Grain-oriented electrical steel sheet and method for manufacturing grain-oriented electrical steel sheet

Abstract

The present invention provides a grain-oriented electrical steel sheet and a method for manufacturing the grain-oriented electrical steel sheet, in which the amount of oxidation of the primary recrystallization annealed sheet is adjusted to control the maximum Al fraction in the metal oxide layer of the final product sheet, and the magnetic domain width ratio on both sides of the steel sheet is adjusted to simultaneously improve iron loss and excitation power. The present invention relates to a method for manufacturing a magnetic steel sheet comprising the steps of: providing a grain-oriented electrical steel sheet substrate and metal oxide layers present on both sides of the grain-oriented electrical steel sheet substrate; a maximum Al fraction in the metal oxide layer is 0.15 to 1.0% by weight; and determining whether the average magnetic domain width (DW) of one side or the other side of the magnetic steel sheet substrate is smaller than the average magnetic domain width (DW) of the other side. S ) vs. the average domain width on the larger surface (DW L ) ratio (DW L / DW S ) is 1.2 to 1.8, the metal oxide layer has a thickness of 1.5 to 4 μm, and the grain-oriented electrical steel sheet base material contains, by weight%, 2.5 to 4.0% Si, 0.020 to 0.040% Al, 0.20% or less Mn, 0.0060% or less N, 0.005% or less C, and 0.0055% or less S, with the balance being Fe and unavoidable impurities.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a grain-oriented electrical steel sheet and a manufacturing method thereof in which iron loss and excitation power are simultaneously improved by adjusting the maximum Al content in a metal oxide layer present between an insulating coating and a base steel and adjusting the magnetic domain width ratio on both sides of the steel sheet. [Background technology]

[0002] Grain-oriented electrical steel sheets are used as the iron core of transformers, and in general, along with the core loss and magnetic flux density characteristics, there has been a recent demand for improvements in the excitation power related to the no-load current. Core loss is a characteristic that directly affects the efficiency of a transformer and is the main characteristic that distinguishes the grades of grain-oriented electrical steel sheets, while magnetic flux density is a characteristic that determines the copper loss and the size of the transformer.

[0003] In order to improve the above characteristics, the final grain oriented electrical steel sheet is <001> The degree of Goss texture must be increased. To create a Goss texture, complex processes such as controlling the composition during steelmaking, reheating the slab during hot rolling, controlling hot rolling process factors, annealing the hot rolled sheet, first recrystallization annealing, and second recrystallization annealing are required, and these processes must be managed very precisely and strictly. The resulting excellent grain-oriented electrical steel sheet has a degree of Goss texture within 3 degrees and usually has coarse crystal grains of several mm to several cm in size. When the grain size is coarse, the width of the magnetic domain becomes wider and the speed of the magnetic wall becomes faster, increasing abnormal eddy current loss. To reduce abnormal eddy current loss, various methods of magnetic domain refinement such as laser, plasma, and electron beam are used. These methods form magnetic pole energy by local residual stress and reduce the size of the magnetic domain, so that despite the increase in hysteresis loss, the overall iron loss is improved due to the reduction in abnormal eddy current loss.

[0004] However, the local residual stress limits the mobility of the magnetic domain walls, which immediately leads to a decrease in the magnetic permeability, and thus deteriorates the excitation power, which is closely related to the magnetic permeability. If the excitation power deteriorates, the no-load current of the transformer increases, which places a burden on the transformer power meter, and additional electrical components are required or the design must be changed. Therefore, a method for improving iron loss that takes the excitation power into consideration is necessary. To solve this problem, a method has been presented to improve magnetic flux density or permeability by optimizing the magnetic domain refinement conditions, particularly the magnetic domain line spacing, depending on the Cr content in the steel.A method has also been presented to improve permeability in an excitation magnetic field (H field) in the range of several A / m by optimizing the laser output.A method has also been proposed to optimize magnetic flux density by optimizing the size and wavelength of the laser, or a method has been presented to optimize magnetic domain conditions depending on adhesion. However, while the above-mentioned method was able to improve the permeability when the H value was 800 A / m or several A / m, it was not sufficient to improve the permeability and the resulting excitation power in the region of several tens of A / m, which affects the no-load current of a normal transformer. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a grain-oriented electrical steel sheet and a manufacturing method thereof, which adjusts the amount of oxidation of a primary recrystallization annealed sheet to control the maximum Al fraction of the metal oxide layer of the final product sheet, and adjusts the magnetic domain width ratio on both sides of the steel sheet to simultaneously improve iron loss and excitation power. [Means for solving the problem]

[0006] The grain-oriented electrical steel sheet of the present invention comprises a grain-oriented electrical steel sheet substrate and metal oxides present on both sides of the grain-oriented electrical steel sheet substrate, and the metal oxide layer has a maximum Al fraction of 0.15 to 1.0 wt %. Here, the maximum Al fraction refers to the Al content at the point where the Al content is the highest when the Al content is measured in the thickness direction of the metal oxide layer. The average magnetic domain width (DW) of the surface with the smaller average magnetic domain width on one side and the other side of the magnetic steel sheet substrate S ) vs. the average domain width (DW L ) ratio (DW L / DW S ) is 1.2 to 1.8. The metal oxide layer may have a thickness of 1.5 to 4 μm.

[0007] The grain-oriented electrical steel sheet substrate contains, by weight, 2.5 to 4.0% Si, 0.020 to 0.040% Al, 0.20% or less Mn, 0.0060% or less N, 0.005% or less C, and 0.0055% or less S, with the remainder being Fe and unavoidable impurities. The grain-oriented electrical steel sheet substrate may further contain one or more of P: 0.02 to 0.075% by weight and Cr: 0.05 to 0.35% by weight. The grain oriented electrical steel sheet may further include an insulating coating present on the metal oxide layer. Magnetic domain width ratio (DW L / DW S ) is the maximum Al fraction (wt%) in the metal oxide layer. Al,Max In that case, 0.23 x C Al,Max +1.0~0.23×C Al,Max Within the +1.8 range. The heat-affected zone may be present on only one of the one surface and the other surface of the electrical steel sheet.

[0008] The heat-affected zone may be in the form of a line extending in a direction intersecting the rolling direction. There may be a plurality of heat-affected zones, and the average distance between the heat-affected zones may be 3 to 7 mm. The method for producing a grain-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab to produce a hot-rolled sheet, cold rolling the hot-rolled sheet to produce a cold-rolled sheet, subjecting the cold-rolled sheet to primary recrystallization annealing, subjecting the steel sheet that has been subjected to primary recrystallization annealing to secondary recrystallization annealing, and subjecting one surface of the steel sheet that has been subjected to secondary recrystallization annealing to a magnetic domain refinement treatment. The dew point of the atmosphere in the primary recrystallization annealing step may be 69 to 72.5° C., and the input energy in the magnetic domain refinement step may be 6.5 to 10 J / m. The steel sheet that has been subjected to the primary recrystallization annealing may have an oxygen content of 800 to 1100 ppm.

[0009] The oxygen content and the intake energy in the first recrystallization annealed sheet can satisfy the following formula 2. [Formula 2] 35.8 x oxygen content (wt%) + 2.5 ≦ Intake energy (J / m) ≦ 35.8 x oxygen content (wt%) + 7 In the magnetic domain refining step, the steel sheet may be irradiated with a laser, and the laser beam length in the direction perpendicular to the rolling of the steel sheet may be 5 to 15 mm, and the beam width in the rolling direction of the steel sheet may be 10 to 200 μm. Effect of the Invention

[0010] According to the present invention, it is possible to minimize the heat-affected zone that hinders the movement of magnetic domains, while simultaneously maximizing the reduction in iron loss, and simultaneously improving the excitation power and magnetic permeability. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a cross section of a grain-oriented electrical steel sheet according to the present invention; [Diagram 2] 1 is a diagram showing a cross section of a grain-oriented electrical steel sheet according to the present invention; [Diagram 3] 1 is a diagram showing a schematic view of a surface of a grain-oriented electrical steel sheet according to the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 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. Thus, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention. 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 text clearly indicates otherwise. As used in the specification, the term "comprising" refers to the inclusion of particular 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.

[0013] When a part is referred to as being "on" or "on" another part, this may be immediately on or above the other part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person having ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the currently disclosed content, and are not interpreted as ideal or very formal meanings unless defined.

[0014] The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 1 and 2 show schematic diagrams of a grain-oriented electrical steel sheet 100 according to the present invention. As shown in FIG. 1, a grain-oriented electrical steel sheet 100 of the present invention comprises a grain-oriented electrical steel sheet substrate 10 and metal oxide layers 20 present on both sides of the grain-oriented electrical steel sheet substrate 10 . In the present invention, the maximum Al fraction of the metal oxide layer 20 is adjusted, and at the same time, the average magnetic domain width (DW) of the surface having the smaller average magnetic domain width among the one surface and the other surface of the electrical steel sheet substrate 10 is adjusted. S ) vs. the average domain width on the larger surface (DW L ) ratio (DW L / DW S ) to 1.2~1.8.

[0015] The maximum Al fraction of the metal oxide layer 20 contributes to improving the heat resistance and adhesion of the metal oxide layer 20. The maximum Al fraction of the metal oxide layer 20 is 0.15 to 1.0 wt %. Here, the maximum Al fraction means the Al content value at the point where the Al content is highest when the Al content is measured in the thickness direction of the metal oxide layer. More specifically, it means the largest Al content value among the Al content values ​​measured when the metal oxide layer 20 is analyzed in the thickness direction by GDS (Glow Discharge Spectroscopy). If the maximum Al fraction of the metal oxide layer 20 is below the lower limit, the movement of elements such as C, N, and O is hindered, suppressing the formation of the metal oxide layer, and the metal oxide layer is not formed firmly, resulting in surface defects. If the maximum Al fraction of the metal oxide layer 20 is above the upper limit, the bond between the oxides is weakened, which may result in surface defects. More specifically, the durability of the metal oxide layer 20 may become weak, which may not only cause surface defects but also weaken the tensile effect of the insulating coating and the base steel during laser irradiation.

[0016] In addition, the average magnetic domain width (DW S ) vs. the average domain width on the larger surface (DW L ) ratio (DW L / DW S) is adjusted to 1.2 to 1.8. In the present invention, the heat-affected zone 40 can be formed on only one of the first and second surfaces to refine the magnetic domains, and therefore the average magnetic domain widths on the first and second surfaces may differ. Meanwhile, laser, plasma, or electron beam can be used to refine the magnetic domains. In this case, the heat-affected zone 40 can be formed by irradiating the laser, plasma, or electron beam on only one of the first and second surfaces. If the pull-in energy for forming the heat-affected zone 40 is increased, the magnetic domains are clearly refined on the opposite surface, and the iron loss is reduced. However, if the pull-in energy is too high, the heat-affected zone 40 increases due to the refinement of the magnetic domains, and the iron loss increases. From the viewpoint of excitation power or magnetic permeability, the heat-affected zone 40 must be minimized since it hinders the movement of the magnetic domains.

[0017] In the present invention, in order to minimize iron loss while simultaneously improving the excitation power or magnetic permeability, the input energy for forming the heat-affected zone 40 and the magnetic domain width ratio (DW L / DW S ) is derived. L / DW S When the ratio of the magnetic domain width (DW) is between 1.2 and 1.8, the deterioration rate of the iron loss is low and the excitation power can be stably low. L / DW S ) may be 1.25 to 1.75. The method for measuring the magnetic domain width of the present invention is not particularly limited, and the magnetic domain width can be measured by taking images of the magnetic domain patterns of the irradiated and non-irradiated surfaces using the Bitter method, and determining the average magnetic domain width over the entire measurement surface. For accuracy of the measurement, the area of ​​the test piece may be 50 mm x 50 mm or more.

[0018] The maximum Al fraction and the magnetic domain width ratio (DW L / DW S ) can satisfy the following formula 1. [Formula 1] 0.23×C Al,Max +1.0≦DW L / DW S ≦0.23×CAl,Max +1.8 In formula 1, C Al,Max means the maximum Al fraction (wt%) in the metal oxide layer. The metal oxide layer 20 is also called a base coating layer or a glass coating layer, and is formed when the oxide film formed during the first recrystallization annealing process reacts with the components in the annealing separator during the second recrystallization annealing process. The metal oxide layer 20 may contain one or more metals selected from Mg and Mn in addition to the above-mentioned Al. More specifically, when MgO is used as the main component of the annealing separator, the metal oxide layer 20 may contain Mg, which may be combined with Si and O to exist in the form of forsterite (Mg2SiO4). The Al in the metal oxide layer exists in a spinel state, and if the amount of Al increases due to the structural difference with forsterite, it is difficult to maintain the adhesion between the insulating coating and the base steel, so it is advantageous to reduce the laser irradiation intensity and decrease the magnetic domain width ratio.

[0019] The thickness of the metal oxide layer 20 may be 1.5 to 4 μm. If the thickness of the metal oxide layer 20 is too thin, a large amount of heat-affected zone 40 is generated, and the magnetic domain width ratio (DW L / DW S ) may decrease, ultimately adversely affecting the excitation power and magnetic permeability. Conversely, if the thickness of the metal oxide layer 20 is excessively thick, the heat-affected zone 40 may not be properly formed in the steel sheet substrate 10, which may adversely affect the core loss. More specifically, the thickness of the metal oxide layer 20 may be 1.7 to 3.7 μm.

[0020] The grain-oriented electrical steel sheet substrate 10 contains, by weight, 2.5 to 4.0% Si, 0.020 to 0.040% Al, 0.20% or less Mn, 0.0060% or less N, 0.005% or less C, and 0.0055% or less S, with the balance being Fe and unavoidable impurities. Regardless of the alloy composition of the grain-oriented electrical steel sheet substrate 10 of the present invention, the thickness of the metal oxide layer 20 and the average magnetic domain width ratio (DW L / DW S ) is the reason why the effect is produced, and the grain-oriented electrical steel sheet substrate 10 can be any grain-oriented electrical steel sheet substrate 10 that is commonly used, without any restrictions.

[0021] The alloy components of the grain-oriented electrical steel sheet substrate 10 will be described below. Si:2.5~4.0wt% Silicon (Si) is a basic component of electrical steel sheets and plays a role in increasing the resistivity of the material and reducing core loss. If the Si content is too low, the resistivity decreases, eddy current loss increases, and core loss characteristics deteriorate. During secondary recrystallization annealing, phase transformation between ferrite and austenite occurs, making the secondary recrystallization unstable and severely damaging the texture. On the other hand, if the Si content is too high, cold rolling may become difficult. Therefore, the Si content may be 2.5 to 4.0 wt %. More specifically, the Si content may be 2.3 to 3.7 wt %.

[0022] Al:0.020~0.040wt% Aluminum (Al) acts as a powerful grain growth inhibitor by forming nitrides in the form of (Al, Si, Mn)N and AlN when nitrogen ions introduced by ammonia gas in the first recrystallization annealing process after cold rolling combine with Al, Si, and Mn present in solid solution in the steel, in addition to finely precipitated AlN during hot rolling and hot-rolled sheet annealing. If Al is too little, the inhibitory effect is weak, and if Al is too much, coarse nitrides are formed, thereby reducing the inhibitory effect on grain growth. Therefore, the content of Al is limited to 0.02 to 0.04 wt%. More specifically, it can be contained in 0.025 to 0.035 wt%.

[0023] Mn: 0.20% by weight or less Manganese (Mn), like Si, has the effect of increasing resistivity and reducing eddy current loss, thereby reducing overall iron loss. It is an important element for suppressing the growth of primary recrystallization grains and causing secondary recrystallization by reacting with nitrogen introduced by nitriding together with Si to form (Al,Si,Mn)N and (Mn,Cu)S precipitates. However, if Mn is included too much, a large amount of Mn oxide is formed, which induces a phase transformation between ferrite and austenite during the secondary recrystallization annealing process, which severely damages the texture and greatly deteriorates the magnetic properties. Therefore, Mn can be included in an amount of 0.20 wt% or less. More specifically, Mn can be included in an amount of 0.15 wt% or less.

[0024] N: 0.0060% by weight or less Nitrogen (N) is an important element that reacts with Al and Si to form (Al, Si, Mn)N, and can be contained in slabs at 0.0060 wt% or less. If nitrogen is contained in excessive amounts, it can cause surface defects called blisters due to nitrogen diffusion during processes after hot rolling, and excessive nitrides can be formed in the slab state, making rolling difficult and complicating the next process, which can lead to increased manufacturing costs. On the other hand, the additional N required to form (Al, Si, Mn)N nitrides can be reinforced by carrying out a nitriding treatment in the steel using ammonia gas during the annealing process after cold rolling. In addition, since some N is removed during the secondary recrystallization process, the nitrogen contained in the final grain-oriented electrical steel sheet is 0.0060 wt% or less.

[0025] C: 0.005% by weight or less Carbon (C) is an element that contributes to improving the elongation rate by causing a phase transformation between ferrite and austenite to refine the crystal grains. It is an essential element for improving the rollability of electrical steel sheets, which are brittle and have poor rollability. However, if it remains in the final grain-oriented electrical steel sheet substrate 10, it is an element that deteriorates the magnetic properties by precipitating carbides formed by the magnetic aging effect in the product sheet. Therefore, it must be controlled to an appropriate content. In the slab, C can be contained at 0.04 to 0.07 wt %. If C is contained too little, the phase transformation between ferrite and austenite does not work sufficiently, leading to non-uniformity of the slab and hot-rolled microstructure. On the other hand, if carbon is too much, not only is sufficient decarburization not achieved during the primary recrystallization annealing, but the secondary recrystallization texture is severely damaged by the phase transformation caused by this, and further, when the final product is applied to power equipment, the magnetic properties are deteriorated due to magnetic aging. Therefore, the slab may contain 0.04 to 0.07 wt % of C. Meanwhile, since carbon is removed through the above-mentioned decarburization, the final grain-oriented electrical steel sheet substrate 10 may contain 0.005 wt % or less of C.

[0026] S: 0.0055% by weight or less If sulfur (S) is contained in an excessive amount, MnS precipitates are formed in the slab, which inhibits grain growth and segregates in the center of the slab during casting, making it difficult to control the microstructure in subsequent processes. In addition, since MnS is not used as a grain growth inhibitor in the present invention, it is not preferable to add more than the amount that is inevitably included and cause precipitation. Therefore, the S content can be 0.0055 wt% or less. More specifically, it can be contained at 0.0050 wt% or less. The grain-oriented electrical steel sheet substrate may further contain one or more of P: 0.02 to 0.075% by weight and Cr: 0.05 to 0.35% by weight.

[0027] P:0.02~0.075wt% Phosphorus (P) segregates at the grain boundaries, hindering the movement of the grain boundaries and simultaneously playing an auxiliary role in suppressing grain growth. <001> It has the effect of improving the texture. If the content of P is too low, there is no effect of adding it, and if it is added too much, brittleness increases and rollability may be significantly deteriorated. Therefore, when P is further contained, it may be contained in an amount of 0.02 to 0.075 wt %. More specifically, it may be contained in an amount of 0.025 to 0.05 wt %.

[0028] Cr:0.05~0.35wt% Chromium (Cr) increases resistivity, thereby reducing eddy current loss, and at the same time, promotes oxidation during the decarburization-nitriding process, improving subsequent coating adhesion. If the amount of Cr is too small, the effect of addition is low, but if too much is added, the magnetic flux density deteriorates and there is an effect of inhibiting nitriding and purification annealing. Therefore, if Cr is further included, it may be included in an amount of 0.05 to 0.035 wt. %. More specifically, it may be included in an amount of 0.10 to 0.25 wt. %.

[0029] In addition to the above-mentioned components, the present invention includes Fe and inevitable impurities. The addition of other effective components is not excluded. When additional components are included, they are included to replace the remaining Fe. As shown in FIG. 2, the grain-oriented electrical steel sheet 100 of the present invention may further include an insulating coating 30 present on the metal oxide layer 20 . The insulating coating 30 is widely known, and therefore a detailed description thereof will be omitted. Specifically, an insulating coating 30 containing silica as a main component may exist. More specifically, an insulating coating 30 containing silica and metal phosphate may exist. The heat-affected zone 40 may be present on only one of the surfaces of the electrical steel sheet 100. The heat-affected zone 40 may be formed by irradiating a laser, plasma, or an electron beam. More specifically, the heat-affected zone 40 may be formed by irradiating a laser.

[0030] 1 and 2, the heat-affected zone 40 may exist across the electrical steel sheet substrate 10, the metal oxide layer 20, and, if an insulating coating 30 is present, the insulating coating 30. In the case of an electrical steel sheet substrate 10, the heat-affected zone 40 can be distinguished from other electrical steel sheet substrates 10 that are not the heat-affected zone 40 by using a Kerr microscope to confirm an area in which the magnetic domain morphology has an irregular arrangement. The heat-affected zone 40 in the metal oxide layer 20 can be identified by observing the damaged portion of the metal oxide layer through a scanning electron microscope. 3 is a schematic diagram showing the shape of the heat-affected zone 40. As shown in FIG. 3, the heat-affected zone 40 may be in the form of a line extending in a direction intersecting the rolling direction. More specifically, the heat-affected zone 40 may form an angle of 85 to 90 degrees with the rolling direction.

[0031] 4, there may be a plurality of heat-affected zones 40, and the average distance between the heat-affected zones in the rolling direction may be 3 to 7 mm. By adjusting the distance between the heat-affected zones 40, the core loss can be further improved. The width of the heat-affected zone 40 in the rolling direction may be 50 to 500 μm, and the depth within the electromagnetic steel sheet substrate 10 may be 10 to 200 μm. The grain-oriented electrical steel sheet of the present invention may have an iron loss (W17 / 50) of 0.85 W / kg or less and an excitation power of 2.0 VA / kg or less. More specifically, the iron loss (W17 / 50) may be 0.83 W / kg or less and an excitation power of 1.8 VA / kg or less.

[0032] The method for producing a grain-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab to produce a hot-rolled sheet, cold rolling the hot-rolled sheet to produce a cold-rolled sheet, subjecting the cold-rolled sheet to primary recrystallization annealing, subjecting the steel sheet that has been subjected to primary recrystallization annealing to secondary recrystallization annealing, and subjecting one surface of the steel sheet that has been subjected to secondary recrystallization annealing to a magnetic domain refinement treatment.

[0033] Each step will be described in detail below. First, the slab is hot-rolled to produce a hot-rolled sheet. The alloy components of the slab have been described above for the grain-oriented electrical steel sheet substrate 10, so a repeated description will be omitted. The alloy components of the slab are substantially the same as those of the grain-oriented electrical steel sheet substrate 10, except for the C content. The slab may be heated before hot rolling. The slab may be heated at a temperature range where dissolved N and S are incompletely dissolved. If N and S are completely dissolved, a large amount of fine nitrides and sulfides may be formed after the hot-rolled sheet annealing heat treatment, making the subsequent cold rolling difficult, and the size of the primary recrystallized grains may become very fine, making it impossible to achieve proper secondary recrystallization. That is, the redissolved N determines the size and amount of additional AlN formed in the decarburization nitriding annealing process, and if the amount is too large, the grain growth inhibition force increases and it becomes impossible to obtain a suitable secondary recrystallized microstructure consisting of a Goss texture, when the size of AlN is the same. Conversely, if the amount is too small, the grain growth driving force of the primary recrystallized microstructure increases, and as with the above phenomenon, it becomes impossible to obtain a suitable secondary recrystallized microstructure. The content of N redissolved in the raw steel through slab heating may be 20 to 50 ppm. The content of redissolved N must take into account the content of Al contained in the steel, because the nitrides used as grain growth inhibitors are (Al, Si, Mn)N and AlN.

[0034] If the slab is heated above 1280℃, Fayalite, a compound of low melting point silicon and base metal iron, is formed in the steel plate, melting off the surface of the steel plate and making hot rolling work very difficult, leading to increased furnace repairs due to melted iron. For the reasons mentioned above, i.e., to perform furnace repairs, cold rolling, and incomplete solution treatment that allows proper control of the primary recrystallization texture, the slab can be heated at a temperature below 1250℃.

[0035] In the hot-rolled sheet, a deformation structure elongated in the rolling direction due to stress is present, and AlN, (Mn.Cu)S, etc. are precipitated during hot rolling. Therefore, in order to have a uniform recrystallized microstructure and fine precipitate distribution before cold rolling, it is necessary to recrystallize the deformed structure by heating the hot-rolled sheet again to a temperature below the slab heating temperature and secure sufficient austenite phase to promote solid solution of the grain growth inhibitor of the precipitate. Therefore, after hot rolling, a hot-rolled sheet annealing step of annealing the hot-rolled sheet may be further included. The hot-rolled sheet annealing temperature may be heated to 900 to 1200 ° C to maximize the austenite fraction, and then cooled after performing a soaking heat treatment. After hot-rolled sheet annealing, the average precipitate size in the hot-rolled sheet may be in the range of 200 to 3000 Å.

[0036] Next, the hot rolled sheet is cold rolled to produce a cold rolled sheet. The cold rolling step can be performed by cold rolling to a thickness of 0.10 mm to 0.50 mm using a reverse rolling mill or a tandem rolling mill, and rolling from the initial hot rolling thickness to the final product thickness immediately without annealing heat treatment for the deformed structure in between. <001> The orientations with low concentration of orientations rotate to deformation orientations, {110} <001> Only the Goss crystal grains with the best orientation will be present in the cold-rolled sheet. Therefore, if rolling is performed more than twice, orientations with low concentration will also be present in the cold-rolled sheet, and they will undergo secondary recrystallization during secondary recrystallization annealing, which may result in poor magnetic flux density and core loss. Therefore, cold rolling can be performed in one strong cold rolling. More specifically, the cold rolling reduction rate can be 87% or more.

[0037] Next, the cold-rolled sheet undergoes primary recrystallization annealing. Decarburization and nitriding can be performed during the primary recrystallization annealing process. First, let us explain nitriding. Nitridation can be performed by introducing nitriding gas as an atmospheric gas during the primary recrystallization annealing process. The nitriding gas can include ammonia gas. Nitridation helps to introduce nitrogen ions into the steel sheet and precipitate inhibitors such as (Al, Si, Mn)N and AlN.

[0038] The decarburization and nitridation can be performed as follows: decarburization followed by nitridation, nitridation followed by decarburization, or nitridation and decarburization can be performed simultaneously. Decarburization can be performed by adjusting the atmospheric dew point to 69.0 to 72.5°C. The higher the dew point temperature, the more efficient the decarburization, but in the present invention, the dew point can be adjusted within the above range in relation to the magnetic domain refinement process described below. If the dew point temperature is too low, the metal oxide layer 20 may not be formed properly. From the viewpoint of forming the metal oxide layer 20, the higher the dew point temperature, the more advantageous it is. In this case, however, the metal oxide layer may fall off due to reduced adhesion, resulting in surface defects and magnetic inferiority, so the upper limit of the dew point temperature must be appropriately adjusted. More specifically, the dew point temperature may be 69.5 to 71.5°C.

[0039] . The primary recrystallization annealing temperature may be 800 to 950°C. If the annealing temperature of the steel sheet is too low, it takes a long time for decarburization and nitridation, and the metal oxide layer 20 is difficult to form properly. If the annealing temperature is too high, the primary recrystallized grains grow coarsely, the driving force for crystal growth decreases, and stable secondary recrystallization may not be formed. The annealing time is not a major issue in achieving the effects of the present invention, but the annealing time may be 5 minutes or less in consideration of productivity. After the first recrystallization annealing, the oxygen content of the steel sheet may be 800 to 1100 ppm. The oxygen content may be adjusted by the dew point temperature, annealing temperature, and time during the first recrystallization annealing. At this time, the oxygen content is measured by cutting the entire steel sheet into a size of 3 mm x 3 mm, melting the entire steel sheet, and therefore the oxygen content means the average content for the entire steel sheet. The oxygen content may be adjusted by the dew point temperature, annealing temperature, and time during the first recrystallization annealing. More specifically, the oxygen content may be 820 to 1070 ppm.

[0040] The method may further include a step of applying an annealing separator to the steel sheet that has been subjected to the primary recrystallization annealing. The annealing separator may be any commonly known annealing separator without any restrictions. In the secondary recrystallization annealing process, the steel sheets are annealed for a long time in a coil shape, and the annealing separator is applied to prevent the steel sheets from bonding together during this process. The components of the annealing separator combine with oxygen and Si in the oxide layer to form the metal oxide layer 20. Specifically, the annealing separator may include one or more of magnesium oxide, aluminum oxide, and manganese oxide. More specifically, the annealing separator may include MgO.

[0041] Next, the steel sheet that has been subjected to the first recrystallization annealing is subjected to the second recrystallization annealing. During the second recrystallization annealing process, the {110} plane of the steel sheet is parallel to the rolling surface, <001> {110} with orientation parallel to the rolling direction <001> This produces grain-oriented electrical steel sheets with excellent magnetic properties by forming a texture. The purpose of the secondary recrystallization annealing is, broadly speaking, to remove the {110} <001> The metal oxide layer 20 is formed by the reaction of the oxide layer formed during the texture formation and primary recrystallization annealing process with the annealing separator, imparting insulation and removing impurities that impair magnetic properties. The secondary recrystallization annealing is performed in a nitrogen and hydrogen mixed gas atmosphere during the temperature rise section before the secondary recrystallization occurs, protecting the nitride, which acts as a grain growth inhibitor, to allow the secondary recrystallization to develop well, and after the secondary recrystallization is completed, it is maintained in a 100% hydrogen atmosphere for a long time to remove impurities.

[0042] After the secondary recrystallization annealing, an insulating coating composition can be applied to form an insulating coating. In this process, flattening annealing can be performed to correct the sheet shape. The insulating coating composition is not particularly limited, and an insulating coating composition containing silica can be used. Alternatively, an insulating coating composition containing silica and a metal phosphate can be used.

[0043] Next, one surface of the steel sheet that has been subjected to secondary recrystallization annealing is subjected to magnetic domain refinement. The method of magnetic domain refinement is not particularly limited, but in the present invention, magnetic domain refinement can be performed by forming a heat-affected zone 40 without forming a groove. The method of forming the heat-affected zone 40 is not particularly limited, and it can be formed by irradiating a laser, plasma, or electron beam. More specifically, it can be irradiated with a laser.

[0044] In the present invention, the core loss and the excitation power can be improved at the same time by appropriately adjusting the pull-in energy during the magnetic domain refinement process. The pull-in energy may be 6.5 to 10 J / m. In this case, the pull-in energy means the value obtained by dividing the laser energy applied to the steel sheet by the laser irradiation line length (the width of the steel sheet when the entire width of the steel sheet is irradiated). That is, it means the value obtained by dividing the total energy for forming one heat-affected zone 40 by the length of the heat-affected zone 40. If the pull-in energy is too small, it is difficult to obtain a sufficient magnetic domain refinement effect. If the pull-in energy is too large, a large amount of the heat-affected zone 20 is formed, which may result in poor excitation power and magnetic permeability. More specifically, the pull-in energy is 7 to 9 J / m.

[0045] The pull-in energy can be adjusted in conjunction with the amount of oxygen in the oxide layer formed after the first recrystallization annealing. That is, when the amount of oxygen in the oxide layer is small, sufficient magnetic domain refinement can be achieved even if the pull-in energy is reduced. Conversely, when the amount of oxygen in the oxide layer is large, sufficient magnetic domain refinement can be achieved only by increasing the pull-in energy, and conversely, even if the pull-in energy is increased, the excitation power and magnetic permeability are relatively little affected. More specifically, the relationship between the oxygen content in the oxide layer and the pull-in energy can satisfy the following formula 2. [Formula 2] 35.8 x oxygen content (wt%) + 2.5 ≦ Intake energy (J / m) ≦ 35.8 x oxygen content (wt%) + 7 The magnetic domain refinement treatment may be performed on only one side of the steel sheet, and the other side does not need to be subjected to the magnetic domain refinement treatment. The details regarding the shape of the heat-affected zone 20 during the magnetic domain refinement process have been described above in relation to the heat-affected zone 20, so a duplicated description will be omitted. That is, when irradiating with a laser, plasma, or electron beam, the irradiation may be performed in a linear shape extending in intersecting directions, and the average interval may be 3 to 7 mm. For example, in the case of irradiating a steel sheet with a laser, the laser beam length in the direction perpendicular to the rolling direction of the steel sheet may be 5 to 15 mm, and the beam width in the rolling direction of the steel sheet may be 10 to 200 μm.

[0046] The present invention will be described in more detail with reference to the following examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. EXAMPLES

[0047] Experimental Example 1 The alloy contains, by weight, 3.5% Si, 0.06% C, 0.12% Mn, 0.0045% S, 0.0050% N, 0.03% Al, 0.03% P, 0.11% Cr, with the balance being Fe and other unavoidable impurities. The alloy is vacuum melted to produce an ingot, which is then heated to 1150°C and hot rolled to a thickness of 2.6mm. The hot rolled sheet is heated to 1100°C, maintained at 950°C for 180 seconds, and quenched in water. The hot rolled annealed sheet is pickled and then intensively cold rolled once to a thickness of 0.27mm. The cold rolled sheet is simultaneously decarbonitrided and annealed at 870°C for 180 seconds in a wet hydrogen, nitrogen and ammonia mixed gas atmosphere to reduce the nitrogen content to 200ppm. During this process, the average oxygen content in the steel sheet was adjusted in various ways by adjusting the dew point of the atmosphere, as summarized in Table 1.

[0048] The steel sheet was coated with MgO, an annealing separator, and then subjected to secondary recrystallization annealing. The secondary recrystallization annealing was performed in a mixed atmosphere of 25v% nitrogen and 75v% hydrogen up to 1200°C, and after reaching 1200°C, the atmosphere was maintained at 100v% hydrogen for 10 hours or more, and then the steel sheet was cooled in the furnace. After that, an insulating coating composition mainly composed of silica was applied, and the insulating coating was formed by heat treatment. The magnetic domains were refined by adjusting the pulling energy using a laser magnetic domain refinement device. Using a single sheet magnetic measurement device, the iron loss and excitation power were measured under the conditions of 1.7 Tesla 50 Hz, and the magnetic domain patterns of the irradiated and non-irradiated surfaces were photographed using the Bitter method to calculate the average magnetic domain width. The results are summarized in Table 1 below.

[0049] [Table 1]

[0050] As shown in Table 1, the inventive material with properly adjusted pull-in energy and dew point during the first recrystallization annealing process has a magnetic domain width ratio (DW L / DW S ) is appropriately adjusted, it can be confirmed that the iron loss and excitation power are excellent at the same time. On the other hand, it can be seen that comparative materials 1, 3, and 6, which have excessively small pull-in energy, have excessively large magnetic domain width ratios and are unable to obtain appropriate core loss. Conversely, it can be seen that comparative materials 2, 4, 5, 7, and 8, which have excessively large pull-in energy, have excessively small magnetic domain width ratios and inferior excitation power. In the case of comparative materials 9 and 10, the amount of oxidation is excessively high or low, so that the subsequent metal oxide layer is not properly formed, the secondary recrystallized grains do not grow smoothly, and there are excessive surface defects, so that even if the pull-in energy is appropriately adjusted, the core loss or excitation power is also inferior. The present invention is not limited to the embodiments, but can be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative and not limiting in all respects. [Explanation of symbols]

[0051] 10 Grain-oriented electrical steel sheet base material 20 Metal oxide layer 30 Insulating Coating 40 Heat-affected zone 100 grain-oriented electrical steel sheet

Claims

1. The present invention comprises a grain-oriented electrical steel sheet substrate and metal oxides present on both sides of the grain-oriented electrical steel sheet substrate, the maximum Al fraction in the metal oxide layer is 0.15 to 1.0 wt. %; The average magnetic domain width (DW) of the surface having the smaller average magnetic domain width among the one surface and the other surface of the electromagnetic steel sheet substrate Ｓ ) vs. the average domain width (DW Ｌ ) ratio (DW Ｌ / D.W. Ｓ ) is 1.2 to 1.

8.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the metal oxide layer has a thickness of 1.5 to 4 μm.

3. The grain-oriented electrical steel sheet according to claim 1, characterized in that the grain-oriented electrical steel sheet base material contains, by weight%, Si: 2.5 to 4.0%, Al: 0.020 to 0.040%, Mn: 0.20% or less, N: 0.0060% or less, C: 0.005% or less, and S: 0.0055% or less, with the balance being Fe and unavoidable impurities.

4. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the grain-oriented electrical steel sheet substrate further contains at least one of P: 0.02 to 0.075 wt % and Cr: 0.05 to 0.35 wt %.

5. The grain-oriented electrical steel sheet according to claim 1 , further comprising an insulating coating present on the metal oxide layer.

6. The maximum Al content (wt%) in the metal oxide layer and the magnetic domain width ratio (DW Ｌ / D.W. Ｓ 2. The grain-oriented electrical steel sheet according to claim 1, wherein the relationship between the grain boundaries satisfies the following formula 1: [Formula 1] 0.23×C Ａｌ，Ｍａｘ +1.0≦DW Ｌ / DW Ｓ ≦0.23×C Ａｌ，Ｍａｘ +1.8 (In formula 1, C Ａｌ，Ｍａｘ means the maximum Al fraction (wt%) in the metal oxide layer.)

7. 2. The grain-oriented electrical steel sheet according to claim 1, wherein a heat-affected zone is present on only one of the one surface and the other surface of the electrical steel sheet.

8. The grain-oriented electrical steel sheet according to claim 7 , wherein the heat-affected zone exists in a linear shape extending in a direction intersecting the rolling direction.

9. The grain-oriented electrical steel sheet according to claim 7, characterized in that there are a plurality of heat-affected zones, and the average distance between the heat-affected zones is 3 to 7 mm.

10. hot rolling the slab to produce a hot rolled sheet; cold rolling the hot rolled sheet to produce a cold rolled sheet; subjecting the cold-rolled sheet to a first recrystallization annealing; A step of subjecting the steel sheet subjected to the first recrystallization annealing to a second recrystallization annealing; and A step of subjecting one surface of the steel sheet that has been subjected to secondary recrystallization annealing to a magnetic domain refinement treatment, In the first recrystallization annealing step, the dew point of the atmosphere is 69 to 72.5°C, The method for producing a grain-oriented electrical steel sheet, wherein the magnetic domain refining step has a pull-in energy of 6.5 to 10 J / m.

11. The method for producing a grain-oriented electrical steel sheet according to claim 10, wherein the steel sheet that has been subjected to the primary recrystallization annealing has an oxygen content of 800 to 1100 ppm.

12. The method for producing a grain-oriented electrical steel sheet according to claim 11, wherein the oxygen content and the pull-in energy of the steel sheet that has been subjected to the primary recrystallization annealing satisfy the following formula 2: [Formula 2] 35.8 x oxygen amount (wt%) + 2.5 ≦ Intake energy (J / m) ≦ 35.8 x oxygen amount (wt%) + 7

13. 11. The method of claim 10, wherein in the magnetic domain refining step, a laser is irradiated onto the steel sheet, and the laser has a beam length of 5 to 15 mm in a direction perpendicular to the rolling direction of the steel sheet and a beam width of 10 to 200 μm in a rolling direction of the steel sheet.

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