Grain-oriented electrical steel sheet and method for refining magnetic domains therein

Abstract

An object of the present invention is to provide a grain-oriented electrical steel sheet and a method for refining magnetic domains thereof, which have excellent iron loss characteristics while preventing surface damage by irradiating the surface of an electrical steel sheet that has undergone secondary recrystallization with superimposed lasers having different wavelengths. [Solution] The grain-oriented electrical steel sheet of the present invention comprises an electrical steel sheet substrate and an insulating coating layer located on the electrical steel sheet substrate, wherein a linear deformation portion exists on the surface of the insulating coating layer, a overlapping irradiation boundary portion exists within the deformation portion, and a molten solidified layer exists below the overlapping irradiation boundary portion, and the molten solidified layer contains 5% by weight or less of P.

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a method for refining its magnetic domains, and more particularly to a grain-oriented electrical steel sheet that has excellent iron loss characteristics while preventing surface damage by irradiating a superimposed laser beam onto the surface of an electrical steel sheet that has undergone secondary recrystallization, and a method for refining its magnetic domains. [Background technology]

[0002] Grain-oriented electrical steel sheets have excellent magnetic properties and are generally used as iron core materials for transformers. The production of grain-oriented electrical steel sheets involves rolling and annealing processes unique to the electrical steel sheet manufacturing process. <001> The Goss texture, which is recrystallized in the direction of the grain boundary, is formed throughout the steel sheet.

[0003] In response to climate change, the world is tightening greenhouse gas emission standards by the day. In the case of transformer cores, factors that affect the greenhouse gas emission standards are related to the improvement of efficiency when using magnetic steel sheets. The efficiency of transformer cores is determined by the iron loss and magnetic flux density of the magnetic steel sheets, i.e., their magnetic properties.

[0004] The magnetic flux density of an electrical steel sheet is determined by the degree to which crystal axes that are easy to magnetize are concentrated in the crystal structure, i.e., the higher the crystal orientation, the higher the magnetic flux density is, so the manufacturing process of the electrical steel sheet can have a significant impact.

[0005] The iron loss of magnetic steel sheets is measured at a value of W17 / 50 [W / kg] when a magnetic field of 50Hz frequency is applied at a maximum magnetic flux density of 1.7T. This value is called the guaranteed iron loss value of the iron core material, and this value is generally used as a measure of the iron loss of magnetic steel sheets. However, when designing transformers, a value of W15 / 50 [W / kg] measured when a magnetic field of 50Hz frequency is applied at a lower maximum magnetic flux density of 1.5T is sometimes used. The lower the iron loss value, the better the efficiency of the transformer is evaluated.

[0006] Therefore, in the case of electrical steel sheets, the higher the magnetic flux density and the lower the iron loss, the more efficient the transformer core they can be used for. Of these, the magnetic flux density is considered to be a more important indicator because the process technology for ensuring high magnetic flux density through upward leveling in the manufacturing process of electrical steel sheets has developed to the point where it can support the efficiency of transformers, and iron loss is considered to be a more important indicator.

[0007] This iron loss is divided into eddy current loss and hysteresis loss, and since hysteresis loss tends to decrease as magnetic flux density increases, eddy current loss plays an important role in controlling overall iron loss in grain-oriented electrical steel. Eddy current loss within iron loss is divided into classical eddy current loss and anomalous eddy current loss, and since classical eddy current loss is proportional to the thickness of the steel sheet, the thinner the steel sheet, the less classical eddy current loss there is. Therefore, controlling anomalous eddy current loss is an important technology for reducing iron loss.

[0008] Eddy current loss, which is one type of iron loss, decreases as the magnetic wall spacing of the 180° magnetic domain, which is the magnetic domain in the rolling direction, becomes narrower. Therefore, iron loss can be reduced by miniaturizing the magnetic domain of the electrical steel sheet.

[0009] Magnetic domain refinement in electrical steel sheet refers to the process of applying a physical stimulus to crystal grains with magnetic domain characteristics to separate them into multiple magnetic domains. Methods for magnetic domain refinement include laser irradiation, electron beam irradiation, plasma treatment, etching, and roll pressing. These magnetic domain refinement processes are classified as permanent magnetic domain refinement and temporary magnetic domain refinement, depending on whether the magnetic domain refinement effect is maintained even after stress relief annealing (SRA).

[0010] In the manufacturing process of the electrical steel sheet, the magnetic domain refinement step may be carried out before the decarburization step or after the insulating coating step.

[0011] Meanwhile, the manufactured electrical steel sheets are shipped in a coiled state and processed into the final cores, which takes a long time due to transportation of the products, etc. During this transportation period or while being processed into the cores, there is a possibility that the parts of the electrical steel sheets that are physically stimulated by the magnetic domain refinement may corrode.

[0012] When corrosion occurs in areas of the surface of an electromagnetic steel sheet that have been subjected to physical stimulation, it means that the insulating coating on the surface has peeled off, exposing the base material of the electromagnetic steel sheet. If this is used as an iron core by laminating it as is, the insulating coating formed on the surface of the electromagnetic steel sheet will be destroyed, causing electricity to flow between the upper and lower laminated iron cores, which could even lead to an explosion of the transformer.

[0013] Therefore, even if a physical stimulus is applied to the surface of the electrical steel sheet to refine the magnetic domains, it is necessary to apply the stimulus within a range that does not damage the insulating coating. Summary of the Invention [Problem to be solved by the invention]

[0014] An object of the present invention is to provide a grain-oriented electrical steel sheet and a method for refining its magnetic domains. Specifically, the present invention provides a grain-oriented electrical steel sheet and a method for refining its magnetic domains that prevent surface damage and at the same time have excellent core loss characteristics by irradiating the surface of an electrical steel sheet that has undergone secondary recrystallization with superimposed lasers having different wavelengths. [Means for solving the problem]

[0015] The grain-oriented electrical steel sheet of the present invention comprises an electrical steel sheet substrate and an insulating coating layer located on the electrical steel sheet substrate, wherein a linear deformation portion exists on the surface of the insulating coating layer, a multiple irradiation boundary portion exists within the deformation portion, and a molten solidified layer exists below the multiple irradiation boundary portion, and the molten solidified layer contains 10 wt % or less of P.

[0016] The width of the deformation part of the melted and solidified layer in the direction perpendicular to the length (M W ) may be 0.05 to 10 μm.

[0017] Thickness of the molten and solidified layer (M D ) may be 20% or less of the thickness of the insulating coating layer.

[0018] The insulating coating layer below the deformed portion, excluding the overlapping irradiation boundary, may have a P content of 10 to 30 wt % within a range of 100 nm from the surface in the thickness direction of the steel sheet.

[0019] The thickness of the insulating coating layer under the deformed portion may be 60 to 90% of the thickness of the insulating coating layer where the deformed portion is not formed.

[0020] A metal oxide layer may be interposed between the substrate and the insulating coating layer.

[0021] The method for refining magnetic domains in grain-oriented electrical steel sheet of the present invention includes a first irradiation step of irradiating a first laser beam having a first wavelength; and a second irradiation step of irradiating a second laser beam having a second wavelength, wherein the first beam spot of the first laser beam and the second beam spot of the second laser beam can overlap by 10% or more.

[0022] The first and second lasers are selected from a CO2 laser, an optical fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, or a UV laser.

[0023] The first laser and the second laser may each have an output of 10 to 2000 W.

[0024] The first laser and the second laser may have different wavelengths.

[0025] At the overlapping position, the interval between the time when the first laser beam is irradiated and the time when the second laser beam is irradiated may be 18 ms or less. [Effects of the Invention]

[0026] According to the present invention, by using a superimposed laser to perform optimal magnetic domain refinement, it is possible to further improve the magnetic properties and at the same time to sufficiently suppress damage to the steel sheet surface.

[0027] According to the present invention, it is possible to easily increase the average output by using a long wavelength laser, thereby ensuring the reliability of the processing line, and at the same time, it is possible to minimize the magnetic domains by irradiating a short wavelength laser, thereby effectively improving the magnetism.

[0028] According to the present invention, it is possible to suppress magnetic deviation due to the coating while maintaining the iron loss improvement effect by using lasers in a superimposed manner.

[0029] According to the present invention, the steel sheet can be stably preheated without destroying the insulating coating layer, and residual stress due to thermoelastic deformation of the steel sheet can be induced with a width exactly required for closure domain formation, regardless of the thickness of the insulating coating layer, thereby enabling accurate magnetic domain refinement.

[0030] According to the present invention, it is possible to provide a directional magnetic domain refined product with excellent core loss in low and high magnetic fields by maximizing thermal shock in the thickness direction even under low laser output conditions. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a graph showing the light absorptance of a steel sheet depending on the laser wavelength. [Figure 2] 1A and 1B are schematic diagrams illustrating the concept of magnetic domain refinement in which a deformation portion is formed using a superimposed laser according to an embodiment of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing a beam spot of a superimposed laser according to an embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram showing a beam spot of a superimposed laser according to still another embodiment of the present invention. [Figure 5] 1 is a schematic diagram showing a steel plate surface where a deformed portion and an overlapping irradiation boundary portion exist in one embodiment of the present invention. FIG. [Figure 6]1 is a schematic diagram showing a cross section in the thickness direction (Z direction) of a steel plate in which a deformed portion and an overlapping irradiation boundary portion exist in one embodiment of the present invention. [Figure 7] 1 is a photograph of a molten and solidified layer analyzed by FIB (Focused Ion Beam)-TEM (Transmission Electron Microscopy) in Example 1. [Figure 8] 8 is a graph showing elemental analysis of the molten and solidified layer in the thickness direction of FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0032] Terms such as "first," "second," and "third" are used to describe various portions, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Therefore, a first portion, component, region, layer, or section described below can be referred to as a second portion, component, region, layer, or section without departing from the scope of the present invention.

[0033] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in this specification, the term "comprising" refers to the inclusion of specific features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0034] When a part is referred to as being "on" or "on" another part, it means that it is directly on or above the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0035] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or very formal meaning unless otherwise defined.

[0036] Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0037] An object of one embodiment of the present invention is to irradiate the surface of an electromagnetic steel sheet with a superimposed laser beam to prevent surface damage while simultaneously imparting excellent core loss characteristics.

[0038] One embodiment of the present invention includes a first irradiation step of irradiating a first laser beam having a first wavelength; and a second irradiation step of irradiating a second laser beam having a second wavelength, wherein the first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by 10% or more.

[0039] One of the preferred methods for improving the core loss of grain-oriented electrical steel sheets is to refine the magnetic domains using a laser.

[0040] As shown in Figure 2, the magnetic domain refinement process for grain-oriented electrical steel sheet involves irradiating a laser beam in a direction intersecting the rolling direction (RD) to form linear deformations 10. The linear deformations are dotted or continuous. Here, linear or linear deformations include not only solid lines but also intermittent lines such as dotted or dashed lines, and also include zigzag lines seen microscopically but also straight lines seen macroscopically, essentially including all deformations that form a line.

[0041] The formation of deformations in steel sheets by laser irradiation refers to the deformation of the crystal lattice caused by the thermal shock of laser irradiation. This deformation of the crystal lattice occurs when the steel sheet is rapidly heated locally by the laser and then immediately cooled. At this time, the heating rate of the steel sheet is proportional to the energy density (power density) of the laser per unit time.

[0042] However, since the deformation of the crystal lattice due to thermal shock during laser irradiation increases as the total laser irradiation energy increases, if the steel sheet is irradiated with energy greater than that required for magnetic domain refinement, a heat source greater than that required for closure domain formation will diffuse to the surrounding area, resulting in greater magnetic deformation. Therefore, the deformation of the crystal lattice due to thermal shock during laser irradiation requires exactly the amount of lattice deformation energy required to form closure domains, and in order to suppress thermal diffusion, it is preferable to irradiate the laser incident energy only over a narrow area for a short period of time.

[0043] The interaction conditions between the laser beam and the steel sheet are affected by the laser characteristics and the laser beam absorption rate of the steel sheet. The laser beam absorption rate is affected by the surface roughness of the steel sheet, the temperature of the steel sheet, the absorption characteristics of the coating on the steel sheet surface, and the laser wavelength. However, when the manufacturing conditions of the grain-oriented electrical steel sheet on which the coating is formed are constant, the surface roughness of the steel sheet, the temperature of the steel sheet, and the absorption characteristics of the coating on the steel sheet surface should also be constant, and in this case the laser beam absorption rate of the steel sheet depends on the laser wavelength.

[0044] That is, when the manufacturing conditions of a steel sheet are constant, the laser absorptance is affected by the laser wavelength. As shown in Figure 1, the laser absorptance of a steel sheet is approximately 35 to 40% when the wavelength is short (e.g., YAG or fiber laser at 1.06 μm), but is relatively low at approximately 5 to 10% when the wavelength is long (e.g., CO2 laser at 10.6 μm).

[0045] In this way, in the process of refining the magnetic domains of grain-oriented electrical steel sheets using a laser, it is more efficient to use a short-wavelength laser than a long-wavelength laser in order to ensure stable iron loss characteristics.

[0046] On the other hand, the surface of the electrical steel sheet to be subjected to magnetic domain refinement treatment is coated with an insulating coating several to several tens of micrometers thick, primarily composed of phosphate and silica. These coatings have relatively low absorption of laser beams with short wavelengths (e.g., YAG or fiber lasers at 1.06 μm), but exhibit high absorption with long wavelengths (e.g., CO2 lasers at 10.6 μm). As a result, the thickness of the insulating coating must be taken into consideration with long wavelength lasers, but the thickness of the insulating coating does not need to be considered as much with short wavelength lasers as with long wavelength lasers.

[0047] As mentioned above, short-wavelength lasers and long-wavelength lasers have different characteristics. Therefore, when short-wavelength lasers and long-wavelength lasers are used simultaneously, the advantages of each laser applied to magnetic domain miniaturization are exhibited preferentially without side effects, resulting in a synergistic effect.

[0048] Here, the term "using overlapping lasers" refers to the use of two or more types of laser beams irradiated onto the surface of a steel sheet, with the spot of one laser beam partially or entirely located within the spot of another laser beam. Therefore, in one embodiment of the present invention, overlapping lasers with different wavelengths include not only lasers in which the spot of one laser beam completely overlaps the spot of another laser beam, but also lasers in which the spots partially overlap. Furthermore, the irradiation times at the overlapping positions do not necessarily need to be simultaneous, and overlapping irradiation at regular time intervals is also acceptable. That is, even if the laser beams do not overlap at a specific time point, as shown in FIG. 4, when a first laser beam moves horizontally in the traveling direction (X direction) over time and overlaps with the previously irradiated second laser beam, this is considered to be overlapping. However, overlapping of first laser beams as the first laser beams advance in the irradiation traveling direction (X direction) is not considered to be overlapping.

[0049] In one embodiment of the present invention, the beam spot refers to the beam spot on the steel sheet surface 40. In Figure 3, a first beam spot of the first laser beam 21 and a second beam spot of the second laser beam 22 are shown schematically.

[0050] The first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by 10% or more. 10% or more means that the width (B 1W ) and the width of the second laser beam (B 2W ) with respect to the width of the small laser beam W ) ratio. In FIG. 3, the width (B 1W ) is small, in which case the overlap ratio is O W / B 1W It can be calculated as follows.

[0051] The width of the laser beam is the length of the laser beam in the direction (Y direction) perpendicular to the length direction of the deformed portion (or the laser irradiation direction, X direction). The length of the laser beam is the length of the laser beam in the length direction of the deformed portion (or the laser irradiation direction, X direction). In FIG. 3, the length of the first laser beam (B 1L ) and the length of the second laser beam (B 2L ) was displayed.

[0052] As shown in Figure 4, when the laser beams do not overlap at a specific time, the width of the overlapping area (O W ) is the longest, which is considered to be the overlap ratio.

[0053] Meanwhile, in one embodiment of the present invention, an overlapping region exists, and therefore overlapping irradiation boundaries 23 exist at both ends of the overlapping region in a direction (Y direction) perpendicular to the longitudinal direction of the deformed portion (or the laser irradiation direction, X direction). A molten and solidified layer 11 exists below the overlapping irradiation boundaries 23. This molten and solidified layer 11 will be described later in connection with grain-oriented electrical steel sheets.

[0054] The first and second lasers can be selected from a CO2 laser, an optical fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, or a UV laser.

[0055] More specifically, the first laser (A), which is a short wavelength laser, may be a laser with a relatively short wavelength, such as an optical fiber (Er-Fiber, Yb-Fiber, Tm-Fiber) laser, a YAG (Nd:YAG, Yb:YAG) laser, a ruby ​​laser, a sapphire laser, etc. In addition, the first laser may be a disk laser (1.03 μm), a diode laser (0.808 to 0.980 μm), or a UV laser (0.150 to 0.355 μm).

[0056] The second laser, which is a long-wavelength laser, can be a laser with a wavelength relatively longer than the short-wavelength laser. For example, a CO2 laser is preferable as the second laser. However, if a UV laser (0.150-0.355 μm) is used as the first laser, which is a short-wavelength laser, any laser with a longer wavelength than the first laser can be used as the second laser. For example, if a UV laser (0.150-0.355 μm) is used as the first laser, a YAG laser can also be used as the second laser.

[0057] Below, the magnetic domain miniaturization method using the superimposed laser 30 will be explained in more detail using an example in which an optical fiber laser is used as the first laser with a short wavelength and a CO2 laser is used as the second laser with a long wavelength.

[0058] The first laser, an optical fiber laser, uses a short wavelength laser with a relatively high laser absorption rate for steel sheets, making it possible to irradiate a narrow area with incident energy sufficient to precisely induce lattice deformation and residual stress due to thermoelastic deformation, just enough to form closure domains, for a short period of time. Furthermore, because the optical fiber laser used as the first laser has a narrow incident energy range, it can suppress thermal diffusion to the surrounding area, minimizing unnecessary thermal deformation.

[0059] On the other hand, the second laser, a CO2 laser, can be used with an average output ranging from several hundred watts to several kilowatts or more, depending on the steel sheet speed, and can easily induce thermoelastic deformation in the irradiated area of ​​the steel sheet. Furthermore, the second laser, a CO2 laser, has high absorption in the insulating coating made of phosphate and silica, allowing it to steadily pass through the coating layer. Therefore, the second laser, a CO2 laser, can steadily induce thermoelastic deformation in the steel sheet without destroying the insulating coating layer, making it suitable for a type of preheating role. However, because the second laser, a CO2 laser, has low laser absorption in steel sheet, it is preferable to irradiate the steel sheet with a laser beam that induces thermoelastic deformation but does not induce permanent deformation.

[0060] That is, when a long wavelength laser such as a CO2 laser is used as the second laser, the area that is subjected to thermal shock on the steel sheet becomes too wide, preventing magnetic domain refinement. Therefore, an optical fiber laser with a relatively short wavelength is used as the first laser, which is the main laser for magnetic domain refinement, and a CO2 laser with a relatively long wavelength is used as an auxiliary laser that serves as a kind of preheating role to induce thermoelastic deformation of the steel sheet.

[0061] The reason why a short-wavelength optical fiber laser was selected as the first laser and used as the main laser for magnetic domain refinement is that the laser absorption rate on the steel sheet surface is high, forming strong compressive stress areas in the laser irradiated areas, and lancet magnetic domains (closure magnetic domains) can be easily formed in these compressive stress areas due to the reduction in magnetoelastic energy.

[0062] In this case, by miniaturizing the magnetic domains, 180° magnetic domains (opposite poles of the lancet magnetic domains) are formed in the surface direction by magnetoelastic energy, and 90° magnetic domains are formed in the thickness direction to reduce the magnetoelastic energy, which narrows the spacing between the magnetic domains and ultimately reduces abnormal eddy current loss.

[0063] As described above, the magnetic domain refinement method according to one embodiment of the present invention uses a short-wavelength optical fiber laser as the first laser to precisely induce residual stress due to thermoelastic deformation in the steel sheet to the width required for closure domain formation, enabling accurate magnetic domain refinement. Meanwhile, the long-wavelength CO laser is used as the second laser to stably preheat the steel sheet without destroying the coating layer.

[0064] In addition, the first laser, a short-wavelength optical fiber laser, can form a small final beam width, which has the advantage of improving the laser absorption rate in the steel sheet, but the depth of field is relatively short. However, the second laser, a long-wavelength CO2 laser, has the advantage of a wide final beam width, which has the advantage of relatively low laser absorption rate in the steel sheet, but a deep depth of field. Therefore, when these two laser beams are simultaneously superimposed and irradiated, the laser absorption rate in the steel sheet can be further increased.

[0065] At this time, the beam spot of the optical fiber laser, which is the first short-wavelength laser irradiated onto the surface of the steel sheet, is preferably approximately circular in shape, and its diameter (B W1 , B L1 The beam spot of the optical fiber laser may have a width (B W1 ) is 10 to 200 μm, and its length (B L1 ) can be equal to or shorter than the length of the beam spot of the second laser, the CO2 laser, or it can be longer.

[0066] The beam width (B W1When the beam width (B) of the first laser, the optical fiber, decreases to less than 10 μm, the energy density is concentrated in a narrow area, which can cause problems such as poor magnetic flux density and iron loss, and the optical system structure becomes complicated. W1 If the thickness θ is 200 μm or more, the thermal effect in the longitudinal direction of the steel sheet increases, which is undesirable as it may result in a decrease in magnetic flux density.

[0067] On the other hand, the beam spot of the CO2 laser, which is the second long-wavelength laser irradiated onto the surface of the steel plate, has a beam width (B 2W ) is 100 to 400 μm, and the beam length (B 2L An elliptical shape with a radius of 0.4 to 20 mm is preferable. Also, the beam spot of a long wavelength CO2 laser can be used even if it is a circle with a radius of 100 μm or more.

[0068] The second laser, CO2, has a beam width (B 2W ) to be formed within 100 μm is not preferable because the mirror optical system, such as an optical fiber laser, becomes complicated, and if it is 400 μm or larger, the thermal effect in the steel sheet length direction becomes large, resulting in a decrease in magnetic flux density, which is also not preferable.

[0069] The reason for limiting the beam spot size of the long-wavelength CO2 laser is to consider the range in which the thermal deformation effect of the laser beam acting on the steel plate can be maintained when the laser is irradiated at high speed onto the surface of a steel plate moving at high speed.

[0070] The case where lasers are used in a superimposed manner according to one embodiment of the present invention will now be described in more detail.

[0071] As shown in Figures 3 and 4, using the first laser beam 21 and the second laser beam 22 in an overlapping manner means controlling the beam spot of the first laser beam 21 and the beam spot of the second laser beam 22 to overlap. In other words, as shown in Figure 3, when the laser beam spot 20 irradiated on the steel sheet surface is viewed in a plan view, the first laser beam 21 is said to be "overlapped" anywhere within the range of the second laser beam 22, which has a larger beam spot. This also means that the first laser beam 21 is "overlapped" partially within the range of the second laser beam 22. Furthermore, as shown in Figure 4, even if the laser beams do not overlap at a specific point in time, if the first laser beam 21 moves horizontally in the traveling direction (X direction) over time and overlaps with the position of the previously irradiated second laser beam 22, this is also considered to be overlapped.

[0072] In one embodiment of the present invention, the oscillation mode of the laser beams used for both the first and second lasers is preferably a continuous wave laser that continuously generates laser light, but a pulse laser can also be used.

[0073] As for the quality of the laser beams used, it is preferable that both the first and second lasers are in Gaussian mode of TEM00, but multi-transverse mode of TEM0i can also be used.

[0074] However, since the superimposed laser beam 20 of different wavelengths irradiated onto the surface of the steel sheet according to one embodiment of the present invention can minimize the thermal impact in the length direction of the steel sheet while maximizing the thermal shock in the thickness direction, the beam shape and beam quality of each laser are not specifically limited.

[0075] The first laser and the second laser may each have an output power of 10 to 2000 W. More specifically, the output power of the first laser may be 1000 to 2000 W, and the output power of the second laser may be 100 to 700 W. These output power ranges of each laser indicate the laser output conditions when the steel sheet advances at a speed of 15 mpm, and the laser output power value can be optimally controlled depending on the advance speed of the steel sheet.

[0076] When the laser beam 30 obtained by superimposing the first and second lasers as described above is irradiated onto the surface of the steel sheet, the interval (i.e., the interval between the deformed portions in the rolling direction of the steel sheet) is 2 to 10 mm, the angle between the rolling direction and the laser traveling direction (the length direction of the deformed portion, X direction) can be 75 to 105°, and the scanning speed is preferably 0.1 to 300 m / sec.

[0077] The electrical steel sheet used here is preferably an electrical steel sheet that has undergone secondary recrystallization.

[0078] If the irradiation interval of the superimposed laser beam 20 irradiated onto the steel sheet surface is too narrow, less than 2 mm, the influence of the heat-affected zone becomes large, resulting in poor magnetic flux density and iron loss. On the other hand, if the irradiation interval is 10 mm or more, the thermal shock effect for ensuring the magnetic domain refinement effect is reduced, making it difficult to achieve the effect.

[0079] In addition, when the superimposed laser beam 20 is irradiated onto the surface of the steel sheet, it can be irradiated in a direction perpendicular to or inclined from the rolling direction of the steel sheet, and the angle between the rolling direction and the laser propagation direction (length direction of the deformed part, X direction) can be 75 to 105°. If this angle range is exceeded, the desired magnetic domain refinement effect may not be achieved.

[0080] The scanning speed of the superimposed laser is the same as the traveling speed of the steel sheet, and as the traveling speed increases, the scanning speed must be increased. Therefore, the scanning speed is preferably 0.1 to 300 m / sec, and this speed means the value exemplified under the condition of 15 mpm.

[0081] Meanwhile, as shown in FIG. 3, the first and second laser beams can be simultaneously irradiated in an overlapping manner, but as shown in FIG. 4, they can also be irradiated in an overlapping manner with a time interval therebetween. However, the time interval between the time when the first laser beam is irradiated and the time when the second laser beam is irradiated at the overlapping position may be 16 ms or less. If this time range is exceeded, it is difficult to fully obtain the effect of irradiating the lasers in an overlapping manner. The time interval is the time between the time when the first laser (or second laser) advances after the second laser (or first laser) is irradiated and the width (O W ) is the time until it reaches its maximum.

[0082] In one embodiment of the present invention, the grain-oriented electrical steel sheet 100 includes an electrical steel sheet substrate 50 and an insulating coating layer 60 disposed on the electrical steel sheet substrate 50, and a linear deformation portion 10 is present on the surface of the insulating coating layer 60, and an overlapping irradiation boundary portion 23 is present within the deformation portion 10.

[0083] As shown in FIG. 3, the overlapping irradiation boundary 23 refers to both ends of the overlapping region in the Y direction when the first laser beam 21 and the second laser beam 22 are irradiated in an overlapping manner. This overlapping irradiation boundary 23 is difficult to identify with the naked eye and can be determined by whether a molten solidified layer 11 is formed in the lower insulating coating layer 10. That is, the molten solidified layer 11 is formed below the overlapping irradiation boundary 23 in the Y direction, starting from the overlapping irradiation boundary 23. This molten solidified layer 11 is formed by the volatilization of phosphorus (P) in the insulating coating layer 10, so there is little phosphorus in the molten solidified layer 11. That is, if the P content is 10 wt% or less, it is determined that the molten solidified layer 11 has been formed. More specifically, if the P content is 8 wt% or less, it is determined that the molten solidified layer 11 has been formed.

[0084] The reason why the molten and solidified layer 11 is formed when the superimposed laser beam is irradiated in this way is that the vaporization point of the phosphate that constitutes the insulating coating layer 60 is low, so phosphorus vaporizes first when the superimposed laser is irradiated, and silicon oxide consisting of Si and O is re-solidified in an amorphous state. When an amorphous re-solidified layer is formed on the surface of the insulating coating layer in this way, the inherent properties of the amorphous state improve corrosion resistance.

[0085] The width of the deformation part of the molten and solidified layer in the direction perpendicular to the length (Y direction) (M W ) may be 0.05 to 10 μm. When it is in the above range, the effect of improving iron loss and corrosion resistance by superimposed irradiation is appropriately exhibited. More specifically, the width (M W ) may be 0.1 to 5 μm.

[0086] Thickness of the molten and solidified layer (M D The thickness of the molten and solidified layer (M D If the thickness (M) of the molten and solidified layer is too thick, the absolute thickness of the insulating coating layer becomes thin, which may have a detrimental effect on corrosion resistance and may reduce the tensile effect of the insulating coating layer, resulting in poor iron loss. Therefore, it is preferable to limit the thickness (M) of the molten and solidified layer within this range. D The thickness of the molten and solidified layer (M D ) means the depth from the surface of the insulating coating to the boundary where P becomes 10%. When a molten and solidified layer is formed within 20% of the thickness of the insulating coating layer 60, it means that sufficient laser energy is applied to the steel sheet without causing further damage to the insulating coating layer. More specifically, the thickness (M D ) may be 50 to 500 nm.

[0087] The insulating coating layer 60 below the deformed portion 10, excluding the overlapping irradiation boundary portion 23, may have a P content of 10 to 30 wt % within a 100 nm range from the surface in the thickness direction of the steel sheet. As described above, the laser energy in the deformed portion 10 and the overlapping irradiation region is sufficiently large that the insulating coating layer 60 itself vaporizes rather than melts, and phosphorus (P) does not selectively volatilize. More specifically, the P content may be 12 to 25 wt %.

[0088] The deformed portion 10 is also indistinguishable from the surface of the insulating coating layer other than the deformed portion with the naked eye, but can be distinguished by the thickness of the insulating coating layer 60 below the deformed portion 10. That is, when irradiating with the first or second laser, the thickness of the insulating coating layer below the irradiated surface is reduced compared to the unirradiated portion. When the deformed portion 10 is formed on the electrical steel sheet by irradiating with the superimposed laser and the molten and solidified layer 11 is formed in the insulating coating layer 60, the formation of the molten and solidified layer 11 causes shrinkage of the insulating coating layer 60, which may change the thickness of the insulating coating layer 60 where the deformed portion of the steel sheet is formed.

[0089] More specifically, the thickness of the insulating coating layer 60 below the deformed portion 10 may be 60 to 90% of the thickness of the insulating coating layer where the deformed portion is not formed. If the coating layer thickness at the deformed portion formed on the steel sheet is excessively thin, the reduced coating thickness may result in a deterioration in corrosion resistance and a decrease in tension, which may result in a deterioration in iron loss. If the coating layer is excessively thick, it means that the molten and solidified layer 11 is not properly formed, making it difficult to expect an appropriate improvement in iron loss. The thickness of the insulating coating layer 60 refers to the depth from the surface of the insulating coating layer 60 to the boundary where the P content is 5 wt% when the phosphorus content increases by 10 wt% or more and then decreases again to 5 wt% or less.

[0090] The grain-oriented electrical steel sheet may further have a metal oxide layer (glass coating layer, not shown) formed between the electrical steel sheet substrate and the insulating coating layer.

[0091] Here, the metal oxide layer is mainly composed of forsterite, and the insulating coating layer is mainly composed of phosphate and colloidal silica. In the present invention, the main component is forsterite, and the amount of oxygen applied to one side of the steel sheet surface is 0.7 g / m. 2 In the case of phosphate insulating coating, the amount of coating on one side of the steel sheet surface is 0.1g / m 2 The colloidal silica in the insulating coating is 0.1g / m2 based on the amount applied to one side of the steel sheet surface. 2 This means that the above is included.

[0092] In one embodiment of the present invention, after magnetic domain refinement treatment is performed by thermal deformation using a superimposed laser beam, not only is the insulating coating peeled off to ensure insulation between steel sheets, but also the glass coating is prevented from peeling off.

[0093] On the other hand, when a superimposed laser is irradiated onto the surface of an electrical steel sheet according to one embodiment of the present invention to form a deformed portion, the W15 / 50 iron loss improvement rate of such a steel sheet is preferably 6% or more. If the W15 / 50 improvement rate is lower than this, the laser absorption rate of the steel sheet is low, making it difficult to expect the desired iron loss reduction effect.

[0094] When forming a deformed portion by irradiating a superimposed laser beam onto the surface of an electrical steel sheet according to an embodiment of the present invention, it is preferable that the W17 / 50 iron loss improvement rate of such a steel sheet is 9% or more. If the W17 / 50 iron loss improvement rate is lower than this, the laser absorption rate of the steel sheet is also low, making it difficult to expect the desired iron loss reduction effect.

[0095] A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail below.

[0096] [Manufacturing of cold-rolled steel sheets] To manufacture grain-oriented electrical steel sheets, first, a slab of electrical steel sheet substrate is manufactured.

[0097] The chemical composition and metal structure of the slab are not particularly limited as long as the axis of easy magnetization is aligned in a certain direction and functions as an electrical steel sheet. However, for example, the chemical composition of the slab is as follows:

[0098] In mass%, C: 0.08% or less (excluding 0%), Si: 1.0 to 6.5%, Mn: 0.005 to 3.0%, (total of one or more of Nb, V, and Ti): 0.070% or less, (total of one or more of Cr, Sn, and Sb): 2.5% or less, Al: 2.0% or less (excluding 0%), (total of one or more of P and S): 0.100% or less (excluding 0%), (total of Cu and Sn): 1.0% or less, the total of rare earth elements and other impurities is 0.2% or less, and the remainder is Fe.

[0099] (C: 0.08% or less (excluding 0%))

[0100] Carbon (C) is an element inevitably mixed into steel, but because it can deteriorate magnetic properties due to magnetic aging, its content is preferably controlled to an appropriate level. If the C content in steel sheet is too low, phase transformation during the manufacturing process may be insufficient, resulting in a non-uniform microstructure of the steel sheet and ultimately an unstable secondary recrystallization texture. On the other hand, if the C content is too high, carbides may become coarse during the manufacturing process and precipitate in excess, resulting in insufficient decarburization, a decrease in the density of the Goss texture, and damage to the secondary recrystallization texture. Therefore, the C content of steel sheet should be 0.08% or less, more preferably 0.001 to 0.040%.

[0101] (Si: 1.0 to 6.5%)

[0102] Silicon (Si) is a basic component of grain-oriented electrical steel sheet, and its role is to increase the resistivity of the steel sheet and reduce iron loss. If the Si content is less than 1.0%, the resistivity decreases, eddy current loss increases, and iron loss characteristics deteriorate, making the effect of adding Si unsatisfactory. If the Si content is 6.5% or more, the brittleness of the steel sheet increases and toughness decreases, which can lead to sheet fracture during rolling. Furthermore, nitrides cannot be sufficiently formed during the manufacturing process, making it difficult to ensure sufficient grain suppression force required for secondary recrystallization during the final high-temperature annealing process. Therefore, the Si content is preferably 1.0 to 6.5%.

[0103] (Mn: 0.005 to 3.0%)

[0104] Manganese (Mn) increases resistivity and reduces eddy current loss, thereby reducing overall iron loss. It also reacts with S in the crude steel to form Mn-based sulfides. It also reacts with Si and nitrogen introduced during nitriding to form (Al, Si, Mn)N precipitates, suppressing the growth of primary recrystallized grains and promoting secondary recrystallization. It is an important element that influences the surface quality of the final product. However, excessively low Mn content can result in poor surface quality. Furthermore, excessive Mn content significantly increases the austenite phase fraction, damaging the Goss texture and reducing magnetic flux density. This can lead to excessive formation of an oxide layer during decarburization annealing, hindering decarburization. Therefore, a Mn content of 0.005 to 3.0% is recommended.

[0105] (Total of one or more of Nb, V, and Ti: 0.05% or less)

[0106] Niobium (Nb), vanadium (V), and titanium (Ti) are elements that react with C and N to form precipitates during the manufacturing process. However, if added in excessive amounts, they remain in the steel sheet even after secondary recrystallization annealing, degrading the magnetic properties of the steel sheet. Therefore, it is preferable to control the total content of one or more elements selected from Nb, V, and Ti to 0.05% or less.

[0107] (Total of one or more of Cr, Sn, and Sb: 2.5% or less)

[0108] Chromium (Cr) is added to promote the formation of Goss texture and reduce iron loss, while Sn is added to inhibit grain growth and ultimately improve magnetic flux density. Antimony (Sb) segregates at grain boundaries, inhibiting grain growth and stabilizing secondary recrystallization. Because all three elements are interrelated with the formation of secondary recrystallization, it is preferable to limit the total content of Sn, Sb, and Cr to 2.5% or less.

[0109] (Al: 2.0% or less (excluding 0%))

[0110] In addition to Al-based nitrides precipitated during the manufacturing process, aluminum (Al) combines with N introduced by nitriding during the primary recrystallization process and Al, Si, and Mn present in solid solution in the steel to form nitrides in the form of (Al, Si, Mn)N and AlN, acting as a strong grain growth inhibitor. However, excessive Al content can lead to uneven precipitates, unstable secondary recrystallization, and reduced magnetic properties of the steel sheet, so it is recommended to add 2.0% or less.

[0111] (The total of one or more of P and S: 0.1% or less (excluding 0%))

[0112] Phosphorus (P) segregates at grain boundaries, hindering their migration and simultaneously suppressing grain growth, while excessive addition of S destabilizes secondary recrystallization. Furthermore, P and S are elements that are inevitably added during the manufacturing process of electrical steel sheets, and it is preferable to keep the total amount of P and S below 0.1%.

[0113] (Cu+Sn total: 0.1% or less)

[0114] Copper (Cu) plays a role in improving the texture as it is partially dissolved in the crystal grains. If the Cu+Sn content is excessive, it may segregate at the crystal grain boundaries and form a liquid phase at high temperatures. Therefore, it is preferable to control the total amount of Cu and Sn to 0.1% or less.

[0115] (Rare earth and other impurities total less than 0.2%)

[0116] The grain-oriented electrical steel sheet according to one embodiment of the present invention may contain rare earth elements such as cerium (Ce) and praseodymium (Pr) and other impurities. The total amount of any rare earth elements and impurities is preferably 0.2% or less. Rare earth elements and inevitable impurities refer to impurities that are intentionally added or inevitably mixed in during the steelmaking and manufacturing process of the grain-oriented electrical steel sheet. Since inevitable impurities are widely known, detailed description thereof will be omitted. In one embodiment of the present invention, additional elements other than the above-described alloy components may be added, and various elements may be included within a range that does not detract from the technical concept of the present invention. When additional elements are further included, they may be included to replace the remaining Fe.

[0117] Next, a steel sheet having the above composition is produced into a slab by continuous casting, and then heated and hot-rolled in a conventional manner, optionally annealed as needed, and then cold-rolled to a thickness of 0.1 to 0.5 mm. Here, cold rolling can be performed once or twice or more times with intermediate annealing in between.

[0118] [Primary recrystallization annealing] The cold-rolled steel sheet is subjected to primary recrystallization annealing through a simultaneous decarbonization-nitriding or decarbonization-nitriding process. In the case of primary recrystallization annealing through simultaneous decarbonization-nitriding, the cold-rolled structure deformed during the annealing process undergoes recrystallization, resulting in decarburization annealing. This is performed in a mixed gas atmosphere containing nitrogen, hydrogen, and moisture. In the case of decarbonization-nitriding, a nitriding treatment can also be performed after decarbonization, using ammonia gas to introduce nitrogen ions into the steel sheet.

[0119] When simultaneous decarbonitriding is performed, the cold-rolled steel sheet is loaded into the furnace at a temperature in the range of 700 to 900°C, the dew point temperature of the atmospheric gas is set to 40 to 70°C, and the Fe2SiO4 / SiO2 ratio on the surface is controlled to 0.5 to 3.0, forming an oxide layer on the surface of the electrical steel sheet.

[0120] [Secondary recrystallization annealing]

[0121] After that, an annealing separator based on MgO is applied to the surface of such electrical steel sheets, and the temperature is raised to over 1,000°C and crack annealing is performed for a long time to cause secondary recrystallization, so that the {110} plane of the steel sheet is parallel to the rolling surface, <001> This results in the formation of a Goss-oriented texture whose direction is parallel to the rolling direction. This final high-temperature annealing process forms a glassy layer containing forsterite on the surface of the steel sheet, and secondary recrystallization occurs inside the steel sheet.

[0122] [Insulating film formation]

[0123] Steel sheets that have undergone secondary recrystallization are coated with a single or combined insulating coating solution of colloidal silica and metal phosphate, and then annealed to form a glass coating layer, on which an insulating coating layer is formed on the surface of the electrical steel sheet.

[0124] The method for forming such an insulating coating layer is not particularly limited, and as an example, the insulating coating layer can be formed by applying an insulating coating liquid containing phosphate. The insulating coating liquid preferably contains colloidal silica and a metal phosphate. In this case, the metal phosphate may be Al phosphate, Mg phosphate, or a combination thereof, and the content of Al, Mg, or a combination thereof relative to the weight of the insulating coating liquid may be 15 wt % or more.

[0125] [Magnetic domain refinement processing] The method for miniaturizing the magnetic domains is as described above, and therefore a detailed explanation will be omitted.

[0126] The present invention will be described in more detail below with reference to specific examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. [Example]

[0127] Experimental Example 1 Cold-rolled steel sheets with thicknesses of 0.20 mm and 0.23 mm were manufactured by hot rolling and cold rolling using slabs having the compositions shown in Table 1. In Table 1, element % means weight %.

[0128] [Table 1]

[0129] These cold-rolled steel sheets were subjected to decarburization annealing including primary recrystallization annealing and nitriding treatment by maintaining the temperature at 840°C for 150 seconds in a mixed gas atmosphere of wet hydrogen, nitrogen, and ammonia (dew point temperature 69°C, Fe2SiO4 / SiO2 ratio controlled to 1.2).

[0130] After the primary recrystallization treatment, the surface of the steel sheet was coated with an annealing separator containing MgO and then subjected to final high-temperature annealing. The final high-temperature annealing was performed in a mixed atmosphere of 25% by volume of nitrogen and 75% by volume of hydrogen up to 1,150°C. After reaching 1,150°C, the atmosphere was maintained at 100% by volume of hydrogen for approximately 8 hours, followed by furnace cooling.

[0131] After the secondary recrystallization annealing was completed through the final high-temperature annealing process, a coating solution containing colloidal silica nanoparticles and metal phosphate was applied to the surface of the steel sheet, which was then heat-treated at 870°C for 55 seconds to form an insulating coating layer for the grain-oriented electrical steel sheet.

[0132] The lasers listed in Table 2 below were then irradiated. At this time, the first and second lasers all had elliptical beam shapes with a beam width / length ratio (beam width / beam length) of 0.55. The diode laser had a wavelength of 1.03 μm, the optical fiber laser had a wavelength of 1.08 μm, and the CO2 laser had a wavelength of 10.6 μm. The beam width of each laser was unified to 200 μm. The instantaneous movement speed of the steel plate in the laser irradiation area was set to 2.3 m / s, the length of the deformed area was 160 mm, the scan speed was set to 60 m / s, and the irradiation interval was set to 5.0 mm.

[0133] In Comparative Example 3, the second laser was irradiated after a 4-second interval following the first laser irradiation.

[0134] The coercive force was measured at the applied magnetic field value required to make the magnetic flux density value zero under an alternating magnetic field measured by an SST (single sheet tester).

[0135] Corrosion resistance was measured according to KS D9502 by dissolving sodium chloride in deionized water to a salt concentration of 5±0.5%, spraying the 35°C salt solution on the specimen for a set period of time, then removing it after the salt spray period, rinsing it with water at room temperature, and drying it to check for surface rust. During the salt spray test, if no laser rust was observed after 8 hours of salt spray, the specimen was classified as good (◎); if no laser rust was observed after 7 hours of salt spray, the specimen was classified as average (○); and if laser rust was observed after 4 hours of salt spray, the specimen was classified as poor (△).

[0136] [Table 2]

[0137] As shown in Table 2, when the first and second lasers were irradiated in a superimposed manner, a molten and solidified layer was formed, and it was confirmed that improvements in iron loss and corrosion resistance could be achieved. On the other hand, when a single laser was used or the laser was irradiated over a long period of time, appropriate improvements in iron loss and corrosion resistance could not be achieved.

[0138] FIG. 7 is a photograph of the molten and solidified layer of the steel plate produced in Example 1. As shown in FIG. 7, it can be seen that a molten and solidified layer with a width of approximately 300 nm was formed. As shown in FIG. 8, it can be seen that the thickness of the molten and solidified layer was approximately 200 nm. FIG. 7 is a photograph of the solidified layer analyzed by FIB (Focused Ion Beam)-TEM (Transmission Electron Microscopy). An accelerating voltage was applied to the FIB source to generate ions, and the ions were selectively scanned over the area to be observed using an electric field, processing the desired portion of the sample and observing it with the TEM.

[0139] Experimental Example 2 The same procedures as in Experimental Example 1 were carried out, except that the laser irradiation interval and scan speed were changed as shown in Table 3 below. In Examples 5 to 7, the overlapping ratio was set to 100%. In Comparative Example 6, after the first laser irradiation, the second laser was irradiated with an interval of 4 seconds.

[0140] [Table 3]

[0141] As shown in Table 3, when the first and second lasers were irradiated in a superimposed manner, a molten and solidified layer was formed, and it was confirmed that improvements in iron loss and corrosion resistance could be achieved. On the other hand, when a single laser was used or the laser was irradiated over a long period of time, appropriate improvements in iron loss and corrosion resistance could not be achieved.

[0142] The present invention is not limited to the embodiments, but can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting. [Explanation of symbols]

[0143] 100: Grain-oriented electrical steel sheet 10: Deformation part 11: Melted and solidified layer 20: Laser beam spot 21: First laser beam 22: Second laser beam 23: Duplicate irradiation boundary area 30: Superimposed laser 40: Steel plate surface 50: Steel plate base material 60: Insulating coating layer

Claims

1. Electrical steel sheet substrate and an insulating coating layer located on the electrical steel sheet substrate, a linear deformation portion is present on the surface of the insulating coating layer, an overlapping irradiation boundary exists within the deformation portion, A grain-oriented electrical steel sheet characterized in that a molten and solidified layer exists below the overlapping irradiation boundary, and the molten and solidified layer contains P in an amount of 10 wt % or less.

2. The width (M Ｗ 2. The grain-oriented electrical steel sheet according to claim 1, wherein the grain size is 0.05 to 10 μm.

3. The thickness of the molten and solidified layer (M Ｄ 2. The grain-oriented electrical steel sheet according to claim 1, wherein the thickness of the insulating coating layer is 20% or less.

4. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the insulating coating layer below the deformed portion excluding the overlapping irradiation boundary portion has a P content of 10 to 20 wt % within a range of 100 nm from the surface in the thickness direction of the steel sheet.

5. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the thickness of the insulating coating layer under the deformed portion is 60 to 90% of the thickness of the insulating coating layer where the deformed portion is not formed.

6. 2. The grain-oriented electrical steel sheet according to claim 1, wherein a metal oxide layer is interposed between the electrical steel sheet substrate and the insulating coating layer.

7. a first irradiation step of irradiating a first laser beam having a first wavelength; a second irradiation step of irradiating with a second laser beam having a second wavelength; a first beam spot of the first laser beam and a second beam spot of the second laser beam overlap each other by 10% or more;

8. The first and second lasers are CO ２ 8. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 7, wherein the laser is selected from the group consisting of a laser, an optical fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, and a UV laser.

9. 8. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 7, wherein the first laser and the second laser each have an output of 10 to 2000 W.

10. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 7, wherein the first laser and the second laser have different wavelengths.

11. 8. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 7, wherein an interval between the time when the first laser beam is irradiated and the time when the second laser beam is irradiated at the overlapping position is 16 ms or less.

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