Non-oriented electrical steel sheet and method for manufacturing same

Abstract

The present invention can provide a non-oriented electrical steel sheet having improved surface properties and magnetic properties, and another aspect provides a method for manufacturing the non-oriented electrical steel sheet.

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 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. However, as these elements are highly oxidizing agents, they selectively form reaction products (e.g., scale), such as oxides or nitrides, on the surface during the steel manufacturing process. These reaction products affect the micro-morphology of the steel surface during production, particularly during rolling, thereby degrading surface qualities such as whiteness and gloss. 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] Meanwhile, the electrical steel sheet is provided with an insulating layer formed on the surface of a base steel sheet (also referred to as a substrate steel sheet) containing the aforementioned Si, Al, etc. However, if a large amount of reaction products such as oxides and nitrides are present on the surface of the substrate steel sheet manufactured through a series of processes, the insulating layer may be formed unevenly, and there is a risk that the electromagnetic properties of the electrical steel sheet may be inferior as a result.

[0004] As the global demand for electric vehicles rises as part of carbon neutrality initiatives, and the use of efficient home appliances increases, there is a need for the supply of electrical steel sheets with excellent electromagnetic properties, such as a beautiful surface and low iron loss; therefore, there is a need to develop electrical steel sheets capable of meeting these requirements.

[0005] (Patent Document 1) Korean Published Patent Application No. 10-2005-0066238

[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 insulating layer formed on at least one surface of the base steel sheet, wherein the insulating layer has a surface roughness (Ra) of 0.50 μm or less and a maximum roughness (Rt) of 5.00 μm or less.

[0009] In one embodiment of the present invention, the insulating layer may have a 10-point average roughness (Rz) of 3.50 μm or less.

[0010] Thus, according to the present invention, a non-oriented electrical steel sheet with a controlled insulating layer surface shape can be provided, and the electrical steel sheet can have excellent magnetic properties in addition to surface properties.

[0011] 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.

[0012] In one embodiment of the present invention, the base steel plate may further include one or more types selected from the groups i) to iv) below.

[0013] i) 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.

[0014] ii) 0.005 to 0.200 wt% based on the total content of one or more selected from tin (Sn), antimony (Sb), bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As).

[0015] iii) 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.

[0016] iv) 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.

[0017] According to another aspect of the present invention, a method for manufacturing a oriented electrical steel sheet is provided, comprising the steps of: preparing a slab; heating the slab and then hot-rolling it to obtain a hot-rolled sheet; heating the hot-rolled sheet; descaling the heated hot-rolled sheet; cold-rolling the hot-rolled sheet after descaling to obtain a cold-rolled sheet; annealing the cold-rolled sheet; and forming an insulating layer on the surface of the annealed cold-rolled steel sheet.

[0018] In one embodiment of the present invention, the step of heating the hot-rolled plate may be to heat it to 40 to 150°C at a driving speed of up to 200 mpm.

[0019] In one embodiment of the present invention, before heating the hot-rolled plate, the step of passing the hot-rolled plate through a roller leveler with an intermesh of 5 to 50 mm may be further included.

[0020] 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.

[0021] In one embodiment of the present invention, the step of heating the hot-rolled plate may be performed before the descaling treatment by the chemical method.

[0022] Although not limited thereto, in one embodiment of the present invention, the mechanical method may be a shot blast, and the shot blast may be performed using a ball with an average diameter of 1 to 1000 μm at a projection rate of 300 to 3000 kg / min and a projection speed of 500 to 2000 rpm.

[0023] In addition, although not limited thereto, in one embodiment of the present invention, the chemical method may be performed by immersing in an aqueous acid solution of 15 to 30 weight percent for 30 to 180 seconds.

[0024] In one embodiment of the present invention, the surface Si enrichment ratio of the hot-rolled plate after descaling can satisfy the following relationship 1.

[0025] [Relationship 1]

[0026] 0.80 ≤ (Si(s) / Si(i)) ≤ 4.00

[0027] (In Equation 1, each Si content is in weight%.)

[0028] According to the present invention, defects caused by surface scale occurring during the electrical steel sheet manufacturing process can be suppressed by improving pickling properties. Specifically, according to the present invention, it is possible to provide a non-oriented electrical steel sheet that has excellent adhesion of the insulating coating and excellent corrosion resistance by suppressing the occurrence of red rust in corrosive environments, as well as improved magnetic properties along with surface properties.

[0029] FIG. 1 shows an example of a driving device for a roller leveler according to an embodiment of the present invention.

[0030] 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.

[0031] 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.

[0032] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0033] 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.

[0034] 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.

[0035] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0036] 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.

[0037] Oxides or nitrides (hereinafter referred to as "scale") formed on the surface of the steel sheet during the manufacturing process of electrical steel sheets are not completely removed during the scale removal process and remain embedded in the surface during the rolling process. As this residual scale increases, it becomes unevenly distributed on the steel sheet surface, and the surface morphology becomes rough. Due to this scale, the adhesion between the base steel sheet and the insulation layer constituting the electrical steel sheet is reduced, thickness non-uniformity may occur, and there is a risk that electromagnetic properties may deteriorate, such as increased iron loss.

[0038] Accordingly, the inventors of the present invention have conducted in-depth research on methods to improve the efficiency of removing scale from the surface of steel sheets, as well as on the influence of the surface morphology of electrical steel sheets on the soundness and electromagnetic properties of the insulation coating and methods to control the surface morphology of electrical steel sheets. As a result, they optimized the descaling process for removing scale from the surface of hot-rolled sheets during the manufacturing process of electrical steel sheets, and further confirmed that the average roughness (Ra) and maximum roughness (Rt) among the surface morphologies of electrical steel sheets have an influence on electromagnetic properties, such as improved adhesion of the insulation coating and reduced iron loss, thereby completing the present invention.

[0039] The present invention will be described in detail below.

[0040] According to one aspect of the present invention, a non-oriented electrical steel sheet comprising a base steel sheet and an insulating layer formed on at least one surface of the base steel sheet can be provided.

[0041] 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%.

[0042] 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.

[0043] Silicon (Si): 1.50~6.00%

[0044] 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.

[0045] 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.

[0046] Aluminum (Al): 0.10~2.00%

[0047] Aluminum (Al), similar to Si mentioned above, 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.

[0048] 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.

[0049] Manganese (Mn): Greater than 0% ~ 2.00% or less

[0050] 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.

[0051] 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.

[0052] A steel sheet according to one embodiment of the present invention may further include one or more of carbon (C), titanium (Ti), phosphorus (P), sulfur (S), and nitrogen (N) as follows.

[0053] Carbon (C): 0.0050% or less

[0054] 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.

[0055] 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.

[0056] Titanium (Ti): 0.0050% or less

[0057] 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.

[0058] 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.

[0059] Nitrogen (N): 0.0050% or less

[0060] 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.

[0061] 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.

[0062] Phosphorus (P): 0.1000% or less

[0063] 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.

[0064] 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.

[0065] Sulfur (S): 0.0100% or less

[0066] Sulfur (S) can form fine precipitates such as MnS and CuS, which can degrade magnetic properties and reduce hot workability. Therefore, the content of the above S can be limited.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] According to one embodiment of the present invention, the base steel plate may further include one or more of chromium (Cr), copper (Cu), nickel (Ni), zinc (Zn) and cobalt (Co) as follows.

[0074] Chrome (Cr): 0.010~0.500%

[0075] 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.

[0076] 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.

[0077] Copper (Cu): 0.050% or less

[0078] 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 scale removal and potentially causing surface defects.

[0079] 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.

[0080] Nickel (Ni): 0.050% or less

[0081] 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.

[0082] 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.

[0083] Zinc (Zn): 0.010% or less

[0084] 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.

[0085] 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.

[0086] Cobalt (Co): 0.050% or less

[0087] 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.

[0088] 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.

[0089] According to one embodiment of the present invention, the base steel plate may further include one or more of molybdenum (Mo), boron (B), vanadium (V), calcium (Ca), niobium (Nb), zirconium (Zr), tellurium (Te), and magnesium (Mg) as follows.

[0090] Molybdenum (Mo): 0.0300% or less

[0091] 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.

[0092] 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.

[0093] Boron (B): 0.0050% or less

[0094] 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.

[0095] 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.

[0096] Vanadium (V): 0.0050% or less

[0097] 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.

[0098] 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.

[0099] Calcium (Ca): 0.0050% or less

[0100] 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.

[0101] 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.

[0102] Niobium (Nb): 0.0050% or less

[0103] 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.

[0104] 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.

[0105] Zirconium (Zr): 0.0050% or less

[0106] 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.

[0107] 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.

[0108] Tellurium (Te): 0.0100% or less

[0109] 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 it 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 it beneath the oxide layer to improve hardness.

[0110] 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.

[0111] Magnesium (Mg): 0.0050% or less

[0112] 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.

[0113] 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.

[0114] 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.

[0115] A non-oriented electrical steel sheet according to one embodiment of the present invention may include an insulating layer formed on at least one surface of the aforementioned base steel sheet.

[0116] In one embodiment of the present invention, the insulating layer can be formed by applying an insulating coating composition to the surface of the substrate steel plate, and the insulating layer is formed to have a thickness of approximately 0.5 μm. As such, since the insulating layer is thin, if there is foreign matter on the surface of the substrate steel plate, the coating layer becomes extremely thin locally or the coating does not form, and as the surface protection provided by the insulating layer is weakened, it becomes vulnerable to corrosion or discoloration. In addition, if there is a large amount of oxide (scale) remaining on the surface of the substrate steel plate or if the surface shape is uneven, not only is the adhesion to the insulating layer reduced, but the insulating layer is also formed unevenly, leading to a problem where the iron loss of the electrical steel plate increases. Therefore, the surface of the substrate steel plate for forming the insulating layer needs to be aesthetically pleasing, and this can be achieved through the control of the manufacturing process described in detail below.

[0117] The surface of a non-oriented electrical steel sheet according to one embodiment of the present invention, i.e., the surface of an insulating layer, may have a surface roughness (Ra) of 0.500 μm or less and a maximum roughness (Rt) of 5.00 μm or less.

[0118] Surface roughness (Ra) is a major factor determining the quality of the product surface. A high surface roughness (Ra) of the insulating layer implies that the surface is rough, and an electrical steel sheet containing an insulating layer with a high Ra may have low surface quality, such as whiteness and gloss. Accordingly, in one embodiment of the present invention, the Ra of the insulating layer is limited to 0.50 μm or less. If the surface roughness (Ra) of the insulating layer exceeds 0.50 μm, the surface quality as described above may deteriorate, and there is a risk that the insulating layer may become uneven.

[0119] Meanwhile, among surface shape factors, maximum roughness (Rt) refers to the perpendicular distance between two parallel lines parallel to the centerline of the roughness curve when these two parallel lines include the highest and lowest points of the roughness curve. A larger value of this maximum roughness (Rt) indicates that the surface is rougher. In one embodiment of the present invention, the soundness of the insulating layer can be ensured by limiting the maximum roughness (Rt) value of the insulating layer to 5.00 μm or less. That is, if the Rt value exceeds 5.00 μm, the adhesion of the insulating layer is reduced due to surface non-uniformity, and there is a risk of defects such as flow patterns occurring.

[0120] In one embodiment of the present invention, the lower limit values ​​of the surface roughness (Ra) and the maximum roughness value (Rt) are not specifically limited, but the surface roughness (Ra) may be 0.10 μm or more, and the maximum roughness (Rt) may be greater than 1.00 μm.

[0121] In addition, the 10-point average roughness (Rz) of the surface of the non-oriented electrical steel sheet according to one embodiment of the present invention, i.e., the insulating layer, may be 3.50 μm or less. The 10-point average roughness (Rz) refers to the value obtained by calculating the difference between five peaks and five valleys in a roughness curve and then averaging these five deviations. In one embodiment of the present invention, if the Rz value exceeds 3.50 μm, not only is the robustness of the insulating layer impaired, but the glossiness, which indicates the aesthetic effect of the electrical steel sheet surface, may also be reduced.

[0122] 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.

[0123] According to one embodiment of the present invention, a base steel sheet for obtaining 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 - annealing]. Meanwhile, in order to increase the scale removal efficiency during descaling of a hot-rolled sheet, particularly to increase the scale removal efficiency during chemical descaling, the present invention performs a heating process before the chemical descaling.

[0124] Below, each process step is explained in detail.

[0125] The steel slab used in the manufacturing method of the present invention may be refined and cast through a converter process or an electric furnace process.

[0126] In the converter process, molten iron supplied from a blast furnace is primarily used; however, depending on the supply and demand status of hot metal, some scrap or other iron sources may be added for refining to produce molten steel. In particular, when implementing low HMR operations that reduce the amount of molten iron used to meet requirements such as carbon neutrality, the amount of scrap used may increase, and as a result, elements not intended in this invention may be included in the molten steel within the allowable limits.

[0127] In the electric furnace process, molten steel can be obtained by primarily charging scrap, melting it using arc heat, and refining it. In some cases, molten iron may be added in addition to the scrap. As a result of including a large amount of scrap in this manner, elements not intended in the present invention (e.g., Cr, Cu, Ni, Mo, Sn, etc.) may be included in the molten steel within permissible limits.

[0128] Molten steel that has undergone the converter or electric furnace process may undergo an additional refining (secondary refining) process to adjust its composition and other properties.

[0129] [Slab Heating]

[0130] 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 within 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 it may not be easy to remove scale present on the surface after subsequent hot rolling.

[0131] In one embodiment of the present invention, the slab may have the same alloy composition as previously mentioned, and the specific alloy composition is replaced with the above description.

[0132] [Hot Rolled]

[0133] According to the above, a hot-rolled plate can be obtained by hot-rolling a heated slab.

[0134] In one embodiment of the present invention, when hot rolling the heated slab, the finishing rolling may be terminated at a temperature of 800°C or higher, and in another embodiment of the present invention, the temperature at which the finishing rolling begins may be 870°C to 980°C. If the finishing rolling end temperature is less than 800°C, there is a risk of material variation in the manufactured hot-rolled plate and a decrease in rolling performance.

[0135] In one embodiment of the present invention, the hot rolling may be performed such that the thickness of the hot-rolled plate is in the range of 0.8 to 2.7 mm. If the thickness of the hot-rolled plate being manufactured exceeds 2.7 mm and is too thick, there is a risk of causing a rolling load during cold rolling to obtain a subsequent cold-rolled plate, whereas if it is too thin, there is a risk of shape defects occurring.

[0136] [Record]

[0137] 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.

[0138] [Hot Rolled Plate Heating]

[0139] Prior to descaling the hot-rolled plate manufactured according to the above, it may be heated to a certain temperature. This process is intended to increase the efficiency of the subsequent descaling process. However, this process of heating the hot-rolled plate may be performed before the chemical descaling process among the descaling processes described later. That is, if a mechanical descaling process is performed, this heating process may be omitted.

[0140] Hot-rolled sheets obtained by hot rolling under certain conditions may have a large amount of scale (e.g., oxide scale) on their surface, and this scale is removed through a descaling process. Meanwhile, in order to completely remove the scale present on the surface of the hot-rolled sheet during the descaling process, an excessive descaling process is required. In this case, the descaling process may take a long time, and excessive pickling may affect the surface of the hot-rolled sheet directly beneath the scale. That is, excessive pickling may cause the thickness of the base steel sheet to decrease or localized erosion to occur, which may lead to sheet breakage during subsequent rolling processes. Accordingly, the inventors of the present invention have conducted in-depth research on a method to prevent the aforementioned problems by increasing the efficiency of descaling, and have discovered that when the hot-rolled sheet is heated to a specific temperature prior to descaling treatment, the scale removal rate during the subsequent descaling process is significantly increased.

[0141] In one embodiment of the present invention, the hot-rolled plate may be heated to 40 to 150°C, and the maximum travel speed of the hot-rolled plate may be 200 mpm while heating the hot-rolled plate. When the hot-rolled plate is heated to the aforementioned temperature range, the scale present on the surface of the hot-rolled plate is chemically activated, making it easier to remove the scale during descaling treatment.

[0142] If the heating temperature of the hot-rolled plate is less than 40℃, the efficiency of removing scale present on the surface of the hot-rolled plate is almost the same as before the heat treatment. On the other hand, if the temperature exceeds 150℃, the scale removal effect becomes saturated, and excessive energy costs may be incurred, which may lead to an excessive increase in manufacturing costs.

[0143] At this time, based on the width direction of the hot-rolled plate, the edge portion is more likely to come into contact with air compared to the center portion, so the temperature of the edge portion decreases rapidly; thus, the heating temperature of the edge portion can be set higher than that of the center portion. As one example, the temperature of the edge portion can be set about +10 to +20°C higher than that of the center portion. Here, the edge portion can be defined as extending to a point w / 8 away from the edge in the direction of the center, where the total width length of the hot-rolled plate is w, and it should be noted that this corresponds to both sides in the width direction.

[0144] In one embodiment of the present invention, the means for performing the heating is not specifically limited, but it is advantageous to apply a means that allows for easy heating during the process of the hot-rolled plate traveling. As a non-limiting example, the heating of the hot-rolled plate may be performed using an induction heating furnace, or it may be performed through electric heating. In this case, when using an induction heating furnace, the induction heating furnace may be provided before the scale removal means for subsequent descaling. As one example, when the subsequent descaling process is performed in a pickling bath, heating may be performed in an induction heating furnace before the hot-rolled plate is introduced into the pickling bath.

[0145] In one embodiment of the present invention, when heating the hot-rolled plate, the travel speed of the hot-rolled plate from the time heating starts to the time heating ends may be up to 200 mpm. If the travel speed of the hot-rolled plate is too fast during the heating process, the surface of the hot-rolled plate may be heated locally, and there is a risk that scale may not be uniformly removed during the subsequent descaling process. Although there is no specific limit on the lower limit of the travel speed of the hot-rolled plate, if the travel speed is too slow, productivity may decrease; therefore, considering this, it may be performed at 50 mpm or more.

[0146] The travel speed of the hot-rolled plate is a factor that can determine the heating temperature of the hot-rolled plate. Since the temperature of the hot-rolled plate increases over time as the travel speed of the hot-rolled plate slows down, the temperature applied to the hot-rolled plate can be controlled according to the travel speed. As an example, when the travel speed of the hot-rolled plate is significantly slowed down, if the heating and descaling processes are completed at that speed, an over-acidification may occur. In such cases, the heating can be stopped (e.g., turning off the heater inside the induction heating furnace) and the plate can be introduced into a subsequent descaling means in that state. In addition, in one embodiment of the present invention, the temperature of the hot-rolled plate is measured 4 to 5 meters before the hot-rolled plate enters the heating means, and the output of the heating means is controlled according to this temperature, thereby preventing the heating means from overheating.

[0147] In addition, a series of facilities for manufacturing electrical steel sheets according to one embodiment of the present invention can also be used to manufacture general carbon steels other than electrical steel sheets. In this case, the carbon steels, that is, steel materials from which scale is relatively easy to remove, do not necessarily need to be heated before the descaling process. In this case, the heating means may not be operated, and the steel may pass through the heating means as is. Thus, according to the present invention, there is an advantage that various types of steel can be easily produced in a single process line for manufacturing electrical steel sheets.

[0148] It should be noted that the heating process of a hot-rolled plate performed through one embodiment of the present invention is distinct from the process of annealing a hot-rolled plate. That is, unlike the annealing process of a hot-rolled plate, which requires a long heat treatment period, the present invention provides a process that increases the efficiency of subsequent descaling by rapidly heating the hot-rolled plate in a short time.

[0149] Meanwhile, before heating the hot-rolled plate, an additional process of passing it through a roller leveler may be performed, thereby causing cracks in the scale present on the surface of the hot-rolled plate. As an example, the step of passing it through the roller leveler may utilize an intermesh of 5 to 50 mm. The intermesh is a roll drive device in which two rolls are positioned parallel to each other at the top and three rolls are positioned at the bottom, and the upper and lower rolls are positioned staggered to prevent collisions even when the height changes. To explain one example of the intermesh with reference to the drawings, as shown in FIG. 1, the upper and lower rolls are provided, and the diameter of each roll may be 50 mm, and the horizontal distance between the centers of the upper and lower rolls may be 200 mm, but it should be noted that this is not limited thereto. In addition, as an example, applying an intermesh of 15mm means positioning the lower part of the upper roll and the upper part of the lower roll to overlap by 15mm, and allowing the hot-rolled plate to pass through the space between them (between the upper roll and the lower roll). In this way, when the intermesh is applied using a roller leveler, bending occurs as the hot-rolled plate passes between the upper roll and the lower roll, causing repeated tensile and shrinkage stresses on the surface of the hot-rolled plate, and the stress at this time induces fine cracks in the scale on the surface of the hot-rolled plate. Consequently, scale removal becomes easier during descaling.

[0150] [De-scaled]

[0151] A descaling process can be performed on the hot-rolled plate manufactured according to the above to remove scale present on the surface of the hot-rolled plate. At this time, the hot-rolled plate may have undergone the heating process described above, may have undergone an intermeshing process, or may have undergone a combination of these processes. However, hot-rolled plates that have not undergone the above processes are not excluded, and hot-rolled plates that have undergone descaling by a mechanical method (e.g., shot blasting, etc.) prior to heating are also included.

[0152] 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, if scale persists on the surface of the final electrical steel sheet, electromagnetic properties deteriorate, such as reduced adhesion of the insulation layer and increased iron loss.

[0153] 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 (shot blast), or by a chemical method using an aqueous acid solution (e.g., an aqueous hydrochloric acid (HCl) solution), and may also be performed by a combination of these methods.

[0154] 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. Although the conditions at this time are not specifically limited, as a non-limiting example, the metal balls used during the shot-blasting process may be metal balls with an average diameter of 1 to 1000 μm, 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 projection amount of 300 to 3000 kg / min and a projection speed of 500 to 2000 rpm. After the shot-blasting process according to the above, descaling can be performed additionally using hydrochloric acid, and the scale can be further removed by immersing the shot-blasted hot-rolled plate in an aqueous acid solution of 15 to 30 weight% for 30 to 180 seconds.

[0155] Meanwhile, it should be noted that the process of heat-treating the hot-rolled plate to 900°C or higher prior to the above shot blasting treatment is distinct from the previously mentioned hot-rolled plate heating process. In other words, the above hot-rolled plate heating process is a process that can be performed after the above shot blasting process and before descaling by a chemical method. Therefore, a descaling process using shot blasting is performed before the hot-rolled plate manufactured by hot rolling passes through the heating means. Furthermore, if the above shot blasting process is not performed, the hot-rolled plate manufactured by hot rolling can be directly fed into the heating means. However, this is not the only limitation.

[0156] As another example, descaling may be performed using only chemical methods without performing shot blasting. Likewise, although the conditions are not specifically limited, as a non-limiting example, the scale can be removed by immersing the hot-rolled plate heated to the above-mentioned temperature in an aqueous acid solution (e.g., an aqueous HCl solution) of 15 to 30 weight percent for 50 to 180 seconds. Meanwhile, to enhance descaling by acid, the amount of inhibitor added, the pickling time, and the concentration of the acid can be controlled, and commonly known conditions can be applied.

[0157] As previously mentioned, hot-rolled sheets obtained through a hot rolling process have a large amount of scale on their surface, and this scale may be oxide scale. Due to the characteristics of electrical steel sheets, the base steel sheet contains a relatively large amount of Si, so a large amount of oxide scale originating from Si (e.g., Si oxide (SiO2)) is generated among the scales formed on the surface of the hot-rolled sheet, and such oxide scale is not easy to remove. The present invention can overcome these limitations. Specifically, according to one embodiment of the present invention, by heating the hot-rolled sheet to a certain temperature before the descaling treatment, the Si oxide (SiO2) present on the surface of the hot-rolled sheet after the aforementioned descaling treatment can be significantly reduced.

[0158] Accordingly, the effect of descaling according to one embodiment of the present invention can be determined by the content of silicon (Si) concentrated on the surface of the descaled hot-rolled plate. Specifically, according to one embodiment of the present invention, the degree of Si concentration expressed by the following Equation 1 on the surface of the hot-rolled plate after descaling can satisfy 0.80 to 4.00.

[0159] [Relationship 1]

[0160] 0.80 ≤ (Si(s) / Si(i)) ≤ 4.00

[0161] (In Equation 1, each Si content is in weight%.)

[0162] As an example, the method for evaluating the Si content concentrated on the surface of the hot-rolled plate after the above 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. In this case, even if the manufacturer of the GDS or the acceleration voltage is changed, the same criteria can be applied because the relative change in Si with depth is similar.

[0163] According to one embodiment of the present invention, when measuring the Si content of a descaled hot-rolled plate surface using GDS, let Si(s) be the maximum Si content within 0.5 μm in the thickness direction from the surface of the hot-rolled plate, and let Si(i) be the average Si content at a point 5.0 μm in the thickness direction from the surface of the hot-rolled plate. Then, the Si concentration (%) on the surface of the hot-rolled plate can satisfy the following Equation 1. Here, the average Si content (Si(i)) refers to the average value of the Si 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 Si content is measured, and the vicinity thereof. The term "nearby" refers, for example, to a point 4.9 μm, 5.1 μm, etc. in the thickness direction.

[0164] [Cold Rolled]

[0165] 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.

[0166] 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.

[0167] 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%.

[0168] In one embodiment of the present invention, the cold rolling may be performed using a tandem cold mill (TCM) consisting of 4 to 7 rows regardless of the number of times or the number of turns, or using a Zendsimir Rolling Mill (ZRM) or a Cool Rolling Mill (CRM). 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.

[0169] [Annealing Heat Treatment]

[0170] Annealing heat treatment can be performed on the cold-rolled sheet obtained according to the above.

[0171] In one embodiment of the present invention, the cold rolling process for obtaining a cold-rolled sheet may be performed once or multiple times (e.g., two or more times), and an annealing heat treatment process may be performed after each cold rolling process.

[0172] In one embodiment of the present invention, when only one cold rolling is performed, a hot-rolled plate in which a descaling process is completed before cold rolling may be annealed, and the temperature at this time is not specifically limited but may be 870 to 1150°C.

[0173] 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 after the first cold rolling can be performed in a temperature range of 870 to 1150°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). If the temperature during the annealing heat treatment is less than 870°C, the recrystallization of the cold-rolled sheet is not sufficiently achieved, whereas if the temperature exceeds 1150°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).

[0174] Meanwhile, if the above cold rolling is performed three or more times, a first annealing heat treatment may be performed between the first cold rolling and the second cold rolling, and a second annealing heat treatment may be performed after the final cold rolling. That is, even if the cold rolling is performed three or more times, the above annealing heat treatment may be performed only twice, and annealing heat treatment may not be performed from after the second cold rolling until before the final cold rolling.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] [Insulation Coating]

[0180] After completing the aforementioned annealing heat treatment process, that is, the final annealing heat treatment process, an insulating coating can be applied to form an insulating layer on the surface of the cold-rolled steel sheet that has undergone the annealing heat treatment.

[0181] 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.

[0182] 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. In particular, the present invention can provide a non-oriented electrical steel sheet in which the surface shape of the insulating layer is controlled, specifically a non-oriented electrical steel sheet in which the surface roughness (Ra) of the insulating layer is 0.50 μm or less and the maximum roughness (Rt) is 5.00 μm or less.

[0183] Meanwhile, the quality of the non-oriented electrical steel sheet according to one embodiment of the present invention can be confirmed by evaluating the whiteness, iron loss (W10 / 400), and the degree of whitening of the insulation layer.

[0184] In one embodiment of the present invention, the non-oriented electrical steel sheet may have a whiteness of 60 or higher, which is an indicator of product surface quality, and in another embodiment, it may have a whiteness of 63 or higher or 65 or higher. Since the whiteness of the electrical steel sheet tends to decrease as the 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, where the measured values ​​are expressed as 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. In this case, the measurement was performed using a D65 standard light source in accordance with ISO 7724-2, and the average value was used after measuring at three arbitrary points on the surface of the specimen. On the other hand, since the measured values ​​are similar even when using devices from other manufacturers, there is no specific limitation on the measuring device.

[0185] 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.

[0186] 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 the insulation layer. 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 or distribution of oxides or nitrides formed on the surface. The iron loss can be measured after performing such a stress relief heat treatment.

[0187] 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 ASTM B117 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.

[0188] 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.

[0189] (Example)

[0190] After preparing a slab containing C: 0.002%, Si: 3.62%, Al: 0.68%, Mn: 0.31% by weight, and the remainder being Fe and other unavoidable impurities, the slab was held at 1120°C for 60 minutes, and then finished hot-rolled at 860°C to obtain a hot-rolled plate with a thickness of 2.0 mm, which was then coiled at 620°C to form a coil shape. Subsequently, each hot-rolled plate was descaled under the conditions shown in Table 1 below and cold-rolled to obtain an intermediate cold-rolled plate with a thickness of 0.9 mm. Afterward, each cold-rolled plate was heated to 1050°C for annealing heat treatment, wherein the atmosphere inside the annealing furnace was controlled to 3 volume% H2 and the remainder being N2, and the dew point temperature was set to -40°C. Cold rolling was performed again on the cold-rolled sheet after the above annealing heat treatment was completed to produce a cold-rolled sheet with a thickness of 0.2 mm, and then a final annealing heat treatment was performed. The annealing heat treatment at this time was carried out by heating to 1050°C, the atmosphere inside the annealing furnace was controlled with 20 volume% H2 and the remainder N2, and the dew point temperature was set to -40°C.

[0191] An insulating coating treatment was performed on the cold-rolled plate that had undergone annealing heat treatment according to the above to form an insulating layer with a thickness of 0.5 μm, and at this time, the insulating coating was performed using a resin-based composition.

[0192] As for the above descaling process, when shot blasting was performed, metal balls with an average diameter of 400 μm were used. With the operating speed of the hot-rolled plate set to 100 mpm (meter per minute), the metal balls were impacted onto the surface of the hot-rolled plate with a projection amount of 1,000 kg / min and a projection speed of 1,500 rpm. Subsequently, descaling was performed while passing through a heating means (induction heater) and a hydrochloric acid bath. In addition, when descaling treatment using an acid solution, the treatment was performed for 50 seconds in an 18% HCl solution at 80°C, and when passing through a roller leveler, an intermesh of 15 mm was applied. When descaling was performed in this manner, the sequence was shot blasting, intermesh, and acid solution; if some processes were not performed, the process was carried out in the order excluding those processes. In addition, when heating the hot-rolled plate before descaling with an acid solution, heating was performed by passing it through an induction furnace after applying the above-mentioned intermesh.

[0193] Steel Type Hot Rolled Plate Heating Descaling Classification Heating Temperature (°C) Travel Speed ​​(mpm) Shot Blast Intermesic Acid Solution Time (sec) 180 100○-○60 Invention Example 1 245 100-○○60 Invention Example 2 360 100-○○60 Invention Example 3 480 100-○○60 Invention Example 4 5100 100-○○60 Invention Example 5 6100 60-○○100 Invention Example 6 7100 100-○○60 Invention Example 7 78100 150-○○40 Invention Example 8 9100 200-○○30 Invention Example 9 10110 100-○○60 Invention Example 1011120 100-○○60 Invention Example 1112130 100-○○60 Invention Example In Table 1, '○' is indicated if the corresponding process was performed, and '-' is indicated if it was not performed. In Table 1, the descaling time refers to the time spent immersed in the acid solution.

[0194]

[0195] The surface shape of the insulation layer, surface quality, and electromagnetic properties of the non-oriented electrical steel sheet manufactured according to the above were evaluated, and the results are shown in Table 2 below.

[0196] First, the surface morphology of the insulation layer of each manufactured non-oriented electrical steel sheet was measured using a roughness meter. Specifically, to measure surface roughness (Ra), maximum roughness (Rt), and ten-point average roughness (Rz), a contact roughness meter (KOSAKA, model name Surcorder 700) was used in accordance with the regulations compliant with ISO 4287-1997. At this time, a cut-off value of 2.5 mm was applied.

[0197] Meanwhile, during the process of manufacturing each non-oriented electrical steel sheet, a GDS profile was measured on the descaled hot-rolled sheet to measure the surface Si concentration of the descaled hot-rolled sheet. At this time, the GDS850A model from Leco was used, and the Si content was measured in the thickness direction from the surface of the descaled hot-rolled sheet under conditions of an acceleration voltage of 700 KV and a current of 30 mA. The Si concentration was calculated according to Equation 1, and the results are shown in Table 2 below.

[0198] To verify the surface quality of non-oriented electrical steel sheets, the whiteness of electrical steel sheets coated with an insulation coating was measured using a colorimeter. Additionally, after treating the surface of each non-oriented electrical steel sheet according to the method specified in ASTM B117, the presence or absence of red rust was visually inspected and evaluated. Furthermore, to evaluate whitening of non-oriented electrical steel sheets, an ISO 1499 salt spray test was conducted on the insulation-coated electrical steel sheets for 72 hours, followed by evaluation using the following indicators. At this time, the whitened area was measured by visually observing the surface, and the whiteness was measured using a colorimeter to calculate the reduction in whiteness before and after the whitening evaluation.

[0199] ○ (Excellent): No change on the surface, and a decrease in whiteness of less than 10%

[0200] △ (Insufficient): Whitened area is less than 10% (greater than 0%), or whiteness reduction is 10% or more but less than 20%

[0201] × (Defective): Area of ​​whitening or reddish-blue discoloration is 10% or more, or whiteness reduction is 20% or more

[0202] In addition, to verify magnetic properties, five specimens measuring 60 mm in width × 60 mm in length were prepared for each non-oriented electrical steel sheet with an insulating layer, and then the 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, and 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.

[0203] Classification Hot-rolled Plate Si Concentration Surface Shape Surface Appearance Magnetic Properties Ra(㎛) Rt(㎛) Rz(㎛) Whiteness Equal Red Blue Occurrence Iron Loss (W10 / 400) Magnetic Flux Density (B50) Invention Example 10.90 0.25 2.9 2.20 66 ○ No occurrence 9.9 1.67 Invention Example 23.70 0.37 4.5 3.40 61 ○ No occurrence 10.9 1.65 Invention Example 33.50 0.36 4.4 3.30 63 ○ No occurrence 10.3 1.62 Invention Example 42.70 0.32 3.9 3.00 62 ○ No occurrence 10.1 1.64 Invention Example 52.20 0.30 3.6 2.80 65 ○ No occurrence 10.5 1.63 Invention Example 61.900.293.52.7067○Non-occurred10.21.67Invention Example 72.200.303.62.8064○Non-occurred10.51.65Invention Example 82.700.323.93.0063○Non-occurred10.41.62Invention Example 93.300.354.33.2062○Non-occurred10.61.64Invention Example 102.100.303.62.8064○Non-occurred10.31.66Invention Example 112.100.303.82.7065○Non-occurred10.21.64Invention Example 122.100.323.62.8064○Non-occurred10.41.67Invention Example 132.000.294.12.7063○Non-occurring10.51.62Comparative Example 14.100.535.13.6057△Non-occurring11.21.62Comparative Example 24.700.525.63.4054×Occurring12.21.62Comparative Example 34.100.425.23.7056×Occurring11.71.64Comparative Example 44.100.515.13.2058△Non-occurring11.11.65Comparative Example 54.200.524.93.8059×Occurring11.71.61Comparative Example 64.400.495.33.4057×Occurring11.51.62Comparative Example 74.600.544.83.3055×Occurred12.11.63

[0204]

[0205] As shown in Tables 1 and 2, Invention Examples 1 to 13, which satisfy all conditions according to one embodiment of the present invention, had excellent surface quality and magnetic properties as the surface shape of the insulating layer was controlled as intended.

[0206] On the other hand, Comparative Examples 1 to 7, which did not satisfy the conditions according to one embodiment of the present invention, had a high degree of scale concentration on the surface of the hot-rolled plate even after descaling, and the surface shape of the insulating layer was not formed as intended. As a result, they showed significantly inferior results in the whitening evaluation and had low whiteness. In some of these comparative examples, iron loss increased, and red rust occurred except for Comparative Examples 1 and 4.

Claims

1. A base steel plate and an insulating layer formed on at least one surface of the base steel plate, and The above insulating layer is a non-oriented electrical steel sheet having a surface roughness (Ra) of 0.50 μm or less and a maximum roughness (Rt) of 5.00 μm or less.

2. In Paragraph 1, The above insulating layer is a non-oriented electrical steel sheet having a 10-point average roughness (Rz) of 3.50 μm or less.

3. In Paragraph 1, The above-mentioned base steel sheet is a non-oriented electrical steel sheet comprising, 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.

4. In Paragraph 3, The above-mentioned base steel sheet is a non-oriented electrical steel sheet further comprising one or more types selected from the groups i) to iv) below. i) 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. ii) 0.005 to 0.200 wt% based on the total content of one or more selected from tin (Sn), antimony (Sb), bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As). iii) 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. iv) 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.

5. Step of preparing the slab; A step of obtaining a hot-rolled plate by heating a slab and then hot-rolling it; Step of heating the above hot rolling plate; A step of descaling the above heated hot-rolled plate; A step of obtaining a cold-rolled plate by cold-rolling the hot-rolled plate after the above descaling; Step of annealing the above cold-rolled plate; and The method includes the step of forming an insulating layer on the surface of the annealed cold-rolled steel sheet. A method for manufacturing a non-oriented electrical steel sheet, wherein the step of heating the hot-rolled sheet is to heat it to 40 to 150°C at a maximum driving speed of 200 mpm.

6. In Paragraph 5, A method for manufacturing a non-oriented electrical steel sheet, further comprising the step of passing the hot-rolled sheet through a roller leveler with an intermesh of 5 to 50 mm before heating the hot-rolled sheet.

7. In Paragraph 5, 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.

8. In Paragraph 5 or 7, A method for manufacturing non-oriented electrical steel sheets, wherein the step of heating the hot-rolled sheet is performed before the descaling treatment by the chemical method.

9. In Paragraph 7, The above mechanical method is shot blasting, and A method for manufacturing a non-oriented electrical steel sheet, wherein the above shot blast is performed using balls with an average diameter of 1 to 1000 μm at a projection rate of 300 to 3000 kg / min and a projection speed of 500 to 2000 rpm.

10. In Paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above chemical method is performed by immersing in an aqueous acid solution of 15 to 30 weight percent for 30 to 180 seconds.

11. In Paragraph 5, A method for manufacturing a non-oriented electrical steel sheet in which the surface Si enrichment ratio of the hot-rolled sheet after the above descaling satisfies the following relationship 1. [Relationship 1] 0.80 ≤ (Si(s) / Si(i)) ≤ 4.00 (In Equation 1, each Si content is in weight%.)

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