Non-oriented electrical steel sheet and method for manufacturing non-oriented electrical steel sheet

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percentage, 2.0%-3.5% of silicon (Si), 0.8%-1.5% of aluminum (Al), 0.1%-0.5% of manganese (Mn), more than 0% but not more than 0.005% of carbon (C), more than 0% but not more than 0.005% of nitrogen (N), and a remainder of iron (Fe) and other unavoidable impurities, the surface of the non-oriented electrical steel sheet comprising a coating layer, the average thickness (Tavg) of the coating layer satisfying 100 nm or less, and the thickness (Tavg) of the coating layer satisfying 100 nm or less. The thickness deviation (Tdev) of the coating layer satisfies 10 nm or less.

Description

Technical Field

[0001] This invention relates to non-oriented electrical steel sheets and a method for manufacturing non-oriented electrical steel sheets. Background Technology

[0002] To achieve superior electromagnetic properties, non-oriented electrical steel sheets are steel grades with higher additions of silicon (Si), aluminum (Al), and manganese (Mn) compared to ordinary carbon steel. The magnetic properties of non-oriented electrical steel sheets are primarily evaluated by magnetic flux density and iron loss. Magnetic flux density refers to the degree of magnetization achieved under a specific magnetic field, while iron loss refers to the energy loss generated at a specific magnetic flux density and frequency. Higher magnetic flux density allows for the formation of a larger magnetic field with the same amount of energy, thus increasing energy efficiency; lower iron loss results in less energy loss as heat, further increasing energy efficiency.

[0003] Recently, with the strengthening of environmental regulations worldwide, the automotive industry is moving towards developing environmentally friendly vehicles such as hybrid and electric vehicles. As this trend towards vehicle electrification develops, the magnetic properties of non-oriented electrical steel used as the core material for automotive motors are receiving increasing attention. Therefore, the demand for technologies to reduce iron losses under specific frequency conditions is also constantly increasing.

[0004] In the past, the resistivity of the material itself was increased by increasing the silicon (Si) content, thereby reducing eddy current losses. However, if the silicon content is too high, it will significantly increase brittleness, thus reducing the rolling properties.

[0005] Aluminum is a soft material, so even if its content increases, it will not reduce its rollability. However, in the annealing process, residual nitrogen (N) or oxygen (O) in steel with high aluminum content will react to form a coating layer composed of nitrides (AlN) or oxides (Al2O3). If a thick coating layer is formed, iron loss will actually increase, resulting in reduced coating adhesion.

[0006] Therefore, there is a need to develop technologies that can control the thickness of the coating layer that affects magnetic properties in aluminum-containing non-oriented electrical steel sheets. Summary of the Invention

[0007] Technical issues The present invention is proposed to solve the above-mentioned problems. The purpose of the present invention is to provide a non-oriented electrical steel sheet with improved magnetic properties, namely low iron loss and high magnetic flux density, by controlling the thickness of the coating layer, and a method for manufacturing the non-oriented electrical steel sheet.

[0008] The technical problems of this invention are not limited to those mentioned above. Those skilled in the art to which this invention pertains can clearly understand other technical problems not mentioned through the following description.

[0009] Technical solution By weight percentage, the non-oriented electrical steel sheet of one embodiment of the present invention comprises 2.0% to 3.5% silicon, 0.8% to 1.5% aluminum, 0.1% to 0.5% manganese (Mn), greater than 0% and less than or equal to 0.005% carbon (C), greater than 0% and less than or equal to 0.005% nitrogen (N), the balance being iron (Fe) and other unavoidable impurities, and the surface comprises a coating layer, the average thickness (T) of which is... avg The thickness deviation (T) of the coating layer is below 100 nm. dev It meets the requirement of being below 10nm.

[0010] The average thickness of the coating layer (T) avg It can satisfy equation 1.

[0011] Formula 1

[0012] Where N = the number of measurement points, T i =Thickness at the i-th measurement point, nt = Number of extreme points within the measurement point, T i,nt =Thickness at the i-th extreme point.

[0013] The thickness deviation of the coating layer (T) dev It can satisfy equation 2.

[0014] Formula 2

[0015] Among them, T max =Measured T i The maximum value among the values.

[0016] The thickness can be below 0.35mm.

[0017] The grain size can be 100–130 μm.

[0018] The yield strength can meet the requirement of over 300MPa, and the tensile strength can meet the requirement of over 400MPa.

[0019] Iron loss (W) 10 / 400 It can meet the requirements of below 13.0 W / kg, magnetic flux density (B) 50 It can meet the requirements of 1.60T and above.

[0020] It may also contain less than 0.015% phosphorus (P), less than 0.003% sulfur (S), and less than 0.005% titanium (Ti) by weight percentage.

[0021] By weight percentage, the non-oriented electrical steel sheet of one embodiment of the present invention comprises 2.0% to 3.5% silicon, 0.8% to 1.5% aluminum, 0.1% to 0.5% manganese, greater than 0% and less than or equal to 0.005% carbon, greater than 0% and less than or equal to 0.005% nitrogen, the balance being iron and other unavoidable impurities, and the surface comprising a coating layer, wherein the thickness deviation (T) of the coating layer is... dev The thickness deviation (T) of the coating layer is below 10 nm. dev It satisfies equation 2.

[0022] Formula 2

[0023] Among them, T avg =Average thickness of the coating layer, T max =The maximum value of the measured coating thickness.

[0024] The average thickness of the coating layer (T) avg It can meet the requirements below 100nm.

[0025] The average thickness of the coating layer (T) avg It can satisfy equation 1.

[0026] Formula 1

[0027] Where N = the number of measurement points, T i =Thickness at the i-th measurement point, nt = Number of extreme points within the measurement point, T i,nt =Thickness at the i-th extreme point.

[0028] The coating layer may contain aluminum oxide (Al2O3).

[0029] The iron loss (W) of the final product 10 / 400 It can meet the requirements of below 13.0 W / kg, magnetic flux density (B) 50 It can meet the requirements of 1.60T and above.

[0030] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: step (a) preparing a semi-finished steel product; step (b) forming a hot-rolled steel sheet by hot rolling the steel product; step (c) hot-rolling annealing and pickling the hot-rolled steel sheet; step (d) cold-rolling the hot-rolled steel sheet obtained in step (c) to form a cold-rolled steel sheet; and step (e) cold-rolling annealing and coating the cold-rolled steel sheet to form a final product. In step (e), the cold rolling annealing is performed in an atmosphere containing a hydrogen (H2) concentration of 30% or more by volume and the balance being nitrogen (N2) and unavoidable impurities. When the hydrogen concentration is 30% or more and less than or equal to 50%, the residual oxygen concentration is 300 ppm or less, and when the hydrogen concentration is greater than 50% and less than or equal to 100%, the residual oxygen concentration is 800 ppm or less.

[0031] In step (e), the heating rate can be 5-30℃ / s, the annealing temperature can be 800-1000℃, and the annealing time can be 40-100 seconds.

[0032] Step (e) may include: controlling the internal residual oxygen concentration by cold rolling annealing; and forming a hydrogen atmosphere internally by said cold rolling annealing.

[0033] The final product contains, by weight percentage, 2.0% to 3.5% silicon, 0.8% to 1.5% aluminum, 0.1% to 0.5% manganese, greater than 0% and less than or equal to 0.005% carbon, greater than 0% and less than or equal to 0.005% nitrogen, and the balance iron and other unavoidable impurities.

[0034] The iron loss (W) of the final product 10 / 400 It can meet the requirements of below 13.0 W / kg, magnetic flux density (B) 50 It can meet the requirements of 1.60T and above.

[0035] A coating layer is formed on the surface of the final product, and the average thickness (T) of the coating layer is... avg The thickness deviation (T) of the coating layer can be below 100nm. dev It can meet the requirements below 10nm.

[0036] The average thickness of the coating layer (T) avg ) can satisfy Equation 1, the thickness deviation (T) of the coating layer dev It can satisfy equation 2.

[0037] Formula 1

[0038] Where N = the number of measurement points, Ti =Thickness at the i-th measurement point, nt = Number of extreme points within the measurement point, T i,nt =Thickness at the i-th extreme point.

[0039] Formula 2

[0040] Among them, T max =The maximum value of the measured coating thickness.

[0041] The effects of the invention According to one embodiment of the present invention, non-oriented electrical steel sheets with improved magnetic properties, including low iron loss and high magnetic flux density, can be provided.

[0042] The effects of this invention are not limited to those mentioned above. Those skilled in the art to which this invention pertains can clearly understand other effects not mentioned through the description of the scope of protection of the invention. Attached Figure Description

[0043] Figure 1 A cross-sectional view of a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0044] Figure 2 This is a cross-sectional view of a test piece used to measure the coating thickness of a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0045] Figure 3 This is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention. Detailed Implementation

[0046] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily implement the present invention. However, the present invention is not limited to the following embodiments.

[0047] Furthermore, when it is mentioned that a structural element (or region, layer, part, etc.) is located "on" other structural elements or "connected" or "combined" with other structural elements, it indicates that a third structural element is set on, connected to, or combined directly with other structural elements or between them.

[0048] Terms such as “comprising” or “having” are used to indicate the presence of features, figures, steps, operations, structural elements, accessories, or combinations thereof described in the specification, and should not be construed as precluding the existence or additional possibility of one or more other features, figures, steps, operations, structural elements, accessories, or combinations thereof.

[0049] To clearly illustrate the present invention, detailed descriptions of relevant prior art that are irrelevant to the description or may unnecessarily obscure the essence of the invention will be omitted. Regarding the reference numerals for structural elements in the various figures in this specification, the same or similar structural elements will be given the same or similar reference numerals throughout the specification.

[0050] Furthermore, it should be noted that the terms or vocabulary used in this specification and the scope of protection of the invention should not be limited to their commonly understood meaning or dictionary meaning. Instead, they should be interpreted as meanings and concepts that conform to the technical ideas of the invention, taking into account the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0051] Unless otherwise specified, the expression "A~B" for numerical values ​​A and B means "above A and below B". In such expressions, the case where the unit is marked only after B indicates that the relevant unit also applies to A.

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0053] Non-oriented electrical steel sheet In one embodiment of the present invention, the non-oriented electrical steel sheet is manufactured from steel containing 2.0 to 3.5% by weight silicon, 0.8 to 1.5% by weight aluminum, 0.1 to 0.5% by weight manganese, less than 0.005% by weight carbon, less than 0.005% by weight nitrogen, less than 0.003% by weight sulfur, less than 0.015% by weight phosphorus, less than 0.005% by weight titanium, and the balance iron and other unavoidable impurities. The same alloy composition may also be contained in the final electrical steel sheet.

[0054] The following details the role and content of each alloying element contained in a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0055] Silicon (Si) Silicon is a key additive element in electrical steel sheets, used to improve magnetic properties by increasing resistivity and reducing iron loss. If the silicon content is below a predetermined range, the increase in resistivity is insufficient, making it difficult to achieve the desired low iron loss value. Conversely, if the silicon content exceeds the predetermined range, it increases the material's brittleness, reducing its cold-rollability and causing steel sheet breakage during coiling and rolling, thus reducing productivity. Furthermore, increasing the silicon content reduces magnetic permeability and magnetic flux density.

[0056] Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain 2.0 to 3.5% by weight of silicon.

[0057] Aluminum (Al) Aluminum is an element that enhances magnetic properties by increasing resistivity and reducing iron loss when combined with silicon. Furthermore, unlike silicon, aluminum is a soft material; even excessive addition does not reduce its ductility, thus improving operability during cold rolling.

[0058] Aluminum can combine with nitrogen (N) present in the internal gas atmosphere or in the steel to form nitrides (e.g., AlN) or with oxygen (O) to form oxides (e.g., Al2O3) by annealing. Therefore, a coating layer consisting of at least one of oxides and nitrides can be formed on the surface of the steel.

[0059] If the aluminum content is less than the preset range, the magnetic properties will be reduced due to increased high-frequency iron loss caused by insufficient resistivity. Conversely, if the aluminum content is greater than the preset range, the magnetic properties and coating performance will be reduced due to excessive coating layer formation.

[0060] Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain 0.8 to 1.5% by weight of aluminum.

[0061] Manganese (Mn) Manganese is an element that enhances magnetic properties by increasing resistivity and reducing iron losses, in conjunction with silicon. Furthermore, it inhibits grain growth by reacting with sulfur to form sulfides such as MnS. If the manganese content is below a predetermined range, the effect of increasing resistivity is reduced, thereby increasing high-frequency iron losses. Conversely, if the manganese content is above a predetermined range, it reduces magnetic flux density due to the formation of coarse precipitates. Furthermore, the formation of a coarse second phase and the increase of {112} texture, which is detrimental to magnetization, further degrade magnetic properties.

[0062] Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain 0.1 to 0.5% by weight of manganese.

[0063] Carbon (C) Carbon is an effective element for increasing strength. However, it increases iron loss by combining with titanium, niobium (Nb), etc., to form carbides such as TiC and NbC. If the carbon content is greater than 0.005% by weight, it will reduce magnetic properties due to magnetic aging. Therefore, in one embodiment of the present invention, the carbon content of the non-oriented electrical steel sheet can be less than 0.005% by weight.

[0064] Nitrogen (N) Nitrogen is an element that plays a role in the strength and corrosion resistance of steel, and it improves the toughness of steel by stabilizing austenite. However, if the nitrogen content is greater than 0.005% by weight, nitrogen will combine with aluminum and titanium to form precipitates such as aluminum nitride (AlN) and titanium nitride (TiN), thereby increasing iron loss. Furthermore, it inhibits grain growth; therefore, it is preferable to add as little nitrogen as possible. Therefore, a non-oriented electrical steel sheet according to an embodiment of the present invention may contain less than 0.005% by weight of nitrogen.

[0065] Phosphorus (P) Phosphorus is a grain boundary segregating element that increases resistivity by improving texture, thus playing a role in reducing iron loss. However, if the phosphorus content exceeds 0.015% by weight, it will cause grain miniaturization and form a texture that is detrimental to magnetism. Furthermore, excessive grain boundary segregation will occur, reducing cold rollability. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain less than 0.015% by weight of phosphorus.

[0066] Sulfur (S) Sulfur is an unavoidable impurity in steel during the manufacturing process, and its addition in large quantities can cause brittleness. Furthermore, it can increase iron loss and inhibit grain growth by forming precipitates such as MnS. Therefore, it is preferable to add as little sulfur as possible. Thus, the non-oriented electrical steel sheet of one embodiment of the present invention may contain less than 0.003% by weight of sulfur.

[0067] Titanium (Ti) Titanium is an element with a very strong tendency to form precipitates in steel. It combines with carbon or nitrogen to form tiny precipitates such as TiC and TiN, which inhibit grain growth. If titanium exceeds 0.005% by weight, it will increase the fraction of these precipitates, which will reduce magnetic properties by forming a {112} texture that is detrimental to magnetization. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain less than 0.005% by weight of titanium.

[0068] In addition to the above-mentioned components, the steel may contain a balance of Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking process and the manufacturing process of electrical steel sheets, and are well known in the relevant fields, so their specific descriptions will be omitted here.

[0069] In one embodiment of the present invention, the addition of elements other than those described above in the alloy composition is not excluded; various combinations are possible without impairing the technical concept of the present invention. When additional elements are included, they may replace the remaining Fe.

[0070] Figure 1 A cross-sectional view of a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0071] Reference Figure 1 In one embodiment of the present invention, the non-oriented electrical steel sheet may include a substrate layer 1 and a coating layer 2. For example, the coating layer 2 may contain aluminum oxide (Al2O3).

[0072] However, this is not a limitation. The coating layer 2 may include an aluminum oxide (Al2O3) layer and an aluminum nitride (AlN) layer therebetween, or may be composed of aluminum nitride (AlN). Alternatively, it may include other oxides and nitrides such as silicon oxide (Si2O3).

[0073] Figure 2 This is a cross-sectional view of a test piece used to measure the coating thickness of a non-oriented electrical steel sheet according to an embodiment of the present invention. The following is a more detailed description. Figure 1 The coating layer 2 is shown.

[0074] In a non-oriented electrical steel sheet according to an embodiment of the present invention, the average thickness (T) of the coating layer is... avg It can satisfy equation 1.

[0075] Formula 1

[0076] In Equation 1, N can represent the number of points measured by the measurement experiment, and T i The thickness of the coating layer at the i-th measurement point can be represented by nt, and the number of extreme points within the measurement point can be represented by T. i,nt It can represent the thickness of the i-th extreme point.

[0077] Reference Figure 2 This allows for the preparation of test pieces to measure the thickness of the coating layer on a non-oriented electrical steel sheet according to an embodiment of the present invention. i The value can be calculated by measuring the thickness of the coating layer along the D1 direction at specified intervals (L / (N-1)). Here, N represents the number of measurement points and is a natural number greater than 2.

[0078] According to one embodiment of the present invention, the thickness of the coating layer can be measured by non-destructive methods such as laser or ultrasonic inspection, but is not limited thereto.

[0079] Extreme point (T) k () can be defined as the point where the thickness of the coating layer starts to decrease from thick to thin, and the point where the thickness of the coating layer starts to increase from thin to thick, with D1 as the reference.

[0080] Specifically, the extreme point (T) k The extreme point (T) can be defined as the point where, among three adjacent points (k-1, k, k+1) along the D1 direction, the coating thickness of the middle point (k) is greater or less than the coating thickness of the other two adjacent points (k-1, k+1). Here, k represents any natural number greater than or equal to 2 and less than N. In this embodiment, the extreme point (T) k This includes two endpoints (T1, T2). N ).

[0081] According to one embodiment of the present invention, the number of extreme points (nt) can be 30% to 40% of the number of measurement points (N), but is not limited thereto.

[0082] In Equation 1, the average thickness of the coating layer (T) avg This includes not only the thickness at different measurement points (T) i The arithmetic mean of the extreme points (T) also includes the thickness of the extreme points (T). i,nt The arithmetic mean of the measured coating thickness (T) is more reliable than the average thickness of the measured coating layer (T). avg () Value is high.

[0083] The average thickness (T) of the coating layer can be calculated using Equation 1 above. avg The nanometer size is controlled to be below 100nm, which can improve the magnetic properties, coating properties and other properties of electrical steel sheets.

[0084] In a non-oriented electrical steel sheet according to an embodiment of the present invention, the thickness deviation (T) of the coating layer is... dev It can satisfy equation 2.

[0085] Formula 2

[0086] In Equation 2, T avg The average thickness of the coating layer can be the value calculated in Equation 1 above. However, it is not limited to this; the average thickness of the coating layer (T) avg ) can be the thickness of the coating layer measured at the measurement point (T) i The arithmetic mean of T. max It can represent the thickness of the measured coating layer (T) i The maximum value in ).

[0087] Formula 2 can be used to control the thickness deviation of the coating layer to make the coating layer form uniformly, thereby further improving the magnetic properties and coating properties of electrical steel sheets.

[0088] The following describes in detail a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0089] Manufacturing method of non-oriented electrical steel sheet Figure 3 This is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0090] The following is for reference Figure 3 This invention describes a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0091] An embodiment of the present invention provides a method for manufacturing non-oriented electrical steel sheets, comprising: a first step a, preparing semi-finished steel; a second step b, forming a hot-rolled steel sheet by hot rolling the steel prepared in the first step a; a third step c, hot-rolling annealing and pickling the hot-rolled steel sheet; a fourth step d, forming a cold-rolled steel sheet by cold rolling the hot-rolled steel sheet in the third step c; and a fifth step e, forming a final product by cold-rolling annealing and coating the cold-rolled steel sheet.

[0092] Furthermore, in the fifth step e of one embodiment of the present invention, the cold rolling annealing can be carried out in an atmosphere with a hydrogen concentration of 30% or more by volume. This will be explained later.

[0093] The following describes the various steps of a method for manufacturing non-oriented electrical steel sheets according to an embodiment of the present invention.

[0094] The first step a in preparing the semi-finished steel is to prepare steel with the aforementioned alloy composition range for manufacturing non-oriented electrical steel sheets as the final product. More specifically, it can be a step of designing the alloy composition within the aforementioned alloy composition range to manufacture the semi-finished product. The semi-finished product can be a slab, but is not necessarily limited to it. Furthermore, the slab can be manufactured using processes well-known in related fields such as steelmaking and continuous casting.

[0095] In a method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention, the second step b involves hot rolling the steel material that has undergone the first step a to form a hot-rolled steel sheet. The second step b may include a reheating step, a hot rolling step, and a coiling step.

[0096] First, the reheating step is a step performed prior to the hot rolling step, and can be a step of reheating the steel for subsequent processes. Specifically, it can be a step of uniformly heating the steel after it has been placed in a heating furnace to facilitate plastic deformation.

[0097] The steel can be reheated at a temperature of 1000–1200°C. If the reheating temperature is below 1000°C, the deformation resistance will increase during hot rolling, and the ductility will decrease due to the increased rolling load. Conversely, if the reheating temperature is above 1200°C, the resolution of precipitates such as carbon, sulfur, and nitrogen within the steel will produce tiny precipitates in subsequent rolling and annealing processes, thereby inhibiting grain growth and reducing magnetic properties. Therefore, in this invention, the steel can be reheated at a temperature of 1000–1200°C.

[0098] Next, a hot rolling step is performed. The hot rolling step may include rough rolling and fine grain rolling processes. The rough rolling process may be a process of forming steel into a rolled material with appropriate shape, thickness, and width, while the fine grain rolling process may be a process of adjusting the steel to a specified thickness and width and rolling it to a good surface and shape at a suitable application-appropriate finishing temperature.

[0099] In this case, the final rolling temperature can be 860–900°C. If the final rolling temperature is less than 860°C, the calenderability will decrease due to the increased rolling load. Furthermore, if it is greater than 900°C, a sharp decrease in strength will occur. Therefore, a final rolling temperature of 860–900°C is preferred.

[0100] Preferably, the thickness of the hot-rolled steel sheet after the hot rolling step is 1.8–2.6 mm. A thicker hot-rolled steel sheet will increase the reduction rate during cold rolling, leading to a deterioration of the texture and consequently reducing magnetic properties. Conversely, if the hot-rolled steel sheet is too thin, insufficient thickness obtained after cold rolling will induce shape defects in product applications.

[0101] Furthermore, a coiling step can be performed after the hot rolling step. This can be represented as the step of forming a coil from the hot-rolled steel sheet for ease of storage and transportation.

[0102] The curling step can be performed at a temperature of 550–650°C. If the curling temperature is below 550°C, the grains will be too small and insufficient grain growth will not be achieved after annealing. If the curling temperature is above 650°C, the magnetic properties will be reduced due to the increase in tiny precipitates. Therefore, a curling temperature of 550–650°C is preferred.

[0103] Then, the method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention can proceed to a third step c, which involves hot rolling annealing and pickling of the hot-rolled steel sheet that has undergone the second step. The third step c may include a hot rolling annealing step and a pickling step.

[0104] The hot rolling annealing step is performed to ensure the uniformity of the microstructure and cold rollability of the hot-rolled steel.

[0105] The hot rolling annealing step can be performed at a temperature range of 950–1100°C for 30–150 seconds. In this case, the heating rate can be above 20°C, and the cooling rate can be above 20°C.

[0106] If the hot-rolling annealing temperature is less than 950°C, residual stretched casting structure will remain after hot rolling, inducing fibrous structure. In this case, the magnetic properties of the final product will decrease due to the formation of small grains. Conversely, if the annealing temperature is greater than 1100°C, excessive grain growth will induce uneven texture in the final product, resulting in excessive oxidation of the hot-rolled steel sheet and reduced magnetic properties. Furthermore, in order to form appropriate grain sizes under various temperature conditions, the hot-rolling annealing time can be in the range of 30 to 150 seconds.

[0107] Then, a pickling step is performed to remove the oxide layer formed on the surface of the hot-rolled annealed steel sheet using a pickling solution. This pickling step can be performed using sulfuric acid, hydrochloric acid, nitric acid, and hydrofluoric acid, or a pickling solution prepared by mixing these substances, but is not limited to these methods.

[0108] Then, the non-oriented electrical steel sheet manufacturing method of one embodiment of the present invention can proceed to a fourth step d, which involves cold rolling the hot-rolled steel sheet that has undergone the third step c to form a cold-rolled steel sheet.

[0109] Step d can be a process of thinning the steel sheet by rolling it at a temperature of 150–200°C. More specifically, cold rolling can be a process of rolling the hot-rolled steel sheet to a thickness and width that conforms to the final product specifications.

[0110] The fourth step d can be carried out at a reduction rate of 80% to 90%, and the thickness of the cold-rolled steel sheet formed by the cold rolling can be less than 0.35 mm, more specifically, less than 0.25 mm.

[0111] Then, a fifth step e can be performed to cold-roll anneal and coat the cold-rolled steel sheet to form the final product. The fifth step e may include a cold-roll annealing step and a coating step.

[0112] The cold rolling annealing step can be carried out at a temperature of 800 to 1100°C for 40 to 100 seconds.

[0113] If the cold rolling annealing temperature is less than 800℃, hysteresis loss will increase due to the small grain size; if it is greater than 1100℃, eddy current loss will increase due to the large grain size. Furthermore, the heating rate during cold rolling annealing can be 5–30℃ / s, and the cooling rate can be above 30℃ / s.

[0114] In the cold rolling annealing step, the cold rolling annealing furnace can be operated in a gaseous atmosphere with a hydrogen concentration of 30% or more by volume, and the balance being nitrogen and other unavoidable impurities.

[0115] To create the hydrogen atmosphere, the cold rolling annealing step may include controlling the residual oxygen concentration inside the cold rolling annealing furnace and introducing hydrogen and nitrogen into the cold rolling annealing furnace to create a hydrogen atmosphere inside the furnace.

[0116] For example, the step of controlling the residual oxygen concentration may include the process of removing oxygen (O2) after creating a vacuum (or sub-vacuum) state inside the cold rolling annealing furnace. However, it is not limited to this.

[0117] In the cold rolling annealing step, if cold rolling annealing is carried out in an atmosphere with a hydrogen concentration of less than 30%, iron loss will increase due to the formation of an excessively thick oxide or nitride layer on the surface. Therefore, cold rolling annealing can be carried out in an atmosphere with a hydrogen concentration of 30% or higher.

[0118] Specifically, when cold rolling annealing is performed in an atmosphere inside the cold rolling annealing furnace with a hydrogen concentration of 30% or more and 50% or less, the residual oxygen concentration can be 300 ppm or less, preferably 50 ppm or more and 285 ppm or less. If the residual oxygen concentration is less than 50 ppm, the cost of removing oxygen from inside the cold rolling annealing furnace will increase.

[0119] Under the above conditions, if the residual oxygen concentration is greater than 300 ppm, iron loss will increase due to the formation of an excessively thick oxide layer on the surface.

[0120] If cold rolling annealing is carried out in an atmosphere where the hydrogen concentration inside the cold rolling annealing furnace is greater than 50% and less than or equal to 100%, the reduction of the cold-rolled steel sheet caused by hydrogen will occur more frequently than when the hydrogen concentration is less than 50%.

[0121] Therefore, compared with cold rolling annealing at a hydrogen concentration of less than 50%, a thinner oxide layer is formed when cold rolling annealing is performed at a hydrogen concentration of more than 50%.

[0122] Specifically, under the above conditions, if the residual oxygen concentration is greater than 800 ppm, iron loss will increase due to the formation of an excessively thick oxide layer on the surface. Conversely, if the residual oxygen concentration is less than 50 ppm, it will increase the cost of removing oxygen from the inside of the cold rolling annealing furnace.

[0123] Therefore, when cold rolling annealing is performed in an atmosphere inside the cold rolling annealing furnace with a hydrogen concentration greater than 50% and less than or equal to 100%, the residual oxygen concentration can be less than 800 ppm, preferably more than 50 ppm and less than 740 ppm.

[0124] A coating step can be performed after the cold rolling annealing step. The coating step can be performed to improve the stamping formability of the non-oriented electrical steel sheet and ensure its insulation, and can be a process of forming an insulating film on the surface of the cold-rolled steel sheet after the cold rolling annealing step.

[0125] According to an embodiment of the present invention, in the case of an electrical steel sheet manufactured by the aforementioned manufacturing process, the average thickness (T) of the coating layer formed on the surface is... avg The thickness deviation (T) can be below 100nm, and the thickness deviation of the coating layer is... dev The nanometer diameter can be below 10 nm. This can improve the magnetic properties and coating properties of electrical steel sheets.

[0126] The iron loss (W) of the non-oriented electrical steel sheet manufactured by the non-oriented electrical steel sheet manufacturing method according to an embodiment of the present invention at 400Hz and 1.0T. 10 / 400 The magnetic flux density (B) can be below 13.0 W / kg. 50 It can be 1.60T or more.

[0127] Furthermore, the yield strength (YS) of the non-oriented electrical steel sheet manufactured by the non-oriented electrical steel sheet manufacturing method of an embodiment of the present invention can be 300 MPa or more, the tensile strength (TS) can be 400 MPa or more, and the grain size can be 100 to 130 μm.

[0128] Comparative Examples and Embodiments The present invention will be further explained below through preferred comparative examples and experimental examples. However, the following comparative examples and experimental examples are only for the purpose of helping to understand the present invention, and the present invention is not limited to the following experimental examples.

[0129] Table 1 shows the alloying elements of the comparative examples and embodiments, and Table 2 shows the cold rolling annealing conditions, coating type, and average thickness (T) of the measurement examples. avg ), thickness deviation of the coating layer (T) dev The results of the magnetic properties.

[0130] The comparative and experimental examples were manufactured using steel with the alloy composition described in Table 1 below. Furthermore, the hot rolling process was carried out under conditions of a reheating temperature of 1150°C, a rolling end temperature of 890°C, and a coiling temperature of 610°C, resulting in a final hot-rolled sheet thickness of 2.0 mm.

[0131] Furthermore, the hot rolling annealing step is carried out at a temperature of 1000°C for 60 seconds with a heating rate of 20°C / s, followed by cooling at a cooling rate of 25°C / s. The steel sheet after hot rolling annealing is then pickled.

[0132] The cold rolling process was carried out at a temperature of 180°C with a reduction rate of 87.5%, and the final thickness of the cold-rolled sheet was 0.25 mm.

[0133] The cold rolling annealing process is carried out at a temperature of 1000°C for 60 seconds with a heating rate of 30°C / s, followed by cooling at a cooling rate of 40°C / s. A coating treatment is then applied to the cooled steel sheet.

[0134] Except for the conditions described above and the process conditions listed in Table 2 below, the manufacturing processes of the comparative examples and experimental examples of the present invention are controlled under the same conditions as those described in the non-oriented electrical steel sheet manufacturing method of an embodiment of the present invention.

[0135] In Table 2 below, the average thickness of the coating layer (T) avg ) and thickness deviation (T) dev The values ​​were obtained by measuring 10 mm long specimens obtained from the examples and comparative examples. Table 2 shows the average thickness (T) of the coating layer. avg The value is calculated by substituting N=30 into Equation 1. Table 2 below shows the thickness deviation (T) of the coating layer. dev It can be calculated using Equation 2.

[0136] In Table 2 below, iron loss (W) 10 / 400 The value represents the iron loss at 400Hz and 1.0T, expressed in W / kg. Furthermore, the magnetic flux density (B0) 50 The value represents the magnitude of the magnetic flux density induced when a magnetic field of 5000 A / m is applied, and the unit is T (Tesla).

[0137] Table 1.

[0138]

[0139] Table 2

[0140] Referring to Tables 1 and 2, Comparative Examples 1 to 6 were cold-rolled and annealed in an atmosphere with a hydrogen concentration of less than 30%. In Comparative Examples 1 to 6, the average thickness of the coating layer (T...) avg ) and thickness deviation (T) dev The values ​​are greater than 100nm and 10nm respectively, which do not satisfy Equation 1 and Equation 2 above.

[0141] Therefore, it can be confirmed that the iron loss (W) below 13.0 W / kg does not meet the magnetic properties targeted by this invention. 10 / 400 ), magnetic flux density above 1.60T (B 50 ).

[0142] Comparative Examples 7 to 9 were subjected to cold rolling annealing in an atmosphere with a hydrogen concentration of 30% or more and 50% or less. Under these conditions, the residual oxygen concentration of Comparative Example 7 was 358 ppm, the residual oxygen concentration of Comparative Example 8 was 319 ppm, and the residual oxygen concentration of Comparative Example 9 was 497 ppm.

[0143] In Comparative Examples 7 to 9, the residual oxygen concentration inside the cold rolling annealing furnace did not meet the requirement of 300 ppm or less, which is within the range of one embodiment of the present invention described above, and the average thickness of the coating layer (T) was... avg ) and thickness deviation (T) dev The values ​​are greater than 100nm and 10nm respectively, which do not satisfy Equation 1 and Equation 2 above.

[0144] Therefore, it can be confirmed that Comparative Examples 7 to 9 do not satisfy the magnetic property target of the present invention, which has an iron loss of less than 13.0 W / kg (W). 10 / 400 ), magnetic flux density above 1.60T (B 50 Any one of the following.

[0145] Comparative Example 10 is a comparative example in which cold rolling annealing was performed in an atmosphere with a hydrogen concentration of 80%. Under this condition, the residual oxygen concentration of Comparative Example 10 is 813 ppm.

[0146] In Comparative Example 10, the residual oxygen concentration inside the cold rolling annealing furnace did not meet the range of 800 ppm or less as described in the above embodiment of the present invention, thus confirming the average thickness (T) of the coating layer. avg The thickness deviation of the coating layer is 101 nm, and the thickness deviation of the coating layer is (T). dev The wavelength is 16nm.

[0147] In other words, the average thickness (T) of the coating layer in Comparative Example 10 avg ) and thickness deviation (T) dev The values ​​are greater than 100 nm and 10 nm respectively, which do not satisfy Equations 1 and 2 above. Therefore, it can be confirmed that the iron loss (W) of less than 13.0 W / kg, which is the magnetic property targeted by this invention, is not met. 10 / 400 ), magnetic flux density above 1.60T (B 50 ).

[0148] Conversely, it can be confirmed that the hydrogen concentration inside the cold rolling annealing furnace of Embodiments 1 to 12 of the present invention meets the requirement of 30% or more as defined in the above-described embodiment of the present invention, and the residual oxygen concentration also meets the above-described conditions.

[0149] This confirms the average thickness of the coating layer (T). avg ) and thickness deviation (T) devThe wavelengths are below 100 nm and below 10 nm, respectively, both satisfying Equations 1 and 2, and both satisfying the iron loss (W / kg) below 13.0 W / kg, which is the magnetic property targeted by this invention. 10 / 400 ), magnetic flux density above 1.60T (B 50 This confirms that it possesses excellent magnetic properties.

[0150] The preferred embodiments of the present invention have been described above. However, it will be apparent to those skilled in the art that, in addition to the embodiments described above, other specific forms can be embodied without departing from the spirit and scope of the present invention. Therefore, the above embodiments should be considered as illustrative rather than limiting, and the present invention is not limited to the above description, but can be modified within the scope of the claims and their equivalents.

[0151] Explanation of reference numerals in the attached figures 1: Matrix layer 2: Coating layer L: Length of the test piece T: Thickness of the coating layer.

Claims

1. A non-oriented electrical steel sheet, characterized in that, By weight percentage, it contains 2.0% to 3.5% silicon, 0.8% to 1.5% aluminum, 0.1% to 0.5% manganese, greater than 0% and less than or equal to 0.005% carbon, greater than 0% and less than or equal to 0.005% nitrogen, and the balance being iron and other unavoidable impurities. The surface contains a coating layer. The average thickness T of the coating layer avg Meets the requirements below 100nm. The thickness deviation T of the coating layer dev Meets the requirements of 10nm and below.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that, The average thickness T of the coating layer avg Satisfying Equation 1: Formula 1: ， Where N = the number of measurement points, T i =Thickness at the i-th measurement point, nt = Number of extreme points within the measurement point, T i,nt =Thickness at the i-th extreme point.

3. The non-oriented electrical steel sheet according to claim 2, characterized in that, The thickness deviation T of the coating layer dev Satisfying Equation 2: Formula 2: ， Among them, T max =Measured T i The maximum value among the values.

4. The non-oriented electrical steel sheet according to claim 1, characterized in that, The thickness must be less than 0.35mm.

5. The non-oriented electrical steel sheet according to claim 1, characterized in that, The grain size is 100–130 μm.

6. The non-oriented electrical steel sheet according to claim 1, characterized in that, The yield strength must be above 300 MPa, and the tensile strength must be above 400 MPa.

7. The non-oriented electrical steel sheet according to claim 1, characterized in that, Iron loss W 10 / 400 The magnetic flux density B must be below 13.0 W / kg. 50 It meets the requirements of 1.60T and above.

8. The non-oriented electrical steel sheet according to claim 1, characterized in that, It also contains less than 0.015% phosphorus, less than 0.003% sulfur, and less than 0.005% titanium by weight percentage.

9. A non-oriented electrical steel sheet, characterized in that, By weight percentage, it contains 2.0% to 3.5% silicon, 0.8% to 1.5% aluminum, 0.1% to 0.5% manganese, greater than 0% and less than or equal to 0.005% carbon, greater than 0% and less than or equal to 0.005% nitrogen, and the balance being iron and other unavoidable impurities. The surface contains a coating layer. The thickness deviation T of the coating layer dev Meets the requirements below 10nm. The thickness deviation T of the coating layer dev Satisfying Equation 2: Formula 2: ， Among them, T avg =Average thickness of the coating layer, T max =The maximum value of the measured coating thickness.

10. The non-oriented electrical steel sheet according to claim 9, characterized in that, The average thickness T of the coating layer avg Meets the requirement of being below 100nm.

11. The non-oriented electrical steel sheet according to claim 10, characterized in that, The average thickness T of the coating layer avg Satisfying Equation 1: Formula 1: ， Where N = the number of measurement points, T i =Thickness at the i-th measurement point, nt = Number of extreme points within the measurement point, T i,nt =Thickness at the i-th extreme point.

12. The non-oriented electrical steel sheet according to claim 9, characterized in that, The coating layer contains aluminum oxide.

13. The non-oriented electrical steel sheet according to claim 9, characterized in that, The iron loss W of the final product 10 / 400 The magnetic flux density B must be below 13.0 W / kg. 50 It meets the requirements of 1.60T and above.

14. A method for manufacturing a non-oriented electrical steel sheet, characterized in that, include: Step (a): Prepare semi-finished steel materials; Step (b) involves hot-rolling the steel to form a hot-rolled steel sheet; Step (c) involves hot rolling annealing and pickling the hot-rolled steel sheet; Step (d) involves cold rolling the hot-rolled steel sheet from step (c) to form a cold-rolled steel sheet; and Step (e) involves cold-rolling and annealing the cold-rolled steel sheet and then coating it to form the final product. In step (e), cold rolling annealing is performed in an atmosphere containing at least 30% hydrogen by volume, with the balance being nitrogen and unavoidable impurities. When the hydrogen concentration is 30% or more and 50% or less, the residual oxygen concentration is 300 ppm or less. When the hydrogen concentration is greater than 50% and less than or equal to 100%, the residual oxygen concentration is less than 800 ppm.

15. The method for manufacturing non-oriented electrical steel sheet according to claim 14, characterized in that, In step (e), the heating rate is 5-30℃ / s, the annealing temperature is 800-1000℃, and the annealing time is 40-100 seconds.

16. The method for manufacturing non-oriented electrical steel sheet according to claim 14, characterized in that, Step (e) includes: The step of controlling the internal residual oxygen concentration through cold rolling annealing; and The step of forming a hydrogen atmosphere inside by means of cold rolling annealing.

17. The method for manufacturing non-oriented electrical steel sheet according to claim 14, characterized in that, The final product contains, by weight percentage, 2.0% to 3.5% silicon, 0.8% to 1.5% aluminum, 0.1% to 0.5% manganese, greater than 0% and less than or equal to 0.005% carbon, greater than 0% and less than or equal to 0.005% nitrogen, and the balance iron and other unavoidable impurities.

18. The method for manufacturing non-oriented electrical steel sheet according to claim 14, characterized in that, The iron loss W of the final product 10 / 400 The magnetic flux density B must be below 13.0 W / kg. 50 It meets the requirements of 1.60T and above.

19. The method for manufacturing non-oriented electrical steel sheet according to claim 14, characterized in that, A coating layer is formed on the surface of the final product. The average thickness T of the coating layer avg Meets the requirements below 100nm. The thickness deviation T of the coating layer dev Meets the requirements of 10nm and below.

20. The method for manufacturing non-oriented electrical steel sheet according to claim 19, characterized in that, The average thickness T of the coating layer avg Satisfying Equation 1, The thickness deviation T of the coating layer dev Satisfying Equation 2: Formula 1: ， Where N = the number of measurement points, T i =Thickness at the i-th measurement point, nt = Number of extreme points within the measurement point, T i,nt =Thickness at the i-th extreme point Formula 2: ， Among them, T max =The maximum value of the measured coating thickness.

Images