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

Abstract

A method for refining the magnetic domains of grain-oriented electrical steel sheets that have excellent transformer design iron loss values ​​and coercive force characteristics while preventing surface damage by irradiating the surface of the secondary recrystallized electrical steel sheet with superimposed lasers of 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 one or more linear deformation portions are present on the surface of the insulating coating layer, a resolidified layer is formed at either the front or rear boundary of the deformation portion, the P concentration in the resolidified layer in the thickness direction of the insulating coating layer is lower than the P concentration in a lower insulating coating layer where no resolidified layer is formed, the position where the P concentration of the resolidified layer begins to decrease is located in the thickness direction of the insulating coating layer at a distance of 15% or less of the total thickness of the insulating coating layer from the surface of the insulating coating layer, and the position where the P concentration of the resolidified layer begins to decrease is located in the thickness direction of the insulating coating layer at a distance of 500 nm or less from the surface of the insulating coating layer.

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 method for refining the magnetic domains of a grain-oriented electrical steel sheet that has undergone secondary recrystallization by irradiating the surface of the sheet with superimposed lasers having different wavelengths to prevent surface damage and simultaneously have excellent core loss and coercive force. [Background technology]

[0002] Grain-oriented electrical steel sheets have excellent magnetic properties and are used as iron core materials for transformers. These grain-oriented electrical steel sheets are produced through the rolling and annealing processes unique to the manufacturing process of electrical steel sheets, resulting in a {110} <001> The Goss texture, which is recrystallized in the direction of the grain boundary, is formed throughout the steel sheet. In response to climate change, the world is tightening greenhouse gas emission standards day by day. In the case of transformer cores, factors that affect the greenhouse gas emission standards are related to the improvement in efficiency when using magnetic steel sheets. The efficiency of transformer cores is determined by the core loss, magnetic flux density, and coercive force of the magnetic steel sheets, that is, their magnetic properties.

[0003] The magnetic flux density of an electrical steel sheet is determined by the concentration of crystal axes that are easy to magnetize in the crystal structure, i.e., the higher the crystal orientation, the higher the magnetic flux density, so the manufacturing process of the electrical steel sheet can have a significant impact. The iron loss of magnetic steel sheets is measured at a value of W17 / 50 [W / kg] when a magnetic field with a maximum magnetic flux density of 1.7T and a frequency of 50Hz is applied. This value is called the guaranteed iron loss value of the 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 with a frequency of 50Hz and a maximum magnetic flux density of 1.5T is also used. The lower the designed iron loss value of a transformer, the better its efficiency is evaluated.

[0004] Therefore, in the case of magnetic 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. Among these, magnetic flux density is considered to be a more important indicator than iron loss, as the process technology for ensuring high magnetic flux density through upward leveling of the magnetic steel sheet manufacturing process has advanced to the point where it can boost transformer efficiency. Iron loss is divided into eddy current loss and hysteresis loss. Hysteresis loss tends to decrease as magnetic flux density increases, so eddy current loss plays an important role in controlling overall iron loss in grain-oriented electrical steel sheets. Eddy current loss within iron loss is divided into classical eddy current loss and anomalous eddy current loss. Classical eddy current loss is proportional to the thickness of the steel sheet, so the thinner the steel sheet, the less classical eddy current loss there is. Therefore, controlling anomalous eddy current loss is positioned as an important technology for reducing iron loss.

[0005] Eddy current loss, which is a 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, so iron loss can be reduced by miniaturizing the magnetic domains of the electrical steel sheet. "Magnetic domain refinement" in electrical steel sheet refers to the process of applying a physical stimulus to crystal grains with a single magnetic domain characteristic, thereby separating and refining them into several 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).

[0006] Generally, temporary magnetic domain refinement involves reducing the width of 180° magnetic domains formed from the magnetic domain refinement-treated surface of a steel sheet to the unrefined surface on the opposite side using various means such as a laser. Reducing the width of the 180° magnetic domains in this way reduces the movement distance of the magnetic domains when an external magnetic field is applied to the steel sheet, and also increases residual tensile stress in the rolling direction, resulting in improved magnetic properties.

[0007] To reduce the 180° magnetic domain width of steel sheet using a laser, the laser output (energy density) must be increased to increase the laser energy density per unit area. Another method is to reduce the diameter of the final beam of the laser, increasing its length and increasing the duration per unit length. However, if an energy source such as a laser strong enough to reduce the 180° magnetic domain width is applied to the surface of the steel sheet during the temporary magnetic domain refinement process, the surface of the steel sheet may be damaged. To achieve this temporary magnetic domain refinement, the magnetic flux density is increased while minimizing surface damage on the laser irradiated surface, thereby improving the transformer's design iron loss value (W15 / 50). However, the temporary magnetic domain refinement process inevitably causes surface damage to the steel sheet, which inevitably leads to a deterioration in the corrosion resistance of the steel sheet. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for refining magnetic domains in a grain-oriented electrical steel sheet, and more specifically, to provide a method for refining magnetic domains in a grain-oriented electrical steel sheet that has excellent iron loss and coercive force characteristics for transformers while preventing surface damage by irradiating the surface of the secondary recrystallized electrical steel sheet with superimposed laser beams having different wavelengths. [Means for solving the problem]

[0009] 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 one or more linear deformation portions are present on the surface of the insulating coating layer, a resolidified layer is formed at either the front or rear boundary of the deformation portion, and the P concentration in the resolidified layer in the thickness direction of the insulating coating layer is lower than the P concentration in a lower insulating coating layer where no resolidified layer is formed.

[0010] In such a grain-oriented electrical steel sheet, the position where the P concentration in the resolidified layer starts to decrease is preferably located at a position 15% or less of the total thickness of the insulating coating layer from the surface of the insulating coating layer in the thickness direction of the insulating coating layer.

[0011] In the grain-oriented electrical steel sheet, the position where the P concentration in the resolidified layer begins to decrease is preferably located 500 nm or less from the surface of the insulating coating layer in the thickness direction of the insulating coating layer.

[0012] In the grain-oriented electrical steel sheet, the width of the boundary where the resolidified layer is formed is preferably 10 μm or less on either the front or rear side of both ends of the deformed portion.

[0013] Meanwhile, in the grain-oriented electrical steel sheet, a glass coating layer may be further formed between the electrical steel sheet substrate and the insulating coating layer.

[0014] The grain-oriented electrical steel sheet of the present invention preferably has an iron loss (W15 / 50 of magnetic domain material) improvement rate of 7% or more and a coercive force improvement rate of 11% or more.

[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 one or more linear deformation portions are present on the surface of the insulating coating layer, a resolidified layer is formed at either the front or rear boundary of the deformation portion, and the Si concentration in the resolidified layer in the thickness direction of the insulating coating layer is higher than the Si concentration in a lower insulating coating layer where no resolidified layer is formed. In such a grain-oriented electrical steel sheet, the P concentration in the resolidified layer is lower than the P concentration in the lower insulating coating layer where no resolidified layer is formed.

[0016] In the grain-oriented electrical steel sheet, the position at which the P and Si concentrations in the resolidified layer begin to change is preferably 15% or less of the total thickness of the insulating coating layer from the surface of the insulating coating layer in the thickness direction of the insulating coating layer.

[0017] In addition, in such grain-oriented electrical steel sheets, it is preferable that the iron loss (W15 / 50) improvement rate of the electrical steel sheets is 7% or more, and the coercive force improvement rate of the electrical steel sheets is 11% or more.

[0018] The method for manufacturing grain-oriented electrical steel sheet of the present invention is characterized in that a superimposed laser beam, which includes a first beam spot formed by irradiation with a first laser beam of a first wavelength and a second beam spot formed by irradiating with a second laser beam of a second wavelength, is formed by controlling the width of the second beam spot on the surface of the electrical steel sheet so that it is positioned within the width of the first beam spot, based on the direction of travel of the electrical steel sheet, onto the surface of the electrical steel sheet to form a linear deformed portion.

[0019] In the method for refining magnetic domains in grain-oriented electrical steel sheet, the first laser is preferably a CO2 laser, and the second laser is preferably a disk laser.

[0020] In such a method for refining the magnetic domains of a grain-oriented electrical steel sheet, it is preferable that the length of the disk laser beam, which is the second laser beam, is longer or shorter than the length of the CO laser beam, which is the first laser beam, based on the width direction of the electrical steel sheet.

[0021] In this method for refining the magnetic domains of grain-oriented electrical steel sheets, the CO2 laser as the first laser and the disk laser as the second laser can be irradiated by sharing a light path in a laser beam scanning device. In addition, in the method for refining the magnetic domains of a grain-oriented electrical steel sheet, the first CO laser and the second disk laser may be scanned separately by a laser beam scanning device, so that the laser beams overlap each other on the surface of the electrical steel sheet.

[0022] In the method for refining the magnetic domains of grain-oriented electrical steel sheet, the beam spot of the CO2 laser of the first laser is preferably an elliptical beam spot having a width of 100 to 400 μm and a length of 0.4 to 20 mm.

[0023] Furthermore, in the method for refining the magnetic domains of grain-oriented electrical steel sheet, it is preferable that the beam spot of the disk laser of the second laser has a width of 10 to 200 μm and an elliptical or circular shape with a length equal to or less than the length of the CO laser beam spot of the first laser or greater.

[0024] In the method for refining magnetic domains in grain-oriented electrical steel sheets, it is preferable that the irradiation interval of the superimposed laser beams is 2 to 7 mm, and the scanning speed is 1 to 300 m / sec.

[0025] In the method for refining magnetic domains in a grain-oriented electrical steel sheet, the inclination direction of the superimposed laser beam is preferably ±10° or less.

[0026] In the method for refining magnetic domains in grain-oriented electrical steel sheet of the present invention, it is preferable that the output of the CO 2 laser as the first laser is 200 to 2,000 W, and the output of the disk laser as the second laser is 10 to 550 W. [Effects of the Invention]

[0027] According to the present invention, by using superimposed lasers with different wavelengths to optimally refine the magnetic domains, it is possible to further improve the magnetic properties and at the same time sufficiently suppress damage to the steel sheet surface. Furthermore, 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] The magnetic domain refinement method of the present invention uses a CO laser as a long-wavelength laser to stably preheat the steel sheet without destroying the insulating coating layer, and uses a disk laser as a short-wavelength laser to accurately induce residual stress due to thermoelastic deformation in the steel sheet with a width sufficient to form closure domains, thereby enabling accurate magnetic domain refinement. In addition, the magnetic domain refinement method of the present invention can provide a directional magnetic domain refined product with excellent low magnetic field core loss by irradiating laser beams with different wavelengths simultaneously in an overlapping state onto the surface of a steel sheet on which secondary recrystallization has been completed, thereby maximizing thermal shock in the thickness direction even under low laser output conditions. [Brief explanation of the drawings]

[0029] [Figure 1A] 1 is a photograph taken with an electron microscope of the surface of a steel sheet after magnetic domain refinement is performed using a superimposed laser beam according to an embodiment of the present invention. [Figure 1B] 1B is a FIB-TEM photograph of the cross section of the steel plate in the G1 portion in FIG. 1A, taken at an enlarged scale in the thickness direction from the surface of the steel plate. [Figure 2] 1C is a graph showing changes in components in the thickness direction of the steel sheet analyzed along lines T1 and T2 in the FIB-TEM photograph of FIG. 1B. [Figure 3] FIG. 3 is a schematic diagram illustrating the changes in the main components in the graph of FIG. 2. [Figure 4] 1 is a schematic diagram showing a case where a steel plate is scanned with beam spots of superimposed lasers having different wavelengths according to an embodiment of the present invention. FIG. [Figure 5] 1 is a schematic diagram illustrating a case where a beam spot of a superimposed laser having different wavelengths is scanned on a surface of a steel plate according to an embodiment of the present invention. [Figure 6] FIG. 10 is a schematic diagram illustrating a case where a beam spot of a superimposed laser having different wavelengths is scanned on a surface of a steel sheet according to another embodiment of the present invention. [Figure 7] FIG. 2 is a schematic diagram showing energy density when beam spots of superimposed lasers with different wavelengths are scanned on the surface of a steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] 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 form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain 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. When we say that a part is "on" another part, it means that it is exactly on top of the other part, or there may be other parts between them. In contrast, when we say that a part is "directly on top of" another part, there are no other parts between them.

[0032] 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. Commonly used dictionary-defined terms are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined.

[0033] While the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the embodiments set forth herein.

[0034] The present invention provides a grain-oriented electrical steel sheet comprising an electrical steel sheet substrate and an insulating coating layer located on the electrical steel sheet substrate, in which one or more linear deformations are present on the surface of the insulating coating layer, a resolidified layer is formed at either the front or rear boundary of the deformations, and the P concentration in the resolidified layer in the thickness direction of the insulating coating layer is lower than the P concentration in a lower insulating coating layer in which no resolidified layer is formed.

[0035] The electrical steel sheet substrate is preferably an electrical steel sheet that has been subjected to final annealing in the manufacturing process for grain-oriented electrical steel sheet, and in which a GOSS texture has been formed inside the steel sheet, completing secondary recrystallization. An insulating coating layer is formed on the electrical steel sheet substrate, and a glass coating layer may be further formed between the electrical steel sheet substrate and the insulating coating layer.

[0036] The insulating coating layer mainly contains phosphate and colloidal silica, and the glass coating layer mainly contains forsterite. In the present invention, the main component means that, in the case of phosphate in the insulating coating layer, the main component is 0.1 g / m2 based on the amount of coating on one side of the steel sheet surface. 2 The colloidal silica in the insulating coating layer is 0.1 g / m2 based on the amount applied to one side of the steel sheet surface. 2 In the case of forsterite in the glass coating layer, the amount of oxygen applied to one side of the steel sheet surface is 0.7 g / m 2 This means that the above is included.

[0037] In the present invention, one or more linear deformations exist on the surface of the insulating coating layer. In the present invention, linear deformation portions include not only solid lines but also those that extend intermittently such as dotted lines and dashed lines, and also include those that have a zigzag shape when viewed microscopically but a straight line shape when viewed macroscopically, and include all deformation portions that form substantially linear shapes.

[0038] As shown in Figure 1A, such a deformed portion is formed in the region between C and D in Figure 1A, and is formed linearly on the surface of the electrical steel sheet along a direction perpendicular to the rolling direction of the electrical steel sheet (TD direction). In FIG. 1A, line C indicates the end of the deformation formed in the front direction of the rolling direction of the steel sheet when a superimposed laser beam (described later) is irradiated onto the surface of the steel sheet, and line D indicates the rear end of the deformation. Lines C and D are formed along the line scanned by the superimposed laser and form the boundary of the deformation. In addition, in FIG. 1A, G1 and G2 respectively indicate certain regions forming the boundary within a range of ±5 to 10 μm from line C and line D as the center lines. In addition, in FIG. 1A, G1 indicates the front region in the rolling direction of the steel sheet, and G2 indicates the rear region in the rolling direction of the steel sheet.

[0039] The linear deformations formed on the surface of the electromagnetic steel sheet are formed by irradiating the electromagnetic steel sheet with superimposed laser beams having different wavelengths in a direction perpendicular to the rolling direction (TD direction). When the superimposed laser beam is incident on the surface of the steel sheet in this way, the superimposed laser beam is simultaneously irradiated in the thickness direction of the electromagnetic steel sheet not only to the electromagnetic steel sheet itself but also to the insulating coating or the glass coating and insulating coating formed on top of the steel sheet, resulting in a deformation to a material state different from that immediately before the superimposed laser beam was irradiated.

[0040] The deformation of the electromagnetic steel sheet itself, which occurs in the thickness direction of the sheet, occurs when the incident superimposed laser beam creates strong compressive stress areas in the crystalline structure of the steel sheet below the insulating coating layer. When compressive stress areas form in the electromagnetic steel sheet, lancet magnetic domains (closure domains) are formed to reduce magnetoelastic energy. As a result, 180° magnetic domains are formed in the steel sheet area affected by the superimposed laser, and 90° magnetic domains are formed in the thickness direction of the steel sheet to reduce magnetoelastic energy, narrowing the spacing between the magnetic domains and refining the magnetic domains. Refining the magnetic domains in the electromagnetic steel sheet by the superimposed laser results in a reduction in the abnormal eddy current loss of the steel sheet.

[0041] When a superimposed laser is irradiated onto the surface of an electrical steel sheet, residual stress due to thermoelastic deformation can be induced in the thickness direction of the electrical steel sheet by the width of the superimposed laser beam, enabling precise magnetic domain refinement. In this case, the width of the superimposed laser beam is roughly similar to the region between C and D in Figure 1A.

[0042] When a superimposed laser beam is irradiated onto the top of an electrical steel sheet to form a deformation in the steel sheet itself, a deformation is also formed on the top of the steel sheet, i.e., on the surface of the insulating coating layer where the superimposed laser beam directly contacts. This deformation in the insulating coating layer (the region between C and D) is formed along the trajectory of the superimposed laser beam, and can form a recessed groove shape due to shrinkage caused by evaporation of some of the component elements that make up the insulating coating layer. The depth of this groove can be controlled by adjusting the energy density of the incident superimposed laser.

[0043] On the other hand, a re-solidified layer is formed in the thickness direction of the insulating coating layer at the boundary of the deformed part formed on the surface of the insulating coating layer (G1, G2 in Fig. 1A). This re-solidified layer of the insulating coating layer is formed by immediate re-solidification after the insulating coating layer is partially melted by irradiation with the superimposed laser beam.

[0044] 1B, the re-solidified layer formed at the boundary of the deformed portion of the insulating coating layer may be formed along lines C and D in FIG. 1A from the portion directly irradiated with the superimposed laser beam, and such a re-solidified layer may appear in a linear form intermittently or continuously along the path scanned by the superimposed laser beam. The width of the boundary where such a re-solidified layer is formed is preferably within a range of 10 μm or less from lines C and D, which are both ends of the deformed portion, as the center.

[0045] The resolidified layer of the insulating coating layer is presumably formed when a superimposed laser is irradiated onto the surface of a steel sheet on which an insulating coating has been formed, and when some of the phosphates forming the insulating coating layer are melted by the superimposed laser and solidified immediately after the superimposed laser beam passes through. Therefore, such a resolidified layer is also called a phosphate resolidified layer. The formation of a re-solidified layer on the insulating coating layer is a phenomenon that does not occur when each of the lasers constituting the superimposed laser beam is irradiated individually.

[0046] When the superimposed laser beam is irradiated in this way, the reason why a resolidified layer of the insulating coating layer appears mainly at the boundary of the area irradiated with the superimposed laser beam is presumably that the vaporization point of the phosphate constituting the insulating coating is low, so when the superimposed laser is irradiated, phosphorus vaporizes first, and silicon oxide consisting of Si and O resolidifies in an amorphous state. When a resolidification layer is formed on the insulating coating layer by irradiation with a superimposed laser beam, changes occur in the components that make up the insulating coating layer in the thickness direction of the insulating coating layer (from T1 to T2), as shown in Figures 2 and 3.

[0047] That is, phosphorus (P) vaporizes in the area where a re-solidified layer is formed, i.e., in the boundary area irradiated with the superimposed laser beam, and the phosphorus (P) concentration in the re-solidified layer becomes low. However, the P concentration in the lower insulating coating layer, which is irradiated with the superimposed laser beam but is too deep to form a re-solidified layer, becomes higher than the phosphorus (P) concentration in the re-solidified layer. Therefore, the P concentration in the portion of the insulating coating layer where a re-solidified layer is formed by irradiation with the superimposed laser beams is lower than the P concentration in the lower insulating coating layer where no re-solidified layer is formed.

[0048] Unlike this change in the phosphorus (P) concentration in the resolidified layer, the silicon (Si) concentration in the resolidified layer becomes higher than the silicon (Si) concentration in the lower insulating coating layer where no resolidified layer is formed. This is presumably because silicon oxide consisting of Si and O resolidifies in an amorphous state in the resolidified layer due to irradiation with the superimposed laser beam. The changes in the phosphorus (P) and silicon (Si) concentrations in such a resolidified layer are shown in Figures 2 and 3.

[0049] When a resolidified layer of the insulating coating layer is formed by irradiation with a superimposed laser beam, the resolidified layer is formed by solidifying silicon oxide in an amorphous state, and the corrosion resistance of such a resolidified layer is improved due to the inherent properties of the amorphous state.

[0050] On the other hand, it is preferable that the thickness of the resolidified layer of the insulating coating layer formed by irradiating the surface of the steel sheet with a superimposed laser beam is within 15% of the average cross-sectional thickness of the entire insulating coating layer, based on the non-deformed portion (surface not irradiated with the superimposed laser).

[0051] If the thickness of the resolidified layer formed on the insulating coating layer is 15% or more larger than the average cross-sectional thickness of the insulating coating layer not irradiated with the superimposed laser beam, the absolute thickness of the insulating coating layer becomes thin, which can have a detrimental effect on corrosion resistance and can reduce the tension effect of the insulating coating layer, resulting in deterioration of iron loss. Therefore, it is preferable to limit the thickness to this range.

[0052] When a resolidified layer forms on the insulating coating layer, the physical properties of the insulating coating layer change, making the insulating coating layer stable overall and preventing partial peeling or damage. If a resolidified layer forms over 15% of the thickness of the insulating coating layer, the insulating coating layer will be damaged and the tensile effect of the insulating coating will be lost, which is undesirable.

[0053] When a re-solidified layer is formed on the insulating coating layer by irradiation with the superimposed laser, the formation of such a re-solidified layer may cause shrinkage of the insulating coating layer, resulting in a change in the thickness of the insulating coating layer. On the other hand, the portion in the re-solidified layer where the changes in the phosphorus (P) and silicon (Si) concentrations begin is preferably 500 nm or less from the surface of the insulating coating layer in the thickness direction of the insulating coating layer, based on the insulating coating layer not irradiated with the superimposed laser beam. If the re-solidified layer is formed at a depth of 500 nm or more from the surface of the insulating coating layer, the insulating coating layer will be damaged and the tension effect of the insulating coating layer will be lost, which is not preferable.

[0054] When forming one or more deformed portions on the surface of the electrical steel sheet of the present invention by irradiating a superimposed laser beam, it is preferable that the W15 / 50 iron loss improvement rate of such steel sheet is 7% or more. If the W15 / 50 iron loss improvement rate is 7% or less, the effect of reducing the post-design efficiency of the transformer is slight. When the surface of the electrical steel sheet of the present invention is irradiated with a superimposed laser to form one or more deformed portions, the coercive force improvement rate of such steel sheet is preferably 11% or more. If the coercive force improvement rate is 11% or less, the eddy current loss effect is not significantly exhibited, which is not preferable.

[0055] In yet another embodiment of the present invention, there is provided a method for refining magnetic domains in a grain-oriented electrical steel sheet, which comprises irradiating the surface of the steel sheet with a superimposed laser beam, the superimposed laser beam comprising a first beam spot formed by irradiation with a first laser beam of a first wavelength and a second beam spot formed by irradiating with a second laser beam of a second wavelength, the superimposed laser beam being controlled so that the width of the second beam spot on the surface of the steel sheet is positioned within the width of the first beam spot, based on the direction of travel of the electrical steel sheet, to form a deformed portion.

[0056] In another embodiment of the magnetic domain refinement process for grain-oriented electrical steel sheet according to the present invention, as illustrated in FIG. 4, a superimposed laser is irradiated along the entire length of the electrical steel sheet in a direction perpendicular or inclined to the rolling direction (RD direction) of the steel sheet, i.e., along the width direction (TD direction) of the steel sheet, to form a linear deformation portion 10.

[0057] The formation of the deformation 10 in the steel sheet by the laser means the deformation of the crystal lattice caused by the thermal shock caused by the laser irradiation. This deformation of the crystal lattice is formed in the process in which the steel sheet is rapidly heated locally by the laser and then cooled immediately. At this time, the heating rate of the steel sheet is proportional to the energy density (power density) of the laser per unit time.

[0058] However, the deformation of the crystal lattice due to thermal shock during laser irradiation increases as the total laser irradiation energy increases, so if the steel sheet is irradiated with energy greater than that required for magnetic domain refinement, a heat source greater than that required for forming closure domains 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 onto a narrow area for a short period of time.

[0059] The interaction conditions between the laser beam and the steel sheet are affected by the laser characteristics and the laser beam's absorption rate in the steel sheet, and when the steel sheet manufacturing conditions are constant, the laser absorption rate is affected by the laser wavelength. In other words, the laser absorption rate in steel sheet is approximately 10% or less for a long-wavelength CO2 laser (wavelength: 10.6 μm), which is three to five times higher than that of a short-wavelength disk laser (wavelength: 1.03 μm).

[0060] However, unlike the steel plate, the insulating coating layer formed on the steel plate exhibits a large absorption of the long-wavelength CO2 laser, but a relatively small absorption of the short-wavelength disk laser laser beam. Therefore, when a long wavelength CO2 laser and a short wavelength disk laser are used in combination, the advantages of each laser applied to magnetic domain refinement are exhibited preferentially without any side effects, thereby inducing a synergistic effect.

[0061] In other words, long-wavelength CO2 lasers can be used with average powers ranging from several hundred watts to several kilowatts or more, depending on the steel plate's speed, and can easily induce thermoelastic deformation in the irradiated area of ​​the steel plate. Furthermore, long-wavelength CO2 lasers have a high absorption rate in insulating coatings made of phosphate and silica, allowing them to stably pass through the coating layer. Therefore, long-wavelength CO2 lasers can stably induce thermoelastic deformation in steel plates without destroying the insulating coating layer, making them suitable for a type of preheating function.

[0062] In contrast, a short-wavelength disk laser has a relatively high laser absorption rate for steel sheets, making it possible to irradiate a narrow area with enough incident energy for a short time to induce the lattice deformation and residual stress due to thermoelastic deformation required for the precise formation of closure domains. Furthermore, since the range of incident energy is narrow, a short-wavelength disk laser can suppress thermal diffusion to the surrounding area, minimizing unnecessary thermal deformation.

[0063] As described above, in order to achieve the characteristics of combining superimposed laser beams of different wavelengths by simultaneously superimposing a long-wavelength CO2 laser and a short-wavelength disk laser, it is preferable that the width of the disk laser beam B is positioned within the width of the CO2 laser beam A, as shown in Figures 5 and 6. In other words, as shown in Figures 5 and 6, the lattice deformation and thermoelastic deformation occur only in the width of the short-wavelength disk laser beam B, forming a deformed portion, while the width of the long-wavelength CO2 laser beam A can easily induce thermoelastic deformation due to preheating in an area wider than the width of the disk laser beam B.

[0064] However, the lengths of CO2 laser beam A and disk laser beam B are different from the widths of these beams A and B. In other words, it is sufficient that either one of the CO2 laser beam A or disk laser beam B passes first along the traveling line in the direction in which the superimposed laser beam 20 travels on the surface of the steel sheet to preheat the steel sheet, and therefore the preheating function can be performed even if either one of the laser beams constituting the superimposed laser beam passes first. Therefore, when the length of CO2 laser beam A is longer than the length of disk laser beam B as shown in Figure 5, the CO2 laser beam A of the superimposed laser beams can scan the surface of the steel sheet first and play a role in preheating. Also, when the length of disk laser beam B is longer than the length of CO2 laser beam A as shown in Figure 6, the disk laser beam B can scan the surface of the steel sheet first and play a role in preheating. Therefore, the length of the disk laser beam B may be longer or shorter than the length of the CO2 laser beam A.

[0065] However, as shown in Figure 7, even when the length of the disk laser beam B is shorter than the length of the CO2 laser beam A, it is preferable that the center of the disk laser beam B is located at position "a" where the energy density of the disk laser beam B is high. In the opposite case, that is, when the length of the disk laser beam B is longer than the length of the CO2 laser beam A, the center of the disk laser beam B can be easily located at position "a" where the energy density of the disk laser beam B is high. On the other hand, the method of forming a superimposed laser beam is a method in which a first CO2 laser and a second disk laser are each generated by a laser oscillator and share an optical path in an optical system that processes the laser beam. In this method of sharing an optical path, two different laser beams use a single optical path in the optical system to form a superimposed laser beam 30 as shown in Figure 4, and then irradiate the surface of the steel sheet with the superimposed laser beam 20.

[0066] Another method for forming a superimposed laser beam is to use a laser oscillator for the first CO2 laser A' and a disk laser B' for the second laser, each of which uses its own optical path in the laser beam processing optical system. In this method, two different laser beams use their own optical paths in the optical system to reach the surface of the steel sheet and irradiate it with a superimposed laser beam 20', as shown in Figure 4.

[0067] The beam spot of the CO2 laser of the first laser A, A' among the superimposed lasers of the present invention is preferably an elliptical beam spot with a width (length in the "RD direction" in FIG. 4) of 100 to 400 μm and a length (length in the "TD direction" in FIG. 4) of 0.4 to 20 mm. Also, a circular CO2 laser beam spot with a radius of 100 μm or more can be used. In order to form the beam width of the CO2 laser of the first laser A within 100 μm, the mirror optical system would become complex like a disk laser, which is not desirable, and if it becomes larger than 400 μm, the thermal effect in the longitudinal direction of the steel plate would become large, resulting in a decrease in magnetic flux density, which is also not desirable.

[0068] The beam spot of the disk laser, which is the second laser B, B' among the superimposed lasers, has a width (length in the "RD direction" in Figure 4) of 10 to 200 μm, and its length (length in the "TD direction" in Figure 4) is less than or greater than the length of the beam spot of the CO2 laser, which is the first laser A, and the shape of the beam spot is preferably elliptical or circular.

[0069] If the beam spot width of the disk laser is reduced to less than 10 μm, the energy density is concentrated in a narrow area, which can cause deterioration in magnetic flux density and iron loss, and the optical system structure becomes complicated. On the other hand, if the beam spot width of the disk laser is increased to 200 μm or more, the thermal effect in the longitudinal direction of the steel sheet increases, which can cause a decrease in magnetic flux density, which is undesirable.

[0070] As for the laser beam emission mode used in the present invention, it is preferable to use a continuous wave laser that continuously generates laser light for both the first laser A, A' and the second laser B, B', but a pulse laser may also be used.

[0071] Furthermore, the quality of the laser beams used is preferably a Gaussian mode TEM00 for both the first lasers A, A' and the second lasers B, B', but a multi-transverse mode TEM0i can also be used. However, the superimposed laser beams 20, 20' irradiated onto the surface of the steel sheet according to one embodiment of the present invention can minimize the thermal impact in the width direction of the steel sheet while maximizing the thermal shock in the thickness direction, and therefore the beam shape and beam quality of each laser are not specifically limited.

[0072] Meanwhile, the output of the CO2 laser of the first laser is preferably 200 to 2,000 W, and the output of the disk laser of the first laser is preferably 10 to 550 W. These output ranges of each laser indicate the laser output conditions when the steel sheet travels at a speed of 15 mpm, and it is preferable that the output value of each laser is optimally controlled taking into consideration the incident energy density according to the travel speed of the steel sheet.

[0073] On the other hand, the irradiation interval of the superposed laser beams 20, 20' is preferably 2 to 7 mm. If the irradiation interval of the superposed laser beams 20, 20' irradiated onto the steel sheet surface is too narrow, less than 2 mm, the influence of the heat-affected zone increases, deteriorating the magnetic flux density and iron loss. If the irradiation interval is 7 mm or more, the thermal shock effect for ensuring the magnetic domain refinement effect decreases, making it difficult to exert the effect. It is preferable that the superimposed laser beam is scanned at an angle of ±10° or less in the direction perpendicular to the rolling direction. If the superimposed laser beam is irradiated at an angle greater than this angle, the required magnetic domain refinement effect may not be achieved.

[0074] 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 also increase. Therefore, the scanning speed is preferably 1 to 300 m / sec, and this speed means the value exemplified under the condition of 15 mpm.

[0075] The method for producing a grain-oriented electrical steel sheet and the method for refining magnetic domains according to the present invention will be described in detail below.

[0076] To manufacture grain-oriented electrical steel sheets, a slab of electrical steel sheet substrate is first manufactured. 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 the slab functions as an electrical steel sheet. However, for example, the chemical composition of the slab is as follows:

[0077] In other words, the chemical composition of the slab is, 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 sum of rare earth elements and other impurities is 0.2% or less, and the remainder is Fe.

[0078] The present invention does not exclude the addition of other elements in addition to the alloy components described above, and various other elements may be included within the scope of the technical concept of the present invention. When an additional element is further included, it is included to replace the remaining Fe.

[0079] A steel sheet having such a composition is produced into a slab by continuous casting, and then heated and hot-rolled by a conventional method, optionally annealed as needed, and then cold-rolled to a thickness in the range of 0.1 to 0.5 mm. Here, the cold rolling can be performed in one pass or two or more passes with intermediate annealing in between.

[0080] The produced cold-rolled steel sheet is then subjected to primary recrystallization annealing by a simultaneous decarbonitriding or post-decarbonitriding process. When primary recrystallization annealing by simultaneous decarbonitriding is carried out, the cold-rolled structure deformed during the annealing process undergoes primary recrystallization and undergoes decarburization annealing. For this purpose, the process is carried out in a mixed gas atmosphere containing nitrogen, hydrogen, and moisture. In the case of post-decarbonitriding, a nitriding treatment may be carried out after decarburization to introduce nitrogen ions into the steel sheet using ammonia gas. When simultaneous decarbonitriding is performed, the dew point temperature of the atmospheric gas is set to 40-70°C in the range of 700-900°C for the cold-rolled steel sheet charged into the furnace, and the Fe2SiO4 / SiO2 ratio on the surface is controlled to 0.5-3.0, forming an oxide layer on the surface of the electrical steel sheet.

[0081] After that, an MgO-based annealing separator is applied to the surface of the steel sheet where primary recrystallization has been completed, and then the temperature is raised to over 1,000°C and the steel sheet is subjected to long-term soaking annealing to induce secondary recrystallization. This causes the {110} plane of the steel sheet to be parallel to the rolling surface, <001> A Goss-oriented texture is formed, with the direction parallel to the rolling direction. By this final high-temperature annealing process, a glass coating layer containing forsterite is formed on the surface of the steel sheet, and secondary recrystallization is formed inside the steel sheet. The steel sheet that has undergone secondary recrystallization in this manner is coated with an insulating coating solution containing colloidal silica and metal phosphate, either alone or in combination, and then annealed to form an insulating coating layer on the surface of the electrical steel sheet on which the glass coating layer has been formed.

[0082] 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. The content of Al, Mg, or a combination thereof relative to the weight of the insulating coating liquid may be 15 wt % or more.

[0083] By the above process, the surface of the electromagnetic steel sheet on which the glass coating and the insulating coating have been sequentially formed is simultaneously irradiated with laser beams 20, 20' formed by superimposing the first laser A, A' and the second laser B, B', to form a linear deformation portion 10 on the surface of the steel sheet. At this time, the electromagnetic steel sheet can be irradiated with the superimposed laser beam while moving at a constant speed. Here, the irradiation angle of the superimposed laser beam, the quality of the laser beam used, and the type of laser mode are as explained above, so a detailed explanation will be omitted.

[0084] The present invention will be described in more detail with reference to the following specific examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. Experimental Example

[0085] A slab having the composition shown in Table 1 below was hot-rolled and cold-rolled in sequence to produce a cold-rolled steel sheet having a thickness of 0.23 mm. In Table 1, element % means weight %.

[0086] [Table 1] These cold-rolled steel sheets were subjected to decarburization annealing including primary recrystallization annealing and nitriding treatment by maintaining them at a temperature of 845°C in a mixed gas atmosphere of moist hydrogen, nitrogen, and ammonia (dew point temperature 68°C, Fe2SiO4 / SiO2 ratio controlled to 1.2) for 160 seconds. An annealing separator containing MgO was applied to the surface of the steel sheet that had undergone primary recrystallization treatment, and the steel sheet was 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 1,200°C, and after reaching 1,200°C, the atmosphere was changed to 100% by volume of hydrogen, which was maintained for approximately 8 hours, followed by furnace cooling.

[0087] A coating solution containing colloidal silica particles and metal phosphate was applied to the surface of the steel sheet that had completed secondary recrystallization annealing through the final high-temperature annealing process, and the steel sheet was hardened by heat treatment at a temperature of 880°C for 50 seconds, and the tension of the steel sheet was maintained at 3.1 MPa or less in a furnace. Through these processes, a grain-oriented electrical steel sheet was manufactured in which a forsterite layer and an insulating coating layer were sequentially formed on the surface of the steel sheet. Thereafter, the surface of the steel sheet was simultaneously irradiated with a laser beam 20 obtained by superimposing the first laser (CO2) and the second laser (disc) to form a linear deformation portion 10 on the surface. At this time, linear deformed portions 10 were formed on the surface of the steel sheet in a direction intersecting the rolling direction while changing the irradiation interval of the superimposed laser beam 20 irradiated onto the surface of the steel sheet from 2.0 to 7.0 mm. The lasers used for magnetic domain miniaturization were a 150-3.0 kW CO2 laser as the first laser A and a disk laser with an output of 40-550 W as the second laser B. At this time, the scanning speed of the superimposed laser beam 20 was changed within the range of 5-150 m / s, and the irradiation angle was set to 1° or less.

[0088] The test conditions and measured magnetic values ​​for a 0.23 mm thick steel sheet are shown in Table 2. In Table 2, the W15 / 50 iron loss improvement rate and coercive force improvement rate refer to the improvement rate of iron loss and coercive force for the magnetically treated test specimen compared to the original sheet.

[0089] [Table 2]

[0090] In Table 2, if a linear deformation was present after laser irradiation and a resolidified layer was formed at either the front or rear boundary of the deformation, it was marked with "◎", and if no resolidified layer was formed, it was marked with "X". In addition, in Table 2, the laser irradiation method for Comparison 1 is "sequential irradiation," in which the CO2 laser of the first laser A is first irradiated, and then, after a certain time has passed and the steel plate in the irradiated area has cooled to room temperature, the disk laser of the second laser B is irradiated on top of the position where the CO2 laser passed. As shown in Table 2, when the steel plate thickness was 0.23 mm, the scanning interval of the superimposed laser was the same at 5 mm, and the output value of each laser was the same, Experiment 4 shows that the iron loss improvement rate with the superimposed laser was 12.1%, which is a significant improvement compared to the 3.5% improvement rate with sequential irradiation in Comparison 1, the 6.8% improvement rate with CO2 alone in Comparison 2, and the 6.1% improvement rate with the disc alone in Comparison 7.

[0091] Going a step further, as shown in Table 2, in the case of Comparison 6, in which the output value of the single CO2 laser was significantly increased to 2000 W from the output value of the CO2 laser of the superimposed laser (350 W), it was found that the iron loss improvement rate was lower than that of Experiments 7 to 10, in which the CO2 laser output value was low, and in the case of Comparison 13, in which the output of the disk laser was increased, it was found that the iron loss improvement rate was lower than that of Experiments 7 to 12.

[0092] Furthermore, as shown in Table 2, even when the thickness of the steel plate was 0.23 mm and the scanning interval of the superimposed laser was changed to 2 to 7 mm, it was found that the iron loss and coercive force were significantly improved in each experimental example in which the superimposed laser according to the present invention was irradiated at each scanning interval. As shown in Table 2, in the case of Comparative Examples 2 to 6, which are CO2 only, the iron loss improvement rate is very poor and the coercive force is also poor, despite the output (W: 350 to 2000) being within the range of the present invention.

[0093] In addition, in Table 2, in the cases of Comparative Examples 7 to 13, which are single disks, when the output (W: 10 to 550) is within the range of the present invention, the iron loss improvement rate is not very good and the coercive force is also poor. On the other hand, as shown in Table 2, a "resolidified layer" was formed in the Examples, whereas no "resolidified layer" was formed in the Comparative Examples. From these results, it can be seen that when a "resolidified layer" is formed, the iron loss improvement rate and coercivity improvement rate become higher.

[0094] The present invention is not limited to the examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the above-described examples are illustrative in all respects and not limiting.

Claims

1. an electromagnetic steel sheet substrate; an insulating coating layer located on the electrical steel sheet substrate, one or more linear deformations are present on the surface of the insulating coating layer, a resolidification layer is formed at one of the front and rear boundaries of the deformation portion; A grain-oriented electrical steel sheet, characterized in that the P concentration in the resolidified layer in the thickness direction of the insulating coating layer is lower than the P concentration in a lower insulating coating layer in which no resolidified layer is formed.

2. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the position where the P concentration of the resolidified layer starts to decrease is located at a distance of 15% or less of the entire thickness of the insulating coating layer from the surface of the insulating coating layer in the thickness direction of the insulating coating layer.

3. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the position where the P concentration of the resolidified layer begins to decrease is located 500 nm or less from the surface of the insulating coating layer in the thickness direction of the insulating coating layer.

4. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the width of the boundary where the resolidified layer is formed is formed to be 10 μm or less on either the front or rear side of both ends of the deformed portion.

5. The grain-oriented electrical steel sheet according to claim 1, wherein a glass coating layer is formed between the electrical steel sheet substrate and the insulating coating layer.

6. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the improvement rate of iron loss (W15 / 50 of magnetic domain material) of the electrical steel sheet is 7% or more.

7. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the electrical steel sheet has a coercive force improvement rate of 11% or more.

8. an electromagnetic steel sheet substrate; an insulating coating layer located on the electrical steel sheet substrate, one or more linear deformations are present on the surface of the insulating coating layer, a resolidification layer is formed at one of the front and rear boundaries of the deformation portion; A grain-oriented electrical steel sheet, characterized in that the Si concentration in the resolidified layer in the thickness direction of the insulating coating layer is higher than the Si concentration in a lower insulating coating layer where no resolidified layer is formed.

9. The grain-oriented electrical steel sheet according to claim 8, wherein the P concentration in the resolidified layer is lower than the P concentration in the lower insulating coating layer in which no resolidified layer is formed.

10. 10. The grain-oriented electrical steel sheet according to claim 9, wherein the position where the P and Si concentrations in the resolidified layer start to change is located at a position that is 15% or less of the total thickness of the insulating coating layer from the surface of the insulating coating layer in the thickness direction of the insulating coating layer.

11. The grain-oriented electrical steel sheet according to claim 8, wherein the electrical steel sheet has an iron loss (W15 / 50) improvement rate of 7% or more.

12. 9. The grain-oriented electrical steel sheet according to claim 8, wherein the electrical steel sheet has a coercive force improvement rate of 11% or more.

13. a first beam spot formed by irradiation with a first laser beam having a first wavelength; a second beam spot formed by irradiation with a second laser beam having a second wavelength, a superimposed laser beam that is controlled and formed so that the width of the second beam spot is positioned within the width of the first beam spot on the surface of the electromagnetic steel sheet, based on the traveling direction of the electromagnetic steel sheet; A method for refining magnetic domains in grain-oriented electrical steel sheets, characterized by irradiating the surface of the electrical steel sheet with radiation to form linear deformations.

14. The first laser is a CO ２ The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 13, wherein the first laser is a laser and the second laser is a disk laser.

15. The length of the disk laser beam, which is the second laser beam, is determined based on the width direction of the electromagnetic steel sheet. ２ The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 14, wherein the length of the laser beam is longer or shorter than the length of the laser beam.

16. CO of the first laser ２ The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 14, wherein the laser and the disk laser of the second laser share a light path in a laser beam scanning device.

17. CO of the first laser ２ 15. The method of claim 14, wherein the first laser and the second laser disk laser are scanned separately by a laser beam scanning device, and the laser beams overlap each other on the surface of the electrical steel sheet.

18. CO of the first laser ２ 15. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 14, wherein the laser beam spot is an elliptical beam spot having a width of 100 to 400 μm and a length of 0.4 to 20 mm.

19. The beam spot of the disk laser of the second laser has a width of 10 to 200 μm and a length of 10 μm to 200 μm. ２ The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 14, wherein the shape is an ellipse or a circle that is equal to or shorter than the length of the laser beam spot or is longer than the length of the laser beam spot.

20. 15. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 14, wherein the irradiation interval of the superimposed laser beam is 2 to 7 mm, and the scanning speed is 1 to 300 m / sec.

21. The method for refining magnetic domains in a grain-oriented electrical steel sheet according to claim 14, wherein the inclination direction of the superimposed laser beam is ±10° or less.

22. CO of the first laser ２ 15. The method for refining magnetic domains in grain-oriented electrical steel sheets according to claim 14, wherein the laser output is 200 to 2,000 W, and the disk laser output of the second laser is 10 to 550 W.

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