JP4091749B2 - Oriented electrical steel sheet with excellent magnetic properties - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a grain-oriented electrical steel sheet having improved magnetic properties by irradiation with a laser beam.
[0002]
[Prior art]
Conventionally, in a method for producing grain-oriented electrical steel sheets, a 180 ° magnetic domain is formed by forming a glass film on the steel sheet surface, further applying an insulating coating, and then introducing mechanical stress strain on the steel sheet surface to form local reflux magnetic domains. Various methods have been proposed to reduce the iron loss. In particular, as disclosed in Japanese Patent Application Laid-Open No. 55-18566, a method of focusing and irradiating a surface of a steel sheet with a pulsed YAG laser beam and introducing strain by an evaporation reaction force of a film at an irradiated portion is an iron method. This is a method for producing an excellent grain-oriented electrical steel sheet that has a large loss improvement effect and high reliability and controllability because of non-contact processing.
[0003]
In this method, the insulating film on the surface of the steel sheet is broken, and a laser irradiation mark is generated in which the ground iron is exposed. Therefore, the coating for preventing rust and insulation must be performed again after the laser irradiation. Therefore, as a further advanced method, various techniques for introducing strain while suppressing damage to the coating have been devised, such as US Pat. No. 204533, etc. In addition, as an example of the laser irradiation method, an example in which the laser is irradiated to the opposite positions on both sides of the steel sheet is disclosed in one embodiment of the above-mentioned U.S. patent, which is particularly superior to the irradiation example from only one side. It did not indicate an improvement in iron loss.
[0004]
Here, the principle of iron loss improvement by laser irradiation is explained as follows. The 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 on the surface layer due to the evaporation reaction force of the film or rapid heating / cooling. A reflux magnetic domain having a width almost equal to the width is generated from this strain, and the 180 ° magnetic domain is subdivided so as to minimize the magnetostatic energy. As a result, the eddy current loss proportional to the 180 ° magnetic domain width decreases and the iron loss decreases. On the other hand, the hysteresis loss increases when strain is introduced. In other words, the iron loss reduction by the laser is the optimum stress strain that minimizes the iron loss that is the sum of the decrease in eddy current loss and the increase in hysteresis loss as the amount of strain increases as shown in the schematic diagram of FIG. Is to give. Therefore, it is ideal to sufficiently reduce the eddy current loss and suppress the increase in 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 along with iron loss, affects the generation of noise when the electrical steel sheets are formed on the iron core of a transformer. When an external magnetic field is applied, the return magnetic domain expands and contracts in the magnetic field direction, thereby increasing magnetostriction. Therefore, although the iron loss can be reduced by forming the reflux magnetic domain, there is a drawback that the magnetostriction may be increased.
[0006]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to provide a grain-oriented electrical steel sheet that effectively maximizes the iron loss improvement and suppresses an increase in magnetostriction as much as possible, as a grain-oriented electrical steel sheet with improved magnetic properties by laser irradiation. There is. It is another object of the present invention to provide higher magnetic properties with a grain-oriented electrical steel sheet that does not require re-coating because the steel plate iron is not exposed to the irradiated portion after laser irradiation.
[0007]
[Means for Solving the Problems]
The present invention is a grain-oriented electrical steel sheet that has improved magnetic properties by irradiating a laser beam to a pair of positions on both sides of the steel sheet to form a thin reflux magnetic domain, and the rolling direction width of the reflux magnetic domain is 0.3 mm or less. and the amount of deviation of the rolling direction of the closure domain positions of both sides in a pair is the rolling direction width hereinafter of the closure domains, in oriented electrical steel sheet towards you, characterized in that the closure domains penetrate the plank direction is there. It is also oriented electrical steel sheet towards you, it characterized in that there is a laser irradiation signatures on the surface of the steel sheet. Furthermore, the grain-oriented electrical steel sheet is characterized in that no laser irradiation trace is generated in the laser irradiated portion on the steel sheet surface.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments and effects of the present invention will be described using examples.
<Example 1>
First, the range in which the iron loss improvement rate higher than that of single-sided irradiation can be obtained in the electromagnetic steel sheet in which the iron loss is improved by irradiating laser from both sides will be described. Example 1 is an electrical steel sheet in which a laser beam is condensed into a minute circle, a film on the steel sheet surface is evaporated and scattered by irradiation with a laser pulse having a relatively high pulse energy density, and the iron loss is improved by the stress distortion.
[0009]
FIG. 8 is an explanatory diagram of an apparatus for manufacturing an electromagnetic steel sheet that irradiates a laser only on one side. The laser beam 1 is output from a Q switch pulse CO 2 laser (not shown), and is scanned and condensed and irradiated by an fθ lens 4 via a total reflection mirror 2 and a scan mirror 3. The scanning direction is a direction substantially perpendicular to the rolling direction of the electrical steel sheet. The condensing shape of the laser beam was almost circular, and the condensing diameter d was changed in the range of 0.2 to 0.6 mm by adjusting the focus of the lens. The rolling direction pitch Pl 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 almost equal to the irradiation beam diameter by adjusting the scanning speed. Accordingly, the laser irradiation traces are arranged so as to be almost in contact with each other in the plate width direction. FIG. 9 is a schematic diagram of laser irradiation traces. The pulse energy Ep was adjusted to 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 expressed 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 producing an electrical steel sheet in which laser is irradiated on both sides according to the present invention. The laser beam 1 is output from a Q-switch pulse CO2 laser (not shown), divided into two by a beam splitter 5, and irradiated to substantially opposite positions on the front and back surfaces by independent light collecting devices. The laser pulse energy applied to each surface is controlled in the range of 2 to 5 mJ. Other irradiation conditions are the same as those described with reference to FIG. Adjustment of the rolling direction of the irradiation position of the front surface and the back surface was finely adjusted with a moving table (not shown).
[0010]
Using these devices, laser irradiation was performed on 0.23 mm thick directional electrical steel sheets, and the iron loss was improved in the rolling direction width Wcd and the magnetic field 1.7 T, 50 Hz of the reflux magnetic domain starting from the stress strain generated in the laser irradiated part. The relationship between rates was examined. The iron loss improvement rate η is expressed 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 an electron microscope for magnetic domain observation.
[0011]
FIG. 2 shows the relationship between Wcd and iron loss improvement rate in the case of single-sided laser irradiation and double-sided laser irradiation. In single-sided laser irradiation, the pulse energy was fixed at 8 mJ, and the focused beam diameter was changed to 0.2 to 0.6 mm. For irradiation on both sides, the irradiation energy on each side was fixed at 4 mJ, and the focused beam diameter was changed to 0.2 to 0.6 mm. The relationship between Wcd and irradiation beam diameter d is also shown in the figure. The deviations in the rolling direction of the reflux magnetic domains that are paired on both sides are all 0 mm. With double-sided irradiation, Wcd almost proportional to the beam diameter was obtained, but with single-sided irradiation, Wcd obtained even when the condensing system was made small did not decrease to 0.27 mm or less. 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, and a stress strain that is larger than the beam diameter is generated. It is to do. As a result, the hysteresis loss becomes excessive, and the iron loss improvement rate decreases.
[0012]
In the region where the reflux magnetic domain width Wcd is 0.3 mm or more, when the iron loss improvement rate is compared between single-sided and double-sided irradiation, the single-sided irradiation shows a somewhat higher improvement rate. In single-sided irradiation, the energy density decreases as the irradiation beam diameter increases. As a result, an excessive plasma effect is eliminated, an increase in hysteresis loss is suppressed, and a high iron loss improvement is achieved. On the other hand, although the stress strain per one side is small in the case of double-sided irradiation, a relatively large strain is introduced when both sides are added, and the effect of increasing the hysteresis loss is relatively large compared to the case of single-sided irradiation, and the iron loss improvement rate is It is thought to decline.
[0013]
On the other hand, in the region where Wcd is 0.3 mm or less, the distortion width is small and the increase in hysteresis loss is small. At the same time, the reflux 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 plate 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 a reflux magnetic domain that is narrow in the rolling direction and deep in the thickness direction, the eddy current loss is sufficiently reduced, and at the same time, the increase in hysteresis loss is suppressed as much as possible.
[0014]
Attempts were made to form a reflux domain with a width of 0.3 mm or less in single-sided irradiation. In order to form a narrow reflux magnetic domain width, there is no choice but to reduce the energy density Ed in order to suppress an excessive plasma serving as a secondary heat source. Therefore, the pulse energy was reduced in accordance with the reduction of the focused beam diameter, and the energy density Ed was made almost the same as the double-sided irradiation. The relationship between Wcd and iron loss improvement rate in this case was compared with the result of double-sided irradiation. The result is shown in FIG. The relationship between Wcd and irradiation beam diameter d is also shown in the figure. Even with a beam diameter of 0.3 mm or less, a reflux domain width almost equal to the beam diameter was obtained by single-sided irradiation. The characteristics of double-sided irradiation are the same data as the results shown in FIG.
[0015]
When Wcd is 0.3 mm or less, double-sided irradiation 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 reflux magnetic domain are the same. In double-sided irradiation, the reflux magnetic domains from both sides supplement the penetration depth in the plate thickness direction, so the effect of reducing eddy current loss is high. On the other hand, single-sided irradiation has no effect, and as a result, the iron loss improvement rate is low. In the range of Wcd of 0.3 mm or more, as described above, when stress strain is introduced on both sides, the effect of increasing hysteresis loss is relatively large, and single-sided irradiation shows a slightly higher iron loss improvement rate than double-sided irradiation. .
[0016]
Next, an optimum range for the positional deviation in the rolling direction of the reflux magnetic domains that are paired on the front and back surfaces will be described. FIG. 1 is a schematic diagram of an electrical steel sheet according to the present invention, and is a diagram for explaining a positional deviation of a return magnetic domain. The width of the reflux magnetic domain b based on the stress strain a of each surface is Wcd, | ΔL | is the absolute value of the deviation amount of the center of the reflux magnetic domain on each surface, and the equivalent width of the reflux magnetic domain in the rolling direction. Is defined by Wcd ′. FIG. 4 shows that when the laser beam diameter is focused to 0.3 mm by double-sided irradiation and Wcd is 0.3 mm, | ΔL | / Wcd when the positional deviation amount | ΔL | is changed from 0 to 0.6 mm. This is the relationship of the magnetostriction ratio λ ′. Here, the magnetostriction ratio λ ′ is the ratio between the magnetostriction λ when | ΔL |> 0 and the magnetostriction λ0 when | ΔL | = 0. The magnetostriction increases with the increase of | ΔL |, but in the range of | ΔL | / Wcd> 1, that is, the increase in magnetostriction of the reflux magnetic domain is remarkable. This is due to an increase in the equivalent width Wcd ′ of the reflux magnetic domain that causes magnetostriction.
[0017]
FIG. 5 shows the relationship between | ΔL | / Wcd and the iron loss improvement rate ratio η ′. Here, η ′ is the ratio between the iron loss improvement rate η0 when | ΔL | = 0 and the iron loss improvement rate η when | ΔL |> 0. As a result, the iron loss improvement rate greatly decreases in the range of | ΔL | / Wcd> 1. This is because the return magnetic domain from both sides has no effect of compensating the penetration depth, and as a result, the iron loss improvement effect is reduced.
[0018]
As described above, in the electrical steel sheet according to the present invention, by setting the deviation | ΔL | in the rolling direction width of the reflux magnetic domain to be formed to be equal to or less than the reflux magnetic domain width Wcd, excellent characteristics can be obtained in terms of both magnetostriction and iron loss. .
<Example 2>
Next, an embodiment using an irradiation method in which laser irradiation traces are not generated on the steel sheet surface will be described. In an irradiation method in which no laser irradiation trace is generated on the surface of the steel sheet, stress strain is imparted by rapid heating / cooling below the temperature at which the surface glass coating and insulating coating evaporate and scatter. Therefore, the condensing area of the laser beam is larger than that in the first embodiment, and the energy density needs to be 1/20 to 1/30.
[0019]
FIG. 10 is an explanatory diagram of an irradiation beam shape in an irradiation method in which laser irradiation traces are not generated on the steel sheet surface. The laser beam is focused on an ellipse having a long 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, but a cylindrical lens (not shown) is inserted in the course of beam propagation, and the focus of the focused beam is adjusted by adjusting the focus of the fθ lens 4 and changing the focal length of the cylindrical lens. The ellipse 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 scan speed.
[0020]
In this embodiment, the laser beam condensing shape is a combination of dl = 0.2 to 0.6 mm and dc = 4.0 to 10.0 mm, and the rolling direction pitch at the irradiation position is Pl = 6.5 mm. The C direction irradiation pitch is 0.5 mm.
FIG. 6 shows the relationship between Wcd and the iron loss improvement rate in the case of laser irradiation on only one surface and laser irradiation on both surfaces in an irradiation method in which no irradiation mark is generated on the surface. In single-sided laser irradiation, the pulse energy is fixed at 8 mJ, the L-direction focused beam diameter dl is changed to 0.2 to 0.6 mm, and the C-direction beam diameter dc is the minimum value within the range where no surface irradiation trace is generated at each dl. I chose. In the irradiation on both sides, the irradiation energy on each side was fixed at 4 mJ, the diameter of the focused beam was changed to 0.2 to 0.6 mm, and dc was selected to be the minimum value within the range where no irradiation marks were generated. The deviations in the rolling direction of the reflux magnetic domains that are paired on both sides are all 0 mm. The relationship between Wcd and rolling direction irradiation beam diameter dl is also shown in the figure.
[0021]
The reflux domain width Wcd observed for both single-sided and double-sided irradiation almost coincided with the focused beam diameter dl. This is probably because the energy density is low enough that the surface film does not evaporate, so that there is little plasma generation as a secondary heat source, and therefore the stress strain width almost matches the beam diameter.
From this result, even in the irradiation method in which the irradiation mark does not occur on the steel sheet surface, the iron loss improvement rate is higher than that in the case where the steel sheet having the Wcd of 0.3 mm or less and the reflux magnetic domain formed on both surfaces is formed on only one surface as in FIG. Indicates. Moreover, the improvement allowance was remarkable compared with the case where a film | membrane is evaporated. This is because the stress strain due to rapid heating / cooling is slightly weaker than the strain due to evaporation reaction force, and the effect of generating reflux magnetic domains from both sides becomes more remarkable.
[0022]
In the following, a method for distinguishing the difference between an electromagnetic steel sheet imparted with strain from both sides of the present invention and having a reflux magnetic domain having a width of 0.3 mm or less and a conventional electromagnetic steel sheet irradiated only from one side will be described. The confirmation of the reflux magnetic domain width can be made with a magnetic domain observation electron microscope. Whether or not distortion is introduced from both sides can be determined by the following method.
Since the reflux magnetic domain is generated based on the stress strain of the surface layer portion of each surface, the reflux magnetic domain based on this is also eliminated by removing the strained extreme surface layer portion by etching. In the steel sheet of the present invention imparted with strain from both sides, the reflux magnetic domain generated from the other side remains even if the surface layer on one side is removed. On the other hand, in the case of applying strain from only one surface, the reflux magnetic domain is completely extinguished by removing the surface layer portion of one of the surfaces. Therefore, even when the surface irradiation trace is not visible, it is possible to determine whether or not the reflux magnetic domain is formed from both sides.
[0023]
In the embodiment of the present invention, the return magnetic domain was formed by irradiating the Q-switched pulse CO2 laser. However, if the return magnetic domain within the range of the present invention can be formed, a continuous wave laser can be used, and a laser other than the CO2 laser can be used. May be used.
[0024]
【The invention's effect】
As described above, in the grain-oriented electrical steel sheet of the present invention, a reflux magnetic domain is formed by applying stress strain from both sides, the width in the rolling direction is 0.3 mm or less, and the amount of positional deviation in the rolling direction is By being below the width in the rolling direction, there is an advantage that a higher iron loss improvement effect and lower magnetostriction can be achieved than in the prior art. In addition, 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 according to the present invention and an explanatory view of a deviation of a reflux magnetic domain formation position.
FIG. 2 shows a directional electrical steel sheet whose iron loss has been improved by the film evaporation reaction force by laser irradiation. The magnetic steel sheet irradiated with laser from both sides according to the present invention and the reflux magnetic domain of the electromagnetic steel sheet irradiated with laser only from one side. It is explanatory drawing of the relationship between a width | variety and an iron loss improvement rate.
FIG. 3 shows a grain-oriented electrical steel sheet that has improved iron loss due to the film evaporation reaction force caused by laser irradiation. The magnetic steel sheet is irradiated with laser from both sides according to the present invention. It is explanatory drawing of the relationship between the return magnetic domain width | variety of an electromagnetic steel plate, and an iron loss improvement rate at the time of controlling an energy density so that a return magnetic domain width | variety substantially corresponds.
FIG. 4 shows the relationship between the deviation of the position of the reflux magnetic domains on the front and back surfaces of the magnetic steel sheet according to the present invention and the magnetostriction ratio.
FIG. 5 shows the relationship between the deviation of the reflux magnetic domain positions on the front and back surfaces of the electrical steel sheet according to the present invention and the iron loss improvement ratio.
[Fig. 6] A steel sheet and a single-sided steel sheet that have been improved in iron loss by rapid heating / cooling of the steel sheet surface by laser irradiation, and are irradiated with laser from both sides according to the present invention. It is explanatory drawing of the relationship between the return magnetic domain width | variety and iron loss improvement rate of the electromagnetic steel plate which irradiated the laser only from.
FIG. 7 is an example of a method for producing an electrical steel sheet according to the present invention.
FIG. 8 is an example 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 caused by laser irradiation.
FIG. 10 is a schematic diagram of an irradiation beam shape in a case where iron loss is improved by rapid heating / cooling of a steel sheet surface by laser irradiation.
FIG. 11 is a diagram showing a relationship between stress distortion caused by laser irradiation and abnormal eddy current loss hysteresis loss.
[Explanation of symbols]
a ... stress strain region b ... reflux magnetic domain c ... 180 ° magnetic domain 1 ... laser beam 2 ... total reflection mirror 3 ... scan mirror 4 ... fθ lens 5 ... beam splitter 6 ... electromagnetic steel plate
Ed ... Pulse energy density
Ep ... Pulse energy S ... Condensed beam area Wcd ... Reflux magnetic domain width Wcd '... Equivalent width of return magnetic domain ΔL ... Deviation of formation position of 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 dl in the rolling direction of the reflux magnetic domain
dl… Ellipse focused laser beam rolling width
dc: The width of the elliptical focused laser beam in the plate width direction d: Diameter of the circular focused laser beam

Claims (3)

In a grain-oriented electrical steel sheet that has improved magnetic properties by irradiating a laser beam to a pair of steel plates on both sides to form a thin reflux magnetic domain, the rolling direction width of the reflux magnetic domain is 0.3 mm or less, and the pair der rolling direction width following the rolling direction of the deviation amount is the reflux magnetic domain of the closure domain positions of both sides made is, oriented electrical steel sheet towards you, characterized in that the closure domains penetrate the plank direction. Oriented electrical steel sheets towards according to claim 1, wherein there are laser irradiation signatures on the surface of the steel sheet. Oriented electrical steel sheet towards the claim 1, wherein the laser irradiation signatures does not occur in the laser irradiated portion of the steel sheet surface.

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