JP2006144058A - Grain-oriented electromagnetic steel sheet having superior magnetic property, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grain-oriented electromagnetic steel sheet which has a low iron loss at a high magnetic flux density, and to further provide the grain-oriented electromagnetic steel sheet having low magnetostriction as well. <P>SOLUTION: The grain-oriented electromagnetic steel sheet after having been irradiated with a laser beam to reduce the iron loss shows a magnetic flux density B8 of 1.92 T or higher when a magnetizing force of 800 A/m is applied to the steel sheet, and has crystals that include both of the region in which the absolute value of an angle β is 0° and the region in which the absolute value of an angle β is 2°in the same crystal grain, so as to occupy 30% or more in the total area of the steel sheet by an area rate. The steel sheet also includes the region in which the absolute value of the angle β is 2°or higher, in the crystal grain, so as to occupy 20% to 70% in the crystal grain area by the area rate. The steel sheet also has a mark which has been formed by irradiation with the laser beam on the surface or a circulating current magnetic domain which has been formed in a laser-irradiated part, controlled to have a width of 10 μm to 200 μm in a rolling direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a grain-oriented electrical steel sheet with excellent magnetic properties, in which iron loss is reduced by irradiating a laser, and a manufacturing method thereof.

An electromagnetic steel sheet having an easy axis of magnetization of iron crystals substantially aligned in the rolling direction of the steel sheet manufacturing process is called a directional electromagnetic steel sheet, and is extremely excellent as a material for a transformer iron core. Important indicators that indicate the performance of grain-oriented electrical steel sheets are magnetic flux density, iron loss, and magnetostriction.
The magnetic flux density tends to increase as the degree of alignment of the easy axes of crystal, that is, the material with higher crystal orientation. B8 [T] is generally used as a parameter representing the magnetic flux density, which is a magnetic flux density generated in the steel plate at a magnetizing force of 800 A / m. That is, a material having a larger value of B8 has a higher crystal orientation and a higher magnetic flux density generated with a constant magnetizing force, so that there is an advantage that a transformer having a small size and excellent efficiency can be manufactured.
Generally, the index of iron loss is W17 / 50 [W / kg]. W17 / 50 is an iron loss value when AC excitation is performed at a maximum magnetic flux density of 1.7 T and a frequency of 50 Hz, and a smaller one can produce a transformer with higher efficiency.
Magnetostriction is a parameter serving as an index representing transformer noise, and is a value indicating the expansion / contraction rate of a steel sheet in the rolling direction under a constant magnetizing force. When a material having a large value is used for a transformer iron core, noise tends to increase in an alternating magnetic field.

That is, the higher the magnetic flux density and the lower the iron loss and magnetostriction, the better the grain-oriented electrical steel sheet as a transformer material. Among them, iron loss is the most important index, and various measures for reducing iron loss have been devised.
Iron loss is separated into eddy current loss and hysteresis loss. In grain oriented electrical steel sheets, eddy current loss accounts for more than half of iron loss. Hysteresis loss tends to be lower for materials with higher B8, and development of high B8 materials has been performed from the viewpoint of reducing iron loss.
Eddy current loss is divided into classical eddy current loss and abnormal eddy current loss. Since the classical eddy current loss is proportional to the plate thickness of the steel plate, it has been reduced by making the material thinner. On the other hand, it has been elucidated by a detailed study of the magnetic domain structure that the abnormal eddy current loss is reduced as the domain wall interval of the 180 ° magnetic domain, which is a magnetic domain in the rolling direction, is reduced. Therefore, various techniques for subdividing magnetic domains have been devised.

  Among them, the magnetic domain refinement effect is the highest, and a practical technique is a method using a laser. Patent Document 1 discloses a method of reducing iron loss by introducing a linear residual strain that is substantially perpendicular to the rolling direction by irradiation with a YAG laser. This method is based on the principle that the 180 ° magnetic domain is subdivided so that the non-uniformity of energy in the entire steel sheet is alleviated because the circulating magnetic domain generated from the residual strain increases the magnetostatic energy in the vicinity. ing. This technique is generally called laser magnetic domain control, has a very high iron loss reduction effect, and the volume of the introduced recirculating magnetic domain is relatively small, so that it hardly affects the crystal orientation of the material and changes in B8. There is almost no feature. An electromagnetic steel sheet that uses residual strain to reduce iron loss cannot be used for a wound transformer that performs strain relief annealing in the manufacturing process of the transformer, but is suitable for a product transformer that does not perform strain relief annealing.

As a magnetic domain control method that can withstand strain relief annealing, for example, as disclosed in Patent Document 3, there is a method of forming grooves on the surface. As a principle of this method, it is considered that there is a magnetic domain refinement effect based on an increase in magnetostatic energy by magnetic pole generation on the wall surface of the groove. However, since the gap in the groove blocks the flow of magnetic flux, B8 tends to decrease, which is not suitable for a large product transformer that requires downsizing. Therefore, the laser magnetic domain control material is the most suitable steel plate for high-performance product transformer materials.
Various methods have been disclosed as laser magnetic domain control techniques. For example, Patent Document 2 uses a pulsed CO ₂ laser, and Patent Document 1 uses a continuous-wave YAG laser. A method is also disclosed in which power, scanning speed, etc. are defined and surface irradiation traces are not generated.

FIG. 2 is a schematic diagram showing the change between the W17 / 50 average value and B8 before and after laser irradiation. As indicated by the dotted line in the figure, there is a substantially linear relationship that W17 / 50 decreases with increasing B8. After the laser magnetic domain control, B8 hardly changes and the eddy current loss decreases. As a result, B8 and W17 / 50 move substantially in parallel to the low W17 / 50 side while maintaining the linear relationship. That is, the iron loss reduction margin was almost the same over the entire B8 region. However, lower iron loss is demanded as a high-performance product transformer material, and reduction of iron loss in the high B8 region, which is advantageous for transformer miniaturization, has been desired. Furthermore, there has been a demand for an electromagnetic steel sheet that can suppress magnetostriction and reduce transformer noise and a method for manufacturing the same.
Japanese Patent Publication No. 6-19112 JP-A-6-57333 Japanese Examined Patent Publication No. 63-44840

  An object of the present invention is to provide a grain-oriented electrical steel sheet capable of obtaining a very low iron loss at a high magnetic flux density. It is another object of the present invention to provide a grain-oriented electrical steel sheet having a small magnetostriction and a method for producing the same.

The gist of the present invention for achieving the above object is as follows.
(1) A grain-oriented electrical steel sheet in which iron loss is reduced by irradiating a laser beam, where the magnetic flux density of the steel sheet generated by a magnetizing force of 800 A / m is B8, the rolling direction and the easy axis (100) <001 The thickness deviation component of the angle deviation of> is the β angle, B8 is 1.92T or more, and the region where the absolute value of β angle is 0.5 ° or less and the region of 2 ° to 6 ° are simultaneously included in the crystal grains. A grain-oriented electrical steel sheet having excellent magnetic properties, wherein Rs is 30% to 100%, where Rs is a ratio of the total area of crystal grains to be included in the total area of the steel sheet.
(2) When the average value in the whole steel sheet of the ratio of the total area of the region where the β angle absolute value is 2 ° to 6 ° to the total area of the crystal grain is defined as Rt in the crystal grain, Rt is The grain-oriented electrical steel sheet having excellent magnetic properties according to (1), characterized by being 20% to 70%.
(3) The magnetism according to (1) or (2), wherein the width in the rolling direction of the surface irradiation trace of the laser beam or the width in the rolling direction of the circulating magnetic domain formed in the laser irradiation portion is 10 μm to 200 μm. Oriented electrical steel sheet with excellent characteristics.
(4) The method for producing a grain-oriented electrical steel sheet according to (3), wherein the laser device for generating the laser beam is a fiber laser having a fiber core diameter of 5 μm to 400 μm. A method for producing a grain-oriented electrical steel sheet.

  The present invention can provide a grain-oriented electrical steel sheet having extremely low iron loss and magnetostriction, particularly in a grain-oriented electrical steel sheet having a high magnetic flux density. By using the grain-oriented electrical steel sheet of the present invention, a highly efficient, small and low noise transformer can be manufactured. Further, when the grain-oriented electrical steel sheet is manufactured by laser irradiation, it can be stably manufactured by a simple method.

  The present inventors have discovered that the ultimate iron loss W17 / 50 after laser magnetic domain control of a grain-oriented electrical steel sheet having a relatively high B8 depends on the crystal structure of the steel sheet. By irradiating a material having a relationship with a laser, the present invention has been achieved in which an unprecedented low iron loss is obtained. In addition, the invention has led to the invention of a grain-oriented electrical steel sheet having a low magnetostriction by limiting the rolling direction width of the laser irradiation trace or the rolling direction width of the circulating magnetic domain formed immediately below the laser irradiation part to a specific range. Hereinafter, the electrical steel sheet of the present invention will be described.

  FIG. 2 shows the relationship between B8 and W17 / 50 before and after laser irradiation when laser magnetic domain control is performed on a grain-oriented electrical steel sheet. B8 and W17 / 50 were measured with a single plate magnetometer. The steel plate of the present example contains Si: 3.0 to 3.4 mass% as a base iron component of a general grain-oriented electrical steel plate, and no subcomponent that increases the specific resistance is added. The component concentration of Cr is 0.04 mass% or less. It has an electrically insulating coating on the surface of the ground iron, and the plate thickness is 0.23 mm.

From the result of FIG. 2, although the variation of B17 dependency of W17 / 50 is relatively large before laser irradiation, it tends to converge to a specific linear relationship after laser irradiation. Among them, the present inventors paid attention to a steel plate as shown in the frame of FIG. 2 that can obtain a very low iron loss value by deviating from the linear relationship, particularly in a high B8 region. Therefore, the crystal structure was examined in detail by paying attention to the crystal orientation of the steel sheet sample.
As an index of crystal orientation, the β angle, which is the thickness direction component of the angle deviation between the rolling direction and the easy axis (100) <001>, was examined in detail. X-ray Laue method was used for the crystal orientation angle. Since the steel sheet is flattened after being annealed at high temperature and recrystallized in a coiled shape with a curvature in the rolling direction, the β angle changes in the rolling direction within the crystal grains.

  FIG. 1 is a diagram showing a magnetic domain pattern of a grain-oriented electrical steel sheet. The grain boundaries are indicated by thick lines for easy identification. As shown in FIG. 1 as an example, the portion with a coarse magnetic domain pattern is a region where the absolute value of the β angle is approximately 0 °, and the portion with a very fine magnetic domain pattern has an absolute value of the β angle of 2 ° to 6 °. It is an area. As a result of the investigation, as a characteristic of the steel plate that has obtained a very low iron loss value by deviating from the linear relationship in the high B8 region, the region where the absolute value of the β angle is 0 ° in one crystal grain ( It was found that there are relatively many crystal grains simultaneously including a region from 2 ° to 6 ° (hereinafter referred to as β2). Here, the measurement accuracy of the X-ray Laue method used for measuring the β angle is ± 0.5 °. Therefore, the effective range of the absolute value of the β angle in the β0 region is defined as 0.5 ° or less. A crystal grain containing β0 and β2 simultaneously is shown as crystal grain A in FIG. The present inventors speculated that the presence of a certain amount or more of such crystal grains is a cause of presenting a very low iron loss after the laser magnetic domain control. Therefore, the following verification experiment was conducted to verify this.

  First, in a steel plate sample of 60 mm × 300 mm long in the rolling direction, the ratio of the total area of crystal grains containing β0 and β2 simultaneously in the total area of the steel plate was defined as Rs. Using a single plate magnetometer, B8 of the same sample and W17 / 50 before and after laser irradiation were measured. Table 1 shows the measurement results of Rs and W17 / 50 before and after the laser in a steel plate that is substantially constant in the vicinity of B8 = 1.92T. From this result, although the steel loss before laser irradiation tends to be somewhat higher in the steel plate with Rs exceeding 30% in the same B8, the iron loss after laser irradiation is lower than that in the steel plate with Rs less than 30%. It was found to show a very low value.

Next, as shown in Table 2, Rs was approximately constant at about 40%, and a sample having a difference in B8 was prepared. Similarly, W17 / 50 before and after laser irradiation was examined. As a result, it was found that W17 / 50 after laser irradiation was significantly lower in the latter when B8 was less than 1.92T and more than that.
Therefore, it has been found that a grain-oriented electrical steel sheet that has been subjected to laser magnetic domain control on a steel sheet having B8 of 1.92 T or more and Rs exceeding 30% can obtain a much lower iron loss than other steel sheets.
Furthermore, the present inventors examined the influence of the area ratio of the β2 region in the steel sheet satisfying the above-described conditions of the present invention. Therefore, in the material of B8 = 1.925-1.940T and Rs = 30-40%, which satisfies the characteristics of the present invention, the average value of the occupied area ratio of β2 in each crystal grain is Rt (% ) And different Rt materials were prepared, and the characteristics before and after laser magnetic domain control were examined. The results are shown in Table 3. From this, it was found that even with a material having an equivalent B8 and Rs value, the iron loss after laser irradiation was a lower value when Rt was 20% to 70%.

The reason why such characteristics are obtained will be discussed below.
First, the basic properties of the magnetic domain structure in the β0 and β2 regions will be described.
In the crystal grains, the β0 region has an ideal crystal orientation as a grain-oriented electrical steel sheet and forms a 180 ° magnetic domain. However, in such a region, since all the magnetization components are oriented in the rolling direction, surface magnetic poles appearing on the surface of the steel sheet are difficult to be generated, so that the magnetostatic energy is low regardless of the domain wall interval, and the domain wall is lowered in the direction of reducing the domain wall generation energy. Spacing increases. The wider the domain wall spacing, the greater the domain wall moving speed for the same change in magnetic flux density. Since the local eddy current accompanying the reversal of the magnetization direction of the portion where the domain wall has moved is proportional to the square of the domain wall moving speed, the abnormal eddy current loss increases if the domain wall interval is wide and the number of domain walls is small. Therefore, in a state where there is no magnetic domain subdivision effect due to laser irradiation, the β0 region has a magnetic domain structure with a wide 180 ° domain wall interval, and the abnormal eddy current loss is relatively large.

On the other hand, in the β2 region where the absolute value of the β angle is 2 ° or more and 6 ° or less, the surface magnetic pole is easily generated because of the magnetization component vector in the plate thickness direction, and although the 180 ° magnetic domain is formed, The magnetostatic energy increases. However, this surface magnetic pole relaxes the magnetostatic energy by generating a circulating magnetic domain magnetized in the plate thickness direction, and at the same time, the 180 ° domain wall interval is somewhat narrowed to reduce abnormal eddy current loss. Therefore, in a state where there is no magnetic domain subdivision effect by laser irradiation, the β2 region has a magnetic domain structure in which a circulating magnetic domain exists in a slightly narrow 180 ° domain wall interval, and the abnormal eddy current loss is small compared to the β0 region. In the region where the β angle exceeds 6 °, the deviation from the ideal crystal orientation is excessive, so that the 180 ° magnetic domain is not stably formed, and B8 is also greatly reduced, so that good magnetic characteristics can be obtained. Absent. Therefore, in the definition of the β2 region of the present invention, the β angle is set to 2 ° or more and 6 ° or less.
If the β0 and β2 regions are present in separate crystal grains, there is almost no interaction between the β0 and β2 regions, and it is considered that each has a unique magnetic domain structure as described above due to an independent magnetostatic energy balance.

Next, the magnetic flux density and magnetic permeability in the β0 and β2 regions when an external magnetic field is applied will be described.
When an AC magnetic field is applied from the outside, the domain wall moves, the width of the magnetic domain whose magnetization direction is the same as that of the external magnetic field is widened, and the width of the magnetic domain in the opposite direction is narrowed. In the β0 region, even if the magnetic domain width is expanded, the magnetostatic energy does not increase and the domain wall is likely to move. However, in the β2 region, the magnetostatic energy increases with the expansion of the magnetic domain width. It tries to relax the magnetostatic energy. The generation process of the recirculating magnetic domain becomes a resistance force against the domain wall movement, which increases as the absolute value of the β angle increases. Therefore, more magnetic flux flows with respect to a constant magnetic field in the β0 region, that is, the magnetic flux density is high. Conversely, the magnetic flux density in the β2 region is small. That is, the spatial non-uniformity of the magnetic flux density generated in a constant magnetic field is large in a steel sheet having a large β-angle variation.

In the iron loss measurement, for example, W17 / 50 is the iron loss when the average magnetic flux density generated in the steel plate is 1.7T. However, when the magnetic flux density varies spatially in the steel plate, the local iron loss value changes. Here, the average magnetic flux density at the time of measuring the iron loss is Bm, and the deviation from the average value of the local magnetic flux density is ΔB. Since the iron loss is proportional to the square of the magnetic flux density, the iron loss when there is no deviation and when there is a deviation is proportional to Bm ² and (Bm ± ΔB) ² , respectively, even if the steel sheet has the same average iron loss Bm. . Accordingly, the iron loss increases as the deviation increases. Therefore, it can be said that the iron loss is smaller as a material with less variation in magnetic flux density distribution or a material with higher uniformity of magnetic permeability, which is a ratio between the magnetic field and the generated magnetic flux density.

In view of the above basic properties, the present inventors presume the reason why a very excellent iron loss characteristic is obtained after laser irradiation in the crystal structure of the electrical steel sheet of the present invention as follows.
In the special case where the β0 region and the β2 region exist simultaneously in the crystal grains as in the present invention, since the domain wall penetrates the β0 region and the β2 region, the magnetostatic energy is relaxed between the β0 region and the β2 region. And a stable magnetic domain structure. Specifically, in the β2 region, it is considered that a spike magnetic domain extending from the grain boundary is generated, and the magnetostatic energy is relaxed by adopting a structure that interrupts the 180 ° magnetic domain of the β0 region. The spike magnetic domain consists of a 180 ° domain wall, but its tip is closed and does not contribute to the magnetization of the crystal grains, but it expands in the magnetic domain where the magnetic domain width expands, and shrinks in the magnetic domain where the magnetic domain width becomes narrower. It contributes to the relaxation of the accompanying magnetostatic energy. The expansion and contraction of the spike magnetic domain accompanying the domain wall movement becomes a resistance against the domain wall movement, but is considered to be smaller than the resistance accompanying the generation and disappearance of the circulating domain.

  When such a crystal grain including the β0 region and the β2 region is formed with a laser beam irradiation in the form of a linear or dot-circular circulating magnetic domain across the plate width direction, β0 and β2 are divided by the laser circulating magnetic domain. Many areas occur. As a result, in the β0 region, the 180 ° magnetic domain is subdivided and the abnormal eddy current loss is reduced. In the β2 region separated from the β0 region by the circulating magnetic domain by the laser, it is no longer necessary to balance the β0 region and the magnetostatic energy, and the spike magnetic domain changes to the 180 ° magnetic domain, and the It is thought that it contributes to the magnetization of the crystal grains in conjunction. In addition, since the magnetic domains are subdivided into circulating magnetic domains, the abnormal eddy current is considered to be greatly reduced.

  Furthermore, since the β0 and β2 regions exist close to each other in the same crystal grain, it is considered that the magnetic flux density generated in each region has an effect of being averaged. The effect of homogenizing the magnetic flux density occurs somewhat even when the β0 and β2 regions are dispersed in separate crystals, but since the β0 and β2 regions are separated, the effect is presumed to be more remarkable in the case of the present invention. The That is, in the case of the present invention, the variation in the magnetic flux density distribution is reduced, and the iron loss of the entire steel sheet is considered to be lower. That is, it is considered that the iron loss of the steel sheet after laser irradiation is greatly reduced by including many crystal grains containing β0 and β2 regions simultaneously in the crystal grains.

Such excellent characteristics were remarkable in a material having B8 of 1.92T or more. A material having a low B8 has a low average crystal orientation, that is, it is estimated that a ratio of 5 to 6 ° having a relatively large β angle is large even in the β2 region. In such a crystal structure, since the magnetization direction tends to be in the direction of the plate thickness, the spike magnetic domain in the β2 region after laser irradiation cannot be completely changed to a 180 ° magnetic domain, that is, it is estimated that the iron loss is limited. The Therefore, in the present invention, B8 is preferably 1.92T or more.
From the above consideration, as shown in Tables 1 and 2, B8 is 1.92T or more and a material containing a lot of β0 and β2 regions, specifically, in a grain-oriented electrical steel sheet with Rs of 30 to 100% after laser irradiation. It is considered that very good iron loss characteristics were obtained.

Next, let us consider a case where a crystal grain that does not include the β0 region and the β2 region is a dominant material. For example, in the case of a crystal grain that includes only the β0 region and does not include the β2 region, since the magnetostatic energy is low in the β0 region, the 180 ° domain wall interval is very wide and the abnormal eddy current loss becomes very large. By irradiating such a material with a laser, the domain wall spacing can be narrowed to reduce anomalous eddy current loss to some extent. Necessary. However, when excessive laser energy is input, an increase in hysteresis loss cannot be ignored. As a result, when compared with the total iron loss of eddy current loss and hysteresis loss, the iron loss is higher than that of the electrical steel sheet of the present invention.
On the contrary, in the material only including the β2 region without including the β0 region, the domain wall interval is subdivided to some extent by the generation of the surface magnetic pole in the β2 region, and the abnormal eddy current loss as the material before laser irradiation is relatively low. However, since it does not have an ideal crystal orientation, the iron loss value that can be reached after laser irradiation does not reach the electrical steel sheet of the present invention that includes many ideal orientations.

  Therefore, it is presumed that the volume ratio of the β0 region and the β2 region is important in the electrical steel sheet of the present invention from the viewpoint of the magnetostatic energy relaxation action between the β0 region and the β2 region, that is, the energy balance. The volume ratio can be considered as an area ratio when the plate thickness is constant. That is, it is estimated that there is an optimum range for Rt, which is the average area ratio of the β2 region. If Rt is excessively small, the same tendency as that of the crystal grains of the β0 region described above is exhibited, and if Rt is excessively large, the same tendency as that of the crystal grains of the β2 region is likely to be exhibited. On the contrary, if Rt is limited to a specific range, it is considered that the effect of the present invention that the β0 region and the β2 region exist simultaneously is exhibited to the maximum extent. From the above consideration, as shown in the results of Table 3, it is considered that a lower iron loss was obtained when Rt was in the range of 20 to 70%.

Next, the electrical steel sheet of the present invention that is excellent in magnetostriction characteristics will be described.
In the laser magnetic domain control technique according to the present invention, the insulating film on the surface of the steel sheet may be altered or evaporated by laser irradiation, or in some cases, the ground iron directly under the film may be exposed and a part of the melted part may be generated. This irradiation part becomes a laser irradiation mark that can be discriminated by visual observation or optical microscope observation. In that case, the rolling direction width h of the irradiation mark can be defined. Further, by suppressing the laser beam condensing power density to a low level, it is possible to perform laser irradiation that avoids alteration and evaporation of the coating and does not generate irradiation marks. The feature at that time is that a circulating magnetic domain having a rolling direction width substantially equal to the laser beam condensing diameter is formed immediately below the laser irradiation portion. The magnetic domain structure can be observed with a conventionally known magnetic domain observation method, for example, a scanning electron microscope having an accelerating voltage of 200 kV, and the circulating magnetic domain width h can be defined.

FIG. 3 shows the result of examining the relationship between the width of the laser irradiation trace or the recirculation magnetic domain width h and the magnetostriction λ17 by irradiating the electromagnetic steel sheet with B8 = 1.930T and Rs = 40%, which is the characteristic range of the invention. is there. λ17 is a steel sheet expansion / contraction rate at a maximum magnetic flux density of 1.7 T, which is defined by equation (1). Note that λ17 was measured at an AC excitation frequency of 50 Hz without applying compressive stress in the steel sheet rolling direction. The maximum stretching length due to magnetization was measured using a laser displacement meter.
λ17 = (maximum stretch length due to magnetization) / (steel plate length in a demagnetized state) (1)
As λ17 increases, the amount of expansion / contraction increases, and the noise of the transformer tends to increase.

  As the laser device, a fiber laser was used, and the condensing diameter was changed in the range of 10 to 300 μm. The laser irradiation interval in the rolling direction is 4 mm. The fiber laser has a fiber core diameter of 10 μm and a wavelength of 1.085 μm. FIG. 3 shows that the magnetostriction is remarkably low at h ≦ 200 μm.

  The present inventors consider the reason why magnetostriction decreases in a narrow range of h as follows. The circulating magnetic domain generated by laser irradiation has a magnetization component different from the rolling direction. Therefore, a large change in magnetic moment is required when magnetized in the rolling direction, and it is considered that a slight change occurs in the distance between iron atoms constituting the crystal. Therefore, the steel sheet expansion / contraction characteristics are affected by the introduction of the circulating magnetic domain. Here, if a wide circulating magnetic domain is formed in the rolling direction, the degree of influence on expansion / contraction increases, and conversely, if it is narrow, the influence on expansion / contraction is considered to be small. Therefore, it is considered that magnetostriction increases when h> 200 μm. Further, the magnetostriction is kept low until h is in a very narrow range, but the region of h <10 μm is below the condensing limit of a practical fiber laser. Therefore, the range in which good magnetostriction characteristics can be obtained in the present invention is set to 10 ≦ h ≦ 200 μm. Therefore, a steel plate in which h is limited to the above range of the present invention has a very low magnetostriction, so that a transformer with low noise can be manufactured.

In order to realize h ≦ 200 μm, the laser beam to be irradiated may be condensed to 200 μm or less. Of course, conventionally used lasers such as YAG laser and CO ₂ laser can also be used, but it is most suitable to use a fiber laser having a fiber core diameter of 400 μm or less. This is because the focusing ability of the fiber laser can be easily and stably focused up to about half the core diameter. Therefore, in the method of the present invention, a fiber laser having a core diameter of 400 μm or less is used. On the other hand, the minimum core diameter that can be oscillated by a fiber laser having a wavelength of 1 to 2 μm that is industrially used is about 5 μm. Therefore, the minimum core diameter of the fiber laser used is 5 μm.

  The essence of the present invention lies in the application of crystal structure / structure of grain-oriented electrical steel sheet, B8, and laser magnetic domain control, so that the elemental composition is not limited to the materials of the above-described embodiments. Further, in this example, the grain-oriented electrical steel sheet having a thickness of 0.23 mm was used. However, the present invention is also applied to grain-oriented electrical steel sheets having a thickness of 0.27 mm, 0.30 mm, etc. that are generally manufactured at present. it can.

It is explanatory drawing of the crystal grain of the grain-oriented electrical steel sheet of this invention. It is a related figure of B8 and W17 / 50 of the grain-oriented electrical steel sheet concerning this invention. It is a related figure of the rolling direction width W of a laser irradiation trace, and magnetostriction.

Explanation of symbols

β0: The region where the absolute value of the β-angle component of the plate thickness direction component of the angle deviation between the rolling direction and the easy axis (100) <001> is 0 ° β2: The region where the absolute value of the β angle is 2 ° or more and 6 ° or less A: Crystal grains containing β0 and β2 simultaneously

Claims (4)

  A grain-oriented electrical steel sheet in which iron loss is reduced by irradiating a laser beam, where the magnetic flux density of the steel sheet generated by a magnetizing force of 800 A / m is B8, and the rolling direction and the easy axis (100) <001> angle A crystal grain having a component in the thickness direction of the deviation as a β angle, B8 being 1.92T or more, and a region having an absolute value of β angle of 0.5 ° or less and a region of 2 ° to 6 ° simultaneously in the crystal grain A grain-oriented electrical steel sheet having excellent magnetic properties, wherein Rs is 30% to 100%, where Rs is a ratio of the total area of the steel sheet to the total area of the steel sheet.   When the average value in the whole steel sheet of the ratio of the total area of the region where the β angle absolute value is 2 ° to 6 ° to the total area of the crystal grain is defined as Rt in the crystal grain, Rt is 20% to The grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the grain-oriented electrical steel sheet is 70%.   The direction with excellent magnetic properties according to claim 1 or 2, wherein the width in the rolling direction of the laser beam surface irradiation trace or the width in the rolling direction of the circulating magnetic domain formed in the laser irradiation portion is 10 µm to 200 µm. Electrical steel sheet.   4. The method for producing a grain-oriented electrical steel sheet according to claim 3, wherein the laser device for generating the laser beam is a fiber laser having a fiber core diameter of 5 μm to 400 μm. Method for producing an electrical steel sheet.