EP4707420A1

EP4707420A1 - Grain-oriented electromagnetic steel sheet and magnetic domain control method

Info

Publication number: EP4707420A1
Application number: EP24797206.0A
Authority: EP
Inventors: Masataka IWAKI; Tomohito Tanaka; Takashi Kataoka
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2023-04-27
Filing date: 2024-04-26
Publication date: 2026-03-11
Also published as: JPWO2024225463A1; KR20250171365A; CN121219430A; WO2024225463A1

Abstract

In a grain-oriented electrical steel sheet, in a cross section that is orthogonal to an extending direction of an irradiation trace of an energy ray, and is parallel to a sheet thickness direction, in a case where an imaginary line is drawn in the sheet thickness direction to include a position where compressive elastic stress measured by using EBSD is 20 MPa or more, the degree of change in the compressive elastic stress on the imaginary line is 4 MPa or less per 1 µm over the entire region in the sheet thickness direction.

Description

TECHNICAL FIELD

The present invention relates to a grain-oriented electrical steel sheet and a magnetic domain control method that is applicable in a process of manufacturing the grain-oriented electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2023-073595, filed April 27, 2023 , the content of which is incorporated herein by reference.

BACKGROUND ART

A grain-oriented electrical steel sheet is a soft magnetic material, and is mainly used as a core material of a transformer. Therefore, it is requested that the grain-oriented electrical steel sheet have magnetic characteristics such as a high magnetization characteristic and a low iron loss.
An iron loss is a power loss due to thermal energy consumption that occurs in a case where a core is excited by an AC magnetic field, and it is requested that the iron loss be as low as possible from the viewpoint of energy saving. A level of the iron loss is affected by magnetic susceptibility, a sheet thickness, coating tension, an impurity amount, electric resistivity, a crystal grain size, a magnetic domain size, or the like. Even at present when various techniques have been developed regarding the grain-oriented electrical steel sheet, research and development for reducing the iron loss is being continued in order to increase energy efficiency.
As an example of a method for reducing the iron loss, a technique for performing laser irradiation has been proposed. In this technique, it has been considered that an eddy-current loss can be reduced by performing laser irradiation to refine a magnetic domain width.
For example, Patent Document 1 discloses a method for manufacturing a grain-oriented electrical steel sheet for which a magnetic domain is controlled by irradiation with a laser beam, the method including a process of irradiating a surface of the grain-oriented electrical steel sheet with a condensed continuous wave laser beam while scanning the grain-oriented electrical steel sheet from a rolling direction toward an inclined direction of the grain-oriented electrical steel sheet, and a process of repeating while shifting a portion to be scanned with the continuous wave laser beam at predetermined intervals, in which when the average power of the continuous wave laser beam is expressed as P (W), speed of the scanning is expressed as Vc (mm/s), the predetermined interval is expressed as PL (mm), and an input energy Ua is defined in such a way that Ua = P/(Vc × PL) (mJ/mm²), 1.0 mm ≤ PL ≤ 3.0 mm, and 0.8 mJ/mm² ≤ Ua ≤ 2.0 mJ/mm² are satisfied.
Patent Document 1 describes that iron losses in both directions of an L direction and a C direction of the grain-oriented electrical steel sheet can be easily reduced while ensuring high productivity.
In addition, Patent Document 2 discloses a method for manufacturing a grain-oriented electrical steel sheet in which iron loss characteristics have been improved by performing scanning irradiation with a continuous oscillation laser beam to form a linear closure domain roughly perpendicularly to a rolling direction of a steel sheet and at roughly fixed intervals.
Patent Document 2 describes that a laser is in the TEM₀₀ mode in which a laser beam intensity profile in a cross section perpendicular to a beam propagation direction has a maximum intensity in the vicinity of the center of an optical axis, and a rolling-direction condensing diameter d [mm] of an irradiation beam, the scanning line velocity V [mm/s] of the laser beam, and an average power P [W] of the laser fall within ranges of 0 < d ≤ 0.2 and 0.001 ≤ P/V ≤ 0.012, so that a grain-oriented electrical steel sheet having a reduced iron loss is obtained.
Patent Document 3 discloses a method for improving an iron loss value of an electrical steel sheet by irradiating a surface of a grain-oriented electrical steel sheet with a continuous oscillation laser beam in a direction substantially perpendicular to a rolling direction, in which a circular spot of YAG condensed by a flat field lens is irradiated in such a way that predetermined conditions are satisfied, and an extremely low iron loss value is obtained.
Patent Document 4 discloses a grain-oriented electrical steel sheet manufacturing method for refining a magnetic domain of a grain-oriented electrical steel sheet in which a forsterite film is included on a surface of a steel sheet, a Se concentrated portion is included at least either inside the film or on an interface between the film and the steel sheet, and an existence rate of the concentrated portion is 2% or more per 10000 µm² of the surface of the steel sheet in terms of area fraction, by irradiating the grain-oriented electrical steel sheet with an electron beam under the conditions of diameter: 0.05 mm or more and 0.5 mm or less, scanning speed: 1.0 m/s or more, and acceleration voltage: 30 kV or more.

Citation List

Patent Document

Patent Document 1: Japanese Patent No. 4669565
Patent Document 2: Japanese Patent No. 4510757
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. S63-83227
Patent Document 4: PCT International Publication No. WO 2012/017669

SUMMARY OF INVENTION

Technical Problem

In conventional techniques including the above, an iron loss reduction effect can be obtained by reducing a certain degree of eddy-current loss. However, as a result of consideration performed by the present inventors, it has been found that, in the conventional techniques, the effect of reducing an iron loss as expected is not obtained by refining a magnetic domain width, and there is room for improvement.
Therefore, an object of the present invention is to provide a magnetic domain control method for achieving an iron loss that is lower than is conventional in a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet that is obtained by applying the magnetic domain control method, and has an iron loss that is lower than is conventional.

Solution to Problem

The present inventors have considered the reason why the effect of reducing an iron loss as expected is not obtained by refining a magnetic domain width in the conventional techniques.
As a result, it has been found that strain generated by irradiation with laser or the like is essential for a reduction in an iron loss due to irradiation with laser or the like, but the strain generated by irradiation with laser or the like significantly varies depending on the place, and in a region where there is a significant difference in intensity of the strain, a domain wall is difficult to move, and this hinders the effect of reducing the iron loss.
Accordingly, the present inventors have considered that a strain distribution is controlled to make a domain wall easy to move while maintaining the effect of refining a magnetic domain width, and a reduction in the iron loss is achieved.
As a result, the present inventors have found that strain (compressive strain) generated due to irradiation with an energy ray such as laser can be evaluated as compressive elastic stress, the domain wall easily moves by moderating a change in the compressive elastic stress, and this enables a reduction in an iron loss.
The present invention has been made in view of the findings described above. The gist of the present invention is as follows.

[1] In a grain-oriented electrical steel sheet in one aspect of the present invention, in a cross section that is orthogonal to an extending direction of an irradiation trace of an energy ray, and is parallel to a sheet thickness direction, in a case where an imaginary line is drawn in the sheet thickness direction to include a position where compressive elastic stress measured by using EBSD is 20 MPa or more, the degree of change in the compressive elastic stress on the imaginary line is 4 MPa or less per 1 µm over the entire region in the sheet thickness direction.
[2] In the grain-oriented electrical steel sheet according to [1], when it is assumed that the length of the irradiation trace of the energy ray in a unit µm in a direction orthogonal to the extending direction and the sheet thickness direction is a width W of the irradiation trace, and the widths W in five positions in one irradiation trace are W₁, W₂, W₃, W₄, and W₅, respectively, an average value W_Avc. expressed by Formula (6) described below may satisfy Formula (7) described below: $W_{Ave .} = (W_{1} + W_{2} + W_{3} + W_{4} + W_{5}) / 5$ ; and $25 \leq W_{Ave .} \leq 200$
[3] A magnetic domain control method in another aspect of the present invention is a method for performing magnetic domain control on a grain-oriented electrical steel sheet by irradiating the grain-oriented electrical steel sheet with an energy ray while scanning the grain-oriented electrical steel sheet in a direction that crosses a rolling direction of the grain-oriented electrical steel sheet, and when it is assumed that the power density of the energy ray in a unit W/mm² is Ip, the average irradiation energy density in a unit mJ/mm² is Ua, a beam diameter in a scanning direction of the energy ray in a unit mm is d, and scanning speed of the energy ray in a unit m/s is v, the Ip, the Ua, the d, and the v satisfy Formulae (1) to (3) described below: $Ip \leq 1500$ $Ua \geq 1.5$ and $d / v \geq 0.00010$
[4] In the magnetic domain control method according to [3], the Ip and the Ua may satisfy Formulae (4) and (5) described below: $Ip \leq 1000$ and $Ua \geq 2.5$

Advantageous Effects of Invention

In the aspects described above of the present invention, it is possible to provide a magnetic domain control method for achieving an iron loss that is lower than is conventional in a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet that is obtained by applying the magnetic domain control method, and has an iron loss that is lower than is conventional.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A diagram showing a measurement position of an elastic stress distribution.
[FIG. 2] A graph that is used to measure the width of an irradiation trace of an energy ray, and has been obtained by ImageJ, and in which a horizontal axis indicates DISTANCE and a vertical axis indicates GRAY VALUE.

DESCRIPTION OF EMBODIMENTS

A grain-oriented electrical steel sheet according to an embodiment of the present invention (a grain-oriented electrical steel sheet according to the present embodiment) and a magnetic domain control method that is applicable to the manufacturing of the grain-oriented electrical steel sheet (a magnetic domain control method according to the present embodiment) are described.

[Grain-Oriented Electrical Steel Sheet]

As described above, in a case where magnetic domain control is performed on a grain-oriented electrical steel sheet, strain (compressive strain) is introduced by performing irradiation with an energy ray such as laser. However, in a region where there is a difference in magnitude of strain generated by irradiation with laser or the like, a domain wall is difficult to move, and the effect of reducing an iron loss is hindered. Therefore, in the grain-oriented electrical steel sheet according to the present embodiment, in order to make the domain wall easy to move while maintaining the effect of refining a magnetic domain width, the degree of change in magnitude of the strain generated by irradiation with the energy ray is moderated. In the present embodiment, compressive elastic stress is used as an index of the magnitude of the strain.
Specifically, in the grain-oriented electrical steel sheet according to the present embodiment, in a cross section that is orthogonal to an extending direction of an irradiation trace of an energy ray (a scanning direction of the energy ray), and is parallel to a sheet thickness direction, in a case where an imaginary line has been drawn in the sheet thickness direction to include a position where compressive elastic stress measured by using EBSD is 20 MPa or more, the degree of change in the compressive elastic stress on the imaginary line is 4 MPa or less per 1 µm over the entire region in the sheet thickness direction.
In a case where a change in the compressive elastic stress (hereinafter, unless otherwise specified, in the case of simply using the term "elastic stress", it means compressive elastic stress) exceeds 4 MPa per 1 µm (in a case where a difference in elastic stress between adjacent regions is significant), the domain wall is difficult to move, and a sufficient effect of reducing an iron loss fails to be obtained.
A case where a change in the elastic stress is 4 MPa or less per 1 µm over the entire region in the sheet thickness direction means that when comparing an elastic stress at an arbitrary point on the imaginary line with an elastic stress in a position of 1 µm in the sheet thickness direction from the point, a difference (an absolute value) is 4 MPa or less.
In order to reduce a change in the elastic stress, the irradiation condition of the energy ray may be adjusted, as described later.
It is assumed that a cross section in which the elastic stress is measured is a cross section that is orthogonal to the extending direction of the irradiation trace of the energy ray, and is parallel to the sheet thickness direction (ND), and a change in compressive elastic stress on the imaginary line in the sheet thickness direction that includes a position where the elastic stress is 20 MPa or more is measured. The reason for this is as follows.
Specifically, the elastic stress is introduced below an irradiation position of the energy ray, and in a case where a region where the introduced elastic stress (compressive elastic stress) is 20 MPa or more (in some cases, referred to as a high elastic stress region) is formed under a conventional irradiation condition, it is considered that a change in elastic stress in the sheet thickness direction is the largest.
Only by reducing a change in elastic stress in another direction, for example, a sheet width direction, a sufficient magnetic domain refinement effect fails to be obtained, and a magnetism improvement effect also fails to be obtained. The elastic stress in the sheet thickness direction is dominated by an energy ray introduction condition such as a beam shape, and therefore even if the change in elastic stress in the sheet width direction is reduced, the change in elastic stress in the sheet thickness direction is not necessarily reduced.
Normally, magnetic domain control is performed by irradiating a surface of a grain-oriented electrical steel sheet with an energy ray such as laser while scanning the grain-oriented electrical steel sheet in a direction roughly parallel to the sheet width direction of the grain-oriented electrical steel sheet (for example, a direction of 75 to 105° with respect to a rolling direction). Therefore, the direction orthogonal to the extending direction of the irradiation trace of the energy ray is often a direction roughly parallel to the rolling direction.
In a case where a region where the compressive elastic stress is 20 MPa or more (the high elastic stress region) is absent, magnetic domain control is not sufficiently performed. Therefore, the grain-oriented electrical steel sheet according to the present embodiment is based on the premise that the high elastic stress region is present.
The elastic stress and a change in the elastic stress in the sheet thickness direction are obtained according to the following method.
FIG. 1 illustrates a case where laser irradiation and scanning are performed in a direction orthogonal to the rolling direction (RD) (a direction parallel to the sheet width direction (TD)). In this case, as illustrated in FIG. 1, a cross section that is parallel to each of the rolling direction (RD) and the sheet thickness direction (ND) is taken as a measurement surface.
The elastic stress is introduced by performing irradiation with an energy ray, and therefore map measurement is performed according to electron backscatter diffraction (EBSD), by using, as a measurement region MR, a region that has a width twice as large as an irradiation width IW of the energy ray with an irradiation position IM of the energy ray as a center, and extends over the entire region in the sheet thickness direction.
In map measurement, a sample in which a measurement surface is inclined at 70 degrees with respect to an irradiation direction of an electron beam is irradiated with the electron beam in a step of 1 µm or less, and an EBSD image is obtained. The obtained image is stored in 956 × 956 pixels, and strain calculation is performed using CrossCourt4 from BLG Vantage to calculate elastic stress. As a result, a high elastic stress region R into which an elastic stress (a compressive elastic stress) of 20 MPa or more was introduced is identified. In the measurement, an EBSD analysis surface needs to be subjected to surface treatment for removing mechanical strain due to polishing or cross-sectional processing. For example, it is sufficient if a method in which the analysis surface is mirror-polished and then a processing strain layer generated by polishing is removed by sputtering with an argon ion beam is used.
Thereafter, an imaginary line VL that passes through the high elastic stress region R and is parallel to the sheet thickness direction (ND) is drawn, and at each measurement point on the imaginary line VL, the intensity of strain is compared with the intensity of strain at a measurement point that has shifted by 1 µm in the sheet thickness direction. If a difference in elastic stress from the measurement point that has shifted by 1 µm in the sheet thickness direction is 4 MPa or less at all of the measurement points, it is determined that a difference in elastic stress is 4 MPa or less per 1 µm over the entire region in the sheet thickness direction.
Normally, a region having a large elastic stress is often formed in a position slightly away from the surface below the irradiation position (in a direction toward the thickness center), but a reference position of the imaginary line is not limited as long as the point has an elastic stress of 20 MPa or more.
Normally, as illustrated in FIG. 1, irradiation with the energy ray for magnetic domain control is performed at fixed intervals a plurality of times in such a way that irradiation positions (in a final grain-oriented electrical steel sheet, they are determined based on irradiation traces (which can be distinguished visually or by observing a surface magnetic domain)) are parallel.
If the condition described above is satisfied at least one irradiation position, an effect in the position is obtained, but from the viewpoint of improving the characteristics of the grain-oriented electrical steel sheet, it is preferable that the degree of change in elastic stress be as described above at all of the positions.
Furthermore, in the grain-oriented electrical steel sheet according to the present embodiment, it is preferable that the irradiation trace have a continuous linear shape, and in one irradiation trace, a change in the width of the irradiation trace be small. A small change in the width of the irradiation trace causes the elastic stress to be introduced in the sheet width direction without omissions or duplications, and a sufficient magnetic domain refinement effect is obtained. As a result, a sufficient magnetism improvement effect is obtained.
Specifically, when it is assumed that a length of the irradiation trace in a unit µm in a direction that is orthogonal to the extending direction and the sheet thickness direction is a width W, and widths W in five positions in one irradiation trace are W₁, W₂, W₃, W₄, and W₅, it is preferable that an average value W_Avc., which can be expressed by Formula (6), satisfy Formula (7) described below: $W_{Ave .} = (W_{1} + W_{2} + W_{3} + W_{4} + W_{5}) / 5$ ; and $25 \leq W_{Ave .} \leq 200$
The width W of the irradiation trace is measured by using a method called reflected X-ray topography.
As an X-ray topography device, XRTmicron made by Rigaku Corporation is used, and an X-ray source is a Cu target. In addition, a diffraction plane at the time of imaging is (310). A CCD resolution is 2.4 µm, and a Digital resolution is 16 bits.
Specifically, first, a material with insulating coating of 100 mm × 100 mm (× sheet thickness) into which an irradiation trace of an energy ray was introduced is prepared, and topography images of five fields of view on an identical energy ray with respect to the sheet width direction are taken as Snap Shot imaging in a high resolution mode. The diameter of a field of view at the time of imaging is 6 to 7 mm in the sheet width direction, and 7 to 8 mm in the rolling direction. In order to determine an imaging position, time delay integration (TDI) scanning may be performed in advance.
Next, an irradiation trace width is specifically calculated from the captured topography image, by using image analysis software called ImageJ.
Specifically, the topography image is developed on ImageJ, and a range of interest (ROI) serving as an analysis range is set (the width and the height of a pixel are 2.406 µm). The ROI has a rectangular shape, and its range has 646 pixels (corresponding to approximately 1.55 mm) in the rolling direction and 84 pixels (corresponding to approximately 0.20 mm) in the sheet width direction. Hereinafter, a side that is parallel to the rolling direction is referred to as a ROI long side, and a side that is parallel to the sheet width direction is referred to as a ROI short side. The ROI is set in such a way that the irradiation trace is included in the rectangle shape. At this time, the irradiation trace is set to be located at the center of the ROI long side, but this may be performed in visual observation.
After the ROI setting was finished, a graph in which a horizontal axis indicates DISTANCE and a vertical axis indicates GRAY VALUE is then drawn in a ROI setting range. A graph drawing function is one of the functions of ImageJ, and this function is used. As a result, a spectrum having a negative peak, as illustrated in FIG. 2, is obtained.
Gray scales at both ends of the spectrum are read, and the average value thereof is calculated. Hereinafter, this average value is referred to as I_Ave.. It is assumed that the negative peak intensity in the spectrum (the minimum value of the spectrum) is I_Bottom. The difference between I_Ave. and I_Bottom is defined as ΔI_Height. Here, the concept I_HH (half height), which can be defined by Formula (8) described below, is introduced. I_HH is a gray scale value that corresponds to half of the peak intensity. The width W of the irradiation trace is defined as DISTANCE between two points that correspond to I_HH. $I_{HH} = I_{Height} + (0.5 \times I_{Height})$
In accordance with this method, W (µm) in each of the five fields of view is measured, and the numbers 1 to 5 are assigned to the respective fields of view in such a way that five widths W are W₁, W₂, W₃, W₄, and W₅. The arithmetical mean of W₁, W₂, W₃, W₄, and W₅ described above is calculated, and this is assumed to be W_Ave..

A sheet thickness of the grain-oriented electrical steel sheet (in a case where glass coating and insulating coating are included, a sheet thickness of a base steel sheet excluding the glass coating and the insulating coating) is not limited. The effect of magnetic domain control increases as the sheet thickness decreases, and therefore it is preferable that the sheet thickness be 0.15 mm to 0.23 mm.

A chemical composition of the grain-oriented electrical steel sheet (in a case where the glass coating and the insulating coating are included, a chemical composition of the base steel sheet excluding the glass coating and the insulating coating) is not limited, and the chemical composition may be selected from a publicly known range according to characteristics required as the grain-oriented electrical steel sheet. For example, the chemical composition contains C: 0.010% or less, Si: 3.00 to 4.00%, Mn: 0.01 to 0.50%, N: 0.010% or less, sol. Al: 0.020% or less, S: 0.010% or less, P: 0.030% or less, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Cu: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, Mo: 0 to 0.10%, and a balance including Fe and impurities.

In the grain-oriented electrical steel sheet according to the present embodiment, publicly known glass coating may be formed on a surface of the base steel sheet. The glass coating is inorganic coating containing magnesium silicate as a main component. The glass coating is formed in final annealing as a result of a reaction between an annealing separator containing magnesia (MgO) applied on the surface of the base steel sheet and a component of the surface of the base steel sheet. The glass coating has a composition derived from the annealing separator and the component of the base steel sheet, and has a microstructure including a Mg₂SiO₄ phase serving as a main phase (50 area% or more) and an MgAl₂O₄ phase. In addition to these phases, a precipitate of about 1 area% or less is included in some cases.

In the grain-oriented electrical steel sheet according to the present embodiment, publicly known insulating coating (tension-applying insulating coating) may be formed on the surface of the base steel sheet or on a surface of the glass coating.
The insulating coating imparts electrical insulation properties to the grain-oriented electrical steel sheet, reduces an eddy-current loss, and improves the iron loss characteristics of the grain-oriented electrical steel sheet (reduce an iron loss). Furthermore, due to the insulating coating, various properties such as corrosion resistance, heat resistance, or slippage can be obtained in addition to the electrical insulation properties as described above. Moreover, the insulating coating has a function of applying tension to the grain-oriented electrical steel sheet. By applying tension to the grain-oriented electrical steel sheet to facilitate a movement of the domain wall in the grain-oriented electrical steel sheet, the iron loss properties of the grain-oriented electrical steel sheet can be improved (the iron loss can be reduced). The insulating coating is formed, for example, by applying a coating liquid containing metal phosphate and silica as main components onto the surface of the glass coating, and baking the coating liquid.

[Magnetic Domain Control Method]

In the magnetic domain control method according to the present embodiment, magnetic domain control is performed on a grain-oriented electrical steel sheet by irradiating the grain-oriented electrical steel sheet with an energy ray while scanning the grain-oriented electrical steel sheet in a direction that crosses a rolling direction (for example, in a direction of 30 to 150°, and preferably, 75 to 105°, relative to the rolling direction).
In a conventional method for introducing strain (and elastic stress associated therewith) due to a difference in temperature generated in a steel sheet at the time of irradiation with an energy ray, elastic stress is introduced by performing irradiation with a high-energy beam in a short time. A difference in temperature generated in the steel sheet at this time is large, and a portion into which a large elastic stress has been locally introduced is generated.
In the magnetic domain control method according to the present embodiment, irradiation with the energy ray is performed in such a way that the irradiation time at each position becomes longer than the irradiation time under conventional general irradiation conditions, and therefore a sufficient elastic stress (compressive elastic stress) is introduced, and a change in the elastic stress is moderated. For this purpose, the power density of the energy ray is reduced, the average irradiation energy density is increased, and a time period during which one point of the steel sheet is irradiated with the energy ray is increased.
Specifically, in the magnetic domain control method according to the present embodiment, when it is assumed that a power density of an energy ray in a unit W/mm² is Ip, the average irradiation energy density in a unit mJ/mm² is Ua, the beam diameter in a scanning direction of the energy ray in a unit mm is d, and the scanning speed of the energy ray in a unit m/s is v, irradiation with the energy ray is performed in such a way that Ip, Ua, d, and v described above satisfy Formulae (1) to (3) described below: $Ip \leq 1500$ $Ua \geq 1.5$ and $d / v \geq 0.00010$ d/v corresponds to a time period (s) at one point during which the one point of the steel sheet is irradiated with the energy ray.
In a case where any one of Formulae (1) to (3) is not satisfied, there is a concern that the degree of change in the elastic stress in the sheet thickness direction exceeds 4 MPa per 1 µm.
The lower limit of Ip is not limited, but Ip may be 100 or more from the viewpoint of causing effective magnetic domain refinement.
The upper limit of Ua is not limited, but Ua may be 5.0 or less from the viewpoint of preventing noise characteristics from deteriorating, or may be 3.0 or less because more satisfactory noise characteristics can be obtained.
The upper limit of d/v is not limited, but d/v may be 0.00100 or less.
As described above, in the conventional method for introducing elastic stress due to a difference in temperature generated in a steel sheet at the time of irradiation with an energy ray, a beam of the energy ray is generally applied in a short time. In a case where coating is formed on a surface of the grain-oriented electrical steel sheet, it has been considered to increase the beam diameter in such a way that the coating is not broken, but it has not been considered to further increase the irradiation time within a range in which the coating does not deteriorate, because the elastic stress is reduced and productivity is lowered.
The present inventors have focused on the degree of change in elastic stress, and have found that a significant effect can be obtained by performing irradiation with an energy ray under the conditions described above that would not be conventionally set.
It is preferable that Ip and Ua described above satisfy Formulae (4) and (5) described below: $Ip \leq 1000$ and $Ua \geq 2.5$
In the magnetic domain control method according to the present embodiment, the energy ray is, for example, laser or an electron beam. However, in the case of pulse waves, the elastic stress also changes in the scanning direction, and it is difficult to secure a long irradiation time as in the magnetic domain control method according to the present embodiment.
Therefore, as the energy ray, an energy ray that is a continuous wave, such as continuous wave laser, is used. For example, by using the continuous wave laser or the like, it is possible to obtain a grain-oriented electrical steel sheet having an irradiation trace that satisfies 25 µm ≤ W_Ave. ≤ 200 µm.
A steel sheet subjected to the magnetic domain control may be a publicly known grain-oriented electrical steel sheet, and a method for manufacturing the same is not particularly limited. Stated another way, the magnetic domain control may be performed on a grain-oriented electrical steel sheet manufactured according to any manufacturing method. A general grain-oriented electrical steel sheet is manufactured according to a manufacturing method including the following processes:

a hot rolling process of heating a steel piece such as a slab, and hot-rolling the steel piece into a hot-rolled steel sheet;
a hot-band annealing process of performing hot-band annealing on the hot-rolled steel sheet;
a pickling process of pickling the hot-rolled steel sheet after the hot-band annealing process;
a cold rolling process of performing cold rolling on the hot-rolled steel sheet after the pickling process once or a plurality of times between which annealing is performed to obtain a cold-rolled steel sheet;
a decarburization annealing process of performing decarburization annealing on the cold-rolled steel sheet;
a final annealing process of forming glass coating by applying an annealing separator containing MgO powder as a main component to front and reverse surfaces of the cold-rolled steel sheet after the decarburization annealing process, the cold-rolled steel sheet serving as a base material steel sheet, drying the annealing separator, and then performing final annealing; and
a coating forming process of forming insulating coating on the glass coating.

Furthermore, in the case of obtaining a grain-oriented electrical steel sheet having the chemical composition described above as an example, considering that the amount of some elements changes due to decarburization, final annealing, or the like, it is sufficient if, as the steel piece, a steel piece containing, in mass%, C: 0.010 to 0.200%, Si: 3.00 to 4.00%, sol. Al: 0.010 to 0.040%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.040%, P: 0.030% or less, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, and Mo: 0 to 0.10%, with the balance of Fe and impurities, is used.

Examples

The grain-oriented electrical steel sheet according to the present invention will be described in further detail by using examples. The examples described below are merely examples of the grain-oriented electrical steel sheet according to the present invention and a method for manufacturing the same, and the grain-oriented electrical steel sheet according to the present invention and the method for manufacturing the same are not limited to the examples described below.
Magnetic domain control was performed on a grain-oriented electrical steel sheet by performing laser irradiation and scanning the laser in a direction orthogonal to a rolling direction at a pitch of 5 mm in the rolling direction under the conditions of Table 1, the grain-oriented electrical steel sheet containing C: 0.010%, Si: 3.30%, Mn: 0.10%, S: 0.007%, acid-soluble Al: 0.030%, N: 0.008%, Sn: 0.06%, and the balance: Fe and impurities, and having a sheet thickness of 0.23 mm.
A plurality of samples of 500 mm in the rolling direction and 100 mm in a sheet width direction including an irradiation position were cut out from the grain-oriented electrical steel sheet after the magnetic domain control.
For these samples, a distribution of elastic stress and magnetic characteristics were evaluated according to the method described below.

[Distribution of Elastic Stress]

Map measurement is performed according to electron backscatter diffraction (EBSD) method, by using, as a measurement region, a region that extends over the entire region in a sheet thickness direction (ND), and having a width twice as large as an irradiation width of an energy ray with an irradiation position of one energy ray as a center in a cross section parallel to each of a rolling direction (RD) and the sheet thickness direction. In map measurement, a sample in which a cross section serving as a measurement surface is inclined at 70 degrees with respect to an irradiation direction of an electron beam was irradiated with the electron beam in a step of 2 µm or less, and an EBSD image was obtained.
The obtained image was stored in 956 × 956 pixels, strain calculation was performed by using CrossCourt4 from BLG Vantage, and elastic stress in the rolling direction was calculated. As a reference point of strain or elastic stress, a point farthest away from the irradiation position of the energy ray or the vicinity thereof (within a range of about 10 pixels) within a measurement range of a cross section of the grain-oriented electrical steel sheet was used. A measurement point having a compressive elastic stress of 20 MPa or more was selected, and a compressive elastic stress at each of the measurement points on an imaginary line that passes through a corresponding measurement point and is parallel to the sheet thickness direction was compared with a compressive elastic stress at a point that shifted by 1 µm in the sheet thickness direction.
However, in a case where there is no measurement point at which the compressive elastic stress is 20 MPa or more (an example in which "NO" is described in the column "Is maximum compressive elastic stress 20 MPa or more?" in the table), a compressive elastic stress at each of the measurement points on an imaginary line that passes through a measurement point at which the compressive elastic stress is maximized and is parallel to the sheet thickness direction was compared with the compressive elastic stress at a point that shifted by 1 µm in the sheet thickness direction.
If a maximum value of a difference in elastic stress is 4 MPa or less, it was determined that the degree of change in elastic stress is small.

[Magnetic Characteristics]

A sample having 60 mm width × 300 mm length and including a sheet width center position of the grain-oriented electrical steel sheet was collected. A length direction of the sample is parallel to the rolling direction. By using this sample, an iron loss W_17/50 (W/kg) at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T was measured in accordance with JIS C 2556 (2015).
If the iron loss W_17/50 is less than 0.740 W/Kg, it was determined that the iron loss is low.

Moreover, a single-sheet magnetic characteristics test (SST test) was performed in accordance with JIS C2556 (2015), by using the sample described above, and a magnetic flux density (T) was obtained. Specifically, a magnetic field of 800 A/m was applied to the sample, and the magnetic flux density (T) is obtained.

[Table 1]

	Ip	Ua	Beam diameter d in scanning direction	Scanning speed v	d/V	W_Ave.	Maximum value of difference in compressive elastic stress	Is maximum compressive elastic stress 20 MPa or more?	B8	Iron loss W_17/50
	W/mm²	mJ/mm²	mm	m/s	s	µm	MPa	Is maximum compressive elastic stress 20 MPa or more?	T	W/kg
Comparative Example 1	7639	2.0	0.5	30	0.00002	123	10	YES	1.921	0.746
Comparative Example 2	3820	2.0	1.0	30	0.00003	119	8	YES	1.921	0.743
Comparative Example 3	1910	2.0	2.0	30	0.00007	107	5	YES	1.922	0.741
Invention Example 1	764	2.0	5.0	30	0.00017	204	3	YES	1.920	0.735
Invention Example 2	382	2.0	10.0	30	0.00033	186	2	YES	1.923	0.728
Comparative Example 4	255	0.5	5.0	40	0.00013	210	1	NO	1.925	0.751
Comparative Example 5	509	1.0	5.0	40	0.00013	208	2	NO	1.924	0.747
Invention Example 3	764	1.5	5.0	40	0.00013	20	3	YES	1.924	0.739
Invention Example 4	1019	2.0	5.0	40	0.00013	217	4	YES	1.923	0.738
Invention Example 5	1273	2.5	5.0	40	0.00013	204	4	YES	1.922	0.734
Comparative Example 6	1528	3.0	5.0	40	0.00013	211	6	YES	1.920	0.741
Invention Example 6	637	5.0	5.0	10	0.00050	125	4	YES	1.915	0.716
Invention Example 7	637	2.5	5.0	20	0.00025	89	4	YES	1.920	0.722
Invention Example 8	637	1.7	5.0	30	0.00017	209	3	YES	1.921	0.737
Comparative Example 7	637	1.3	5.0	40	0.00013	55	3	NO	1.922	0.742
Comparative Example 8	637	1.0	5.0	50	0.00010	69	2	NO	1.923	0.748
Comparative Example 9	1485	1.7	3.0	35	0.00009	56	5	YES	1.920	0.741

As is apparent from Table 1, in Invention Examples 1 to 8 in which magnetic domain control was performed under the condition where Ip, Ua, and d/v are within a range of the present invention, a maximum compressive elastic stress was 20 MPa or more, and a difference in compressive elastic stress was 4 MPa or less. As a result, excellent iron loss characteristics were obtained.
In contrast, in Comparative Examples 1 to 9, Ip, Ua, or d/v fell outside the range of the present invention, and the maximum compressive elastic stress was less than 20 MPa, or a maximum value of the difference in compressive elastic stress exceeded 4 MPa. As a result, the iron loss characteristics were poor.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide a magnetic domain control method for achieving an iron loss that is lower than is conventional in a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet that is obtained by applying the magnetic domain control method, and has an iron loss that is lower than is conventional.

REFERENCE SIGNS LIST

TD Sheet width direction
RD Rolling direction
ND Sheet thickness direction
IM Irradiation position
IW Irradiation width
MR Measurement region
R Region where compressive elastic stress is 20 MPa or more (high elastic stress region)
VL Imaginary line

Claims

A grain-oriented electrical steel sheet, wherein
in a cross section that is orthogonal to an extending direction of an irradiation trace of an energy ray, and is parallel to a sheet thickness direction,

in a case where an imaginary line is drawn in the sheet thickness direction to include a position where compressive elastic stress measured by using EBSD is 20 MPa or more,

a degree of change in the compressive elastic stress on the imaginary line is 4 MPa or less per 1 µm over an entire region in the sheet thickness direction.
The grain-oriented electrical steel sheet according to claim 1, wherein
when it is assumed that a length of the irradiation trace of the energy ray in a unit µm in a direction orthogonal to the extending direction and the sheet thickness direction is a width W of the irradiation trace, and the widths W in five positions in one irradiation trace are W₁, W₂, W₃, W₄, and W₅,

an average value W_Ave. expressed by Formula (6) described below satisfies Formula (7) described below: $W_{Ave .} = (W_{1} + W_{2} + W_{3} + W_{4} + W_{5}) / 5$ and $25 \leq W_{Ave .} \leq 200$
A magnetic domain control method for performing magnetic domain control on a grain-oriented electrical steel sheet by irradiating the grain-oriented electrical steel sheet with an energy ray while scanning the grain-oriented electrical steel sheet in a direction that crosses a rolling direction of the grain-oriented electrical steel sheet, wherein
when it is assumed that a power density of the energy ray in a unit W/mm² is Ip, an average irradiation energy density in a unit mJ/mm² is Ua, a beam diameter in a scanning direction of the energy ray in a unit mm is d, and scanning speed of the energy ray in a unit m/s is v,

the Ip, the Ua, the d, and the v satisfy Formulae (1) to (3) described below: $Ip \leq 1500$ $Ua \geq 1.5$ and $d / v \geq 0.00010$
The magnetic domain control method according to claim 3, wherein
the Ip and the Ua satisfy Formulae (4) and (5) described below: $Ip \leq 1000$ and $Ua \geq 2.5$