Non-oriented electrical steel sheet and manufacturing method thereof

Abstract

The present invention relates to a non-oriented electrical steel sheet used as a material for an iron core material of an electric power machine and, more specifically, to a non-oriented electrical steel sheet having excellent surface properties and electromagnetic properties, and a manufacturing method thereof.

Description

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

[0001] The present invention relates to a non-oriented electrical steel sheet used as a material such as a core material for electric power machinery, and more specifically, to a non-oriented electrical steel sheet and a method for manufacturing the same.

[0002] Silicon (Si) and aluminum (Al) are well known as effective elements for reducing iron loss by increasing the resistivity of non-oriented electrical steel sheets. However, as these elements are highly oxidizing agents, they form stable scales, such as oxides or nitrides, on the surface during the steel manufacturing process, thereby degrading the surface quality of the product (steel sheet). Consequently, not only is the appearance quality of the steel sheet compromised, but problems such as poor adhesion of the insulation coating and increased iron loss may also arise.

[0003] In particular, when using a series of processes to manufacture electrical steel sheets, it is difficult to fundamentally prevent the formation of scale, such as oxides or nitrides, caused by specific elements. Specifically, scale formed before the annealing process is mainly distributed on the surface of the steel sheet, making the surface rough; if the annealing process is performed in this state, the amount of newly formed scale increases. As a result, the aforementioned problems occur.

[0004] Accordingly, in the manufacturing of electrical steel sheets, not only is the development of technology capable of suppressing the formation of scale, such as oxides and nitrides, required from the hot-rolled steel sheet to the final annealed steel sheet manufacturing process, but the application of descaling to remove scale physically and / or chemically is also emerging as an important technology.

[0005] (Patent Document 1) Japanese Published Patent Application No. 2010-087961

[0006] According to one aspect of the present invention, a non-oriented electrical steel sheet with improved surface characteristics and magnetic characteristics may be provided, and according to another aspect, a method for manufacturing said non-oriented electrical steel sheet may be provided.

[0007] The problems of the present invention are not limited to those described above. A person skilled in the art to which the present invention pertains will have no difficulty understanding additional problems of the present invention from the overall contents of this specification.

[0008] According to one aspect of the present invention, a non-oriented electrical steel sheet is provided, comprising a base steel sheet and an anti-oxidation coating film formed on at least one surface of the base steel sheet.

[0009] In one embodiment of the present invention, the base steel sheet may contain, in weight percent, silicon (Si): 1.50~6.00%, aluminum (Al): 0.10~2.00%, manganese (Mn): greater than 0%~2.00% or less, and the remainder being Fe and other unavoidable impurities.

[0010] In one embodiment of the present invention, the anti-oxidation coating film may have a thickness of 0.05 to 0.50 μm.

[0011] In one embodiment of the present invention, the non-oriented electrical steel sheet has a maximum Al content in an area within 0.05 μm in the thickness direction from the surface of the anti-oxidation coating film. max , when the average Al content at a point 5.00 μm in the thickness direction from the surface is denoted as Al0, the following relationship 1 can be satisfied.

[0012] [Relationship 1]

[0013] (Al max / Al0) ≤ 20.0

[0014] (In Equation 1, each Al content is in weight%.)

[0015] Thus, the non-oriented electrical steel sheet according to one embodiment of the present invention can reduce scale caused by Al, etc. on its surface by forming an anti-oxidation coating film, and can have excellent magnetic properties along with surface quality.

[0016] A non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 180 μm.

[0017] In one embodiment of the present invention, the anti-oxidation coating film may be composed of one or more of a metal and an oxide of the metal, wherein the absolute value of the reduction in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C.

[0018] In one embodiment of the present invention, Al scales of Al oxide and / or Al nitride exist within the anti-oxidation coating film, and the average diameter of the Al scales may be 100 nm or less.

[0019] In one embodiment of the present invention, the base steel sheet may further include the following elements in addition to the alloy composition described above.

[0020] As an example, in weight percent, it may further include one or more selected from carbon (C): 0.0050% or less, titanium (Ti): 0.0050% or less, phosphorus (P): 0.1000% or less, sulfur (S): 0.0100% or less, and nitrogen (N): 0.0050% or less.

[0021] As another example, one or more selected from tin (Sn), antimony (Sb), bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) may be further included in an amount of 0.005 to 0.200 weight% based on the total content.

[0022] As another example, in weight percent, it may further include one or more selected from chromium (Cr): 0.010~0.500%, copper (Cu): 0.050% or less, nickel (Ni): 0.050% or less, zinc (Zn): 0.010% or less, and cobalt (Co): 0.050% or less.

[0023] As another example, in weight percent, it may further include one or more selected from molybdenum (Mo): 0.0300% or less, boron (B): 0.0050% or less, vanadium (V): 0.0050% or less, calcium (Ca): 0.0050% or less, niobium (Nb): 0.0050% or less, zirconium (Zr): 0.0050% or less, tellurium (Te): 0.0100% or less, and magnesium (Mg): 0.0050% or less.

[0024] According to another aspect of the present invention, a method for manufacturing a non-oriented electrical steel sheet is provided, comprising the steps of: heating a slab and then hot-rolling it to obtain a hot-rolled sheet; descaling the hot-rolled sheet; cold-rolling the hot-rolled sheet after descaling to obtain a cold-rolled sheet; applying an anti-oxidation coating to the surface of the cold-rolled sheet; and annealing the cold-rolled sheet after the anti-oxidation coating treatment.

[0025] According to another aspect of the present invention, a method for manufacturing a non-oriented electrical steel sheet is provided, comprising the steps of: heating a slab and then hot-rolling it to obtain a hot-rolled sheet; descaling the surface of the hot-rolled sheet; first cold-rolling the hot-rolled sheet after descaling to obtain an intermediate cold-rolled sheet; a first annealing heat treatment step of annealing the intermediate cold-rolled sheet; second cold-rolling the cold-rolled sheet after the first annealing heat treatment to obtain a final cold-rolled sheet; and a second annealing heat treatment step of annealing the final cold-rolled sheet after the second cold-rolling, and further comprising the step of applying an anti-oxidation coating to the surface of the cold-rolled sheet before the first annealing heat treatment step and / or before the second annealing heat treatment step.

[0026] In one embodiment of the present invention, the slab for manufacturing a non-oriented electrical steel sheet may have the aforementioned alloy composition.

[0027] In one embodiment of the present invention, the descaling treatment may be performed by one or more methods selected from mechanical methods and chemical methods.

[0028] In one embodiment of the present invention, when the maximum Al content in the region within 0.5 μm in the thickness direction from the surface of the hot-rolled plate after descaling is denoted as Al(s) and the average Al content at a point 5.0 μm in the thickness direction from the surface of the hot-rolled plate is denoted as Al(i), the following relationship 2 can be satisfied.

[0029] [Relationship 2]

[0030] (Al(s) / Al(i))×100 < 100

[0031] (In Equation 2, each Al content is in weight%.)

[0032] In one embodiment of the present invention, the anti-oxidation coating may be one or more of a metal and an oxide thereof, wherein the absolute value of the reduction in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C.

[0033] In one embodiment of the present invention, the anti-oxidation coating treatment can be performed such that the coating rate is 80% or more of the total surface area.

[0034] In one embodiment of the present invention, when the annealing heat treatment step is performed only once, it can be performed in a reducing atmosphere of 3 to 50 volume% hydrogen (H2) and the remainder nitrogen (N2) at a temperature range of 870 to 1050°C.

[0035] In one embodiment of the present invention, when the annealing heat treatment step is performed twice, the first annealing heat treatment step and the second annealing heat treatment step may be performed in a reducing atmosphere of 3 to 50 volume% hydrogen (H2) and the remainder nitrogen (N2), in a temperature range of 870 to 1050°C.

[0036] According to the present invention, the scale remaining on the surface of the steel plate can be effectively reduced, thereby providing a non-directional electrical steel plate with improved surface characteristics as well as magnetic properties.

[0037] Figure 1 is a graph showing the Al content distribution when analyzing the thickness direction on the surface of a hot-rolled plate after descaling according to one embodiment of the present invention using GDS.

[0038] Figure 2 is a graph showing the Al content distribution when analyzing the thickness direction on the surface of a hot-rolled plate after descaling according to one embodiment of the present invention, as shown in Invention Example 1.

[0039] FIG. 3 is a graph showing the content distribution of Fe, Si, Al, and O when analyzed in the thickness direction from the surface of the cold-rolled plate (surface of the anti-oxidation coating film) after the anti-oxidation coating of Invention Example 3 according to one embodiment of the present invention.

[0040] Figure 4 is a graph showing the distribution of Al and N content when analyzed in the thickness direction from the surface of a cold-rolled sheet after final annealing (secondary annealing) of Comparative Example 3 according to one embodiment of the present invention.

[0041] FIG. 5 is a graph showing the distribution of Al and N content in the thickness direction from the surface of the cold-rolled plate (surface of the anti-oxidation coating film) after final annealing (secondary annealing) of Example 3 according to one embodiment of the present invention, when analyzed by GDS.

[0042] Figure 6 shows an example of a conceptual diagram when measuring the glossiness of a steel plate.

[0043] FIG. 7 is a graph showing the distribution of O content when analyzed in the thickness direction from the surface of a cold-rolled plate (surface of the anti-oxidation coating film) after the anti-oxidation coating of Example 3 according to one embodiment of the present invention, and indicates the section including the high point parallel part of the coating film and the high point parallel part and the thickness point of the coating film.

[0044] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0045] In addition, embodiments of the present invention are provided to more fully explain the invention to those with average knowledge in the relevant technical field.

[0046] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0047] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or practices of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0048] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0049] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0050] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0051] Oxides or nitrides formed on the surface of the steel sheet during the manufacturing process of electrical steel sheets (hereinafter referred to as "scale") are not removed during the rolling process and remain embedded in the surface. This scale is unevenly distributed on the surface of the steel sheet and has a rough nature.

[0052] During the annealing process, which is one of the steps in manufacturing electrical steel sheets, heat treatment is performed under a reducing atmosphere mixed with hydrogen to suppress oxidation or nitridation. However, it is fundamentally impossible to completely suppress scales such as oxides and nitrides. Furthermore, if a large amount of scale remains on the surface of the steel sheet prior to the annealing process and the surface morphology is non-uniform, new scale is formed during the annealing process, causing it to become even thicker.

[0053] Accordingly, the inventors of the present invention conducted in-depth research to effectively remove steel plate scale and discovered that scale formation on the steel plate surface during annealing can be minimized by performing descaling after the hot rolling process to reduce residual scale and applying an anti-oxidation coating before the subsequent annealing process. Furthermore, it was expected that this would improve the aesthetic appearance of the steel plate and the adhesion of the insulating coating, ultimately leading to a reduction in iron loss.

[0054] Meanwhile, the anti-oxidation coating must possess the characteristic of delaying the time the steel sheet surface comes into direct contact with the annealing atmosphere during annealing, while ensuring that the coating film itself does not oxidize. To this end, it is advantageous to apply the coating using materials containing manganese (Mn), metals with weaker oxidation properties than Mn, or oxides that readily undergo reduction in the annealing atmosphere. However, if the surface of the steel sheet to which the anti-oxidation coating is applied is rough or contains a large amount of residual scale, the effectiveness of the coating may be significantly reduced even if applied.

[0055] Accordingly, the inventors of the present invention extensively investigated the scale behavior on the surface of a steel plate and methods for descaling. As a result, they confirmed that by effectively descaling a hot-rolled plate to minimize residual scale on the surface of the steel plate, performing cold rolling, and applying an anti-oxidation coating under specific conditions to the surface of the steel plate prior to annealing, it is possible to provide an electrical steel plate with a beautiful surface and excellent insulation coating adhesion and electromagnetic properties, and thus completed the present invention. In other words, the technical significance of the present invention lies in providing a non-oriented electrical steel plate with excellent surface quality and excellent electromagnetic properties.

[0056] The present invention will be described in detail below.

[0057] According to one embodiment of the present invention, a non-oriented electrical steel sheet comprising a base steel sheet and an anti-oxidation coating film formed on at least one surface of the base steel sheet can be provided.

[0058] In one embodiment of the present invention, the base steel sheet may contain, in weight percent, silicon (Si): 1.50~6.00%, aluminum (Al): 0.10~2.00%, and manganese (Mn): greater than 0% and less than or equal to 2.00%.

[0059] The reasons for limiting the alloy composition of the steel sheet as described above are explained in detail below. Meanwhile, unless otherwise specified, the content of each element is based on weight, and the ratio of the microstructure is based on area.

[0060] Silicon (Si): 1.50~6.00%

[0061] Silicon (Si) plays a role in increasing the resistivity of the material to lower iron loss and increasing strength through solid solution strengthening. If the content of Si is low, the effect of improving iron loss and strength may be insufficient, whereas if the content is excessive, the brittleness of the material increases, leading to a sharp decrease in rolling productivity and the formation of surface oxide layers and oxides that are harmful to magnetism.

[0062] In one embodiment of the present invention, considering the above-mentioned matters, the Si may be included in an amount of 1.50 to 6.00%. In another embodiment of the present invention, the Si may be included in an amount of 2.00% or more, or 2.10% or more, and according to yet another embodiment, it may be included in an amount of 5.95% or less, or 4.50% or less.

[0063] Aluminum (Al): 0.10~2.00%

[0064] Aluminum (Al), similar to Si, is an element that increases the resistivity of the material to lower iron loss and improves workability during cold rolling by improving rollability. If too little Al is added, it may be difficult to obtain the effect of reducing high-frequency iron loss, and the temperature at which AlN precipitates is lowered, which can degrade magnetism as fine nitrides are formed. On the other hand, if the content of Al is excessive, excessive nitrides are formed, degrading magnetism and causing problems in all processes such as steelmaking and continuous casting, which can significantly reduce productivity.

[0065] In one embodiment of the present invention, taking into account the above-mentioned matters, the Al may be included in an amount of 0.10 to 2.00%. In another embodiment of the present invention, the Al may be included in an amount of 0.20% or more, or 0.30% or more, and according to yet another embodiment, it may be included in an amount of 1.70% or less, or 1.60% or less.

[0066] Manganese (Mn): Greater than 0% ~ 2.00% or less

[0067] Manganese (Mn) also plays a role in improving iron loss by increasing the resistivity of the material, and it also combines with sulfur (S) in the steel to form sulfides. If the content of Mn is excessive, there is a problem of increased brittleness during slab and hot rolling, so it is advantageous to control the content appropriately.

[0068] In one embodiment of the present invention, the Mn may be included in an amount greater than 0%, but it is advantageous for the content to be 2.00% or less. In another embodiment of the present invention, the Mn may be included in an amount of 0.01% or more or 0.05% or more, and according to yet another embodiment, it may be included in an amount of 1.90% or less or 1.80% or less.

[0069] A steel sheet according to one embodiment of the present invention may further include one or more of C, Ti, P, S, and N as follows.

[0070] Carbon (C): 0.0050% or less

[0071] Carbon (C) causes self-aging and can degrade the magnetic properties of electrical steel sheets by hindering grain boundary or domain wall movement through the formation of carbides by combining with impurity elements present in the steel; therefore, it is advantageous to limit its content.

[0072] In one embodiment of the present invention, the C may be included in an amount of 0.0050% or less, but may be included in an amount exceeding 0% as it may be inevitably added. In another embodiment of the present invention, the C may be included in an amount of 0.0001% or more or 0.0010% or more, and in yet another embodiment, may be included in an amount of 0.0045% or less or 0.0040% or less.

[0073] Titanium (Ti): 0.0050% or less

[0074] Titanium (Ti) has a very strong tendency to form precipitates within steel and can degrade iron loss by forming fine carbides, nitrides, or sulfides within the base material, thereby inhibiting grain growth and domain wall movement. Accordingly, the content of the above-mentioned Ti can be limited.

[0075] In one embodiment of the present invention, the Ti may be included in an amount of 0.0050% or less, but may be included in an amount exceeding 0% as it may be inevitably added. In another embodiment of the present invention, the Ti may be included in an amount of 0.0001% or more or 0.0005% or more, and according to yet another embodiment, may be included in an amount of 0.0045% or less or 0.0040% or less.

[0076] Nitrogen (N): 0.0050% or less

[0077] Nitrogen (N) can worsen iron loss by inhibiting grain growth and domain wall movement, not only by forming fine AlN precipitates within the base material but also by combining with other impurities to form fine precipitates. Accordingly, the content of N can be limited.

[0078] In one embodiment of the present invention, N may be included in an amount of 0.0050% or less, but may be included in an amount exceeding 0% as it may be inevitably added. In another embodiment of the present invention, N may be included in an amount of 0.0001% or more or 0.0005% or more, and according to yet another embodiment, may be included in an amount of 0.0045% or less or 0.0040% or less.

[0079] Phosphorus (P): 0.1000% or less

[0080] Phosphorus (P) not only plays a role in increasing the resistivity of the material but is also advantageous for improving magnetic flux density as a grain boundary segregation element. However, if the content of P is excessive, there is a problem in that it increases the brittleness of the steel sheet and impairs weldability.

[0081] In one embodiment of the present invention, the P may be included in an amount of 0.1000% or less. In another embodiment of the present invention, the P may be included in an amount of 0.0900% or less, or 0.0850% or less, and according to yet another embodiment, it may be included in an amount of 0.0001% or more, or 0.0010% or more.

[0082] Sulfur (S): 0.0100% or less

[0083] Sulfur (S) can form fine precipitates such as MnS and CuS, which can degrade magnetic properties and hot workability. Therefore, the content of the above S can be limited.

[0084] In one embodiment of the present invention, the S may be included in an amount of 0.0100% or less, but the content may exceed 0% considering the level that may inevitably be added. In another embodiment of the present invention, the S may be included in an amount of 0.0001% or more or 0.0005% or more, and according to yet another embodiment, it may be included in an amount of 0.0090% or less or 0.0085% or less.

[0085] According to one embodiment of the present invention, the base steel sheet may further include one or more selected from tin (Sn), antimony (Sb), bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) in an amount of 0.005 to 0.200 weight% based on the total content.

[0086] Tin (Sn) and antimony (Sb) play a role in improving the texture of materials and suppressing surface oxidation by segregating at grain boundaries and surfaces, so the magnetism of steel can be improved by adding these elements. However, when adding Sn or Sb, if the content is excessive, grain boundary segregation becomes severe, the surface quality deteriorates, and the hardness increases, which may cause the cold-rolled sheet to fracture and reduce rolling performance.

[0087] When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are additionally added, they segregate at grain boundaries, thereby alleviating stress concentration at grain boundaries during cold rolling, and thus in the subsequent annealing process (recrystallization annealing). <111> Magnetic flux density can be improved by suppressing the recrystallization of / ND orientation grains. However, if the content of these elements is excessive when added, a large amount of segregation occurs, which may inhibit grain growth and potentially lead to inferior magnetic flux density and iron loss.

[0088] Accordingly, when the above elements are added according to one embodiment of the present invention, if added alone or if at least two types are added, the content may be 0.200% or less based on the total sum. Meanwhile, in order to sufficiently obtain the above-described effect, when added alone or at least two types are added, the content may be 0.005% or more based on the total sum.

[0089] In one embodiment of the present invention, it is noted that when at least two or more of the above elements are added, the lower limit of the content of each element is not separately limited.

[0090] According to one embodiment of the present invention, the base steel plate may further include one or more of Cr, Cu, Ni, Zn and Co as follows.

[0091] Chrome (Cr): 0.010~0.500%

[0092] Chromium (Cr) can be additionally included as it plays a role in improving iron loss by increasing resistivity. If the content of such Cr is less than 0.010%, the aforementioned upward effect of resistivity cannot be sufficiently obtained. On the other hand, if the content is excessive and exceeds 0.500%, the magnetic flux density may decrease.

[0093] Accordingly, in one embodiment of the present invention, the Cr may be included in an amount of 0.010 to 0.500%. In another embodiment of the present invention, the Cr may be included in an amount of 0.050% or more, and according to yet another embodiment, it may be included in an amount of 0.400% or less.

[0094] Copper (Cu): 0.050% or less

[0095] Copper (Cu) has the effect of suppressing the formation of oxides and nitrides by being concentrated on the surface of the steel substrate under specific ranges of hot rolling and annealing process conditions. In addition, it is an element advantageous for descaling as it has the effect of weakening the adhesion between the steel substrate and the scale formed on its surface. Due to the addition of such Cu, oxides and nitrides on the steel surface can be reduced and the grain size of the steel sheet can be increased, thereby achieving the effect of reducing iron loss along with an increase in the magnetic flux density of the product. However, if the content is too excessive, it may be concentrated in specific parts of the steel surface, leading to uneven removal of scale and potentially causing surface defects.

[0096] In one embodiment of the present invention, Cu may be included in excess of 0% to obtain the aforementioned effect of Cu, but the upper limit thereof may be limited to 0.050% or less. In another embodiment of the present invention, the Cu may be included in excess of 0.002%, and according to yet another embodiment, it may be 0.045% or less or 0.040% or less.

[0097] Nickel (Ni): 0.050% or less

[0098] Nickel (Ni) can react with impurity elements present in steel to form fine sulfides, carbides, nitrides, etc., which can have a harmful effect on magnetism, so its content may be limited.

[0099] In one embodiment of the present invention, the Ni may be limited to 0.050% or less, but since it may be inevitably added, its content may exceed 0%. In another embodiment of the present invention, the Ni may be 0.030% or less, and in yet another embodiment, it may be 0.001% or more.

[0100] Zinc (Zn): 0.010% or less

[0101] If the content of zinc (Zn) is excessive, it can act as an impurity and impair the quality of the work, so its content can be limited.

[0102] In one embodiment of the present invention, the Zn may be limited to 0.010% or less, but since it may be inevitably added, its content may exceed 0%. In another embodiment of the present invention, the Zn may be 0.005% or less, and in yet another embodiment, it may be 0.001% or more.

[0103] Cobalt (Co): 0.050% or less

[0104] Although cobalt (Co) does not form fine precipitates that reduce the magnetism of the steel sheet, it increases the high-temperature strength of the steel sheet, which can cause the coil shape to be defective after hot rolling, so its content may be limited.

[0105] In one embodiment of the present invention, the Co may be limited to 0.050% or less, but since it may be inevitably added, its content may exceed 0%. In another embodiment of the present invention, the Co may be 0.040% or less, and in yet another embodiment, it may be 0.001% or more.

[0106] According to one embodiment of the present invention, the base steel plate may further include one or more of Mo, B, V, Ca, Nb, Zr, Te, and Mg as follows.

[0107] Molybdenum (Mo): 0.0300% or less

[0108] When a large amount of molybdenum (Mo) is added to steel, the segregation of segregated elements is suppressed, which may reduce the effect of improving texture. Accordingly, the content of the said Mo can be controlled.

[0109] In one embodiment of the present invention, the Mo may be limited to 0.0300% or less. However, the lower limit of the Mo is not specifically limited, but since it plays a role in improving the texture by segregating at the surface and grain boundaries when present in trace amounts, it may be included at 0.0010% or more. In another embodiment of the present invention, the Mo may be included at 0.0050% or more, and according to yet another embodiment, it may be included at 0.0100% or less.

[0110] Boron (B): 0.0050% or less

[0111] If a large amount of boron (B) is added to the steel, it can cause deterioration of magnetic properties through the formation of inclusions within the steel. Accordingly, the content of the above-mentioned B can be controlled.

[0112] In one embodiment of the present invention, B may be limited to 0.0050% or less. However, the lower limit of B is not specifically limited, but may be 0.0001% or more due to steelmaking costs. In another embodiment of the present invention, B may be 0.0040% or less.

[0113] Vanadium (V): 0.0050% or less

[0114] Vanadium (V) is an element with a very strong tendency to form precipitates in steel, and it degrades iron loss by forming fine carbides or nitrides within the base material, thereby inhibiting grain growth and domain wall movement. Accordingly, the content of V can be controlled.

[0115] In one embodiment of the present invention, V may be limited to 0.0050% or less. However, the lower limit of V is not specifically limited, but may be 0.0003% or more considering steelmaking costs. In another embodiment of the present invention, V may be 0.0040% or less.

[0116] Calcium (Ca): 0.0050% or less

[0117] Calcium (Ca) is also an element with a very strong tendency to form precipitates in steel, and it degrades iron loss by forming fine sulfides within the base material, thereby inhibiting grain growth and domain wall movement. Accordingly, the content of the above-mentioned Ca can be controlled.

[0118] In one embodiment of the present invention, the Ca may be limited to 0.0050% or less. However, the lower limit of the Ca is not specifically limited, but may be included at 0.0003% or more considering steelmaking costs. In another embodiment of the present invention, the Ca may be included at 0.0040% or less.

[0119] Niobium (Nb): 0.0050% or less

[0120] Niobium (Nb) is also an element with a very strong tendency to form precipitates in steel, and it degrades iron loss by forming fine carbides or nitrides within the base material, thereby inhibiting grain growth and domain wall movement. Accordingly, the content of the above Nb can be controlled.

[0121] In one embodiment of the present invention, the Nb may be limited to 0.0050% or less. However, the lower limit of the Nb is not specifically limited, but may be included at 0.0003% or more considering steelmaking costs. In another embodiment of the present invention, the Nb may be included at 0.0040% or less.

[0122] Zirconium (Zr): 0.0050% or less

[0123] If a large amount of zirconium (Zr) is added to steel, it can cause deterioration in magnetic properties through the formation of inclusions within the steel. Accordingly, the content of the said Zr can be controlled.

[0124] In one embodiment of the present invention, the Zr may be limited to 0.0050% or less. However, the lower limit of the Zr is not specifically limited, but may be 0.0001% or more considering steelmaking costs. In another embodiment of the present invention, the Zr may be 0.0005% or more, and according to yet another embodiment, it may be 0.0040% or less.

[0125] Tellurium (Te): 0.0100% or less

[0126] Tellurium (Te) can be added to prevent the fractured oxide layer from being pressed into the base material during rolling and to detach it by diffusing into the oxide layer on the surface of the hot-rolled coil, increasing the coefficient of friction between the oxide layer and the rolling work rolls, and concentrating beneath the oxide layer to improve hardness.

[0127] In one embodiment of the present invention, in order to sufficiently obtain the effect of Te, it may be included in an amount of 0.0001% or more. However, if the content is too excessive, the oxide layer is easily detached, causing the base material to come into direct contact with the work roll, thereby reducing the effect described above, and excessive deformation bands may be generated within the steel sheet during cold rolling, which may lead to the development of a {111} / ND texture that is unfavorable to magnetism. Accordingly, Te may be included in an amount of 0.0100% or less. In another embodiment of the present invention, Te may be 0.0005% or more, and according to yet another embodiment, it may be included in an amount of 0.0090% or less.

[0128] Magnesium (Mg): 0.0050% or less

[0129] Magnesium (Mg) is an element that mainly combines with S in steel to form sulfides, and can affect the surface oxide layer of the steel base.

[0130] In consideration of this, in one embodiment of the present invention, the Mg may be limited to 0.0050% or less. However, the lower limit of the Mg is not specifically limited, but may be 0.0001% or more considering the steelmaking cost. In another embodiment of the present invention, the Mg may be 0.0005% or more, and according to yet another embodiment, it may be 0.0040% or less.

[0131] A base steel sheet according to one embodiment of the present invention comprises, in addition to the aforementioned alloy composition, Fe and unavoidable impurities as the remainder components. The unavoidable impurities are impurities 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 description 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.

[0132] A non-oriented electrical steel sheet according to one embodiment of the present invention may include an anti-oxidation coating film formed on at least one surface of the above-mentioned base steel sheet.

[0133] As will be explained in detail below, an anti-oxidation coating film according to one embodiment of the present invention can be formed by applying an anti-oxidation coating to a cold-rolled sheet obtained by cold rolling before annealing. By forming the anti-oxidation coating film before the annealing process in this manner, the formation of scale, such as oxides or nitrides, generated during the annealing process in the annealing furnace can be suppressed.

[0134] In one embodiment of the present invention, the thickness of the anti-oxidation coating film may be 0.05 to 0.50 μm. If the thickness of the anti-oxidation coating film is less than 0.05 μm, there is a problem with the uniformity and coverage rate of the coating film being reduced. On the other hand, if the thickness exceeds 0.50 μm and is excessively thick, it is advantageous for suppressing oxide formation, but the manufacturing cost increases significantly, and there is a risk of breakage due to increased brittleness of the coating film.

[0135] In one embodiment of the present invention, the thickness of the antioxidant coating film can be measured using a transmission electron microscope (TEM) as one example among methods generally capable of measuring film thickness, or using a glow discharge spectrometer (GDS) as another example. When measuring using GDS, the distance from the point parallel to the peak of the oxygen (O) component forming the antioxidant coating film to the point where it decreases by half can be substituted.

[0136] Here, the peak parallel of the oxygen (O) component is defined as a point corresponding to the average value of oxygen content in the range where the standard deviation of the oxygen content is less than 1 and is greater than or equal to the average value of the oxygen content measured for the anti-oxidation coating film. Here, the measurement area (measurement depth) for obtaining the average value of the oxygen content can be defined, for example, as a point from the initial content (oxygen (O) content at the outermost surface of the anti-oxidation coating film) when measured using GDS to a depth where the oxygen (O) content is reduced to approximately 1.0%. More specifically, if the oxygen (O) content is greater than 1.0% (O content > 1.0%), it can be defined as a depth where it becomes 1.0% when rounded down to the second decimal place, and if the oxygen (O) content is less than 1.0% (O content < 1.0%), it can be defined as a depth where it becomes 1.0% when rounded up to the second decimal place.

[0137] Referring to Fig. 7, the point corresponding to the peak parallel section in the section where the average value of the oxygen content relative to the total thickness of the anti-oxidation coating film is greater than or equal to 1 and the standard deviation is less than 1 (indicated by the thick line) is the point where the oxygen content is 19%. At this time, the depth of the point corresponding to half of that value (9.5%) can be set as the thickness of the anti-oxidation coating film. In this case, the thickness of the anti-oxidation coating film becomes 0.13㎛.

[0138] An anti-oxidation coating film according to one embodiment of the present invention may include one or more of a metal and an oxide thereof, wherein the absolute value of the Gibbs energy reduction is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C. For example, the metal having an absolute value of the Gibbs energy reduction smaller than that of manganese (Mn) may be Fe, Ni, Cu, Sn, etc. Generally, the larger the absolute value of the Gibbs energy reduction, the stronger the oxidation characteristic of the metal.

[0139] In the interior of an anti-oxidation coating film according to one embodiment of the present invention, Al scales of Al oxide and / or Al nitride may exist, and the average diameter of the Al scales may be 100 nm or less. At this time, the Al scales may not be clustered in one place but may be uniformly dispersed throughout the entire coating film.

[0140] In addition, in one embodiment of the present invention, the anti-oxidation coating film may contain an average of 5 to 25 weight percent of oxygen, which can be confirmed by a GDS profile as shown in FIG. 3 as one example.

[0141] A non-oriented electrical steel sheet according to one embodiment of the present invention has a maximum Al content in an area within 0.05 μm in the thickness direction from the surface of the anti-oxidation coating film. max , when the average Al content at a point 5.00 μm in the thickness direction from the above surface is denoted as Al0, the following Equation 1 can be satisfied. Meanwhile, even when an anti-oxidation coating is not applied, the maximum Al content in the region within 0.05 μm in the thickness direction from the surface of the steel is Al max By defining the average Al content at a point 5.00 μm in the thickness direction from the surface as Al0, Equation 1 is derived and can be compared with the case where an anti-oxidation coating film is formed.

[0142] [Relationship 1]

[0143] (Al max / Al0) ≤ 20.0

[0144] (In Equation 1, each Al content is in weight%.)

[0145] Generally, the scale that accumulates on the surface of an electrical steel sheet may consist of Al oxide, Si oxide, Al nitride, or complex oxides of Al and Si or Fe, depending on the elements contained within the electrical steel sheet. In this case, the indicator for evaluating the scale can be determined by the Al accumulated on the surface of the steel sheet after annealing is completed. As Al accumulates on the steel sheet surface, oxygen and nitrogen also accumulate together; therefore, it can be determined that the accumulated Al forms Al oxide and Al nitride.

[0146] In one embodiment of the present invention, a method for evaluating the degree of Al enrichment on the surface of an electrical steel sheet, that is, on the surface of the anti-oxidation coating film, can be analyzed using a Glow Discharge Spectrometer (GDS) as an example. When the scale remaining on the surface of the final steel sheet or the surface scale formed during the annealing process was measured using GDS, it was confirmed that most of it was concentrated within 0.05 μm in the thickness direction from the surface. Accordingly, the highest concentration of oxide enriched on the surface of the non-oriented electrical steel sheet according to one embodiment of the present invention is defined as the highest concentration of Al within 0.05 μm in the thickness direction from the surface of the anti-oxidation coating film, and this is Al max It is referred to as [Name]. Meanwhile, the average Al concentration of the electrical steel sheet, that is, the average Al concentration of the substrate steel sheet, is defined as a value measured at a point 5.00 μm in the thickness direction from the surface of the anti-oxidation coating film, and this is referred to as Al0. Here, the surface of the anti-oxidation coating film refers to the outermost layer of the electrical steel sheet containing the anti-oxidation coating film, i.e., the outermost surface.

[0147] In this way, Al max With Al0 defined, the electrical steel sheet according to one embodiment of the present invention is [Al maxIt is preferable that the value of [ / Al0] be 20.0 or less. If the above value exceeds 20.0, it implies that the surface concentration is excessive; in this case, not only is the surface quality degraded, but there is also a risk that the adhesion and iron loss characteristics of the insulating coating will be inferior. In another embodiment of the present invention, [Al max The value of / Al0] may be 15.0 or less, or 10.0 or less.

[0148] A non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 180 μm. If the average grain size of the electrical steel sheet is 50 μm or more, excellent characteristics such as magnetic flux density and iron loss can be secured in the finally manufactured product. However, if the average grain size of the electrical steel sheet exceeds 180 μm, the improvement in electromagnetic properties becomes saturated, and heat treatment at excessive temperature and time is required, which is economically disadvantageous. Here, the term "average grain size" refers to the average value of the grain size measured in the steel sheet after the annealing process is completed, and the grain size at this time remains unchanged thereafter. As an example, the grain size can be measured based on the equivalent diameter of a circle when measuring the microstructure using an SEM, etc., at the 1 / 4t point in the thickness direction of the electrical steel sheet according to ASTM E112-13. However, it is not limited thereto.

[0149] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to another aspect of the present invention will be described in detail. It should be noted that the following manufacturing method corresponds to one example for manufacturing a steel sheet according to one embodiment of the present invention.

[0150] According to one embodiment of the present invention, an electrical steel sheet can be manufactured by heating a prepared steel slab and then undergoing a series of processes including [hot rolling - descaling - cold rolling - anti-oxidation coating - annealing].

[0151] Below, each process step is explained in detail.

[0152] [Slab Heating]

[0153] Prior to hot rolling, the slab may be heated. The heating process of the steel slab is a process intended to facilitate the hot rolling process described later, and the heating temperature at this time is not specifically limited. However, as an example, the heating of the slab may be performed in a temperature range of 1000 to 1180°C. If the heating temperature of the slab is too low, the rolling performance may be reduced during subsequent hot rolling, whereas if the temperature is too high, the growth of oxides containing Si accelerates, and the concentration of Cu, etc., on the surface of the base steel may not occur.

[0154] [Hot Rolled]

[0155] According to the above, a hot-rolled plate can be obtained by hot-rolling a heated slab.

[0156] In one embodiment of the present invention, the heated slab can be rough-rolled to obtain a plate with a thickness of 30 to 60 mm, and then finished-rolled to obtain a hot-rolled plate with a thickness of 0.8 to 2.7 mm.

[0157] If the thickness after the above rough rolling is too thick, the latent heat on the surface of the steel plate is large, and the rolling speed slows down, which increases scale growth during rolling and makes it difficult to descale the subsequent hot-rolled plate. On the other hand, if the thickness after the above rough rolling is too thin, the cooling of the rolled plate is accelerated, which may reduce rolling performance. As another embodiment, the above rough rolling can be performed with a thickness of 55 mm or less.

[0158] Prior to performing finish rolling on the plate obtained after the above-described rough rolling, a scale removal process may be performed. At this time, the scale can be removed from the surface through mechanical methods; for example, high-pressure water can be sprayed to remove the scale through the impact. If an excessive amount of time elapses after rough rolling, the surface temperature decreases, increasing the adhesion of the scale, and in this case, removing the scale becomes difficult. Accordingly, the temperature of the material (roughly rolled plate) immediately after rough rolling may be 950°C or higher and less than 1050°C, and the scale can be removed within 25 seconds immediately after rough rolling. On the other hand, if the temperature of the material after rough rolling is too low, the scale growth rate is low, but the surface cools, making it difficult to remove the scale. Furthermore, if the temperature of the material after rough rolling is excessively high, the scale growth rate accelerates, internal oxidation develops, and residual oxides on the surface increase. In one embodiment of the present invention, the scale refers to oxides or nitrides.

[0159] According to the above, a hot-rolled plate can be obtained by finishing rolling the plate (rolled plate) obtained after rough rolling, and as one embodiment, finishing rolling can be performed so that the thickness of the hot-rolled plate is in the range of 0.8 to 2.7 mm. As another embodiment, finishing rolling can be performed so that a hot-rolled plate with a thickness of 1.60 to 2.30 mm is obtained.

[0160] In one embodiment of the present invention, finish rolling may be performed at a temperature of 800°C or higher. In another embodiment of the present invention, the temperature may be 870°C to 950°C. If the temperature during finish rolling is less than 800°C, excessive cooling must be performed for finish rolling after rough rolling, and there is a risk that rolling performance may be reduced.

[0161] In one embodiment of the present invention, a process of winding the hot-rolled plate manufactured according to the above into a coil shape may be performed. The winding process may be performed within a temperature range of 500 to 700°C of the hot-rolled plate. If the temperature during winding is less than 500°C, there is a risk that the coil shape will deteriorate, whereas if the temperature exceeds 700°C, there is a risk that internal oxidation will occur.

[0162] [De-scaled]

[0163] A descaling process can be performed to remove surface scale from the hot-rolled plate obtained according to the above. As an example, the descaling process can be performed while uncoiling a coil-shaped hot-rolled plate.

[0164] If scale remains on the surface of hot-rolled sheets, it penetrates into the interior of the sheet during the subsequent cold rolling process, roughening the surface of the electrical steel sheets produced through the subsequent annealing process and causing point defects. Furthermore, the electromagnetic properties deteriorate, such as reduced iron loss, due to the scale remaining on the finally manufactured electrical steel sheets.

[0165] According to one embodiment of the present invention, an anti-oxidation coating is applied to a cold-rolled plate obtained by cold rolling. However, if oxides remain on the hot-rolled plate undergoing cold rolling, the surface of the plate becomes rough during the subsequent cold rolling process. When an anti-oxidation coating is applied to a plate (cold-rolled plate) with such a roughened surface, the effect cannot be sufficiently obtained. Therefore, it is necessary to sufficiently remove the scale from the hot-rolled plate.

[0166] In one embodiment of the present invention, the descaling of the hot-rolled plate may be performed by a mechanical method using a brush or shot peening, or by a chemical method using an aqueous acid solution (e.g., an aqueous hydrochloric acid (HCl) solution).

[0167] As an example, the hot-rolled plate can be heat-treated in a temperature range of 900 to 1050°C to eliminate internal oxides, and then a descaling process can be performed by shot-blasting the surface of the hot-rolled plate. The metal balls used during the shot-blasting process may have an average diameter of 1 to 1000 μm, or the operating speed of the steel plate may be controlled to 50 to 150 mpm (meter per minute), or the metal balls may be controlled to collide with the surface of the steel plate at a speed of 300 to 3000 kg / min. After the shot-blasting process according to the above, descaling can be performed additionally using hydrochloric acid, and at this time, the shot-blasted hot-rolled plate can be immersed in an aqueous acid solution of 15 to 30 weight% for 50 to 150 seconds to further remove scale.

[0168] As another example, descaling can be performed using only chemical methods without shot blasting. As one example, scale can be removed by immersing a hot-rolled plate in an aqueous acid solution (e.g., an aqueous HCl solution) of 15 to 30 weight percent for 50 to 180 seconds. At this time, to promote descaling, the hot-rolled plate may be heated to a temperature of 40 to 120°C before being immersed in the aqueous acid solution, and this can be applied in the same way to chemical methods performed after mechanical methods. Meanwhile, to enhance descaling by acid, the pickling time and acid concentration can be controlled, and commonly known conditions can be applied.

[0169] The effect of descaling according to one embodiment of the present invention can be determined by the concentration (content, %) of aluminum (Al) concentrated on the surface of the hot-rolled plate. Al has strong oxidizing properties and forms stable Al2O3 or AlN. Since these Al concentrations are formed to the deepest depths in the thickness direction of the hot-rolled plate, the degree of descaling can be determined by measuring the Al concentrated on the surface after descaling. As an example, the method for evaluating the Al concentrated on the surface of the hot-rolled plate after descaling can be analyzed using GDS. As a non-limiting example, it can be performed using the Leco GDS850A model under conditions of an acceleration voltage of 700 KV and a current of 30 mA. At this time, even if the manufacturer of the GDS or the acceleration voltage is changed, the same criteria can be applied because the relative change in Al with respect to depth is similar. Meanwhile, the aforementioned evaluation method using GDS can be applied in the same way to the GDS evaluation method for other manufacturing process steps described later.

[0170] According to one embodiment of the present invention, when measuring the Al content of the surface of a hot-rolled plate using GDS, if the maximum Al content within 0.5 μm in the thickness direction from the surface of the hot-rolled plate is denoted as Al(s) and the average Al content at a point 5.0 μm in the thickness direction from the surface of the hot-rolled plate is denoted as Al(i), the Al concentration (%) of the surface of the hot-rolled plate can satisfy the following Equation 2. That is, if the Al content concentrated at the surface is lower than the average Al content within the hot-rolled plate, it can be evaluated that descaling has been effectively achieved. In another embodiment of the present invention, the value of Equation 2 below may be 95% or less. Here, the average Al content (Al(i)) refers to the average value of the Al values ​​measured at a point 5.0 μm in the thickness direction from the surface of the hot-rolled plate, which is the point where the Al content is measured, and the Al value measured in the vicinity of this point. The term "nearby" refers, for example, to 4.9 μm, 5.1 μm, etc. in the thickness direction.

[0171] [Relationship 2]

[0172] (Al(s) / Al(i))×100 < 100

[0173] (In Equation 2, each Al content is in weight%.)

[0174] [Cold Rolled]

[0175] By cold rolling the hot-rolled plate treated for descaling according to the above, a cold-rolled plate having a target thickness can be obtained.

[0176] In one embodiment of the present invention, a cold-rolled plate of a target thickness can be obtained by performing the cold rolling process only once, or a cold-rolled plate of a target thickness can be obtained by performing the cold rolling process multiple times (e.g., two or more times). Here, in the latter case, for example, when the cold rolling process is performed twice, a first annealing heat treatment can be performed after the first cold rolling, and then a second annealing heat treatment can be performed after the second cold rolling. In this case, the cold-rolled plate obtained by the first cold rolling can be referred to as an intermediate cold-rolled plate, and the annealing heat treatment process performed after obtaining the cold-rolled plate of the target thickness, i.e., the final cold-rolled plate, can be referred to as the final annealing heat treatment. On the other hand, when the cold rolling process is performed only once, the annealing heat treatment process performed immediately after the cold rolling can be referred to as the final annealing heat treatment.

[0177] In one embodiment of the present invention, the cold rolling process may be performed with a cold reduction rate of 35 to 90% based on the total reduction rate. In another embodiment, when the cold rolling process is performed multiple times, for example twice, the first (first) cold rolling process may be performed with a reduction rate of 35 to 70%, and the final (second) cold rolling process may be performed with a reduction rate of 30 to 80%.

[0178] In one embodiment of the present invention, the cold rolling may be performed using a tandem cold mill consisting of 4 to 6 rows regardless of the number of times or the number of rounds, or using a Z-mill or Sendzimir mill. However, the rolling mill and rolling method are not specifically limited, and a person skilled in the art may appropriately select them to obtain a cold-rolled sheet having an intended final thickness.

[0179] [Anti-oxidation coating]

[0180] Prior to performing the subsequent annealing heat treatment on the cold-rolled sheet obtained according to the above, an anti-oxidation coating may be applied. In one embodiment of the present invention, the anti-oxidation coating is intended to minimize the formation of scale on the surface of the cold-rolled sheet during the subsequent annealing heat treatment.

[0181] In one embodiment of the present invention, the anti-oxidation coating may be performed after cold rolling. In the case of performing only one cold rolling, the anti-oxidation coating process may be performed immediately after cold rolling, followed by a subsequent annealing heat treatment process.

[0182] According to another embodiment of the present invention, when the cold rolling is performed multiple times, for example, when two cold rollings are performed, an anti-oxidation coating process may be performed immediately after each cold rolling. In addition, the anti-oxidation coating may be performed only after the first cold rolling, or only after the second cold rolling.

[0183] In this way, by applying an anti-oxidation coating to a cold-rolled sheet followed by an annealing heat treatment, the surface appearance of the final electrical steel sheet can be secured beautifully, and the adhesion of the insulation coating can also be improved. Furthermore, the effect of reducing iron loss can also be obtained.

[0184] In one embodiment of the present invention, the anti-oxidation coating process needs to be performed such that the anti-oxidation coating film formed by the anti-oxidation coating prevents the surface of the cold-rolled sheet from coming into direct contact with the annealing atmosphere during the subsequent annealing heat treatment process, while ensuring that the anti-oxidation coating film itself does not oxidize. To achieve this, it is advantageous for the anti-oxidation coating process to use a metal that has a weaker oxidation characteristic than Mn, or to use the aforementioned metal in conjunction with a coating method that includes an oxide of a metal that undergoes good reduction in the annealing atmosphere.

[0185] Generally, the oxidizing properties of a metal are expressed as the decrease in Gibbs energy when it reacts with 1 mole of oxygen to form an oxide. The greater the absolute value of this decrease in Gibbs energy, the more strongly the metal is classified as having oxidizing properties. In addition, when defining a metal that is less oxidizable than Mn, it is defined as a metal in which the absolute value of the decrease in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction with 1 mole of oxygen occurs at 900°C.

[0186] Accordingly, in one embodiment of the present invention, the anti-oxidation coating process is a process of coating using one or more of a metal and an oxide of the metal, wherein the absolute value of the reduction in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C, and as an example, the metal may be one or more of Fe, Ni, Cu, and Sn.

[0187] In addition, in one embodiment of the present invention, the anti-oxidation coating process may be performed by plating / coating one or more of the aforementioned metal and its oxides, and the method thereof may be performed by methods such as electroplating, CVD coating, and PVD coating, although the method is not specifically limited. Meanwhile, a coating film of a certain thickness may be formed by the aforementioned anti-oxidation coating process.

[0188] An anti-oxidation coating according to one embodiment of the present invention is effective in suppressing the formation of Al oxides and Al nitrides on the surface of the substrate steel. Non-oriented electrical steel sheets containing Al have a strong tendency to form Al oxides and nitrides in the form of a continuous film on the surface of the steel sheet during the annealing heat treatment process. Consequently, if the amount of concentrated Al oxides and nitrides on the surface of the electrical steel sheet is large and a film is formed in a continuous form, not only is the appearance quality of the electrical steel sheet degraded, but the adhesion of the insulation coating is also inferior and iron loss increases. In the present invention, the problem of the electromagnetic properties of the electrical steel sheet deteriorating due to these Al oxides and nitrides can be prevented through the aforementioned anti-oxidation coating process. In other words, by forming an anti-oxidation coating film through the anti-oxidation coating process, a certain amount of time is required for Al within the base steel to diffuse to the surface of the anti-oxidation coating film during the subsequent annealing heat treatment process. As the Al diffused into the anti-oxidation coating film disperses and precipitates within it in the form of oxides or nitrides, the concentration of Al on the surface of the anti-oxidation coating film is relatively suppressed. As a result, the surface quality and iron loss of the electrical steel sheet can be improved.

[0189] As an example, a specimen (Fig. 5) that underwent an annealing heat treatment process as a subsequent process after an anti-oxidation coating process was compared with a specimen (Fig. 4) that underwent annealing heat treatment under the same conditions on a cold-rolled plate obtained by cold rolling without an anti-oxidation coating process. As a result of the observation, the amount of Al oxide decreased on the surface (surface of the anti-oxidation coating film) of the specimen that had an anti-oxidation coating film formed by the anti-oxidation coating process, and the amount of nitride also decreased relatively. In addition, although not explicitly indicated, it was confirmed that Al was dispersed within the anti-oxidation coating film in the form of oxide or nitride. At this time, it was found that the oxide formed within the anti-oxidation coating film was not in a continuous form but was dispersed in the form of particles (e.g., spherical) with an average diameter of 100 nm or less.

[0190] In one embodiment of the present invention, the anti-oxidation coating process may be performed such that the average thickness of the anti-oxidation coating film is in the range of 0.05 to 0.50 μm. While it is most preferable to apply the anti-oxidation coating uniformly over the entire surface of the cold-rolled plate, there may be uncoated areas depending on the surface condition. Taking this into consideration, in order to achieve desirable oxidation inhibition performance, as one example, the surface coverage rate of the coating may be 80% or more of the total surface area, and as another example, it may be 90% or more or 95% or more.

[0191] [Annealing Heat Treatment]

[0192] Annealing heat treatment can be performed on the cold-rolled sheet obtained according to the above.

[0193] Generally, annealing heat treatment is performed immediately on a cold-rolled sheet obtained by cold rolling, but according to one embodiment of the present invention, as described above, an anti-oxidation coating process can be performed on a cold-rolled sheet obtained by cold rolling, and then an annealing heat treatment process can be performed subsequently.

[0194] In one embodiment of the present invention, it has been revealed that the cold rolling process for obtaining the cold rolled plate can be performed once or multiple times (e.g., two or more times), and that an annealing heat treatment process must be performed after such cold rolling process.

[0195] In one embodiment of the present invention, when multiple annealing heat treatments are performed by multiple cold rolling, for example, when two cold rollings are performed, the first annealing heat treatment performed immediately after or after the first cold rolling can be performed in a temperature range of 870 to 1050°C, and the atmosphere at this time can be controlled as a reducing atmosphere of 3 to 50 volume% hydrogen (H2) and the remainder nitrogen (N2). Meanwhile, an anti-oxidation coating process may be performed first on a cold-rolled sheet obtained by first cold rolling prior to the first annealing heat treatment (the cold-rolled sheet here corresponds to an intermediate cold-rolled sheet).

[0196] If the temperature during the above annealing heat treatment is less than 870°C, the recrystallization of the cold-rolled sheet is not sufficiently achieved, whereas if the temperature exceeds 1050°C, the recrystallization effect becomes saturated and the grains become excessively coarse, which may impair the magnetic properties of the final product (electrical steel sheet).

[0197] In one embodiment of the present invention, when a first annealing heat treatment is performed in the aforementioned temperature range, an annealing scale may be formed as the surface of the cold-rolled sheet reacts with the atmosphere gas inside the annealing furnace. Accordingly, during the annealing heat treatment, the atmosphere inside the annealing furnace can be controlled to a reducing atmosphere that can suppress the formation of scale, such as oxides, to the maximum extent. As an example, the reducing atmosphere can be controlled with a mixed gas of N2 and H2, and as a preferred example, the atmosphere can be controlled with a mixed gas of 3 to 50 volume% hydrogen (H2) and the remainder nitrogen (N2). At this time, if the concentration of hydrogen (H2) is less than 3 volume%, the effect of inhibiting scale growth cannot be obtained, whereas if the concentration of hydrogen (H2) exceeds 50 volume%, costs increase excessively, and there is a risk of operational safety issues arising due to the risk of explosion.

[0198] In one embodiment of the present invention, when controlling the atmosphere of the annealing furnace to the aforementioned reducing atmosphere, the effect can be maximized by controlling the dew point temperature of the atmosphere gas to -20°C or lower. In another embodiment, the dew point temperature may be -30°C or lower, or -40°C or lower.

[0199] After performing the first annealing heat treatment according to the above, additional cold rolling may be performed to obtain a target thickness, and a second annealing heat treatment (final annealing heat treatment) may be performed on the obtained cold-rolled sheet. Since the heat treatment conditions at this time can be applied identically to the conditions of the first annealing heat treatment performed earlier, they are not specifically limited.

[0200] Meanwhile, in another embodiment of the present invention, a final annealing heat treatment may be performed on a cold-rolled sheet obtained by cold rolling once to have a target thickness, and since the conditions at this time can be applied in the same way as the conditions (temperature, atmosphere, dew point temperature) described above, the above description is substituted.

[0201] In this way, a non-oriented electrical steel sheet can be obtained by performing a final annealing heat treatment process, and the electrical steel sheet may have an average grain size of 50 to 180 μm.

[0202] [Insulation Coating]

[0203] After completing the aforementioned annealing heat treatment process, that is, the final annealing heat treatment process, an insulating coating can be performed to form an insulating coating film on the surface of the non-oriented electrical steel sheet, i.e., on the anti-oxidation coating film.

[0204] In one embodiment of the present invention, the insulating coating may be selected from an organic film, an inorganic film, or an organic-inorganic composite film. Meanwhile, since the insulating coating is a process generally performed in manufacturing non-oriented electrical steel sheets, the conditions thereof are not specifically limited.

[0205] As described above, a non-oriented electrical steel sheet manufactured through a series of processes according to one embodiment of the present invention can have excellent magnetic properties, such as a beautiful surface appearance and low iron loss.

[0206] In one embodiment of the present invention, the quality of the non-oriented electrical steel sheet can be confirmed by evaluating the whiteness, iron loss (W10 / 400), and the degree of whitening of the insulating coating film.

[0207] In one embodiment of the present invention, the non-oriented electrical steel sheet may have a whiteness of 55 or higher, which is an indicator of product surface quality, and in another embodiment, it may have a whiteness of 60 or higher or 65 or higher. Since the whiteness of the electrical steel sheet tends to decrease as residual scale or annealing scale on the surface of the base steel increases, surface quality can be ensured by managing the whiteness of the final product to a certain level or higher. Meanwhile, whiteness can be measured by irradiating white light onto one spot of the steel sheet and then analyzing the reflected spectrum. As an example, the Minolta CM-3700D can be used, and the measured values ​​are expressed as numerical values ​​for white (L*), red (a*), and yellow (b*). The value indicated as white (L*) is referred to as whiteness, and its range is 0 to 100. Even if equipment from other manufacturers is used, the measured values ​​are similar, so there is no specific limitation on the measuring equipment.

[0208] Meanwhile, along with the aforementioned whiteness, glossiness can also be utilized as an indicator of the surface quality of the product. The glossiness of electrical steel sheets tends to decrease as residual scale, annealing enrichment, and roughness on the surface of the base steel increase, and in this case, the adhesion of the insulating coating film is reduced. In one embodiment of the present invention, the non-oriented electrical steel sheet had a glossiness value of 65 or higher when measured at an angle of 20°, and this increased in proportion to the increase in whiteness. On the other hand, when the glossiness value was less than 65, the adhesion of the insulating coating film was reduced, and the correlation with whiteness was negligible. The glossiness can be measured using the same instrument (e.g., a colorimeter) used to measure the whiteness mentioned earlier. Here, the term "angle" refers to the angle at which a vertical line descends toward the surface of the steel sheet from 0 degrees when a vertical line is set to 0 degrees when a vertical line is erected on the surface of the steel sheet (see FIG. 6). As an example, a mirror gloss meter may be used.

[0209] In addition, a non-oriented electrical steel sheet according to one embodiment of the present invention may have an iron loss (W10 / 400) of 12.5 W / Kg or less. Here, the iron loss (W10 / 400) is the iron loss when a magnetic flux density of 1.0 T (Tesla) is induced at a frequency of 400 Hz, and can be expressed based on a thickness of 0.20 mm. In another embodiment, the non-oriented electrical steel sheet may have an iron loss (W10 / 400) of 9.0 to 12.0 W / kg.

[0210] Meanwhile, for the purpose of increasing the flatness of the non-oriented electrical steel sheet and improving its processability, a stress relief heat treatment may be additionally performed at a temperature range of 750 to 950°C after the formation of an insulating coating film. Before the stress relief heat treatment, residual scale may exist on the surface of the non-oriented electrical steel sheet; however, since the residual scale is in a stable state, it does not affect the size distribution of oxides or nitrides formed on the surface. The iron loss can be measured after performing such a stress relief heat treatment.

[0211] As a method for evaluating the adhesion of an insulating coating on a non-oriented electrical steel sheet according to one embodiment of the present invention, a whitening evaluation method may be applied. As an example, the whitening evaluation may be performed by conducting a salt spray test according to ISO 1499 standards and then measuring the reduction in whiteness of the product or the whitened area. At this time, if the reduction in whiteness is within 10%, the adhesion may be evaluated as excellent.

[0212] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0213] (Example)

[0214] Using the alloy composition shown in Table 1 below, a slab with a thickness of 250 mm was held at 1120°C for 60 minutes, and then rough rolling was performed to produce a plate with a thickness of 40 mm. The temperature of the plate (rolled plate) after the completion of the rough rolling was 1020°C, and 23 seconds after the completion of the rough rolling, high-pressure water at 150 Bar was sprayed onto the surface of the plate to remove scale. Subsequently, finishing hot rolling was performed to produce a hot-rolled plate with a thickness of 2.0 mm in a coil shape. The temperature of the hot-rolled plate immediately after the finishing hot rolling was 910°C, and the temperature of the coil after being produced in a coil shape was 600°C.

[0215] For the hot-rolled plate manufactured according to the above, a final non-oriented electrical steel sheet was manufactured through a series of processes under the conditions shown in Table 2 below.

[0216] At this time, the descaling process of the hot-rolled plate was carried out by combining mechanical descaling using shot blasting and chemical descaling using a hydrochloric acid solution only for steel grade 1. In addition, for the remaining steel grades, only chemical descaling using a hydrochloric acid solution was carried out. Specifically, after heat-treating the hot-rolled plate of steel grade 1 at 1000°C, metal balls with an average diameter of 400 μm were sprayed onto the surface of the hot-rolled plate at a speed of 3000 kg / min, and the plate passing speed was set to 50 MPM. Afterward, the plate was pickled by immersing it in an 18 wt% HCl aqueous solution at 80°C for 60 seconds. For the remaining steel grades excluding steel grade 1, descaling was performed by immersing them in an 18 wt% HCl aqueous solution at 80°C for 40 to 180 seconds.

[0217] Meanwhile, an anti-oxidation coating was applied to the cold-rolled sheet in one or two stages. The anti-oxidation coating was applied by applying a coating solution containing Fe metal ions and oxides of this metal to obtain the film thickness shown in Table 2, and the coating solution was applied by electroplating. During the electroplating, an electrolyte containing ferrous and ferric ions and a complexing agent was used, with an iron ion concentration of 80 g / L. Additionally, the current density was 50 A / dm². 2 The time was adjusted according to the thickness of the anti-oxidation coating. In addition, an insoluble metal plate was used as the anode during the electroplating process.

[0218] In addition, the atmosphere inside each annealing furnace for the annealing heat treatment process is shown in Table 2 below, where the remainder, excluding hydrogen (H2), was nitrogen (N2) and unavoidable impurities. Also, the dew point temperature of each annealing furnace was controlled to be the same at -40℃.

[0219] After completing the final annealing heat treatment, each non-oriented electrical steel sheet was obtained, and an insulating coating treatment was performed on the electrical steel sheet. The insulating coating treatment was performed by forming an insulating coating film with a thickness of 0.5 μm using a resin-based coating.

[0220]

[0221]

[0222]

[0223]

[0224] The degree of Al enrichment, surface characteristics, and electromagnetic characteristics of the non-oriented electrical steel sheet manufactured according to the above were evaluated, and the results are shown in Table 3 below.

[0225] First, to verify the descaling effect of the hot-rolled plate, the degree of surface Al enrichment of the descaled hot-rolled plate was measured. At this time, the GDS850A model from Leco was used, and the Al content was measured from the surface of the hot-rolled plate in the thickness direction under conditions of an acceleration voltage of 700 KV and a current of 30 mA, and the Al enrichment value was calculated according to Equation 2.

[0226] In addition, for cold-rolled sheets (electrical steel sheets) that had undergone the final annealing heat treatment process prior to insulation coating, the Al content was measured using the same equipment and under the same conditions as above, and the Al enrichment (%) was calculated according to Equation 1. At this time, for specimens that had undergone an anti-oxidation coating, the Al content was measured on the surface of the anti-oxidation coating film, and for specimens that had not undergone an anti-oxidation coating (Comparative Examples 3 to 7 in Table 3), the Al content was measured on the surface of the cold-rolled sheet to calculate the enrichment (%).

[0227] To evaluate the whitening of electrical steel sheets, an ISO 1499 standard salt spray test was conducted on electrical steel sheets with an insulating coating for 72 hours, and then evaluated using the following indicators. At this time, the whitening area was measured by visually observing the surface, and the whiteness was measured using a colorimeter to calculate the decrease in whiteness before and after the whitening evaluation.

[0228] ○ (Excellent): No change on the surface, and a decrease in whiteness of less than 10%

[0229] △ (Insufficient): Whitened area is less than 10% (greater than 0%), or whiteness reduction is 10% or more but less than 20%

[0230] × (Defective): Area of ​​whitening or reddish-green is 10% or more, or whiteness reduction is 20% or more

[0231] In addition, glossiness was also measured using the colorimeter used for the whiteness measurement mentioned above.

[0232] Meanwhile, for magnetic properties such as magnetic flux density and iron loss, five specimens measuring 60 mm in width × 60 mm in length were prepared for electrical steel sheets coated with insulation, and magnetic flux density was measured for each specimen in the rolling direction and in a direction corresponding to 55° from the rolling direction using a single sheet tester, after which the average value was calculated. In the above test, W10 / 400 represents the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, and B50 represents the magnetic flux density induced in a magnetic field of 5000 A / m.

[0233]

[0234]

[0235] As shown in Tables 1 to 3, Invention Examples 1 to 8, which satisfy the alloy composition and manufacturing conditions according to one embodiment of the present invention, can be confirmed to have Al enrichment on the surface, i.e., the surface of the anti-oxidation coating film, suppressed by descaling and anti-oxidation coating. As a result, excellent surface characteristics and magnetism were observed.

[0236] On the other hand, comparative examples that did not satisfy one or more of the alloy composition and manufacturing conditions had inferior magnetic properties because Al enrichment on the plate surface was not sufficiently suppressed.

[0237] Among them, Comparative Examples 1 and 2 had inferior surface characteristics in the final electrical steel sheet because the descaling of the hot-rolled sheet was not sufficiently performed, and scale remained on the surface of the sheet.

[0238] Comparative Examples 3 to 7 are cases in which the alloy composition and manufacturing conditions are identical to those of Inventive Examples 3 to 7, except for whether an anti-oxidation coating was applied. Compared to the Inventive Examples, the Al concentration on the surface of the cold-rolled sheet after final annealing was 15.5 or higher, and since the Al concentration on the steel sheet surface was high, it can be seen that scale remains, and as a result, the surface quality was inferior and high iron loss was observed.

[0239] Comparative Example 8 is a case where the temperature during final annealing (secondary annealing) was excessively high, resulting in inferior surface quality and magnetism, and Comparative Example 9 is a case where the anti-oxidation coating was applied too thickly, resulting in inferior surface quality and magnetism.

[0240] Meanwhile, Comparative Examples 10 and 11 are cases where the content of Si and Mn in the steel is excessive, and in both of them, surface cracks occurred during cold rolling (first step), so subsequent processes could not be performed.

[0241] Comparative Example 12 is a case where the Al content in the steel is excessive, and showed inferior results in surface quality and magnetism.

[0242] Figures 1 and 2 are graphs showing the Al content distribution in the thickness direction on the surface of hot-rolled plates after descaling of Comparative Example 1 and Invention Example 1, respectively, measured by GDS.

[0243] In Comparative Example 1, it can be seen that the Al content on the surface of the hot-rolled plate is high because the processing time during descaling was short, so the scale was not sufficiently removed from the surface of the hot-rolled plate. On the other hand, in the case of Inventive Example 1, in which descaling was performed by mechanical and chemical methods, it can be seen that the Al content on the surface of the hot-rolled plate was significantly lower compared to the point at 5.0 μm in the thickness direction of the hot-rolled plate. This means that descaling was sufficiently achieved.

[0244] Figure 3 is a graph showing the concentration distribution of Fe, Si, Al, and O in the thickness direction from the surface of the anti-oxidation coating film of a cold-rolled sheet that has been coated with an anti-oxidation coating before the second annealing heat treatment of Invention Example 3, measured by GDS.

[0245] As shown in Fig. 3, the content of Si and Al on the surface of the cold-rolled sheet, that is, the surface of the anti-oxidation coating film, is close to 0.0, and it can be confirmed that the content of Si and Al remains almost constant from a depth of about 0.2 μm in the thickness direction to 1.0 μm. These results indicate that the tendency of Al and Si contained in the steel to diffuse to the surface of the steel sheet and form scales such as oxides and nitrides is suppressed by the anti-oxidation coating film.

[0246] Figures 4 and 5 are graphs showing the distribution of Al and N content in the thickness direction on the surface of cold-rolled plates after final annealing (secondary annealing) of Comparative Example 3 and Invention Example 3, measured by GDS.

[0247] In Comparative Example 3, since no anti-oxidation coating was applied before annealing, the Al content in the surface layer of the cold-rolled sheet after annealing (e.g., at a point 0.1 μm in the thickness direction from the outermost surface) was significantly high. In contrast, in Inventive Example 3, where an anti-oxidation coating was applied before annealing, it can be confirmed that the Al content on the surface of the cold-rolled sheet (i.e., the surface of the anti-oxidation coating film) was significantly reduced even after annealing. These results indicate that the anti-oxidation coating applied before annealing can have the effect of reducing the amount of scale generated during the subsequent annealing process.

Claims

1. A base steel sheet comprising, in weight%, silicon (Si): 1.50~6.00%, aluminum (Al): 0.10~2.00%, manganese (Mn): greater than 0%~2.00% or less, and the remainder being Fe and other unavoidable impurities; and It includes an anti-oxidation coating film with a thickness of 0.05 to 0.50 μm formed on at least one surface of the above-mentioned steel sheet, and The maximum Al content in the region within 0.05㎛ in the thickness direction from the surface of the above antioxidant coating film is Al max A non-oriented electrical steel sheet satisfying the following relationship 1, where Al0 is the average Al content at a point 5.00 μm in the thickness direction from the surface. [Relationship 1] (Al max / Al0) ≤ 20.0 (In Equation 1, each Al content is in weight%.) 2. In Paragraph 1, The above electrical steel sheet is a non-oriented electrical steel sheet having an average grain size of 50 to 180 μm.

3. In Paragraph 1, The above-mentioned anti-oxidation coating film is a non-oriented electrical steel sheet composed of one or more types of a metal and oxides thereof, wherein the absolute value of the reduction in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C.

4. In Paragraph 1, A non-oriented electrical steel sheet having Al scales of Al oxide and / or Al nitride present inside the above-mentioned anti-oxidation coating film, wherein the Al scales have an average diameter of 100 nm or less.

5. In Paragraph 1, The above-mentioned base steel sheet is a non-oriented electrical steel sheet further comprising, in weight%, one or more selected from carbon (C): 0.0050% or less, titanium (Ti): 0.0050% or less, phosphorus (P): 0.1000% or less, sulfur (S): 0.0100% or less, and nitrogen (N): 0.0050% or less.

6. In Paragraph 1, The above-mentioned base steel sheet is a non-oriented electrical steel sheet further comprising one or more selected from tin (Sn), antimony (Sb), bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) in an amount of 0.005 to 0.200 weight% based on the total content.

7. In Paragraph 1, The above-mentioned base steel sheet is a non-oriented electrical steel sheet further comprising, in weight%, one or more selected from chromium (Cr): 0.010~0.500%, copper (Cu): 0.050% or less, nickel (Ni): 0.050% or less, zinc (Zn): 0.010% or less, and cobalt (Co): 0.050% or less.

8. In Paragraph 1, The above-mentioned base steel sheet is a non-oriented electrical steel sheet further comprising, in weight%, one or more selected from molybdenum (Mo): 0.0300% or less, boron (B): 0.0050% or less, vanadium (V): 0.0050% or less, calcium (Ca): 0.0050% or less, niobium (Nb): 0.0050% or less, zirconium (Zr): 0.0050% or less, tellurium (Te): 0.0100% or less, and magnesium (Mg): 0.0050% or less.

9. A step of obtaining a hot-rolled plate by heating and then hot-rolling a slab containing, in weight percent, silicon (Si): 1.50~6.00%, aluminum (Al): 0.10~2.00%, manganese (Mn): greater than 0%~2.00% or less, and the remainder being Fe and other unavoidable impurities; A step of descaling the above hot-rolled plate; A step of obtaining a cold-rolled plate by cold-rolling the hot-rolled plate after the above descaling; A step of applying an anti-oxidation coating to the surface of the above cold-rolled plate; and The method includes the step of annealing the cold-rolled sheet after the above-mentioned anti-oxidation coating treatment, A method for manufacturing a non-oriented electrical steel sheet, wherein the above-mentioned anti-oxidation coating treatment involves coating one or more types of a metal and oxides thereof, wherein the absolute value of the reduction in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C.

10. A step of obtaining a hot-rolled plate by heating and then hot-rolling a slab containing, in weight%, silicon (Si): 1.50~6.00%, aluminum (Al): 0.10~2.00%, manganese (Mn): greater than 0%~2.00% or less, and the remainder being Fe and other unavoidable impurities; A step of descaling the surface of the above hot-rolled plate; A step of obtaining an intermediate cold-rolled plate by first cold-rolling the hot-rolled plate after the above descaling; A first annealing heat treatment step for annealing the above intermediate cold-rolled plate; A step of obtaining a final cold-rolled plate by performing a second cold rolling after the first annealing heat treatment; and It includes a second annealing heat treatment step of annealing the final cold-rolled plate after the second cold rolling above, and The method further includes a step of applying an anti-oxidation coating before the first annealing heat treatment step and / or before the second annealing heat treatment step, A method for manufacturing a non-oriented electrical steel sheet, wherein the above-mentioned anti-oxidation coating treatment involves coating one or more types of a metal and oxides thereof, wherein the absolute value of the reduction in Gibbs energy is smaller than that of manganese (Mn) when an oxidation reaction occurs with 1 mole of oxygen at 900°C.

11. In Paragraph 9 or 10, A method for manufacturing non-oriented electrical steel sheets, wherein the above descaling treatment is performed by one or more methods selected from mechanical and chemical methods.

12. In Paragraph 9 or 10, A method for manufacturing a non-oriented electrical steel sheet satisfying the following equation 2, where Al(s) is the maximum Al content in a region within 0.5 μm in the thickness direction from the surface of the hot-rolled sheet after descaling, and Al(i) is the average Al content at a point 5.0 μm in the thickness direction from the surface of the hot-rolled sheet. [Relationship 2] (Al(s) / Al(i))×100 < 100 (In Equation 2, each Al content is in weight%.) 13. In Paragraph 9 or 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the above-mentioned anti-oxidation coating treatment is performed such that the coating rate is 80% or more of the total surface area.

14. In Paragraph 9, A method for manufacturing non-oriented electrical steel sheets, wherein the above annealing heat treatment step is performed in a reducing atmosphere of 3 to 50 volume% hydrogen (H2) and the remainder nitrogen (N2) in a temperature range of 870 to 1050°C.

15. In Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the first annealing heat treatment step and the second annealing heat treatment step are performed in a reducing atmosphere of 3 to 50 volume% hydrogen (H2) and the remainder nitrogen (N2) in a temperature range of 870 to 1050°C.

16. In Paragraph 9 or 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises, in weight %, one or more selected from carbon (C): 0.0050% or less, titanium (Ti): 0.0050% or less, phosphorus (P): 0.1000% or less, sulfur (S): 0.0100% or less, and nitrogen (N): 0.0050% or less.

17. In Paragraph 9 or 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises one or more selected from tin (Sn), antimony (Sb), bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) in an amount of 0.005 to 0.200 weight% based on the total content.

18. In Paragraph 9 or 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises, in weight %, one or more selected from chromium (Cr): 0.010~0.500%, copper (Cu): 0.050% or less, nickel (Ni): 0.050% or less, zinc (Zn): 0.010% or less, and cobalt (Co): 0.050% or less.

19. In Paragraph 9 or Paragraph 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises, in weight%, one or more selected from molybdenum (Mo): 0.0300% or less, boron (B): 0.0050% or less, vanadium (V): 0.0050% or less, calcium (Ca): 0.0050% or less, niobium (Nb): 0.0050% or less, zirconium (Zr): 0.0050% or less, tellurium (Te): 0.0100% or less, and magnesium (Mg): 0.0050% or less.

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