JP2007002334A - Low core loss grain-oriented electrical steel sheet and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grain-oriented electrical steel sheet with low core loss and low magnetostriction, and a method for producing the same. <P>SOLUTION: The grain-oriented electrical steel sheet is excellent in reduced core loss and magnetostriction while under a high flux density of 1.9 T, comprises a refined magnetic domain comprising a laser irradiated portion which has melted and resolidified to form a solidified layer, wherein the thickness of the solidified layer is 4 μm or less. The grain-oriented electrical steel sheet may further comprise a laser irradiated portion where a surface roughness Rz is small and a cross section viewed from a transverse direction has a concave portion having a width of 200 μm or less and a depth of 10 μm or less for further improvement. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for reducing iron loss of grain-oriented electrical steel sheets used for static inductors such as transformers.

  The grain-oriented electrical steel sheet is mainly used for a static inductor represented by a transformer. The characteristics to be satisfied are: (1) low energy loss, ie, iron loss, when excited with alternating current, (2) high permeability in the excitation range of equipment, and easy excitation, and (3) cause of noise. For example, the magnetostriction is small. In particular, for (1), T. is an index representing the value of the transformer because it continuously energizes and generates energy loss over a long period from when the transformer is installed until it is discarded. O. C. This is the main parameter that determines (Total Owning Cost).

  Many developments have been made so far in order to reduce the iron loss of the grain-oriented electrical steel sheet. (1) Increasing the accumulation in the (110) [001] orientation, called the Goss orientation, (2) Increasing the content of solid solution elements such as Si, which increases the electrical resistance, (3) These include thinning, (4) applying a ceramic coating or insulating coating that imparts surface tension to the steel sheet, and (5) reducing the size of crystal grains. However, iron loss improvement by these metallurgical methods is limited, and reduction of iron loss by other methods has been demanded.

In response to this problem, A. Fiedler and W. Pepperhof proposed in Patent Document 1 a method for reducing iron loss by changing the magnetic domain structure by grooving the surface of a grain-oriented electrical steel sheet with a cutter or the like. A grain-oriented electrical steel sheet generally has a magnetic domain structure in which slab-like magnetic domains having magnetization components in opposite directions are alternately arranged, and magnetization is performed by expanding / reducing these magnetic domains under an external magnetic field. Therefore, when the grain-oriented electrical steel sheet is magnetized, the magnetization change occurs only at the boundary (domain wall) between adjacent magnetic domains. With this magnetization change, eddy current flows in the steel sheet, accounting for 60 to 70% of the cause of the iron loss described above (eddy current loss).
The eddy current loss is proportional to the square of the eddy current, and the eddy current is proportional to the moving speed of the domain wall. When the magnetic domain width is narrowed, more eddy currents are generated, but the domain wall moving speed decreases in inverse proportion to the magnetic domain width. As a result, the eddy current loss decreases approximately in proportion to the magnetic domain width.

In order to make this magnetic domain subdivision technique industrially applicable, various inventions have been made. For example, as disclosed in Patent Document 2, a method of introducing a strain without scratching the surface by rotating while pressing a small sphere having a diameter of 0.2 to 10 mm on the steel plate surface, as disclosed in Patent Document 3, the rolling direction. There are a method of applying a small plastic strain by irradiating a laser beam in a substantially right angle direction, a method of radiating a plasma flame linearly in a direction substantially at right angles to the rolling direction as disclosed in Patent Document 4, and the like.
These are techniques for introducing a small plastic strain into a steel sheet and subdividing the magnetic domain using a magnetic domain having a magnetization component perpendicular to the rolling direction stabilized by the inverse effect of magnetostriction. In particular, grain-oriented electrical steel sheets that have been subdivided by laser irradiation (hereinafter referred to as laser domain-controlled grain-oriented electrical steel sheets) are widely used industrially for laminated large-scale transformers for electric power that require low loss. In the recent trend of reducing energy consumption for the purpose of reducing CO ₂ emissions, the demand has increased greatly.

  However, in Patent Document 2, only mechanical strain is introduced, and a large reduction in iron loss cannot be expected. In addition, it is necessary to move the steel ball in the direction perpendicular to the rolling, so that it is difficult to realize industrially. It is. In Patent Document 3, although the iron loss reduction rate is high, further improvement is desired in terms of compatibility with magnetostriction. In Patent Document 4, there is a problem that it is difficult to control the amount of strain and it is difficult to stably obtain a low iron loss.

  Furthermore, in Patent Document 5, the surface of a grain-oriented electrical steel sheet is irradiated with a laser beam, the width is 50 to 300 μm, the depth is 5 to 35% of the thickness of the steel sheet, and the interval is within ± 15 ° from the right angle to the sheet passing direction. A method for producing a low iron loss grain-oriented electrical steel sheet is disclosed in which a tension-imparting insulating coating is applied after forming a 5-30 mm melt-solidified line portion. However, the above technique is intended to reduce iron loss in small wound core transformers that are subjected to strain relief annealing, and large strain core transformers that do not perform strain relief annealing introduce excessive strain. There is a problem that it is difficult to stably obtain low iron loss and low magnetostriction, but rather iron loss becomes large.

  On the other hand, static inductors such as transformers and reactors generate noise when the iron core is AC-excited. This noise is due to the fact that a large number of transformers are installed in cities with increasing demand for power. Due to the environment-oriented trend, there is a strong need to reduce it. Possible causes of noise include vibration due to electromagnetic force between exciting coils, vibration due to magnetic force between the joints and layers of the iron core, vibration due to magnetostriction of the electromagnetic steel sheet, and the like.

  Among these, the method for reducing the noise from the iron core, for example, uses the low magnetostriction property of the electrical steel sheet at a low magnetic flux density by reducing the design magnetic flux density of the iron core, or is shown in Non-Patent Document 1. As described above, it is known that it is effective to reduce magnetostriction using a highly oriented grain-oriented electrical steel sheet and to increase the tension of the surface film. Further, as disclosed in Patent Document 6, noise can also be reduced by limiting the iron core fastening method. Further, as disclosed in Patent Document 7, the noise can be reduced by surrounding the iron core with a sound insulation case, and as disclosed in Patent Document 8, by installing the transformer on the anti-vibration rubber. it can.

  However, in these techniques, it is necessary to install incidental equipment in the transformer, and there is a problem that the cost is significantly increased.

It is reported in Non-Patent Document 2 that the magnetostriction characteristics of the above-described laser magnetic domain control grain-oriented electrical steel sheet change depending on the laser irradiation conditions. Specifically, it has been reported that magnetostriction characteristics change by changing the irradiation energy density Ua value of the laser, and magnetostriction can be reduced by selecting an appropriate Ua value. However, the above technique has a problem that the maximum effect cannot be obtained with respect to magnetostriction reduction.
US Pat. No. 3,647,575 Japanese Patent Publication No.58-5968 Japanese Patent Publication No.57-2252 JP-A 62-96617 Japanese Patent No. 2647322 JP 47-28419 A JP-A-48-83329 JP-A-56-40123 IEEE Transactions, MAG-8 (1972), p.677 Journal of Japan Society of Applied Magnetics, Vol.25, No.4-2, 2001

In this way, the iron loss of grain-oriented electrical steel sheets has been remarkably improved. However, energy consumption has increased due to civilization and industrialization, and there are concerns about the depletion of fossil energy resources and the demand for global warming due to CO _2. Therefore, there is a demand for further reduction of iron loss. In addition, substation facilities have been built in urban areas, and it has been required to further reduce noise generated by transformers.

  As a result of earnest research on the low iron loss directional electrical steel sheet subjected to magnetic domain control by laser irradiation, the present inventors have found that the thickness of the solidified layer introduced by the laser irradiation, the surface roughness of the laser irradiation part, and the concave cross section By controlling the shape, it was possible to realize a grain-oriented electrical steel sheet having a very low iron loss and low noise and a method for manufacturing the same.

That is, the gist of the present invention is as follows.
(1) In a grain-oriented electrical steel sheet that performs magnetic domain control by laser irradiation, the laser irradiation portion has a solidified layer thickness of 4 μm or less, and excels in iron loss in a high magnetic field with an excitation magnetic flux density of 1.9 T, A grain-oriented electrical steel sheet with low magnetostriction.
(2) Iron loss in a high magnetic field with an excitation magnetic flux density of 1.9 T, wherein the surface roughness Rz is 4 μm or less when the laser irradiation part is scanned in the rolling direction to measure the roughness. Oriented electrical steel sheet that is excellent in resistance and low magnetostriction.
(3) In a grain-oriented electrical steel sheet that performs magnetic domain control by irradiating a laser beam in the plate width direction in a line or a sequence of dots, a concave shape having a cross-sectional shape of 200 μm or less in width and 10 μm or less in depth when viewed from the direction perpendicular to the rolling direction. The grain-oriented electrical steel sheet according to (1) or (2), which has a shape.
(4) The grain-oriented electrical steel sheet according to (1) or (2), wherein a distance between adjacent continuous or point-sequence-like lines on the steel sheet is 30 mm or less.
(5) The grain-oriented electrical steel sheet according to (4), wherein a distance between adjacent continuous or point-sequence-like lines on the steel sheet is 3 to 5 mm.
(6) The grain-oriented electrical steel sheet according to (3), wherein the concave shape portion has a width of 30 to 180 μm and a depth of 1 to 4 μm.

(7) In a method for manufacturing a grain-oriented electrical steel sheet that performs magnetic domain control by laser irradiation, the solidified layer thickness of the laser irradiation portion is 4 μm or less, and the iron loss in a high magnetic field with an excitation magnetic flux density of 1.9 T Of a grain-oriented electrical steel sheet that is excellent in resistance and low magnetostriction.
(8) In a method for manufacturing a grain-oriented electrical steel sheet in which magnetic domain control is performed by irradiating a laser beam linearly or in a sequence of dots in the width direction of the plate, the cross-sectional shape of the laser irradiation part viewed from the direction perpendicular to the rolling is 200 μm or less in width and 10 μm in depth. A method for producing a grain-oriented electrical steel sheet having the following concave shape, wherein the solidified layer thickness of the concave bottom portion is 4 μm or less.
(9) Production of grain-oriented electrical steel sheet having excellent magnetic properties according to (7) or (8), wherein the laser irradiation is performed by a fiber laser device having a fiber having a core diameter of 500 μm or less. Method.
(10) Production of grain-oriented electrical steel sheet having excellent magnetic properties according to (7) or (8), wherein the laser irradiation is performed by a fiber laser device having a fiber having a core diameter of 200 μm or less. Method.
(11) The method for producing a grain-oriented electrical steel sheet according to (7) or (8), wherein a distance between adjacent continuous or point-sequence-like lines on the steel sheet is 30 mm or less.
(12) The method for producing a grain-oriented electrical steel sheet according to (11), wherein a distance between adjacent continuous or point-sequence-like lines on the steel sheet is 3 to 5 mm.
(13) The grain-oriented electrical steel sheet according to (7) or (8), wherein the concave shape portion has a width of 30 to 180 μm and a depth of 2 to 4 μm.

  By this invention, the iron loss and magnetostriction of a grain-oriented electrical steel sheet can be reduced.

The inventors of the present invention applied a fiber laser apparatus having a fiber diameter of 10 μm in a direction substantially perpendicular to the rolling direction of one surface of a steel sheet on a product plate (thickness 0.23 mm) of a grain-oriented electrical steel sheet containing 3.3% Si by mass. A linear laser irradiation was applied. The interval between the laser irradiation lines was 4 mm, and the length of the irradiated portion in the rolling direction was changed from 50 μm to 200 μm. Further, by changing the laser irradiation conditions of the laser irradiation diameter, laser power, power density, and scanning speed, the concave cross-sectional shape and the solidified layer thickness (illustrated in FIG. 1) as viewed from the direction perpendicular to the rolling were changed. Moreover, CO ₂ laser as a comparative example was also performed for the YAG laser. Table 1 shows the magnetic measurement results of each sample. Iron loss, magnetic flux density, and magnetostriction are values measured under magnetic flux sine wave conditions without applying stress to the steel sheet.
As can be seen from Table 1, the samples (1), (2), (4), and (5) are iron loss (high magnetic field iron loss) W _19/50 in a high magnetic field with an excitation magnetic flux density of 1.9 T, magnetostriction λ19. Both _pp are superior to other samples.

The present inventors consider the reason why the present invention satisfies the low iron loss and the low magnetostriction at the same time in a high magnetic field (high magnetic flux density) with an excitation magnetic flux density of 1.9 T as follows.
The mechanism by which the magnetic domain width is subdivided by laser irradiation and the iron loss is reduced is the total volume of the high-energy return magnetic domain formed by residual strain (thermal strain or impact strain by plasma reaction force) introduced by laser irradiation. It is considered that the driving force is to reduce the frequency (for example, Non-Patent Document 3).
Journal of Japan Society of Applied Magnetics, vol.25, No12, P.1612

  As a result of laser irradiation under various conditions as described above, it has been found that a high iron loss reduction effect can be obtained by controlling the thickness of the solidified layer and the cross-sectional shape of the recess of the irradiated portion within the range of the present invention. It was. This is presumed to be because the appropriate amount of residual strain was introduced in a narrow range by controlling the thickness of the solidified layer, and also the recess width and recess depth of the irradiated area, thereby reducing the total volume of the return magnetic domain. ing. This effect is particularly noticeable in high magnetic flux density iron losses. This is because when the excitation magnetic flux density is low, the magnetization of the entire volume of the magnetic steel sheet does not change, and the return magnetic domain also only partially changes the magnetization due to the domain wall movement, but the saturation magnetic flux density is 1.9T. When excited to a close high magnetic flux density, the reflux magnetic domain also changes so that most of it has a magnetization component parallel to the rolling direction. This change is considered to cause a loss. Therefore, it is considered that the control of the thickness of the solidified layer has a remarkable effect in reducing the iron loss particularly at a high magnetic flux density.

The solidified layer in the present invention is a fine layer different from the single crystal structure of the grain-oriented electrical steel sheet, which is observed when a steel sheet cross section that is parallel to the rolling direction of the laser irradiation part and is orthogonal to the steel sheet surface is observed with an SEM or the like. This refers to the solidified tissue part. For observation of the solidified structure, an SEM (scanning electron microscope) observation method using etching, an SEM observation method using a backscattered electron image, an observation method using an FE-SEM (field emission SEM), and an optical microscope were used. There are methods, but the observation method is not particularly limited. In order to change the thickness of the solidified layer, it is effective to change the laser irradiation diameter, laser power, power density, and scanning speed of the laser irradiation conditions.
FIG. 5 of Patent Document 9 discloses a laser irradiation portion having a solidified layer thickness of about 2 μm. However, as described in paragraph [0003] in the text of Patent Document 9, the present invention reduces iron loss. The effect is aimed at a method for reducing the iron loss of grain-oriented electrical steel sheets that remains even after strain relief annealing. The iron loss value is obtained under the condition that the thickness exceeds 20 μm with only a molten layer as shown in FIG. Rather deteriorate. The present invention aims to provide a low iron loss directional electrical steel sheet used for an iron core that does not undergo strain relief annealing, for example, an iron core for a large transformer, and its technical idea is completely different.
JP, 2005-59014, A FIG. 6 (b) discloses a re-solidified layer using a fiber laser, but this does not satisfy the conditions of the present invention because the solidified layer thickness of the laser irradiation part is about 6 μm. WO2004 / 083465A1 publication

The introduction of strain only in a narrow range in the rolling direction has the effect of suppressing magnetostriction deformation that causes noise in iron cores such as transformers as well as reducing iron loss. The introduction of residual strain by a laser is effective in subdividing the magnetic domain width through the above-mentioned reflux magnetic domain, but if this range is large, it can also be a source of magnetostriction. However, it is important to generate a residual strain that generates a reflux magnetic domain as effectively as possible. In the present invention, by setting the average value of the solidified layer thickness of the laser irradiation portion to 4 μm or less, it is possible to achieve both low iron loss in a high magnetic field and reduction of magnetostriction λ19 _pp .

In the present invention, iron loss and magnetostriction can also be reduced by reducing the surface roughness Rz of the bottom surface of the recess of the laser irradiation portion. Hereinafter, this point will be described in detail.
The inventors of the present invention applied a fiber laser device having a fiber diameter of 10 μm in a direction substantially perpendicular to the rolling direction of one surface of a steel sheet on a product plate (thickness 0.27 mm) of a grain-oriented electrical steel sheet containing 3.3% Si by mass. A linear laser irradiation was applied. The distance between the laser irradiation lines was 4 mm, and the length of the irradiation part in the rolling direction was (1) 50 μm, (2) 100 μm, and (3) 200 μm.
Further, the same grain-oriented electrical steel sheet was irradiated with a point-sequence laser beam using a YAG laser. The irradiation line interval was 4 mm, and the maximum irradiated portion length in the rolling direction (corresponding to the diameter of the points) was (4) 100 μm and (5) 200 μm.

Table 2 shows the surface roughness Rz and the magnetic measurement result of the laser irradiated portion of each sample.
The surface roughness Rz is an index indicating the maximum height of the contour curve defined in ISO 4287 (1997). The surface roughness Rz of the laser irradiated portion was measured by scanning a stylus so as to cross the center line of the laser irradiated portion at a right angle (rolling direction) using a normal surface roughness meter for measuring the surface roughness. As a result, it was found that the surface roughness Rz, iron loss, and magnetostriction are highly correlated.
When measuring the surface roughness Rz, dust on the surface was sufficiently removed, measurement was performed 10 times or more, and a single abnormal value was removed, and then an average value was obtained. In measuring the surface roughness, only the steel plate part is related to the magnetization, so it is ideal to measure the surface by removing the high-tensile insulation coating and ceramic coating on the surface with alkali. On the other hand, even if these acids are removed using strong non-corrosive acids, the surface profile is not greatly changed, and there is no problem in practical use. The iron loss, magnetic flux density, and magnetostriction are values measured under magnetic flux sine wave conditions without applying stress to the steel sheet.

As can be seen from Table 2, the samples of (1), (2), and (3) are superior in the high magnetic field iron loss and magnetostriction compared to other samples.
In the case of (4) and (5) using a YAG laser, a sharp protrusion with a large surface roughness is observed at the laser irradiation part (bottom part), which seems to deteriorate the high magnetic field iron loss and magnetostriction. .

The reason why the low iron loss and the low magnetostriction at the high magnetic flux density are satisfied at the same time by the present invention affects the iron loss reduction effect from the influence on the leakage magnetic domain due to the leakage magnetic flux from the protrusion at the bottom of the laser irradiation part. Can be considered. In this case, the iron loss W _19/50 at a high magnetic flux density at which the magnetic steel sheet approaches magnetic saturation is particularly affected. The absence of a portion having a large surface roughness in the laser irradiation portion is effective in reducing iron loss at a high magnetic flux density.

Hereinafter, specific modes for carrying out the present invention will be described.
The grain-oriented electrical steel sheet used in the present invention may be a general product plate. In addition, although it is common to have the primary film by a forsterite etc. on a steel plate surface, and an insulating film, the product board which does not have a film on the steel plate surface is also within the scope of the present invention.

Regarding the laser conditions, the laser irradiation length (width) in the rolling direction affects the amount of magnetic domain of the reflux type caused by the inverse effect of magnetostriction by causing elastic deformation around the irradiated portion due to thermal strain. The reflux-type magnetic domain serves as a driving force for magnetic domain subdivision, and is effective in reducing iron loss. However, since it also causes magnetostriction deformation, there is an appropriate range for satisfying both characteristics.
In order to reduce magnetostriction, the laser irradiation width in the rolling direction is 200 μm or less, preferably 180 μm or less, more preferably 140 μm or less, 120 μm or less, and even more preferably 100 μm or less. On the other hand, in order to obtain a low iron loss, the laser irradiation width in the rolling direction is preferably 20 μm or more, more preferably 30 μm or more, and further preferably 50 μm or more.

The power per unit area of the laser irradiation beam, that is, the power density is preferably increased as much as possible in order to efficiently subdivide the magnetic domain, but if it is excessively large, the solidified layer thickness increases, so 150 kW / mm ² In the following, it is more preferable or 100 kW / mm ² or less. If it is too small, the thickness of the solidified layer becomes small, so 0.5 kW / mm ² or more, more preferably 1 kW / mm ² or more is preferable.

  If the laser beam stays on the steel plate, that is, the irradiation duration is too long, the thickness of the solidified layer becomes too thick, so that it is preferably 1 msec or less, more preferably 0.3 msec or less. On the other hand, if it is too short, the thickness of the solidified layer becomes too small, so that it is 1 μsec or more, more preferably 5 μsec or more.

The product of power density and irradiation duration is also an important control factor for the solidified layer thickness. 5 mJ / mm ² or more, preferably to 500 mJ / mm ² or less, 10 mJ / mm ² or more, still more preferably 300 mJ / mm ² or less.

Next, a laser suitable for the method of the present invention will be described.
First, in the manufacture of the electrical steel sheet according to the present invention, it is preferable that a high-power laser beam is set to a condensing shape of 200 μm or less. A general YAG laser has a beam quality with low focusing performance called multimode, and it is very difficult to focus 200 μm of a high power YAG laser. In addition, the CO ₂ laser generally has multimode oscillation and the wavelength is longer than that of the YAG laser, so that it is difficult to collect light of 200 μm or less. In order to obtain a single-mode output with high condensing performance with these lasers, a special device configuration such as using a spatial filter inside the laser resonator is required. In this case, however, the laser output is remarkably reduced, so that it is not suitable for industrial mass production.

On the other hand, the fiber laser can easily achieve single mode oscillation with high light condensing performance. Further, by increasing the number of semiconductor lasers as the excitation light source and increasing the fiber length, it is easy to increase the output. Further, it is possible to collect light with a relatively simple lens configuration up to about 40 to 50% of the fiber core diameter, and a minute light collection diameter of 200 μm or less can be easily achieved. Therefore, a fiber laser having a fiber core diameter of 500 μm or less is preferable for the production method of the present invention.
The upper limit of the fiber core diameter of 500 μm is limited because a desired solidified layer thickness cannot be obtained when the fiber core diameter is greater than this value, and a desired cross-sectional shape is difficult to obtain. Furthermore, the core diameter is preferably 200 μm or less. More preferably, the core diameter is preferably 40 μm or less.

A multimode beam used in a YAG laser or the like is a beam in which various spatial intensity distributions are superposed, and oscillates due to a time distribution of a laser medium temperature distribution and excitation intensity in a cross section perpendicular to the laser output direction. The mode may change. In that case, there exists a problem that control of the solidified layer thickness of this invention becomes unstable.
On the other hand, since the mode of the fiber laser is a single mode regulated by the fiber core diameter, there is no such instability factor, and it is possible to always form a stable solidified layer. Also from this viewpoint, it is preferable to use a fiber laser in the present invention.

  Under the above laser irradiation conditions, the surface of the grain-oriented electrical steel sheet is irradiated with laser. Laser irradiation may be performed linearly or in a dot array in the plate width direction. The sheet width direction may be substantially perpendicular to the rolling direction, but is within ± 30 ° from the direction perpendicular to the rolling and is within the scope of the present invention. The term “linear” refers to the case where the laser is irradiated linearly in the plate width direction, and the point sequence refers to the case where the laser is irradiated in a dotted manner with a period on a certain straight line in the plate width direction. Moreover, the range of 1-100 mm is suitable for the space | interval of the rolling direction of the said linear or point sequence-like laser irradiation line. This interval is more preferably 30 mm or less, and further preferably 3 to 5 mm.

Moreover, the solidified layer thickness of the laser irradiation part irradiated by the said laser conditions needs to be 4 micrometers or less. The thickness of the solidified layer is determined by measuring the length in the thickness direction of the solidified layer at the thickest part of the solidified layer when the solidified layer is observed in a cross section. It may be a position corresponding to the center part (width direction center part in the rolling direction) of the part, and the laser irradiation center line (laser irradiation area or the width center line of the laser irradiation mark) may be measured as a representative part. In the measurement, it is preferable that the solidified thickness within a certain range from the portion (for example, a range of ± 10 μm from the center line) is an average value so that a substantial solidified layer thickness can be measured.
The solidified layer can be observed by an SEM observation method using etching together, an SEM observation method using a backscattered electron image, an observation method using an FE-SEM, a method using an optical microscope, and the like. At this time, the solidified layer thickness can be obtained more accurately by using an SEM photograph measured by performing inclined polishing as shown in FIG.
The upper limit value of 4 μm for the solidified layer thickness is limited because it does not deteriorate the magnetostriction and improves the high magnetic field iron loss. The lower limit value of the solidified layer thickness is preferably 0.1 μm or more from the viewpoint of securing a heat deformation volume that is considered necessary for maintaining elastic deformation of the steel sheet for magnetic domain refinement. Furthermore, 0.5 μm or more and 2 μm or less are more preferable.

FIG. 2 shows a solidified layer structure ((a) an example of the present invention and (b) a comparative example) in a laser irradiation part. (A) is a laser irradiation condition with an irradiation part length (width) of 70 μm in the rolling direction and a power density of 3 kW / mm ² , and (b) is a laser irradiation condition with a laser irradiation condition of a rolling direction irradiation width of 250 μm and a power density of 30 kW / mm ^2. Carried out. The scanning speed of the irradiation beam in the direction perpendicular to the rolling was the same for both. With the linear continuous laser irradiation in the direction perpendicular to the rolling, the distance between the irradiation lines was 5 mm.

Here, the power density is obtained by dividing the laser irradiation power on the steel plate by the area of the irradiation part, and indicates the laser irradiation power per unit area of the irradiation part. FIG. 2 shows that the steel plate cross section is slanted as shown in FIG. 3, and the length in the vertical direction is extended to 5 times the length in the cross section perpendicular to the rolling surface and including the rolling direction. It is. From these observation results, the solidified layer thickness is 3.3 μm for (a), 4.7 μm for (b), and (a) is the iron loss W _19/50 (W / kg) = 1.34 W / kg, magnetostriction λ19 _pp = 0.45 × 10 ⁻⁶ , (b) shows iron loss W _19/50 (W / kg) = 1.67 W / kg, magnetostriction λ19 _pp = 0.7 × 10 ⁻⁶ Excellent magnetic field iron loss and low magnetostriction are obtained in the inventive examples. The plate thickness of these steel plates was 0.27 mm.

Further, it is desirable that the cross-sectional shape seen from the direction perpendicular to the rolling direction of the laser irradiation irradiated under the laser conditions is a concave shape having a width of 200 μm or less and a depth of 10 μm or less. If the upper limit of the width is 200 μm, the space factor decreases if it is too large, and it is also preferable for achieving both iron loss and low magnetostriction in a high magnetic field. The width is preferably 30 to 180 μm. The upper limit of the depth of 10 μm is preferable to reduce the space factor when the depth is too deep as well as the width, and to prevent the iron loss and the magnetic flux density from being deteriorated in a high magnetic field. The depth is preferably 1 to 4 μm.
In addition, the schematic diagram of the concave cross-sectional shape seen from the rolling orthogonal direction of the laser irradiation part in FIG. 1 is shown. In the figure, tm is the maximum thickness of the solidified layer, d is the depth of the concave shape, and W is the width of the concave shape (irradiation width in the rolling direction).

Next, a specific mode for carrying out the present invention when the surface roughness of the laser irradiation portion is small will be described.
In the present invention, magnetic domain control is performed by irradiating a grain-oriented electrical steel sheet with a laser beam in the form of a line or a point sequence in the sheet width direction. In the sheet width direction, laser irradiation is performed in the form of a line or a point sequence within a range of 0 ° to 30 ° from the direction perpendicular to the rolling direction. The term “linear” refers to irradiation in a straight line with continuous irradiation marks, and the term “dot” refers to irradiation in such a way that circular or elliptical irradiation marks are arranged on a straight line. However, even if these irradiation traces are not a perfect straight line and are wavy, implementation of this invention is not prevented. In the case of wavy irradiation, the plate width direction is defined with the center line of the wavy line.

In the present invention, it is preferable to use a fiber laser device because the bottom shape of the irradiation mark can be reduced and the iron loss in a high magnetic field can be reduced in the present invention. Note that it is relatively easy to reduce the shape of the irradiation mark in the YAG laser, but there is a drawback that the equipment becomes large in order to have sufficient power, and in the multimode oscillation generally used, the bottom part is It is difficult to reduce the surface roughness of the laser irradiation part. The CO ₂ laser has a drawback that it is difficult to reduce the shape of the irradiation mark because of its long wavelength. Similarly to the YAG laser, the surface roughness of the laser irradiation part at the bottom of the irradiation part is commonly used in multimode oscillation. Is difficult to reduce.

  Further, it is desirable that the core diameter of the fiber is 500 μm or less because the optical system for improving the laser beam quality and reducing the bottom shape can be simplified. If the upper limit is 500 μm or more, there is a problem that a desired bottom shape cannot be obtained. Furthermore, the core diameter is preferably 200 μm or less. More preferably, the core diameter is preferably 40 μm or less.

The bottom portion irradiated with a laser means a portion that is affected until the surface of the steel sheet is partially melted when the laser irradiation is performed. Even when there is a ceramic coating on the surface of the grain-oriented electrical steel sheet, the portion where the steel sheet portion under the ceramic coating is partially melted is used as the laser irradiation section. FIG. 2 shows a cross-sectional photograph. In the present invention, the portion affected by the steel plate surface until it partially melts refers to a surface layer portion showing a solidified structure, which is different from the homogeneous portion of the base iron portion.
From this point of view, if the cross-sectional shape viewed from the direction perpendicular to the rolling direction of the laser irradiation is too narrow, the surface roughness may increase, and therefore it is 30 μm or more, preferably 50 μm or more.

  In the present invention, the surface roughness Rz is 4 μm or less. In order to confirm Rz focused on in the present invention, it is preferable to measure the roughness at a plurality of locations where a wider range of information is obtained, and obtain the average value thereof. For example, it is preferable to measure Rz of a range (for example, a range of the laser irradiation width) that covers all of the concave bottom portion of the laser irradiation portion having a width in the rolling direction from the irradiation center line, and to average these values. . Rz is preferably 3.5 μm or less, more preferably 3.0 μm or less, and even more preferably 2.5 μm or less.

Hereinafter, the present invention will be further described based on examples.
The inventors of the present invention provided a fiber laser device having a fiber diameter of 10 μm in a direction substantially perpendicular to the rolling direction of one surface of a steel sheet on a product plate (thickness 0.23 mm) of a grain-oriented electrical steel sheet containing 3.2% Si by mass. A linear laser irradiation was applied. The interval between the laser irradiation lines was 3 mm, and the irradiation part length (width) in the rolling direction was 30 μm. At the time of irradiation, the thickness of the solidified layer in the irradiated portion was changed by changing the laser power by changing the scanning speed of the irradiation beam in the direction perpendicular to the rolling direction. Table 3 shows the magnetic measurement results of each sample. The iron loss, magnetic flux density, and magnetostriction are values measured under magnetic flux sine wave conditions without applying stress to the steel sheet.
As can be seen from Table 3, the samples of (1) and (2) are superior in both high-field iron loss and magnetostriction compared to the comparative example.

The inventors of the present invention applied a fiber laser apparatus having a fiber diameter of 10 μm in a direction substantially perpendicular to the rolling direction of one surface of a steel sheet on a product plate (thickness 0.23 mm) of a grain-oriented electrical steel sheet containing 3.3% Si by mass. A linear laser irradiation was applied. The distance between the laser irradiation lines was 4 mm, and the length of the irradiated portion in the rolling direction was (1) 30 μm, (2) 80 μm, and (3) 250 μm.
Further, linear laser irradiation was performed on the same grain-oriented electrical steel sheet using a CO ₂ laser. The irradiation line interval was 5 mm, and the irradiation part length in the rolling direction was (4) 300 μm and (5) 500 μm. Table 4 shows the magnetic measurement results of each sample in which the thickness of the solidified layer was controlled by changing the laser power and the irradiation time. Iron loss, magnetic flux density, and magnetostriction are values measured under magnetic flux sine wave conditions without applying stress to the steel sheet.
As can be seen from Table 4, the samples of (1), (2), and (3) are superior in the high magnetic field iron loss and magnetostriction compared to other samples.

The inventors of the present invention applied a fiber laser apparatus having a fiber diameter of 20 μm in a direction substantially perpendicular to the rolling direction of one surface of a steel sheet to a product plate (thickness 0.27 mm) of a grain-oriented electrical steel sheet containing 3.2% Si by mass. A linear laser irradiation was applied. The interval between the laser irradiation lines was 5 mm, and the length of the irradiated part in the rolling direction was 50 μm. At the time of irradiation, the scanning speed of the irradiation beam in the direction perpendicular to the rolling direction was changed to change the presence or absence of protrusions in the laser irradiation portion. Table 5 shows the shape of the laser irradiated portion of each sample and the magnetic measurement results. The roughness of the laser irradiated portion was measured by scanning a stylus type surface roughness meter parallel to the rolling direction including the laser irradiated portion. Moreover, iron loss, magnetic flux density, and magnetostriction are values measured under magnetic flux sine wave conditions without applying stress to the steel sheet.
As can be seen from Table 5, the samples of (1) and (2) are superior to the other samples in both high magnetic field iron loss and magnetostriction.

The inventors of the present invention applied a fiber laser apparatus having a fiber diameter of 10 μm in a direction substantially perpendicular to the rolling direction of one surface of a steel sheet on a product plate (thickness 0.23 mm) of a grain-oriented electrical steel sheet containing 3.3% Si by mass. A linear laser irradiation was applied. The interval between the laser irradiation lines was 5 mm, and the length of the irradiated part in the rolling direction was (1) 50 μm, (2) 100 μm, and (3) 200 μm. Further, linear laser irradiation was performed on the same grain-oriented electrical steel sheet using a CO ₂ laser. The irradiation line interval was 5 mm, and the irradiation part length in the rolling direction was (4) 200 μm and 400 μm.
Table 6 shows the shape of the laser irradiated portion of each sample and the magnetic measurement results. The shape of the laser irradiation portion is a concave cross-sectional shape as viewed from the direction perpendicular to the rolling. Moreover, iron loss, magnetic flux density, and magnetostriction are values measured under magnetic flux sine wave conditions without applying stress to the steel sheet.
As can be seen from Table 6, the samples of (1), (2), and (3) are superior in the high magnetic field iron loss and magnetostriction compared to other samples.

It is a schematic diagram of a laser irradiation part. It is a solidified layer structure in a laser irradiation part ((a) example of the present invention, (b) comparative example). The cross section is polished with an inclination, and the length in the vertical direction is extended to 5 times the length in the cross section including the rolling direction and perpendicular to the rolling surface. It is a schematic diagram which shows the cross-section grinding | polishing method at the time of performing observation of FIG. It is a schematic diagram which shows the method of measuring the surface roughness of a laser irradiation part. It is a figure which shows the definition of surface roughness Rz.

Explanation of symbols

1: Steel plate W: Concave cross-sectional width d: Concave bottom depth tm: Solidified layer thickness

Claims (13)

  In a grain-oriented electrical steel sheet that performs magnetic domain control by laser irradiation, the laser irradiation portion has a solidified layer thickness of 4 μm or less, and is excellent in iron loss in a high magnetic field with an excitation magnetic flux density of 1.9 T and has low magnetostriction. Is a grain-oriented electrical steel sheet.   The surface roughness Rz when the roughness is measured by scanning the laser irradiation part in the rolling direction is excellent in iron loss in a high magnetic field with an excitation magnetic flux density of 1.9 T, characterized by being 4 μm or less, A grain-oriented electrical steel sheet with low magnetostriction.   In a grain-oriented electrical steel sheet that performs magnetic domain control by irradiating a laser beam linearly or in a sequence of dots in the width direction of the plate, the cross-sectional shape of the laser irradiated portion viewed from the direction perpendicular to the rolling is a concave shape having a width of 200 μm or less and a depth of 10 μm or less. The grain-oriented electrical steel sheet according to claim 1 or 2.   The grain-oriented electrical steel sheet according to claim 1 or 2, wherein a distance between adjacent continuous or point-like lines on the steel sheet is 30 mm or less.   The grain-oriented electrical steel sheet according to claim 4, wherein a distance between adjacent continuous or point-like lines on the steel sheet is 3 to 5 mm.   The grain-oriented electrical steel sheet according to claim 3, wherein the concave shape portion has a width of 30 to 180 µm and a depth of 1 to 4 µm.   In the method of manufacturing a grain-oriented electrical steel sheet that performs magnetic domain control by laser irradiation, the solidified layer thickness of the laser irradiation portion is 4 μm or less, and excels in iron loss in a high magnetic field with an excitation magnetic flux density of 1.9 T, And the manufacturing method of the grain-oriented electrical steel sheet which is low magnetostriction.   In a method for manufacturing a grain-oriented electrical steel sheet in which magnetic domain control is performed by irradiating a laser beam linearly or in a sequence of dots in the plate width direction, a concave shape having a cross-sectional shape of a laser irradiation portion viewed from a direction perpendicular to the rolling is 200 μm or less and a depth is 10 μm or less. A method for producing a grain-oriented electrical steel sheet having a shape and a solidified layer thickness of 4 μm or less at the concave bottom.   The method for producing a grain-oriented electrical steel sheet according to claim 7 or 8, wherein the laser irradiation is performed by a fiber laser device having a fiber having a core diameter of 500 µm or less.   The method for producing a grain-oriented electrical steel sheet according to claim 7 or 8, wherein the laser irradiation is performed by a fiber laser device having a fiber having a core diameter of 200 µm or less.   The method for producing a grain-oriented electrical steel sheet according to claim 7 or 8, wherein a distance between adjacent continuous or point-like lines on the steel sheet is 30 mm or less.   The method for producing a grain-oriented electrical steel sheet according to claim 11, wherein a distance between adjacent continuous or point-like lines on the steel sheet is 3 to 5 mm. The grain-oriented electrical steel sheet according to claim 7 or 8, wherein the concave-shaped portion has a width of 30 to 180 µm and a depth of 1 to 4 µm.

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