Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, by wt%: 4.0 to 7.0% of Si; 0.001 to 2.0% of Al; 0.03 to 2.0% of Mn; and the remainder of Fe and inevitable impurities, wherein the RPc value of the surface of the steel sheet is 30 to 100, and the sum of oxygen (O) and carbon (O) components in a surface region of 1 mm2 is 1 wt% or less, as measured by EDS compositional analysis using scanning electron microscopy.

Description

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

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet capable of obtaining excellent magnetic flux density and iron loss by diffusing Si from the surface of the steel sheet into the interior of the steel sheet and appropriately imparting surface characteristics, and a method for manufacturing the same.

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

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

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

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

[0006] Accordingly, a method was proposed in which a composition containing Si powder is applied and then diffusion annealed to diffuse the Si component onto the surface of the electrical steel sheet. In this case, shot blasting or immersion in an acid solution was proposed to remove unreacted residues after diffusion annealing. However, the shot blasting method has the problem of making the surface roughness of the steel sheet very rough. Immersion in an acid solution can lower the surface roughness, but it causes surface contamination and has an adverse effect on iron loss.

[0007]

[0008] One embodiment of the present invention aims to provide a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention aims to provide a non-oriented electrical steel sheet and a method for manufacturing the same, in which Si is diffused from the surface of the steel sheet into the interior of the steel sheet and surface characteristics are appropriately controlled at the same time to improve iron loss along with magnetic flux density.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percent, Si: 4.0 to 7.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and the remainder is Fe and unavoidable impurities, the RPc value of the steel sheet surface is 30 to 100, and in scanning electron microscope (EDS) component measurement, the surface 1 mm 2The sum of the oxygen (O) and carbon (C) components in the region is 1 weight% or less.

[0010] The Rp value may be 0.5 to 2.0 μm, and the Rv may be 0.5 to 2.0 μm.

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

[0012] Al content at the center of plate thickness (t / 2) [CM Al ] and maximum Al content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Al The difference of ] ([SM Al ]-[ CM Al ΔAl, defined as ]), may be 0.1 weight% or more.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of C: 0.005 wt% or less (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%).

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less (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%).

[0015] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more types of Bi: 0.200 wt% or less (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%).

[0016] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less (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%).

[0017] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a cold-rolled sheet comprising, in weight percent, Si: 0.3 to 4.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and the remainder being Fe and unavoidable impurities; a coating step of applying a Si diffusion composition comprising a Si compound to the surface of the cold-rolled sheet; a diffusion annealing step of the cold-rolled sheet; and a diffusion annealing step of pickling the diffusion-annealed steel sheet.

[0018] The pickling step involves immersing in a mixed solution in which the concentration of nitric acid (HNO3) is 30 g / L to 100 g / L and the concentration of hydrofluoric acid (HF) is 3 g / L to 10 g / L.

[0019] The mixed solution may have a concentration ratio of nitric acid to hydrofluoric acid (HNO3 / HF) of 10 to 30.

[0020] A brushing step can be included before the pickling step.

[0021] In the brushing step, the strength of the brush bristles may be 50 MPa to 90 MPa.

[0022] After the pickling step, a secondary brushing step may be included.

[0023] After the second brushing step, a second acid cleaning step of immersing the steel plate in an acid solution may be further included.

[0024] The step of manufacturing a cold-rolled sheet may include: a step of manufacturing a hot-rolled sheet by hot-rolling a slab comprising, in weight percent, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and the remainder being Fe and unavoidable impurities; and a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet.

[0025] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and high-frequency iron loss.

[0026] 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.

[0027] A non-oriented electrical steel sheet according to one embodiment of the present invention has surface characteristics appropriately controlled, so that surface contamination does not occur and iron loss is further improved.

[0028] Figure 1 is a photograph taken with an optical microscope after the surface of the steel plate was polished in an aqueous solution (H2O) following diffusion annealing in Example 1.

[0029] Figure 2 is an optical microscope image of the surface of the steel plate after it was polished following diffusion heat treatment in No. 1 and then pickled with a hydrochloric acid solution.

[0030] Figure 3 is a photograph of the steel plate surface observed with an optical microscope after the steel plate surface was polished in a mixed acid (nitric acid + hydrofluoric acid) solution following diffusion heat treatment in No. 1.

[0031] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0032] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0033] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0034] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0035] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0036] In one embodiment of the present invention, the meaning of including additional elements is that the remainder of iron (Fe) is replaced by an amount of the additional element.

[0037] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0038]

[0039] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 4.0 to 7.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and the remainder is Fe and unavoidable impurities.

[0040] First, I will explain the reason for the composition limitation of non-oriented electrical steel sheets.

[0041] Si: 4.0 to 7.0 wt%

[0042] Silicon (Si) plays a role in lowering iron loss by increasing the resistivity of the material, so it must be added in relatively large amounts. As the Si content increases, eddy current losses are reduced, which can lower iron loss at high frequencies. In particular, when Si is included at 6.0 wt% or more, magnetostriction, which is a cause of noise, decreases to zero and permeability increases to the maximum, making it possible to manufacture electrical steel sheets with excellent high-frequency characteristics. However, when the Si content is 4 wt% or more, the ductility of the electrical steel sheet decreases significantly, and there is a limit where it is difficult to manufacture electrical steel sheets using a conventional rolling process.

[0043] In one embodiment of the present invention, Si is diffused from the surface of the steel plate into the interior of the steel plate to add 4 weight percent or more of Si to the steel plate. If the amount of Si in the steel plate is too low, it is difficult to expect the aforementioned effects due to Si. If too much Si is included, there is a problem where the processability of the electrical steel plate becomes inferior when processed into products such as motors. In one embodiment of the present invention, due to the diffusion of Si from the surface to the interior, a Si concentration gradient may exist in the thickness direction of the steel plate, and unless otherwise stated, the Si content in the steel plate refers to the average content in the thickness direction. Average content refers to the content assuming that the Si in the steel plate is uniformly distributed in the thickness direction of the steel plate. More specifically, Si may be included in 4.5 to 6.5 weight percent.

[0044] The maximum Si content in the region from the surface of the non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness may be 4.0 to 7.0 weight%, and the Si content at the center of the sheet thickness position (t / 2) may be 0.3 to 7.0 weight%.

[0045] In one embodiment of the present invention, since a steel sheet containing a high concentration of Si is manufactured by diffusing Si from the surface of the steel sheet into the interior of the steel sheet, a concentration gradient may occur in the thickness direction of the steel sheet. That is, the maximum Si content in the region from the surface of the non-oriented electrical steel sheet to 5% of the total thickness in the interior direction (i.e., the surface portion) may be 4.0 to 7.0 weight%. If the Si content in the surface portion is low, it means that sufficient Si has not diffused, and thus the improvement in high-frequency iron loss through high-concentration Si may not be sufficiently obtained. If the Si content is too high, it means that a large amount of Si exists only in the surface portion and has not diffused into the interior of the steel sheet, and this also means that the improvement in high-frequency iron loss through high-concentration Si may not be sufficiently obtained. The maximum Si content refers to the highest Si content when measuring the Si concentration in the surface portion in the thickness direction. The maximum Si content can be measured using non-destructive analysis methods such as EPMA (Electron Probe Micro-Analyzer) or Scanning Electron Microscope / Energy-dispersive, X-ray spectroscopy (SEM / EDX). More specifically, the maximum Si content at the surface may be 4.5 to 7.5 weight%.

[0046] The center of the plate thickness refers to the position at half the total thickness of the plate. Hereinafter, it is referred to as the center. If the Si content is low at the center, it means that sufficient Si has not diffused, and the improvement in high-frequency iron loss through high-concentration Si may not be sufficiently achieved. If the Si content is too high at the center, a problem of reduced processability may occur. More specifically, the Si content at the center may be 2.5 to 6.0 weight%.

[0047] Si content at the center of plate thickness (t / 2) [CM Si] and maximum Si content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Si The difference of ] ([SM Si ]-[ CM Si ΔSi, defined as ]), may be 0.1 wt% or more. When there is an appropriate difference in Si content between the center and the surface, high-frequency iron loss and processability can be further improved. More specifically, ΔSi may be 0.5 to 3.0 wt%.

[0048] As previously described, in one embodiment of the present invention, Si within the Si compound in the Si diffusion composition is diffused by diffusion annealing, thereby increasing the Si content, and the steel sheet prior to Si diffusion may contain less Si than previously described. Specifically, the slab and the cold-rolled sheet prior to diffusion may contain 2.0 to 3.5 weight% of Si. If the Si content in the slab and the cold-rolled sheet prior to diffusion is too low, the amount of Si required for diffusion increases, and the diffusion annealing process takes a long time, resulting in low efficiency; furthermore, the difference in Si content by sheet thickness becomes large, making it difficult to obtain appropriate high-frequency iron loss. If the Si content in the slab and the cold-rolled sheet prior to diffusion is too high, the steel sheet may fracture during the cold rolling process or defects may occur within the steel sheet. More specifically, the Si content in the slab may be 2.3 to 3.3 weight%.

[0049] Al: 0.001 to 2.0 wt%

[0050] Aluminum (Al) plays a role in lowering high-frequency iron loss by increasing the resistivity of the material. In one embodiment of the present invention, since the resistivity of the material can be sufficiently increased through the diffusion of Si, the addition of Al may be unnecessary. However, the high-frequency iron loss can be further improved by adding more Al. However, if too much Al is added, the iron loss and surface quality may deteriorate due to the formation of an aluminum silicate-based composite. More specifically, Al may be included in an amount of 0.01 to 2.0 weight%. In one embodiment of the present invention, due to the diffusion of Al from the surface to the interior, a concentration gradient of Al may exist in the thickness direction of the steel plate, and unless otherwise stated, the Al content in the steel plate refers to the average content in the thickness direction. More specifically, Al may be included in an amount of 0.1 to 1.5 weight%.

[0051] In one embodiment of the present invention, since Al is diffused together with Si to produce a steel plate containing a high concentration of Si, a concentration gradient of Al may occur in the thickness direction of the steel plate.

[0052] Al content at the center of plate thickness (t / 2) [CM Al ] and maximum Al content [SM in the region from the surface of the above non-oriented electrical steel sheet in the inward direction up to 5% of the total thickness Al The difference of ] ([SM Al ]-[ CM Al ΔAl, defined as ]), may be 0.1 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.

[0053] The maximum Al content in the region extending from the surface to 5% of the total thickness (i.e., the surface portion) of the non-oriented electrical steel sheet may be 0.1 to 2.0 weight%. If the Al content in the surface portion is low, it means that sufficient Al has not diffused, and thus, sufficient improvement in high-frequency iron loss through Al diffusion may not be 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 sufficient improvement in high-frequency iron loss through Al diffusion may not be 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, or SEM-GDS methods. More specifically, the maximum Al content in the surface portion may be 0.5 to 1.0 weight%.

[0054] The Al content in the center may be 0.001 to 2.0 wt%. If the Al content in the center is low, it means that sufficient Al has not diffused, and the improvement in high-frequency iron loss through Al diffusion may not be sufficiently obtained. If the Al content in the center is too high, a problem of deterioration in magnetic flux density may occur. More specifically, the Al content in the center may be 0.5 to 1.0 wt%.

[0055] As previously described, in one embodiment of the present invention, Al within the Al compound in the Si diffusion composition is diffused by diffusion annealing, thereby increasing the Al content, and the steel sheet prior to Al diffusion may contain less Al than previously described. Specifically, the slab and the cold-rolled sheet prior to diffusion may contain 0.001 to 2.0 weight% of Al. If the Al content in the slab and the cold-rolled sheet prior to diffusion is too low, the amount of Al required for diffusion increases, and the diffusion annealing process takes a long time, resulting in low efficiency; furthermore, the difference in Al content by sheet thickness becomes large, making it difficult to obtain appropriate high-frequency iron loss. If the Al content in the slab is too high, Al oxides may clump together in some locations, causing cracking during the rolling process. More specifically, the Al content in the slab and the cold-rolled sheet prior to diffusion may be 0.001 to 1.8 weight%. Even more specifically, the Al content in the slab and the cold-rolled sheet prior to diffusion may be 0.01 to 1.0 weight%.

[0056] Mn: 0.03 to 2.0 wt%

[0057] Manganese (Mn) plays a role in improving iron loss by increasing the resistivity of the material and forming sulfides. If too little Mn is added, fine MnS precipitates, which can degrade magnetism. If too much Mn is added, it promotes the formation of a

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

[0058] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less, Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Sn: 0.1 wt% or less, Sb: 0.1 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

[0059] P: 0.1 wt% or less

[0060] Phosphorus (P) is a grain boundary segregation element, and if added in excessive amounts, it can delay recrystallization and degrade strength uniformity in the rolling direction and the rolling perpendicular direction. More specifically, P may be 0.005 to 0.03 weight%.

[0061] Cu: 0.005 to 0.200 wt%

[0062] Copper (Cu) plays a role in forming sulfides together with Mn. If more Cu is added, or if too little is added, fine precipitation of (Cu·Mn)S may occur, which can degrade magnetism. If too much Cu is added, high-temperature brittleness may occur, which can form cracks during continuous casting or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.100 weight%.

[0063] Cr: 0.010 to 0.50 wt%

[0064] Chromium (Cr) plays a role in improving iron loss by increasing resistivity. If too little Cr is added, the effect of increasing resistivity may not be sufficient. If too much Cr is included, magnetic flux density may decrease. More specifically, the lower limit of Cr can be 0.05 wt% or 0.30 wt%.

[0065] Sn: 0.10 wt% or less

[0066] Tin (Sn) is added to improve magnetic properties by acting as a segregating element at grain boundaries to inhibit the diffusion of nitrogen through the grain boundaries, suppressing the {111} texture harmful to magnetism, and increasing the {100} texture beneficial to magnetism. If too much Sn is added, it hinders grain growth, reduces magnetism, and results in poor rolling properties. Therefore, Sn can be added within the aforementioned range. More specifically, Sn may be included in an amount of 0.005 to 0.08 weight%.

[0067] Sb: 0.10 wt% or less

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

[0069] Ni: 0.05 wt% or less

[0070] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a harmful effect on magnetism. More specifically, Ni may be included in an amount of 0.005 to 0.03 weight%.

[0071] Zn: 0.01 wt% or less

[0072] If the content of zinc (Zn) is excessive, it can act as an impurity and impair magnetism. Therefore, Zn may be added within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 weight%.

[0073]

[0074] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more types of Bi: 0.200 wt% or less, Pb: 0.200 wt% or less, Ge: 0.200 wt% or less, and As: 0.200 wt% or less.

[0075] When the aforementioned elements are added, they segregate at the grain boundaries, alleviating stress concentration at the grain boundaries during cold rolling, and thus during the subsequent recrystallization annealing process <111> By suppressing the recrystallization of the / ND orientation grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained, but if they are included in too much, a large amount of segregation occurs, which suppresses grain growth and may result in inferior magnetic flux density and iron loss. More specifically, one or more of Bi: 0.001 to 0.100 wt%, Pb: 0.001 to 0.100 wt%, Ge: 0.001 to 0.100 wt%, and As: 0.001 to 0.100 wt% may be further included.

[0076]

[0077] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0078] Since these can react with inevitably included C, S, N, etc. to form fine carbides, nitrides, or sulfides that may adversely affect magnetism, an upper limit may be set as described above. More specifically, one or more of Mo: 0.001 to 0.01 wt%, B: 0.0010 to 0.0030 wt%, Ca: 0.0010 to 0.0030 wt%, Zr: 0.0010 to 0.0030 wt%, Te: 0.0010 to 0.0050 wt%, and Mg: 0.0010 to 0.0050 wt% may be further included.

[0079]

[0080] Other impurities

[0081] In addition to the aforementioned elements, inevitably incorporated impurities such as carbon (C), sulfur (S), nitrogen (N), titanium (Ti), niobium (Nb), and vanadium (V) may be included.

[0082] N combines with Ti, Nb, and V to form nitrides and plays a role in reducing grain growth.

[0083] C reacts with N, Ti, Nb, V, etc., to form fine carbides, which hinder grain growth and domain movement.

[0084] S forms sulfides, which impair grain growth.

[0085] In cases where additional impurity elements are included as such, one or more of C: 0.005 wt% or less (excluding 0%), N: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), Nb: 0.005 wt% or less (excluding 0%), and V: 0.005 wt% or less (excluding 0%) may be additionally included. More specifically, it may further include one or more of C: 0.001 to 0.003 wt%, N: 0.001 to 0.005 wt%, S: 0.001 to 0.005 wt%, Ti: 0.001 to 0.005 wt%, Nb: 0.001 to 0.005 wt%, and V: 0.001 to 0.005 wt%.

[0086] In addition, unavoidable impurities may be included. These unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets; since this is widely known in the field, a detailed explanation is omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. If additional elements are included, they are included to replace the remainder, Fe.

[0087]

[0088] A non-oriented electrical steel sheet according to one embodiment of the present invention has an Roughness Profile Count (RPc) value of 30 to 100 on the surface of the steel sheet. Generally, surface roughness is expressed by the Ra value, which is the arithmetic surface roughness; however, in one embodiment of the present invention, iron loss can be further improved by controlling the specific surface area of ​​the surface through appropriately adjusting the Roughness Profile Count value rather than adjusting the Ra value. The Roughness Profile Count (RPc) value refers to the number of peaks, specifically the number of peaks in a unit length area of ​​1 cm, and can be measured using a two-dimensional surface roughness meter. If the Roughness Profile Count value is too small, it is judged that the iron loss value is excellent. Since the Roughness Profile Count value is also related to the grain size, it is generally impossible to control it to less than 30 for typical grain sizes of 100 µm to 300 µm; therefore, the Roughness Profile Count value can be set to 30 or higher. Furthermore, as the Roughness Profile Count value increases, the iron loss value tends to increase. This is because abrasive fingerprints caused by a brush remain on the surface due to brush polishing, etc., and residual stress remains in these abrasive fingerprints, causing the iron loss value to increase. Therefore, in the present invention, if the RPc value exceeds 100, the iron loss value exhibits a rapidly inferior characteristic, so the RPc value can be set to 100 or less. More specifically, it can be set to 50 to 85.

[0089] In one embodiment of the present invention, the non-oriented electrical steel sheet has a surface Rp of the steel sheet with a Profile Peak Height value, and the value of Rp may be 0.50 to 2.00 μm. Rv is the Profile Valley Depth, and the value of Rv may be 0.50 to 2.00 μm. If the Rp and Rv values ​​of the roughness are too large, the surface roughness increases, and the iron loss value tends to decrease. More specifically, the values ​​of Rp and Rv may each be 0.60 to 1.90 μm.

[0090] Surface roughness values ​​such as RPc, Rp, Rv, and Ra were measured based on the JIS B0601 surface roughness measurement standard, and the measurement length can be based on measuring in a 1cm area.

[0091] Surface 1mm in scanning electron microscope (SEM) measurement and EDS component analysis 2 The sum of oxygen (O) and carbon (C) components in the region may be 1.00 weight% or less. If the sum of oxygen and carbon components on the surface is too high, the surface properties may be inferior. More specifically, it may be 0.01 to 1.00 weight%.

[0092] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a cold-rolled sheet comprising, in weight percent, Si: 0.3 to 4.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and the remainder being Fe and unavoidable impurities; a coating step of applying a Si diffusion composition comprising a Si compound to the surface of the cold-rolled sheet; a diffusion annealing step of the cold-rolled sheet; and a diffusion annealing step of pickling the diffusion-annealed steel sheet.

[0093] Below, each step is explained in detail.

[0094] First, a cold-rolled sheet is manufactured containing, in weight percent, 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. Since the alloy composition of the cold-rolled sheet is the same as that described above, a redundant description is omitted.

[0095] The method for manufacturing a cold-rolled sheet is not particularly limited and may include the step of manufacturing a hot-rolled sheet by hot-rolling a slab containing Si: 0.3 to 4.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0% by weight; and the step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled sheet.

[0096] First, a slab is manufactured. The reason for limiting the addition ratio of each component within the slab is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated explanation is omitted. Since the composition of the slab does not substantially change during the manufacturing processes described later, such as hot rolling, hot-rolled sheet annealing, and cold rolling, the composition of the slab and the composition of the cold-rolled sheet are substantially the same. Furthermore, in the diffusion annealing process, only Si and Al diffuse, and the alloy composition of the non-oriented electrical steel sheet may be the same as the remaining components excluding Si and Al.

[0097] Prior to the step of manufacturing a hot-rolled plate, the slab may be heated to 1100°C or higher. Specifically, the slab is loaded into a heating furnace and heated to 1100 to 1250°C. When heated at a temperature exceeding 1250°C, precipitates may be redissolved and finely precipitated after hot rolling. More specifically, the slab heating temperature may be 1100°C to 1200°C.

[0098] The heated slab is hot-rolled to a thickness of 1.5 to 4.0 mm to produce a hot-rolled plate. In one embodiment of the present invention, a step of pre-cold rolling before cold rolling is also included, so that a non-oriented electrical steel plate of appropriate thickness can be produced even if the thickness of the hot-rolled plate is relatively thick. More specifically, the thickness of the hot-rolled plate may be 1.5 mm to 3.5 mm.

[0099] The step of manufacturing a hot-rolled plate may include a step of finishing rolling at a temperature of 850°C or higher.

[0100] If the finishing rolling temperature of hot rolling is too low, the rolling load increases, leading to reduced hot rolling workability. Furthermore, a significant amount of deformation remains in the hot-rolled steel sheet, which causes an increase in the rolling load during the subsequent pre-cold rolling process. In addition, from the deformation during intermediate annealing <111> / ND Recrystallization of the grains is promoted, resulting in lower magnetic flux density. Therefore, the hot rolling finish rolling temperature should be as high as possible, and more specifically, the finish rolling temperature can be 850 to 1000℃.

[0101] The step of manufacturing a hot-rolled plate may include a coiling step at a temperature of 600 to 800°C. It may also include a rough rolling step before the finish rolling step.

[0102] If the temperature during the coiling stage is managed too low, the recovery and recrystallization of the hot-rolled deformed structure do not occur effectively. Additionally, the cooling load increases to rapidly cool the steel sheet to a low temperature, which may cause difficulties in coiling the supercooled coil. Conversely, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during coiling, leading to the formation of a thicker scale and problems with intergranular oxidation. Intergranular oxidation of the hot-rolled sheet promotes intergranular corrosion during the subsequent pickling process, increasing the likelihood of surface streak defects and causing severe wear on the rolling rolls. More specifically, the coiling temperature may be 650 to 750°C.

[0103] After the step of manufacturing a hot-rolled plate, the process may further include a step of annealing the hot-rolled plate at a temperature range of 600 to 1100°C. If the annealing temperature of the hot-rolled plate is too low, a recrystallization structure is not formed or grows finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, magnetic properties may actually deteriorate, and rolling workability may be poor due to deformation of the plate shape. More specifically, the annealing temperature of the hot-rolled plate may be 750 to 1000°C.

[0104] Annealing of hot-rolled plates is performed as needed to increase the magnetic orientation, and it may be omitted. The form of annealing is not particularly limited and can be performed in batch or continuous motion.

[0105] Hot-rolled plates can be pickled as needed.

[0106] Next, the hot-rolled sheet is pickled and cold-rolled to a predetermined thickness. Depending on the thickness of the hot-rolled sheet, a reduction rate of 70 to 95% may be applied to cold-roll the sheet so that the final thickness is 0.10 to 0.65 mm. To achieve the reduction rate, one cold-rolling step or two or more cold-rolling steps with intermediate annealing in between may be performed. More specifically, the reduction rate may be 75 to 90%. The thickness of the cold-rolled sheet may be 0.15 to 0.35 mm.

[0107] Next, in the coating step, a Si diffusion composition containing a Si compound is applied to the cold-rolled plate.

[0108] As for the Si compound, any material capable of diffusing Si into the interior of the steel sheet through long-term annealing may be used without limitation. Specifically, it may include one or more of pure Si, Si alloys, Si oxides, nitrides or carbides, and silane compounds. In addition, it may include one or more of FeSi, Fe3Si, Fe3Al, and FeAl.

[0109] More specifically, it may include pure Si, Si alloys, and Fe3Si.

[0110] The average particle size of the Si compound may be 1 to 1500 nm. If the particle size of the Si compound is too small, problems may arise where they aggregate during slurry mixing, causing surface defects. If the particle size of the Si compound is too large, it may be difficult to apply it uniformly to the surface of the steel plate, which may hinder smooth Si diffusion into the interior of the steel plate. The average particle size of the Si compound is the average particle size relative to the number of compound particles and can be measured using a particle size analyzer (PSA) utilizing laser diffraction. More specifically, the average particle size of the Si compound may be 10 nm to 1500 nm. Even more specifically, it may be 20 nm to 1000 nm.

[0111] The Si diffusion composition further comprises an Al compound and may include 100 parts by weight of the Si compound and 10 to 50 parts by weight of the Al compound as solid content. In one embodiment of the present invention, solid content refers to the weight after heating each compound at 180°C for 20 minutes or more to remove all volatile matter.

[0112] Al compounds improve insulation, increase bonding with Si compounds, and also play a role in promoting the formation of intermetallic compounds. If too little Al compound is included, it may be difficult to obtain the aforementioned effects adequately. If too much Al compound is included, a problem may arise where numerous Al inclusions are formed, resulting in reduced magnetism. More specifically, the Al compound may be included in an amount of 15 to 30 parts by weight.

[0113] As for Al compounds, any material capable of diffusing Al into the steel sheet can be used without restriction. For example, pure Al and aluminum alkoxides may be used.

[0114] The average particle size of the Al compound may be 1 to 1000 nm. If the particle size of the Al compound is too small, a problem of aggregation between Al compounds may occur. If the particle size of the Al compound is too large, Al diffusion into the steel sheet may not occur smoothly. More specifically, the lower limit of the average particle size of the Al compound may be 5 nm. The upper limit of the average particle size of the Al compound may be 750 nm.

[0115] The Si diffusion composition may further include ceramic powder comprising oxides, nitrides, carbides, or oxynitrides, comprising at least one component selected from Li, B, Ca, Sr, Mg, Al, P, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Sn, and Ba. The ceramic powder serves to control the amount of slurry applied and to determine the Si content of the final steel sheet.

[0116] The ceramic powder may be included in an amount of 10 to 1,000 parts by weight as a solid content. If too little ceramic powder is included, problems may arise in terms of securing the coating amount. If too much ceramic powder is included, the slurry viscosity increases, which may cause problems in terms of surface defects. More specifically, the ceramic powder may be included in an amount of 20 to 500 parts by weight.

[0117] The ceramic powder may be one or more of Al2O3, TiO2, MgO·Al2O3, MgO·TiO2, 3Al2O3·2SiO2, ZrO2·SiO2, TiN, CrN, SrTiO3, MgAl2O4, Y2O3, FeTiO3, and Li2O·Al2O3·SiO2.

[0118] The average particle size of the ceramic powder may be 8 to 2500 nm. If the particle size of the ceramic powder is too small, there may be a problem in securing a sufficient coating amount. If the particle size of the ceramic powder is too large, the viscosity increases, the surface quality deteriorates, and Si diffusion into the steel plate may not proceed smoothly. More specifically, the average particle size of the ceramic powder may be 10 nm to 1500 nm.

[0119] The Si diffusion composition may further include a solvent in addition to the aforementioned components. The solvent enables the uniform application of the Si diffusion composition. If the amount of solvent is too small, the application of the Si diffusion composition may not be easy. If the amount of solvent is too large, the viscosity of the Si diffusion composition may be too low, making it difficult to apply a sufficient amount of the composition onto the steel plate. The solvent may be included in an amount of 10 to 1,500 parts by weight per 100 parts by weight of the Si compound. More specifically, the solvent may be included in an amount of 50 to 1,000 parts by weight. The solvent may include one or more of water and alcohol.

[0120] In the first coating step, the coating amount of the Si diffusion composition is 0.1 to 300 g / m² 2This may be the case. In this instance, the coating amount is based on the solid content. If the coating amount is too small, sufficient Si diffusion does not occur, making it difficult to fully achieve the effects of Si diffusion. If the coating amount is too large, a problem may arise where processability deteriorates.

[0121] Application methods include using a roll coater, brush, and dipping. From a productivity standpoint, application can be performed using a roll coater.

[0122] In terms of the coating direction, the coating can be applied by forming an angle of -10 to 10° with respect to the rolling direction or an angle of 80 to 100° with respect to the rolling direction. More specifically, in terms of the coating direction, the coating can be applied by forming an angle of -5 to 5° with respect to the rolling direction or an angle of 85 to 95° with respect to the rolling direction. From the perspective of productivity, the coating can be applied by forming an angle of -10 to 10° with respect to the rolling direction.

[0123] After the coating step, the method may further include a step of forming a Si diffusion coating layer by drying the Si diffusion composition through drying. The drying temperature is sufficient if it is a temperature capable of removing the solvent within the Si diffusion composition, and specifically, it may be 300 to 850°C. The time may be 10 seconds to 180 seconds. More specifically, the temperature may be 500 to 800°C. The time may be 15 seconds to 150 seconds. After drying at the drying temperature, cooling may be performed at a cooling rate of 20°C / second or higher. By rapidly cooling in this manner, the automatic detachment of the unreacted residual composition can be induced by utilizing the difference in thermal shrinkage between the steel plate and the unreacted composition layer. The cooling range may be from the drying temperature to 100°C.

[0124] Next, the cold-rolled sheet is diffusion annealed. During this process, Si and Al diffuse into the interior of the steel sheet from the Si diffusion composition applied to the surface of the cold-rolled sheet.

[0125] Prior to the diffusion annealing step, the temperature can be increased in a range of 20 to 700°C at a rate of 5 to 50°C / hr. In this way, uniform quality can be obtained by increasing the temperature at a relatively slow rate. If the rate of increase is too slow, the process time becomes unnecessarily long and productivity decreases. If the rate of increase is too fast, the aforementioned effects cannot be properly obtained. More specifically, the temperature can be increased at a rate of 10 to 30°C / hr.

[0126] The diffusion annealing temperature may be 850°C to 1250°C. If the diffusion annealing temperature is too low, the diffusion of Si may not occur sufficiently, and the desired effect may not be obtained. If the diffusion annealing temperature is too high, pores may form, and the magnetic properties may be degraded. More specifically, it may be 900°C to 1150°C.

[0127] The time may be 30 minutes to 600 minutes. If the time is too short, the diffusion of Si and Ti may not occur sufficiently, and the desired effect may not be obtained. If the time is too long, it is difficult to control the amount of diffusion, and processability may be inferior. More specifically, it may be 60 to 300 minutes.

[0128] During diffusion annealing, the atmosphere may be an atmosphere containing one or more of hydrogen, nitrogen, or argon. The oxidizing power of the atmosphere (PH2O / PH2) may be 6.4 or less. If the oxidizing power is too high, an oxide may form inside Al2O3, which may degrade the magnetic properties. Specifically, the oxidizing power of the atmosphere (PH2O / PH2) may be 3.0 or less. Specifically, the oxidizing power of the atmosphere (PH2O / PH2) may be 1.0 or less.

[0129]

[0130] After diffusion annealing, the final thickness of the steel sheet may be 0.10 to 0.65 mm, and due to the application and diffusion of the Al diffusion composition, the thickness may increase slightly compared to the cold-rolled sheet.

[0131] Next, the diffusion-annealed steel sheet is pickled. At this time, the pickling is performed in a mixed solution of nitric acid and hydrofluoric acid (mixed acid) in which the concentration of nitric acid is 30 g / L to 100 g / L and the concentration of hydrofluoric acid is 3 g / L to 10 g / L.

[0132] If the concentration of nitric acid is too low, it is impossible to remove Si and Al oxides remaining on the surface, so a minimum concentration of nitric acid must be added at 30 g / L or higher. In addition, if the concentration of nitric acid is too high, the dissolution rate of the specimen base material may increase rapidly.

[0133] In the case of hydrofluoric acid concentration, if the concentration is too low, the removal of Si and Al oxides becomes impossible. Furthermore, if the concentration of hydrofluoric acid is too high, the dissolution of the base material may increase rapidly.

[0134] The concentration ratio of nitric acid to hydrofluoric acid (HNO3 / HF) can be 10 to 30. If the concentration ratio is low, the high concentration of HF leads to the formation of pits on the specimen surface, causing a rapid increase in surface roughness values; in particular, the Rv value of surface roughness increases sharply, which may result in inferior iron loss. Furthermore, if the concentration ratio is high, the concentration of hydrofluoric acid is too low to remove residual Si or Al oxides on the surface, which may lead to increased iron loss.

[0135] At this time, the temperature of the mixed acid can be carried out at 60°C or lower. If the temperature of the solution exceeds 60°C, the generation of NOx may increase rapidly or the dissolution rate of the base material may increase rapidly. More specifically, it may be 30 to 50°C.

[0136] Immerse in a mixed acid solution in which the concentration ratio of nitric acid and hydrofluoric acid (HNO3 / HF) is between 10 and 30. At this time, it is preferable to perform the process at a temperature of 60°C or lower.

[0137] A brushing step may be additionally included prior to the pickling step. In this process, unreacted compositions remaining on the surface of the cold-rolled plate can be removed.

[0138] In the brushing stage, the strength of the brush bristles may be 50 to 90 MPa. If the strength of the brush bristles is too low, the removal of unreacted composition and oxide layer may not be properly performed. If the strength of the brush bristles is too high, the surface roughness (Ra, Rz, Rt) of the steel plate surface increases significantly, and surface properties may be significantly degraded. More specifically, when polyethylene is used for the brush bristles, the strength may be 50 to 80 MPa, and when nylon is used for the brush bristles, the strength may be 70 to 90 MPa.

[0139] The strength of the brush bristles can be appropriately adjusted by changing the amount of abrasive material added to the brush bristles. In this case, the types of abrasive materials may include one or more of SiC and Al2O3. In this case, the average particle size of the abrasive material may be 50 to 250 μm. If the average particle size of the abrasive material is too small, the brush polishing characteristics become inferior, and the possibility of residual slurry and oxides remaining on the surface after polishing increases. Furthermore, if the average particle size of the abrasive material is too large, polishing characteristics increase, but a problem may arise where the surface roughness becomes rough after polishing. More specifically, the average particle size of the abrasive material may be 50 to 230 μm.

[0140] In addition to the abrasive material, the brush body may be composed of multiple strands of general polymer fibers combined into a spiral shape. The polymer fibers may include one or more of polyethylene and nylon. The diameter of the polymer fibers may be 0.4 to 1.5 mm. The brush body may be formed by twisting 2 to 8 strands of polymer fibers together.

[0141] After the step of pickling the steel plate, a second brushing step may be further included. The second brushing step may be performed under the same conditions as the brushing step described above.

[0142] After the second brushing step, a second acid cleaning step in which the steel plate is immersed in an acid solution may be further included. In the second acid cleaning step, the acid solution may include one or more of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid. Specifically, it may include nitric acid and hydrofluoric acid. The concentration of the acid solution may be 50 to 150 g / L, and the temperature of the acid solution may be 50 to 90°C.

[0143] After the acid cleaning step, a washing step may be additionally included to remove residual acid components on the surface. In the washing step, water may be sprayed onto the surface of the steel plate to clean it. At this time, to prevent yellow discoloration caused by corrosion products remaining on the surface, 1 to 10 g of hydrogen peroxide (H2O2) may be added per 1 L of water to prevent yellow discoloration of the surface.

[0144] After the acid washing step, a drying step may be further included. At this time, the temperature of the drying air may be 200 to 350°C. If the air temperature is too low, it takes a long time for moisture to evaporate from the surface of the steel plate, and stains may occur on the surface. If the temperature is too high, there is a high possibility of oxidative discoloration occurring on the surface of the steel plate.

[0145] Subsequently, a step of forming an insulating film may be further included. Since insulating films are widely known, a detailed description is omitted. Specifically, an insulating coating layer can be formed by applying an insulating coating layer forming composition comprising metal phosphate and silica as main components and heat treating.

[0146]

[0147] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0148]

[0149] Experimental Example

[0150] A slab was prepared containing 2.0 wt% silicon (Si), 0.002 wt% aluminum (Al), 0.10 wt% manganese (Mn), 0.04 wt% tin (Sn), 0.04 wt% antimony (Sb), and 0.013 wt% phosphorus (P), with the remainder being Fe and other unavoidable impurities.

[0151] A hot-rolled plate was manufactured by heating a slab to 1100℃ and then hot-rolling it to a thickness of 1.8mm.

[0152] A hot-rolled plate was coiled at 700°C, cooled in air, annealed at 1030°C for 2 minutes, then rapidly cooled in water and pickled, and then cold-rolled to a thickness of 0.25 mm to produce a cold-rolled plate.

[0153] A Si diffusion composition was prepared by stirring 30 parts by weight of silicon powder (Si: 99.99 wt% or more) with an average particle size of 1 μm, 10 parts by weight of a ceramic powder mixture (3:1 SrTiO3, MgAl2O4), and 50 parts by weight of water.

[0154] The prepared Si diffusion composition was applied to a cold-rolled plate. The composition was applied to both surfaces of the cold-rolled plate, with a coating amount of 20 g / m² per surface. 2 It was applied uniformly.

[0155] A cold-rolled sheet coated with a Si diffusion composition was diffusion annealed in a 100v% H2 atmosphere at 1000℃ for 1 hour.

[0156] Subsequently, the steel plate after diffusion annealing was polished using a brush in both the forward and reverse directions of the brush rotation speed. The brush used was composed of polyethylene resin and consisted of three strands with a diameter of 0.6 mm. The bristles were mixed with SiC abrasive stones of size #240. The brush rotation speed was set to 1000 RPM, the steel plate travel speed was fixed at 100 MPM, and the experiment was conducted with a fixed gap of 2 mm between the specimen and the brush. After the brushing was completed, the steel plate was cleaned in an aqueous solution (H2O) and then subjected to pickling.

[0157] Table 1 shows the pickling solution conditions and surface roughness measurement results for steel plates that had been brushed and washed in an aqueous solution (H2O) (Specimen 21), steel plates that had been pickled in a hydrochloric acid solution environment after washing (Specimen 22), and steel plates that had been pickled in a mixed acid solution environment after washing (Specimens 1 to 20). At this time, the pickling conditions in the hydrochloric acid solution environment were such that the hydrochloric acid concentration was 100 g / L, 0.03 of inhibitor was added to the hydrochloric acid concentration of 100 g / L, and the temperature condition was immersion at 80℃ for 30 seconds.

[0158] At this time, the nitric acid (HNO3) and hydrofluoric acid (HF) solutions of the mixed acid solution were varied as shown in conditions 1 to 20 of Table 1, and the experiment was conducted with the temperature condition set to 40℃ and the immersion time set to 30 sec.

[0159]

[0160] Surface roughness was measured using a two-dimensional contact method, and the surface roughness values ​​such as RPc, Rp, Rv, and Ra were measured based on the JIS B0601 surface roughness measurement standard. The measurement length was based on measuring in a 1 cm area.

[0161] Subsequently, through EDS component observation using a scanning electron microscope on each specimen, a surface area of ​​1 mm² 2 The degree of oxides and surface contaminants was measured. In this case, if the sum of the oxygen (O) and carbon (C) components was 1% or less, it was indicated as a good condition with no oxides or contaminants remaining on the surface, and if the sum of the oxygen (O) and carbon (C) components exceeded 1%, it was indicated as a poor condition with oxides and contaminants on the surface.

[0162] In addition, observation by scanning electron microscope indicated that grain detachment or corrosion such as pitting occurred, which was labeled as “pit occurrence,” and that excessive pickling caused a decrease in the thickness of the base material by more than 10 µm after pickling compared to after brush polishing, which was labeled as “surge in base material corrosion.”

[0163] Afterward, magnetic flux density and iron loss values ​​were measured for each specimen. Those with iron loss and magnetic flux density values ​​superior to the measured values ​​in Category 22 of Table 2, which are comparative examples, were marked as "Good" with an "○", and those with at least 1 to 2 grades superior were marked as "Excellent" with an "◎".

[0164] In addition, values ​​with iron loss and magnetic flux density lower than the 22 measured values ​​in Table 2 were marked as inferior “X”, and those with at least 1 to 2 grades lower were marked as defective “XX”.

[0165] Figure 1 shows a photograph of the surface after diffusion heat treatment under the conditions of specimen 21, followed by brush polishing and rinsing with an aqueous solution. As seen in the figure, the brush polishing fingerprint remains intact after brush polishing, and the RPC value is 100 or higher.

[0166] Figure 2 shows a photograph of the surface after diffusion heat treatment under the conditions of specimen 22, followed by brush polishing and pickling in a hydrochloric acid solution. As seen in the figure, the brush polishing fingerprints remain intact after brush polishing, resulting in an RPC value of 100 or higher and indicating a form of surface contamination.

[0167] In the case of Figure 3, the crystal grains are exposed due to good pickling under mixed acid conditions under the condition of specimen 7, and the polishing fingerprints such as brushes disappear after pickling, so it can be confirmed that the RPC value is 43.

[0168] Specimen Nitric Acid Concentration (g / L) Hydrofluoric Acid Concentration (g / L) Nitric Acid / Hydrofluoric Acid Ratio Ra(㎛)RPcRp(㎛)Rv(㎛)11002052.151232.143.452501051.751252. 452.65330651.631092.613.56410250.251130.540.36510010100.7 5651.851.566505100.85531.750.957303100.65431.621.068101100.251230.630.46910010100.32630.950.85101005200.29690.820. 6511603200.25630.750.7012201200.26520.650.621330010300.65742.652.65141505300.56802.152.1315903300.23750.350.4116301300.19600.420.391740010401.651252.653.45182005401.231202.652.65191203401.651242.322.1320401400.351350.650.4221Brush Rinsing after polishing 0.25 10 30.8 50.70 22 Hydrochloric acid pickling after brush polishing 0.2 9 50.7 00.50

[0169] Specimen C, O Content (Wt%) Magnetic Flux Density (B25, T) Magnetic Flux Density (B50, T) Iron Loss (W10 / 50, W / kg) Iron Loss (W10 / 400, W / kg) Iron Loss (W10 / 1000) Surface Shape Classification 10.44 XXXXXXXXXX Pit Occurrence Failure 20.61 XXXXXXXXXX Pit Occurrence Failure 30.38 XXXXX Pit Occurrence Failure 43.65 XXXXX Oxide Residue Failure 50.05 ○○○○○ - Good 60.63 ○○○○○ - Good 70.11 ○○○○○ - Good 84.15 XXXXX Oxide Residue Failure 90.79 ○○○○○ - Good 100.23 ○○○○○ - Good 110.10 ◎◎◎◎◎ - Good 125.65 XXXXXX Oxide Residual Defect 130.21XXXXXXXXXX Base Material Corrosion Surge Defect 140.30XXXXXXXXXX Base Material Corrosion Surge Defect 150.87○○○○○-Good 163.46○○○○○ Oxide Residual Defect 170.16XXXXXXXXXX Base Material Corrosion Surge Defect 180.64XXXXXXXXXX Base Material Corrosion Surge Defect 190.34XXXXXXXXXX Base Material Corrosion Surge Defect 204.35XXXXX Oxide Residual Defect 215.651.541.6420.8212.20547.641 Si Oxide Formation Comparative Example 223.031.561.6520.81512.16546.652 Contamination Occurrence Comparative Example

[0170] In addition, as shown in Tables 1 and 2, it can be confirmed that appropriate surface characteristics can be obtained by using an appropriate acid solution, and consequently, iron loss is improved. On the other hand, if the concentration of nitric acid or hydrofluoric acid is not appropriate, or if hydrochloric acid is used, it can be confirmed that appropriate surface characteristics cannot be obtained and iron loss is somewhat inferior.

[0171] The present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Containing Si: 4.0 to 7.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0% by weight, with the remainder being Fe and unavoidable impurities, having an RPc value of 30 to 100 on the steel sheet surface, and surface 1 mm in EDS component measurement using scanning electron microscopy 2 Non-oriented electrical steel sheet in which the sum of oxygen (O) and carbon (C) components in the region is 1 weight% or less.

2. In claim 1, the Rp value of the steel sheet surface is 0.5 to 2.0 μm and the Rv is 0.5 to 2.0 μm, and the non-oriented electrical steel sheet.

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

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

5. In Paragraph 1, A non-oriented electrical steel sheet further comprising 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%).

6. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more 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%).

7. In Paragraph 1, A non-oriented electrical steel sheet further comprising 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%).

8. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more 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%).

9. A step of manufacturing a cold-rolled sheet comprising, by weight, Si: 0.3 to 4.0%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and the remainder being Fe and unavoidable impurities; A coating step of applying a Si diffusion composition containing a Si compound to the surface of the above cold-rolled plate; The step of diffusion annealing the above cold-rolled plate and It includes a step of pickling a diffusion-annealed steel plate, and A method for manufacturing non-oriented electrical steel sheets, wherein the pickling step involves immersing the sheets in a mixed solution having a concentration of nitric acid (HNO3) of 30 g / L to 100 g / L and a concentration of hydrofluoric acid (HF) of 3 g / L to 10 g / L.

10. In Paragraph 9, The above mixed solution is a method for manufacturing a non-oriented electrical steel sheet in which the concentration ratio of nitric acid to hydrofluoric acid (HNO3 / HF) is 10 to 30.

11. In Paragraph 9, A method for manufacturing non-oriented electrical steel sheets comprising an additional brushing step prior to the above pickling step.

12. In Paragraph 11, A method for manufacturing a non-oriented electrical steel sheet in which the strength of the brush bristles in the brushing step is 50 MPa to 90 MPa.

13. In Paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, further comprising a secondary brushing step after the above-mentioned pickling step.

14. In Paragraph 13, A method for manufacturing a non-oriented electrical steel sheet, further comprising a second acid cleaning step of immersing the steel sheet in an acid solution after the second brushing step.

15. In Paragraph 9, The step of manufacturing the above cold-rolled plate is, A step of manufacturing a hot-rolled plate by hot-rolling a slab comprising, in weight percent, Si: 0.01 to 3.5%, Al: 0.001 to 2.0%, and Mn: 0.03 to 2.0%, and 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 above hot-rolled sheet to produce a cold-rolled sheet.

Images