rolled sheet described in the examples, the effect of improving the iron loss by the fine crystal grains is not particularly limited to this material. That is, if it is a component system capable of secondary recrystallization, it does not contain Si or 6.5
The content may be up to about wt%, and the hot rolling, cold rolling, and annealing methods are not particularly limited as long as a treatment that can generate secondary recrystallized grains is performed. Further, once the oxide film is formed during the finish annealing, the film may be removed by subsequent high temperature reaction or polishing, and the mirror surface treatment may be performed.

The width of the groove may be any width so long as the annealing separating agent can penetrate into the groove, and the width of the groove is set within a range that does not prevent both improvement of iron loss and reduction of B ₈ deterioration allowance, which is the intention of the present invention. Spreading is allowed.

[0013]

EXAMPLES C: 0.05 wt%, Si: 3.25 wt%, M
n: 0.15 wt%, S: 0.006 wt%, Al: 0.0
Hot-rolled sheet containing 28 wt% and N: 0.007 wt% with the balance being iron is annealed, cold-rolled, and decarburized-annealed.
A groove having a width of 25 μm and a width of 20 μm was formed, MgO coating and finish annealing were performed, and the results shown in FIGS. 1, 2 and 3 were obtained.

[0014]

According to the present invention, the iron loss can be improved while keeping the deterioration of the magnetic flux density (B ₈ ) and the space factor to a minimum, so that the industrial effect thereof is great.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a crystal grain size, an iron loss improvement margin, and a B ₈ deterioration margin.

FIG. 2 is a diagram showing the relationship between groove depth, iron loss improvement margin, and B ₈ deterioration margin.

FIG. 3 is a diagram showing a relationship between an angle formed by a groove forming direction and a rolling direction and an iron loss improving margin.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kishio Mochinaga 2-6-3 Otemachi, Chiyoda-ku, Tokyo Shin Nippon Steel Corp.

Claims (2)

[Claims] 1. Fine crystal grains having a grain size of ⅕ or less of the plate thickness are linearly aligned at a position of 0 to 80 μm from the surface of the base metal in a direction of an angle of 30 to 90 ° with the rolling direction. Low iron loss unidirectional electrical steel sheet. 2. A linear groove having a depth of 80 μm or less is formed on the surface of the steel sheet before the finish annealing step, and after applying an annealing separating agent,
Finishing annealing is performed, The manufacturing method of the low iron loss unidirectional electrical steel sheet of Claim 1 characterized by the above-mentioned.