Grain-oriented electrical steel sheet and magnetic domain control method

Abstract

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

Description

[Technical Field]

[0001] The present invention relates to grain-oriented electrical steel sheets and a magnetic domain control method applicable in the manufacturing process of grain-oriented electrical steel sheets. This application claims priority based on Japanese Patent Application No. 2023-073595, filed in Japan on April 27, 2023, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are soft magnetic materials and are mainly used as core materials for transformers. Therefore, grain-oriented electrical steel sheets are required to have magnetic properties such as high magnetization characteristics and low iron loss. Iron loss refers to the power loss that occurs when an iron core is excited by an alternating magnetic field, resulting in the consumption of thermal energy. From an energy-saving perspective, iron loss should be kept as low as possible. Factors such as magnetic susceptibility, sheet thickness, coating tension, impurity content, electrical resistivity, grain size, and magnetic domain size all influence the level of iron loss. Even with the development of various technologies for grain-oriented electrical steel sheets, research and development to reduce iron loss continues in order to improve energy efficiency. One proposed method for reducing iron loss involves laser irradiation. This technique is said to reduce eddy current loss by refining the magnetic domain width through laser irradiation.

[0003] For example, Patent Document 1 describes a process that includes irradiating the surface of a grain-oriented electrical steel sheet with focused continuous-wave laser light while scanning in a direction inclined from the rolling direction of the grain-oriented electrical steel sheet, and repeating the process while shifting the scanning portion of the continuous-wave laser light at predetermined intervals, wherein the average power of the continuous-wave laser light is denoted as P (W), the scanning speed as Vc (mm / s), the predetermined interval as PL (mm), and the input energy Ua as Ua = P / (Vc × PL) (mJ / mm). 2 When defined as follows, 1.0 mm ≤ PL ≤ 3.0 mm and 0.8 mJ / mm 2 ≤Ua ≤ 2.0 mJ / mm 2A method for manufacturing a directionally electromagnetic steel sheet in which magnetic domains are controlled by laser light irradiation, characterized by satisfying [conditions]. In Patent Document 1, it is shown that iron loss in both the L direction and the C direction of a directionally electromagnetic steel sheet can be reduced easily and with high productivity.

[0004] Further, Patent Document 2 discloses a method for manufacturing a directionally electromagnetic steel sheet in which linear circular magnetic domains are formed substantially perpendicular to the rolling direction of the steel sheet and at substantially constant intervals by scanning irradiation with a continuous oscillation laser beam, thereby improving iron loss characteristics. In Patent Document 2, the laser is in the TEM 00 mode in which the laser light intensity distribution in a cross section perpendicular to the beam propagation direction has a maximum intensity near the optical axis center. It is shown that a directionally electromagnetic steel sheet with reduced iron loss can be obtained when the condensing diameter d [mm] of the irradiation beam in the rolling direction, the scanning linear velocity V [mm / s] of the laser beam, and the average output P [W] of the laser are in the range of 0 < d ≤ 0.2 and 0.001 ≤ P / V ≤ 0.012.

[0005] Patent Document 3 discloses a method for improving the iron loss value of an electromagnetic steel sheet. In a method of irradiating a continuous oscillation laser beam substantially perpendicular to the rolling direction on the surface of a directionally electromagnetic steel sheet to improve the iron loss value, a circular spot of YAG condensed by a flat-field lens is irradiated so as to satisfy predetermined conditions to obtain an extremely low iron loss value.

[0006] Patent Document 4 discloses a directionally electromagnetic steel sheet having a forsterite film on the steel sheet surface, having a Se enrichment part in at least one of the film and the interface between the film and the steel sheet, and the proportion of the enrichment part being 2% or more per 10000 μm of the steel sheet surface in terms of area ratio. A method for manufacturing a directionally electromagnetic steel sheet in which the magnetic domains of the directionally electromagnetic steel sheet are subdivided by irradiating with an electron beam under the conditions of a diameter of 0.05 mm or more and 0.5 mm or less, a scanning speed of 1.0 m / s or more, and an acceleration voltage of 30 kV or more is disclosed. 2

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the conventional technology including the above, an iron loss reduction effect can be obtained by reducing a certain amount of eddy current loss. However, as a result of the study by the present inventors, it has been found that in the conventional technology, the iron loss reduction effect expected from the subdivision of the magnetic domain width has not been obtained, and there is room for improvement.

[0009] Therefore, an object of the present invention is to provide a magnetic domain control method for realizing lower iron loss than conventional in a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet having lower iron loss than conventional obtained by applying the magnetic domain control method.

Means for Solving the Problems

[0010] The present inventors have studied the reason why the iron loss reduction effect expected from the subdivision of the magnetic domain width has not been obtained in the conventional technology. As a result, although distortion generated by irradiation with a laser or the like is indispensable for reducing iron loss by irradiation with a laser or the like, the distortion generated by irradiation with a laser or the like varies greatly depending on the location, and in a region where there is a large difference in the intensity of the distortion, it becomes difficult for the magnetic wall to move, and it has been found that the iron loss reduction effect is inhibited accordingly.

[0011] Therefore, the present inventors have studied to make the magnetic wall easy to move while maintaining the effect of subdividing the magnetic domain width by controlling the strain distribution, and to realize reduction of iron loss. As a result, the inventors have found that the strain (compressive strain) generated by irradiation with an energy beam such as a laser can be evaluated as compressive elastic stress, and by moderating the change in this compressive elastic stress, the magnetic domain walls can move more easily, and as a result, it is possible to reduce iron loss.

[0012] The present invention has been made in view of the above findings. The gist of the present invention is as follows. [1] The grain-oriented electrical steel sheet according to one aspect of the present invention includes a position where the compressive elastic stress measured using EBSD is 20 MPa or more in a cross-section orthogonal to the extending direction of the irradiation trace of the energy beam and parallel to the plate thickness direction. When a virtual line is drawn in the plate thickness direction, the degree of change in the compressive elastic stress on the virtual line is 4 MPa or less per 1 μm over the entire plate thickness direction. [2] In the grain-oriented electrical steel sheet according to [1], the length per unit μm in the direction orthogonal to the extending direction and the plate thickness direction of the irradiation trace of the energy beam is defined as the width W of the irradiation trace. When the widths W at five locations in one irradiation trace are respectively W1, W2, W3, W4, and W5, the average value W Ave. may satisfy the following formula (7). W Ave. =(W1 + W2 + W3 + W4 + W5) / 5 (6) 25 ≦ W Ave. ≦ 200 (7) [3] A magnetic domain control method according to another aspect of the present invention is a method for controlling the magnetic domain of a grain-oriented electrical steel sheet by irradiating the energy beam while scanning in a direction intersecting the rolling direction of the grain-oriented electrical steel sheet, where the power density of the energy beam per unit W / mm 2 is Ip, the average irradiation energy density per unit mJ / mm 2 is Ua, the beam diameter in the scanning direction of the energy beam per unit mm is d, and the scanning speed of the energy beam per unit m / s is v. The Ip, Ua, d, and v satisfy the following formulas (1) to (3). Ip ≦ 1500 (1) Ua ≧ 1.5 (2) d / v ≧ 0.00010 (3) The magnetic domain control method described in [4][3] may also satisfy the following equations (4) and (5) for Ip and Ua. Ip ≤ 1000 (4) Ua≧2.5 (5) [Effects of the Invention]

[0013] According to the above aspects of the present invention, it is possible to provide a magnetic domain control method for achieving lower iron loss in grain-oriented electrical steel sheets than in conventional methods, and a grain-oriented electrical steel sheet having lower iron loss than in conventional methods obtained by applying the magnetic domain control method. [Brief explanation of the drawing]

[0014] [Figure 1] This diagram illustrates the measurement locations for the elastic stress distribution. [Figure 2] This graph, obtained using ImageJ, is used to measure the width of the irradiation trace of energy rays. The horizontal axis represents DISTANCE and the vertical axis represents GRAY VALUE. [Modes for carrying out the invention]

[0015] A grain-oriented electrical steel sheet (grain-oriented electrical steel sheet according to this embodiment) and a magnetic domain control method applicable to the manufacture of the grain-oriented electrical steel sheet (magnetic domain control method according to this embodiment) according to one embodiment of the present invention will be described.

[0016] [Grain-oriented electrical steel sheet] <Compressive elastic stress> As described above, when controlling the magnetic domains of grain-oriented electrical steel sheets, strain (compressive strain) is introduced by irradiation with energy rays such as lasers. However, in regions where there is a difference in the magnitude of the strain generated by irradiation with lasers, etc., the magnetic domain walls become less mobile, and the effect of reducing iron loss is hindered. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, in order to make the magnetic domain walls more mobile while maintaining the effect of refining the magnetic domain width, the degree of change in the magnitude of the strain generated by irradiation with energy rays is made more gradual. In this embodiment, compressive elastic stress is used as an indicator of the magnitude of this strain. Specifically, in the grain-oriented electrical steel sheet according to this embodiment, when a virtual line is drawn in the thickness direction such that it includes a position where the compressive elastic stress measured using EBSD is 20 MPa or more in a cross section perpendicular to the direction of extension of the irradiation trace of the energy rays (scanning direction of the energy rays) and parallel to the thickness direction, the degree of change of the compressive elastic stress along the virtual line is 4 MPa or less per 1 μm over the entire thickness direction.

[0017] If the change in compressive elastic stress (hereinafter, when simply referred to as elastic stress, unless otherwise specified, it means compressive elastic stress) exceeds 4 MPa per 1 μm (indicating a large difference in elastic stress between adjacent regions), the magnetic domain wall becomes difficult to move, and a sufficient reduction in iron loss cannot be obtained. The statement that the change in elastic stress is 4 MPa or less per 1 μm across the entire thickness direction means that when comparing the elastic stress at any point on the imaginary line with the elastic stress at a point 1 μm away from that point in the thickness direction, the difference (absolute value) is 4 MPa or less. To minimize changes in elastic stress, the irradiation conditions for the energy rays can be adjusted, as will be described later.

[0018] The reason for measuring elastic stress using a cross-section perpendicular to the direction of extension of the energy ray irradiation trace and parallel to the plate thickness direction (ND), and for measuring the change in compressive elastic stress along a virtual line in the plate thickness direction that includes a position where the elastic stress is 20 MPa or more, is as follows: In other words, elastic stress is introduced below the energy ray irradiation position, and under conventional irradiation conditions, when a region is formed in which the introduced elastic stress (compressive elastic stress) exceeds 20 MPa (sometimes called a high-elasticity stress region), the change in elastic stress in the plate thickness direction is considered to be the largest. Simply reducing changes in elastic stress in other directions, such as the plate width direction, is not sufficient to achieve a adequate magnetic domain refinement effect, nor does it improve magnetism. Since elastic stress in the plate thickness direction is dominated by energy ray introduction conditions such as beam shape, reducing changes in elastic stress in the plate width direction does not necessarily reduce changes in elastic stress in the plate thickness direction. Typically, magnetic domain control is performed by irradiating the surface of a grain-oriented electrical steel sheet with an energy beam, such as a laser, while scanning it in a direction approximately parallel to the sheet's width (for example, at an angle of 75 to 105° to the rolling direction). Therefore, the direction perpendicular to the direction of the energy beam's irradiation trace is often approximately parallel to the rolling direction.

[0019] If there is no region where the compressive elastic stress is 20 MPa or higher (high elastic stress region), the magnetic domain control will not be sufficient. Therefore, the grain-oriented electrical steel sheet according to this embodiment assumes the existence of a high elastic stress region.

[0020] The elastic stress and the change in elastic stress in the thickness direction of the plate are determined by the following method. Figure 1 shows the case where the laser irradiation is scanned in a direction perpendicular to the rolling direction (RD) (parallel to the plate width direction (TD)). In this case, as shown in Figure 1, the measurement surface is a cross section parallel to both the rolling direction (RD) and the plate thickness direction (ND). Since elastic stress is introduced by irradiation with energy rays, a measurement area MR is defined as the measurement area that extends across the entire thickness direction of the plate, with a width twice the irradiation width IW centered on the irradiation position IM of the energy rays, and a map measurement is performed using electron beam backscatter diffraction (EBSD). For map measurement, the sample is tilted 70 degrees relative to the electron beam irradiation direction, and the electron beam is irradiated in steps of 1 μm or less to obtain an EBSD image. The obtained image is saved at 956 × 956 pixels, and strain calculation is performed using CrossCourt4 from BLG Vantage to calculate the elastic stress. This identifies the high-elasticity stress region R in which elastic stress (compressive elastic stress) of 20 MPa or more is introduced. For measurement, the EBSD analysis surface must be surface-treated to remove mechanical strain caused by polishing or cross-sectional processing. For example, the analysis surface can be mirror-polished, and then the processing strain layer caused by polishing can be sputtered off with an argon ion beam. Subsequently, a virtual line VL parallel to the plate thickness direction (ND) is drawn through this high-elasticity stress region R. At each measurement point on this virtual line VL, the strain intensity is compared with that of a measurement point moved 1 μm in the plate thickness direction. If the difference in elastic stress between all measurement points and the measurement point moved 1 μm in the plate thickness direction is 4 MPa or less, it is determined that the difference in elastic stress is 4 MPa or less per μm across the entire plate thickness direction. Typically, a region of high elastic stress is formed below the irradiation point (towards the center of the plate thickness) and slightly away from the surface. However, any point with an elastic stress of 20 MPa or more is acceptable, regardless of the reference position of the imaginary line.

[0021] The irradiation of energy rays for magnetic domain control is usually performed multiple times at regular intervals, as shown in Figure 1, so that the irradiation positions (determined by the irradiation marks in the final grain-oriented electrical steel sheet, which can be identified by visual inspection or observation of surface magnetic domains) are parallel. While the above conditions, if satisfied at least one irradiation position, will yield an effect at that position, from the viewpoint of improving the properties of grain-oriented electrical steel sheets, it is preferable that the degree of change in elastic stress be as described above at all positions.

[0022] Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, it is preferable that the irradiation marks are continuous and linear, and that the change in the width of each irradiation mark is small. By having a small change in the width of the irradiation marks, elastic stress is introduced without leakage or overlap in the width direction of the sheet, resulting in a sufficient magnetic domain subdivision effect, and as a result, a sufficient magnetic improvement effect is obtained. Specifically, when the length in units of μm in the direction perpendicular to the extension direction and the thickness direction is defined as the width W of the irradiation mark, and the widths W of five points in a single irradiation mark are W1, W2, W3, W4, and W5, the average value W that can be expressed by equation (6) is Ave. It is preferable that the following equation (7) is satisfied. W Ave. =(W1+W2+W3+W4+W5) / 5 (6) 25≦W Ave. ≤200 (7)

[0023] The width W of the irradiation mark is measured using a technique called reflected X-ray topography. The X-ray topography system used is a Rigaku XRTmicron, with a Cu target as the X-ray source. The diffraction plane during imaging is set to (310). The CCD resolution is 2.4 μm, and the digital resolution is 16 bits. Specifically, a 100mm x 100mm (x plate thickness) insulating coated material with energy ray irradiation marks is prepared, and five topographic images of the same energy ray in the plate width direction are captured as snap shots in high-resolution mode. The field diameter during acquisition is 6-7mm in the plate width direction and 7-8mm in the rolling direction. A TDI (Time Delay Integration) scan may be performed in advance to determine the acquisition locations. Next, the irradiation marks are specifically calculated from the acquired topographic images using image analysis software called ImageJ. Specifically, in ImageJ, the topography image is unfolded and the Range of Interest (ROI), which is the analysis area, is set (pixel width and height are 2.406 μm). The ROI is rectangular, with a range of 646 pixels (approximately 1.55 mm) in the rolling direction and 84 pixels (approximately 0.20 mm) in the plate width direction. Hereafter, the side parallel to the rolling direction will be called the ROI long side, and the side parallel to the plate width direction will be called the ROI short side. The ROI is set so that the irradiation marks are contained within the rectangle. At this time, it is acceptable to visually check so that the irradiation marks are located at the center of the ROI long side. Once the ROI setting is complete, the next step is to plot a graph within the ROI setting range, with the horizontal axis representing DISTANCE and the vertical axis representing GRAY VALUE. The graph plotting function is part of ImageJ's capabilities and will be used for this. This will yield a spectrum with negative peaks, as shown in Figure 2. Read the Gray Scale at both ends of the spectrum and calculate their average value. From now on, this average value will be used as I Ave. This is called the negative peak intensity (minimum value of the spectrum) in the spectrum. Bottom Let's assume that. Ave. and I BottomThe difference is ΔI Height This is defined as follows. Here, I can be defined by the following equation (8). HH Let's introduce the concept of (Half Weight). HH This is a Gray Scale value that corresponds to half of the peak intensity. The width W of the irradiation mark is I HH This is defined as the distance between two corresponding points. I HH =I Height +(0.5 × I Height )···(8) Following this method, the W (μm) in each of the five fields of view is measured, and each field of view is assigned a number from 1 to 5, i.e., the five widths W are designated as W1, W2, W3, W4, and W5. The arithmetic mean of W1, W2, W3, W4, and W5 is calculated and this is used as W Ave. Let's assume that.

[0024] <plate thickness> The thickness of the grain-oriented electrical steel sheet (or the thickness of the base steel sheet excluding glass coatings and insulating coatings, if applicable) is not limited. A thinner sheet is preferable as it enhances the effect of magnetic domain control.

[0025] <Chemical composition> The chemical composition of grain-oriented electrical steel sheets (or, if glass coatings and insulating coatings are included, the chemical composition of the base steel sheet excluding these) is not limited and can be selected within a known range according to the properties required for the grain-oriented electrical steel sheet. For example, a chemical composition containing C: 0.010% or less, Si: 3.00~4.00%, Mn: 0.01~0.50%, N: 0.010% or less, sol.Al: 0.020% or less, S: 0.010% or less, P: 0.030% or less, Cr: 0~0.50%, Sn: 0~0.50%, Cu: 0~0.50%, Se: 0~0.020%, Sb: 0~0.50%, and Mo: 0~0.10%, with the remainder being Fe and impurities, is exemplified.

[0026] <Glass coating> The grain-oriented electrical steel sheet according to this embodiment may have a known glass coating formed on the surface of the base steel sheet. The glass coating is an inorganic coating mainly composed of magnesium silicate. The glass coating is formed during finish annealing by a reaction between an annealing separating agent containing magnesia (MgO) applied to the surface of the base steel sheet and the components of the surface of the base steel sheet. It has a composition derived from the annealing separating agent and the components of the base steel sheet, and consists of a structure containing a main phase (50 area % or more) of Mg2SiO4 and a MgAl2O4 phase. In addition to these phases, precipitates may be present in amounts of about 1 area % or less.

[0027] <Insulating coating> In the grain-oriented electrical steel sheet according to this embodiment, a known insulating film (tension-applying insulating film) may be formed on the surface of the base steel sheet or on the surface of the glass coating. The insulating coating improves the iron loss characteristics of the grain-oriented electrical steel sheet by reducing eddy current losses through electrical insulation, thereby lowering iron loss. In addition to the electrical insulation mentioned above, the insulating coating also provides various other properties such as corrosion resistance, heat resistance, and slipperiness. Furthermore, the insulating coating has the function of applying tension to the grain-oriented electrical steel sheet. By applying tension to the grain-oriented electrical steel sheet and facilitating magnetic domain wall movement in the sheet, the iron loss characteristics of the grain-oriented electrical steel sheet can be improved (iron loss reduced). The insulating coating is formed, for example, by applying a coating liquid mainly composed of metal phosphate and silica to the surface of a glass coating and baking it.

[0028] [Magnetic Domain Control Method] In the magnetic domain control method according to this embodiment, the magnetic domains of the grain-oriented electrical steel sheet are controlled by irradiating the sheet with energy rays while scanning them in a direction intersecting the rolling direction (for example, a direction of 30 to 150° with respect to the rolling direction, preferably a direction of 75 to 105°). In conventional methods that introduce strain (and the resulting elastic stress) into a steel plate by generating a temperature difference during energy beam irradiation, elastic stress is introduced by irradiating with a high-energy beam for a short time. In this case, the temperature difference generated in the steel plate is large, resulting in areas where large localized elastic stress is introduced. In the magnetic domain control method according to this embodiment, compared to conventional irradiation conditions, the irradiation time at each position is extended by irradiating with energy rays in such a way that sufficient elastic stress (compressive elastic stress) is introduced while slowing down the change in elastic stress. To achieve this, the power density of the energy rays is reduced, the average irradiation energy density is increased, and the time that the energy rays are irradiated to a single point on the steel plate is extended. Specifically, in the magnetic domain control method according to this embodiment, the unit is W / mm 2 The power density of energy rays at a given time is expressed as Ip, in units of mJ / mm². 2 When the average irradiation energy density is Ua, the beam diameter in the scanning direction of the energy ray in units of mm is d, and the scanning speed of the energy ray in units of m / s is v, the energy ray is irradiated such that Ip, Ua, d, and v satisfy the following equations (1) to (3). Ip ≤ 1500 (1) Ua≧1.5 (2) d / v≧0.00010 (3) d / v corresponds to the time (s) that an energy ray is irradiated onto a single point on a steel plate at a given location. If any one of equations (1) to (3) is not satisfied, there is concern that the degree of change in elastic stress in the thickness direction of the plate may exceed 4 MPa per μm. While there is no lower limit to Ip, Ip may be 100 or higher in terms of producing effective magnetic domain subdivision. While there is no upper limit to Ua, a Ua of 5.0 or less, or 3.0 or less, is preferable from the perspective of not degrading noise characteristics, as it will result in better noise characteristics. There is no upper limit to d / v, but d / v may be 0.00100 or less.

[0029] As mentioned above, in conventional methods of introducing elastic stress through the temperature difference generated in steel sheets during energy beam irradiation, it was common to irradiate the steel sheet with the energy beam for a short period of time. When a coating was formed on the surface of the grain-oriented electrical steel sheet, measures such as widening the beam diameter to prevent damage to the coating were considered, but further extending the irradiation time within a range that does not degrade the coating would reduce the elastic stress and lead to a decrease in productivity, so this was not considered. The inventors focused on the degree of change in elastic stress and found that significant effects could be obtained by irradiating with energy rays under the above conditions, which have not been conventionally set.

[0030] Preferably, Ip and Ua satisfy the following equations (4) and (5). Ip ≤ 1000 (4) Ua≧2.5 (5)

[0031] In the magnetic domain control method according to this embodiment, the energy beam is, for example, a laser or an electron beam. However, in the case of a pulsed wave, changes in elastic stress occur in the scanning direction, and it is difficult to secure a long irradiation time like that of the magnetic domain control method according to this embodiment. Therefore, a continuous wave energy beam, such as a continuous wave laser, is used as the energy beam. For example, by using a continuous wave laser, 25 μm ≤ W Ave. A grain-oriented electrical steel sheet having irradiation marks satisfying ≤200 μm can be obtained.

[0032] The steel sheet used for magnetic domain control may be any known grain-oriented electrical steel sheet, and its manufacturing method is not particularly limited. In other words, magnetic domain control may be performed on grain-oriented electrical steel sheets manufactured by any manufacturing method. A typical grain-oriented electrical steel sheet is manufactured by a manufacturing method that includes the following steps. The hot rolling process involves heating steel billets such as slabs and hot rolling them to produce hot-rolled steel sheets. A hot-rolled sheet annealing process is performed on the aforementioned hot-rolled steel sheet, A pickling step is performed to pickle the hot-rolled steel sheet after the hot-rolled sheet annealing step, A cold rolling process is performed on the hot-rolled steel sheet after the pickling process, by cold rolling it once or multiple times with annealing in between, to obtain a cold-rolled steel sheet. A decarburization annealing process is performed on the cold-rolled steel sheet, A finish annealing step is performed in which an annealing release agent mainly composed of MgO powder is applied to the front and back surfaces of the cold-rolled steel sheet, which is the base material steel sheet after the decarburization annealing step, and after drying, a finish annealing is performed to form a glass coating. A coating formation step, which involves forming an insulating coating on the glass coating. Furthermore, when obtaining grain-oriented electrical steel sheets having the chemical composition exemplified above, considering that the content of some elements changes due to decarburization, finish annealing, etc., it is acceptable to use steel billets containing, by mass%, C: 0.010~0.200%, Si: 3.00~4.00%, sol.Al: 0.010~0.040%, Mn: 0.01~0.50%, N: 0.020% or less, S: 0.005~0.040%, P: 0.030% or less, Cu: 0~0.50%, Cr: 0~0.50%, Sn: 0~0.50%, Se: 0~0.020%, Sb: 0~0.50%, Mo: 0~0.10%, with the remainder being Fe and impurities. [Examples]

[0033] The grain-oriented electrical steel sheet of the present invention will be described in more detail using examples. The following examples are merely examples of the grain-oriented electrical steel sheet and its manufacturing method according to the present invention, and the grain-oriented electrical steel sheet and its manufacturing method according to the present invention are not limited to the examples below.

[0034] For a grain-oriented electrical steel sheet with a thickness of 0.23 mm, consisting of 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 remainder being Fe and impurities, magnetic domain control was performed by laser irradiation, scanning in a direction perpendicular to the rolling direction at a 5 mm pitch in the rolling direction under the conditions shown in Table 1. Multiple samples were cut from the grain-oriented electrical steel sheet after magnetic domain control, measuring 500 mm in the rolling direction including the irradiation position and 100 mm in the sheet width direction. For these samples, the distribution of elastic stress and magnetic properties were evaluated using the methods described below.

[0035] [Distribution of elastic stress] Map measurements were performed using electron beam backscatter diffraction (EBSD) on a measurement area encompassing the entire thickness direction, with a width twice the irradiation width of the energy beam centered on the irradiation position of one energy beam, in a cross section parallel to both the rolling direction (RD) and the thickness direction (ND). For the map measurements, the sample, with its measurement surface inclined at 70 degrees to the electron beam irradiation direction, was irradiated with an electron beam in steps of 2 μm or less to obtain an EBSD image. The obtained images were saved at 956 x 956 pixels, and strain calculations were performed using CrossCourt4 from BLG Vantage to calculate the elastic stress in the rolling direction. The reference points for strain and elastic stress were set to the point furthest from the energy ray irradiation position within the measurement range of the grain-oriented electrical steel sheet cross-section, or to its vicinity (within a range of about 10 pixels). Measurement points with a compressive elastic stress of 20 MPa or more were selected, and the compressive elastic stress at each measurement point on a virtual line parallel to the thickness direction passing through that measurement point was compared with the compressive elastic stress at a point moved 1 μm in the thickness direction. However, if there are no measurement points where the compressive elastic stress is 20 MPa or higher (for example, if "NO" is written in the "Is the maximum compressive elastic stress 20 MPa or higher?" column in the table), the compressive elastic stress at each measurement point on a virtual line parallel to the plate thickness direction passing through the measurement point with the maximum compressive elastic stress was compared with the compressive elastic stress at a point moved 1 μm in the plate thickness direction. If the maximum difference in elastic stress is 4 MPa or less, it was determined that the degree of change in elastic stress is small.

[0036] [Magnetic properties] A sample measuring 60 mm in width and 300 mm in length was taken from a grain-oriented electrical steel sheet, including the center of the sheet width. The length of the sample was parallel to the rolling direction. Using this sample, the iron loss W was measured in accordance with JIS C2556 (2015) at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T. 17 / 50 (W / kg) was measured. Iron loss W 17 / 50However, if the value was less than 0.740 W / Kg, it was determined to be a low iron loss. Furthermore, using the above samples, the magnetic flux density (T) was determined by a single-sheet magnetic property test (SST test) in accordance with JIS C2556 (2015). Specifically, a magnetic field of 800 A / m was applied to the samples, and the magnetic flux density (T) was determined.

[0037] [Table 1]

[0038] As can be seen from Table 1, in Invention Examples 1 to 8, where magnetic domain control was performed under conditions where Ip, Ua, and d / v were within the scope of the present invention, the maximum compressive elastic stress was 20 MPa or more and the difference in compressive elastic stress was 4 MPa or less. As a result, excellent iron loss characteristics were obtained. In contrast, in Comparative Examples 1-9, Ip, Ua, or d / v were outside the scope of the present invention, and the maximum compressive elastic stress was less than 20 MPa, or the maximum difference in compressive elastic stress exceeded 4 MPa. As a result, the iron loss characteristics were inferior. [Industrial applicability]

[0039] According to the present invention, it is possible to provide a magnetic domain control method for achieving lower iron loss in grain-oriented electrical steel sheets than in conventional methods, and a grain-oriented electrical steel sheet having lower iron loss than in conventional methods obtained by applying this magnetic domain control method. [Explanation of Symbols]

[0040] TD Sheet width direction RD (Rolling Direction) ND Thickness direction IM irradiation position IW irradiation width MR measurement area R: Region with compressive elastic stress of 20 MPa or higher (high elastic stress region) VL virtual line

Claims

1. In a cross-section perpendicular to the direction of extension of the energy ray irradiation trace and parallel to the plate thickness direction, If a virtual line is drawn in the plate thickness direction such that it includes a position where the compressive elastic stress measured using EBSD is 20 MPa or more, The degree of change in the compressive elastic stress along the aforementioned dashed line is 4 MPa or less per 1 μm over the entire thickness direction of the plate. A grain-oriented electrical steel sheet characterized by the following features.

2. The length in units of μm of the irradiation mark of the energy ray in the direction perpendicular to the extension direction and the plate thickness direction is defined as the width W of the irradiation mark, and the width W of five locations in one irradiation mark is defined as W １ , W ２ , W ３ , W ４ , W ５ In that case, The average value W can be expressed by the following formula (6). Ａｖｅ． The following equation (7) is satisfied, The grain-oriented electrical steel sheet according to claim 1. W Ａｖｅ． =(W １ +W ２ +W ３ +W ４ +W ５ ) / 5 (6) 25≦W Ａｖｅ． ≦200 (7)

3. A magnetic domain control method included in the manufacturing method of a grain-oriented electrical steel sheet according to Claim 1 or 2, wherein the magnetic domain control of the grain-oriented electrical steel sheet is performed by irradiating the sheet with energy rays while scanning in a direction intersecting the rolling direction of the grain-oriented electrical steel sheet, Unit: W / mm ２ The power density of energy rays at that point is expressed as Ip, in units of mJ / mm². ２ When the average irradiation energy density is Ua, the beam diameter in the scanning direction of the energy line in units of mm is d, and the scanning speed of the energy line in units of m / s is v, The Ip, Ua, d, and v satisfy the following equations (1) to (3): A magnetic domain control method characterized by the following features. Ip ≤ 1500 (1) Ua ≥ 1.5 (2) d / v≧0.00010 (3)

4. The Ip and Ua satisfy the following equations (4) and (5): The magnetic domain control method according to feature 3. Ip ≤ 1000 (4) Ua ≥ 2.5 (5)

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