JPH11279645A - Low core loss and low magnetostriction grain-oriented electrical steel sheet and method for producing the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To clarify the relationship between the magnetic properties and the distribution of the strain depth and the width of the return magnetic domain when performing magnetic domain control on a grain-oriented electrical steel sheet by using a laser. A grain-oriented electrical steel sheet having magnetostriction characteristics is provided. SOLUTION: A magnetic domain control is performed by irradiating a laser beam on a surface of a grain-oriented electrical steel sheet, a width of a return magnetic domain generated on the irradiated surface in a rolling direction is 150 μm or less, and a distortion in a thickness direction by a laser is 30 μm. A low-loss, low-magnetostriction grain-oriented electrical steel sheet characterized by the above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented electrical steel sheet having good iron loss and magnetostriction characteristics used for an iron core of a transformer.

[0002]

2. Description of the Related Art At present, unidirectional electrical steel sheets that have been put to practical use have an axis of easy magnetization in the rolling direction of the steel sheet and are mainly used for electrical equipment such as transformers. In recent years, there has been an increasing demand for improvement of iron loss for reducing energy loss and improvement of magnetostriction for reducing noise during use.

When a magnetic domain is subdivided by introducing local strain or forming a groove in the steel sheet, eddy current flowing in the cross section of the steel sheet is reduced, and generation of heat energy is suppressed, so that iron loss is reduced. Energy loss of equipment can be reduced. For example, as disclosed in Japanese Patent Application Laid-Open No. 53-137016, by forming a linear minute strain on the surface of a grain-oriented electrical steel sheet and optimizing the interval of introducing strain, it is possible to improve the strain compared to before strain introduction. Low iron loss. Among them, as disclosed in Japanese Patent Application Laid-Open No. 55-18566, a method of condensing and irradiating a surface of a steel sheet with a pulsed YAG laser beam to introduce distortion by an evaporation reaction force of a film at an irradiated portion is known as iron. This is a method for manufacturing a highly grain-oriented electrical steel sheet which has a great loss-reducing effect and high reliability and controllability because of non-contact processing.

[0004]

On the other hand, the magnetostriction of a grain-oriented electrical steel sheet correlates with noise when used in a transformer, and the larger the magnetostriction, the greater the noise. Therefore, magnetostriction is one of the important qualities of a grain-oriented electrical steel sheet along with iron loss. However, in the case of laser domain control, it has been found that the magnetostriction has a positive correlation with the total irradiation energy of the laser, and an increase in the magnetostriction is inevitable as compared with the case where no laser is irradiated.

The present invention provides a grain-oriented electrical steel sheet which improves iron loss by laser irradiation and further reduces magnetostriction.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is to provide an excellent low-iron alloy characterized by adjusting the relationship between the reflux domain generation region, the strain depth distribution and the magnetic properties of a steel sheet to optimal conditions. The present invention relates to a grain-oriented electrical steel sheet having low loss and low magnetostriction characteristics and a method for producing the same. Specific means of the present invention are as follows.

(1) The magnetic domain is controlled by irradiating the surface of the grain-oriented magnetic steel sheet with a laser beam, and the width of the return magnetic domain generated on the irradiated surface, which is perpendicular to the irradiation direction, is 150 μm or less,
A low iron loss and low magnetostriction unidirectional magnetic steel sheet characterized in that a strain in a thickness direction by laser reaches 30 μm or more. (2) The laser is pulsed, and 60 to 12 with respect to the rolling direction of the steel sheet so that irradiation marks by the laser beam overlap.
The low-loss and low-magnetostriction unidirectional electrical steel sheet according to (1), which is irradiated in a direction of 0 °.

[0008] (3) The one-way electromagnetic wave having low iron loss and low magnetostriction according to (1) and (2), wherein the irradiation mark of the laser has an elliptical shape having a long axis in the irradiation direction. Steel plate manufacturing method.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present inventors have conducted various studies on the iron loss and magnetostriction characteristics after giving a strain to a steel sheet. As a result, by changing the strain distribution in the cross section of the steel sheet, the iron loss and the magnetostriction after the magnetic domain refinement can be changed. I found that. Therefore, the following experiment was conducted to see the relationship between the strain distribution and the iron loss and the magnetic strain after the magnetic domain refinement.

[0010] A unidirectional magnetic steel sheet having a thickness of 0.23 mm on which a glass film was formed by a known manufacturing method was irradiated with a pulse laser for subdividing magnetic domains to introduce minute strain. The irradiation direction is a direction (C direction) perpendicular to the rolling direction (L direction) of the steel sheet, and the irradiation interval is 6,500 μm in the rolling direction and 500 μm in a direction perpendicular to the rolling direction, which is good in reducing iron loss from the conventional knowledge. did. The width of the return magnetic domain was adjusted by changing the diameter of the laser beam in the L direction, and the depth of the distortion was adjusted by changing the diameter of the laser beam in the C direction.

[0011] In the treated steel sheet, the width of the return magnetic domain is observed using reflected electrons of the SEM, and the depth distribution of the strain in the portion irradiated with the laser is obtained by etching the steel sheet surface.
Observed with magnetic particles. Also, the result of iron loss at B = 1.7 T when excited at 50 Hz, and B =
The magnetostriction at 1.9T was measured. FIGS. 1 and 2 show the relationship between the strain depth and iron loss, and the relationship between the return magnetic domain width in the L direction and magnetostriction, respectively. A material having a strain depth of 0 and a width of the return magnetic domain of 0 in the L direction is a material that has not been subjected to laser treatment as a comparative material.

From the results shown in FIGS. 1 and 2, it can be seen that when the width of the return magnetic domain in the L direction is 150 μm or less and the strain depth is 30 μm or more, both good iron loss and magnetostriction characteristics can be achieved. When the width of the return magnetic domain in the L direction exceeds 150 μm, the magnetostriction increases exponentially, and the depth of the strain is 3 μm.
If it is less than 0 μm, almost no improvement in iron loss is observed. The principle of iron loss improvement by laser irradiation is that, due to distortion using the irradiation point as a heat source, a return domain having a magnetic moment perpendicular to the direction of easy magnetization is generated, and the 180 ° domain wall is minimized so that the magnetostatic energy here is minimized. The main domain formed by the above is subdivided, and as a result, the eddy current loss depending on the domain wall interval in the iron loss is reduced. Laser distortion is introduced by rapid heating and rapid cooling of the steel sheet.
The heating rate is proportional to the energy density of the irradiated laser per unit time, that is, the power density. Therefore, the strain introduction efficiency by the laser is higher when the laser beam having the higher peak power is irradiated.

On the other hand, as described above, the magnetostriction increases as the total irradiation energy of the laser increases. It is considered that the cause is that a large amount of irradiation energy is diffused also in the L direction and the C direction of the steel sheet, the return magnetic domain becomes unnecessarily large, the amount of magnetic moment for magnetization rotation increases, and the magnetostriction increases. . In order to suppress such thermal diffusion, it is necessary to irradiate a region with a smaller introduced energy of laser for a shorter time.

As a laser irradiation method that satisfies the above two conditions at the same time, the irradiation width is reduced and the irradiation energy (energy density) per unit area is irradiated several times within a range in which magnetic domain segmentation can occur. Is considered good. Such an irradiation method may be performed by irradiating the same line several times with a continuous wave laser, but is industrially difficult. On the other hand, a pulsed laser may be irradiated so that the laser beam is superimposed, and the width in the L direction is reduced, and the irradiation diameter in the C direction is appropriately adjusted so as to obtain an appropriate strain depth, thereby improving magnetic properties. And reduction of magnetostriction can be easily achieved at the same time.

Next, the reasons for the limitations of the respective numerical values specified in the present invention will be described. The reason why the width of the return magnetic domain perpendicular to the irradiation direction is 150 μm or less is that when the return magnetic domain generation region is further expanded, the magnetic moment in the magnetic domain causes magnetization rotation at the time of excitation and changes the volume, so that magnetostriction is generated. It is because it becomes large. Although there is no particular limitation on the lower limit, the lower limit is set as the minimum size that can have the magnetic domain refining effect, and the lower limit of the current laser focus capability is taken into consideration.
It is considered that 0 μm or more is necessary.

The reason why the strain depth is 30 μm or more in the plate thickness direction is that the magnetic domain refining effect is reduced when the width of the return magnetic domain in the rolling direction is reduced, so that the magnetic domain refining effect is maintained by the deeper strain. This is to reduce iron loss. The upper limit can be up to the plate thickness, but the magnetic domain refining effect is about 50
Since the saturation occurs at about μm, the cost and the processing capacity decrease further, and the deeper the depth, the more difficult it is to avoid heat diffusion in the surface direction, resulting in an increase in magnetostriction.

Further, the laser irradiation direction is set at a direction of 60 to 120 ° with respect to the rolling direction of the steel sheet. In order to reduce iron loss, it is necessary to subdivide magnetic domains at right angles to the magnetization direction. That's why. Therefore, 90 ° to the rolling direction
Is most effective, but if the deviation is within 30 °, the domain refining effect can be obtained, so the limited range of the irradiation direction is as described above.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. <Example 1> A pulse-type laser was applied to a 0.26 mm-thick unidirectional electrical steel sheet having a glass coating and manufactured by a known method, and iron loss and magnetostriction were measured. The irradiation direction was perpendicular to the rolling direction of the steel sheet, and the irradiation interval was 6,500 μm in the rolling direction and 500 μm in the perpendicular direction from the rolling direction, which was good for reducing iron loss from conventional knowledge.

The following two conditions were used as the beam diameter of the laser. The first is a circular laser spot having a diameter of about 500 μm, which is a conventional method.
C = elliptical laser spot of about 9,000 μm.
At this time, the total irradiation energy density received by the steel sheet was about 80 mJ / mm ² .

For the laser-irradiated material, the magnetostriction at B = 1.9 T when excited at 50 Hz, and B
Table 1 shows the results of measuring the iron loss at = 1.7T.
Compared to the conventional method, the method of the present invention reduced magnetostriction by 23% despite the same iron loss.

[0021]

[Table 1]

FIGS. 3 and 4 show the results of observing the state of the magnetic domains according to the conventional method and the present invention, respectively, using SEM reflected electrons. The width of the return magnetic domain formed in the portion irradiated with the laser is clearly smaller in the present invention than in the conventional product. FIG. 5 shows a magnetic domain pattern obtained by etching the surface of a steel sheet and observing it with magnetic particles in order to examine the depth distribution of strain. Table 2 shows the presence or absence of a return magnetic domain formed in the portion irradiated with the laser at each etching depth. In the conventional method, reflux domains could not be confirmed at a depth of 32 μm, but in the steel sheet of the present invention, reflux domains could be confirmed even at a depth of 52 μm.

[0023]

[Table 2]

From the above results, under the condition that the width in the rolling direction of the return magnetic domain generated on the irradiated surface of the steel sheet by the laser is less than 150 μm and the strain in the thickness direction reaches a depth of 30 μm or more, that is, as compared with the conventional method. By narrowing the strain distribution narrowly in the plane of the steel sheet and deeply introducing it in the thickness direction,
A steel sheet with reduced magnetostriction and reduced iron loss compared to conventional products could be obtained. <Example 2> A 0.23 mm-thick unidirectional electromagnetic steel sheet having a glass film formed thereon by a known manufacturing method was irradiated with a pulse laser for subdividing magnetic domains. The irradiation interval was set to 6,500 μm in the rolling direction, which is good for reducing iron loss, and 500 μm in the direction perpendicular to the rolling direction, based on the conventional knowledge.

The following two conditions were used as the laser beam diameter. The first is a conventional laser spot having a circular shape with a diameter of about 500 μm, the second is L = about 200 μm having a major axis in a direction C perpendicular to the rolling direction L of the steel sheet,
C = elliptical laser spot of about 9,000 μm.
At this time, the total irradiation energy density received by the steel sheet was about 80 mJ / mm ² .

Table 3 shows the results of the amplitude of the magnetostriction at B = 1.9 T and the iron loss at B = 1.7 T when the treated steel sheet was excited at 50 Hz. In the present invention, the magnetostriction is reduced by about 31% as compared with the conventional product despite the same iron loss.

[0027]

[Table 3]

FIG. 6 shows a magnetic domain pattern when the steel sheet surface is etched in order to examine the strain depth distribution. In the conventional product, reflux domains due to strain could not be confirmed at a depth of 20 μm, but in the steel sheet of the present invention, reflux domains due to strain could be confirmed even at a depth of 44 μm. This satisfies the conditions specified in the present invention and the strain at a depth of 30 μm or more.

Table 4 shows the presence or absence of a magnetic domain pattern when the steel sheet surface was chemically polished in order to examine the strain depth distribution. In the conventional method, reflux domains due to strain could not be confirmed at a depth of 33 μm, but in the steel sheet of the present invention, reflux domains due to strain could be confirmed even at a depth of 50 μm. This satisfies the conditions specified in the present invention and the strain at a depth of 30 μm or more.

[0030]

[Table 4]

From the above results, it was possible to obtain a grain-oriented electrical steel sheet having a low core loss and a low magnetostriction in the range of the present invention in which the width of the magnetic recirculation domain and the strain distribution are within the range of the present invention.

[0032]

As described above, the iron loss and magnetostriction characteristics of a grain-oriented electrical steel sheet can be reduced by using the effect of domain refining based on the reflux magnetic domain width and strain distribution described in the present invention. Since it can be further improved and the energy loss and noise of the transformer can be further reduced, its industrial significance is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the depth of strain and iron loss.

FIG. 2 is a diagram illustrating a relationship between a width of a return magnetic domain L direction and magnetostriction.

FIG. 3 is a diagram in which a reflux domain width according to a conventional method is observed.

FIG. 4 is a view showing the reflux domain width of the present invention.

FIG. 5 is a diagram of a magnetic domain pattern observed to observe distortion remaining in a steel sheet depth direction.

FIG. 6 is a diagram of a magnetic domain pattern observed to observe distortion remaining in the depth direction of the steel sheet.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kimihiko Sugiyama 1-1 Niwahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Nippon Steel Corporation Yawata Works (72) Inventor Tomoji Kumano Tobata-ku, Kitakyushu-shi, Fukuoka 1-1 Hatabicho Inside Nippon Steel Corporation Yawata Works

Claims (3)

[Claims] 1. A magnetic domain control is performed by irradiating a laser beam on a surface of a grain-oriented electrical steel sheet, and a width of the return magnetic domain generated on the irradiated surface, which is perpendicular to an irradiation direction, is 150 μm or less, and a thickness in a sheet thickness direction by a laser is reduced. A low-loss and low-magnetostriction unidirectional electrical steel sheet, wherein the strain has reached 30 μm or more. 2. The method according to claim 1, wherein the laser is of a pulse type and the laser beam is superposed with respect to the rolling direction of the steel sheet so that the irradiation mark by the laser beam is superimposed.
The low-loss and low-magnetostriction grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet is irradiated in a direction of 0 to 120 °. 3. The method according to claim 1, wherein the spot of the laser has an elliptical shape having a major axis in an irradiation direction.