Non-oriented electrical steel sheet and method for manufacturing same

Abstract

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, by weight %, 0.3% to 4.0% of Si, 0.001% to 2.0% of Al, and 0.03% to 2.0% of Mn, with the remainder being Fe and unavoidable impurities; a first coating step of applying a Si diffusion composition including a Si compound onto the surface of the cold-rolled sheet; a first drying step of drying the Si diffusion composition to form a Si diffusion coating layer; a second coating step of applying the Si diffusion composition onto the dried surface of the steel sheet; a second drying step of drying the Si diffusion composition; and a step of diffusion annealing the cold-rolled sheet.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[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, which improves magnetism and simultaneously improves insulation by diffusing silicon (Si) from the surface of the steel sheet into the interior of the steel sheet.

[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 Si through SiCl4 gas onto the surface of cold-rolled steel sheets. However, this method utilizes highly toxic and chemically unstable SiCl4 gas, and is constrained by the requirement for equipment that must be produced under high-vacuum conditions, making it difficult to produce electrical steel sheets with a width exceeding 500 mm. Furthermore, the generation of by-product gases such as FeCl2 under high-vacuum conditions is environmentally hazardous and presents problems with poor insulation properties, necessitating a fundamental solution.

[0006] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, wherein silicon (Si) is diffused from the surface of the steel sheet into the interior of the steel sheet to enhance magnetism and simultaneously improve insulation.

[0007] 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 2.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and inevitable impurities, and an unreacted residual composition layer present on the surface of 5 area% or less. Here, the unreacted residual composition layer is a residual Si composition layer that is not involved in diffusion and contains Si by 90% or more.

[0008] The surface roughness (Ra) of the steel plate can be 0.3㎛ to 1.0㎛.

[0009] 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.

[0010] 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.

[0011] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one 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%).

[0012] 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 (excluding 0%), Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.1 wt% or less (excluding 0%), Sb: 0.1 wt% or less (excluding 0%), Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Bi: 0.200 wt% or less (excluding 0%), Pb: 0.200 wt% or less (excluding 0%), Ge: 0.200 wt% or less (excluding 0%), and As: 0.200 wt% or less (excluding 0%).

[0014] 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 (excluding 0%), B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0015] 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 including, in wt%, 0.3 to 4.0% of Si, 0.001 to 2.0% of Al, and 0.03 to 2.0% of Mn, with the remainder being Fe and unavoidable impurities; a first coating step of applying a Si diffusion composition including a Si compound to a surface of the cold-rolled sheet; a first drying step of drying the Si diffusion composition to form a Si diffusion coating layer; a second coating step of applying the Si diffusion composition to the dried surface of the steel sheet; a second drying step of drying the Si diffusion composition; and a step of diffusion annealing the cold-rolled sheet.

[0016] The Si diffusion composition further comprises an Al compound, and may comprise 100 parts by weight of the Si compound and 1 to 50 parts by weight of the Al compound as a solid content.

[0017] The Si diffusion composition may further comprise 10 to 1000 parts by weight of a ceramic powder comprising an oxide, nitride, carbide or oxynitride comprising at least one selected from Li, B, Ca, Sr, Mg, Al P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn and Ba as a component.

[0018] The average particle size of the Si compound may be 1 to 850 nm.

[0019] The average particle size of the Al compound may be 8 to 2500 nm.

[0020] The average particle size of the ceramic powder may be 8 to 2500 nm.

[0021] In the first and second application steps, the application amount of the Si diffusion composition is 0.1 to 300 g / m 2 It could be.

[0022] Before cracking in each of the first diffusion annealing step and the second annealing step, the temperature range of 300 to 400°C can be increased at a rate of 5 to 50°C / hr.

[0023] In either the first or second application steps, the application direction of the Si diffusion composition may form an angle of 80 to 100° with the rolling direction.

[0024] In the first application step, the application direction may form an angle of -10 to 10° with the rolling direction, and in the second application step, the application direction of the Si diffusion composition may form an angle of 80 to 100° with the rolling direction.

[0025] In each of the first drying step and the second drying step, the cooling rate after drying may be 20°C / sec or more.

[0026] The cracking temperature in the diffusion annealing step can be 800 to 1200°C.

[0027] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and high-frequency iron loss.

[0028] 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.

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent surface characteristics because there is no residual unreacted composition on the surface.

[0030] Figure 1 is a photograph of a cross-section of a non-oriented electrical steel sheet manufactured in Example 1, analyzed using an optical microscope.

[0031] Figure 2 is a photograph of a cross-section of a non-oriented electrical steel sheet manufactured in Comparative Example 11, analyzed using an optical microscope.

[0032]

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

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

[0038] 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.

[0039] 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.

[0040]

[0041] 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 3.0%, with the remainder being Fe and unavoidable impurities.

[0042] First, let's explain the reason for the limitation of the components of non-oriented electrical steel sheets.

[0043] Si: 4.0 to 7.0 wt%

[0044] 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.

[0045] 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 within the steel sheet. If there is too little Si within the steel sheet, it is difficult to expect the aforementioned effect due to Si. If too much Si is included, there is a problem of poor workability when processing the electrical steel sheet into products such as motors. In one embodiment of the present invention, due to Si diffusion 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 within the steel sheet refers to the average content in the direction of the thickness. The average content refers to the content assuming that Si within the steel sheet is uniformly distributed in the direction of the thickness of the steel sheet. More specifically, 4.5 to 6.5 wt% of Si may be included.

[0046] 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 0.3 to 7.5 wt%.

[0047] 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 into 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 a 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 area can be 4.5 to 7.5 wt%.

[0048] 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 that sufficient Si has not been diffused, and the improvement in high-frequency iron loss through high-concentration Si may not be fully achieved. An excessively high Si content in the center may result in poor processability. More specifically, the Si content in the center may be 2.5 to 6.0 wt%.

[0049] 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 ]) can be 0.1 wt% or more. When there is an appropriate difference in Si content between the center and the surface, high-frequency iron loss and processability can be further improved. More specifically, ΔSi can be 0.5 to 3.0 wt%.

[0050] As described above, in one embodiment of the present invention, Si in the Si compound 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 2.0 to 3.5 wt% of Si. If there is too little Si in the slab and the cold-rolled sheet before diffusion, the amount of Si required for diffusion increases, diffusion annealing takes a long time, which is not efficient, and the difference in Si content depending on the sheet thickness becomes large, making it difficult to obtain an appropriate high-frequency iron loss. If there is too much Si in the slab and the cold-rolled sheet before diffusion, the steel sheet may be broken during the cold rolling process, or defects may occur in the steel sheet. More specifically, the Si in the slab may be 2.3 to 3.3 wt%.

[0051]

[0052] Al: 0.001 to 3.0 wt%

[0053] 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 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 wt%. 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 0.1 to 1.5 wt%.

[0054] 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 of Al can occur in the direction of the thickness of the steel sheet.

[0055] 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 ]) can be 0.1 wt% or more. When there is an appropriate difference in Al content between the center and the surface, high-frequency iron can be further improved.

[0056] 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 0.1 to 3.0 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 diffused into the interior of 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 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 by GOD, FTIR, wet analysis, TEM-GDS, and SEM-GDS methods. More specifically, the maximum Al content in the surface portion can be 0.5 to 1.0 wt%.

[0057] The Al content in the center may be 0.001 to 2.0 wt%. A low Al content in 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. An excessively high Al content in the center may result in a problem of deterioration in magnetic flux density. More specifically, the Al content in the center may be 0.5 to 1.0 wt%.

[0058] As described above, in one embodiment of the present invention, Al in the Al compound 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 2.0 wt% 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, Al oxide may clump together in some locations, which may cause cracking during rolling. More specifically, the slab and the cold-rolled sheet before diffusion may contain 0.001 to 1.8 wt% Al. More specifically, the slab and the cold-rolled sheet before diffusion may contain 0.01 to 1.0 wt% Al.

[0059]

[0060] Mn: 0.03 to 3.0 wt%

[0061] Manganese (Mn) improves iron loss by increasing the resistivity of the material and plays a role in forming sulfides. If too little Mn is added, MnS may precipitate finely, which may deteriorate the magnetism. If too much Mn is added, it may promote the formation of

[0111] texture which 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 from the surface to the center, but from the center to the surface. This is because Mn volatilizes at the surface during the Si diffusion annealing process, and Mn diffuses 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 inside, and at this time, the diffusion direction is similar to the direction of diffusion. <100> / ND is formed in an environment favorable for its formation. More specifically, Mn may be 0.05 to 2.0 wt%.

[0062] 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.

[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 0.005 to 0.03 wt%.

[0065] Cu: 0.005 to 0.200 wt%

[0066] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu·Mn)S may occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement may occur, leading to cracks during casting or hot rolling. More specifically, Cu may be present in an amount of 0.01 to 0.100 wt%.

[0067] Cr: 0.010 to 0.50 wt%

[0068] 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, the lower limit for Cr is 0.05 wt% and 0.30 wt%.

[0069] Sn: 0.10 wt% or less

[0070] 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 to improve 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 aforementioned range. More specifically, Sn may be included in an amount of 0.005 to 0.08 wt%.

[0071] Sb: 0.10 wt% or less

[0072] Antimony (Sb) is added to suppress the diffusion of nitrogen through grain boundaries as a segregating element at grain boundaries, suppress the {111} texture detrimental to magnetism, and increase the {100} texture, thereby improving magnetic properties. If too much Sb is added, it hinders grain growth, lowering magnetism and deteriorating rolling properties. Therefore, Sb may be added within the aforementioned range. More specifically, Sb may be included in an amount of 0.005 to 0.08 wt%.

[0073] Ni: 0.05 wt% or less

[0074] 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 can be included in an amount of 0.005 to 0.03 wt%.

[0075] Zn: 0.01 wt% or less

[0076] Zinc (Zn) can act as an impurity and degrade magnetism if the content is excessive. Therefore, Zn may be added further within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 wt%.

[0077]

[0078] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 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.

[0079] 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, it may further include at least one 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%.

[0080]

[0081] 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, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0082] Since these may react with the inevitably included C, S, N, etc. to form fine carbides, nitrides, or sulfides, which may adversely affect magnetism, the upper limit may be limited as described above. More specifically, it may further include at least one 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%.

[0083]

[0084] Other impurities

[0085] 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.

[0086] N combines with Ti, Nb, and V to form nitrides and plays a role in reducing grain growth.

[0087] C reacts with N, Ti, Nb, V, etc. to form fine carbides, which hinder grain growth and domain movement.

[0088] S forms sulfides, which impairs grain growth.

[0089] In this case, when impurity elements are further included, 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 further included. More specifically, it may further include at least one 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%.

[0090] 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.

[0091]

[0092] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have an unreacted residual composition layer of 5% by area or less on the surface. In one embodiment of the present invention, Si is diffused from the surface of the steel sheet to the inside using a Si diffusion composition. When a Si diffusion composition is used, even if the reaction proceeds for a long time, an unreacted residual composition inevitably exists, and when a large amount of this unreacted residual composition exists, the surface properties of the steel sheet are deteriorated and the adhesion between the steel sheets and the space factor are adversely affected. To remove the unreacted residual composition, a pickling method may be considered, but in this case, the roughness of the steel sheet surface may rather worsen. The unreacted residual composition layer is distinguished from the steel sheet surface outside the unreacted residual composition layer in that it contains Si by 90% by weight or more. The unreacted residual composition layer refers to an area fraction with respect to the area of ​​the steel sheet surface. More specifically, the unreacted residual composition layer may contain 0.1 to 3% by area.

[0093] In one embodiment of the present invention, a Si diffusion composition is applied in multiple portions and dried, thereby utilizing the difference in thermal expansion coefficient between the unreacted residual composition on the surface and the internally diffused iron, thereby naturally causing the unreacted residual composition to fall off. This allows the unreacted residual composition layer attached to the surface to be removed as much as possible. The unreacted residual composition layer can be distinguished from other steel sheets by having an Si content of 90 wt% or more.

[0094] The surface roughness (Ra) of the steel sheet may be 0.30 ㎛ to 1.00 ㎛. As mentioned above, when pickling to remove unreacted residual composition, the surface roughness increases, which adversely affects the adhesion between the steel sheets and the space factor. When diffusing Si using a Si diffusion composition, some roughness may inevitably be formed. More specifically, the surface roughness (Ra) of the steel sheet may be 0.33 ㎛ to 0.75 ㎛.

[0095] Surface roughness (Ra) can be measured using a surface roughness meter.

[0096] 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. Specifically, the iron loss (W 10 / 1000 ) may be 45.0 W / kg or less. At this time, the 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 1.0 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 ) can be 25.00 W / kg to 35.00 W / kg.

[0097] Also, iron loss (W 5 / 2000 ) may be less than 16.5 W / kg. At this time, the 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 0.5 T is induced at a frequency of 2000 Hz. More specifically, the iron loss (W 5 / 2000 ) can be 10.0 W / kg to 15.0 W / kg.

[0098] 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 1.50 to 1.65T.

[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 including, in wt%, Si: 0.3 to 4.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and unavoidable impurities; a first coating step of applying a Si diffusion composition including a Si compound to a surface of the cold-rolled sheet; a first drying step of drying the Si diffusion composition to form a Si diffusion coating layer; a second coating step of applying a Si diffusion composition including a Si compound on the Si diffusion coating layer; a second drying step of drying the Si diffusion composition; and a step of diffusion annealing the cold-rolled sheet.

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

[0101] First, a cold-rolled sheet is manufactured containing Si: 0.3 to 4.0% by weight, 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.

[0102] The 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 Si: 0.3 to 4.0% by weight, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0% by weight; and a 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 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, during the diffusion annealing process, only Si and Al are diffused, and the alloy composition of the non-oriented electrical steel sheet and the remaining components excluding Si and Al may be the same.

[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 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 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 sheet. In one embodiment of the present invention, a step of preliminary cold rolling prior to cold rolling is also included, so that even if the thickness of 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 1.5 to 3.5 mm.

[0106] The step of manufacturing the hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher.

[0107] 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 850 to 1000°C.

[0108] 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.

[0109] If the temperature during the coiling step is controlled too low, the recovery and recrystallization of the hot-rolled deformation structure will not occur well, and the cooling load will increase in order 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 coiling, which may cause thicker scale formation and the problem of intergranular oxidation. Intergranular oxidation of the hot-rolled sheet may promote intergranular corrosion during the subsequent pickling process, which may increase the possibility of surface stripe defects and severely wear out the rolling rolls. More specifically, the coiling temperature may be 650 to 750°C.

[0110] 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 actually deteriorate, and the rolling workability may deteriorate due to deformation of the sheet shape. More specifically, the hot-rolled sheet annealing temperature may be 750 to 1000°C.

[0111] 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.

[0112] Hot-rolled hot-rolled sheets 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, 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 0.15 to 0.35 mm.

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

[0115] Any Si compound that can diffuse Si into the steel sheet through prolonged annealing may be used without limitation. Specifically, the Si compound may include one or more of pure Si, Si alloys, Si oxides, nitrides, or carbides, and silane compounds. Additionally, the Si compound may include one or more of FeSi, Fe3Si, Fe3Al, and FeAl.

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

[0117] The average particle size of the Si compound may be 1 to 850 nm. If the particle size of the Si compound is too small, the Si compounds may clump together during slurry mixing, which may cause surface defects. If the particle size of the Si compound is too large, it may be difficult to uniformly apply the Si compound 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 compound is the average particle size for the number of compound particles, and can be measured using a particle size analyzer (PSA) using a laser diffraction method. More specifically, the average particle size of the Si compound may be 10 nm to 500 nm. More specifically, it may be 20 nm to 100 nm.

[0118] The Si diffusion composition further includes 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 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.

[0119] Al compounds improve insulation, increase bonding with Si compounds, and facilitate the formation of intermetallic compounds. If too little Al is included, it may be difficult to achieve the aforementioned effects. If too much Al is included, numerous Al inclusions may form, resulting in reduced magnetism. More specifically, the Al compound may be included in an amount of 15 to 30 parts by weight.

[0120] Any substance capable of diffusing Al into the steel plate may be used as the Al compound without limitation. Examples include pure Al 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, the Al compounds may agglomerate with each other. If the particle size of the Al compound is too large, the Al may not diffuse smoothly into the steel sheet. 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 comprise a ceramic powder comprising an oxide, nitride, carbide or oxynitride comprising at least one selected from Li, B, Ca, Sr, Mg, Al, 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 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 in terms of solid content. If the ceramic powder is included in too little, problems may arise in securing the coating amount. If the ceramic powder is included in too much, the slurry viscosity may increase, which may lead to 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 at least one of Al2O3, TiO2, MgO·Al2O3, MgO·TiO2, 3Al2O3·2SiO2, ZrO2·SiO2, TiN, CrN, SrTiO3, MgAl2O4, Y2O3, FeTiO3, and Li2O·Al2O3·SiO2.

[0125] 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 Si into the steel sheet. More specifically, the average particle size of the ceramic powder may range from 10 nm to 1500 nm.

[0126] 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 Si compound. More specifically, the solvent may be included in an amount of 50 to 1000 parts by weight. The solvent may include at least one of water and alcohol.

[0127] In addition to the components 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 additional components may include phosphoric acid, sodium silicate, and fluoride ion solutions.

[0128] In the first application step, the application amount of the Si diffusion composition is 0.1 to 300 g / m 2 This may be the case. The application amount is based on the solid content. If the application amount is too small, sufficient Si diffusion will not occur, making it difficult to fully achieve the effects of Si diffusion. If the application amount is too large, poor processability may occur.

[0129] Application methods include roll coaters, brushes, and dipping. From a productivity perspective, a roll coater is preferred.

[0130] The coating may be applied at an angle of -10 to 10° with respect to the rolling direction, or at an angle of 80 to 100° with respect to the rolling direction. More specifically, the coating may be applied at an angle of -5 to 5° with respect to the rolling direction, or at an angle of 85 to 95° with respect to the rolling direction. From a productivity perspective, the coating may be applied at an angle of -10 to 10° with respect to the rolling direction.

[0131] After the first coating step, in the first drying step, the Si diffusion composition is dried to form a Si diffusion coating layer. The drying temperature is sufficient as long as it can remove the solvent in the Si diffusion composition, and may be specifically 300 to 850°C. The drying time may be 10 to 180 seconds. More specifically, the temperature may be 500 to 800°C. The drying time may be 15 to 150 seconds. After drying at the drying temperature, cooling may be performed at a cooling rate of 20°C / sec or more. By rapidly cooling in this manner, the difference in heat shrinkage between the steel sheet and the unreacted composition layer can be utilized to induce automatic shedding of the unreacted residual composition. The cooling section may be from the drying temperature to 100°C.

[0132] Next, in the second application step, a Si diffusion composition is applied to the dried steel plate surface. At this time, the Si diffusion composition may be the same as or different from the Si diffusion composition applied in the first application step. Since the Si diffusion composition has been described above, a redundant description will be omitted.

[0133] In one embodiment of the present invention, the phenomenon of natural sloughing off of the unreacted residual composition on the surface is utilized by utilizing the difference in thermal expansion coefficient between the unreacted residual composition on the surface and the internally diffused iron through multiple applications of the first and second application steps. This removes as much unreacted residual composition as possible, thereby improving surface properties. The application step can be applied not only twice, but also three or more times. In other words, the application and drying steps of the Si diffusion composition can be repeated three or more times.

[0134] In the second application step, the application amount of the Si diffusion composition is 0.1 to 300 g / m 2 This may be the case. The application amount is based on the solid content. If the application amount is too small, sufficient Si diffusion will not occur, making it difficult to fully achieve the effects of Si diffusion. If the application amount is too large, poor processability may occur.

[0135] Application methods include roll coater, brush, and dipping. From a productivity perspective, application can be done using a roll coater.

[0136] The coating may be applied in an angle of -10 to 10° with respect to the rolling direction, or in an angle of 80 to 100° with respect to the rolling direction. More specifically, the coating may be applied in an angle of -5 to 5° with respect to the rolling direction, or in an angle of 85 to 95° with respect to the rolling direction. In order to more easily remove the unreacted residual composition, the coating may be applied in the second coating step in an angle of 80 to 100° with respect to the rolling direction. In this case, the bonding with the previously applied and dried Si diffusion composition is not sufficient, and some space remains. Due to this, a gap opens between the unreacted slurry and the steel sheet due to the difference in thermal expansion coefficient between the unreacted residual composition on the surface and the thermal expansion coefficient of the internally diffused iron, and at this time, the unreacted slurry naturally falls off.

[0137] After the second coating step, in the second drying step, the Si diffusion composition is dried to form a Si diffusion coating layer. The drying temperature is sufficient as long as it can remove the solvent in the Si diffusion composition, and may be specifically 300 to 850°C. The drying time may be 10 to 180 seconds. More specifically, the temperature may be 500 to 800°C. The drying time may be 15 to 150 seconds. After drying at the drying temperature, cooling may be performed at a cooling rate of 20°C / sec or more. By rapidly cooling in this manner, the difference in heat shrinkage between the steel sheet and the unreacted composition layer can be utilized to induce automatic shedding of the unreacted residual composition. The cooling section may be from the drying temperature to 100°C.

[0138] 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.

[0139] 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 rate of temperature increase allows for consistent quality. If the temperature increase rate is too slow, the process time will be unnecessarily prolonged and productivity will decrease. If the temperature increase rate is too fast, the aforementioned effects cannot be adequately achieved. More specifically, the temperature can be increased at a rate of 10 to 30°C / hr.

[0140] The diffusion annealing temperature may be between 850°C and 1250°C. If the diffusion annealing temperature is too low, Si diffusion 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 temperature may be between 900°C and 1150°C.

[0141] The time can range from 30 to 600 minutes. If the time is too short, the diffusion of Si and Ti 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 diffusion, and processability may be poor. More specifically, the time can range from 60 to 300 minutes.

[0142] During diffusion annealing, the atmosphere 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 Al2O3 may be formed, which may deteriorate the magnetism. Specifically, the oxidation capacity (PH2O / PH2) of the atmosphere may be 3.0 or less. Specifically, the oxidation capacity (PH2O / PH2) of the atmosphere may be 1.0 or less.

[0143] After diffusion annealing, the final thickness of the steel sheet can be 0.10 to 0.65 mm, and the thickness can be increased somewhat compared to the cold rolled sheet due to the application and diffusion of the Al diffusion composition.

[0144] The steel sheet after diffusion annealing may further include a washing and drying step to remove unreacted substances.

[0145] Steel sheets that have undergone diffusion annealing may further include a pickling step to make their surface more attractive.

[0146] The acid may be prepared using at least one acid selected from hydrochloric acid, nitric acid, sulfuric acid, and hydrofluoric acid.

[0147] The steel sheet after diffusion annealing may further include a plasma treatment step to make the surface more beautiful.

[0148] Afterwards, a step of forming an insulating film may be further included. Since insulating films are widely known, a detailed description thereof will be omitted. Specifically, an insulating coating layer may be formed by applying an insulating coating layer-forming composition containing metal phosphate and silica as main components and performing heat treatment.

[0149]

[0150] 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.

[0151]

[0152] Experimental example

[0153] 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.

[0154] The slab was heated at 1100℃ and then hot-rolled to a thickness of 1.8 mm to produce a hot-rolled plate.

[0155] 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 0.20 mm to produce a cold-rolled plate.

[0156] On the surface of a cold-rolled sheet, 100 parts by weight of silicon powder (Si: 99.99 wt% or more) having an average particle size of 15 nm and 80 parts by weight of Al2O3 ceramic powder having an average particle size of 1000 nm were added and stirred with water to prepare a Si diffusion composition.

[0157] The manufactured Si diffusion composition was applied to a cold-rolled plate. The application direction was as shown in Table 1. It was dried at 600°C for 1 minute. After drying, the cooling rate to 100°C was as shown in Table 1 below.

[0158] A Si diffusion composition was applied to a dried steel plate. The application direction was as shown in Table 1. Drying was performed at 600°C for 1 minute. After drying, the cooling rate to 100°C was as shown in Table 1 below.

[0159]

[0160] A cold-rolled sheet coated with a Si diffusion composition was diffusion annealed at 1000°C for 1 hour.

[0161] The surface of the steel plate on which diffusion annealing was completed was washed with water, dried at room temperature, and then immersed in a nitric acid solution containing 0.5% hydrofluoric acid at 65°C for 12 seconds to remove unreacted substances, washed again with water, and finally dried to manufacture a 0.2 mm thick non-oriented electrical steel plate.

[0162] The Si content of the final manufactured steel plate was 5.3 wt%, the Al content was 1.2 wt%, ΔSi was 2.3 wt%, and ΔAl was 0.4 wt%.

[0163] The presence or absence of peeling of the unreacted layer was measured by observing the thickness direction using an optical microscope. If the area of ​​the unreacted layer remaining on the steel plate surface was 5% or less, it was expressed as complete peeling. If the area of ​​the unreacted layer remaining was 50% or less but more than 5%, it was expressed as partial peeling. If the area of ​​the unreacted layer remaining was more than 50%, it was expressed as non-peeling.

[0164] Steel grade 1 Application direction 2 Application direction 1 Dry cooling rate (℃ / sec) 2 Dry cooling rate (℃ / sec) 1 Rolling direction Rolling vertical direction 20 20 2 Rolling direction Rolling vertical direction 25 35 3 Rolling direction Rolling vertical direction 35 25 4 Rolling direction Rolling vertical direction 40 40 5 Rolling direction Not performed 30 Not performed 6 Rolling vertical direction Not performed 30 Not performed 7 Rolling direction Not performed 15 Not performed 8 Rolling direction Rolling direction 30 30 9 Rolling direction Rolling direction 40 40 10 Rolling direction Rolling vertical direction 10 30 11 Rolling direction Rolling vertical direction 30 10 12 Rolling vertical direction Rolling vertical direction 30 30

[0165] Steel type Unreacted residual layer peeling presence or absence Surface roughness (Ra, ㎛) B25 (T) W10 / 1000 (W / kg) Type 1 Peeling 0.34 1.66 32.5 Example 2 Peeling 0.42 1.60 33.2 Example 3 Peeling 0.38 1.67 31.9 Example 4 Peeling 0.53 1.67 34.7 Example 5 Not peeled 1.23 1.47 51.2 Comparative example 6 Not peeled 2.32 1.44 50.4 Comparative example 7 Not peeled 2.34 1.48 53.4 Comparative example 8 Partially Not peeled 0.57 1.51 42.4 Comparative example 9 Partially Non-peeling 0.65 1.55 47.2 Comparative Example 10 Non-peeling 1.1 2 1.54 47.4 Comparative Example 11 Non-peeling 0.76 1.48 46.3 Comparative Example 12 Peeling 0.35 1.52 35.9 Example

[0166] As shown in Tables 1 and 2, when the Si diffusion composition is applied twice, the application direction is appropriately performed, and the material is rapidly cooled after drying, the increase in iron loss caused by the unreacted residual composition is significantly reduced, the surface properties are improved, and it can be confirmed that the magnetism is excellent. Figure 1 shows the results of an optical microscope analysis of a cross-section of a steel grade. As shown in Figure 1, it can be confirmed that the unreacted residual composition layer is peeled off from the surface, and a steel plate with low roughness is produced.

[0167] On the other hand, steel types 5 to 7 were coated with the Si diffusion composition only once, and a large amount of unreacted residual composition was present, so that the unreacted residual composition was present and the surface roughness characteristics were deteriorated, confirming poor magnetism. The results of an optical microscope analysis of the cross-section of the steel types are shown. As shown in Fig. 2, it can be confirmed that a layer of unreacted residual composition that was not peeled off on the surface was present, and a steel plate with high roughness was produced.

[0168] Steel types 8 and 9 were applied twice, but it can be confirmed that some unreacted residual composition was present that was not peeled off because it was applied twice only in the rolling direction.

[0169] It can be confirmed that steel types 10 and 11 have a low cooling rate after drying, and thus an unreacted residual composition layer exists.

[0170]

[0171] 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

Containing Si: 4.0 to 7.0% by weight, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, with the remainder being Fe and inevitable impurities; A non-oriented electrical steel sheet having an unreacted residual composition layer on the surface of 5 area% or less. In the first paragraph, The above steel plate is a non-oriented electrical steel plate having a surface roughness (Ra) of 0.3 ㎛ to 1.0 ㎛. In the first paragraph, 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. In the first paragraph, 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 a non-oriented electrical steel sheet having ΔAl of 0.1 wt% or more. In the first paragraph, Non-oriented electrical steel sheet further comprising at least one 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%). In the first paragraph, A non-oriented electrical steel sheet further comprising at least one of P: 0.1 wt% or less (excluding 0%), Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.1 wt% or less (excluding 0%), Sb: 0.1 wt% or less (excluding 0%), Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%). In the first paragraph, Non-oriented electrical steel sheet further comprising at least one of Bi: 0.200 wt% or less (excluding 0%), Pb: 0.200 wt% or less (excluding 0%), Ge: 0.200 wt% or less (excluding 0%), and As: 0.200 wt% or less (excluding 0%). In the first paragraph, Non-oriented electrical steel sheet further comprising at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%). A step for manufacturing a cold rolled sheet comprising Si: 0.3 to 4.0% by weight, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0% by weight, with the remainder being Fe and unavoidable impurities; A first application step of applying a Si diffusion composition containing a Si compound to the surface of the cold-rolled plate; A first drying step of drying the above Si diffusion composition; A second application step of applying a Si diffusion composition onto the surface of a dried steel plate; A second drying step of drying the above Si diffusion composition; and A method for manufacturing a non-oriented electrical steel sheet, comprising the step of diffusion annealing the cold rolled sheet. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the Si diffusion composition further comprises an Al compound and comprises 100 parts by weight of the Si compound and 1 to 50 parts by weight of the Al compound as a solid content. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the Si diffusion composition further comprises 10 to 1000 parts by weight of a ceramic powder comprising an oxide, nitride, carbide or oxynitride containing at least one selected from Li, B, Ca, Sr, Mg, Al, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn and Ba as a component. In Article 9, A method for manufacturing a non-oriented electrical steel sheet wherein the average particle size of the Si compound is 1 to 850 nm. In Article 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the average particle size of the Al compound is 1 to 1000 nm. In Article 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the average particle size of the ceramic powder is 8 to 2500 nm. In Article 9, In the first and second coating steps, the coating amount of the Si diffusion composition is 0.1 to 300 g / m. 2 A method for manufacturing a non-oriented electrical steel sheet. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein in any one of the first and second coating steps, the coating direction of the Si diffusion composition forms an angle of 80 to 100° with respect to the rolling direction. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein in the first coating step, the coating direction forms an angle of -10 to 10° with respect to the rolling direction, and in the second coating step, the coating direction of the Si diffusion composition forms an angle of 80 to 100° with respect to the rolling direction. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the cooling rate after drying in each of the first drying step and the second drying step is 20°C / sec or more. In Article 9, A method for manufacturing a non-oriented electrical steel sheet having a cracking temperature of 800 to 1200°C in the above diffusion annealing step.

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