Directional electromagnetic steel sheet

Abstract

This grain-oriented electrical steel sheet has a surface on which a plurality of linear strains extending in a direction of 60 to 120° relative to the longitudinal direction have been introduced, wherein the longitudinal spacing between adjacent ones of the linear strains is 2 to 10 mm, the width of the linear strain, which is the width perpendicular to the extension direction of the linear strain, increases and decreases periodically in the extension direction of the linear strain, with a period of 200 to 400 μm, the period of change in the width of adjacent ones of the linear strains is shifted by 0.4 to 0.6 periods in the extension direction of the linear strain, the ratio of the maximum width to the minimum width is 1.2 to 8.0, and the minimum width is 30 μm or more.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2023-073596, filed on April 27, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are soft magnetic materials and are primarily used as iron core materials for transformers, and therefore require magnetic properties such as high magnetization characteristics and low core loss. Iron loss is the power loss consumed as heat energy when an iron core is excited by an AC magnetic field, and from the perspective of energy conservation, it is desirable to have as low iron loss as possible. The level of iron loss is affected by factors such as magnetic susceptibility, sheet thickness, coating tension, amount of impurities, electrical resistivity, crystal grain size, and magnetic domain size. Even now, when various technologies have been developed for grain-oriented electrical steel sheets, research and development into reducing iron loss is ongoing in order to increase energy efficiency. One method proposed for reducing iron loss is to irradiate the steel sheet surface with a laser. With this technology, it is said that the laser irradiation introduces distortion into the surface, which subdivides the 180° magnetic domain width and reduces eddy current loss, which is a part of iron loss.

[0003] For example, Patent Document 1 describes a process for irradiating a surface of a grain-oriented electrical steel sheet with a focused continuous wave laser beam while scanning the surface in a direction inclined from the rolling direction of the grain-oriented electrical steel sheet, and a process for repeating the process while shifting the area scanned with the continuous wave laser beam at a predetermined interval, in which the average power of the continuous wave laser beam is represented 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 ), 1.0 mm ≦ PL ≦ 3.0 mm, and 0.8 mJ / mm 2 ≦Ua≦2.0mJ / mm 2The present invention discloses a method for producing a grain-oriented electrical steel sheet in which magnetic domains are controlled by irradiation with laser light, the method being characterized by satisfying the above requirements. Patent Document 1 shows that it is possible to easily reduce iron loss in both the L direction and the C direction of a grain-oriented electrical steel sheet while ensuring high productivity.

[0004] The technique of Patent Document 1 achieves a certain degree of iron loss reduction effect by reducing eddy current loss, but the iron loss reduction effect is not as great as expected from the subdivision of the magnetic domain width, and there is room for improvement. In addition, while laser irradiation of grain-oriented electrical steel sheet as proposed in Patent Document 1 is effective in reducing iron loss, there was a problem in that the closure domains formed by laser irradiation increased magnetostriction, thereby degrading noise characteristics.

[0005] Patent Document 2 discloses a method for producing a grain-oriented electrical steel sheet with excellent magnetic properties, in which the effect of reducing iron loss is not lost even after stress relief annealing. Patent Document 2 also discloses that in a method for locally forming grooves in a final cold-rolled sheet, by improving the shape of the grooves, it is possible to obtain even lower iron loss than in the past.

[0006] However, the technology of Patent Document 2 is insufficient in reducing eddy current loss compared to the technology of imparting minute thermal strain to a steel sheet by irradiating it with laser light and plasma, and does not take noise characteristics into consideration.

[0007] Patent Document 3 discloses a grain-oriented electrical steel sheet in which a plurality of strain regions are formed in the rolling direction at periodic intervals s (mm) in the rolling direction, the strain regions being locally introduced into a surface layer portion of the steel sheet and extending in a direction transverse to the rolling direction, and in which closure domain regions are formed continuously over 200 mm or more in the width direction, in which the width in the rolling direction at the steel sheet surface changes periodically, and in which each of the closure domain regions satisfies the following conditions: the ratio (Wmax / Wmin) of the maximum width Wmax in the rolling direction at the steel sheet surface to the minimum width Wmin is 1.2 to 2.2, the average width Wave in the rolling direction at the steel sheet surface is 80 μm or more and 250 μm or less, the maximum depth D in the sheet thickness direction is 32 μm or more, and (Wave×D) / s is 0.0007 mm or more and 0.0016 mm or less. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent No. 4669565 [Patent Document 2] Japanese Patent Publication No. 6-299244 direction [Patent Document 3] Japanese Patent No. 6060988 Summary of the Invention [Problem to be solved by the invention]

[0009] Patent Document 3 describes that by periodically changing the width of the closure domain region in the rolling direction, it is possible to lower the magnetostrictive harmonic level and achieve both low iron loss and low noise. However, as a result of investigations by the present inventors, in the technology of Patent Document 3, the width of the region where no strain is introduced changes, which inhibits the movement of the domain walls and increases hysteresis loss, and therefore the effect of reducing iron loss by subdividing the magnetic domain width cannot be fully obtained. Moreover, the reason why Patent Document 1 does not achieve the reduction in iron loss expected from the refinement of the magnetic domain width is believed to be because the movement of the magnetic domain walls is hindered and hysteresis loss increases.

[0010] In view of the above problems, an object of the present invention is to provide a grain-oriented electrical steel sheet having lower core loss than conventional steel sheets. [Means for solving the problem]

[0011] The inventors focused on the fact that in technology that achieves low iron loss and low noise by lowering the magnetostrictive harmonic level, although eddy current loss is reduced, hysteresis loss increases, and investigated methods for suppressing the increase in hysteresis loss and achieving even lower iron loss. As a result, they discovered that when introducing linear strain into the surface of a grain-oriented electrical steel sheet by laser irradiation or other means to refine magnetic domains, an increase in hysteresis loss can be suppressed by periodically increasing and decreasing the width of the introduced strain and by shifting the period of increase and decrease of the strain width between adjacent linear strains.

[0012] The present invention has been made in view of the above findings. [1] A grain-oriented electrical steel sheet according to one embodiment of the present invention has a surface into which a plurality of linear strains extending in a direction at an angle of 60 to 120° to the longitudinal direction have been introduced, wherein the longitudinal spacing between adjacent ones of the linear strains is 2 to 10 mm, the width of the linear strains, which is the width perpendicular to the extension direction of the linear strains, periodically increases and decreases in the extension direction of the linear strain, with a period of 200 to 400 μm, the period of change in the width of adjacent ones of the linear strains is shifted by 0.4 to 0.6 periods in the extension direction of the linear strain, the ratio of the maximum width to the minimum width is 1.2 to 8.0, and the minimum width is 30 μm or more. Effect of the Invention

[0013] According to the above-described aspect of the present invention, by realizing magnetic domain refinement that does not hinder the movement of domain walls, it is possible to suppress an increase in hysteresis loss while reducing eddy current loss, and as a result, a grain-oriented electrical steel sheet with low iron loss can be obtained. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic diagram showing an example of a grain-oriented electrical steel sheet according to the present embodiment, in which linear strain is introduced into the surface. [Diagram 2] This is an example of a graph drawn using ImageJ, with the horizontal axis representing DISTANCE and the vertical axis representing GRAY VALUE. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The grain-oriented electrical steel sheet according to one embodiment of the present invention (the grain-oriented electrical steel sheet according to this embodiment) will be described. As shown in FIG. 1 , the grain-oriented electrical steel sheet 1 according to this embodiment is a grain-oriented electrical steel sheet having a surface on which a plurality of linear strains 2 extending in a direction of 60 to 120° with respect to a longitudinal direction (longitudinal direction of the grain-oriented electrical steel sheet) RD (which can also be said to be a direction of ±30° with respect to a width direction TD) have been introduced, in which the spacing PL of adjacent linear strains 2 in the longitudinal direction RD is 2 to 10 mm, the width of the linear strains 2, which is the width in the direction perpendicular to the extension direction of the linear strains 2, increases and decreases periodically in the extension direction of the linear strain 2, with a period CYC of 200 to 400 μm, the period of the width change of adjacent linear strains 2, 2' among the plurality of linear strains 2 is shifted by 0.4 to 0.6 periods in the extension direction of the linear strain, the ratio (Tmax / Tmin) of the maximum width Tmax to the minimum width Tmin is 1.2 to 8.0, and the minimum width Tmin is 30 μm or more. The reasons for each limitation will be explained below.

[0016] <Multiple linear strains extending in directions of 60 to 120 degrees to the longitudinal direction (rolling direction) are introduced on the surface> <The distance between adjacent linear distortions in the longitudinal direction is 2 to 10 mm.> In grain-oriented electrical steel sheets, the axis of easy magnetization is aligned in the longitudinal direction (rolling direction in the manufacturing process) RD. When strain is introduced into the surface of grain-oriented electrical steel sheets by irradiating them with energy rays such as a laser or electron beam in a direction nearly perpendicular to the longitudinal direction while scanning, the iron loss is further reduced due to the 180° magnetic domain refinement effect. In this embodiment, the extension direction of the strain (corresponding to the scanning direction when strain is introduced by energy rays such as a laser or an electron beam) is set at an angle of 60 to 120° with respect to the longitudinal direction (rolling direction). If the angle is outside this range, the 180° magnetic domain refinement effect of the steel sheet decreases, and a sufficient iron loss reduction effect cannot be obtained. In addition, if the distance between adjacent linear distortions in the longitudinal direction (normal rolling direction) RD exceeds 10 mm, the effect of refining the 180° magnetic domains is reduced, resulting in insufficient iron loss improvement. Therefore, the distance between adjacent linear distortions in the longitudinal direction is set to 10 mm or less. It is preferable that the distance between the linear distortions is approximately equal. On the other hand, while reducing the irradiation interval basically reduces the iron loss, if the irradiation interval is too small, the magnetic domain refinement effect saturates and eddy current loss hardly decreases, while the increase in hysteresis loss due to distortion becomes significant, worsening iron loss. Also, noise characteristics may deteriorate. Therefore, the longitudinal interval between adjacent linear distortions is set to 2 mm or more. A linear distortion is a continuous distortion extending in one direction. In this embodiment, the width of the linear distortion is intentionally increased or decreased as described below. Here, in this embodiment, the distance PL in the longitudinal direction between a plurality of linear distortions is the distance from the center of a linear distortion to the center of an adjacent linear distortion.

[0017] <The width of the linear strain, which is the width in the direction perpendicular to the extension direction of the linear strain, periodically increases and decreases in the extension direction of the linear strain> As mentioned above, eddy current loss can be reduced by introducing linear strain by irradiating the surface of grain-oriented electrical steel sheets with energy beams. On the other hand, the introduced strain inhibits the movement of magnetic domain walls. Iron loss consists of eddy current loss and hysteresis loss, and the introduction of strain increases the hysteresis loss of iron loss. In order not to increase the hysteresis loss, it is preferable to reduce the amount of strain. On the other hand, however, if the amount of strain is small, the magnetic domain refinement effect becomes small. The present inventors discovered that by periodically increasing and decreasing the width of a single linear strain (the width in the direction perpendicular to the extension direction), a magnetic domain refinement effect can be obtained with a small amount of strain. However, in order to obtain a sufficient effect, the period of the change and the magnitude of the change must be within the range described below. Here, in this embodiment, "periodically" means that an error of about ±5% or less of the period is allowed (for example, ±10 μm is allowed for 200 μm, and ±20 μm is allowed for 400 μm).

[0018] <The period of change in width of the linear distortion is 200~400μm> <The ratio of the maximum width to the minimum width of the linear distortion is 1.2 to 8.0> In the grain-oriented electrical steel sheet according to this embodiment, the width of part of the linear distortion is changed and part is made larger to control the position at which the closure domains occur (to occur at the largest position), and the period of the width change is controlled to match the domain width. If the ratio of the maximum width to the minimum width of the linear distortion (width ratio) is less than 1.2, the result will be the same as in the conventional case (when a distortion of uniform width is introduced), and there is a concern that the closure domains will occur in unintended locations, and sufficient domain refinement effects will not be obtained. On the other hand, if the width ratio exceeds 8.0, the closure domains may occur in unintended positions, and there is a concern that a sufficient effect of refining the magnetic domains may not be obtained. Therefore, the width ratio is set to 1.2 to 8.0. Regarding the maximum width, it is preferable that when an isosceles triangle is drawn with the length of one period (the length from one valley to the next valley when the width profile is illustrated) as its base and the position where the maximum width of the linear distortion is the apex, the base angle of the triangle is 45° or less. In order to obtain a sufficient magnetic domain refining effect, the width of the linear distortion is set to 30 μm or more even at its smallest portion (narrowest portion). Moreover, the cycle of the width change corresponds to the final magnetic domain width. If the cycle of the change exceeds 400 μm, the magnetic domain width is wide and a sufficient effect of improving iron loss cannot be obtained. Furthermore, although shortening the period reduces the magnetic domain width, if the period is too short, the magnetic domain width will correspond to multiple periods (for example, even if the period is 150 μm, the magnetic domain width will be twice that, 300 μm), and there is a concern that the magnetic domain width may actually become wider. For this reason, the period of width change is set to 200 μm or more.

[0019] <Among the multiple linear strains, adjacent linear strains have width change periods shifted by 0.4 to 0.6 periods in a direction perpendicular to the extension direction of the linear strains> As described above, the width of the introduced strain is changed periodically to obtain the same magnetic domain width as one period of the strain. However, when introducing multiple linear strains, if the linear strains are introduced uniformly, the magnetic domain walls become difficult to move, and the effect of reducing iron loss by dividing the magnetic domain width cannot be fully obtained. This is thought to be because the periodic change in the width of the linear distortion causes the width of the non-distorted area to vary depending on the position when viewed in the longitudinal direction of the grain-oriented electrical steel sheet, making it difficult for the domain walls to move. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, the width of the region where no strain is introduced is made substantially constant by shifting the period of the change in width of adjacent linear strains among the multiple linear strains. The shift in period is approximately half a period (0.5 period) as shown in Fig. 1, and is permissible if it is 0.4 to 0.6 period. The amount of shift is evaluated by using the direction perpendicular to the extension direction of the linear strain as a reference and the amount of shift in the extension direction as a unit of period.

[0020] The location where the linear strain is introduced into the grain-oriented electrical steel sheet can be identified by the following method. In other words, where distortion has been applied to the steel plate, the distortion causes distortion in the iron crystal lattice. A method known as X-ray topography is used to detect this distortion. An overview of this method is given below. Normally, when X-rays are incident on a crystal lattice, the X-rays are reflected at specific angles of incidence and reflection that correspond to each crystal lattice plane, and in this case the angles of incidence and reflection are equal. This is called the Bragg diffraction condition, but depending on the distortion of the crystal, in this case the magnitude of the distortion of the iron crystal, the reflection angle changes slightly relative to the angle of incidence or the reflection intensity is weakened. This is an analytical method that makes use of this phenomenon. The X-ray topography equipment used in the analysis is Rigaku's XRTmicron, with a Cu target as the X-ray source. The diffraction plane during imaging is iron (310). The CCD resolution is 2.4 μm, and the digital resolution is 16 bits. The procedure is as follows: first, a grain-oriented electrical steel sheet in which strain has been imparted by energy rays is cut to a length of 100 mm in the rolling direction and 100 mm in the sheet width direction to prepare a sample. If processing strain is imparted to the steel sheet during processing, it will affect the X-ray reflection behavior, so it must be done carefully. Regarding the obtained sample, an insulating coating is applied to the surface of a normal grain-oriented electrical steel sheet, but whether or not an insulating coating is applied, the location of the strain can be identified, so it is important to prepare the sample so that as little processing strain as possible is imparted depending on the state of the original sample. Then, a topography image is taken in the sheet width direction using a snap shot in high resolution mode. The field of view diameter during the photographing is 6 to 7 mm in the sheet width direction and 7 to 8 mm in the rolling direction. In order to determine the photographing location, a TDI (Time Delay Integration) scan may be performed in advance. Next, the specific locations where distortion has been applied are identified from the captured topography image using image analysis software called ImageJ. To identify the defect, the topography image is expanded on ImageJ, and the range of interest (ROI) is set (pixel width and height are 2.406 μm). The ROI is rectangular, and its range is 646 pixels (equivalent to approximately 1.55 mm) in the rolling direction and 84 pixels (equivalent to approximately 0.20 mm) in the strip width direction. Hereafter, the side parallel to the rolling direction is called the long side of the ROI, and the side parallel to the strip width direction is called the short side of the ROI. Set the ROI so that the part where the distortion is given is contained within the rectangle. At this time, it is okay to check visually, so set the part where the distortion is given to be located at the center of the long side of the ROI. After setting the ROI, next draw a graph with the horizontal axis as DISTANCE and the vertical axis as GRAY VALUE in the ROI setting range. The graph drawing function is part of the functions of ImageJ, and this is used. This results in a spectrum with a negative peak, as shown in Figure 2. The gray scale is read for the plateau-shaped parts at both ends of the spectrum, and their average value is calculated. Hereafter, this average value is called I Ave. The negative peak intensity (minimum value of the spectrum) is called I Bottom Let us assume that Ave. and I Bottom The difference between these two is ΔI Height Here, I can be defined as follows: HH The concept of (Half Height) is introduced. HH is the gray scale value equivalent to half the peak intensity. The width W of the strained area is defined as I HH is defined as the DISTANCE between two points corresponding to I HH = I Height +(0.5×I Height ) · · · (1)

[0021] <Manufacturing method> The grain-oriented electrical steel sheet according to the present embodiment can obtain the above-mentioned effects regardless of the manufacturing method, however, the manufacturing method including the following configuration is preferable because it can be manufactured relatively stably. (1) An irradiation step in which an energy beam is irradiated onto the surface of a grain-oriented electrical steel sheet obtained by a known method at approximately constant intervals of 2 to 10 mm in the longitudinal direction by scanning in a direction of 60 to 120° to the longitudinal direction while periodically changing the width (thickness) of the energy beam in the direction perpendicular to the scanning direction, thereby introducing multiple linear strains into the grain-oriented electrical steel sheet.

[0022] The grain-oriented electrical steel sheet to be irradiated with the energy beam may be a steel sheet obtained by a known method, for example, a grain-oriented electrical steel sheet that satisfies JIS C2553: 2019. The grain-oriented electrical steel sheet preferably has a magnetic flux density B8 (magnetic flux density at 800 A / m) of 1.90 T or more, and more preferably has a grain-oriented electrical steel sheet B8 of 1.92 T or more.

[0023] The energy beam is irradiated by scanning the energy beam in a direction from 60 to 120° to the longitudinal direction at approximately constant intervals of 2 to 10 mm in the longitudinal direction (rolling direction) to introduce multiple linear strains that extend in a direction from 60 to 120° to the longitudinal direction, with adjacent linear strains spaced 2 to 10 mm apart. The energy beam is preferably a continuous wave laser to obtain a linear distortion that is continuous in the extension direction. In addition, since an electron beam or a pulse wave is likely to cause distortion in the plate width direction, a continuous wave laser is preferably used. The laser irradiation conditions may be any known conditions as long as they are within a range in which strain can be introduced into the surface of the grain-oriented electrical steel sheet.

[0024] In the case of a continuous wave laser, when scanning with a polygon mirror, the width of the energy line in the direction perpendicular to the scanning direction can be changed periodically by installing a shutter whose width varies periodically in the scanning direction immediately after the lens. Furthermore, by changing the position of the shutter during scanning, when the periods of adjacent linear distortions are shifted within a given range, the periods of the width changes can be shifted. EXAMPLES

[0025] A grain-oriented electrical steel sheet with a Si content of 3.25% and a thickness of 0.23 mm was prepared. The magnetic flux density B8 of this grain-oriented electrical steel sheet was 1.93 T and the core loss W17 / 50 was 0.90 W / kg. This grain-oriented electrical steel sheet was irradiated by scanning a continuous wave laser in the longitudinal direction (rolling direction) at a constant interval (pitch) shown in Table 1, in the direction (angle relative to the longitudinal direction) shown in Table 1. During scanning, a polygon mirror was used for scanning, and a shutter with a width that periodically varies in the scanning direction was installed immediately after the lens, changing the width of the distortion at the period shown in Table 1. The shift in the period of the change in the width of the strain between adjacent linear strains was as shown in Table 1. The magnetic properties of the obtained grain-oriented electrical steel sheets were evaluated in the following manner.

[0026] [Magnetic property evaluation] A sample with a width of 60 mm and a length of 300 mm was taken from the center of the sheet width of each grain-oriented electrical steel sheet with each test number. The length of the sample was parallel to the rolling direction. Using this sample, the magnetic flux density was determined by a single sheet magnetic property test (SST test) in accordance with JIS C 2556 (2015). Specifically, a magnetic field of 800 A / m was applied to the sample to determine the magnetic flux density B8 (T). Furthermore, using the above sample, the iron loss W17 / 50 (W / kg) was measured at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T in accordance with JIS C 2556 (2015). In addition, the hysteresis loop was measured when the maximum magnetic flux density was set to 1.7 T, and the eddy current loss was calculated from the hysteresis loss obtained from the measurement and W17 / 50. The results are shown in Table 2.

[0027] [Table 1]

[0028] [Table 2]

[0029] As can be seen from Tables 1 and 2, in invention examples Nos. 2, 3, 5, 7, 11-16, 18, 20, 21, 24-26, 30, and 31, in which multiple linear strains whose widths change at a specified period were introduced at specified intervals in a specified direction, the iron loss (W17 / 50) was low, at 0.79 W / kg or less. In contrast, in the comparative examples Nos. 1, 4, 6, 8-10, 17, 19, 22, 23, and 27-29, at least one of the period of change in width of the linear strain, the maximum / minimum width of the strain, the minimum width of the strain, the periodic shift, the spacing between multiple linear strains, and the extension direction was outside the range of the present invention, and the iron loss was large. [Industrial Applicability]

[0030] According to the present invention, by realizing magnetic domain refinement that does not inhibit the movement of magnetic domain walls, it is possible to suppress an increase in hysteresis loss while keeping eddy current loss low, and as a result, it is possible to obtain a grain-oriented electrical steel sheet with low iron loss, which has high industrial applicability. [Explanation of symbols]

[0031] 1 Grain-oriented electrical steel sheet 2 Linear distortion 2' 2 and adjacent linear distortion Longitudinal direction of RD steel sheet (grain-oriented electrical steel sheet) Width direction of TD steel sheet (grain-oriented electrical steel sheet) PL: The distance between linear strains in the longitudinal direction of a steel sheet (grain-oriented electrical steel sheet) CYC cycle Tmin Minimum width Tmax Maximum width

Claims

[Claim 1] A grain-oriented electrical steel sheet having a surface on which a plurality of linear strains extending in a direction of 60 to 120 degrees with respect to a longitudinal direction are introduced, The intervals between adjacent linear strains in the longitudinal direction are each 2 to 10 mm, The width of the linear strain, which is a width in a direction perpendicular to the extension direction of the linear strain, increases and decreases periodically in the extension direction of the linear strain, and the period is 200 to 400 μm; Among the plurality of linear distortions, adjacent linear distortions have a period of change in width that is shifted by 0.4 to 0.6 periods in the extension direction of the linear distortion, a ratio of said maximum width to said minimum width is between 1.2 and 8.0; The minimum width is 30 μm or more. Grain-oriented electrical steel sheet.

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