JPS6342331A - Production of low iron loss grain oriented electrical steel sheet - Google Patents

Abstract

PURPOSE:To produce a low iron loss grain oriented electrical steel sheet with which the effect of decreasing the iron loss is not lost even if the steel sheet is subjected to a heat treatment such as stress relief annealing by heating the grain oriented electrical steel sheet subjected to finish annealing to an adequate temp. and imparting local plastic strain to the surface thereof in this state. CONSTITUTION:The grain oriented electrical steel sheet subjected to the finish annealing is kept heated at >=500 deg.C in; for example, the soaking zone of a continuous annealing furnace and is passed in this state between a roll having many knife edges extending along the axial direction on the surface of a cylindrical barrel and a flat roll, by which the linear plastic distortions in the rolling strain in the direction perpendicular to the rolling direction is locally imparted to the above-mentioned steel sheet. A high-dislocation density region is thereby formed linearly to the steel sheet and the iron loss is decreased by the segmentation of the magnetic domain width. The segmentation of the magnetic domain width is by the local plastic strain and the effect of decreasing the iron loss is not lost in spite of the subsequent heat treatment of high temp. such as stress relief annealing.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing grain-oriented electrical steel sheets with low core loss, in which the core loss improvement effect does not disappear even after heat treatment such as stress relief annealing. It is.

Grain-oriented electrical steel sheets are mainly used as cores of transformers, and are required to have low magnetic properties, especially low iron loss.

In order to reduce iron loss, it is necessary to bring the crystal orientation of the secondary recrystallized grains that make up the copper plate closer to the (110) <001> orientation, the so-called Goss orientation, and to reduce impurities in the steel. This method does indeed reduce iron loss, but as the crystal orientation approaches the Goss orientation, the crystal grains become larger and the iron loss cannot be reduced as much as expected. This is because as the crystal grains become larger, the magnetic domain width expands in proportion to the size and eddy current loss increases.

(Prior Art) So-called magnetic domain refining technology has emerged as a technology to eliminate this phenomenon and reduce iron loss. A currently industrialized example is a technique disclosed in Japanese Patent Publication No. 57-2252, etc., in which a finish annealed grain-oriented electrical steel sheet is linearly irradiated with a laser beam in a direction substantially perpendicular to the rolling direction. By irradiating the laser beam, linear high dislocation density regions are formed in the steel sheet, and the magnetic domain width is subdivided. These technologies have made it possible to significantly reduce iron loss.

However, the iron loss reducing effect of the steel plate obtained by the above technique is due to magnetic domain refining due to the strain introduced by the laser, so the iron loss improving effect disappears when the steel plate is annealed. Therefore, this steel plate cannot be used in wound core type transformers that require stress relief annealing. On the other hand, as a magnetic domain refining technology that allows strain relief annealing, Japanese Patent Application Laid-Open No. 60-1031
Japanese Patent No. 24 and the like disclose a method of locally arranging foreign matter on a steel plate. However, in this case, the manufacturing method is complicated and industrialization is difficult, and an increase in cost is unavoidable.

(Problems to be Solved by the Invention) The present invention is directed toward a low core loss in which the core loss improvement effect does not disappear even after heat treatment such as strain relief annealing, without the drawbacks and disadvantages of the above-mentioned prior art. The purpose is to manufacture magnetic steel sheets.

(Means for solving the problem) In order to achieve the above objective, we conducted many experiments and studied the results by applying local plastic strain to finish annealed grain-oriented electrical steel sheets under heating conditions of 500°C or higher. We have newly discovered that an iron loss improvement effect that does not disappear even when strain relief annealing is performed has been newly discovered, and the present invention has been completed.

In other words, the present invention uses 500 grain-oriented electrical steel sheets with a finish-sintered purity.
This is a method for producing a grain-oriented electrical steel sheet with low core loss, characterized in that local plastic strain is imparted to the surface of the steel sheet in a heated state at a temperature of .degree. C. or higher.

The present invention will be explained in detail below based on the experimental results that led to the discovery of the present invention.

A ceramic roll having a large number of knife-like protrusions extending along the axial direction of the cylinder at a circumferential pitch of 2 to 50+r+m on the surface of the cylinder and a flat roll made of ceramic are installed in the soaking zone of a continuous annealing furnace and finished. The grain-oriented electrical steel sheet after baking 24 was heated in the soaking zone and passed between the rolls to introduce plastic strain through pressure contact with the protrusions. In this way, a linear plastic strain imparted region is locally formed in the steel plate in a direction perpendicular to the rolling direction. The interval between the linear strain applying regions depends on the circumferential pitch of the projections, and the amount of plastic strain can be varied by changing the degree of tightening between the rolls.

The steel plate to which plastic strain has been applied in this manner continues to pass through a cooling zone and reach room temperature.

After cooling, the steel plate was subjected to strain relief annealing at 800° C. for 3 hours in an N2 gas atmosphere, and then its magnetic properties were measured.

Figure 1 shows the influence of the soaking temperature to which plastic strain is applied on improving the iron loss value. W l taken on the vertical axis of the figure
1/S Q indicates iron loss at a magnetic flux density of 1.7 Tesla and 50 Hertz.

The thickness of the test steel plate is 0.23 mm.

In this case, even at the same processing temperature, the effect differed depending on the distance between the linear applied regions and the amount of plastic strain, but below 500°C, the properties were almost the same as those without processing without applying any processing strain, while at 500°C Although it was not possible to specify the temperature above ℃, a reduction in iron loss was observed under some conditions (Figure 1 shows the conditions under which the iron loss reduction force q was tolerated).

(Function) As is clear from the experimental effects shown in Figure 1, when the heating temperature is increased to 500°C or higher, there is a significant reduction in iron loss compared to the comparative material. By introducing linear plastic strain, an iron loss reducing effect that does not disappear even after strain relief annealing was introduced.

The finish-sintered grain-oriented electrical steel sheet used in the present invention is manufactured by a known method. Therefore, the steel plate of finishing firing is usually covered with a forsterite (2!, IgO・SlO It has been confirmed that applying strain is effective regardless of whether it is applied before or after the top coating, or even when applying strain to a bare steel plate without the above-mentioned coating.

When applying plastic strain at high temperatures, it is desirable to introduce linear plastic strain in a direction perpendicular to the rolling direction of the steel plate, but generally it may be deviated by up to 30° from the perpendicular direction. Further, the plastic strain is not necessarily introduced in a continuous linear manner, but may be in the form of a dotted line or a broken line, but it is particularly desirable that the interval between the linear plastic strain applying portions be 3 mm to 3 Q mm.

Introducing plastic strain at high temperatures may cause recesses on the surface of the steel plate.If the width of the recess exceeds 1mm or the depth of the recess exceeds 0.1mm, the excitation current will increase significantly even if the iron loss value decreases. Therefore, the formation of the concave portion has a width of 1
It is desirable that the depth be within 1 mm and the depth O be within 1 mm.

The method of introducing strain is not limited, but it is easy to introduce strain by passing the strain between a roll with protrusions and a flat roll in a furnace.

Alternatively, strain may be introduced mechanically by irradiating the heated steel plate with an energy beam such as a laser or by marking it with a heat-resistant material.

Example: A 3.2% Si grain-oriented electrical steel sheet coated with a 0.23 mm thick and 300 mm wide top coat was heated at room temperature (25° C.) to temperatures of 300° C., 600° C., and 800° C. while rolling it in the rolling direction. Linear plastic strain was introduced in the orthogonal direction.

This plastic strain was introduced by passing a steel plate between a ceramic roll with protrusions and a flat roll, and the interval between the linear plastic strain imparting parts was 5 mm. The protrusions of the ceramic roll used had an edge width of 0. Q5mm, height from roll guard 0.92mm.

The thus treated steel plate was subjected to strain relief annealing at 800° C. for 3 hours in N2 gas, and its magnetic properties were measured. The results are shown in Table 1, and the iron loss is significantly reduced by locally introducing plastic strain especially at temperatures above 500°C.

Table 1 The reason why low core loss was maintained even after strain relief annealing by introducing strain at high temperature is that the strain introduced at high temperature did not recover even after strain relief annealing as a result of magnetic domain observation. It is expected that magnetic domain segmentation is maintained by the residual of .

<Effects of the Invention> By using the present invention, the iron loss of a wound core that requires stress relief annealing can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between heating temperature when strain is introduced during heating and iron loss after strain relief annealing.

Claims (1)

[Claims] 1. A method for producing a grain-oriented electrical steel sheet with low core loss, which comprises applying local plastic strain to the surface of a finish-annealed grain-oriented electrical steel sheet in a state of heating to 500° C. or higher.