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

Abstract

A grain-oriented electrical steel sheet according to one embodiment of the present invention has an overlapping irradiation deformed part on a surface of an insulating film layer, wherein the overlapping irradiation deformed part is composed of: a complete overlapping irradiation deformed part having a width of 90% or more of the maximum width of the overlapping irradiation deformed part; and an incomplete overlapping irradiation deformed part having a width of less than 90% of the maximum width of the overlapping irradiation deformed part.

Description

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

[0001] One embodiment of the present invention relates to a oriented electrical steel sheet and a method for refining the magnetic domains thereof. More specifically, one embodiment of the present invention relates to a oriented electrical steel sheet having excellent iron loss characteristics while preventing surface damage by irradiating a superimposed laser onto the surface of an electrical steel sheet that has undergone secondary recrystallization, and a method for refining the magnetic domains thereof.

[0002] Grain-oriented electrical steel has excellent magnetic properties and is generally used as a core material for transformers. The manufacturing of such grain-oriented electrical steel involves the unique rolling and annealing processes inherent only to the electrical steel manufacturing process {110} <001> A Goss texture that is recrystallized by orientation is formed over the entire steel plate.

[0003] To address climate change, countries are increasingly tightening their greenhouse gas emission classification standards. In the case of transformer cores, the factors influencing the classification are related to the improvement in efficiency achieved when using electrical steel sheets. Furthermore, the efficiency of the transformer core is significantly influenced by the iron loss and magnetic flux density of the electrical steel sheets—that is, their magnetic properties.

[0004] Since the magnetic flux density of electrical steel sheets is higher when the crystal orientation—that is, the degree to which crystal axes that facilitate magnetization are clustered in the crystal structure—is higher, the manufacturing process of electrical steel sheets can have a significant impact.

[0005] Furthermore, the iron loss of electrical steel sheets is defined as the W17 / 50 [W / kg] value, measured when a magnetic field with a frequency of 50 Hz is applied at a maximum magnetic flux density of 1.7 T; this value is referred to as the guaranteed iron loss of the core material and is generally used as a measure of the iron loss of electrical steel sheets. However, when designing transformers, the W15 / 50 [W / kg] value, measured when a magnetic field with a frequency of 50 Hz is applied at a lower maximum magnetic flux density of 1.5 T, is sometimes used. In transformers, efficiency is evaluated as superior the lower these iron loss values ​​are.

[0006] Therefore, in the case of electrical steel sheets, the higher the magnetic flux density within the transformer design range and the lower the iron loss, the more efficient they can be used as transformer cores. Among these factors, iron loss is considered a more important indicator because, due to the upward standardization of electrical steel manufacturing processes, process technologies for securing high magnetic flux densities have advanced to a level capable of supporting transformer efficiency.

[0007] These iron losses are classified into eddy current losses and hysteresis losses. Since hysteresis losses tend to decrease as magnetic flux density increases, eddy current losses play a crucial role in controlling overall iron losses in oriented electrical steel sheets. Among the iron losses, eddy current losses are classified into classical eddy current losses and abnormal eddy current losses. Because classical eddy current losses are proportional to the thickness of the steel sheet, classical eddy current losses decrease as the sheet becomes thinner. Therefore, controlling abnormal eddy current losses has established itself as an important technology for reducing iron losses.

[0008] Among these iron losses, eddy current losses decrease as the spacing between the magnetic walls of the 180° domains in the rolling direction narrows, so iron losses can be reduced by refining the magnetic domains of the electrical steel sheet.

[0009] In electrical steel sheets, domain refinement refers to the process of separating a crystal grain with a single domain characteristic into multiple domains by applying physical stimulation. Methods for domain refinement include laser irradiation, electron beam irradiation, plasma treatment, etching, or roll indentation. Depending on whether the domain refinement effect is maintained even after stress relaxation annealing (SRA) is performed following such domain refinement treatment, it is classified into permanent domain refinement and temporary domain refinement.

[0010] In the manufacturing process of a series of electrical steel sheets, the domain refinement process may be performed before the decarburization process or after the insulation coating.

[0011] Meanwhile, a significant amount of time is required from the time the produced electrical steel sheets are shipped in coil form until they are processed into final iron cores due to reasons such as product transportation. During this transportation period or while processing into iron cores, there is a possibility that parts of the electrical steel sheets that have been physically stimulated for domain refinement may corrode.

[0012] The occurrence of corrosion on the surface of an electrical steel sheet due to physical stimulation means that the insulating film on the surface has partially or completely peeled off, exposing the substrate of the electrical steel sheet. If this is used as a laminated core, the insulating film formed on the surface of the electrical steel sheet is destroyed, causing the upper and lower laminated cores to conduct electricity, and in this case, there is even a possibility that the transformer may explode.

[0013] Therefore, even when applying physical stimulation to the surface of the electrical steel sheet for domain refinement, it is necessary to apply stimulation within a range that does not damage the insulating film.

[0014] In one embodiment of the present invention, a oriented electrical steel sheet and a method for refining the magnetic domains thereof are provided. More specifically, in one embodiment of the present invention, a oriented electrical steel sheet having excellent iron loss characteristics while preventing surface damage is irradiated with superposition lasers of different wavelengths on the surface of an electrical steel sheet that has undergone secondary recrystallization, and a method for refining the magnetic domains thereof are provided.

[0015] A oriented electrical steel sheet according to one embodiment of the present invention has a redundant irradiation deformation portion on the surface of an insulating film layer, and the redundant irradiation deformation portion is composed of a complete redundant irradiation deformation portion having a width of 90% or more of the maximum width of the redundant irradiation deformation portion and an incomplete redundant irradiation deformation portion having a width of less than 90% of the maximum width of the redundant irradiation deformation portion.

[0016] The ratio of the incomplete overlapping investigation deformation part within the total length of the overlapping investigation deformation part is 1.5 to 10%.

[0017] The Mg content in the insulating film layer of the overlapping irradiation deformation part is at least 5 times higher than the Mg content in the insulating film layer of the non-overlapping irradiation deformation part.

[0018] The incomplete overlapping investigation deformation part may exist at one end or both ends of the overlapping investigation deformation part.

[0019] The width of the overlapping investigation deformation section may decrease towards the ends of the overlapping investigation deformation section.

[0020] A method for refining magnetic domains of a oriented electrical steel sheet according to one embodiment of the present invention includes the step of irradiating a first laser beam having a first wavelength and irradiating a second laser beam having a second wavelength in a superposition to form a linear superposition irradiation deformation portion.

[0021] The step of forming an overlapping irradiation deformation part includes a step of forming a fully overlapping irradiation deformation part by irradiating so that the first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by 90% or more, and a step of forming an incompletely overlapping irradiation deformation part by irradiating so that the first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by less than 90%.

[0022] The ratio of the length of the incomplete overlapping irradiation deformation part to the total length of the overlapping irradiation deformation part is 1.5 to 10%.

[0023] The first laser and the second laser are selected from a CO2 laser, a fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, or a UV laser.

[0024] The ratio of the energy density of the first laser to the energy density of the second laser may be 30 to 60%.

[0025] The first laser and the second laser may have different wavelengths.

[0026] In the overlapping position, the interval between the time the first laser beam is irradiated and the time the second laser beam is irradiated may be 16ms or less.

[0027]

[0028] According to one embodiment of the present invention, by performing optimal magnetic domain refinement using an overlapping laser, the magnetic properties can be further enhanced while simultaneously sufficiently suppressing damage to the surface of the steel plate.

[0029] According to one embodiment of the present invention, using a long-wavelength laser makes it easy to increase the average output power and ensures the reliability of the processing line, and simultaneously irradiating with a short-wavelength laser allows for the formation of magnetic domains to be minimized, thereby effectively improving magnetism.

[0030] According to one embodiment of the present invention, it is possible to suppress magnetic deviation caused by the film while maintaining the effect of improving iron loss by using superimposed lasers.

[0031] According to one embodiment of the present invention, a steel plate can be stably preheated without destroying the insulating film layers, and residual stress resulting from the thermoelastic deformation of the steel plate can be induced with a width precisely sufficient for the formation of circulating magnetic domains without considering the thickness of the insulating film layers, thereby enabling accurate magnetic domain refinement.

[0032] According to one embodiment of the present invention, by maximizing thermal shock in the thickness direction even under low laser output conditions, it is possible to provide a directional magnetic domain refinement product with excellent iron loss in low and high magnetic fields.

[0033] FIG. 1 is a schematic diagram illustrating the concept of domain refinement for forming a superimposed irradiation deformation portion using a superimposed laser according to one embodiment of the present invention.

[0034] FIG. 2 is a schematic diagram showing a duplicate investigation deformation part according to one embodiment of the present invention.

[0035] FIG. 3 is a schematic diagram showing a fully redundant investigation deformation part and an incompletely redundant investigation part according to one embodiment of the present invention.

[0036] FIG. 4 is a schematic diagram showing a cross-section of a redundant investigation deformation part according to one embodiment of the present invention.

[0037] FIG. 5 is a schematic diagram showing the beam spot of an overlapping laser according to one embodiment of the present invention.

[0038] FIG. 6 is a schematic diagram showing a beam spot of an overlapping laser according to another embodiment of the present invention.

[0039]

[0040] 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 solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0041] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0042] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0043] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0044] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0045] The magnetic domain refinement method for oriented electrical steel sheets utilizes a method of reducing the width of the 90° magnetic domains, which are the main magnetic domains of the sheet, through magnetic domain refinement treatment, thereby providing nucleation sites for the magnetic domains when a magnetic field is applied, which reduces the magnetic domain travel distance and increases residual tensile stress in the rolling direction. Therefore, by increasing the laser output (energy density) to increase the laser energy density per unit area, or by reducing the diameter of the final beam or increasing its length to increase the duration time per unit length, the iron loss (W17 / 50) is improved while minimizing surface damage to the laser irradiation surface. However, improving iron loss has the disadvantage that corrosion resistance deterioration cannot be avoided because the increase in laser output leads to an increase in the energy density per unit area of ​​the irradiated laser, which in turn causes surface damage to the laser irradiation surface.

[0046] In one embodiment of the present invention, a manufacturing method is disclosed that can secure excellent iron loss characteristics at a lower laser output compared to single laser irradiation by refining the 180° magnetic domains of the laser irradiation surface while preventing corrosion caused by surface damage during laser irradiation, and an oriented electrical steel sheet having excellent iron loss characteristics obtained by the manufacturing method disclosed in this way is provided. That is, in one embodiment of the present invention, the purpose is to irradiate the surface of an electrical steel sheet with an overlapping laser to prevent surface damage while simultaneously imparting excellent iron loss characteristics.

[0047] One preferred method for improving iron loss in grain-oriented electrical steel is to refine magnetic domains using a laser.

[0048] As illustrated in FIG. 1, the magnetic domain refinement process of the oriented electrical steel sheet is performed by irradiating a laser in a direction intersecting the rolling direction (RD direction) to form a linear deformation part (10). Here, the linear or linear deformation part includes not only solid lines but also intermittently connected lines such as dotted or dashed lines, and furthermore, includes zigzag shapes when viewed microscopically but straight shapes when viewed macroscopically, and substantially includes all deformation parts that form a linear shape.

[0049] The formation of deformation zones in steel sheets by lasers refers to the deformation of magnetic domain structures caused by thermal shock from laser irradiation. This deformation occurs during the process in which the steel sheet is locally and rapidly heated and immediately cooled by the laser. In this case, the heating rate of the steel sheet is proportional to the laser energy density (power density) per unit time.

[0050] However, since the deformation of the magnetic domain structure due to thermal shock during laser irradiation increases with the total laser irradiation energy, if energy exceeding the amount required for magnetic domain refinement is irradiated onto the steel plate, heat sources exceeding those required for the formation of circulating magnetic domains diffuse to the surroundings, causing magnetic deformation to increase. Therefore, the deformation of the magnetic domain structure due to thermal shock during laser irradiation requires exactly the amount of lattice deformation energy required for the formation of circulating magnetic domains, and in order to suppress heat diffusion, it is desirable to irradiate the laser incident energy to a narrow area for a shorter period of time.

[0051] In addition, the interaction conditions between the laser beam and the steel sheet are influenced by the characteristics of the laser and the absorption rate of the laser beam on the steel sheet. The absorption rate of the laser beam is influenced by the surface roughness of the steel sheet, the temperature of the steel sheet, the absorption characteristics of the film on the surface of the steel sheet, and the laser wavelength. However, when the manufacturing conditions of the oriented electrical steel sheet forming the film are kept constant, the surface roughness of the steel sheet, the temperature of the steel sheet, and the absorption characteristics of the film on the surface of the steel sheet will be constant, and in this case, the absorption rate of the laser beam on the steel sheet depends on the wavelength of the laser.

[0052] In other words, assuming constant manufacturing conditions for the steel plate, the laser absorption rate is influenced by the wavelength of the laser. The laser absorption rate of the steel plate is relatively high for short wavelengths, while it appears relatively low for long wavelengths.

[0053] In this way, using a short-wavelength laser is more efficient than using a long-wavelength laser to secure stable iron loss characteristics in the process of refining magnetic domains of oriented electrical steel sheets using a laser.

[0054] Meanwhile, an insulating film composed mainly of phosphate and silica, with a thickness of several to tens of micrometers, is formed on the surface of the electrical steel sheet to be treated for domain refinement. These films absorb the laser beam relatively little for short-wavelength lasers but exhibit large absorption for long-wavelength lasers. As a result, the thickness of the insulating film must be considered for long-wavelength lasers, but the thickness of the insulating film can be considered less for short-wavelength lasers than for long-wavelength lasers.

[0055] As described above, short-wavelength and long-wavelength lasers have different characteristics. Therefore, when a short-wavelength green laser and a long-wavelength fiber laser are used in combination, the advantages of each laser applicable to magnetic domain miniaturization are preferentially exerted without side effects, thereby inducing a mutual synergistic effect.

[0056] Meanwhile, when an overlapping laser is irradiated, the width (T) of the overlapping irradiation deformation part (10) formed in the overlapping irradiation deformation part (10) w If the optical system is formed uniformly, the configuration is complex and requires precise control, making it vulnerable to vibration or heat.

[0057] In one embodiment of the present invention, a laser is superimposed to form a superimposed irradiation deformation part, and by reducing the width of the superimposed irradiation deformation part in at least one part within the superimposed irradiation deformation part, the optical system configuration can be simplified and a structure more robust against vibration or heat can be secured.

[0058] As illustrated in FIG. 1, a laser is advanced and irradiated in a direction intersecting the rolling direction (RD direction) to form a linear deformation part (10). Here, the linear or linear deformation part includes not only solid lines but also intermittent lines such as dotted or dashed lines, and furthermore, includes zigzag shapes when viewed microscopically but straight shapes when viewed macroscopically, and substantially includes all deformation parts that form a linear shape.

[0059] FIGS. 2 and 3 illustrate a redundant investigation deformation section (10) according to an embodiment of the present invention. FIGS. 2 and 3 represent the length of the redundant investigation deformation section (10) in a direction perpendicular to the length direction (X direction) of the deformation section (10) (Y direction). The length direction (X direction) of the deformation section (10) may form an angle of 15° or less with the rolling vertical direction (TD direction) of the steel plate. More specifically, the length direction (X direction) of the deformation section (10) may form an angle of 5° or less with the rolling vertical direction (TD direction) of the steel plate.

[0060] In one embodiment of the present invention, the width (T) of the overlapping investigation deformation part (10) W ) means the length of the overlapping investigation deformation part (10) in the direction perpendicular to the length direction (X direction) and the direction (Y direction) of the overlapping investigation deformation part (10).

[0061] As shown in FIGS. 2 and 3, in a directional electrical steel sheet (100) according to one embodiment of the present invention, an overlapping irradiation deformation portion (10) exists on the surface of an insulating film layer (50), and the overlapping irradiation deformation portion (10) has a width (T W ) Maximum width of the deformation section of the overlapping investigation (T Wmax A fully duplicated investigation deformation section (13) that is more than 90% of ) and a maximum width (T) of the duplicated investigation deformation section Wmax It consists of an incomplete duplicate investigation modified part (14) of less than 90% of ).

[0062] In FIG. 3, the total length (T) of the overlapping investigation deformation part (10) TL ), complete duplicate investigation deformation part (13) length (T CL ) and the length (T) of the incomplete overlapping investigation deformation part (14) PL It represents ).

[0063] As shown in FIG. 4, a directional electrical steel sheet according to one embodiment of the present invention includes a metal oxide film layer (40) and an insulating film layer (50) on the surface of an electrical steel sheet base material (60).

[0064] The overlapping investigation deformation section (10) can be made of continuous or discontinuous lines or regions.

[0065] Maximum width (T) of the overlapping investigation deformation part (10) Wmax ) is the width (T) of the deformation part (10) within the overlapping investigation deformation part (10). W It means the point where ) is maximum.

[0066] The method of forming the complete overlapping irradiation deformation part (13) and the incomplete overlapping irradiation deformation part (14) is explained together with FIG. 2. As explained in FIG. 2, when a plurality of lasers including a first laser beam and a second laser beam are superimposed and irradiated, a first laser irradiation part (11) resulting from the irradiation of the first laser and a second laser irradiation part (12) resulting from the irradiation of the second laser are respectively present. Unlike the example in FIG. 2, if the irradiation position and width of the first laser irradiation part (11) and the second laser irradiation part (12) are completely superimposed, the laser irradiation deformation part with a narrow width in the direction perpendicular to the length of the deformation part (10) among the first laser irradiation part (11) and the second laser irradiation part (12) becomes the overlapping irradiation deformation part (10), and the width (T) of the overlapping irradiation deformation part (10) in the length direction (X direction) of the deformation part (10) w It is difficult to change ).

[0067] In one embodiment of the present invention, by adjusting the overlapping area of ​​the first laser irradiation deformation part (11) and the second laser irradiation deformation part (12) and forming a part of the overlapping irradiation deformation part (10) as an incomplete overlapping irradiation deformation part (14), the optical system configuration can be simplified and a structure robust against vibration or heat can be secured.

[0068] FIG. 2 illustrates an example in which an incomplete overlapping irradiation deformation part (14) is formed within an overlapping irradiation deformation part (10) by making the angles in the irradiation length direction of the first laser irradiation deformation part (11) and the second laser irradiation deformation part (12) partially different. As shown in FIG. 2, the widths of the first laser irradiation deformation part (11) and the second laser irradiation deformation part (12) do not change, but by making the angles in the irradiation length direction of the first laser irradiation deformation part (11) and the second laser irradiation deformation part (12) partially different, an incomplete overlapping irradiation deformation part (14) is created. In addition to the method exemplified in FIG. 2, it is also possible to form an incomplete overlapping irradiation deformation part (14) by partially reducing the width of the first laser irradiation deformation part (11) or the second laser irradiation deformation part (12). Alternatively, it is also possible to form an incomplete overlapping irradiation deformation section (14) by adjusting the first laser irradiation deformation section (11) or the second laser irradiation deformation section (12), which is substantially linear, into a partially curved shape, while making the curvatures different from each other.

[0069] The completely duplicate investigation deformation part (13) is the width (T) of the duplicate investigation deformation part (10). W ) refers to the part that is 90% or more of the maximum width of the overlapping investigation deformation part (10). The complete overlapping investigation deformation part (13) has a width (T W By sufficiently securing ), the magnetic domain displacement distance is reduced and the residual tensile stress in the rolling direction is increased.

[0070] In one embodiment of the present invention, the width (T) of the overlapping investigation deformation part (10) W ) refers to the length of the overlapping irradiation deformation part (10) in the direction perpendicular to the length direction (X direction) of the overlapping irradiation deformation part (10) (Y direction). In one embodiment of the present invention, the complete overlapping irradiation deformation part (13) is also called the wide deformation part.

[0071] The incomplete overlapping investigation deformation part (14) is the width (T) of the overlapping investigation deformation part (10). W) refers to the part that is less than 90% of the maximum width of the overlapping investigation deformation part (10). The incomplete overlapping investigation deformation part (14) has a width (T W ) is smaller than the complete overlapping irradiation deformation section (13), so it is insufficient compared to the complete overlapping irradiation deformation section (13) in terms of increasing residual tensile stress in the rolling direction. However, it may be more advantageous compared to the complete overlapping irradiation deformation section (13) in terms of suppressing damage to the steel plate surface, thereby reducing the possibility of corrosion and electrical conduction. In one embodiment of the present invention, the incomplete overlapping irradiation deformation section (14) is also called the narrow deformation section.

[0072] In one embodiment of the present invention, by appropriately adjusting the length of the incomplete overlapping irradiation deformation section (14) within the overlapping irradiation deformation section (10), it is possible to manufacture a directional electrical steel sheet having excellent iron loss characteristics while preventing surface damage. Specifically, the total length (T) of the overlapping irradiation deformation section (10) TL Length (T) of the deformation part (14) of the incomplete overlapping investigation regarding ) PL ) ratio(T PL / T TL ) is 1.5 to 10%. If the ratio of the incomplete overlapping irradiation deformation part (14) is too small, the optical system configuration is complex and requires precise control, so it may be vulnerable to vibration or heat, and the permeability may decrease significantly in terms of magnetism. Conversely, if the ratio of the incomplete overlapping irradiation deformation part (14) is too large, iron loss increases and the magnetic strain improvement effect decreases significantly. More specifically, the total length (T) of the overlapping irradiation deformation part (10) TL Length (T) of the deformation part (14) of the incomplete overlapping investigation regarding ) PL ) ratio(T PL / T TL ) can be 1.5 to 10%, preferably 1.5 to 7%, more preferably 1.5 to 5%, and particularly preferably 1.5 to 3%. Alternatively, the ratio (T PL / T TLThe minimum value of ) may exceed 1%. Alternatively, the ratio (T PL / T TL The maximum value of ) may be less than 13%.

[0073] Figure 4 shows a cross-section of a redundant investigation deformation part (10) according to one embodiment of the present invention.

[0074] As shown in FIG. 4, a directional electrical steel sheet according to one embodiment of the present invention includes a metal oxide film layer (40) and an insulating film layer (50) on the surface of an electrical steel sheet base material (60).

[0075] The metal oxide film layer (40) refers to a film layer formed by the reaction between the oxide layer and the annealing separator component when a cold-rolled steel sheet is decarburized to form an oxide layer on the surface of the cold-rolled steel sheet and then an annealing separator is applied to perform a second recrystallization annealing. For example, if MgO is included in the annealing separator component, the metal oxide film layer (40) will contain forsterite.

[0076] The insulating film layer (50) is formed by coating with a single or composite insulating coating solution of colloidal silica and metal phosphate. The insulating film layer (50) typically contains Si and P as main components.

[0077] As shown in FIG. 4, Mg can be diffused from the metal oxide film layer (40) into the insulating film layer (50) in which the overlapping irradiation modified portion (10) is formed. Due to the diffusion of Mg from the metal oxide film layer (40), the Mg content contained in the insulating film layer (50) can be increased by more than 5 weight% compared to the portion outside the overlapping irradiation modified portion (10) (the uncolored portion in FIG. 3 to 5). More specifically, the Mg content of the overlapping irradiation modified portion (10) within the insulating film layer (50) can be 5 to 40 weight% higher than the Mg content within the insulating film layer (50) other than the overlapping irradiation modified portion (10). For example, if the Mg content in the insulating film layer (50) other than the overlapping irradiation deformation part (10) is 10 weight%, the Mg content in the insulating film layer (50) below the overlapping irradiation deformation part (10) may be 10.5 to 14.0 weight%.

[0078] When the first laser or the second laser is irradiated alone onto the insulating film layer (50), the energy required for Mg diffusion is not sufficiently transmitted, so the Mg content in the insulating film layer (50) may be lower than that in the overlapping irradiation modified portion (10) within the insulating film layer (50). Conversely, the Mg content in the overlapping irradiation modified portion (10) within the insulating film layer (50) is higher than that in the insulating film layer (50) that is not the overlapping irradiation modified portion (10). That is, in FIG. 2, the Mg content in the insulating film layer (50) may be low in the first laser irradiation portion (11) and the second laser irradiation portion (12) other than the overlapping irradiation modified portion (10). Also, naturally, the Mg content may be low in the portion of the insulating film layer (50) that is not irradiated by a laser.

[0079] The Mg content in the insulating film layer (50) can be quantitatively measured by methods such as EDS (Energy Dispersive Spectroscopy) analysis on the surface or cross-section. The Mg content in the insulating film layer (50) may have a concentration gradient depending on the thickness of the insulating film layer (50), and if a concentration gradient exists, it can be determined by the average over the entire thickness.

[0080]

[0081] Hereinafter, a method for refining magnetic domains of a oriented electrical steel sheet according to one embodiment of the present invention will be described.

[0082] In one embodiment of the present invention, using lasers in a superposition manner means using two or more lasers for the laser beams irradiated onto the surface of a steel plate, and having a spot of one laser beam formed on the surface of the steel plate partially or entirely located within the spot of another laser beam. The aforementioned complete superposition irradiation deformation part (13) means irradiating such that the first beam spot of the first laser beam (21) and the second beam spot of the second laser beam (22) overlap by 90% or more. Additionally, the incomplete superposition irradiation deformation part (14) means irradiating such that the first beam spot of the first laser beam (21) and the second beam spot of the second laser beam (22) overlap by less than 90%.

[0083] In addition, the investigation time for the overlapping positions does not need to be investigated simultaneously, and it is acceptable to investigate them overlappingly at regular intervals. That is, even if the laser beams do not overlap at a specific point in time, if time passes and the first laser beam (21) moves horizontally in the direction of travel (X direction) and overlaps with the position of the second laser beam (22) that was investigated before or after, it is considered to be overlapping. However, if the first laser beams (21) overlap with each other while the first laser beam (21) is moving in the direction of travel (X direction), it is not considered to be overlapping. FIG. 6 illustrates the case where the first laser beam (21) moves horizontally in the direction of travel (X direction) after a specific point in time and overlaps with the second laser beam (22).

[0084] In one embodiment of the present invention, a beam spot refers to a beam spot on the surface of a steel plate. FIG. 5 schematically shows the beam spot of the first laser beam (21) and the beam spot of the second laser beam (22).

[0085] In one embodiment of the present invention, the beam spot of the first laser (21) and the beam spot of the second laser (22) overlap. The overlap value of the lasers is the width (B) of the first laser. 1W ) and the width of the second laser (B 2W For the width of the smaller laser beam among ), the width of the overlapping region (O W It refers to the ratio of ). In Fig. 2, the width of the first laser (B 1W This is the case where ) is small, and in this case, the overlap ratio is O W / B 1W It can be calculated as.

[0086] The width of the laser beam is the length of the laser beam in the direction perpendicular to the longitudinal direction of the deformation section (or the direction of laser irradiation propagation, X-direction) (Y-direction). The length of the laser beam is the length of the laser beam in the longitudinal direction of the deformation section (or the direction of laser irradiation propagation, X-direction). In FIG. 5, the length of the first laser beam (B 1L ) and the length of the second laser beam (B 2L displayed ).

[0087] As previously mentioned, in the case where the laser beams do not overlap at a specific point in time as shown in FIG. 6, the laser beam is moved horizontally in the direction of travel (X-direction) to determine the width of the overlapping area (O W The point where ) becomes longest is considered the overlap ratio.

[0088] The first laser and the second laser may be selected from a CO2 laser, a fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, or a UV laser.

[0089] More specifically, the first laser (21), which is a short-wavelength laser, can 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, and a sapphire laser. In addition, as this first laser, 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) may be used.

[0090] And for the second laser (22), which is a long-wavelength laser, a laser with a relatively longer wavelength than the short-wavelength laser can be used. For example, a CO2 laser is preferred for the second laser. However, if a UV laser (0.150 to 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 to 0.355 μm) is used as the first laser, a YAG laser may be used as the second laser.

[0091] Below, a method for refining magnetic domains using superposition lasers (20) is described in more detail, using an example where a 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.

[0092] The first laser (21) may have a shorter wavelength compared to the second laser (22). In one embodiment of the present invention, since the absorption rate of the short-wavelength green laser within the steel plate is maximized by forming an overlap portion by the first laser (21) and the second laser (22), thereby enabling low iron loss in a lower laser output range, there is no reason to limit the laser beam quality (beam parameter product, BPP), oscillation form (continuous oscillation or pulse), and final beam shape in the simultaneous irradiation of heterogeneous wavelength lasers. However, for the purpose of minimizing thermal effects in the rolling direction of the steel plate, an incomplete irradiation deformation portion (14) is formed so that the first beam spot of the first laser beam (21) and the second beam spot of the second laser beam (22) overlap less than 90% within the irradiation deformation portion (10). Since the complete irradiation deformation portion (13) and the incomplete irradiation deformation portion (14) have been described above in relation to oriented electrical steel plates, a redundant description is omitted.

[0093] As described in FIG. 2, when multiple lasers, such as a first laser and a second laser, are superimposed, a first laser irradiation section (11) and a second laser irradiation section (12) exist respectively according to the irradiation of the first laser. When the irradiation position and width of the first laser irradiation section (11) and the second laser irradiation section (12) completely overlap, the laser irradiation deformation section with the narrower width among the first laser irradiation section (11) and the second laser irradiation section (12) becomes the overlapping irradiation deformation section (10), and the width (T) of the overlapping irradiation deformation section (10) w It is difficult to change ).

[0094] In one embodiment of the present invention, by adjusting the overlapping area of ​​the first laser irradiation deformation part (11) and the second laser irradiation deformation part (12), an incomplete overlapping irradiation deformation part (14) within the overlapping irradiation deformation part (10) is partially formed, thereby simplifying the optical system configuration and minimizing the reduction in permeability.

[0095] FIG. 2 illustrates an example of forming an incomplete overlapping irradiation deformation section (14) within an overlapping irradiation section (10) by making the irradiation length direction angles of the first laser irradiation deformation section (11) and the second laser irradiation deformation section (12) partially different. That is, as shown in FIG. 2, the widths of the first laser irradiation deformation section (11) and the second laser irradiation deformation section (12) do not change, but by making the irradiation length direction angles of the first laser irradiation deformation section (11) and the second laser irradiation deformation section (12) partially different, an incomplete overlapping irradiation deformation section (14) is created. In addition to the method exemplified in FIG. 2, it is also possible to form an incomplete overlapping irradiation deformation section (14) by partially reducing the width of the first laser irradiation deformation section (11) or the second laser irradiation deformation section (12). Alternatively, it is also possible to form an incomplete overlapping irradiation deformation section (14) by adjusting the first laser irradiation deformation section (11) or the second laser irradiation deformation section (12), which is substantially linear, into a partially curved shape, while making the curvatures different from each other.

[0096] Since the first laser, a fiber laser, uses a short wavelength with a relatively high laser absorption rate by the steel plate, it is possible to irradiate a narrow area with incident energy for a shorter duration that causes only the necessary changes in magnetic domain structure and residual stress due to thermoelastic deformation, precisely for the formation of circulating magnetic domains. Furthermore, because the fiber laser used as the first laser has a narrow incident energy range, it can suppress heat diffusion to the surroundings, thereby minimizing unnecessary thermal deformation.

[0097] Meanwhile, the second laser, the CO2 laser, can be used at high outputs ranging from several hundred watts to over several kilowatts depending on the steel plate speed, and can easily induce thermoelastic deformation in the irradiated portion of the steel plate. Furthermore, the second laser, the CO2 laser, has high transmittance through insulating films composed of phosphate and silica, allowing it to stably pass through the film layers. Therefore, the second laser, the CO2 laser, is suitable for a preheating role as it can stably induce thermoelastic deformation of the steel plate without destroying the insulating film layers. However, since the laser absorption rate of the second laser, the CO2 laser, is low for steel plates, it is desirable to irradiate the steel plate with a laser intensity that induces thermoelastic deformation but does not cause permanent deformation.

[0098] In other words, since using a long-wavelength laser, such as the second laser (CO2 laser), results in a thermal shock being applied to the steel plate over too wide a region, hindering effective domain refinement, a fiber laser with a relatively short wavelength is used as the first laser to serve as the primary laser for domain refinement, while the CO2 laser with a relatively long wavelength is used as an auxiliary laser that acts as a kind of preheater to induce thermoelastic deformation of the steel plate.

[0099] The reason a short-wavelength 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 surface of the steel plate is high, forming a strong compressive stress zone in the laser irradiation area, and in this compressive stress zone, a lancet domain (circulating domain) can be easily formed to reduce magnetoelastic energy.

[0100] In this case, by refining the magnetic domains, 180° magnetic domains (opposite poles of lancet domains) are formed in the surface direction by magnetoelastic energy, and 90° magnetic domains are formed in the plate thickness direction to reduce magnetoelastic energy, thereby narrowing the spacing of the magnetic domains and consequently reducing abnormal eddy current losses.

[0101] As described above, the magnetic domain refinement method according to one embodiment of the present invention uses a short-wavelength fiber laser as the first laser to induce residual stress due to the thermoelastic deformation of the steel plate with a width sufficient for precisely forming circulating magnetic domains, thereby enabling accurate magnetic domain refinement, while using a long-wavelength CO2 laser as the second laser to stably preheat the steel plate without destroying the coating layers.

[0102] In addition, the first laser, a short-wavelength fiber laser, has the advantage of being able to form a small final beam width and improve the laser absorption rate within the steel plate, but has the disadvantage of having a relatively short depth of field. However, the second laser, a long-wavelength CO2 laser, has the advantage of having a wide final beam width and a relatively low laser absorption rate within the steel plate, but has a deep depth of field. Therefore, when these two laser beams are superimposed and irradiated simultaneously, the laser absorption rate within the steel plate can be further increased.

[0103] At this time, the beam spot of the fiber laser, which is the first short-wavelength laser irradiated on the surface of the steel plate, is preferably approximately circular in shape, and its diameter (B 1W , B 1L ) can be 10 to 200 μm. In addition, the beam spot of the fiber laser has a width (B 1W ) is 10 to 200 μm and its length (B 1L ) can be used for a length less than or greater than the length of the CO2 laser beam spot, which is the second laser.

[0104] Beam width (B) of the optical fiber, which is the first laser 1W If ) decreases to less than 10㎛, energy density becomes concentrated in a narrow area, which may lead to lower magnetic flux density and iron loss, and there is a problem of the optical system structure becoming complex. Also, the beam width (B) of the optical fiber, which is the first laser 1WIf ) becomes larger than 200㎛, the thermal effect in the longitudinal direction of the steel plate increases, which may lead to a decrease in magnetic flux density, so it is not desirable.

[0105] Meanwhile, the beam spot of the CO2 laser, which is a long-wavelength second 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 preferred. In addition, the beam spot of the long-wavelength CO2 laser can also be used as a circular shape with a radius of 100 μm or more.

[0106] CO2 beam width of the second laser (B 2W It is not desirable to form it within 100㎛ because the mirror optical system becomes complex like a fiber laser, and it is not desirable to increase it to 400㎛ or more because the thermal effect along the length of the steel plate increases, causing a decrease in magnetic flux density.

[0107] The reason for limiting the beam spot size of the CO2 laser, a long-wavelength second laser, in this manner is to consider the range in which the thermal deformation effect of the laser beam acting on the steel plate is maintained when the laser is irradiated at high speed onto the surface of a high-speed moving steel plate.

[0108] In one embodiment of the present invention, the oscillation mode of the laser beam used is preferably a continuous wave laser that continuously generates laser light for both the first laser and the second laser, but a pulse laser may also be used.

[0109] In addition, regarding the quality of the laser beam used, for both the first and second lasers, a Gaussian mode of TEM00 is preferred, but a multi-transverse mode of TEM0i can also be used.

[0110] However, since the superimposed laser beam (20) of different wavelengths irradiated onto the surface of a steel plate according to one embodiment of the present invention can minimize thermal effects in the longitudinal direction of the steel plate while maximizing thermal shock in the thickness direction, the beam shape or beam quality of each laser is not specifically limited.

[0111] The ratio of the energy density of the first laser to the energy density of the second laser may be 30 to 80%. By setting the ratio of the energy density of the second laser to be somewhat lower than the ratio of the energy density of the first laser in this way, the reduction in permeability and magnetic flux density can be minimized. More specifically, the ratio of the energy density of the first laser to the energy density of the second laser may be 30 to 60%.

[0112] The first laser and the second laser may each have an output of 10 to 2000 W. More specifically, the output of the first laser may be 1000 to 2000 W, and the output of the second laser may be 100 to 700 W. These output ranges for each laser specify the laser output conditions when the steel plate travels at a speed of 15 mpm, and the laser output values ​​can be optimally controlled according to the speed of the steel plate.

[0113] When a laser beam (20) in which the first laser and the second laser are superimposed as described above is irradiated onto the surface of a steel plate, the spacing (i.e., the spacing between the deformation parts in the steel plate rolling direction) may be 2 to 10 mm, the angle between the rolling direction and the laser propagation direction (the length direction of the deformation part, X direction) may be 75 to 105°, and the scanning speed is preferably 0.1 to 300 m / sec.

[0114] It is preferable to use electrical steel sheets that have undergone secondary recrystallization.

[0115] And if the irradiation interval of the superimposed laser beam (20) irradiated on the steel plate surface becomes too narrow, less than 2 mm, the influence of the heat-affected zone increases, and the magnetic flux density and iron loss become inferior, and if the irradiation interval is 10 mm or more, the thermal shock effect for securing the magnetic domain refinement effect decreases, making it difficult to exert the effect.

[0116] In addition, when irradiating the superimposed laser beam (20) onto the surface of the steel plate, it can be irradiated at a right angle or at an angle to the rolling direction of the steel plate, and the angle between the rolling direction and the laser propagation direction (the length direction of the deformation part, X direction) can be 75 to 105°. If the angle is outside this range, the necessary magnetic domain refinement effect may not appear.

[0117] And since the scanning speed of the superimposed laser must be faster as the speed of the steel plate increases, it is desirable to have a scanning speed of 0.1 to 300 m / sec, and this speed refers to the value exemplified under the condition of 15 mpm.

[0118] The travel speed of the steel plate can be 0.016 to 2.83 m / s.

[0119]

[0120] Meanwhile, when a deformation portion is formed by irradiating a superimposed laser onto the surface of an electrical steel sheet according to one embodiment of the present invention, it is preferable that the W15 / 50 iron loss improvement rate of such steel sheet be 6% or higher. If the W15 / 50 improvement rate is lower than this, it is difficult to expect the desired iron loss reduction effect because the laser absorption rate of the steel sheet is low.

[0121] In addition, when a deformation portion is formed by irradiating a superimposed laser onto the surface of an electrical steel sheet according to one embodiment of the present invention, it is desirable that the W17 / 50 iron loss improvement rate of such steel sheet be 9% or higher. If the W17 / 50 iron loss improvement rate is lower than this, it is difficult to expect the desired iron loss reduction effect because the laser absorption rate of the steel sheet is also low.

[0122] Hereinafter, a method for manufacturing a oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0123] [Manufacture of Cold-Rolled Steel Sheets]

[0124] In order to manufacture oriented electrical steel sheets, a slab of electrical steel sheet substrate is first manufactured.

[0125] The chemical composition and metallographic structure of the slab are not separately limited as long as the easy magnetization axis is aligned in a certain direction and it functions as an electrical steel sheet. However, to illustrate with an example, the chemical composition of the slab is as follows.

[0126] By weight %, 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, Ti): 0.070% or less, (total of one or more of Cr, Sn, Sb): 2.5% or less, Al: 2.0% or less (excluding 0%), (total of one or more of P, 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, the total of H2, O2 and N2 is 0.02% or less, and the remainder is Fe.

[0127] (C: 0.08% or less (excluding 0%))

[0128] Carbon (C) is an element that is inevitably incorporated into steel, but since it degrades magnetic properties due to magnetic aging, it is desirable to control its content to an appropriate level. If the C content in the steel sheet is too low, phase transformation does not occur sufficiently during the manufacturing process, which can lead to non-uniformity in the microstructure of the steel sheet and ultimately destabilize the secondary recrystallization structure. If too much C is included, carbides become coarse during the manufacturing process and the amount of precipitation is excessive, which results in insufficient decarburization and a decrease in the density of the Goss texture, thereby damaging the secondary recrystallization texture. Therefore, the C content of the steel sheet is 0.08% or less, and more preferably 0.001 to 0.040%.

[0129] (Si:1.0 ~ 6.5 %)

[0130] Silicon (Si) serves as the basic composition of oriented electrical steel sheets and plays a role in lowering iron loss by increasing the resistivity of the steel sheet. If the content is less than 1.0%, resistivity decreases, leading to increased eddy current losses and deterioration of iron loss characteristics, making it impossible to expect the effect of Si addition. If the content is 6.5% or more, the brittleness of the steel sheet increases and toughness decreases, which may cause sheet fracture during the rolling process. Furthermore, insufficient nitrides are formed during the manufacturing process, making it impossible to secure sufficient grain suppression power necessary for secondary recrystallization formation during the final high-temperature annealing process. Therefore, a Si content of 1.0 to 6.5% is desirable.

[0131] (Mn: 0.005 ~ 3.0%)

[0132] Manganese (Mn) is an important element that affects the surface quality of the final product. It has the effect of reducing overall iron loss by increasing resistivity and thereby decreasing eddy current losses. Furthermore, it not only forms Mn-based sulfides by reacting with S during the quenching process to create Mn-based sulfides, but also inhibits the growth of primary recrystallized grains and induces secondary recrystallization by reacting with nitrogen introduced through nitriding treatment along with Si to form (Al,Si,Mn)N precipitates. However, if the Mn content is too low, the surface quality of the final product may deteriorate. Conversely, if the Mn content is too high, the austenite phase fraction increases significantly, damaging the Goss texture and reducing magnetic flux density. Additionally, excessive oxide layers may form during decarburization annealing, which can hinder decarburization. Therefore, an Mn content of 0.005 to 3.0% is desirable.

[0133] (Sum of any one or more of Nb, V, and Ti: 0.05% or less)

[0134] Niobium (Nb), vanadium (V), and titanium (Ti) are elements that react with C and N during the manufacturing process to form precipitates, but if added in excessive amounts, they remain in the steel sheet even after secondary recrystallization annealing and degrade the magnetic properties of the steel sheet. Therefore, it is desirable to control the total amount of at least one element selected from Nb, V, and Ti to 0.05% or less.

[0135] (Sum of any one or more of Cr, Sn, and Sb: 2.5% or less)

[0136] Chromium (Cr) is added to reduce iron loss by promoting the formation of a Goss texture, and Sn is added to ultimately improve magnetic flux density by inhibiting grain growth. Additionally, Antamon (Sb) has the effect of stabilizing secondary recrystallization by segregating at grain boundaries and inhibiting grain growth. Since all three of these elements are interrelated with the formation of a secondary recrystallization structure, it is desirable to control the total of Sn, Sb, and Cr to 2.5% or less.

[0137] (Al: 2.0% or less (excluding 0%))

[0138] Aluminum (Al) acts as a strong grain growth inhibitor by combining with N introduced by nitriding treatment during the primary recrystallization process and Al, Si, and Mn existing in solid solution in the steel to form nitrides in the form of (Al, Si, Mn)N and AlN, in addition to Al-based nitrides precipitated during the manufacturing process. However, if too much Al is included, the precipitates become non-uniform, making the formation of secondary recrystallization unstable and degrading the magnetic properties of the steel sheet; therefore, it is desirable to add it at 2.0% or less.

[0139] (Sum of any one or more of P and S: 0.1% or less (excluding 0%))

[0140] Phosphorus (P) plays an auxiliary role in hindering grain boundary movement and inhibiting grain growth by segregating at grain boundaries, while S, if added in excessive amounts, destabilizes the formation of secondary recrystallization. Additionally, P and S are elements that are inevitably added during the process of manufacturing electrical steel sheets, and it is desirable to control the total of P and S to 0.1% or less.

[0141] (Cu + Sn Total: 0.1% or less)

[0142] Copper (Cu) plays a role in improving the texture as it is partially dissolved within the grains, and since excessive Cu + Sn content can cause segregation at grain boundaries and form a liquid phase at high temperatures, it is desirable to control the total amount of Cu and Sn to 0.1% or less.

[0143] (Total of rare earth elements and other impurities is 0.2% or less)

[0144] A grain-oriented electrical steel sheet according to one embodiment of the present invention may contain rare earth elements such as cerium (Ce) or praseodymium (Pr) and other impurities, and it is preferable that the total amount of any rare earth elements and impurities included is 0.2% or less. Rare earth elements and unavoidable impurities refer to impurities that are intentionally introduced or inevitably incorporated during the steelmaking and manufacturing process of grain-oriented electrical steel sheets. Since unavoidable impurities are widely known, a detailed description is omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. If additional elements are included, they are included to replace the remainder, Fe.

[0145] (Total of O2+ N2+ H2: 0.02 wt% or less)

[0146] Oxygen (O2) forms metal (non-metal) oxides with elements that have a high affinity for oxygen, such as Al, Mn, and Ti, and remains even after hot / cold rolling, which can hinder magnetic domain movement when a magnetic field is applied; nitrogen (N2) forms nitrides such as AlN, which hinders crystal growth during primary grain boundary growth and increases the degree of grain boundary non-uniformity when distributed non-uniformly, which can increase the deviation in the coil width and length direction during secondary recrystallization; and hydrogen (H2) can cause brittle fracture if hydrogen aggregation occurs at grain boundaries, inclusions, or precipitates, so it is desirable to control the total amount of oxygen + nitrogen + hydrogen to 0.02% or less.

[0147] Next, a steel plate having the above composition is manufactured into a slab by a continuous casting method, then heated by a conventional method and hot-rolled, and optionally annealed as needed, then cold-rolled to produce a thickness in the range of 0.1 to 0.5 mm. Here, cold rolling may be performed once or two or more times with intermediate annealing in between.

[0148] [1st Recrystallization Annealing]

[0149] The previously described cold-rolled steel sheet is subjected to primary recrystallization annealing through a simultaneous decarburization or post-decarburization nitriding process. In the case of primary recrystallization annealing by simultaneous decarburization, the microstructure of the cold-rolled steel deformed during the annealing process undergoes decarburization including recrystallization. To achieve this, the process is carried out in a mixed gas atmosphere containing nitrogen, hydrogen, and moisture. Additionally, in the case of post-decarburization nitriding, a nitriding treatment may be performed by introducing nitrogen ions into the steel sheet using ammonia gas after decarburization.

[0150] When performing simultaneous decarburization, cold-rolled steel sheets charged into the furnace are heated to a temperature of 700 to 900°C, the dew point temperature of the atmosphere gas is set to 40 to 70°C, and the Fe2SiO4 / SiO2 ratio on the surface is controlled to 0.5 to 3.0 to form an oxide layer on the surface of the electrical steel sheets.

[0151] [Secondary Recrystallization Annealing]

[0152] Next, an MgO-based annealing separator is applied to the surface of these electrical steel sheets, and then the temperature is raised to over 1,000°C and crack annealed for a long time to induce secondary recrystallization, thereby making the {110} plane of the steel sheet parallel to the rolling plane, and <001> A texture with a Goss orientation parallel to the rolling direction is formed. Through this final high-temperature annealing process, a glass film layer containing forsterite is formed on the surface of the steel sheet, and secondary recrystallization is formed inside the steel sheet.

[0153] [Formation of insulating film]

[0154] A steel sheet that has undergone secondary recrystallization is coated with an insulating coating solution of colloidal silica and metal phosphate, either alone or in combination, and then annealed to form an insulating film layer on the surface of the electrical steel sheet on which the glass film layer is formed.

[0155] The method for forming such an insulating film layer can be used without particular limitation, and for example, the insulating film layer can be formed by applying an insulating coating solution containing a phosphate. It is preferable to use a coating solution containing colloidal silica and a metal phosphate as such an insulating coating solution. 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 solution may be 15 weight% or more.

[0156] [Ground Micronization Process]

[0157] As the method for grain refinement has been explained previously, a detailed explanation is omitted.

[0158] The present invention will be explained in more detail below through specific embodiments. However, these embodiments are merely for illustrating the invention and the invention is not limited thereto.

[0159]

[0160] Experimental Example 1

[0161] A cold-rolled steel sheet with a thickness of 0.27 mm was manufactured by using a slab having the composition of Table 1 below and performing hot rolling and cold rolling. In Table 1, % represents weight %.

[0162] C(%)Si(%)Mn(%)Cr(%)Sn(%)Sb(%)Al(%)Remainder 0.05 3.5 180.10 30.11 30.06 990.01 90.00 3Fe

[0163] These cold-rolled steel sheets were held at a temperature of 840°C for 150 seconds in a humid atmosphere of hydrogen, nitrogen, and ammonia (the dew point temperature was controlled to 69°C, and the Fe2SiO4 / SiO2 ratio was controlled to 1.2), and decarburization annealing including primary recrystallization annealing and nitriding treatment were performed.

[0164] A final high-temperature annealing agent containing MgO was applied to the surface of the steel sheet that had undergone primary recrystallization treatment. At this time, the final high-temperature annealing was performed up to 1,215°C in a mixed atmosphere of 25 vol% nitrogen and 75 vol% hydrogen, and after reaching 1,215°C, it was maintained in a 100 vol% hydrogen atmosphere for about 8 hours and then furnace-cooled.

[0165] An insulating coating layer for oriented electrical steel sheets with a thickness of 2.0 μm was formed by applying a coating solution mixed with colloidal silica nanoparticles and metal phosphate to the surface of a steel sheet that had completed secondary recrystallization annealing through the above final high-temperature annealing process and heat-treating it for 55 seconds at a temperature of 870 °C.

[0166] Next, the lasers summarized in Table 2 below were irradiated. At this time, both the first and second lasers had elliptical beam shapes with a beam width / length ratio (beam width / beam length) of 0.55. The wavelength of the fiber laser was 1.08 μm, and the wavelength of the CO2 laser was 10.6 μm. The beam width of the first laser was set to 100 μm, and the beam width of the second laser was set to 200 μm. The steel plate moving speed in the laser irradiation section was set to 2.3 m / s, the length of the deformation section to 160 mm, the scan speed to 60 m / s, and the irradiation interval to 5.0 mm for laser irradiation. The first and second lasers were irradiated simultaneously (i.e., without a time interval).

[0167] For steel plates before and after domain refinement, iron loss, relative permeability (μr), and magnetostriction reduction rate were measured at 1.5T 50Hz and summarized in Table 2 below.

[0168] Relative permeability (μr) is the relative permeability value under an alternating magnetic field, and according to IEC60404-3, it was calculated as the vacuum permeability value as the ratio of the rate of change of magnetic flux density at the maximum applied magnetic field value.

[0169] Magnetostriction was measured according to IEC 60404-17 as the rate of change of Peak-to-Peak value when an alternating magnetic field is applied, based on the value under the 1.7T / 50Hz condition using the following formula.

[0170]

[0171] λ 0 p-p The value is the Peak-to-Peak magnetostrain value of the product before laser irradiation, and λ' p-p The value represents the Peak-to-Peak magnetostrain value after laser irradiation. Therefore, the above equation represents the rate of change of magnetostrain after laser irradiation, and as the rate of change increases, the volume of the 90° magnetic domain increases, and it means that the movement of the magnetic domain occurs more easily when a magnetic field is applied.

[0172] In addition, the Mg content in the insulating film was analyzed by EDS (Energy Dispersive Spectroscopy) at the overlapping irradiation area and at a location other than the overlapping irradiation area, and it was confirmed that the Mg content in the overlapping irradiation area was about 25 wt% higher.

[0173] Classification 1st Laser (Fiber) 2nd Laser (CO2) Incomplete Overlap Irradiation Length of Deformed Section / Total Length of Deformed Section (%) Before Irradiation After Irradiation Before Irradiation After Irradiation Magnetic Strain (%) Energy Density (J / mm²) 2 Energy density (J / mm²) 2)W15 / 50(W / kg)W15 / 50(W / kg)μr, 1.7T / 50Hzμr, 1.7T / 50Hz Example 10.210.0651.50.6220.570240521545632 Example 20.210.1003.00.6190.571242601664530 Example 30.210.1305.00.6100.571244911742127 Example 40.210.1007.00.6100.572241571768725 Example 50.210.10010.00.6200.583246581843821 Comparative Example 10.210.0021.00.6200.59024575264573 Comparative Example 20.210.15013.00.6200.6402457815245-5 Comparative Example 30.21-None0.6100.59224125218742 Comparative Example 4-0.15(Single)None0.6200.58724577121312 Comparative Example 5-0.09(Single)None0.6200.59424645228351

[0174] As shown in Table 2, when the length of the incomplete overlapping irradiation deformation section within the total length of the overlapping irradiation deformation section is appropriately adjusted, it can be confirmed that iron loss, relative permeability, and magnetostriction are all improved after laser domain refinement.

[0175] On the other hand, it can be confirmed that Comparative Example 1, in which the incomplete overlapping investigation deformation part is formed too short, has a particularly inferior relative permeability.

[0176] As shown in Comparative Example 2, when the incomplete overlapping investigation deformation section is formed too long, it can be confirmed that the improvement in iron loss and relative permeability is insufficient.

[0177] As shown in Comparative Examples 3 to 5, when irradiated alone without overlapping laser irradiation, it can be confirmed that there is not a large amount of Mg in the insulating film layer and that the improvement in iron loss and relative permeability is insufficient.

[0178]

[0179] The present invention is not limited to the embodiments described above but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without altering the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0180] [Explanation of the symbol]

[0181] 100: Grain-oriented electrical steel sheet, 10: Overlapping inspection deformation section,

[0182] 11: 1st laser irradiation unit, 12: 2nd laser irradiation unit,

[0183] 13: Complete duplicate investigation variant, 14: Incomplete duplicate investigation variant,

[0184] 20: Superimposed laser, 21: First laser,

[0185] 22: Second laser, 40: Metal oxide film layer

[0186] 50: Insulating film layer 60: Electrical steel sheet base material

Claims

Overlapping irradiation deformation zones exist on the surface of the insulating film layer, and The above-mentioned overlapping investigation deformation section is composed of a complete overlapping investigation deformation section having a width of 90% or more of the maximum width of the overlapping investigation deformation section and an incomplete overlapping investigation deformation section having a width of less than 90% of the maximum width of the overlapping investigation deformation section, and The ratio of the incomplete overlapping investigation deformation part within the total length of the overlapping investigation deformation part is 1.5 to 10%, and The above-mentioned overlapping investigation deformation part is a oriented electrical steel sheet in which the Mg content in the insulating film layer is 5% or more higher than the Mg content in the insulating film layer that is not the overlapping investigation deformation part. In paragraph 1, The above-mentioned incomplete overlapping investigation deformation part is a directional electrical steel sheet existing at one end or both ends of the overlapping investigation deformation part. In paragraph 1, The above-mentioned overlapping investigation deformation section is a directional electrical steel sheet whose width decreases towards the end of the overlapping investigation deformation section. The method includes the step of irradiating a first laser beam having a first wavelength and overlappingly irradiating a second laser beam having a second wavelength to form a linear overlapping irradiation deformation portion. The step of forming the above-mentioned overlapping irradiation deformation part includes a step of forming a fully overlapping irradiation deformation part by irradiating such that the first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by 90% or more, and a step of forming an incompletely overlapping irradiation deformation part by irradiating such that the first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by less than 90%. A method for refining magnetic domains of a oriented electrical steel sheet in which the ratio of the length of the incompletely overlapping irradiated deformation part to the total length of the overlapping irradiated deformation part is 1.5 to 10%. In paragraph 4, The above first laser and second laser are selected from among a CO2 laser, a fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, or a UV laser, in a method for refining magnetic domains of an oriented electrical steel sheet. In paragraph 4, A method for refining magnetic domains of an oriented electrical steel sheet, wherein the ratio of the energy density of the first laser and the energy density of the second laser is 30 to 80%. In paragraph 4, The above first laser and the above second laser are a method for refining magnetic domains of oriented electrical steel sheets having different wavelengths. In paragraph 4, A method for refining magnetic domains of an oriented electrical steel sheet, wherein, at the above-mentioned overlapping position, the interval between the time of irradiation of the first laser beam and the time of irradiation of the second laser beam is 16 ms or less.

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