JP2023121125A - Grain-oriented electromagnetic steel sheet - Google Patents

Abstract

To provide a grain-oriented electromagnetic steel sheet exhibiting low core loss, while having high magnetic permeability and excellent magneto-striction properties.SOLUTION: On one surface of a grain-oriented electromagnetic steel sheet, linear fusion solidification parts intersecting a rolling direction are periodically formed. In an anisotropic energy distribution from a surface of the fusion solidification parts on a cross section in the rolling direction of the grain-oriented electromagnetic steel sheet to a plate thickness direction, a deepest location of a region in which ΔE(KJ/m3) becomes negative is 4 μm or more, by a distance from the surface of the fusion solidification parts.SELECTED DRAWING: Figure 3

Description

The present invention relates to grain-oriented electrical steel sheets.

A grain-oriented electrical steel sheet is used, for example, as a core material for a transformer. Transformers are required to suppress energy loss. Of these, the energy loss is affected by the iron loss of the grain-oriented electrical steel sheet.

Here, iron loss of a grain-oriented electrical steel sheet mainly consists of hysteresis loss and eddy current loss. Among these, as a method of improving hysteresis loss, a method of highly orienting the (110) [001] orientation called GOSS orientation in the rolling direction of the steel plate, a method of reducing impurities in the steel plate, etc. have been developed. . In addition, as a technique for improving eddy current loss, a technique of increasing the electrical resistance of a steel sheet by adding Si, a technique of applying film tension in the rolling direction of the steel sheet, and the like have been developed. However, these methods have limitations in manufacturing grain-oriented electrical steel sheets.

Therefore, magnetic domain refining techniques have been developed in order to further reduce iron loss in grain-oriented electrical steel sheets. Magnetic domain refining technology is a technology for reducing iron loss, especially eddy current loss, in grain-oriented electrical steel sheets as follows. In other words, after finish annealing (hereinafter also referred to as final annealing) or after baking the insulating coating, the non-uniformity of the magnetic flux is corrected by physical means such as forming grooves in the steel sheet or introducing local strain. Introduce. As a result, the width of the 180° magnetic domain (main magnetic domain) formed along the rolling direction of the steel sheet is subdivided, and the iron loss, particularly the eddy current loss, of the grain-oriented electrical steel sheet is reduced.

For example, in Patent Document 1,
"A unidirectional electrical steel sheet formed on one surface with linear grooves having a groove width of 300 µm or less, a groove depth of 100 µm or less, a groove centerline interval of 1 mm or more in the rolling direction, and an angle of 30° or more with the rolling direction. A wound core for a transformer with low iron loss, wherein the linear groove faces the inner winding side, and the radius of curvature of the innermost bent portion is 30 mm or less. ."
is disclosed.
In addition, the technique of forming grooves on the surface of the steel sheet to refine the magnetic domains as described in Patent Document 1 does not lose the magnetic domain refining effect even if strain relief annealing is performed, so the heat-resistant magnetic domain refining technology Also called Here, the strain relief annealing is a heat treatment for releasing strain that is inevitably introduced into the grain-oriented electrical steel sheet by, for example, bending for forming the grain-oriented electrical steel sheet into a wound core. This strain, unlike the strain introduced by the magnetic domain refining process, adversely affects iron loss.

Moreover, in Patent Document 2,
"A method of manufacturing a low core loss grain oriented silicon steel sheet characterized by radiating a sheet-like plasma flame with high convergence onto the surface of a grain oriented silicon steel sheet that has undergone final annealing to subdivide the magnetic domains. ."
is disclosed.
The technique of refining magnetic domains by introducing thermal strain into a steel sheet as described in Patent Document 2 is also called a non-heat-resistant magnetic domain refining technique because the magnetic domain refining effect disappears due to strain relief annealing. be.

Furthermore, as a technique for refining the magnetic domains by forming grooves on the surface of the steel sheet described above (heat-resistant magnetic domain refining technique), Patent Document 3 discloses an electrolytic etching method for forming grooves on the surface of the steel sheet by electrolytic etching. Proposed. Patent Document 4 proposes a laser method in which a steel sheet is locally melted and vaporized by a high-power laser. Patent Literature 5 proposes a gear press method in which a roll on a gear is pressed against a steel plate to give an impression.

Japanese Patent Publication No. 6-022179 JP-A-7-192891 JP 2012-77380 A JP-A-2003-129135 JP-A-62-086121

By the way, in recent years, from the viewpoint of energy conservation and environmental regulations, in addition to reducing the energy loss of transformers, it is also required to reduce noise during operation of transformers. Here, the noise during operation of the transformer is affected by the magnetostrictive properties of the grain-oriented electrical steel sheets. Therefore, it is extremely important to develop a grain-oriented electrical steel sheet that achieves both further reduction in core loss and good magnetostrictive properties.

Among the magnetic domain refining techniques described above, the non-heat-resistant magnetic domain refining technique disclosed in Patent Document 2 can greatly reduce the eddy current loss by introducing local strain in the steel sheet. On the other hand, however, non-heat-resistant magnetic domain refining causes an increase in hysteresis loss and a deterioration in magnetostriction characteristics due to the introduction of such strain. In addition, as described above, in the grain-oriented electrical steel sheet to which the non-heat-resistant magnetic domain refining technique has been applied, the effect of magnetic domain refining disappears due to strain relief annealing, so the use thereof is limited.

On the other hand, in the heat-resistant magnetic domain refining techniques such as Patent Documents 1, 3 to 5, the greater the area of the grooves in the cross section of the steel sheet in the rolling direction, the greater the effect. However, if the groove is formed deep in the thickness direction of the steel sheet, the deterioration of the magnetic properties of the steel sheet, such as a decrease in magnetic permeability, is caused. In addition, manufacturing disadvantages such as breakage of the steel plate also occur. In this way, the heat-resistant magnetic domain refining technology limits the depth of the grooves in the steel sheet. This is the current situation.

The present invention has been developed in view of the above-mentioned current situation, and an object of the present invention is to provide a grain-oriented electrical steel sheet having low core loss, high magnetic permeability, and good magnetostrictive properties.

In order to achieve the above object, the inventors have made intensive studies and obtained the following findings.
(a) In the magnetic domain refining technique, by forming regions with different magnetic permeability in the rolling direction, magnetic poles are formed at the interfaces of the regions. In order to reduce the magnetostatic energy increased by this pole, the main magnetic domain width of the steel sheet is subdivided.
(b) In the heat-resistant magnetic domain refining technology, gaps of grooves are used as regions with different magnetic permeability. Since the voids do not change even if the strain relief annealing is performed, the magnetic domain refining effect is maintained. However, the magnetic permeability of the entire steel sheet is lowered by the gaps of the grooves.
(c) On the other hand, in the non-heat-resistant magnetic domain refining technique, thermal strain is introduced into the steel sheet by irradiation with an energy beam. Due to the residual stress generated by this thermal strain, a new magnetic domain (closure magnetic domain) having a magnetization component of the [010] orientation or [100] orientation of the crystal (when the [001] orientation of the crystal is the rolling direction) is formed. be. Here, the [010] orientation or the [100] orientation of the crystal respectively corresponds to the intermediate direction between the plate width direction and the plate thickness direction (the direction at 45° from the plate width direction to the plate thickness direction). Since the direction of magnetization differs between the main magnetic domain and the closure magnetic domain, the magnetic permeability in the rolling direction changes, resulting in domain refining. Since this thermal strain is eliminated by strain relief annealing, the magnetic domain refining effect also disappears by strain relief annealing. However, since both the main magnetic domain and the closure domain are formed inside the grain-oriented electrical steel sheet, the magnetic permeability of the steel sheet as a whole hardly changes.

Therefore, the inventors of the present invention have proposed that, in a heat-resistant magnetic domain refining technique, if a closure domain can be formed by maintaining residual stress inside the steel sheet even after strain relief annealing, grooves can be formed deep in the thickness direction of the steel sheet. It was thought that even without it, an extremely high iron loss reduction effect could be obtained, and a decrease in magnetic permeability could also be suppressed.

Based on the above idea, the inventors conducted further studies and found that the steel sheet is locally melted and solidified by an energy beam to form a linear melt-solidified portion that crosses the rolling direction on one surface of the steel sheet. As a result, the inventors have found that the residual stress is maintained inside the steel sheet even after strain relief annealing.

式（２）～（４）中、σ_ＲＤ、σ_ＴＤおよびσ_ＮＤはそれぞれ、圧延方向、板幅方向および板厚方向の残留応力である。ε_ＲＤ、ε_ＴＤおよびε_ＮＤはそれぞれ、圧延方向、板幅方向および板厚方向の歪みである。 Further, the inventors formed a linear melt-solidified portion crossing the rolling direction on one surface of a grain-oriented electrical steel sheet under various conditions.
As a result, the inventors found that in the anisotropic energy distribution in the plate thickness direction from the surface of the melt-solidified portion in the cross section in the rolling direction of the grain-oriented electrical steel sheet, the region where ΔE (KJ/m ³ ) is negative. By setting the deepest position at a distance of 4 μm or more from the surface of the melt-solidified portion, high iron loss improvement can be achieved while ensuring high magnetic permeability and good magnetostrictive characteristics as a whole steel sheet even for strain relief annealing. It was found that the effect can be obtained.
Here, ΔE is defined by the following equation (1).
ΔE=E _sub -E _RD (1)
In formula (1), E _RD (KJ/m ³ ) and E _sub (KJ/m ³ ) are the anisotropic energy in the rolling direction and the crystal when the [001] orientation of the crystal is the rolling direction. is the anisotropic energy in the [010] orientation or [100] orientation of , which is obtained by the following equations (2) to (4).

In equations (2) to (4), σ _RD , σ _TD and σ _ND are the residual stresses in the rolling direction, strip width direction and strip thickness direction, respectively. ε _RD , ε _TD and ε _ND are the strains in rolling direction, width direction and thickness direction, respectively.

Further, the inventors conducted further studies and found that a higher effect can be obtained by satisfying the following points.
・In the anisotropic energy distribution from the surface of the molten solidified portion in the rolling direction cross section of the grain-oriented electrical steel sheet to the plate thickness direction, the deepest position of the region where ΔE (KJ/m ³ ) is −2 KJ/m ³ or less is 4 μm to 40 μm from the surface of the melt-solidified portion.
- A groove defined by a melt-solidified portion is formed on one surface of a grain-oriented electrical steel sheet.
- In the depth profile of the groove (cross-sectional shape of the groove) as shown in FIG. 1, the depth d of the deepest point of the groove is less than 8.0 μm.
- In the above depth profile of the groove, at least two minimum values are provided, and d/W × 100 (%), which is the ratio of the depth d of the deepest point of the groove to the width W of the groove, is 5% or more and less than 20%. do.
- The interval in the rolling direction between the melted and solidified parts shall be 1.0 mm or more and less than 5.0 mm.
The present invention has been completed based on the above findings and further studies.

式（２）～（４）中、σ_ＲＤ、σ_ＴＤおよびσ_ＮＤはそれぞれ、圧延方向、板幅方向および板厚方向の残留応力である。ε_ＲＤ、ε_ＴＤおよびε_ＮＤはそれぞれ、圧延方向、板幅方向および板厚方向の歪みである。 That is, the gist and configuration of the present invention are as follows.
1. A grain-oriented electrical steel sheet,
The grain-oriented electrical steel sheet has, on one surface thereof, cyclically linear melt-solidified portions crossing the rolling direction,
In the distribution of anisotropic energy in the thickness direction from the surface of the melt-solidified portion in the cross section of the grain-oriented electrical steel sheet in the rolling direction, the deepest position of the region where ΔE (KJ/m ³ ) is negative is the melt A grain-oriented electrical steel sheet having a distance of 4 μm or more from the surface of the solidified portion.
Here, ΔE is defined by the following equation (1).
ΔE=E _sub -E _RD (1)
In formula (1), E _RD (KJ/m ³ ) and E _sub (KJ/m ³ ) are the anisotropic energy in the rolling direction and the crystal when the [001] orientation of the crystal is the rolling direction. is the anisotropic energy in the [010] orientation or [100] orientation of , which is obtained by the following equations (2) to (4).

In equations (2) to (4), σ _RD , σ _TD and σ _ND are the residual stresses in the rolling direction, strip width direction and strip thickness direction, respectively. ε _RD , ε _TD and ε _ND are the strains in rolling direction, width direction and thickness direction, respectively.

2. 1. In the anisotropic energy distribution, the deepest position of the region where the ΔE (KJ/m ³ ) is −2 KJ/m ³ or less is 4 μm to 40 μm from the surface of the melt-solidified portion. The grain-oriented electrical steel sheet according to .

3. 3. The grain-oriented electrical steel sheet according to 1 or 2 above, having grooves defined by the melt-solidified portion.

4. 4. The grain-oriented electrical steel sheet according to 3 above, wherein, in the depth profile of the groove, the depth d of the deepest point of the groove is less than 8.0 μm.

5. Two or more minimum values exist in the depth profile of the groove,
5. The grain-oriented electrical steel sheet according to 3 or 4 above, wherein d/W×100 (%), which is the ratio of the depth d of the deepest point of the groove to the width W of the groove, is 5% or more and less than 20%.

6. 6. The grain-oriented electrical steel sheet according to any one of 1 to 5, wherein the distance between the melt-solidified portions in the rolling direction is 1.0 mm or more and less than 5.0 mm.

According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet having low core loss, high magnetic permeability, and good magnetostrictive properties. In addition, the grain-oriented electrical steel sheet of the present invention has low core loss even after strain relief annealing, and has high magnetic permeability and good magnetostrictive characteristics, so it is suitable for core materials such as transformers, particularly wound core transformers. As, it can be used very advantageously.

It is a schematic diagram which shows an example of the depth profile (cross-sectional shape of a groove part) of a groove part. It is a schematic diagram which shows an example of distribution of anisotropic energy. FIG. 4 is a diagram showing the relationship between the deepest position where ΔE<0 and iron loss W _17/50 ; 4 is an enlarged view of a part of FIG. 3; FIG. FIG. 4 is a diagram showing the relationship between the deepest position where ΔE≦−2 and iron loss W _17/50 ; 6 is an enlarged view of a part of FIG. 5; FIG. FIG. 4 is a diagram showing the relationship between the deepest position of ΔE<0 and the magnetostrictive harmonic MHL _15/50 ; FIG. 4 is a diagram showing the relationship between the deepest position of ΔE≦−2 and the magnetostrictive harmonic MHL _15/50 ; FIG. 10 is a diagram showing the relationship between the deepest position of ΔE<0 and ΔB ₈ ; FIG. 10 is a diagram showing the relationship between the deepest position of ΔE≦−2 and ΔB ₈ ; FIG. 4 is a diagram showing the relationship between the depth d of the deepest point of the groove and the iron loss W _17/50 ; FIG. 4 is a diagram showing the relationship between the depth d of the deepest point of the groove and magnetostrictive harmonics MHL _15/50 . FIG. 4 is a diagram showing the relationship between the depth d of the deepest point of the groove and _ΔB8 . It is a figure which shows the relationship between d/Wx100 and iron loss W _17/50 . FIG. 10 is a diagram showing the relationship between d/W×100 and magnetostrictive harmonics MHL _15/50 ; FIG _{. 10} is a diagram showing the relationship between d/W×100 and ΔB8; FIG. 4 is a diagram showing the relationship between the interval between molten solidified portions and iron loss W _17/50 ; FIG. 4 is a diagram showing the relationship between the interval between molten and solidified portions and magnetostrictive harmonics MHL _15/50 ; FIG. 4 is a diagram showing the relationship between the interval between molten solidified portions and _ΔB8 . It is a schematic diagram which shows the measuring method of the width W of a groove part.

First, the experimental results that led to the completion of the present invention will be described.
(Experiment 1)
A plurality of samples of the same shape are cut out from a grain-oriented electrical steel sheet (steel strip) manufactured by a general manufacturing process, and the magnetic properties, specifically, B ₈ and W ₁₇ , are measured by the Epstein method described in JIS C2550. _/50 was measured. B ₈ and W _17/50 measurements were 1.9350 T and 0.880 W/kg, respectively. Here, _B8 means the magnetic flux density when magnetized in the rolling direction with a magnetizing force of 800 A/m. W _17/50 means the iron loss value when alternating magnetization of 1.7 T and 50 Hz is applied in the rolling direction. Next, each sample is irradiated with a laser under various conditions in the range of laser output density: 0.1 to 1.0 (J/mm ² ) across the rolling direction to locally melt the sample. It was solidified to form a linear molten solidified portion on the surface of the sample. The power density of the laser is expressed as P/(v·Φ) using the scanning velocity (hereinafter also referred to as deflection velocity) v, the spot diameter Φ in the direction perpendicular to the scanning direction, and the laser output P. A single-mode fiber laser was used as the laser source, and no assist gas was used. Laser irradiation was performed at intervals of 4.0 mm in the rolling direction.

After the laser irradiation, each sample was subjected to strain relief annealing at 800° C. for 3 hours in a nitrogen atmosphere. Then, B ₈ and W _17/50 were measured for each sample by the Epstein method described in JIS C2550. Further, for each sample, ΔB ₈ (=[B ₈ measured in the sample after laser irradiation (hereinafter also referred to as the sample after irradiation)]−[Sample before laser irradiation (hereinafter, the sample before irradiation B ₈ ]) measured in (also referred to as ) was calculated.

Then, the magnetostrictive oscillation waveform of each sample after irradiation was measured by a laser Doppler type magnetostrictive vibrometer when subjected to sinusoidal AC magnetization of 1.5 T and 50 Hz. Then, the measured magnetostrictive vibration waveform was subjected to Fourier decomposition into vibration acceleration components of frequencies every 100 Hz. Then, each frequency component was multiplied by 0 to 1000 Hz, which was corrected for audibility on the A scale, and the multiplied value was taken as magnetostriction harmonic MHL _15/50 , which is an index of magnetostriction characteristics.

Then, after each irradiated sample was embedded in a mold and subjected to mirror polishing, the strain distribution in the cross section of the sample in the rolling direction was determined by the EBSD Wilkinson method. Then, from the obtained strain distribution, ΔE is calculated using the above formulas (1) to (4), and the anisotropic energy in the plate thickness direction from the surface of the molten solidified portion in the cross section of the sample in the rolling direction distribution was obtained. For reference, FIG. 2 shows a schematic diagram of an example of the anisotropic energy distribution. Note that the grain-oriented electrical steel sheet having the anisotropic energy distribution illustrated in FIG. 2 does not have grooves defined by the melt-solidified portion, that is, the surface of the grain-oriented electrical steel sheet is flat. .

From the anisotropic energy distribution of each sample thus obtained, the deepest position of the region where ΔE (KJ/m ³ ) is negative (hereinafter also referred to as the deepest position where ΔE < 0) and ΔE (KJ/m ³ ) are The deepest position of the region where the value is −2 KJ/m ³ or less (hereinafter also referred to as the deepest position where ΔE≦−2) was obtained.

3 to 10 show the above measurement results plotted against the deepest position of ΔE<0 and the deepest position of ΔE≦−2.
Here, FIG. 3 shows the relationship between the deepest position of ΔE<0 and the iron loss W _17/50 (of the sample after irradiation), and FIG. 4 is a partially enlarged view of FIG. .
FIG. 5 shows the relationship between the deepest position of ΔE≦−2 and the iron loss W _17/50 (of the sample after irradiation), and FIG. 6 is a partially enlarged view of FIG.
FIG. 7 shows the relationship between the deepest position of ΔE<0 and the magnetostrictive harmonic MHL _15/50 .
FIG. 8 shows the relationship between the deepest position of ΔE≦−2 and the magnetostrictive harmonic MHL _15/50 .
FIG. 9 shows the relationship between the deepest position where ΔE<0 and _ΔB8 .
FIG. 10 shows the relationship between the deepest position of ΔE≦−2 and _ΔB8 .

From FIGS. 3 and 4, it can be seen that a high iron loss improvement effect is obtained when the deepest position of ΔE<0 is 4 μm or more. Moreover, it can be seen that a particularly high iron loss improvement effect is obtained when the deepest position of ΔE<0 is 6 μm or more. The reason for this is considered by the inventors to be that, even after the stress relief annealing, the stress remained inside the steel sheet due to the presence of the melted solidified portion, and the closure domain was generated. On the other hand, when the deepest position of ΔE<0 is less than 4 μm (including those in which the deepest position of ΔE<0 is 0 μm, that is, ΔE is all positive), a sufficient iron loss improvement effect cannot be obtained. The inventors believe that the reason for this is that the closure domain was not generated sufficiently.

From FIGS. 5 and 6, it can be seen that a particularly high iron loss improvement effect is obtained when the deepest position of ΔE≦−2 is 4 μm or more. As to the reason for this, the inventors have found that the magnetic anisotropy of the closure domain is increased, so that the closure domain can exist even in a high magnetic field during excitation, and as a result, a higher magnetic domain refining effect is exhibited. I believe.

It can be seen from FIG. 7 that the magnetostrictive harmonic MHL _15/50 tends to increase as the deepest position of ΔE<0 increases. The inventors believe that the reason for this is that the magnetostriction oscillation is complicated by generation and disappearance of closure domains in the AC magnetization process. In particular, when the deepest position of ΔE<0 reaches 120 μm, the magnetostriction harmonic MHL _15/50 sharply increases. Therefore, the deepest position where ΔE<0 is preferably 100 μm or less, more preferably 50 μm or less.

It can be seen from FIG. 8 that the magnetostrictive harmonic MHL _15/50 tends to increase as the deepest position of ΔE≦−2 becomes deeper, similarly to the deepest position of ΔE<0. Therefore, the deepest position of ΔE≦−2 is preferably 80 μm or less, more preferably 40 μm or less.

9 and 10, even if the deepest position of ΔE<0 and the deepest position of ΔE≦−2 were deepened, _ΔB8 was less than −0.0010 T, and almost no deterioration in magnetic permeability was observed. The inventors believe that the reason for this is that the melt-solidified portion is epitaxially grown from the surrounding GOSS-oriented grains, so that the melt-solidified portion also maintains the GOSS orientation.

From the above results, in order to achieve high low iron loss, low magnetostriction, and high magnetic permeability even after strain relief annealing, it is necessary to set the deepest position of ΔE<0 to 4 μm or more. Further, it is preferable to set the deepest position of ΔE<0 to 6 μm or more. Furthermore, the deepest position of ΔE<0 is preferably 100 μm or less, more preferably 50 μm or less.
Furthermore, in order to obtain a higher effect, the deepest position of ΔE≦−2 is preferably 4 μm or more and 80 μm or less, more preferably 4 μm or more and 40 μm or less.

(Experiment 2)
A plurality of samples having the same shape were cut out from a grain-oriented electrical steel sheet (steel strip) manufactured by a general manufacturing process, and B ₈ and W _17/50 were measured by the Epstein method described in JIS C2550. B ₈ and W _17/50 measurements were 1.9350 T and 0.880 W/kg, respectively. Next, each sample was irradiated with an electron beam across the rolling direction to locally melt and solidify the sample, thereby forming a linear melt-solidified portion and a groove defined by the melt-solidified portion on the surface of the sample. . The power density of the electron beam was adjusted so that the deepest position with ΔE≦−2 was 15 μm. The power density of the electron beam is expressed as P/(v·Φ) using the deflection velocity v, the spot diameter Φ in the direction perpendicular to the scanning direction, and the electron beam power P. As an electron gun, a thermal electron gun with a LaB6 chip as a cathode was used. The electron beam irradiation was performed at intervals of 4.0 mm in the rolling direction. Also, the electron beam was irradiated with a converging coil so that the shape of the beam spot was elliptical with the major axis in the scanning direction, and the ellipticity was varied in the range of 1.1 to 12 for each sample.

After the electron beam irradiation, each sample was subjected to strain relief annealing at 800° C. for 3 hours in a nitrogen atmosphere. Then, B ₈ and W _17/50 were measured for each sample by the Epstein method described in JIS C2550. Further, for each sample, ΔB ₈ (=[B ₈ measured in the sample after laser irradiation (hereinafter also referred to as the sample after irradiation)]−[Sample before laser irradiation (hereinafter, the sample before irradiation B ₈ ]) measured in (also referred to as ) was calculated. Also, in the same manner as in Experiment 1, the magnetostriction harmonic MHL _15/50 , which is an index of magnetostriction characteristics, was obtained for each sample after irradiation.

Next, for each sample after irradiation, a depth profile of the groove is created from the surface using a laser microscope, and the depth d of the deepest point of the groove (in the plate thickness direction between the deepest point of the groove and the surface of the grain-oriented electrical steel sheet distance) was measured.

11 to 13 show the above measurement results plotted against the depth d of the deepest point of the groove.
Here, FIG. 11 shows the relationship between the depth d of the deepest point of the groove and the iron loss W _17/50 (of the sample after irradiation).
FIG. 12 shows the relationship between the depth d of the deepest point of the groove and the magnetostrictive harmonic MHL _15/50 .
FIG. 13 shows the relationship between the depth d of the deepest point of the groove and _ΔB8 .

As can be seen from FIG. 11, the iron loss tends to improve as the depth d of the deepest point of the groove increases, that is, as the groove becomes deeper. In particular, when the depth d of the deepest point of the groove is 1.0 μm or more, a high iron loss improvement effect can be obtained. The inventors believe that the reason for this is that the free magnetic pole formed on the wall surface around the deepest point of the groove promotes the refining of the magnetic domain.

It can be seen from FIG. 12 that the magnetostrictive harmonic MHL _15/50 is hardly affected by the depth d of the deepest point of the groove.

As can be seen from FIG. 13, _ΔB8 , which is an index of permeability change, tends to increase as the depth d of the deepest point of the groove increases, that is, as the groove becomes deeper. In particular, when the depth d of the deepest point of the groove exceeds 8.0 μm, _ΔB8 tends to increase significantly. The inventors believe that the reason for this is that the depth of the groove increases the volume of the groove, which is the air gap, thereby deteriorating the magnetic permeability.

From the above results, it is preferable that the depth d of the deepest point of the groove is less than 8.0 μm in order to achieve high low core loss, low magnetostriction, and high magnetic permeability even after strain relief annealing. The depth d of the deepest point of the groove is more preferably less than 7.0 μm. Further, the depth d of the deepest point of the groove is more preferably 1.0 μm or more.

(Experiment 3)
A plurality of samples having the same shape were cut out from a grain-oriented electrical steel sheet (steel strip) manufactured by a general manufacturing process, and B ₈ and W _17/50 were measured by the Epstein method described in JIS C2550. B ₈ and W _17/50 measurements were 1.9350 T and 0.880 W/kg, respectively. Next, each sample was irradiated with a laser across the rolling direction, and the sample was locally melted and solidified to form a linear melt-solidified portion and a groove defined by the melt-solidified portion on the surface of the sample. The power density of the laser was adjusted so that the deepest position with ΔE≦−2 was 15 μm. The power density of the laser is expressed as P/(v·Φ) using the deflection velocity v, the spot diameter Φ in the direction perpendicular to the scanning direction, and the laser output P. A single-mode fiber laser was used as the laser source, and no assist gas was used. Laser irradiation was performed at intervals of 4.0 mm in the rolling direction. In addition, the laser was irradiated with a cylindrical lens so that the shape of the laser spot was an ellipse having a long axis in the scanning direction, and the ellipticity was varied in the range of 1.1 to 12 for each sample.

After the laser irradiation, each sample was subjected to strain relief annealing at 800° C. for 3 hours in a nitrogen atmosphere. Then, B ₈ and W _17/50 were measured for each sample by the Epstein method described in JIS C2550. Further, for each sample, ΔB ₈ (=[B ₈ measured in the sample after laser irradiation (hereinafter also referred to as the sample after irradiation)]−[Sample before laser irradiation (hereinafter, the sample before irradiation B ₈ ]) measured in (also referred to as ) was calculated. Also, in the same manner as in Experiment 1, the magnetostriction harmonic MHL _15/50 , which is an index of magnetostriction characteristics, was obtained for each sample after irradiation.

Next, for each irradiated sample, a depth profile of the groove was created from the surface using a laser microscope, and the width W of the groove, the depth d of the deepest point of the groove, and the number N of the minimum values were measured. The number of maximum values is N-1. When there is no groove, that is, when the surface of the steel plate is flat, the number of minimum and maximum values of the groove is zero. A method for measuring the depth profile of the groove will be described later.

14 to 16 show the above measurement results plotted against d/W×100(%) for each number N of local minimum values.
Here, FIG. 14 shows the relationship between d/W×100 and iron loss W _17/50 (of the sample after irradiation).
FIG. 15 shows the relationship between d/W×100 and magnetostriction harmonic MHL _15/50 .
FIG. 16 shows the relationship between d/W×100 and _ΔB8 .

From FIG. 14, when d/W×100 is 5% or more, there is a tendency that a high iron loss improvement effect is obtained. The inventors believe that the reason for this is that the slope of the groove defined by the molten solidified portion approaches vertical, or the groove is formed to a great depth, thereby increasing the number of magnetic poles generated on the wall surface. Also, it can be seen that as the number N of the minimum values increases, particularly when it is 2 or more, a high iron loss improvement effect can be obtained. The inventors believe that the reason for this is that a larger stress remains inside the steel sheet due to the complicated shape of the solidified portion of the molten portion, and the closure domain can be maintained up to a higher magnetic field.

From FIG. 15, when d/W×100 is 20% or more, the magnetostriction harmonic MHL _15/50 tends to increase. In particular, this tendency becomes more pronounced as the number N of local minimum values increases. The inventors believe that the reason for this is that as the shape of the melt-solidified portion becomes more complicated, more stress remains inside the steel sheet, and more closure domains are generated.

It can be seen from FIG. 16 that ΔB ₈ , which is an index of permeability change, is hardly affected by d/W×100 and the number N of local minimum values.

From the above results, in order to achieve high low core loss, low magnetostriction, and high magnetic permeability even after strain relief annealing, d/W×100 should be 5% or more and less than 20%, and the minimum value It is preferable that the number N is two or more. d/W×100 is more preferably 7% or more. d/W×100 is more preferably 18% or less.

(Experiment 4)
A plurality of samples having the same shape were cut out from a grain-oriented electrical steel sheet (steel strip) manufactured by a general manufacturing process, and B ₈ and W _17/50 were measured by the Epstein method described in JIS C2550. B ₈ and W _17/50 measurements were 1.9350 T and 0.880 W/kg, respectively. Next, each sample was irradiated with a laser across the rolling direction, and the sample was locally melted and solidified to form a linear melt-solidified portion and a groove defined by the melt-solidified portion on the surface of the sample. The power density of the laser was adjusted so that the deepest position of ΔE≦−2 was 20 μm, the number N of minimum values in the depth profile of the groove was 2, and d/W×100 was 10%. The power density of the laser is expressed as P/(v·Φ) using the deflection velocity v, the spot diameter Φ in the direction perpendicular to the scanning direction, and the laser output P. A single-mode fiber laser was used as the laser source, and no assist gas was used. In addition, the interval of laser irradiation in the rolling direction was varied in the range of 0.5 to 7.0 mm for each sample. Regarding the laser, a diffractive optical element is used to set the shape of the laser spot to a line segment shape in which the scanning direction is the extension direction, and Ll/Lw, which is the ratio of the line segment length Ll to the spot width Lw in the rolling direction, is set to 1.5. Irradiation was carried out with various changes in the range of 1-6.

After the laser irradiation, each sample was subjected to strain relief annealing at 800° C. for 3 hours in a nitrogen atmosphere. Then, B ₈ and W _17/50 were measured for each sample by the Epstein method described in JIS C2550. Further, for each sample, ΔB ₈ (=[B ₈ measured in the sample after laser irradiation (hereinafter also referred to as the sample after irradiation)]−[Sample before laser irradiation (hereinafter, the sample before irradiation B ₈ ]) measured in (also referred to as ) was calculated. Also, in the same manner as in Experiment 1, the magnetostriction harmonic MHL _15/50 , which is an index of magnetostriction characteristics, was obtained for each sample after irradiation.

17 to 19 show the above measurement results plotted against the interval in the rolling direction of laser irradiation, that is, the interval in the rolling direction of the melted and solidified portions (hereinafter also referred to as the interval between the melted and solidified portions).
Here, FIG. 17 shows the relationship between the interval between molten solidified portions and the iron loss W _17/50 (of the sample after irradiation).
FIG. 18 shows the relationship between the distance between the melted solidified parts and the magnetostrictive harmonics MHL _15/50 .
FIG. 19 shows the relationship between the distance between molten solidified portions and _ΔB8 .

From FIG. 17, there is a tendency that the smaller the interval between the molten solidified portions, the higher the effect of improving the iron loss. The inventors believe that the reason for this is that the area of the interface between the melt-solidified portion and the closure domain and the main magnetic domain increases as the space between the melt-solidified portions becomes smaller, and the total amount of magnetic poles increases.

As can be seen from FIG. 18, the magnetostrictive harmonic MHL _15/50 tends to increase as the distance between the molten solidified portions decreases. The inventors believe that the reason for this is that magnetostriction oscillation becomes more complicated as the total amount of closure domains increases.

From FIG. 19, it can be seen that ΔB ₈ , which is an index of the change in magnetic permeability, is hardly affected by the distance between the melted and solidified portions.

From the above results, in order to achieve high low iron loss, low magnetostriction, and high magnetic permeability even after strain relief annealing, it is preferable to set the interval between the molten solidified parts to 1.0 mm or more and less than 5.0 mm. . The interval between the melted and solidified parts is more preferably 2.0 mm or more. The interval between the melted and solidified parts is more preferably 4.0 mm or less.

式（２）～（４）中、σ_ＲＤ、σ_ＴＤおよびσ_ＮＤはそれぞれ、圧延方向、板幅方向および板厚方向の残留応力である。ε_ＲＤ、ε_ＴＤおよびε_ＮＤはそれぞれ、圧延方向、板幅方向および板厚方向の歪みである。
なお、方向性電磁鋼板の圧延方向断面における異方性エネルギーの分布などの測定、および、後述する溝部の形状（深度プロファイル）に係る測定は、板幅中心位置で行えばよく、特に断りがなければ、板幅中心位置で測定したものである。 Next, a grain-oriented electrical steel sheet according to one embodiment of the present invention completed based on the above experimental results will be described.
A grain-oriented electrical steel sheet according to one embodiment of the present invention has linear molten solidified portions periodically crossing the rolling direction on one surface thereof,
In the distribution of anisotropic energy in the thickness direction from the surface of the melt-solidified portion in the cross section of the grain-oriented electrical steel sheet in the rolling direction, the deepest position of the region where ΔE (KJ/m ³ ) is negative is the melt The distance from the surface of the solidified portion is 4 μm or more.
Here, ΔE is defined by the following equation (1).
ΔE=E _sub -E _RD (1)
In formula (1), E _RD (KJ/m ³ ) and E _sub (KJ/m ³ ) are the anisotropic energy in the rolling direction and the crystal when the [001] orientation of the crystal is the rolling direction. is the anisotropic energy in the [010] orientation or [100] orientation of , which is obtained by the following equations (2) to (4).

In equations (2) to (4), σ _RD , σ _TD and σ _ND are the residual stresses in the rolling direction, strip width direction and strip thickness direction, respectively. ε _RD , ε _TD and ε _ND are the strains in rolling direction, width direction and thickness direction, respectively.
The measurement of the distribution of anisotropic energy in the cross section of the grain-oriented electrical steel sheet in the rolling direction, and the measurement of the groove shape (depth profile) described later, may be performed at the center position of the sheet width unless otherwise specified. For example, it is measured at the strip width center position.

First, it is important that the grain-oriented electrical steel sheet according to one embodiment of the present invention has a linear melt-solidified portion crossing the rolling direction on one surface thereof. Here, the melt-solidified portion is a region where the base material of the grain-oriented electrical steel sheet is melted by heat and then cooled and solidified. Also, a heat-affected zone is usually formed adjacent to the melt-solidified zone. Note that the melt-solidified portion is defined as follows. That is, the grain-oriented electrical steel sheet is cut so that the cross section in the rolling direction of the grain-oriented electrical steel sheet becomes the cut surface. Then, the cut surface is subjected to non-strain polishing. Next, the polished surface is analyzed for crystal orientation difference by EBSD (Electron Backscatter Diffraction), and a KAM (Karnel Average Misorientation) value is measured. Then, the region where the KAM value is 3.0 ° or more is the melt-solidified region, and the region where the elastic strain remains in the strain distribution analyzed by the EBSD Wilkinson method described later and the KAM value is the region where the heat-affected zone is less than 3.0 °. , and other regions (regions where elastic strain does not remain and where the KAM value is less than 3.0°) are defined as base material portions.

In addition, in the non-heat-resistant magnetic domain refining technology as described in Patent Document 2, thermal strain introduced into the steel sheet due to non-heat-resistant magnetic domain refining by strain relief annealing, and the residual stress inside the steel plate due to the thermal strain is reduced. To be released. In contrast, in the grain-oriented electrical steel sheet according to one embodiment of the present invention, the residual stress inside the steel sheet caused by the melt-solidified portion is maintained even after the strain relief annealing is performed.
The inventors consider the reason as follows.
That is, when a steel plate is locally heated and melted, it is rapidly cooled and solidified from a molten metal state. It is presumed that through this process, the solidification was completed before the strain due to the phase transformation of the molten portion was fully eliminated. In particular, it is believed that such a residual strain increases when the melt-solidified portion has a complicated shape in which the depth profile of the groove defined by the melt-solidified portion has a plurality of minimum values.

In the grain-oriented electrical steel sheet according to one embodiment of the present invention, the deepest position where ΔE<0 is set to a distance of 4 μm or more (in the sheet thickness direction) from the surface of the melt-solidified portion. It is necessary that the negative region extends to a depth of 4 μm or more from the surface of the molten solidified portion.

Deepest position of ΔE<0: 4 μm or more from the surface of the molten solidified portion From the above experimental results, the deepest position of ΔE<0 must be 4 μm or more from the surface of the molten solidified portion. . The preferred range of the deepest position for ΔE<0 is as shown in the experimental results described above.

The preferred range of the deepest position for ΔE≦−2 is also as shown in the experimental results described above. The deepest position of ΔE≦−2 is most preferably 4 μm to 40 μm in distance from the surface of the melt-solidified portion (in the plate thickness direction).

Here, the deepest position of ΔE<0 and the deepest position of ΔE≦−2 are obtained from the anisotropic energy distribution in the plate thickness direction from the surface of the melt-solidified portion in the cross section of the grain-oriented electrical steel sheet in the rolling direction. The anisotropic energy at each position in the anisotropic energy distribution is basically calculated at a pitch of 1 μm. However, the anisotropic energy may be calculated with a larger pitch, for example, a pitch of 5 to 10 μm, for regions where a certain tendency can be grasped.

For example, in the anisotropic energy distribution, if ΔE from the surface of the melt-solidified portion to a depth of 10 μm is negative and ΔE at a depth of 11 μm is positive, the deepest position where ΔE < 0 is 10 μm. Similarly, if the ΔE from the surface of the molten solidified portion to a depth of 10 μm is −2 KJ/m ³ or less, and the ΔE at a depth of 11 μm is −1 KJ/m ³ , then ΔE≦−2. The deepest position of is 10 μm.

In addition, the distribution of anisotropic energy in the thickness direction from the surface of the melt-solidified portion in the cross section of the grain-oriented electrical steel sheet in the rolling direction (ΔE at various depth positions) is the rolling direction cross section of the grain-oriented electrical steel sheet. It is created using the above equations (1) to (4) from the strain distribution (ε _RD , ε _TD and ε _ND at various depth positions) in the plate thickness direction from the surface of the melt-solidified portion at . Also, the strain distribution (ε _RD , ε _TD and ε _ND at various depth positions) from the surface of the melt-solidified portion in the cross section in the rolling direction of the grain-oriented electrical steel sheet to the plate thickness direction is determined by the EBSD Wilkinson method. In the EBSD Wilkinson method, a cross section of a grain-oriented electrical steel sheet in the rolling direction is irradiated with an electron beam, and a Kikuchi pattern is obtained for each measurement point. Then, using the no-strain point as a reference point, the strain amount is calculated from the deformation amount of the Kikuchi pattern at each measurement point using analysis software such as CrossCourt. If there is a groove defined by the melt-solidified portion, the strain distribution in the plate thickness direction from the deepest point of the groove in the cross section in the rolling direction should be measured to create the anisotropic energy distribution. When there is no groove (the surface of the steel sheet is flat), the strain distribution in the thickness direction from the center of the width of the surface of the melt-solidified portion in the rolling direction is measured, and the anisotropic energy distribution is calculated. Just create it.

Moreover, the grain-oriented electrical steel sheet according to one embodiment of the present invention preferably has grooves defined by the melt-solidified portion. As shown in FIG. 1, even when there are two minimum values in the depth profile of the groove, the groove is defined by one molten solidified portion (the wall surface, bottom (trough) and peak of the groove are ), it shall be regarded as one groove.

Here, the shape of the groove is preferably such that the depth d of the deepest point of the groove is less than 8 μm in the depth profile of the groove. The reason is as shown in the experimental results described above. Moreover, the more preferable range of the depth d of the deepest point of the groove is also as shown in the experimental results described above.

In addition, in the depth profile of the groove, there are two or more minimum values, and d/W × 100 (%), which is the ratio of the depth d of the deepest point of the groove to the width W of the groove, is 5% or more and less than 20%. Preferably. The reason is as shown in the experimental results described above. Also, the number of minimum values N and the more preferable range of d/W×100(%) are as shown in the experimental results described above.

Here, the depth profile of the groove is created as follows.
That is, the surface of the grain-oriented electrical steel sheet is observed using a laser microscope, and the depth of the groove is continuously measured at 1 μm pitch along the direction perpendicular to the stretching direction of the melt-solidified portion. Then, in the plate thickness direction, the side where the groove (melt-solidified part) exists is +, the opposite side is -, and the steel plate surface level is 0, and the measured depth of the groove is smoothed by the three-point moving average method (smoothing). and then plotted to create a groove depth profile. Then, from the created depth profile of the groove portion, the points having the minimum value and the maximum value are determined, and the number of points having the minimum value and the maximum value is obtained. Also, in the depth profile of the groove, the distance from the steel plate surface at the point that takes the minimum value is defined as the depth d of the deepest point of the groove.

In addition, the width W of the groove is measured as the distance between the groove ends in the direction perpendicular to the extension of the melt-solidified portion at the position level of the steel plate surface, as shown in FIG. FIG. 20 is a schematic diagram showing an example of the cross-sectional shape of the melt-solidified portion (groove), and the direction perpendicular to the paper surface is the extension direction of the melt-solidified portion (groove).

In addition, it is preferable that the maximum value of the depth profile of the groove is less than 0 μm, that is, the melt-solidified portion does not protrude from the steel plate surface. The reason for this is that if the melt-solidified portion protrudes outward in the plate thickness direction from the surface of the steel plate, when the grain-oriented electrical steel plates are laminated as a transformer core, the lamination factor will decrease and the steel plate on the upper surface of the lamination will be damaged. This is because distortion is introduced to the core, which causes iron loss and deterioration of noise. Also, the maximum value of the depth profile of the groove is preferably greater than −d (μm), more preferably −d/2 (μm) or more.

Furthermore, it is preferable that the distance between the melted and solidified portions is 1.0 mm or more and less than 5.0 mm. The reason is as shown in the experimental results described above. Moreover, the more preferable range of the interval between the molten solidified portions is also as shown in the experimental results described above.

Here, the interval between the melted and solidified portions is the center-to-center distance between the melted and solidified portions in the rolling direction.

Also, the more the direction of elongation of the molten solidified portion is tilted from the plate width direction (the direction perpendicular to the rolling direction), the fewer magnetic poles appear at the interface between the closure magnetic domain and the main magnetic domain, and the magnetic domain refining effect tends to deteriorate. Therefore, the angle formed by the stretching direction of the molten solidified portion and the plate width direction is preferably within ±30°.

In addition, although the chemical composition of the grain-oriented electrical steel sheet according to one embodiment of the present invention is not particularly limited, for example, as a suitable chemical composition,
C: 50 mass ppm or less,
Si: 2.0 to 8.0% by mass,
Mn: 0.005 to 1.0% by mass,
Al: 0.065% by mass or less,
N: 0.0120% by mass or less,
S: 0.030% by mass or less and Se: 0.030% by mass or less,
optionally,
Ni: 1.50% by mass or less, Sn: 1.50% by mass or less, Sb: 1.50% by mass or less, Cu: 3.0% by mass or less, P: 0.50% by mass or less, Mo: 0.10 % by mass or less, and Cr: containing 1 or more selected from 1.50 mass % or less,
A component composition in which the remainder is Fe and unavoidable impurities can be exemplified. The preferred content of each element will be described below.

C: 50 mass ppm or less C can be contained in the slab to improve the structure of the hot-rolled sheet. However, in order to avoid the occurrence of magnetic aging during the manufacturing process, the C content contained in the slab is preferably reduced to 50 ppm by mass or less by decarburization annealing, and the C content of the grain-oriented electrical steel sheet, which is the final product, is reduced. The content is also equivalent to this. Therefore, the C content is preferably 50 ppm by mass or less. In addition, the lower limit of the C content is not particularly limited, and may be 0 mass ppm.

Si: 2.0 to 8.0% by mass
Si is an effective element for increasing the electric resistance of steel and improving iron loss. Therefore, it is preferable that the Si content is 2.0% by mass or more. However, if the Si content exceeds 8.0% by mass, there is a risk of deterioration in workability and board threadability, and a decrease in magnetic flux density. Therefore, the Si content is preferably in the range of 2.0 to 8.0% by mass.

Mn: 0.005 to 1.0% by mass
Mn is an element useful for improving hot workability. Therefore, the Mn content is preferably 0.005% by mass or more. On the other hand, if the Mn content exceeds 1.0% by mass, the magnetic flux density may decrease. Therefore, the Mn content is preferably in the range of 0.005 to 1.0% by mass.

Al: 0.065% by mass or less, N: 0.0120% by mass or less, S: 0.030% by mass or less, and Se: 0.030% by mass or less As described later, the chemical composition of the grain-oriented electrical steel sheet slab is , It may be a chemical composition that uses an inhibitor or a chemical composition that does not use an inhibitor. % or less, N: 0.0120 mass % or less, S: 0.030 mass % or less, and Se: 0.030 mass % or less. Also, even if the component composition utilizes an inhibitor, the inhibitor component is removed when purification is performed in the final annealing. Therefore, the contents of these elements are more preferably Al: 0.010% by mass or less, N: 0.0050% by mass or less, S: 0.0050% by mass or less, and Se: 0.0050% by mass or less. is. In addition, the lower limit of the content of these elements is not particularly limited, and may be 0% by mass.

As optional additive components, Ni: 1.50% by mass or less, Sn: 1.50% by mass or less, Sb: 1.50% by mass or less, Cu: 3.0% by mass or less, P: 0.50% by mass or less, One or more selected from Mo: 0.10% by mass or less and Cr: 1.50% by mass or less Ni is an effective element for improving the structure of the hot-rolled sheet and improving the magnetic properties. . Therefore, when Ni is contained, the content is preferably 0.03% by mass or more. However, if the Ni content exceeds 1.50% by mass, secondary recrystallization may become unstable and the magnetic properties may deteriorate. Therefore, when Ni is contained, the content is preferably 1.50% by mass or less.

Sn, Sb, Cu, P, Mo and Cr are also elements that improve magnetic properties. Therefore, when these elements are contained, Sn: 0.01% by mass or more, Sb: 0.005% by mass or more, Cu: 0.03% by mass or more, P: 0.03% by mass or more, Mo: 0.005% by mass or more and Cr: 0.03% by mass or more are preferable. However, Sn: more than 1.50 mass%, Sb: more than 1.50 mass%, Cu: more than 3.0 mass%, P: more than 0.50 mass%, Mo: more than 0.10 mass%, and Cr : When it exceeds 1.50% by mass, the growth of secondary recrystallized grains is suppressed, so that the magnetic properties may deteriorate. Therefore, when these elements are contained, Sn: 1.50% by mass or less, Sb: 1.50% by mass or less, Cu: 3.0% by mass or less, P: 0.50% by mass or less, Mo: 0.5% by mass or less, 10% by mass or less and Cr: 1.50% by mass or less are preferred.

Elements other than the above are Fe (iron) and unavoidable impurities.

Although the thickness of the grain-oriented electrical steel sheet according to the embodiment of the present invention is not particularly limited, it is preferably 0.15 mm or more and 0.30 mm or less.

In addition, in the grain-oriented electrical steel sheet according to one embodiment of the present invention, "having low core loss, high magnetic permeability, and good magnetostrictive properties" means W _17/50 , ΔB ₈ and MHL _{15/ 50} respectively means that the acceptance criteria of the examples described later are satisfied at the same time.

Next, an example of a method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention will be described.

A steel material (slab) for a grain-oriented electrical steel sheet is subjected to hot rolling to obtain a hot-rolled steel strip. Then, the hot-rolled steel strip is subjected to hot-rolled sheet annealing. Then, the hot-rolled steel strip is cold-rolled once or twice or more to finish a cold-rolled steel strip (hereinafter also referred to as a steel strip) having a final thickness. Then, the steel strip is subjected to decarburization annealing and coated with an annealing separator containing MgO as a main component. The steel strip is then coiled and subjected to final annealing for the purpose of secondary recrystallization and formation of a forsterite coating. After flattening annealing is applied to the steel strip after the final annealing, a magnesium phosphate-based tension film is formed to form a steel strip or a grain-oriented electrical steel sheet as a product. The conditions for hot rolling, hot-rolled sheet annealing, cold rolling, decarburizing annealing, final annealing, and flattening annealing are not particularly limited, and conventional methods may be followed.

In addition, the chemical composition of the steel material (slab) of the grain-oriented electrical steel sheet is not particularly limited as long as it is a chemical composition that causes secondary recrystallization, but the above-mentioned suitable chemical composition of the grain-oriented electrical steel sheet can be obtained. A component composition is preferred.
for example,
C: 0.08% by mass or less,
Si: 2.0 to 8.0% by mass,
Mn: 0.005 to 1.0% by mass
Al: 0.065% by mass or less,
N: 0.0120% by mass or less,
S: 0.030% by mass or less and Se: 0.030% by mass or less,
optionally,
Ni: 1.50% by mass or less, Sn: 1.50% by mass or less, Sb: 1.50% by mass or less, Cu: 3.0% by mass or less, P: 0.50% by mass or less, Mo: 0.10 % by mass or less, and Cr: containing 1 or more selected from 1.50 mass % or less,
A component composition in which the remainder is Fe and unavoidable impurities can be exemplified.

In the above component composition, when using an inhibitor, for example, when using an AlN-based inhibitor, Al and N may be contained, and the preferred contents of Al and N are as follows. .
Al: 0.010 to 0.065% by mass
N: 0.0050 to 0.0120% by mass
In the case of using an MnS/MnSe-based inhibitor, Se and/or S may be contained in addition to the above Mn, and the preferred contents of S and Se are as follows.
S: 0.005 to 0.030% by mass
Se: 0.005 to 0.030% by mass
Both the AlN-based inhibitor and the MnS/MnSe-based inhibitor may be used together.

Moreover, when the inhibitor is not used, the preferred contents of Al, N, S and Se are as follows.
Al: 0.010% by mass or less N: 0.0050% by mass or less S: 0.0050% by mass or less Se: 0.0050% by mass or less

Also, C can be contained in the slab to improve the structure of the hot-rolled sheet. However, in order to avoid the occurrence of magnetic aging during the manufacturing process, it is preferable to reduce the C content contained in the slab to 50 mass ppm or less by decarburization annealing. Therefore, the C content is preferably 0.08% by mass or less. Since secondary recrystallization occurs even if C is not contained, the lower limit of the C content is not particularly limited, and may be 0% by mass.

The reason for limiting the elements other than the above is basically the same as the chemical composition of the grain-oriented electrical steel sheet described above, so the explanation is omitted here.

Then, in any of the steps after the cold rolling described above, or during any of the steps, the surface of the grain-oriented electrical steel sheet (or steel strip) is subjected to a process for forming a melt-solidified portion. The method for forming the melt-solidified portion is not particularly limited as long as it can form the above-described melt-solidified portion. Hereinafter, (A) suitable conditions for electron beam irradiation and (B) suitable conditions for laser irradiation will be described.

(A) Suitable Conditions for Electron Beam Irradiation To form a melt-solidified portion on the surface of a grain-oriented electrical steel sheet, for example, it is effective to use an electron beam with high penetrability. In particular, the temperature of the base material is raised above its melting temperature at the irradiation part of the energy beam, and the base material is melted to a certain depth. It is necessary to control the conditions. In such control, for example, the beam power density is adjusted in the range of 0.1 to 1.0 (J/mm ² ) according to the steel type and thickness of the grain-oriented electrical steel sheet, and each of the following It can be carried out by adjusting the conditions within the ranges shown below. In the case of an electron beam, the power density of the beam is calculated as P/(v·Φ) using the deflection velocity v, the spot diameter Φ in the direction perpendicular to the scanning direction, and the electron beam power P. Further, the electron beam output P is calculated by multiplying the acceleration voltage by the beam current. In addition, in the grain-oriented electrical steel sheet having the chemical composition used in the examples described later, the melt-solidified portion can be formed in the range of 0.1 ≤ P (J/mm ² ) ≤ 0.5, and 0.5 < P ≤ A melt-solidified portion and a groove defined by the melt-solidified portion could be formed in the range of 1.0 (J/mm ² ). However, even if the electron beam output P is within the above range, the amount of heat input and temperature history will change depending on the deflection velocity v, the electron beam output P, the steel type and thickness of the grain-oriented electrical steel sheet, and so on. There are cases where only strain is introduced and no solidification is formed, or the molten metal is vaporized and no solidification is formed. Therefore, for example, it is preferable to perform a preliminary irradiation test or the like to determine in advance appropriate irradiation conditions according to the steel type and thickness of the grain-oriented electrical steel sheet (the same applies to laser irradiation, which will be described later). .

Further, the formation of the groove defined by the molten solidified portion and the control of the shape of the groove are performed by adjusting the output density as described above, and furthermore, the elliptical shape and line segment shape having the major axis in the scanning direction. , by adjusting the spot shape to have a dot-sequence-shaped beam energy distribution. As a result, even higher effects can be expected.

• Acceleration voltage: 60 kV or more and 300 kV or less A higher acceleration voltage is preferable because the straightness of the electrons increases and the thermal effect on the outside of the beam irradiation portion decreases. For this reason, the acceleration voltage is preferably 60 kV or higher. The acceleration voltage is more preferably 90 kV or higher, still more preferably 120 kV or higher. On the other hand, if the acceleration voltage is too high, it becomes difficult to shield the X-rays generated along with the electron beam irradiation. Therefore, from a practical point of view, it is preferable to set the acceleration voltage to 300 kV or less. The acceleration voltage is more preferably 200 kV or less.

・Beam current: 0.5 to 40mA
A smaller beam current is preferable from the viewpoint of the beam diameter. This is because when the current is increased, the beam diameter tends to widen due to Coulomb repulsion. Therefore, the beam current is preferably 40 mA or less. On the other hand, if the beam current is too small, there may be insufficient energy to create strain. Therefore, the beam current is preferably 0.5 mA or more.

・Degree of Vacuum in Beam Irradiation Area An electron beam is scattered by gas molecules, resulting in an increase in beam diameter and halo diameter and a decrease in energy. Therefore, it is preferable that the degree of vacuum in the beam irradiation region is high, and the pressure is preferably 3 Pa or less. There is no particular lower limit, but if it is excessively lowered, the cost of vacuum systems such as vacuum pumps will increase. Therefore, in practice, it is preferable to set the pressure to 1×10 ⁻⁵ Pa or more.

• Spot diameter in the direction orthogonal to scanning: 300 µm or less The smaller the spot diameter, the more preferable it is so that distortion can be introduced locally. Therefore, the spot diameter of the energy beam in the scanning orthogonal direction is preferably 300 μm or less. The spot diameter of the energy beam in the scanning orthogonal direction is more preferably 280 μm or less, still more preferably 260 μm or less. Although the lower limit of the spot diameter of the energy beam in the scanning orthogonal direction is not particularly limited, the spot diameter of the energy beam in the scanning orthogonal direction is preferably 50 μm or more, for example. Note that the spot diameter refers to the full width at half maximum of the beam profile obtained by the slit method using a slit with a width of 30 μm.

・Ratio of the spot diameter in the scanning direction to the spot diameter in the orthogonal scanning direction (=[spot diameter in the scanning direction (μm)]÷[spot diameter in the orthogonal scanning direction (μm)]): more than 1 and 20 or less Spot in the orthogonal scanning direction As the ratio of the spot diameter in the scanning direction to the diameter (hereinafter also referred to as the spot diameter ratio) approaches 1, the amount of heat input to the spot increases, making it easier to melt the base material steel plate. However, due to the concentration of the heat input region, spatters are likely to scatter, and there is a possibility that the lamination factor when laminated as an iron core may deteriorate. In addition, the depth of the groove may become excessive. Therefore, the spot diameter ratio is preferably greater than 1, more preferably 1.5 or more, and even more preferably 2 or more. On the other hand, as the spot diameter ratio increases, the heat input area increases. As a result, spatter scattering can be suppressed, but the heat input energy required for melting the steel plate increases. In this case, there is concern about an increase in the load on the transport system in the case of a laser, and an increase in power source capacity in the case of an electron beam. Therefore, the spot diameter ratio is preferably 20 or less.

As a method for realizing such a spot shape, for example, in the case of an electron beam, different spot diameters can be obtained by adjusting the magnetic field distribution in the direction in which the Lorentz force is applied in the scanning direction and the scanning orthogonal direction in the converging coil. It can converge to a spot shape.
In the case of a laser, a cylindrical lens is installed on the beam path to adjust the spread of the beam in the scanning direction and the scanning orthogonal direction to create an elliptical shape, or a diffraction optical element (diffractive optical element) is placed on the beam path. , and the beam is condensed into an elliptical shape, a line segment shape, or a point sequence shape.

・Deflection speed: 5 to 400m/sec
The slower the deflection speed of the energy beam, the greater the amount of heat incident per unit length of the steel plate. However, if the deflection speed of the energy beam is excessively slowed down, spatters may adhere to the surface of the steel sheet due to scattering of the metal vapor, degrading the space factor when the iron core is laminated. In addition, the depth of the groove may become excessive. Therefore, the deflection speed of the energy beam is preferably 5 m/sec or more. The deflection speed of the energy beam is more preferably 8 m/sec or more, still more preferably 10 m/sec or more. On the other hand, if the deflection speed of the energy beam is excessively increased, a power supply capacity is required to provide the heat input necessary for melting the steel sheet, resulting in an increase in the size of the equipment. Therefore, the deflection speed of the energy beam is preferably 400 m/sec or less.

(B) Suitable Conditions for Laser Irradiation In order to form a melt-solidified portion on the surface of a grain-oriented electrical steel sheet, for example, it is effective to use a laser with a wavelength of 400 nm to 1200 nm, which is highly absorptive to metals. be. In particular, the temperature of the base material is raised above its melting temperature at the irradiation part of the energy beam, and the base material is melted to a certain depth. It is necessary to control the conditions. Such control is adjusted, for example, in the range of 0.1 to 1.0 (J/mm ² ) according to the steel type and thickness of the grain-oriented electrical steel sheet, and the conditions shown below are set as follows. It can be implemented by adjusting each range. In the case of a laser, the power density of the beam is expressed as P/(v·Φ) using the scanning speed (deflection speed) v, the spot diameter Φ, and the laser output P.

Further, the formation of the groove defined by the molten solidified portion and the control of the shape of the groove are performed by adjusting the output density as described above, and furthermore, the elliptical shape and line segment shape having the major axis in the scanning direction. , by adjusting the spot shape so as to have a dot-sequence-shaped beam energy distribution, and by this, a higher effect can be expected.

- Laser output: 50 W or more and 5000 W or less When the output of the laser becomes low, it is necessary to slow down the scanning speed in order to melt the steel plate as the base material. However, if the scanning speed is excessively slowed down, spatter will scatter on the steel sheet, resulting in a decrease in the space factor and deterioration in manufacturing efficiency. There is also the possibility that the molten metal will evaporate and the grooves will become excessively deep. On the other hand, a higher laser power facilitates the melting of the steel sheet. However, the damage to the laser transport system increases, and there is a risk of lowering production efficiency due to an increase in maintenance frequency. Therefore, the output of the laser is preferably 50 W or more and 5000 W or less.

Note that the spot diameter in the direction perpendicular to the scanning direction, the ratio of the spot diameters, and the preferred range of the scanning speed (deflection speed) are the same as the preferred conditions for (A) electron beam irradiation, so description thereof will be omitted here. .

The conditions for stress relief annealing performed after bending the grain-oriented electrical steel sheet include, for example, a nitrogen atmosphere, a treatment temperature of 800° C., and a treatment time of 3 hours. The grain-oriented electrical steel sheet according to one embodiment of the present invention has low iron loss even in strain relief annealing, and has high magnetic permeability and good magnetostrictive properties, so it is suitable for transformers, particularly wound core transformers. It can be used very advantageously as an iron core material.

Conditions other than those described above are not particularly limited, and conventional methods may be followed.

Next, the present invention will be specifically described based on examples. The following example shows a preferred example of the present invention, and is not limited by this example. Modifications can be made within the scope of the present invention, and such modes are also included in the technical scope of the present invention.

・Example 1
A slab of a grain-oriented electrical steel sheet having the chemical composition shown in Table 1 (the balance being Fe and unavoidable impurities) was subjected to hot rolling to obtain a hot-rolled steel strip. Then, the hot-rolled steel strip was subjected to hot-rolled sheet annealing. Then, the hot-rolled steel strip was cold-rolled twice with intermediate annealing to obtain a cold-rolled steel strip (hereinafter also referred to as steel strip) having a thickness of 0.23 mm. Then, the steel strip was subjected to decarburization annealing and coated with an annealing separator containing MgO as a main component. The steel strip was then coiled and subjected to final annealing for the purpose of secondary recrystallization and formation of a forsterite coating.

Then, after the steel strip was flattened and annealed, one surface of the steel strip was irradiated with an electron beam or laser to form a linear melt-solidified portion. At this time, the irradiation conditions, specifically, the power density (accelerating voltage, beam current, laser output and deflection speed) were variously changed. The spot shape was elliptical, and the spot diameter ratio was varied. Both electron beam and laser irradiation were performed at intervals of 4 mm in the rolling direction. In addition, a beam non-irradiation region was provided in a part of the steel strip.

Next, a magnesium phosphate-based tension film was formed on the steel strip to obtain a steel strip (grain-oriented electrical steel sheet) as a final product. In addition, conditions other than those specified in each of the above steps were carried out according to conventional methods. In addition, the chemical compositions of the steel strips as final products all satisfied the preferred chemical compositions of the grain-oriented electrical steel sheets according to the above-described embodiments of the present invention.

The steel strip thus obtained was subjected to a heat treatment simulating strain relief annealing (nitrogen atmosphere, treatment temperature: 800°C, treatment time: 3 hours). Next, a sample was cut from the region where the linear melted solidified portion of the steel strip was formed, embedded in a mold, mirror-polished, and then the strain distribution in the cross section of the sample in the rolling direction was obtained by the EBSD Wilkinson method. Then, from the obtained strain distribution of each sample, ΔE is calculated using the above formulas (1) to (4) to create an anisotropic energy distribution, and the deepest position of ΔE < 0 for each sample, And the deepest position of ΔE≦−2 was obtained.

In addition, B ₈ and W _17/50 were measured for each sample by the Epstein method described in JIS C2550. Further, a reference sample (sample not subjected to magnetic domain refining treatment) was cut from the beam-non-irradiated region of the steel strip, and B ₈ and W _17/50 were measured by the Epstein method described in JIS C2550. Then, ΔB ₈ (=[B 8 measured with a sample cut from a region in which a linear molten solidified portion was formed in the steel strip]−[B ₈ measured with a reference sample]) was calculated as an index of the _change in magnetic permeability. .

In addition, the magnetostrictive vibration waveform of each sample was measured with a laser Doppler type magnetostrictive vibrometer when subjected to sinusoidal AC magnetization of 1.5 T and 50 Hz. Then, the measured magnetostrictive vibration waveform was subjected to Fourier decomposition into vibration acceleration components of frequencies every 100 Hz. Then, each frequency component was multiplied by 0 to 1000 Hz, which was corrected for audibility on the A scale, and the multiplied value was taken as magnetostriction harmonic MHL _15/50 , which is an index of magnetostriction characteristics.

Next, using each sample, a model transformer of a three-phase winding transformer (iron core weight: 500 kg) was manufactured, and the transformer core loss was measured when the magnetic flux density of the core leg portion was 1.7 T at a frequency of 50 Hz. . As for the iron loss of this transformer, the no-load loss was measured using a wattmeter. At the same time, this model transformer was excited in a soundproof room under conditions of a maximum magnetic flux density Bm of 1.7 T and a frequency of 50 Hz, and the noise level (dBA) of the transformer was measured using a sound level meter. Hereinafter, the noise level of the transformer is also referred to as transformer noise.

For comparison, a steel strip (No. 33) prepared without forming a melt-solidified portion (without performing magnetic domain refining treatment) and a steel strip (No. No. 34) was prepared, and W _17/50 , ΔB ₈ , MHL _15/50 , transformer iron loss and transformer noise were measured in the same manner as above. In addition, No. No groove was formed in any of the steel strips other than No. 34.

The above results are summarized in Table 2. The presence or absence of the molten solidified portion was confirmed by the method described above. The evaluation criteria for W _17/50 , ΔB ₈ , MHL _15/50 , transformer iron loss and transformer noise are as follows.
・W _17/50
◎ (Pass, particularly excellent): Iron loss improvement amount ΔW _17/50 is 0.08 W / Kg or more ○ (Pass, excellent): Iron loss improvement amount ΔW _17/50 is 0.05 W / Kg or more (in the case of ◎ except)
× (failed): Iron loss improvement amount ΔW _17/50 is less than 0.05 W/Kg Here, the iron loss improvement amount ΔW _17/50 is the iron loss improvement amount before and after the magnetic domain refining treatment. W _17/50 measured on the sample]−[W _17/50 measured on the sample].
・ΔB ₈
◎ (pass, particularly excellent): -0.0006 T or more ○ (pass, excellent): over -0.0010 T (except for the case of ◎)
× (failure): −0.0010 T or less Here, ΔB ₈ is the amount of change in B ₈ before and after the magnetic domain refining treatment, [B ₈ measured with the sample]−[B ₈ measured with the reference sample ].
・MHL _15/50
◎ (passed, particularly excellent): 26.0 dBA or less ○ (passed, excellent): 27.5 dBA or less (excluding the case of ◎)
× (failed): more than 27.5 dBA, transformer iron loss ◎ (passed, particularly excellent): iron loss improvement amount of transformer iron loss is 0.08 W/Kg or more ○ (passed, excellent): transformer iron loss Iron loss improvement amount of 0.05 W / Kg or more (except for the case of ◎)
× (failed): Iron loss improvement amount of transformer iron loss is less than 0.05 W/Kg Here, iron loss improvement amount of transformer iron loss is iron loss of transformer iron loss before and after magnetic domain refining treatment It is the amount of improvement, and is obtained as [W _17/50 measured with a model transformer made from a reference sample]−[W _17/50 measured with a model transformer made from the sample].
・Transformer noise ◎ (passed, particularly excellent): 32.0 dBA or less ○ (passed, excellent): 33.5 dBA or less (except for the case of ◎)
× (failed): over 33.5 dBA

As can be seen from Table 2, all of the invention examples achieved low core loss, high magnetic permeability, and good magnetostrictive properties. In addition, both the transformer core loss and the transformer noise measured with the model transformer produced from the samples of the invention examples were low and reached the targeted levels. Moreover, the invention examples in which the deepest position of ΔE≦−2 was 4 μm to 40 μm had particularly excellent characteristics.

On the other hand, in all of the comparative examples, low iron loss, high magnetic permeability, and good magnetostrictive properties could not be achieved.

(Example 2)
A slab of a grain-oriented electrical steel sheet having the chemical composition shown in Table 3 (the balance being Fe and unavoidable impurities) was subjected to hot rolling to obtain a hot-rolled steel strip. Then, the hot-rolled steel strip was subjected to hot-rolled sheet annealing. Then, the hot-rolled steel strip was cold-rolled twice with intermediate annealing to obtain a cold-rolled steel strip (hereinafter also referred to as steel strip) having a thickness of 0.23 mm. Then, the steel strip was subjected to decarburization annealing and coated with an annealing separator containing MgO as a main component. The steel strip was then coiled and subjected to final annealing for the purpose of secondary recrystallization and formation of a forsterite coating.

Then, after the steel strip was flattened and annealed, one surface of the steel strip was irradiated with a laser in the rolling direction to form a linear melt-solidified portion. At this time, the irradiation conditions, specifically, the power density (accelerating voltage, beam current, laser output and deflection speed) were variously changed. The spot shape was made into a line segment shape using a diffractive optical element, and the line segment length was adjusted to vary the spot diameter ratio. All the laser irradiations were performed at intervals of 0.5 to 7.0 mm in the rolling direction. In addition, a beam non-irradiation region was provided in a part of the steel strip.

Next, a magnesium phosphate-based tension film was formed on the steel strip to obtain a steel strip (grain-oriented electrical steel sheet) as a final product. In addition, conditions other than those specified in each of the above steps were carried out according to conventional methods. In addition, the chemical compositions of the steel strips as final products all satisfied the preferred chemical compositions of the grain-oriented electrical steel sheets according to the above-described embodiments of the present invention.

The steel strip thus obtained was subjected to a heat treatment simulating strain relief annealing (nitrogen atmosphere, treatment temperature: 800°C, treatment time: 3 hours). Then, in the same manner as in Example 1, an anisotropic energy distribution was created, and the deepest position of ΔE<0 and the deepest position of ΔE≦−2 of each sample were determined. Further, W _17/50 , ΔB ₈ , MHL _15/50 , transformer iron loss and transformer noise were measured for each sample in the same manner as in Example 1.

In addition, the depth profile of the groove of each sample was created in the manner described above, and the depth d (μm) of the deepest point of the groove, the number of minimum values N, and d/W×100 (%) were obtained.

Furthermore, for comparison, a steel strip (No. 58) prepared without forming a melt-solidified portion (without performing a magnetic domain refining treatment) and a steel strip (No. No. 59) was prepared, and W _17/50 , ΔB ₈ , MHL _15/50 , transformer core loss and transformer noise were measured in the same manner as above.

The above results are summarized in Table 4. The presence or absence of the molten solidified portion was confirmed by the method described above. The evaluation criteria for W _17/50 , ΔB ₈ , MHL _15/50 , transformer iron loss and transformer noise are the same as in Example 1, but the amount of change in iron loss ΔW _17/50 , ΔB ₈ , MHL _{15 /50} , transformer iron loss variation ΔW _17/50 , and transformer noise simultaneously satisfy the following ranges, it can be said that extremely excellent characteristics are obtained.
・ΔW _17/50 : 0.14 W/kg or more (especially 0.15 W/kg or more)
・ΔB ₈ : -0.0002T or more (especially -0.0001T or more)
・MHL _15/50 : 26.0dBA or less (especially 25.5dBA or less)
・Transformer iron loss ΔW _17/50 : 0.16 W/kg or more (especially 0.17 W/kg or more)
・Transformer noise: 32.0 dBA or less (especially 31.5 dBA or less)

As can be seen from Table 4, all of the inventive examples achieved low core loss, high magnetic permeability, and good magnetostrictive properties. In addition, both the transformer core loss and the transformer noise measured with the model transformer produced from the samples of the invention examples were low and reached the targeted levels. Furthermore, the deepest position of the region where ΔE (KJ/m ³ ) is −2 KJ/m ³ or less is 4 μm to 40 μm, the groove portion is defined by the molten solidified portion, and the depth d of the deepest point of the groove portion is It is less than 8.0 μm, the number of minimum values N is 2 or more, d/W×100 (%) is 5% or more and less than 20%, and the distance between molten solidified parts is 1.0 mm or more and less than 5.0 mm In the example of the invention which is, extremely excellent characteristics were obtained.

On the other hand, in all of the comparative examples, low iron loss, high magnetic permeability, and good magnetostrictive properties could not be achieved.

Claims (9)

A grain-oriented electrical steel sheet,
The grain-oriented electrical steel sheet has, on one surface thereof, cyclically linear melt-solidified portions crossing the rolling direction,
In the distribution of anisotropic energy in the thickness direction from the surface of the melt-solidified portion in the cross section of the grain-oriented electrical steel sheet in the rolling direction, the deepest position of the region where ΔE (KJ/m ³ ) is negative is the melt A grain-oriented electrical steel sheet having a distance of 4 μm or more from the surface of the solidified portion.
Here, ΔE is defined by the following equation (1).
ΔE=E _sub -E _RD (1)
In formula (1), E _RD (KJ/m ³ ) and E _sub (KJ/m ³ ) are the anisotropic energy in the rolling direction and the crystal when the [001] orientation of the crystal is the rolling direction. is the anisotropic energy in the [010] orientation or [100] orientation of , which is obtained by the following equations (2) to (4).

In equations (2) to (4), σ _RD , σ _TD and σ _ND are the residual stresses in the rolling direction, strip width direction and strip thickness direction, respectively. ε _RD , ε _TD and ε _ND are the strains in rolling direction, width direction and thickness direction, respectively. In the anisotropic energy distribution, the deepest position of the region where the ΔE (KJ/m ³ ) is −2 KJ/m ³ or less is 4 μm to 40 μm from the surface of the molten solidified portion. 2. The grain-oriented electrical steel sheet according to 1. The grain-oriented electrical steel sheet according to claim 1, having grooves defined by said melt-solidified portion. 3. The grain-oriented electrical steel sheet according to claim 2, having grooves defined by said melt-solidified portion. The grain-oriented electrical steel sheet according to claim 3, wherein in the depth profile of the groove, the depth d of the deepest point of the groove is less than 8.0 µm. The grain-oriented electrical steel sheet according to claim 4, wherein in the depth profile of the groove, the depth d of the deepest point of the groove is less than 8.0 µm. Two or more minimum values exist in the depth profile of the groove,
The direction according to any one of claims 3 to 6, wherein d/W x 100 (%), which is the ratio of the depth d of the deepest point of the groove to the width W of the groove, is 5% or more and less than 20%. magnetic steel sheet. The grain-oriented electrical steel sheet according to any one of claims 1 to 6, wherein the interval in the rolling direction between the molten solidified portions is 1.0 mm or more and less than 5.0 mm. The grain-oriented electrical steel sheet according to claim 7, wherein the intervals in the rolling direction of the molten solidified portions are 1.0 mm or more and less than 5.0 mm.

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