JP2002012918A - Grain-oriented electrical steel sheets with excellent magnetic properties - Google Patents

Abstract

(57) [Problem] To improve the iron loss improvement effect efficiently by laser irradiation, suppress the increase in magnetostriction as much as possible, and expose the steel sheet iron to the irradiated part after laser irradiation. Another object of the present invention is to provide a grain-oriented electrical steel sheet that does not require recoating. SOLUTION: In a grain-oriented electrical steel sheet in which magnetic properties are improved by irradiating a laser beam to a pair of positions on both surfaces of a steel sheet to form thin reflux domains, the rolling direction width of the reflux domains is 0.3 mm or less; In addition, the present invention is a grain-oriented electrical steel sheet having excellent magnetic properties, in which the amount of deviation of the position of the return magnetic domain on both surfaces forming a pair in the rolling direction is equal to or less than the width of the return magnetic domain in the rolling direction. Further, it is a grain-oriented electrical steel sheet having excellent magnetic properties in which there is no laser irradiation mark on the surface of the steel sheet, or where the steel sheet base iron is not exposed at the laser-irradiated portion of the steel sheet surface.

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 whose magnetic properties have been improved by laser beam irradiation.

[0002]

2. Description of the Related Art Conventionally, in a method for producing a grain-oriented electrical steel sheet, a glass film is formed on the steel sheet surface, and after applying an insulating coating, a mechanical stress strain is introduced into the steel sheet surface.
Various methods have been proposed for reducing the iron loss by subdividing the 180 ° magnetic domain by forming a local return magnetic domain. Among them, as disclosed in Japanese Patent Application Laid-Open No. 55-18566, a method of condensing and irradiating a pulsed YAG laser beam onto the surface of a steel sheet to introduce distortion by the evaporation reaction force of the film at the irradiated portion is iron. This is a method for producing a grain-oriented electrical steel sheet which has a large loss improvement effect and is excellent in reliability and controllability due to non-contact processing.

[0003] In this method, the insulating film on the surface of the steel sheet is destroyed, and laser irradiation marks exposing the base iron are generated. Therefore,
After laser irradiation, rust prevention and insulation coating must be performed again. Therefore, as a further advanced method, various techniques for introducing a strain while suppressing the damage of the film have been devised.U.S. Pat.No. 4,645,547, Japanese Patent Publication No. 62-49322, Japanese Patent Publication No. 5-32881, Japanese Unexamined Patent Publication No. No. 204533, and the like. In addition, as an example of the laser irradiation method, in one embodiment of the above-mentioned U.S. Patent, an example of irradiating a laser to opposing positions on both surfaces of a steel sheet is disclosed, which is particularly superior to an irradiation example from only one surface. It did not indicate iron loss improvement.

Here, the principle of iron loss improvement by laser irradiation is explained as follows. Iron loss of grain-oriented electrical steel sheet is separated into abnormal eddy current loss and hysteresis loss. When a steel sheet is irradiated with a laser, stress distortion occurs in the surface layer due to the evaporation reaction force of the film or rapid heating / cooling. Due to this distortion, a return magnetic domain having a width almost equal to the width is generated, and the 180 ° magnetic domain is subdivided so as to minimize the magnetostatic energy. As a result, the eddy current loss in proportion to the 180 ° magnetic domain width decreases, and the iron loss decreases. On the other hand, when distortion is introduced, the hysteresis loss increases. That is, as shown in the schematic diagram of FIG. 11, the reduction of the iron loss by the laser is the optimum stress distortion that minimizes the iron loss, which is the sum of the reduction of the eddy current loss and the increase of the hysteresis loss accompanying the increase in the strain amount. Is to be provided. Therefore, it is ideal to sufficiently reduce the eddy current loss and suppress the increase in the hysteresis loss as much as possible, and it has been desired to realize such a grain-oriented electrical steel sheet.

[0005] Magnetostriction, which is an important magnetic property parameter of grain-oriented electrical steel sheets as well as iron loss, affects the generation of noise when the electromagnetic steel sheets are formed into an iron core of a transformer. When an external magnetic field is applied, the return magnetic domain expands and contracts in the direction of the magnetic field, thereby increasing magnetostriction. Accordingly, although the iron loss can be reduced by forming the return magnetic domain, there is a disadvantage that the magnetostriction may be increased.

[0006]

The object of the present invention is to provide a grain-oriented electrical steel sheet having improved magnetic properties by laser irradiation, in which the effect of improving iron loss is efficiently maximized and the increase in magnetostriction is minimized. An object of the present invention is to provide a grain-oriented electrical steel sheet that is suppressed. Another object of the present invention is to provide a magnetic steel sheet which does not need to be re-coated because the steel sheet iron is not exposed to the irradiated part, particularly after the laser irradiation, so as to provide higher magnetic properties.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a grain-oriented electrical steel sheet having improved magnetic properties by irradiating a laser beam to a pair of positions on both sides of a steel sheet to form a narrow reflux domain. A grain-oriented electrical steel sheet having excellent magnetic properties, wherein the width in the rolling direction is 0.3 mm or less, and the amount of deviation in the rolling direction of the return magnetic domain positions on the paired surfaces in the rolling direction is not more than the width in the rolling direction of the return magnetic domain. It is. Further, it is a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by having laser irradiation marks on the surface of the steel sheet. Further, it is a grain-oriented electrical steel sheet having excellent magnetic properties, characterized in that the steel sheet base iron is not exposed at the laser-irradiated portion on the steel sheet surface.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and effects of the present invention will be described below with reference to examples. <Example 1> First, a description will be given of a range in which a higher iron loss improvement ratio than that of single-sided irradiation can be obtained in an electromagnetic steel sheet in which iron loss is improved by irradiating laser beams from both sides. Example 1 is an electromagnetic steel sheet in which a laser beam is condensed into a minute circular shape, and a film on the surface of the steel sheet is evaporated and scattered by irradiation with a laser pulse having a relatively high pulse energy density, and iron loss is improved by the stress strain.

FIG. 8 is an explanatory view of an apparatus for manufacturing an electromagnetic steel sheet that irradiates a laser beam to only one side. The laser beam 1 is output from a Q switch pulse CO2 laser (not shown), passes through a total reflection mirror 2 and a scan mirror 3, and is condensed and scanned by an fθ lens 4. The scanning direction is a direction substantially perpendicular to the rolling direction of the magnetic steel sheet. The focusing shape of the laser beam was substantially circular, and the focusing diameter d was changed in the range of 0.2 to 0.6 mm by adjusting the focus of the lens.
The pitch Pl in the rolling direction of the linear irradiation is 6.5 mm. The laser pulse repetition frequency was 90 kHz, and the irradiation pitch Pc in the plate width direction was selected to be substantially equal to the irradiation beam diameter by adjusting the scanning speed. Therefore, the laser irradiation marks are arranged so as to be almost in contact with each other in the plate width direction. FIG. 9 is a schematic view of a laser irradiation mark. The pulse energy Ep was adjusted at 4 to 10 mJ, and the irradiation energy density Ed was controlled together with the control of the focused beam diameter d. Here, the irradiation energy density Ed is given by the following equation, where S is the focused beam area. Ed = Ep / S (mJ / mm2) FIG. 7 is an explanatory view of an apparatus for manufacturing an electromagnetic steel sheet according to the present invention in which both surfaces are irradiated with a laser. The laser beam 1 is output from a Q-switch pulse CO2 laser (not shown), is split into two by a beam splitter 5, and is irradiated to substantially opposite positions on the front and back surfaces by independent light collecting devices. Laser pulse energy applied to each surface is 2 to 5 mJ
Is controlled within the range. Other irradiation conditions are the same as those described with reference to FIG. The adjustment of the rolling direction of the irradiation position on the front surface and the back surface was finely adjusted using a moving table (not shown).

Using these devices, a grain-oriented electrical steel sheet having a thickness of 0.23 mm is irradiated with laser, and the rolling direction width Wcd and the magnetic field of the return domain starting from the stress strain generated in the laser-irradiated part.
The relationship between the iron loss improvement rate at 1.7T and 50Hz was investigated. The iron loss improvement rate η is represented by the following equation. η = [(iron loss before laser irradiation−iron loss after laser irradiation) / iron loss before laser irradiation] × 100 (%) The reflux magnetic domain width was observed with a magnetic domain observation electron microscope.

FIG. 2 shows the relationship between Wcd and the iron loss improvement rate in the case of single-sided laser irradiation and double-sided laser irradiation. For single-sided laser irradiation, the pulse energy is fixed at 8 mJ and the focused beam diameter is
Changed to 0.2-0.6mm. In the irradiation on both surfaces, the irradiation energy on each surface was fixed at 4 mJ, and the focused beam diameter was similarly changed to 0.2 to 0.6 mm. The relationship between Wcd and the irradiation beam diameter d is also shown in the figure. The amount of displacement in the rolling direction of the return magnetic domains forming a pair on both surfaces is all 0 mm. With double-sided irradiation, Wcd almost proportional to the beam diameter was obtained, but with single-sided irradiation, the obtained Wcd did not decrease to less than 0.27 mm even with a small focusing system. This is because when the energy density Ed increases, the plasma generated when the film evaporates becomes high temperature, and because it becomes spatially large, the stress-strain range using the plasma as a secondary heat source increases, resulting in a large stress strain wider than the beam diameter. To do that. As a result, the hysteresis loss becomes excessive and the iron loss improvement rate decreases.

In the region where the return magnetic domain width Wcd is 0.3 mm or more, when the iron loss improvement ratio is compared between single-sided and double-sided irradiation, the improvement ratio is slightly higher in the case of single-sided irradiation. In single-sided irradiation, the energy density is reduced by the increase in the irradiation beam diameter. As a result, an excessive plasma effect is also eliminated, an increase in hysteresis loss is suppressed, and a high iron loss improvement is achieved. On the other hand, in the case of double-sided irradiation, although the stress strain per side is small, a relatively large distortion is introduced when both sides are combined, and the effect of the increase in hysteresis loss is relatively large compared to the case of single-sided irradiation, and the iron loss improvement rate is small. It is thought to decrease.

On the other hand, in the region where Wcd is 0.3 mm or less, the distortion width is small, and the amount of increase in the hysteresis loss is small. At the same time, the return magnetic domain starting from one side is shallow, and the effect of reducing eddy current loss is reduced. However, since the return magnetic domains from both sides supplement the penetration depth in the thickness direction, a sufficient return magnetic domain penetrating the plate thickness is formed as a result. That is, as a result of the formation of the return magnetic domains narrow in the rolling direction and deep in the sheet thickness direction, the eddy current loss is sufficiently reduced, and at the same time, the increase in the hysteresis loss is suppressed as much as possible.

An attempt was made to form a return magnetic domain having a width of 0.3 mm or less in single-sided irradiation. To form a narrow reflux domain width, the energy density is controlled to suppress excessive plasma which is a secondary heat source.
You can only lower Ed. Therefore, the pulse energy is reduced along with the reduction of the focused beam diameter, and the energy density is reduced.
Ed was almost the same as double-sided irradiation. The relationship between Wcd and the iron loss improvement rate in this case was compared with the result of double-sided irradiation. The result is FIG. The relationship between Wcd and the irradiation beam diameter d is also shown in the figure. Even when the beam diameter was 0.3 mm or less by single-sided irradiation, a return magnetic domain width almost equal to the beam diameter was obtained. The characteristics of the double-sided irradiation are the same data as the results shown in FIG.

When Wcd is 0.3 mm or less, double-sided irradiation also shows a higher iron loss improvement rate. In this comparison, since the energy density is the same, the stress strain per one side and the return magnetic domain are the same. In the double-sided irradiation, the reflux magnetic domains from both sides compensate for the penetration depth in the plate thickness direction, so that the eddy current loss reduction effect is high.
On the other hand, single-sided irradiation has no effect, and as a result, the iron loss improvement rate is low. As described above, when Wcd is 0.3 mm or more, when stress strain is introduced on both sides, the effect of increasing hysteresis loss is relatively large, and single-sided irradiation shows a somewhat higher iron loss improvement rate than double-sided irradiation .

Next, a description will be given of an optimum range of the displacement of the pair of return magnetic domains on the front and back surfaces in the rolling direction. FIG. 1 is a schematic view of an electromagnetic steel sheet according to the present invention, and is a view for explaining the displacement of a return magnetic domain. The width of the return magnetic domain b based on the stress strain a of each surface is Wcd, | △ L | is the absolute value of the amount of displacement of the return magnetic domain center of each surface, and the equivalent width of the return magnetic domain in the rolling direction. Is defined by Wcd '. FIG. 4 shows that when the laser beam diameter is converged to 0.3 mm by double-sided irradiation and Wcd is 0.3 mm, | △ L | when the displacement | ズ L | is changed from 0 to 0.6 mm
/ Wcd and the magnetostriction ratio λ ′. Here, the magnetostriction ratio λ ′ is the magnetostriction λ when | △ L |> 0 and the magnetostriction λ when | △ L | = 0.
It is a ratio with 0. The magnetostriction increases with an increase in | △ L |, but in the range of | △ L | / Wcd> 1, that is, the magnetostriction of the return magnetic domain is remarkable. This is due to an increase in the equivalent width Wcd 'of the return magnetic domain, which causes magnetostriction.

FIG. 5 shows the relationship between | △ L | / Wcd and the iron loss improvement ratio η ′. Here, η ′ is the ratio between the iron loss improvement rate η0 when | △ L | = 0 and the iron loss improvement rate η when | △ L |> 0. From this, the iron loss improvement rate is greatly reduced in the range of | △ L | / Wcd> 1. This is because the reflux domains from both sides have no effect of compensating for the penetration depth, and as a result, the effect of improving iron loss is reduced.

As described above, in the magnetic steel sheet according to the present invention, by setting the deviation | △ L | of the return magnetic domain formed in the rolling direction width to be equal to or less than the return magnetic domain width Wcd, excellent characteristics are obtained in terms of both magnetostriction and iron loss. Is obtained. <Embodiment 2> Next, an embodiment using an irradiation method that does not generate laser irradiation marks on the steel sheet surface will be described. In an irradiation method in which laser irradiation marks are not generated on the steel sheet surface, stress distortion is imparted by rapid heating and cooling at a temperature below the temperature at which the surface glass coating and the insulating coating evaporate and scatter. Therefore, the focusing area of the laser beam is larger than that of the first embodiment, and the energy density is
Must be 1/20 to 1/30.

FIG. 10 is an explanatory view of an irradiation beam shape in an irradiation method in which laser irradiation marks are not generated on the steel sheet surface. The laser beam is focused on an ellipse having a major axis in the plate width direction.
Here, the width in the rolling direction of the focused laser beam is dl, and the width in the plate width direction is dc. The laser beam irradiation device is the same as that shown in FIGS. 7 and 8. However, a cylindrical lens (not shown) is inserted during the propagation of the beam, and the focused beam is adjusted by adjusting the focus of the fθ lens 4 and changing the focal length of the cylindrical lens. The elliptical shape was controlled. The laser pulse repetition frequency was 90 kHz, and the irradiation pitch Pc in the plate width direction was changed by adjusting the scanning speed.

In this embodiment, the focused shape of the laser beam is dl =
0.2 to 0.6 mm, dc = 4.0 to 10.0 mm
The pitch of the irradiation position in the rolling direction is Pl = 6.5 mm. C
The direction irradiation pitch is 0.5 mm. FIG. 6 shows the relationship between Wcd and the iron loss improvement ratio in the case of laser irradiation on only one side and laser irradiation on both sides in an irradiation method in which irradiation marks are not generated on the surface. Pulse energy of 8m for laser irradiation on one side only
The beam diameter dl in the L direction was changed to 0.2 to 0.6 mm while being fixed at J, and the beam diameter dc in the C direction was selected to be a minimum value within a range in which no surface irradiation marks were generated in each dl. For irradiation on both surfaces, the irradiation energy on each surface was fixed at 4 mJ, the focused beam diameter was changed to 0.2 to 0.6 mm, and dc was also selected to the minimum value within a range where no irradiation marks were generated. The amount of displacement in the rolling direction of the return magnetic domains forming a pair on both surfaces is all 0 mm. The relationship between Wcd and the beam diameter dl in the rolling direction is also shown in the figure.

The reflux magnetic domain width Wcd observed for both single-sided and double-sided irradiation almost coincided with the focused beam diameter dl. This is a low energy density that does not evaporate the surface film,
It is considered that the generation of the plasma serving as the secondary heat source is small, and therefore, the stress-strain width almost coincides with the beam diameter. According to the results, even in the irradiation method in which no irradiation marks are formed on the surface of the steel sheet, the steel sheet having Wcd of 0.3 mm or less and having the return magnetic domain formed on both sides has a higher iron loss improvement rate than the case where it is formed on only one side, as in FIG. Is shown. The improvement was more remarkable than when the film was evaporated. This is because the stress distortion caused by rapid heating / quenching is slightly weaker than the distortion caused by the evaporation reaction force, so that the effect of generating reflux magnetic domains from both surfaces becomes more remarkable.

In the following, distortion is applied from both sides of the present invention,
A method for distinguishing between a magnetic steel sheet having a return magnetic domain of 0.3 mm or less and a conventional magnetic steel sheet irradiated only from one side will be described. The width of the return magnetic domain can be confirmed by an electron microscope for observing the magnetic domain. Whether or not distortion is introduced from both sides can be determined by the following method. Since the return magnetic domains are generated based on the stress distortion of the surface layer portion of each surface, by removing the distorted extreme surface layer portion by etching, the return magnetic domains originating therefrom also disappear. In the steel sheet of the present invention in which strain is applied from both surfaces, even if the surface layer on one surface is removed, the return magnetic domain generated from the other surface remains.
On the other hand, in the case of applying strain from only one surface, the return magnetic domain completely disappears due to removal of the surface layer on one of the surfaces. Therefore, even when the surface irradiation mark is not visible, it can be determined whether or not the return magnetic domain is formed from both surfaces.

In the embodiment of the present invention, the return domain is formed by irradiating the Q switch pulse CO2 laser. However, a continuous wave laser can be used as long as the return domain within the scope of the present invention can be formed. May be used.

[0024]

As described above, in the grain-oriented electrical steel sheet of the present invention, a return magnetic domain is formed by applying stress strain from both sides, and the rolling direction width is 0.3 mm or less,
In addition, when the amount of displacement in the rolling direction is equal to or less than the width in the rolling direction, there is an advantage that a higher iron loss improvement effect and lower magnetostriction are achieved as compared with the related art. Further, the present invention has a high iron loss improvement effect regardless of the presence or absence of surface irradiation marks.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a cross section of a grain-oriented electrical steel sheet of the present invention, and is an explanatory view of a displacement of a return magnetic domain forming position.

FIG. 2 shows the magnetic domains of the grain-oriented magnetic steel sheet of which the iron loss is improved by the film evaporation reaction force due to the laser irradiation, the magnetic steel sheet irradiated with laser from both sides and the magnetic steel sheet irradiated with laser only from one side according to the present invention. It is explanatory drawing of the relationship between width | variety and the iron loss improvement rate.

FIG. 3 shows a grain-oriented electrical steel sheet in which iron loss is improved by a coating evaporation reaction force due to laser irradiation.
FIG. 4 is an explanatory diagram of a relationship between a return magnetic domain width of a magnetic steel sheet and an iron loss improvement rate when an energy density is controlled so that a converged beam diameter and a return magnetic domain width substantially match.

FIG. 4 is a graph showing the relationship between the displacement of the return magnetic domain position on the front and back surfaces and the magnetostriction ratio in the electromagnetic steel sheet according to the present invention.

FIG. 5 is a graph showing the relationship between the deviation of the return magnetic domain position on the front and back surfaces and the iron loss improvement ratio in the electromagnetic steel sheet according to the present invention.

FIG. 6 is a grain-oriented electrical steel sheet which has improved the iron loss by rapidly heating and cooling the steel sheet surface by laser irradiation and has no laser irradiation marks on the surface. FIG. 6 is an explanatory diagram showing a relationship between a magnetic domain width of a magnetic steel sheet irradiated with laser only from the above and a core loss improvement rate.

FIG. 7 is an embodiment of the method for producing an electromagnetic steel sheet of the present invention.

FIG. 8 shows an embodiment of a method for improving iron loss of an electromagnetic steel sheet by laser irradiation from one side.

FIG. 9 is a schematic view of an irradiation mark in an irradiation method for improving iron loss by a film evaporation reaction force by laser irradiation.

FIG. 10 is a schematic diagram of an irradiation beam shape when iron loss is improved by rapid heating and rapid cooling of a steel sheet surface by laser irradiation.

FIG. 11 is a diagram showing a relationship between stress distortion due to laser irradiation and abnormal eddy current loss and hysteresis loss.

[Description of Signs] a: Stress-strain region b: Return magnetic domain c: 180 ゜ Magnetic domain 1: Laser beam 2: Total reflection mirror 3: Scan mirror 4: fθ lens 5: Beam splitter 6: Magnetic steel sheet Ed: Pulse energy density Ep ... Pulse energy S ... Condensed beam area Wcd ... Reflux magnetic domain width Wcd '... Equivalent width of the return magnetic domain △ L ... Displacement of the formation position of the front and back return magnetic domains η ... Iron loss improvement rate η' ... Iron loss improvement rate ratio λ ... Magnetostriction λ ': Magnetostriction ratio Pl: Formation pitch of the return magnetic domain in the rolling direction dl dl: Elliptical condensing laser beam rolling direction width dc: Elliptical condensing laser beam in width direction d: Diameter of circular condensing laser beam

Claims (3)

[Claims] 1. A grain-oriented electrical steel sheet whose magnetic properties have been improved by irradiating a laser beam to a pair of positions on both sides of a steel sheet to form thin reflux domains, wherein the width of the reflux domains in the rolling direction is 0.3 mm or less. A grain-oriented electrical steel sheet having excellent magnetic properties, wherein the amount of deviation in the rolling direction of the return magnetic domain positions on both surfaces of the pair is equal to or less than the width of the return magnetic domain in the rolling direction. 2. The grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein a laser irradiation mark is present on the surface of the steel sheet. 3. The grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the steel sheet base iron is not exposed at the laser-irradiated portion on the surface of the steel sheet.