Non-oriented electrical steel sheet and method for manufacturing same

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises 4.0-7.0 wt% of Si, 0.001-3.0 wt% of Al, and 0.03-3.0 wt% of Mn, with the remainder being Fe and inevitable impurities, wherein, in a cross-section in the thickness direction of the steel sheet, the area ratio of Al2O3 in the 1-10 μm area inward from a surface of the steel sheet is 0.010-0.500%.

Description

Non-oriented electrical steel sheet and method of manufacturing the same

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, wherein a large amount of Al2O3 is formed on the surface layer of the steel sheet by increasing the atmospheric pressure during diffusion annealing, thereby improving both magnetic properties and insulation properties.

[0002] Non-oriented electrical steel sheets used as core materials for electronic devices require high magnetic flux density and low iron loss as devices become more efficient and smaller. Since a higher magnetic flux density requires less core material to achieve the same performance, it enables the miniaturization of electrical devices, and since lower iron loss results in less energy loss, securing these characteristics is essential for manufacturing high-efficiency motors.

[0003] Iron loss, which causes energy loss, consists of hysteresis loss and eddy current loss; in the case of high-efficiency motors with high operating frequencies of electronic devices, the impact of eddy current loss increases. Eddy current loss is heat generation caused by eddy currents generated when a magnetic field is induced in the iron core, and generally, increasing the content of resistive elements such as Si or Al within the electrical steel sheet is an effective method to reduce this. Furthermore, when the Si content is increased above a certain level, magnetostriction, which is a cause of noise, decreases to zero, and as permeability increases to its maximum, it becomes possible to manufacture electrical steel sheets with excellent high-frequency characteristics.

[0004] However, as the Si content increases, the ductility of the electrical steel sheet decreases significantly, presenting a limitation in that it is difficult to manufacture thin-film electrical steel sheets using conventional rolling processes.

[0005] To overcome the limitations of this rolling process, a technology has been proposed to manufacture electrical steel sheets with a higher Si content by diffusing SiCl4 gas onto the surface of cold-rolled steel sheets. However, this method utilizes SiCl4 gas, which is highly toxic and chemically unstable, and faces equipment constraints requiring production under high vacuum conditions, making it difficult to produce electrical steel sheets with a width of 500 mm or more. Furthermore, the generation of byproduct gases such as FeCl2 under high vacuum conditions is environmentally harmful and results in inferior insulation properties, necessitating a fundamental solution.

[0006] Accordingly, a method was proposed in which a Si component diffuses to the surface of an electrical steel sheet by applying a composition containing Si powder and then performing diffusion annealing. Simultaneously, it was suggested that insulation properties be improved by forming an oxide layer on the surface during diffusion annealing; however, there is a problem in that if the oxide layer is formed excessively thickly, it actually degrades the magnetic properties.

[0007]

[0008] In one embodiment of the present invention, a non-oriented electrical steel sheet and a method for manufacturing the same are provided. Specifically, in one embodiment of the present invention, by increasing the atmospheric pressure during diffusion annealing, a large amount of Al2O3 is formed on the surface layer of the steel sheet, and a non-oriented electrical steel sheet and a method for manufacturing the same are provided, in which magnetic properties are improved and insulation properties are improved simultaneously.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percent, Si: 4.0 to 7.0%, Al: 0.001 to 3.0%, and Mn: 0.03 to 3.0%, and the remainder is Fe and unavoidable impurities.

[0010] In one embodiment of the present invention, the non-oriented electrical steel sheet has an area ratio of Al2O3 in the region of 1 μm to 10 μm in the inward direction from the surface of the steel sheet in the cross-section in the thickness direction of the steel sheet, which is 0.010 to 0.500%.

[0011] The area ratio of Al2O3 in the region of 20 to 50 μm in the inward direction from the surface of the steel plate may be 0.005% or less.

[0012] The average particle size of Al2O3 in the region of 1 μm to 10 μm in the inward direction from the surface of the steel plate may be 5 to 100 nm.

[0013] Si content at the center of plate thickness (t / 2) [CM Si ] and maximum Si content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Si The difference of ] ([SM Si ]-[ CM Si ΔSi, defined as ]), may be 0.1 wt% or more.

[0014] Al content at the center of plate thickness (t / 2) [CM Al ] and maximum Al content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Al The difference of ] ([SM Al ]-[ CM Al ΔAl, defined as ]), may be 0.1 weight% or more.

[0015] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of C: 0.005 wt% or less, N: 0.005 wt% or less, S: 0.005 wt% or less, Ti: 0.005 wt% or less, Nb: 0.005 wt% or less, and V: 0.005 wt% or less.

[0016] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.1 wt% or less, Sb: 0.1 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

[0017] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more types of Bi: 0.200 wt% or less, Pb: 0.200 wt% or less, Ge: 0.200 wt% or less, and As: 0.200 wt% or less.

[0018] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0019] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a cold-rolled sheet comprising, in weight percent, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 3.0%, and the remainder being Fe and unavoidable impurities; a coating step of applying a Si diffusion composition comprising a Si compound to the surface of the cold-rolled sheet; and a diffusion annealing step of the cold-rolled sheet.

[0020] The diffusion annealing step can be performed in an atmosphere where the pressure of the atmosphere applied to the steel plate is 0.5 to 15 Bar.

[0021] The diffusion annealing step can be performed in an atmosphere where the dew point temperature is between -25°C and 25°C.

[0022] The Si diffusion composition further comprises an Al compound, and may include 100 parts by weight of the Si compound and 10 to 50 parts by weight of the Al compound as solid content.

[0023] The Si diffusion composition may further include 10 to 1,000 parts by weight of a ceramic powder comprising an oxide, nitride, carbide, or oxynitride, comprising at least one component selected from Li, B, Ca, Sr, Mg, Al, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn, and Ba.

[0024] The average particle size of the Si compound can be 1 to 1500 nm.

[0025] The average particle size of the Al compound can be 1 to 1000 nm.

[0026] The average particle size of the ceramic powder can be 8 to 2500 nm.

[0027] In the step of applying the Si diffusion composition, the amount of the Si diffusion composition applied is 0.1 to 300 g / m² 2 It could be.

[0028] In the diffusion annealing step, the cracking temperature may be 850 to 1050°C and the cracking time may be 2.8 to 10 hours.

[0029] During the diffusion annealing stage, the atmosphere may contain 98 volume% or more of hydrogen.

[0030] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and high-frequency iron loss.

[0031] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention provides an environmentally friendly manufacturing method in which no by-product gases harmful to the environment are generated during the manufacturing process.

[0032] A non-oriented electrical steel sheet according to one embodiment of the present invention also possesses excellent magnetic properties and insulation due to the Al2O3 on the surface, and sufficient insulation can be obtained even when a thin insulating film is formed, thereby increasing the packing density.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0038] In one embodiment of the present invention, the meaning of including additional elements is that the remainder of iron (Fe) is replaced by an amount of the additional element.

[0039] 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.

[0040]

[0041] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percent, Si: 4.0 to 7.0%, Al: 0.001 to 3.0%, and Mn: 0.03 to 3.0%, and the remainder is Fe and unavoidable impurities.

[0042] First, I will explain the reason for the limitation of the composition of non-oriented electrical steel sheets.

[0043] Si: 4.0 to 7.0 wt%

[0044] Silicon (Si) plays a role in lowering iron loss by increasing the resistivity of the material, so it must be added in relatively large amounts. As the Si content increases, eddy current losses are reduced, which can lower iron loss at high frequencies. In particular, when Si is included at 6.0 wt% or more, magnetostriction, which is a cause of noise, decreases to zero and permeability increases to the maximum, making it possible to manufacture electrical steel sheets with excellent high-frequency characteristics. However, when the Si content is 4 wt% or more, the ductility of the electrical steel sheet decreases significantly, and there is a limit where it is difficult to manufacture electrical steel sheets using a conventional rolling process.

[0045] In one embodiment of the present invention, Si is diffused from the surface of the steel plate into the interior of the steel plate to add 4 weight percent or more of Si to the steel plate. If the amount of Si in the steel plate is too low, it is difficult to expect the aforementioned effects due to Si. If too much Si is included, there is a problem where the processability of the electrical steel plate becomes inferior when processed into products such as motors. In one embodiment of the present invention, due to the diffusion of Si from the surface to the interior, a Si concentration gradient may exist in the thickness direction of the steel plate, and unless otherwise stated, the Si content in the steel plate refers to the average content in the thickness direction. Average content refers to the content assuming that the Si in the steel plate is uniformly distributed in the thickness direction of the steel plate. More specifically, Si may be included in 4.5 to 6.5 weight percent.

[0046] The maximum Si content in the region from the surface of the non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness may be 4.0 to 8.0 weight%, and the Si content at the center of the sheet thickness position (t / 2) may be 0.3 to 7.5 weight%.

[0047] In one embodiment of the present invention, since a steel sheet containing a high concentration of Si is manufactured by diffusing Si from the surface of the steel sheet into the interior of the steel sheet, a concentration gradient may occur in the thickness direction of the steel sheet. That is, the maximum Si content in the region from the surface of the non-oriented electrical steel sheet to 5% of the total thickness in the interior direction (i.e., the surface portion) may be 4.0 to 8.0 weight%. If the Si content in the surface portion is low, it means that sufficient Si has not diffused, and thus the improvement in high-frequency iron loss through high-concentration Si may not be sufficiently obtained. If the Si content is too high, it means that a large amount of Si exists only in the surface portion and has not diffused into the interior of the steel sheet, and this also means that the improvement in high-frequency iron loss through high-concentration Si may not be sufficiently obtained. The maximum Si content refers to the highest Si content when measuring the Si concentration in the surface portion in the thickness direction. The maximum Si content can be measured using non-destructive analysis methods such as EPMA (Electron Probe Micro-Analyzer) or Scanning Electron Microscope / Energy-dispersive, X-ray spectroscopy (SEM / EDX). More specifically, the maximum Si content on the surface may be 4.5 to 7.5 weight%.

[0048] The center of the plate thickness refers to the position at half the total thickness of the plate. Hereinafter, it is referred to as the center. If the Si content is low at the center, it means that sufficient Si has not diffused, and the improvement in high-frequency iron loss through high-concentration Si may not be sufficiently obtained. If the Si content is too high at the center, a problem of reduced processability may occur. More specifically, the Si content at the center may be 0.3 to 7.5 weight%, specifically 2.5 to 6.0 weight%.

[0049] Si content at the center of plate thickness (t / 2) [CM Si] and maximum Si content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Si The difference of ] ([SM Si ]-[ CM Si ΔSi, defined as ]), may be 0.1 wt% or more. When there is an appropriate difference in Si content between the center and the surface, it is advantageous in terms of high-frequency iron loss and processability. More specifically, ΔSi may be 0.5 to 7.9 wt%. More specifically, ΔSi may be 1.0 to 4.0 wt%. The internal direction may be the thickness direction of the steel sheet. As an example of a measurement method, at any point on the surface of a non-oriented electrical steel sheet, the maximum Si content and the Si content at t / 2 can be measured in the region up to 5% of the total thickness among the Si content according to the steel sheet thickness.

[0050] As previously described, in one embodiment of the present invention, Si within the Si compound in the Si diffusion composition is diffused by diffusion annealing, thereby increasing the Si content, and the steel sheet prior to Si diffusion may contain less Si than previously described. Specifically, the slab and the cold-rolled sheet prior to diffusion may contain 0.01 to 3.5 weight% of Si. If the Si content in the slab and the cold-rolled sheet prior to diffusion is too low, the amount of Si required for diffusion increases, and the diffusion annealing process takes a long time, resulting in low efficiency; furthermore, the difference in Si content by sheet thickness becomes large, making it difficult to obtain appropriate high-frequency iron loss. If the Si content in the slab and the cold-rolled sheet prior to diffusion is too high, the steel sheet may fracture during the cold rolling process or defects may occur within the steel sheet. More specifically, the Si content in the slab and the cold-rolled sheet prior to diffusion may be 0.3 to 3.3 weight%. Even more specifically, the Si content in the slab and the cold-rolled sheet prior to diffusion may be 2.0 to 3.0 weight%.

[0051] Al: 0.001 to 3.0 wt%

[0052] Aluminum (Al) plays a role in lowering high-frequency iron loss by increasing the resistivity of the material. In one embodiment of the present invention, since the resistivity of the material can be sufficiently increased through the diffusion of Si, the addition of Al may be unnecessary. However, the high-frequency iron loss can be further improved by adding more Al. However, if too much Al is added, the iron loss and surface quality may deteriorate due to the formation of an aluminum silicate-based composite. More specifically, Al may be included in an amount of 0.01 to 2.0 weight%. In one embodiment of the present invention, due to the diffusion of Al from the surface to the interior, a concentration gradient of Al may exist in the thickness direction of the steel plate, and unless otherwise stated, the Al content in the steel plate refers to the average content in the thickness direction. More specifically, Al may be included in an amount of 0.01 to 2.5 weight%. More specifically, Al may be included in an amount of 0.1 to 2.0 weight%.

[0053] In one embodiment of the present invention, since Al is diffused together with Si to produce a steel plate containing a high concentration of Si, a concentration gradient of Al may occur in the thickness direction of the steel plate.

[0054] Al content at the center of plate thickness (t / 2) [CM Al ] and maximum Al content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Al The difference of ] ([SM Al ]-[ CM Al ΔAl, defined as ]), may be 0.1 weight% or more. When there is an appropriate difference in Al content between the center and the surface, high-frequency iron may be further improved. More specifically, ΔAl may be 0.1 to 2.9 weight%. More specifically, it may be 0.5 to 2.5 weight%.

[0055] The maximum Al content in the region extending from the surface to 5% of the total thickness (i.e., the surface portion) of the non-oriented electrical steel sheet can be 1.0 to 4.0 weight%. If the Al content in the surface portion is low, it means that sufficient Al has not diffused, and thus, sufficient improvement in high-frequency iron loss through Al diffusion may not be achieved. If the Al content is too high, it means that a large amount of Al exists only in the surface portion and has not diffused into the interior of the steel sheet, and this also means that sufficient improvement in high-frequency iron loss through Al diffusion may not be achieved. The maximum Al content refers to the highest Al content when measuring the Al concentration in the surface portion in the thickness direction. The maximum Al content can be measured using non-destructive analysis methods such as EPMA (Electron Probe Micro-Analyzer) or Scanning Electron Microscope / Energy-dispersive, X-ray spectroscopy (SEM / EDX). More specifically, the maximum Al content on the surface may be 1.5 to 3.5 weight%.

[0056] The Al content at the center of the plate thickness (t / 2) may be 0.001 to 2.9 weight%. If the Al content is low at the center, it means that sufficient Al has not diffused, and the improvement in high-frequency iron loss through Al diffusion may not be sufficiently obtained. If the Al content is too high at the center, the iron loss may be inferior due to the formation of an aluminum silicate-based composite, and the surface quality may be inferior. More specifically, the Al content at the center may be 0.005 to 2.0 weight%.

[0057] As previously described, in one embodiment of the present invention, Al within the Al compound in the Si diffusion composition is diffused by diffusion annealing, thereby increasing the Al content, and the steel sheet prior to Al diffusion may contain less Al than previously described. Specifically, the slab and the cold-rolled sheet prior to diffusion may contain 0.001 to 2.0 weight% of Al. If the Al content in the slab and the cold-rolled sheet prior to diffusion is too low, the amount of Al required for diffusion increases, and the diffusion annealing process takes a long time, resulting in low efficiency; furthermore, the difference in Al content by sheet thickness becomes large, making it difficult to obtain appropriate high-frequency iron loss. If the Al content in the slab is too high, problems such as poor magnetic properties and surface quality may occur. More specifically, the Al content in the slab and the cold-rolled sheet prior to diffusion may be 0.01 to 1.0 weight%.

[0058] Mn: 0.03 to 3.0 wt%

[0059] Manganese (Mn) plays a role in improving iron loss by increasing the resistivity of the material and forming sulfides. If too little Mn is added, fine MnS precipitates, which can degrade magnetism. If too much Mn is added, it promotes the formation of a

[0111] texture, which is unfavorable to magnetism, which can cause a rapid decrease in magnetic flux density. In one embodiment of the present invention, unlike Si and Al, Mn does not diffuse from the surface to the center, but rather diffuses from the center to the surface. This is because Mn volatilizes from the surface during the Si diffusion annealing process, causing Mn to diffuse from the center to the surface. As the amount of Mn decreases and the amount of Si increases, a phase transformation occurs. As the phase transformation occurs, diffusion proceeds from the surface to the interior, and at this time, an orientation similar to the direction of diffusion <100> The environment is configured to be favorable for the formation of / ND. More specifically, Mn may be 0.05 to 2.0 weight%.

[0060] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.1 wt% or less, Sb: 0.1 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

[0061] P: 0.1 wt% or less

[0062] Phosphorus (P) is a grain boundary segregation element, and if added in excessive amounts, it can delay recrystallization and degrade strength uniformity in the rolling direction and the rolling perpendicular direction. More specifically, P may be 0.005 to 0.03 weight%.

[0063] Cu: 0.005 to 0.200 wt%

[0064] Copper (Cu) plays a role in forming sulfides together with Mn. If more Cu is added, or if too little is added, fine precipitation of (Cu·Mn)S may occur, which can degrade magnetism. If too much Cu is added, high-temperature brittleness may occur, which can form cracks during continuous casting or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.100 weight%.

[0065] Cr: 0.010 to 0.50 wt%

[0066] Chromium (Cr) plays a role in improving iron loss by increasing resistivity. If too little Cr is added, the effect of increasing resistivity may not be sufficient. If too much Cr is included, magnetic flux density may decrease. More specifically, the lower limit of Cr can be 0.05 wt% or 0.30 wt%.

[0067] Sn: 0.10 wt% or less

[0068] Tin (Sn) is added to improve magnetic properties by acting as a segregating element at grain boundaries to inhibit the diffusion of nitrogen through the grain boundaries, suppressing the {111} texture harmful to magnetism, and increasing the {100} texture beneficial to magnetism. If too much Sn is added, it hinders grain growth, reduces magnetism, and results in poor rolling properties. Therefore, Sn can be added within the aforementioned range. More specifically, Sn may be included in an amount of 0.005 to 0.08 weight%.

[0069] Sb: 0.10 wt% or less

[0070] Antimony (Sb) is added to improve magnetic properties by acting as a segregating element at grain boundaries to inhibit the diffusion of nitrogen through the grain boundaries, suppressing the {111} texture harmful to magnetism, and increasing the {100} texture beneficial to magnetism. If too much Sb is added, it hinders grain growth, thereby reducing magnetism and resulting in poor rolling properties. Therefore, Sb can be added within the aforementioned range. More specifically, Sb may be included in an amount of 0.005 to 0.08 weight%.

[0071] Ni: 0.05 wt% or less

[0072] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a harmful effect on magnetism. More specifically, Ni may be included in an amount of 0.005 to 0.03 weight%.

[0073] Zn: 0.01 wt% or less

[0074] If the content of zinc (Zn) is excessive, it can act as an impurity and impair magnetism. Therefore, Zn may be added within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 weight%.

[0075]

[0076] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more types of Bi: 0.200 wt% or less, Pb: 0.200 wt% or less, Ge: 0.200 wt% or less, and As: 0.200 wt% or less.

[0077] When the aforementioned elements are added, they segregate at the grain boundaries, alleviating stress concentration at the grain boundaries during cold rolling, and thus during the subsequent recrystallization annealing process <111> By suppressing the recrystallization of the / ND orientation grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained, but if they are included in too much, a large amount of segregation occurs, which suppresses grain growth and may result in inferior magnetic flux density and iron loss. More specifically, one or more of Bi: 0.001 to 0.100 wt%, Pb: 0.001 to 0.100 wt%, Ge: 0.001 to 0.100 wt%, and As: 0.001 to 0.100 wt% may be further included.

[0078]

[0079] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0080] These can react with inevitably included C, S, N, etc. to form fine carbides, nitrides, or sulfides, which may adversely affect magnetism, so an upper limit may be set as described above. More specifically, one or more of Mo: 0.001 to 0.01 wt%, B: 0.0010 to 0.0030 wt%, Ca: 0.0010 to 0.0030 wt%, Zr: 0.0010 to 0.0030 wt%, Te: 0.0010 to 0.0050 wt%, and Mg: 0.0010 to 0.0050 wt% may be further included.

[0081]

[0082] Other impurities

[0083] In addition to the aforementioned elements, inevitably incorporated impurities such as carbon (C), sulfur (S), nitrogen (N), titanium (Ti), niobium (Nb), and vanadium (V) may be included.

[0084] N combines with Ti, Nb, and V to form nitrides and plays a role in reducing grain growth.

[0085] C reacts with N, Ti, Nb, V, etc., to form fine carbides, which hinder grain growth and domain movement.

[0086] S forms sulfides, which impair grain growth.

[0087] In cases where additional impurity elements are included as such, one or more of C: 0.005 wt% or less (excluding 0%), N: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), Nb: 0.005 wt% or less (excluding 0%), and V: 0.005 wt% or less (excluding 0%) may be additionally included. More specifically, it may further include one or more of C: 0.001 to 0.003 wt%, N: 0.001 to 0.005 wt%, S: 0.001 to 0.005 wt%, Ti: 0.001 to 0.005 wt%, Nb: 0.001 to 0.005 wt%, and V: 0.001 to 0.005 wt%.

[0088] In addition, unavoidable impurities may be included. These unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets; since this is widely known in the field, a detailed explanation 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.

[0089]

[0090] In one embodiment of the present invention, in a cross-section in the thickness direction of the steel plate, the area ratio of Al2O3 in the direction from the surface of the steel plate to the interior of 1 μm to 10 μm may be 0.010 to 0.500%. The cross-section in the thickness direction of the steel plate is a cross-section including the thickness direction of the steel plate (ND direction), and more specifically, it may be a TD plane. Al2O3 is formed when Al and O components within the steel plate aggregate to form a granular shape, and it can be detected through transmission electron microscopy (TEM) observation. If the amount of Al2O3 is too small, it may not contribute sufficiently to the improvement of insulation properties. If the amount of Al2O3 is too large, magnetic properties such as increasing iron loss and decreasing magnetic flux density may deteriorate. More specifically, the area ratio of Al2O3 in the direction from the surface of the steel plate to the interior of 1 μm to 10 μm may be 0.050 to 0.480.

[0091] The average particle size of Al2O3 in the direction from the surface of the steel plate inward at 1 μm to 10 μm may be 5 to 100 nm. The particle size of Al2O3 can be measured by calculating the diameter of a virtual circle that occupies the same area as the Al2O3 detected by the aforementioned method. The average particle size refers to the number average particle size. If the average particle size is too small, the action of Al2O3 within the steel plate may not be properly performed. If the particle size of Al2O3 is too large, the magnetic properties may be compromised. More specifically, the average particle size of Al2O3 in the direction from the surface of the steel plate inward at 1 μm to 10 μm may be 10 to 98 nm.

[0092] Al2O3 may not be present in the area of ​​20 to 50 μm from the surface of the steel plate inward. If Al2O3 is present in this area, it does not contribute to insulation and may instead result in inferior magnetic properties. Specifically, the area ratio of Al2O3 in the area of ​​20 to 50 μm from the surface of the steel plate inward may be 0.005% or less. More specifically, it may be 0.004% or less.

[0093]

[0094] A non-oriented electrical steel sheet according to one embodiment of the present invention exhibits excellent high-frequency iron loss due to the diffusion of Si. Specifically, iron loss (W 10 / 1000 ) may be 20.0 W / kg or less. In this case, iron loss is based on a thickness of 0.2 mm. Iron loss (W 10 / 1000 ) is the iron loss when a magnetic flux density of 1.0T is induced at a frequency of 1000 Hz. Iron loss can be measured using the Epstein test or the SST (single sheet test) method. More specifically, iron loss (W 10 / 1000 ) can be 15.00W / kg to 19.50W / kg.

[0095] Also, iron loss (W 5 / 2000) may be 16.5 W / kg or less. In this case, iron loss is based on a thickness of 0.2 mm. Iron loss (W 5 / 2000 ) is the iron loss when a magnetic flux density of 0.5T is induced at a frequency of 2000 Hz. More specifically, iron loss (W 5 / 2000 ) can be 10.0W / kg to 15.0W / kg.

[0096] In one embodiment of the present invention, not only iron loss but also magnetic flux density is excellent simultaneously. Specifically, magnetic flux density (B 25 ) can be 1.45T or more. Specifically, magnetic flux density (B 25 ) can be 1.45 to 1.60T.

[0097] In addition, in one embodiment of the present invention, the insulation value may be 0.5 or less. Specifically, the insulation value may be 0.10 to 0.4. The insulation value can be evaluated by measuring the insulation resistance according to the standard test method ASTM A717.

[0098]

[0099] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a cold-rolled sheet comprising, in weight percent, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 3.0%, and the remainder being Fe and unavoidable impurities; applying a Si diffusion composition comprising a Si compound to the surface of the cold-rolled sheet; and diffusion annealing the cold-rolled sheet.

[0100] Below, each step is explained in detail.

[0101] First, a cold-rolled sheet is manufactured containing, in weight percent, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 3.0%, with the remainder being Fe and unavoidable impurities. Since the alloy composition of the cold-rolled sheet is the same as that described above, a redundant description is omitted.

[0102] The method for manufacturing a cold-rolled sheet is not particularly limited and may include the step of manufacturing a hot-rolled sheet by hot-rolling a slab containing, in weight percent, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 3.0%, with the remainder being Fe and unavoidable impurities; and the step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet.

[0103] First, a slab is manufactured. The reason for limiting the addition ratio of each component within the slab is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated explanation is omitted. Since the composition of the slab does not substantially change during the manufacturing processes described later, such as hot rolling, hot-rolled sheet annealing, and cold rolling, the composition of the slab and the composition of the cold-rolled sheet are substantially the same. Furthermore, in the diffusion annealing process, only Si and / or Al diffuse, and the alloy composition of the non-oriented electrical steel sheet may be the same as the remaining components excluding Si and Al.

[0104] Prior to the step of manufacturing a hot-rolled plate, the slab may be heated to 1100°C or higher. Specifically, the slab is loaded into a heating furnace and heated to 1100 to 1250°C. When heated at a temperature exceeding 1250°C, precipitates may be redissolved and finely precipitated after hot rolling. More specifically, the slab heating temperature may be 1100°C to 1200°C.

[0105] The heated slab is hot-rolled to a thickness of 1.5 to 4.0 mm to produce a hot-rolled plate. In one embodiment of the present invention, a step of pre-cold rolling before cold rolling is also included, so that a non-oriented electrical steel plate of appropriate thickness can be produced even if the thickness of the hot-rolled plate is relatively thick. More specifically, the thickness of the hot-rolled plate may be 1.5 mm to 3.5 mm.

[0106] The step of manufacturing a hot-rolled plate may include a step of finishing rolling at a temperature of 850°C or higher.

[0107] If the finishing rolling temperature of hot rolling is too low, the rolling load increases, leading to reduced hot rolling workability. Furthermore, a significant amount of deformation remains in the hot-rolled steel sheet, which causes an increase in the rolling load during the subsequent pre-cold rolling process. In addition, from the deformation during intermediate annealing <111> / ND Recrystallization of the grains is promoted, resulting in lower magnetic flux density. Therefore, the hot rolling finish rolling temperature should be as high as possible, and more specifically, the finish rolling temperature can be 850 to 1000℃.

[0108] The step of manufacturing a hot-rolled plate may include a coiling step at a temperature of 600 to 800°C. It may also include a rough rolling step before the finish rolling step.

[0109] If the temperature during the coiling stage is managed too low, the recovery and recrystallization of the hot-rolled deformed structure do not occur effectively. Additionally, the cooling load increases to rapidly cool the steel sheet to a low temperature, which may cause difficulties in coiling the supercooled coil. Conversely, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during coiling, leading to the formation of a thicker scale and problems with intergranular oxidation. Intergranular oxidation of the hot-rolled sheet promotes intergranular corrosion during the subsequent pickling process, increasing the likelihood of surface streak defects and causing severe wear on the rolling rolls. More specifically, the coiling temperature may be 650 to 750°C.

[0110] After the step of manufacturing a hot-rolled plate, the process may further include a step of annealing the hot-rolled plate at a temperature range of 600 to 1100°C. If the annealing temperature of the hot-rolled plate is too low, a recrystallization structure is not formed or grows finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, magnetic properties may actually deteriorate, and rolling workability may be poor due to deformation of the plate shape. More specifically, the annealing temperature of the hot-rolled plate may be 750 to 1000°C.

[0111] Annealing of hot-rolled plates is performed as needed to increase the magnetic orientation, and it may be omitted. The form of annealing is not particularly limited and can be performed in batch or continuous motion.

[0112] Hot-rolled plates can be pickled as needed.

[0113] Next, the hot-rolled sheet is pickled and cold-rolled to a predetermined thickness. Depending on the thickness of the hot-rolled sheet, a reduction rate of 70 to 95% may be applied to cold-roll the sheet so that the final thickness is 0.10 to 0.65 mm. To achieve the reduction rate, one cold-rolling step or two or more cold-rolling steps with intermediate annealing in between may be performed. More specifically, the reduction rate may be 75 to 90%. The thickness of the cold-rolled sheet may be 0.15 to 0.35 mm.

[0114] Next, in the coating step, a Si diffusion composition containing a Si compound is applied to the cold-rolled plate.

[0115] As for the Si compound, any material capable of diffusing Si into the interior of the steel sheet through long-term annealing may be used without limitation. Specifically, it may include one or more of pure Si, Si alloys, Si oxides, nitrides or carbides, and silane compounds. In addition, it may include one or more of FeSi, Fe3Si, Fe3Al, and FeAl.

[0116] More specifically, it may include pure Si, Si alloys, and Fe3Si.

[0117] The average particle size of the Si compound may be 1 to 1500 nm. If the particle size of the Si compound is too small, problems may arise where they aggregate during slurry mixing, causing surface defects. If the particle size of the Si compound is too large, it may be difficult to apply it uniformly to the surface of the steel plate, which may hinder smooth Si diffusion into the interior of the steel plate. The average particle size of the Si compound is the average particle size relative to the number of compound particles and can be measured using a particle size analyzer (PSA) utilizing laser diffraction. More specifically, the average particle size of the Si compound may be 10 nm to 1300 nm. Even more specifically, it may be 20 nm to 1000 nm.

[0118] The Si diffusion composition further comprises an Al compound and may include 100 parts by weight of the Si compound and 10 to 50 parts by weight of the Al compound as solid content. In one embodiment of the present invention, solid content refers to the weight after heating each compound at 180°C for 20 minutes or more to remove all volatile matter.

[0119] The Al compound improves insulation, increases bonding with the Si compound, and plays a role in forming Al2O3 appropriately on the surface. If too little Al compound is included, it may be difficult to obtain the aforementioned effects appropriately. If too much Al compound is included, a problem may arise where the magnetic properties are degraded due to the formation of numerous inclusions such as Al2O3. More specifically, the Al compound may be included in an amount of 15 to 30 parts by weight.

[0120] As for Al compounds, any material capable of diffusing Al into the steel sheet can be used without restriction. Examples include pure Al, aluminum oxide, and aluminum alkoxide.

[0121] The average particle size of the Al compound may be 1 to 1000 nm. If the particle size of the Al compound is too small, a problem of aggregation between Al compounds may occur. If the particle size of the Al compound is too large, Al diffusion into the steel sheet may not occur smoothly. More specifically, the lower limit of the average particle size of the Al compound may be 5 nm. The upper limit of the average particle size of the Al compound may be 750 nm.

[0122] The Si diffusion composition may further include ceramic powder comprising oxides, nitrides, carbides, or oxynitrides, comprising at least one component selected from Li, B, Ca, Sr, Mg, Al, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn, and Ba. The ceramic powder serves to control the amount of slurry applied and to determine the Si content of the final steel sheet.

[0123] The ceramic powder may be included in an amount of 10 to 1,000 parts by weight as a solid content. If too little ceramic powder is included, problems may arise in terms of securing the coating amount. If too much ceramic powder is included, the slurry viscosity increases, which may cause problems in terms of surface defects. More specifically, the ceramic powder may be included in an amount of 20 to 500 parts by weight.

[0124] The ceramic powder may be one or more of TiO2, MgO·TiO2, 3Al2O3·2SiO2, ZrO2·SiO2, TiN, CrN, SrTiO3, Y2O3, and FeTiO3.

[0125] The average particle size of the ceramic powder may be 8 to 2500 nm. If the particle size of the ceramic powder is too small, there may be a problem in securing a sufficient coating amount. If the particle size of the ceramic powder is too large, the viscosity increases, the surface quality deteriorates, and Si diffusion into the steel plate may not proceed smoothly. More specifically, the average particle size of the ceramic powder may be 10 nm to 1500 nm.

[0126] The Si diffusion composition may further include a solvent in addition to the aforementioned components. The solvent enables the uniform application of the Si diffusion composition. If the amount of solvent is too small, the application of the Si diffusion composition may not be easy. If the amount of solvent is too large, the viscosity of the Si diffusion composition may be too low, making it difficult to apply a sufficient amount of the composition onto the steel plate. The solvent may be included in an amount of 10 to 1,500 parts by weight per 100 parts by weight of the Si compound. More specifically, the solvent may be included in an amount of 50 to 1,000 parts by weight. The solvent may include one or more of water and alcohol.

[0127] In addition to the aforementioned components, the Si diffusion composition may further include additional components, and this is not excluded in one embodiment of the present invention. Examples of additional components may include phosphoric acid, sodium silicate, fluoride ion solution, etc.

[0128] In the coating step, the coating amount of the Si diffusion composition is 0.1 to 300 g / m² 2 It may be. In this case, the coating amount is based on the solid content. If the coating amount is too small, sufficient Si diffusion does not occur, making it difficult to fully achieve the effect of Si diffusion. If the coating amount is too large, a problem of inferior processability may occur. In one embodiment of the present invention, the Si diffusion composition may be applied to one or both sides of a steel plate, and when applied to both sides, the coating amount for each side is 0.1 to 300 g / m² 2 It could be.

[0129] Application methods include using a roll coater, brush, and dipping. From a productivity standpoint, application can be performed using a roll coater.

[0130] The method may further include the step of applying and drying the Si diffusion composition. The drying temperature is sufficient if it is a temperature capable of removing the solvent within the Si diffusion composition, and specifically, it may be 300 to 750°C. The time may be 10 to 60 seconds. More specifically, the temperature may be 350 to 700°C. The time may be 15 to 50 seconds.

[0131] Next, the cold-rolled sheet is diffusion annealed. During this process, Si and / or Al diffuse into the interior of the steel sheet from the Si diffusion composition applied to the surface of the cold-rolled sheet.

[0132] The diffusion annealing temperature may be 850°C to 1050°C. If the diffusion annealing temperature is too low, the diffusion of Si and Al may not occur sufficiently, and the desired effect may not be obtained. If the diffusion annealing temperature is too high, pores may form, and the magnetic properties may be degraded. More specifically, the diffusion annealing temperature may be 900°C to 1000°C.

[0133] The cracking time may be 2.8 to 10 hours. If the time is too short, the diffusion of Si and Al may not occur sufficiently, and the desired effect may not be achieved. If the time is too long, it may be difficult to control the amount of diffusion of Si and Al, which may result in inferior processability. More specifically, the time may be 3 to 5 hours.

[0134] The diffusion annealing step can be performed in an atmosphere where the atmospheric pressure applied to the steel plate is 0.5 to 15 Bar. If the atmospheric pressure is too low, the amount of oxygen absorbed into the steel plate is insufficient, and oxygen cannot penetrate deep into the steel plate, making it difficult to form a suitable Al2O3 on the surface. Conversely, if the atmospheric pressure is too high, the amount of oxygen absorbed into the steel plate becomes too large, and oxygen penetrates deep into the steel plate, making it difficult to form a suitable Al2O3 on the surface. More specifically, the diffusion annealing step can be performed in an atmosphere where the atmospheric pressure applied to the steel plate is 0.7 to 13.0 Bar. Even more specifically, the diffusion annealing step can be performed in an atmosphere where the atmospheric pressure applied to the steel plate is 1.5 to 10.0 Bar. At this time, the pressure can be measured through a pressure sensor installed inside the heating furnace.

[0135] The diffusion annealing step can be performed in an atmosphere where the dew point temperature is between -25°C and 25°C. If the dew point temperature is too low, adequate oxygen is not supplied to the steel plate, and it is difficult to form adequate Al2O3 on the surface. If the dew point temperature is too high, too much oxygen is supplied to the steel plate, making it difficult to form adequate Al2O3 on the surface. More specifically, the dew point temperature may be between -23°C and 23°C. More specifically, the dew point temperature may be between -20°C and 20°C.

[0136] During the diffusion annealing stage, the atmosphere may contain 98 volume% or more of hydrogen. Including a large amount of hydrogen is advantageous in terms of preventing oxidation. The remainder may be nitrogen, oxygen, and water vapor.

[0137] After diffusion annealing, the final thickness of the steel sheet may be 0.10 to 0.65 mm, and due to the application and diffusion of the Al diffusion composition, the thickness may increase slightly compared to the cold-rolled sheet.

[0138] Next, the method may further include a step of brushing the diffusion-annealed steel sheet to remove unreacted composition remaining on the surface of the cold-rolled sheet and also to partially remove the oxide layer.

[0139] Subsequently, a step of forming an insulating film may be further included. Since insulating films are widely known, a detailed description is omitted. Specifically, an insulating coating layer can be formed by applying an insulating coating layer forming composition comprising metal phosphate and silica as main components and heat treating.

[0140]

[0141] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0142]

[0143] Examples

[0144] A slab was prepared containing 2.0 wt% silicon (Si), 0.002 wt% aluminum (Al), 0.10 wt% manganese (Mn), 0.04 wt% tin (Sn), 0.04 wt% antimony (Sb), and 0.013 wt% phosphorus (P), with the remainder being Fe and other unavoidable impurities.

[0145] A hot-rolled plate was manufactured by heating a slab to 1100℃ and then hot-rolling it to a thickness of 1.8mm.

[0146] A hot-rolled plate was coiled at 700°C, cooled in air, annealed at 1030°C for 2 minutes, then rapidly cooled in water and pickled, and then cold-rolled to a thickness of 0.20 mm to produce a cold-rolled plate.

[0147] A Si diffusion composition was prepared by stirring 100 parts by weight of silicon powder (Si: 99.99 wt% or more) with an average particle size of 1 μm, the amount of aluminum n-butoxide summarized in Table 1 below, and water.

[0148] 50 g / m² of the manufactured Si diffusion composition applied to a cold-rolled plate 2 It was applied in an amount and dried for 8 seconds at 650℃.

[0149] A cold-rolled sheet coated with a Si diffusion composition was subjected to diffusion annealing at 900°C for 3 hours in an atmosphere of 98 volume% hydrogen, the dew point and pressures listed in Table 1 below.

[0150] After the surface of the steel plate that had undergone diffusion annealing was washed with water and dried at room temperature, it was immersed in a nitric acid solution containing 0.5% hydrofluoric acid at 65°C for 12 seconds to remove unreacted material, washed again with water, and finally dried. As a result of analysis using a scanning electron microscope / energy-dispersive X-ray spectroscopy, it was confirmed that the average steel composition in the thickness direction of the steel plate was Mn: 0.10 wt%, Sn 0.04 wt%, Sb 0.04 wt%, and P: 0.013 wt%.

[0151] The final manufactured non-oriented electrical steel sheet had a thickness of 0.2 mm and a width of 500 mm. The Si content and Al content were measured at each position by dividing the width direction into 10 equal parts, and the results are shown in Tables 1 and 2.

[0152] Magnetic flux density and iron loss were measured in the rolling direction and the rolling perpendicular direction, and the averages are shown in Table 2.

[0153] Insulation properties were evaluated by measuring insulation resistance according to the standard test method ASTM A717; a perfect insulator has a value of 0 amperes, and a perfect conductor has a value of 1 ampere. The area and average particle size of Al2O3 were calculated from images captured by a transmission electron microscope (TEM). At this time, the observation magnification was 100,000x, and the observation area per image was 1 µm. 2 And, a total of 10 images were observed.

[0154] Steel Grade Al Compound Content (parts by weight) Atmosphere Pressure (Bar) Dew Point (°C) Average Si Content (weight%) Average Al Content (weight%) ΔSi (weight%) ΔAl (weight%) 1 10 1.0 - 20 4.8 2.0 3.4 1.2 2 4 7 1.0 - 20 6.8 2.4 2.2 1.1 3 2 9 1.0 - 10 6.4 2.8 1.9 2.3 4 2 9 1.0 - 10 6.8 0.8 2.2 1.5 5 3 5 1.0 4.9 0.4 2.8 0.9 6 2 1 1.0 5.0 1.3 2.8 1.1 7 3 7 1.0 10 4.5 1.1 3.8 1.4 8 3 4 1.0 10 6.60 .23.40.89351.0204.02.82.41.510212.0207.00.31.61.41155.005.5<0.0011.00.03127210.006.73.53.30.813120.104.90.43.80.7143920.006.12.71.21.815461.0-306.11.71.40.716221.0306.32.43.71.2

[0155] Steel Type Al2O3 Area Ratio (%) in 1-10㎛ Al2O3 Area Ratio (%) in 20-50㎛ Average Al2O3 Particle Size (nm) in 1-10㎛ B25(T) W10 / 1k(W / kg) W5 / 2k(W / kg) Insulation Resistance (Ωcm² / sheet) Type 10.09 0.00 337 1.45 18.8 13.10.39 Example 20.39 20.00 469 1.48 19.01 2.7 0.22 Example 30.18 70.00 278 1.51 18.1 12.50 .18 Example 40.3790.001751.4618.612.70.21 Example 50.4060.000411.5518.413.50.20 Example 60.2820.002981.5318.213.40.23 Example 70.2220.004681.4518.813.30.40 Example 80.4770.0 02921.4618.612.90.17 Example 90.1220.002271.5118.313.30.31 Example 100.2340.000631.4718.613.00.25 Example 110.0080.00341.6320.415.10.88 Comparative Example 120.8720.0321231.6020.1 15.30.65 Comparative Example 130.0050.00471.6220.915.40.81 Comparative Example 140.7230.025511.6520.715.40.63 Comparative Example 150.0040.003481.6120.015.70.78 Comparative Example 160.5120.0421121.6221.515.90.43 Comparative Example

[0156] As shown in Tables 1 and 2, when the Al compound content in the diffusion annealing composition, the pressure of the atmosphere during diffusion annealing, and the dew point are appropriately controlled, Al2O3 is appropriately formed on the surface layer, and it can be confirmed that magnetic and insulating properties are excellent at the same time.

[0157] On the other hand, when the Al compound content in the diffusion annealing composition, the atmospheric pressure during diffusion annealing, and the dew point are appropriately controlled, Al2O3 is properly formed on the surface layer, and it can be confirmed that the magnetic properties are inferior or the insulating properties are inferior.

[0158]

[0159] The present invention is not limited to the above embodiments and 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 changing 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.

Claims

1. In weight%, it comprises Si: 4.0 to 7.0%, Al: 0.001 to 3.0%, and Mn: 0.03 to 3.0%, and the remainder comprises Fe and unavoidable impurities, A non-oriented electrical steel sheet having an area ratio of Al2O3 of 0.010 to 0.500% in the region of 1 μm to 10 μm inward from the surface of the steel sheet in a cross-section in the thickness direction of the steel sheet.

2. In Paragraph 1, A non-oriented electrical steel sheet having an area ratio of Al2O3 of 0.005% or less in a region of 20 to 50 μm in the inward direction from the surface of the steel sheet in a cross-section in the thickness direction of the steel sheet.

3. In Paragraph 1, A non-oriented electrical steel sheet having an average particle size of Al2O3 of 5 to 100 nm in the region of 1 μm to 10 μm inward from the surface of the steel sheet in a cross-section in the thickness direction of the steel sheet.

4. In Paragraph 1, Si content at the center of plate thickness (t / 2) [CM Si ] and maximum Si content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Si The difference of ] ([SM Si ]-[ CM Si Non-oriented electrical steel sheet having ΔSi defined as ]) of 0.1 wt% or more.

5. In Paragraph 1, Al content at the center of plate thickness (t / 2) [CM Al ] and maximum Al content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Al The difference of ] ([SM Al ]-[ CM Al Non-oriented electrical steel sheet having ΔAl defined as ]) 0.1 wt% or more.

6. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of C: 0.005 wt% or less, N: 0.005 wt% or less, S: 0.005 wt% or less, Ti: 0.005 wt% or less, Nb: 0.005 wt% or less, and V: 0.005 wt% or less.

7. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of P: 0.1 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.1 wt% or less, Sb: 0.1 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

8. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of Bi: 0.200 wt% or less, Pb: 0.200 wt% or less, Ge: 0.200 wt% or less, and As: 0.200 wt% or less.

9. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

10. A step of manufacturing a cold-rolled sheet comprising, in weight%, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 3.0%, and the remainder being Fe and unavoidable impurities; A step of applying a Si diffusion composition containing a Si compound to the surface of the above cold-rolled plate; and The above cold-rolled plate includes the step of diffusion annealing, and A method for manufacturing a non-oriented electrical steel sheet in which the above-mentioned diffusion annealing step is performed in an atmosphere where the pressure of the atmosphere applied to the steel sheet is 0.5 to 15 Bar.

11. In Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet in which the above diffusion annealing step is performed in an atmosphere with a dew point temperature of -25°C to 25°C.

12. In Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the above Si diffusion composition further comprises an Al compound, and the solid content comprises 100 parts by weight of Si compound and 10 to 50 parts by weight of Al compound.

13. In Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet, comprising 10 to 1,000 parts by weight of a ceramic powder comprising an oxide, nitride, carbide, or oxynitride, wherein the above Si diffusion composition comprises at least one component selected from Li, B, Ca, Sr, Mg, Al, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn, and Ba.

14. In Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet in which the average particle size of the above Si compound is 1 to 1500 nm.

15. In Paragraph 12, A method for manufacturing a non-oriented electrical steel sheet in which the average particle size of the above Al compound is 1 to 1000 nm.

16. In Paragraph 13, A method for manufacturing a non-oriented electrical steel sheet in which the average particle size of the ceramic powder is 8 to 2500 nm.

17. In Paragraph 10, In the step of applying the above Si diffusion composition, the amount of the Si diffusion composition applied is 0.1 to 300 g / m² 2 Method for manufacturing non-oriented electrical steel sheets.

18. In Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet in which, in the above diffusion annealing step, the cracking temperature is 850 to 1050℃ and the cracking time is 2.8 to 10 hours.

19. In Paragraph 10, A method for manufacturing non-oriented electrical steel sheets in which the atmosphere in the above diffusion annealing step contains 98 volume% or more of hydrogen.