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, in wt%,: 4.0% to 7.0% of Si; 0.001% to 3.0% of Al; 0.03% to 2.0% of Mn; and the remainder of Fe and inevitable impurities. The non-oriented electrical steel sheet, according to one embodiment of the present invention, has a ΔAl of 0.1 wt% or greater, ΔAl being defined as the difference ([S-MAl]-[C-MAl]) between the Al content [C-MAl] at the sheet thickness-wise center position (t / 2), and the maximum Al content [S-MAl] in the region down to 5% of the total thickness inwardly from the surface of the non-oriented electrical steel sheet, and has a ferrite single phase steel structure, and the average particle diameter of the ferrite is 100 to 300 μm.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] One embodiment of the present invention relates to a Si diffusion composition, 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 having improved magnetism by diffusing Si and Al from the surface of the steel sheet into the interior of the steel sheet, and a method for manufacturing the same.

[0002] Non-oriented electrical steel, used as core material in electronic devices, requires high magnetic flux density and low core loss to meet increasing device efficiency and miniaturization. Higher magnetic flux density requires less core to achieve the same performance, enabling miniaturization of electrical devices. Lower core loss also translates to less energy loss, making securing these characteristics essential for the manufacture of high-efficiency motors.

[0003] Iron loss, which causes energy loss, is composed of hysteresis loss and eddy current loss. The impact of eddy current loss increases in high-efficiency motors with high operating frequencies of electronic devices. Eddy current loss is heat generated by eddy currents when a magnetic field is induced in the iron core. To reduce this, a method that is generally effective is to increase the content of non-resistive elements such as Si or Al within the electrical steel sheet. Furthermore, when the Si content exceeds a certain level, magnetostriction, which causes noise, decreases to zero and magnetic permeability increases to the maximum, making it 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, making it difficult to manufacture thin-film electrical steel sheets using a conventional rolling process.

[0005] To overcome the limitations of this rolling process, a technology has been proposed to manufacture electrical steel sheets with increased Si content by diffusing SiCl4 gas onto the surface of cold-rolled steel sheets. However, this method utilizes highly toxic and chemically unstable SiCl4 gas, and as such, it faces numerous challenges that must be overcome for commercial viability, including the requirement for equipment that requires production under high-vacuum conditions. Furthermore, the generation of by-product gases such as FeCl2 under high-vacuum conditions poses environmental hazards and deteriorates insulation properties, necessitating a fundamental solution.

[0006] In one embodiment of the present invention, a Si diffusion composition, a non-oriented electrical steel sheet, and a method for manufacturing the same are provided. Specifically, in one embodiment of the present invention, a non-oriented electrical steel sheet having improved magnetism by diffusing Si and Al from the surface of the steel sheet into the interior of the steel sheet, and a method for manufacturing the same are provided.

[0007] A non-oriented electrical steel sheet according to one embodiment of the present invention contains Si: 4.0 to 7.0% by weight, Al: 0.001 to 3.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and unavoidable impurities.

[0008] Al content at the center of plate thickness (t / 2) [CM Al ] and the maximum Al content in the area from the surface to the inner direction of the non-oriented electrical steel sheet up to 5% of the total thickness [SM Al ] difference ([SM Al ]-[CM Al ]) may be 0.1 wt% or more.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention has a steel structure of single phase ferrite, and an average grain size of the ferrite is 100 to 300 ㎛.

[0010] The maximum Si content in a region from the surface of the non-oriented electrical steel sheet to 5% of the total thickness in the inner direction may be 4 to 8 wt%, and the Si content at the center position of the plate thickness (t / 2) may be 0.01 to 7.0 wt%.

[0011] Si content at the center of plate thickness (t / 2) [CM Si ] and the maximum Si content in the area from the surface to the inner direction of the non-oriented electrical steel sheet up to 5% of the total thickness [SM Si ] difference ([SM Si ]-[CM Si ]) may be 0.1 wt% or more.

[0012] The roughness (Ra) of the steel plate surface may be 1.00㎛ or less.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of C, N, S, Ti, Nb, and V, each at 0.005 wt% or less.

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one 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.

[0015] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.200 wt% or less of one or more types of Bi, Pb, Ge, and As, individually or in a combined amount.

[0016] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

[0017] A Si diffusion composition for electrical steel sheet according to one embodiment of the present invention comprises Si powder and Al alkoxide, and the Al alkoxide is Al(OR) n (R) 3-n , wherein R is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and n is an integer of 1 to 3.

[0018] The Si diffusion composition may further comprise a ceramic powder comprising an oxide, nitride, carbide or oxynitride comprising at least one selected from Li, B, Ca, Sr, Mg, Al, Si, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn and Ba as a component.

[0019] The Si diffusion composition may include 10 to 70 wt% of Si powder, 1 to 20 wt% of Al alkoxide, and the remainder ceramic powder as a solid content.

[0020] The average particle size of the Si powder can be 1 to 850 nm.

[0021] The average particle size of the ceramic powder may be 8 to 2500 nm.

[0022] 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 containing, in wt%, 0.01 to 3.5% of Si, 0.001 to 3.0% of Al, and 0.03 to 2.0% of Mn, with the remainder being Fe and unavoidable impurities; applying a Si diffusion composition containing Si powder and Al alkoxide to the cold-rolled sheet; and diffusion annealing the cold-rolled sheet.

[0023] The diffusion annealing step can be performed at a soaking temperature of 850°C to 1250°C for 30 to 600 minutes.

[0024] In the step of applying the Si diffusion composition, the amount of the Si diffusion composition applied is 0.1 to 300 g / m 2 It could be.

[0025] Before the diffusion annealing step, the temperature range of 20 to 700°C can be increased at a rate of 5 to 50°C / hr.

[0026] The diffusion annealing step can be performed in an atmosphere with an oxidation capacity (PH2O / PH2) of 6.4 or less.

[0027] The step of manufacturing a cold-rolled sheet may include a step of manufacturing a hot-rolled sheet by hot-rolling a slab containing, in weight %, Si: 0.01 to 3.5%, Al: 0.001 to 3.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and unavoidable impurities; and a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet.

[0028] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent high-frequency iron loss and insulation properties at the same time.

[0029] 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, etc.

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

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0032] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0033] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0034] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0035] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0036] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0037]

[0038] A non-oriented electrical steel sheet according to one embodiment of the present invention contains Si: 4.0 to 7.0% by weight, Al: 0.001 to 3.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and unavoidable impurities.

[0039] First, let's explain the reason for the limitation of the components of non-oriented electrical steel sheets.

[0040]

[0041] Si: 4.0 to 7.0 wt%

[0042] Silicon (Si) increases the resistivity of a material, thereby reducing core loss, and therefore must be added in relatively large amounts. As the Si content increases, eddy current loss decreases, which can lower core loss at high frequencies. Specifically, when Si is present at 6.0 wt% or more, magnetostriction, a source of noise, is reduced to zero and magnetic permeability increases to its maximum, enabling the production of electrical steel sheets with superior high-frequency characteristics. However, when the Si content exceeds 4 wt%, the ductility of the electrical steel sheets is significantly reduced, making it difficult to manufacture electrical steel sheets using conventional rolling processes.

[0043] In one embodiment of the present invention, Si is diffused from the surface of the steel sheet into the interior of the steel sheet to add Si in an amount of 4 wt% or more into the steel sheet. If there is too little Si in the steel sheet, it is difficult to expect the effect due to Si as described above. If too much Si is included, the workability may be poor. In one embodiment of the present invention, due to the diffusion of Si from the surface to the interior, a concentration gradient of Si may exist in the direction of the thickness of the steel sheet, and unless otherwise specified, the Si content in the steel sheet means the average content in the direction of the thickness. The average content means the content assuming that Si in the steel sheet is uniformly distributed in the direction of the thickness of the steel sheet. Specifically, Si may be 4.5 wt% to 6.5 wt%.

[0044] The maximum Si content in a region from the surface of the non-oriented electrical steel sheet to 5% of the total thickness in the inner direction may be 4.0 to 8.0 wt%, and the Si content at the center position of the plate thickness (t / 2) may be 0.03 to 7.0 wt%.

[0045] In one embodiment of the present invention, since the steel sheet containing a high concentration of Si is manufactured by diffusing Si from the surface of the steel sheet to the interior of the steel sheet, a concentration gradient may occur in the direction of the steel sheet thickness. 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 inner direction (i.e., the surface portion) may be 4.0 to 8.0 wt%. If the Si content in the surface portion is low, it means that sufficient Si has not been 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, it means that a large amount of Si exists only in the surface portion and has not been 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 by a non-destructive analysis method such as EPMA (Electron Probe Micro-Analyzer) or Scanning Electron Microscope / Energy-dispersive, X-ray spectroscopy (SEM / EDX). More specifically, the maximum Si content in the surface portion can be 4.3 to 7.5 wt%.

[0046] The center of the plate thickness refers to the position at half the total thickness of the plate. Hereinafter, this will be referred to as the center. A low Si content in the center indicates insufficient Si diffusion, and the improvement in high-frequency iron loss through high Si concentration may not be fully achieved. An excessively high Si content in the center may cause problems in processability for motors. More specifically, the Si content in the center may be 2.0 to 4.0 wt%.

[0047] Si content at the center of plate thickness (t / 2) [CM Si] and the maximum Si content in the area from the surface to the inner direction of the non-oriented electrical steel sheet up to 5% of the total thickness [SM Si ] difference ([SM Si ]-[CM Si ]) may be 0.1 wt% or more. When there is an appropriate difference in Si content between the center and the surface, there is an advantage 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%.

[0048] As described above, in one embodiment of the present invention, Si in the Si powder in the Si diffusion composition is diffused by diffusion annealing, thereby increasing the Si content, and the steel sheet before Si diffusion may contain less Si than described above. Specifically, the slab and the cold-rolled sheet before diffusion may contain 0.01 to 3.5 wt% of Si. If the slab and the cold-rolled sheet before diffusion contain too little Si, the amount of Si required for diffusion increases, diffusion annealing takes a long time, which is not efficient, and the difference in Si content by sheet thickness becomes large, making it difficult to obtain an appropriate high-frequency core loss. If the slab and the cold-rolled sheet before diffusion contain too much Si, the steel sheet may be broken during the cold rolling process, or defects may occur in the steel sheet. More specifically, the Si content in the slab and the cold-rolled sheet before diffusion may be 0.3 to 3.3 wt%. More specifically, the Si content in the slab and the cold-rolled sheet before diffusion may be 2.0 to 3.0 wt%.

[0049]

[0050] Al: 0.001 to 3.0 wt%

[0051] Aluminum (Al) increases the resistivity of the material and lowers the high-frequency core loss. In one embodiment of the present invention, the resistivity of the material can be sufficiently increased through the diffusion of Si, so the addition of Al may be unnecessary. However, the higher the addition of Al, the higher the high-frequency core loss can be further improved. However, if too much Al is added, the core loss may be deteriorated due to the formation of an aluminum silicate-based composite, and the surface quality may deteriorate. In one embodiment of the present invention, due to the diffusion of Al from the surface to the inside, an Al concentration gradient may exist in the direction of the thickness of the steel sheet, and unless otherwise specified, the Al content in the steel sheet means the average content in the direction of the thickness. More specifically, Al may be included in an amount of 0.01 to 2.5 wt%. More specifically, Al may be included in an amount of 0.1 to 2.0 wt%.

[0052] In one embodiment of the present invention, a steel sheet containing a high concentration of Si is manufactured by diffusing Al together with Si, so that a concentration gradient can occur in the direction of the thickness of the steel sheet.

[0053] Al content at the center of plate thickness (t / 2) [CM Al ] and the maximum Al content in the area from the surface to the inner direction of the non-oriented electrical steel sheet up to 5% of the total thickness [SM Al ] difference ([SM Al ]-[CM Al ]) may be 0.1 wt% 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 wt%. More specifically, it may be 0.5 to 2.5 wt%.

[0054] The maximum Al content in the area from the surface to 5% of the total thickness in the inner direction of the non-oriented electrical steel sheet (i.e., the surface portion) can be 1.0 to 4.0 wt%. If the Al content in the surface portion is low, it means that not enough Al has been diffused, and the improvement in high-frequency iron loss through Al diffusion may not be sufficiently obtained. If the Al content is too high, it means that a large amount of Al exists only in the surface portion and has not been diffused into the steel sheet, and this also means that the improvement in high-frequency iron loss through Al diffusion may not be sufficiently obtained. The maximum Al content means the highest Al content when measuring the Al concentration in the surface portion in the thickness direction. The maximum Al content can be measured by a non-destructive analysis method such as EPMA (Electron Probe Micro-Analyzer) or Scanning Electron Microscope / Energy-dispersive, X-ray spectroscopy (SEM / EDX). More specifically, the maximum Al content in the surface area can be 1.5 to 3.5 wt%.

[0055] The Al content at the center of the plate thickness (t / 2) may be 0.001 to 2.9 wt%. A low Al content at the center indicates that sufficient Al has not been diffused, and the improvement in high-frequency iron loss through Al diffusion may not be sufficiently achieved. If the Al content at the center is too high, the iron loss may be degraded due to the formation of an aluminum silicate composite, and the surface quality may be degraded. More specifically, the Al content at the center may be 0.005 to 2.0 wt%.

[0056] As described above, in one embodiment of the present invention, Al in the Al alkoxide in the Si diffusion composition is diffused by diffusion annealing, thereby increasing the Al content, and the steel sheet before Al diffusion may contain less Al than described above. Specifically, the slab and the cold-rolled sheet before diffusion may contain 0.001 to 3.0 wt% of Al. If the slab and the cold-rolled sheet before diffusion contain too little Al, the amount of Al required for diffusion increases, diffusion annealing takes a long time, which is not efficient, and the difference in Al content by sheet thickness becomes large, making it difficult to obtain an appropriate high-frequency iron loss. If the slab contains too much Al, problems such as magnetism and surface roughness may occur. More specifically, the Al content in the slab and the cold-rolled sheet before diffusion may be 0.005 to 2.0 wt%.

[0057]

[0058] Mn: 0.03 to 2.0 wt%

[0059] Manganese (Mn) increases the resistivity of the material, improves iron loss, and plays a role in forming sulfides. If too little Mn is added, MnS may precipitate finely, which may deteriorate magnetism. If too much Mn is added, it may promote the formation of a

[0111] texture that is unfavorable to magnetism, which may cause a rapid decrease in magnetic flux density. In one embodiment of the present invention, unlike Si and Al, Mn does not diffuse, and there may be no concentration difference between the surface and the center of the steel sheet. That is, the content difference between the surface and the center of the steel sheet may be 0.01 wt% or less. More specifically, Mn may be 0.1 to 1.5 wt%.

[0060]

[0061] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one 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.

[0062]

[0063] P: 0.1 wt% or less

[0064] Phosphorus (P) is a grain boundary segregation element, and if added in too large a quantity, it can delay recrystallization and deteriorate the strength uniformity in the rolling direction and the direction perpendicular to the rolling. More specifically, P can be 0.0001 to 0.1 wt%. More specifically, it can be 0.001 to 0.05 wt%.

[0065]

[0066] Cu: 0.005 to 0.200 wt%

[0067] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu·Mn)S can occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement can occur, leading to cracks during casting or hot rolling. More specifically, Cu may be present in an amount of 0.010 to 0.100 wt%.

[0068]

[0069] Cr: 0.010 to 0.50 wt%

[0070] Chromium (Cr) increases resistivity and improves iron loss. If too little Cr is added, the resistivity-enhancing effect may not be sufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr may be present in an amount of 0.02 to 0.30 wt%.

[0071]

[0072] Sn: 0.10 wt% or less

[0073] Tin (Sn) is added to suppress the diffusion of nitrogen through grain boundaries as a segregating element at grain boundaries, suppress the {111} texture that is detrimental to magnetism, and increase the {100} texture that is advantageous, thereby improving magnetic properties. If too much Sn is added, it hinders grain growth, lowering magnetism and deteriorating rolling properties. Therefore, Sn may be added within the above-mentioned range. More specifically, Sn may be 0.001 to 0.10 wt%. More specifically, it may be 0.005 to 0.08 wt%.

[0074]

[0075] Sb: 0.1 wt% or less

[0076] Antimony (Sb) is added to suppress the diffusion of nitrogen through grain boundaries as a segregating element at grain boundaries, suppress the {111} texture that is detrimental to magnetism, and increase the {100} texture that is advantageous, thereby improving magnetic properties. If too much Sb is added, grain growth is hindered, which reduces magnetism and deteriorates rolling properties. Therefore, Sb may be added within the above-mentioned range. More specifically, Sb may be 0.001 to 0.10 wt%. More specifically, it may be 0.005 to 0.08 wt%.

[0077]

[0078] Ni: 0.05 wt% or less

[0079] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, Ni may be present in an amount of 0.0001 to 0.050 wt%. More specifically, Ni may be present in an amount of 0.001 to 0.030 wt%.

[0080]

[0081] Zn: 0.01 wt% or less

[0082] Zinc (Zn) can act as an impurity and deteriorate magnetism when the content is excessive. Therefore, Zn can be added further within the aforementioned range. More specifically, Zn can be 0.0001 to 0.01 wt%. More specifically, Zn can be 0.001 to 0.008 wt%.

[0083]

[0084] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.200 wt% or less of one or more types of Bi, Pb, Ge, and As, individually or in a combined amount.

[0085] The aforementioned elements, when added additionally, segregate at grain boundaries and alleviate stress concentration at grain boundaries during cold rolling, thereby reducing the stress concentration at grain boundaries during the subsequent recrystallization annealing process. <111> / ND By suppressing recrystallization of orientation grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effect can be additionally obtained, but if they are included in too much, a large amount of segregation may occur, which may suppress grain growth and deteriorate the magnetic flux density and iron loss. More specifically, one or more kinds of Bi, Pb, Ge, and As may be included, each or a combined amount of 0.0001 to 0.200 wt%. More specifically, one or more kinds of Bi, Pb, Ge, and As may be included, each or a combined amount of 0.001 to 0.100 wt%.

[0086]

[0087] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

[0088] These can react with C, S, N, etc., which are inevitably included, to form fine carbides, nitrides, or sulfides, which can adversely affect magnetism, so the upper limit can be limited as described above.

[0089] More specifically, Mo may be 0.0001 to 0.03 wt%. More specifically, Mo may be 0.001 to 0.02 wt%.

[0090] B, Ca, or Mg may each be included in an amount of 0.0001 to 0.050 wt%. More specifically, B, Ca, or Mg may each be included in an amount of 0.001 to 0.030 wt%.

[0091] Other impurities

[0092] In addition to the elements mentioned above, unavoidable impurities such as carbon (C), sulfur (S), nitrogen (N), titanium (Ti), niobium (Nb), and vanadium (V) may be included.

[0093] N combines with Ti, Nb, and V to form nitrides and plays a role in reducing grain growth.

[0094] C reacts with N, Ti, Nb, V, etc. to form fine carbides, which hinder grain growth and domain movement.

[0095] S forms sulfides, which impairs grain growth.

[0096] In this case, when impurity elements are further included, at least one of C, S, N, Ti, Nb, and V may be included in an amount of 0.005 wt% or less. More specifically, at least one of C, S, N, Ti, Nb, and V may be included in an amount of 0.0001 wt% to 0.005 wt%. More specifically, at least one of C, S, N, Ti, Nb, and V may be included in an amount of 0.0005 wt% to 0.003 wt%.

[0097] In addition, unavoidable impurities may be included. Unavoidable impurities are impurities mixed during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these are widely known in the art, a detailed description will be 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. When additional elements are included, they are included to replace the remaining Fe.

[0098]

[0099] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have a steel structure of a single phase of ferrite, and an average grain size of the ferrite may be 100 to 300 ㎛. If the average grain size of the ferrite is too large, eddy current loss, which is a loss generated by an induced current, may increase, resulting in poor magnetism. If the average grain size of the ferrite is too small, hysteresis loss, which is the energy used to move the magnetic domain wall, may increase, resulting in poor magnetism. More specifically, it may be 120 to 280 ㎛. Even more specifically, it may be 150 to 250 ㎛. These characteristics can be obtained by controlling the ceramic diffusion annealing temperature and time. This will be specifically described with respect to a method for manufacturing a non-oriented electrical steel sheet. A single phase of ferrite means that 99 area% or more of the crystal grains in the steel sheet exist as ferrite, and the remainder may be amorphous, austenite, pearlite, FeSi with a B2 structure, Fe3Si with a DO3 structure, etc. Ferrite single phase can be determined by taking an optical microscope photograph and analyzing the image to determine the area %. To reduce errors, select at least 10 non-overlapping random locations on the steel plate, take a sample of an area of ​​at least 1600 ㎛ × 1200 ㎛, and then average the results to determine the average. The average grain size of ferrite can be measured in a direction parallel to the normal plane perpendicular to the thickness direction of the steel plate.

[0100] Meanwhile, in one embodiment of the present invention, due to the difference in Si and Al concentrations in the central and surface portions, the grain sizes of ferrite may be different in the central and surface portions. Specifically, the average ferrite grain size at the plate thickness center position (t / 2) may be 100 to 500 μm, and the average ferrite grain size in a region from the surface to 5% of the total thickness in an inward direction may be 10 to 100 μm. More specifically, the average ferrite grain size at the plate thickness center position (t / 2) may be 200 to 480 μm, and the average ferrite grain size in a region from the surface to 5% of the total thickness in an inward direction may be 15 to 90 μm. The crystal grain size at a specific thickness position can be measured in a plane parallel to the rolling plane (ND plane).

[0101] In this way, the difference in ferrite grain size at the center position of the plate thickness (t / 2) and at a position of 5% of the total thickness from the surface in the inward direction may be 100 to 450 μm. More specifically, it may be 150 to 400 μm.

[0102]

[0103] The non-oriented electrical steel sheet according to one embodiment of the present invention has excellent high-frequency iron loss due to the diffusion of Si and Al. Specifically, the iron loss (W 10 / 1000 ) may be less than 70.0 W / kg based on a thickness of 0.3 mm. Iron loss (W 10 / 1000 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz. Iron loss can be measured by the Epstein measurement method or the SST (single sheet test) method. More specifically, iron loss (W 10 / 1000 ) is 40 to 65 W / kg based on a thickness of 0.3 mm. In addition, the iron loss (W 10 / 1000 ) may be 55.0 W / kg or less based on a thickness of 0.2 mm. More specifically, the iron loss (W 10 / 1000 ) is 20 to 53 W / kg based on a thickness of 0.2 mm. Also, W 10 / 1000Based on this thickness of 0.1 mm, it can be less than 35.0 W / kg. More specifically, W 10 / 1000 Based on this thickness of 0.1 mm, it can be 10.0 to 33.0 W / kg.

[0104] Also, iron loss (W 5 / 2000 ) can be less than 16.5 W / kg based on a thickness of 0.2 mm. Iron loss (W 5 / 2000 ) is the iron loss when a magnetic flux density of 0.5 T is induced at a frequency of 2000 Hz. More specifically, the iron loss (W) is based on a thickness of 0.2 mm. 5 / 2000 ) can be 5.0 W / kg to 15.5 W / kg. In addition, the iron loss (W 5 / 2000 ) can be less than 7.3 W / kg based on a thickness of 0.1 mm. Iron loss (W 5 / 2000 ) is the iron loss when a magnetic flux density of 0.5 T is induced at a frequency of 2000 Hz. More specifically, the iron loss (W) is based on a thickness of 0.1 mm. 5 / 2000 ) can be 2.0 W / kg to 7.0 W / kg.

[0105]

[0106] In one embodiment of the present invention, not only the iron loss but also the magnetic flux density is excellent at the same time. Specifically, the magnetic flux density (B 25 ) can be 1.46T or more. Specifically, the magnetic flux density (B 25 ) can be 1.55 to 1.70T.

[0107] In one embodiment of the present invention, by appropriately diffusing aluminum from the surface of the steel plate inward, excellent insulation is achieved. Specifically, the insulation may be 200 to 900 mA or more. The insulation can be measured using a Franklin insulation tester. The insulation may be 250 to 850 mA.

[0108] In one embodiment of the present invention, by appropriately using the Si diffusion composition, the roughness of the steel sheet can be reduced, and the surface condition can be manufactured in a good manner. Specifically, the roughness (Ra) of the steel sheet surface can be 1.00㎛ or less. The roughness (Ra) of the steel sheet surface can be measured using a confocal laser scanning microscope. More specifically, the roughness can be 0.10㎛ to 1.00㎛. Even more specifically, it can be 0.20 to 0.95㎛.

[0109]

[0110] A Si diffusion composition for an electrical steel sheet according to one embodiment of the present invention includes Si powder and Al alkoxide.

[0111] The Si diffusion composition contains 10 to 70 wt% of Si powder as a solid content. In one embodiment of the present invention, the solid content means the weight of each compound after heating it at 180°C for 20 minutes or more and removing all volatile matter.

[0112] If the Si powder content is too small, Si diffusion will not occur sufficiently, making it difficult to sufficiently achieve the desired high-frequency iron loss improvement. If the Si powder content is too large, Si will diffuse excessively within the steel sheet, which may cause problems with processability when the steel sheet is later processed into products such as motors. More specifically, the Si powder content may be 15 to 60 wt%.

[0113] The Si powder may include one or more of pure Si, Si alloy, silicon wafer, and polycrystalline silicon. More specifically, it may be a Si alloy containing 90 wt% or more of Si.

[0114] The average particle size of the Si powder can be 1 to 850 nm. If the particle size of the Si powder is too small, it may clump together during slurry mixing, which may cause surface defects. If the particle size of the Si powder is too large, it may be difficult to uniformly apply the Si powder to the surface of the steel sheet, and the Si may not diffuse smoothly into the steel sheet. The average particle size of the Si powder is the average particle size relative to the number of particles, and can be measured using a particle size analyzer (PSA) method using laser diffraction.

[0115] More specifically, the lower limit of the average particle size of the Si powder may be 10 nm to 800 nm.

[0116]

[0117] The Si diffusion composition contains 1 to 20 wt% of Al alkoxide as a solid content. Al alkoxide serves as an Al raw material for diffusing Al in the steel sheet, and plays a role in ensuring the stability of the slurry mixture and ensuring uniform quality. If too little Al alkoxide is contained, the stability of the slurry mixture may be reduced. If too much Al alkoxide is contained, the viscosity of the slurry mixture may increase, which may cause problems in terms of surface quality. More specifically, the lower limit of Al alkoxide may be 1.5 to 16.0 wt%.

[0118] Al alkoxide is Al(OR) n (R) 3-n , wherein each R is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and n is an integer of 1 to 3. More specifically, each R is an alkyl group having 1 to 4 carbon atoms, and n may be 3. More specifically, each R may be an alkyl group having 2 to 4 carbon atoms. More specifically, it may be aluminum tri i-propoxide or aluminum tri n-butoxide.

[0119] When Al oxide or nitride, i.e. Al2O3 or AlN, is included instead of Al alkoxide, a problem of poor surface roughness may occur.

[0120] The Si diffusion composition may further comprise a ceramic powder comprising an oxide, nitride, carbide or oxynitride comprising at least one selected from Li, B, Ca, Sr, Mg, Al, Si, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn and Ba as a component. The ceramic powder serves to control the amount of slurry applied and to regulate the Si diffusion rate of the final steel sheet.

[0121] The ceramic powder may contain Si powder and Al alkoxide as a solid content, i.e., it may contain 10 to 89 wt% of the solid content.

[0122] Incorporating too little ceramic powder can lead to problems in securing the required coating amount. Incorporating too much ceramic powder can increase the slurry's viscosity, potentially leading to surface defects. More specifically, the ceramic powder content can range from 20% to 70% by weight.

[0123] The ceramic powder may be at least one of Al2O3, SiO2, TiO2, MgO·Al2O3, MgO·TiO2, 3Al2O3·2SiO2, ZrO2·SiO2, TiN, CrN, SrTiO3, MgAl2O4, Y2O3, FeTiO3, and Li2O·Al2O3·SiO2.

[0124] The average particle size of the ceramic powder may range from 8 to 2500 nm. If the particle size of the ceramic powder is too small, problems may arise in securing a sufficient coating amount. If the particle size of the ceramic powder is too large, the viscosity may increase, resulting in poor surface quality and preventing smooth diffusion of aluminum into the steel plate. More specifically, the average particle size of the ceramic powder may range from 10 nm to 2000 nm.

[0125] In addition to the components described above, the Si diffusion composition may further include a solvent. The solvent enables the Si diffusion composition to be applied uniformly. 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 1500 parts by weight based on 100 parts by weight of the solid content. More specifically, the solvent may be included in an amount of 20 to 1300 parts by weight. The solvent may include at least one of water and alcohol.

[0126] In addition to the Si powder, Al alkoxide, ceramic powder, and solvent described above, the Si diffusion composition may further include additional components, and this is not excluded in one embodiment of the present invention. Examples of the additional components may include orthophosphoric acid, sodium silicate, fluoride ion solution, etc. When additional components are further included, the content ratio of the Si powder, Al alkoxide, and ceramic powder described above is understood to be a ratio to the total sum of the Si powder, Al alkoxide, and ceramic powder, not the entire Si diffusion composition.

[0127]

[0128] 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 containing, in wt%, 0.01 to 3.5% Si, 0.001 to 2.0% Al, and 0.03 to 2.0% Mn, with the remainder being Fe and unavoidable impurities; applying a Si diffusion composition containing Si powder and Al alkoxide to the cold-rolled sheet; and diffusion annealing the cold-rolled sheet.

[0129] Below, each step is explained in detail.

[0130] 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 2.0%, with the remainder being Fe and unavoidable impurities. The alloy composition of the cold-rolled sheet is the same as described above, so a duplicate description is omitted.

[0131] A method for manufacturing a cold-rolled sheet is not particularly limited, and may include a step of manufacturing a hot-rolled sheet by hot-rolling a slab containing, in wt%, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and unavoidable impurities; and a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet.

[0132] 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 such as hot rolling, hot-rolled sheet annealing, and cold rolling described later, the composition of the slab and the composition of the cold-rolled sheet are substantially the same. In addition, only Si and Al are diffused during the diffusion annealing process, and the alloy composition of the non-oriented electrical steel sheet and the remaining components excluding Si and Al can be the same.

[0133] Prior to the step of manufacturing a hot-rolled sheet, the slab may be heated to 1100°C or higher. Specifically, the slab is placed in a heating furnace and heated to 1100 to 1250°C. When heated at a temperature exceeding 1250°C, precipitates may be re-dissolved and finely precipitated after hot rolling. More specifically, the slab heating temperature may be 1150°C to 1200°C.

[0134] The heated slab is hot-rolled to a thickness of 1.5 to 4.0 mm to produce a hot-rolled sheet. In one embodiment of the present invention, a preliminary cold-rolling step is also included before cold rolling, so that even if the hot-rolled sheet is relatively thick, a non-oriented electrical steel sheet of an appropriate thickness can be produced. More specifically, the thickness of the hot-rolled sheet may be 1.8 to 3.5 mm.

[0135] The step of manufacturing the hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher.

[0136] If the hot rolling finishing temperature is too low, the rolling load increases, which reduces the hot rolling workability. In addition, a lot of deformation structures remain in the hot rolled steel sheet, which can cause an increase in the rolling load during the subsequent preliminary cold rolling process. In addition, during the intermediate annealing, deformation structures are removed. <111> / ND The recrystallization of the orientation grains is promoted, resulting in a lower magnetic flux density. Therefore, the higher the hot rolling finishing temperature, the better. More specifically, the finishing rolling temperature can be 870 to 1000°C.

[0137] The step of manufacturing a hot rolled sheet may include a coiling step at a temperature of 600 to 800°C. A rough rolling step may also be included before the finish rolling step.

[0138] If the temperature during the coiling stage is controlled too low, the recovery and recrystallization of the hot-rolled deformation structure will not occur well, and the cooling load will increase to quickly cool the steel sheet to a low temperature, which may make it difficult to coil the supercooled coil. On the other hand, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during the coiling, which may cause the scale to form thicker and the problem of intergranular oxidation. Intergranular oxidation of the hot-rolled sheet promotes intergranular corrosion during the subsequent pickling process, which increases the possibility of surface stripe defects and may cause severe wear of the rolling rolls. Therefore, the coiling temperature can be 620℃ to 770℃.

[0139] After the step of manufacturing a hot-rolled sheet, an additional step of annealing the hot-rolled sheet at a temperature range of 600 to 1100°C may be included. If the hot-rolled sheet annealing temperature is too low, the recrystallized structure may not be formed or may grow finely, thereby reducing the effect of increasing the magnetic flux density. On the other hand, if the annealing temperature is too high, the magnetic properties may deteriorate, and the rolling workability may deteriorate due to deformation of the plate shape. More specifically, the hot-rolled sheet annealing temperature may be 650°C to 1050°C.

[0140] Hot-rolled sheet annealing is performed to increase the magnetic orientation as needed, and may be omitted. The annealing method is not particularly limited, and can be performed in batch or continuous mode.

[0141] Hot-rolled hot-rolled sheets can be pickled as needed.

[0142] Next, the hot-rolled sheet is pickled and cold-rolled to a predetermined thickness. Depending on the thickness of the hot-rolled sheet, the reduction ratio may be applied differently, but cold-rolling can be performed to a final thickness of 0.10 to 0.65 mm by applying a reduction ratio of 70 to 95%. To adjust the reduction ratio, single cold rolling or two or more cold rollings with intermediate annealing may be performed. More specifically, the reduction ratio may be 75 to 90%. The thickness of the cold-rolled sheet may be 0.10 to 0.35 mm.

[0143]

[0144] Returning to the description of the method for manufacturing non-oriented electrical steel sheets, a Si diffusion composition containing Si powder and Al alkoxide is applied to a cold-rolled sheet. The Si diffusion composition is the same as described above, so a duplicate description is omitted.

[0145] The coating amount of the Si diffusion composition is 0.1 to 300 g / m 2 This may be the case. The coating amount is based on the solid content. If the coating amount is too small, sufficient diffusion of Si and Al will not occur, making it difficult to fully achieve the effect of Si and Al diffusion. If the coating amount is too large, the problem of poor processability may occur due to increased diffusion of Si and Al.

[0146] A step of applying and drying a Si diffusion composition may be further included. The drying temperature is sufficient to remove the solvent within the Si diffusion composition, and may be specifically 300 to 750°C. The drying time may be 10 to 60 seconds. More specifically, the temperature may be 350 to 700°C. The drying time may be 15 to 50 seconds.

[0147] Next, the cold-rolled sheet is diffusion annealed. During this process, Si and Al diffuse into the steel sheet from the Si diffusion composition applied to the surface of the cold-rolled sheet.

[0148] Prior to the diffusion annealing step, the temperature can be increased between 20 and 700°C at a rate of 5 to 50°C / hr. This relatively slow heating rate allows for consistent quality. If the heating rate is too slow, the process time becomes unnecessarily long and productivity decreases. If the heating rate is too fast, the aforementioned effects cannot be adequately achieved. More specifically, the heating rate can be between 10 and 40°C / hr.

[0149] By controlling the diffusion annealing temperature and time, the ferrite single phase and ferrite average grain size can be appropriately controlled.

[0150] The diffusion annealing temperature may be between 850°C and 1250°C. If the diffusion annealing temperature is too low, the diffusion of Si and Al may not be sufficient, failing to achieve the desired effect. If the diffusion annealing temperature is too high, pores may form, resulting in poor magnetism. More specifically, the diffusion annealing temperature may be between 900°C and 1200°C.

[0151] The time can range from 30 to 600 minutes. If the time is too short, the diffusion of Si and Al may not be sufficient, failing to achieve the desired effect. If the time is too long, it may be difficult to control the amount of Si and Al diffusion, resulting in poor processability. More specifically, the time can range from 60 to 480 minutes.

[0152] The atmosphere during diffusion annealing may contain at least one of hydrogen, nitrogen, or argon. The oxidation capacity (PH2O / PH2) of the atmosphere may be 6.4 or less. If the oxidation capacity is too high, internal oxides of SiO2 and Al2O3 may be formed, which may deteriorate magnetism. Specifically, the oxidation capacity may be 0.001 to 5.0. More specifically, the oxidation capacity may be 0.01 to 3.0.

[0153] After the diffusion annealing step, a step of forming an insulating film may be further included. Since the insulating film is widely known, a detailed description thereof will be omitted. Specifically, the insulating coating layer may be formed by applying an insulating coating layer-forming composition comprising metal phosphate and silica as main components and heat-treating the coating layer.

[0154]

[0155] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0156]

[0157] Experimental Example 1: Control of temperature and time conditions during diffusion annealing

[0158] A slab was prepared containing 2.0 wt% of silicon (Si), 0.003 wt% of aluminum (Al), 0.15 wt% of manganese (Mn), 0.02 wt% of tin (Sn), and 0.01 wt% of phosphorus (P), with the remainder being iron and other unavoidable impurities.

[0159] The slab was heated at 1100℃ and then hot-rolled to a thickness of 1.8 mm to produce a hot-rolled plate.

[0160] After coiling the hot-rolled plate at 700°C, it was cooled in the air, annealed at 1030°C for 2 minutes, then rapidly cooled in water, pickled, and then cold-rolled to a thickness of 0.10 mm to produce a cold-rolled plate.

[0161] A Si diffusion composition was prepared by stirring water with 65 wt% of silicon nanoparticles having an average particle size of 25 nm, 1 wt% of aluminum n-butoxide, and 34 wt% of Al2O3 ceramic powder having an average particle size of 1000 nm.

[0162] The manufactured Si diffusion composition was applied to a cold-rolled sheet at 50 g / m 2 It was applied in a quantity and dried at 650℃ for 8 seconds.

[0163] A cold-rolled sheet coated with a Si diffusion composition was diffusion-annealed under the conditions listed in Table 1 below in an atmosphere containing 50% by volume of argon, 50% by volume of hydrogen, and an oxidation capacity of 1.22 at 900°C for 2 hours.

[0164] The surface of the steel plate on which diffusion annealing was completed was washed with water, dried at room temperature, and then etched under atmospheric pressure plasma conditions to remove unreacted substances, thereby manufacturing a 0.1 mm thick non-oriented electrical steel plate.

[0165] As a result of analysis using EPMA (Electron Probe Micro-Analyzer), it was confirmed that the average steel composition in the thickness direction of the steel plate included Si: 7.0 wt%, Al: 0.95 wt%, Mn: 0.15 wt%, P: 0.010 wt%, Sn 0.02 wt%, and the remainder was composed of Fe and other unavoidable impurities. ΔAl was confirmed to be 0.1 wt%.

[0166] Optical microscope photographs of the cross-section of the steel plate were taken and analyzed to confirm the presence of single-phase ferrite.

[0167] In addition, the average grain size of the steel plate is used by utilizing a line parallel to the normal plane perpendicular to the thickness direction of the steel plate. The average grain size of ferrite for the entire thickness of the steel plate, the average grain size of ferrite at the center (the center of the plate thickness (t / 2)) and the average grain size of ferrite at the surface (the position of the plate thickness (t / 20)) were measured.

[0168] Iron loss and magnetic flux density were measured using a single sheet tester.

[0169] Diffusion annealing temperature (℃) Diffusion annealing time (min) Single-phase ferrite or not Total thickness ferrite average grain size (㎛) Center ferrite average grain size (㎛) Surface ferrite average grain size (㎛) B25 (T) W10 / 1k (W / kg) W5 / 2k (W / kg) Example 1-1 900 480 0 1 3 2.5 2 3 4 3 1 1.5 7 3 1.2 4 4 Example 1-2 1 000 240 0 1 2 1.5 2 2 5 1 8 1.5 9 3 0.8 4 5 Example 1-3 1 100 240 0 1 9 2.5 3 4 4 1 1.6 2 2 5 5 4 2 Example 1-4 1 200 60 0 2 4.5 3 8 1 6 1 2 9 4 4 4 Example 1-5120090O241.0408741.6426.14.0 Example 1-61200120O281.5475881.6326.64.1 Comparative Example 1-1700480O63.095311.3549.617.5 Comparative Example 1-2130060O361.05571651.3749.015.8 Comparative Example 1-3900900O231.52671961.4143.113.8 Comparative Example 1-41200900O438.05273491.3847.214.3 Comparative Example 1-51300900X519.55984411.4753.316.5

[0170] As shown in Table 1, if the conditions are not properly controlled in the diffusion annealing process, single-phase ferrite is not formed, the ferrite grain size is not properly formed, and ultimately, the magnetism is inferior.

[0171]

[0172] Experimental Example 2: Types of Al alkoxides

[0173] A slab was prepared containing 2.5 wt% of silicon (Si), 0.002 wt% of aluminum (Al), 0.10 wt% of manganese (Mn), 0.04 wt% of tin (Sn), 0.04 wt% of antimony (Sb), and 0.013 wt% of phosphorus (P), with the remainder being iron and other unavoidable impurities.

[0174] The slab was heated at 1100℃ and then hot-rolled to a thickness of 1.8 mm to produce a hot-rolled plate.

[0175] After coiling the hot-rolled plate at 700°C, it was cooled in the air, annealed at 1030°C for 2 minutes, then rapidly cooled in water, pickled, and then cold-rolled to a thickness of 0.10 mm to produce a cold-rolled plate.

[0176] On the surface of a cold-rolled sheet, 65 parts by weight of silicon nanoparticles (Si: 99.99 wt% or more) having an average particle size of 15 nm in solid content, 7 parts by weight of aluminum alkoxide in solid content, and 28 parts by weight of SrTiO3 ceramic powder having an average particle size of 1500 nm in solid content were added, and stirred with water to prepare a Si diffusion composition. The type of Al alkoxide was changed as shown in Table 2 below.

[0177] The manufactured Si diffusion composition was applied to a cold-rolled sheet at 50 g / m 2 It was applied in a quantity and dried at 650℃ for 8 seconds.

[0178] A cold-rolled sheet coated with a Si diffusion composition was diffusion-annealed at 900°C for 2 hours in an atmosphere containing 50% by volume of argon, 50% by volume of hydrogen, and an oxidation capacity of 1.22.

[0179] The surface of the steel plate on which diffusion annealing was completed was washed with water, dried at room temperature, and then etched under atmospheric pressure plasma conditions to remove unreacted substances, thereby manufacturing a 0.1 mm thick non-oriented electrical steel plate.

[0180] As a result of analysis using a scanning electron microscope / energy-dispersive X-ray spectrometer, it was confirmed that the average steel composition in the thickness direction of the steel plate included Si: 7.0 wt%, Al: 1.5 wt%, Mn: 0.15 wt%, P: 0.01 wt%, Sn: 0.02 wt%, and the remainder was made up of Fe and other unavoidable impurities. ΔSi was confirmed to be 1.3 wt%, and ΔAl was confirmed to be 0.5 wt%.

[0181] Insulation was measured using a Franklin tester.

[0182] Iron loss and magnetic flux density were measured using a single sheet tester.

[0183] Surface characteristics were measured as the surface defect area ratio per unit area through image analysis, and were classified as excellent if less than 0.5%, good if 0.5% or more but less than 5%, fair if 6% or more but less than 10%, poor if 10% or more but less than 20%, and very poor if 20% or more.

[0184] The final steel plate surface roughness characteristics according to the change in Al alkoxide were measured using confocal laser scanning microscopy.

[0185] NoteAl(OR)3, RSingle phase ferriteAverage grain size of ferrite throughout the thickness (㎛)Average grain size of ferrite at the center (㎛)Average grain size of ferrite at the surface (㎛)Surface roughness of steel sheet (㎛)B25(T)W10 / 1k(W / kg)W5 / 2k(W / kg)Surface conditionExample 2-1MethylO202.0353510.781.5630.05.1NormalExample 2-2EthylO200.5349520.631.5531.45.0GoodExample 2-3n-propylO200.5347540.911.5729.44.7GoodExample 2-4i-propylO203.0354520.211.6424.73.8ExcellentExample 2-5n-butylO197.5348470.191.6124.93.6Excellent Example 2-6s-butylO203.5354530.331.5526.73.9Good Comparative Example 2-1n-pentylO200.5348531.051.4935.87.5Poor Comparative Example 2-2n-hexylO201.5355481.041.4840.29.1Poor Comparative Example 2-3n-heptylO199.5353461.241.4842.512.2Very Poor Comparative Example 2-4Al2O3O202.5353521.561.3356.824.6Very Poor Comparative Example 2-5AlNO198.5350471.441.3756.624.3Very poor

[0186] As shown in Table 2, when Al2O3 or AlN is used instead of Al alkoxide, the magnetism and surface quality are inferior to those of the Al(OR)3 compound. Even when Al(OR)3 is used, if the carbon number of R exceeds 4, the carbon content increases, causing defects on the steel plate surface and ultimately inferior magnetism.

[0187]

[0188] Experimental Example 3: Control of Si powder content

[0189] A slab was prepared containing 2.0 wt% of silicon (Si), 0.03 wt% of aluminum (Al), 0.11 wt% of manganese (Mn), 0.06 wt% of tin (Sn), 0.01 wt% of antimony (Sb), and 0.010 wt% of phosphorus (P), with the remainder being iron and other unavoidable impurities.

[0190] The slab was heated at 1100℃ and then hot-rolled to a thickness of 2.0 mm to produce a hot-rolled plate.

[0191] After coiling the hot-rolled plate at 650°C, it was cooled in the air, annealed at 1055°C for 2 minutes and 30 seconds, then rapidly cooled in water, pickled, and then cold-rolled to a thickness of 0.20 mm to produce a cold-rolled plate.

[0192] On the surface of a cold-rolled sheet, silicon nanoparticles having an average particle diameter of 25 nm were adjusted as shown in Table 3 below, and 10 wt% of aluminum n-butoxide and the remaining Al2O3 ceramic powder having an average particle diameter of 1000 nm were mixed with water to prepare a Si diffusion composition.

[0193] The manufactured Si diffusion composition was applied and dried at 350°C for 60 seconds.

[0194] A cold-rolled sheet coated with a Si diffusion composition was subjected to diffusion annealing at 1150°C for 7 hours in a mixed atmosphere of 75% by volume of hydrogen and 25% by volume of nitrogen, with the oxidation capacity adjusted to 0.65.

[0195] The surface of the steel plate after diffusion annealing was washed with water, dried at room temperature, and then etched under atmospheric pressure plasma conditions to remove unreacted substances.

[0196] As a result of analysis using EPMA (Electron Probe Micro-Analyzer), it was confirmed that the average steel composition in the thickness direction of the steel plate included Al: 0.9 wt%, Mn: 0.11 wt%, P: 0.010 wt%, Sn 0.06 wt%, Sb 0.01 wt%, and the remainder was composed of Fe and other unavoidable impurities. ΔAl was confirmed to be 0.25 wt%.

[0197] Si powder (wt%)Si content (wt%)Single phase ferriteOr notTotal thickness ferrite average grain size (㎛)Center ferrite average grain size (㎛)Surface ferrite average grain size (㎛)B25(T)W5 / 2k(W / kg)Example 4-1104.0O195.0375151.61215.4Example 4-2285.0O212.5404211.57313.7Example 4-3496.0O223.5422251.4708.5Example 4-4707.0O257.5481341.46210.9Example 4-5555.5O236.0445271.5259.8Example 4-6164.5O202.0386181.57914.7Comparative example 4-193.9O186.036661.61325.7Comparative example 4-2757.1X282.0523411.45017.5Comparative example 4-3809.2X312.5577481.42218.3Comparative example 4-49010.7X328.0603531.32219.9

[0198] As shown in Table 3, when the content of Si powder is very small, it can be confirmed that the ferrite particle size of the surface is not secured and the magnetism is poor.

[0199] When the content of Si powder is very large, Si is not properly diffused into the center, so only the ferrite grain size in the center becomes very coarse in order to secure the grain size of the surface, ultimately confirming poor magnetism.

[0200]

[0201] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Contains Si: 4.0 to 7.0% by weight, Al: 0.001 to 3.0%, and Mn: 0.03 to 2.0%, and the remainder includes Fe and inevitable impurities. Al content at the center of plate thickness (t / 2) [CM Al ] and the maximum Al content in the area from the surface to the inner direction of the non-oriented electrical steel sheet up to 5% of the total thickness [SM Al ] difference ([SM Al ]-[CM Al ]) is defined as ΔAl of 0.1 wt% or more, A non-oriented electrical steel sheet having a single-phase ferrite structure and an average ferrite grain size of 100 to 300 ㎛.

2. In paragraph 1, A non-oriented electrical steel sheet having a maximum Si content of 4 to 8 wt% in a region from the surface to 5% of the total thickness in the inner direction, and a Si content at the center position of the plate thickness (t / 2) of 0.01 to 7.0 wt%.

3. In paragraph 1, Si content at the center of plate thickness (t / 2) [CM Si ] and the maximum Si content in the area from the surface to the inner direction of the non-oriented electrical steel sheet up to 5% of the total thickness [SM Si ] difference ([SM Si ]-[CM Si ]) is a non-oriented electrical steel sheet having ΔSi of 0.1 wt% or more.

4. In paragraph 1, Non-oriented electrical steel sheet with a surface roughness (Ra) of 1.00㎛ or less.

5. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of C, N, S, Ti, Nb, and V, each in an amount of 0.005 wt% or less.

6. In paragraph 1, A non-oriented electrical steel sheet further comprising at least one 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.

7. In paragraph 1, Non-oriented electrical steel sheet further containing 0.200 wt% or less of each or a combination of Bi, Pb, Ge and As.

8. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

9. A step for manufacturing a cold rolled sheet comprising: Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0% by weight, with the remainder being Fe and unavoidable impurities; A step of applying a Si diffusion composition containing Si powder and Al alkoxide to the cold rolled plate; and Including a step of diffusion annealing the above cold rolled sheet, The above Al alkoxide is Al(OR) n (R) 3-n , wherein R is an alkyl group having 1 to 4 carbon atoms or an alkenyl group having 2 to 4 carbon atoms, and n is an integer of 1 to 3. A method for manufacturing a non-oriented electrical steel sheet, wherein the above diffusion annealing step is performed at a soaking temperature of 850°C to 1,250°C for 30 to 600 minutes.

10. In paragraph 9, In the step of applying the Si diffusion composition, the amount of the Si diffusion composition applied is 0.1 to 300 g / m. 2 A method for manufacturing a non-oriented electrical steel sheet.

11. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the temperature is increased in a temperature range of 20 to 700°C at a rate of 5 to 50°C / hr prior to the above-mentioned diffusion annealing step.

12. In paragraph 9, The above diffusion annealing step is a method for manufacturing a non-oriented electrical steel sheet in which the annealing is performed in an atmosphere having an oxidation capacity (PH2O / PH2) of 6.4 or less.

13. In paragraph 9, The steps for manufacturing the above cold rolled plate are: A step of manufacturing a hot-rolled sheet by hot-rolling a slab containing, by weight %, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and unavoidable impurities; and A method for manufacturing a non-oriented electrical steel sheet, comprising the step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet.