Non-oriented electrical steel sheet and method for producing same

Abstract

The invention provides a non-oriented electrical steel plate. The non-oriented electrical steel sheet includes, in wt%, silicon (Si): 2.0 wt% to 3.8 wt%, aluminum (Al): 0.1 wt% to 1.3 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, carbon (C): 0 wt% (excluding) to 0.003 wt%, sulfur (S): 0 wt% (excluding) to 0.003 wt%, nitrogen (N): 0 wt% (excluding) to 0.003 wt%, titanium (Ti): 0 wt% (excluding) to 0.003 wt%, zirconium (Zr): 0 wt% (excluding) to 0.003 wt%, niobium (Nb): 0 wt% (excluding) to 0.003 wt%, phosphorus (P): 0.001 wt% to 0.015 wt%, and copper (Cu): in terms of wt%. 0 wt% (excluding) to 0.02 wt%, and the balance being iron (Fe) and unavoidable impurities.

Description

Technical Field

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

[0002] In recent years, with the strengthening of global environmental regulations, the automotive industry has shifted from traditional internal combustion engines to environmentally friendly vehicles (such as hybrid and electric vehicles). Unlike traditional internal combustion engines powered by fossil fuels, environmentally friendly vehicles are powered by electric motors driven by batteries.

[0003] To improve motor efficiency, electric vehicle drive motors require improved magnetic properties of non-oriented electrical steel sheets used as motor core materials, and the development of electric vehicle drive motors is accelerating as the demand for electric vehicles increases.

[0004] Generally speaking, electrical steel sheets are divided into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. Grain-oriented electrical steel sheets are mainly used for fixing components such as transformers. On the other hand, non-oriented electrical steel sheets are mainly used for rotating automotive drive motors because they have uniform magnetic properties in all directions, regardless of the rolling direction.

[0005] Non-oriented electrical steel sheets must be produced uniformly across the entire sheet. <100> Orientation texture (which is beneficial for magnetization) is required, and iron losses must be reduced while magnetic flux density is increased to improve energy efficiency. In this context, iron losses refer to the energy loss generated during magnetization, and magnetic flux density refers to the force used for power generation.

[0006] Various factors influencing the magnetic properties of non-oriented electrical steel sheets include chemical composition, sheet thickness, microstructure, insulating coating, texture, and material shape. These factors are also affected by the manufacturing methods of non-oriented electrical steel sheets. Non-oriented electrical steel sheets are manufactured through methods such as steelmaking / continuous casting, hot rolling, hot pre-annealing, cold rolling, and heat treatment / coating, and by optimizing these process conditions, electrical steel sheets with excellent magnetic properties can be produced.

[0007] Additionally, drive motors can be manufactured by stamping and then laminating thin electrical steel sheets of 0.5 mm or less. The stampability of the electrical steel sheet is a factor affecting the final performance of the drive motor, and when burrs appear after stamping, shape defects, stress, and reduced insulation properties may occur during the lamination process. Summary of the Invention

[0008] The embodiments of the present invention can provide a non-oriented electrical steel sheet with excellent stamping properties and a method thereof by controlling the alloy composition of the non-oriented electrical steel sheet.

[0009] According to an embodiment of the present invention, a method for manufacturing non-oriented electrical steel sheet includes manufacturing hot-rolled sheet by hot rolling a slab, said slab comprising 2.0 wt% to 3.8 wt% silicon (Si), 0.1 wt% to 1.3 wt% aluminum (Al), 0.1 wt% to 0.5 wt% manganese (Mn), 0 wt% (excluding) to 0.003 wt% carbon (C), 0 wt% (excluding) to 0.003 wt% sulfur (S), 0 wt% (excluding) to 0.003 wt% nitrogen (N), 0 wt% (excluding) to 0.003 wt% titanium (Ti), and 0 wt% (excluding) to 0.003 wt% zirconium (…). The slab contains Zr, 0% (excluding) to 0.003% (wt) of niobium (Nb), 0.001% to 0.015% (wt) of phosphorus (P), 0% (excluding) to 0.02% (wt) of copper (Cu), the balance of iron (Fe), and unavoidable impurities. It is manufactured by hot annealing the hot-rolled sheet, cold-rolled by cold rolling the hot-annealed sheet, and cold-annealed by cold annealing the cold-rolled sheet. The contents of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the slab satisfy the following relationship 1.

[0010] <Relation 1> 2.75≤log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu])≤3.70 In Equation 1, [S], [N], [Ti], [Zr], [Nb], [P] and [Cu] represent the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) in the slab, respectively.

[0011] In this embodiment, when the non-oriented electrical steel sheet is stamped, shear surfaces, fracture surfaces and burrs may be formed in the non-oriented electrical steel sheet.

[0012] In this embodiment, the proportion of sheared surface can be 45% to 100%, and the proportion of fractured surface can be 0% to 55%.

[0013] In this embodiment, the ratio of the burr length to the thickness of the non-oriented electrical steel sheet can be 3.5% or less.

[0014] In this embodiment, the contents of silicon (Si), manganese (Mn) and aluminum (Al) in the slab can satisfy the following relationship 2.

[0015] <Relation 2> 1.55≤log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al]))≤1.80 In Equation 2, [Si], [Mn] and [Al] can represent the content of silicon (Si), manganese (Mn) and aluminum (Al) in the slab (in weight %), respectively.

[0016] In this embodiment, the average grain size of the non-oriented electrical steel sheet can be from 50 µm to 150 µm.

[0017] In this implementation scheme, the iron loss of non-oriented electrical steel sheet (based on W) 15 / 50 The value can be 3.0 W / kg or less.

[0018] According to another embodiment of the invention, the non-oriented electrical steel sheet comprises 2.0 wt% to 3.8 wt% silicon (Si), 0.1 wt% to 1.3 wt% aluminum (Al), 0.1 wt% to 0.5 wt% manganese (Mn), 0 wt% (excluding) to 0.003 wt% carbon (C), 0 wt% (excluding) to 0.003 wt% sulfur (S), 0 wt% (excluding) to 0.003 wt% nitrogen (N), and 0 wt% (excluding) to 0.003 wt% titanium (Ti). The non-oriented electrical steel sheet contains 0% (excluding) to 0.003% zirconium (Zr), 0% (excluding) to 0.003% niobium (Nb), 0.001% to 0.015% phosphorus (P), 0% (excluding) to 0.02% copper (Cu), the balance being iron (Fe) and unavoidable impurities. The contents of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) in the non-oriented electrical steel sheet satisfy the following relationship 3.

[0019] <Relationship 3> 2.75≤log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu])≤3.70 In Equation 3, [S], [N], [Ti], [Zr], [Nb], [P] and [Cu] represent the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) in the non-oriented electrical steel sheet, respectively.

[0020] In this embodiment, when the non-oriented electrical steel sheet is stamped, shear surfaces, fracture surfaces and burrs may be formed in the non-oriented electrical steel sheet.

[0021] In this embodiment, the proportion of sheared surface can be 45% to 100%, and the proportion of fractured surface can be 0% to 55%.

[0022] In this embodiment, the ratio of the burr length to the thickness of the non-oriented electrical steel sheet can be 3.5% or less.

[0023] In this embodiment, the content of silicon (Si), manganese (Mn) and aluminum (Al) in the non-oriented electrical steel sheet can satisfy the following relationship 4.

[0024] <Relation 4> 1.55≤log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al]))≤1.80 In Equation 4, [Si], [Mn] and [Al] can represent the contents of silicon (Si), manganese (Mn) and aluminum (Al) in the non-oriented electrical steel sheet (in weight %), respectively.

[0025] In this embodiment, the average grain size of the non-oriented electrical steel sheet can be from 50 µm to 150 µm.

[0026] In this implementation scheme, the iron loss of non-oriented electrical steel sheet (based on W) 15 / 50 The value can be 3.0 W / kg or less.

[0027] As described above, according to embodiments of the present invention, stampability can be improved by controlling the alloy composition of the non-oriented electrical steel sheet. However, the scope of the present invention is not limited to these effects. Attached Figure Description

[0028] Figure 1 A flowchart illustrating a method for manufacturing non-oriented electrical steel sheets according to an embodiment of the present invention is provided.

[0029] Figure 2 The cross-section of a non-oriented electrical steel sheet after a stamping process is schematically shown according to an embodiment of the present invention. Detailed Implementation

[0030] This invention may include various embodiments and modifications, and some embodiments are shown in the accompanying drawings and will be described in detail herein. The advantages and features of this invention, as well as methods of implementation thereof, will become apparent from the embodiments described in detail below with reference to the accompanying drawings. However, this invention is not limited to the embodiments described below and may be embodied in various modes.

[0031] It will be understood that although this document may use terms such as “first” and “second” to describe various elements, these elements should not be limited by these terms, and these terms are only used to distinguish one element from another.

[0032] As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “one,” and “the” are intended to include the plural forms as well.

[0033] It will be understood that terms such as “comprising,” “including,” and “having” as used herein indicate the presence of the said feature or component, but do not preclude the presence or addition of one or more other features or components.

[0034] For ease of description, the dimensions of the elements in the accompanying drawings may be enlarged. In other words, since the dimensions and shapes of the components in the drawings are arbitrarily shown for ease of description, the invention is not limited thereto.

[0035] When an implementation scheme can be carried out in different ways, a specific process sequence can be performed differently from the described sequence. For example, two processes described consecutively can be performed substantially simultaneously, or they can be performed in the reverse order of the described sequence.

[0036] As used herein, "A and / or B" means either A, B, or A and B. Furthermore, "at least one of A and B" means either A, B, or A and B.

[0037] In the following description, embodiments will be described in detail with reference to the accompanying drawings, and in the following description, the same reference numerals will denote the same elements, and redundant descriptions thereof will be omitted.

[0038] Figure 1 A flowchart illustrating a method for manufacturing non-oriented electrical steel sheets according to an embodiment of the present invention is provided.

[0039] Reference Figure 1 The method for manufacturing non-oriented electrical steel sheets may include hot rolling operation S100, hot annealing operation S200, cutting operation S300, cold rolling operation S400, cold annealing operation S500, and coating operation S600.

[0040] In the method for manufacturing non-oriented electrical steel sheets according to an embodiment of the present invention, the hot-rolled semi-finished product can be a slab. The slab in a semi-finished state can be obtained by continuous casting after obtaining molten steel with a certain composition through a steelmaking process.

[0041] First, slabs can be produced using a continuous casting process. Slabs can contain silicon (Si), aluminum (Al), manganese (Mn), carbon (C), sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), copper (Cu), the balance iron (Fe), and unavoidable impurities.

[0042] Specifically, the slab may contain 2.0% to 3.8% by weight of silicon (Si), 0.1% to 1.3% by weight of aluminum (Al), 0.1% to 0.5% by weight of manganese (Mn), 0% (excluding) to 0.003% by weight of carbon (C), 0% (excluding) to 0.003% by weight of sulfur (S), 0% (excluding) to 0.003% by weight of nitrogen (N), 0% (excluding) to 0.003% by weight of titanium (Ti), 0% (excluding) to 0.003% by weight of zirconium (Zr), 0% (excluding) to 0.003% by weight of niobium (Nb), 0.001% to 0.015% by weight of phosphorus (P), 0% (excluding) to 0.02% by weight of copper (Cu), the balance of iron (Fe), and unavoidable impurities.

[0043] Silicon (Si) can be a major additive element used to reduce eddy current losses by increasing the resistivity of the manufactured non-oriented electrical steel sheet. The silicon (Si) content can range from 2.0 wt% to 3.8 wt%. When the silicon (Si) content is less than 2.0 wt%, it may be difficult to achieve the target iron loss value of the manufactured non-oriented electrical steel sheet. In particular, when the silicon (Si) content is less than 2.0 wt%, it may be difficult to achieve low iron loss. On the other hand, magnetic permeability and magnetic flux density may decrease with increasing silicon (Si) content. When the silicon (Si) content is greater than 3.8 wt%, the magnetic flux density may decrease, the manufacturing process may become more difficult, and the manufacturing cost may increase. In addition, when the silicon (Si) content is greater than 3.8 wt%, brittleness may increase, and therefore cracks and / or sheet fractures may occur during cold rolling.

[0044] Manganese (Mn) can be combined with silicon (Si) to increase the resistivity and improve the texture of manufactured non-oriented electrical steel sheets. The manganese (Mn) content can range from 0.1 wt% to 0.5 wt%. When the manganese (Mn) content is less than 0.1 wt%, fine MnS precipitates may form, thereby inhibiting grain growth. On the other hand, when the manganese (Mn) content is greater than 0.5 wt%, coarse MnS precipitates may form, leading to a deterioration in magnetic properties, such as a decrease in magnetic flux density. In addition, when the manganese (Mn) content is greater than 0.5 wt%, the reduction in iron loss may be smaller compared to the amount added, and cold rollability may deteriorate.

[0045] Aluminum (Al) can be a major additive element used to reduce eddy current losses by increasing the resistivity of the manufactured non-oriented electrical steel sheet through combination with silicon (Si). The aluminum (Al) content can range from 0.1 wt% to 1.3 wt%. Aluminum (Al) can react with nitrogen to cause AlN precipitation, and when the aluminum (Al) content is greater than 1.3 wt%, AlN may form, thereby increasing the iron loss of the manufactured non-oriented electrical steel sheet and inhibiting grain growth. In addition, when the aluminum (Al) content is greater than 1.3 wt%, cold rollability may deteriorate, and magnetic flux density may decrease, thus deteriorating the magnetic properties.

[0046] Carbon (C) can be a component that increases iron loss by forming carbides such as TiC and NbC, and the carbon (C) content in the slab may be low. The carbon (C) content can range from 0% by weight (excluding) to 0.003% by weight. When the carbon (C) content is greater than 0.003% by weight, magnetic aging may occur, thereby reducing the magnetic properties of the manufactured non-oriented electrical steel sheet. When the carbon (C) content is less than 0.003% by weight, magnetic aging can be suppressed. When the carbon (C) content is converted to parts per million (ppm), the carbon (C) content can range from 0 ppm (excluding) to 30 ppm.

[0047] Phosphorus (P) can be a grain boundary segregating element and a component that forms texture. The phosphorus (P) content can range from 0.001 wt% to 0.015 wt%. When the phosphorus (P) content is greater than 0.015 wt%, grain growth may be inhibited due to the segregation effect, magnetic properties may deteriorate, and cold rollability may worsen. When the phosphorus (P) content is converted to ppm, it can range from 10 ppm to 150 ppm.

[0048] Sulfur (S) can be a component that forms precipitates such as MnS or CuS, increasing iron loss and inhibiting grain growth. Therefore, the sulfur (S) content in slabs may be low. The sulfur (S) content can range from 0% by weight (excluding) to 0.003% by weight. When the sulfur (S) content is greater than 0.003% by weight, precipitates such as MnS or CuS may form, thereby increasing iron loss and inhibiting grain growth. When the sulfur (S) content is converted to ppm, the sulfur (S) content can range from 0 ppm (excluding) to 30 ppm.

[0049] Nitrogen (N) can form precipitates such as AlN, TiN, or NbN, thereby increasing iron loss and inhibiting grain growth. Therefore, the nitrogen (N) content in slabs may be low. The nitrogen (N) content can range from 0% by weight (excluding) to 0.003% by weight. When the nitrogen (N) content is greater than 0.003% by weight, precipitates such as AlN, TiN, or NbN may form, thereby increasing iron loss and inhibiting grain growth. When the nitrogen (N) content is converted to ppm, the nitrogen (N) content can range from 0 ppm (excluding) to 30 ppm.

[0050] Titanium (Ti) can form fine precipitates such as TiC or TiN, thereby inhibiting grain growth. Since magnetic properties deteriorate with increasing titanium (Ti) content, it should be added in the smallest possible amount. The titanium (Ti) content can range from 0% by weight (excluding) to 0.003% by weight. When the titanium (Ti) content exceeds 0.003% by weight, fine precipitates such as TiC or TiN may form, thus inhibiting grain growth and reducing magnetic properties. When converting the titanium (Ti) content to ppm, the titanium (Ti) content can range from 0 ppm (excluding) to 30 ppm.

[0051] Zirconium (Zr) can react with carbon and nitrogen to form fine precipitates and inhibit grain growth. Since the texture formed deteriorates with increasing Zr content, the Zr content can range from 0% by weight (excluding) to 0.003% by weight. When converting the Zr content to ppm, the Zr content can range from 0 ppm (excluding) to 30 ppm.

[0052] Niobium (Nb) can form fine precipitates such as NbC, thereby inhibiting grain growth and forming structures detrimental to magnetism. The niobium (Nb) content can range from 0% by weight (excluding) to 0.003% by weight. When the niobium (Nb) content is greater than 0.003% by weight, fine precipitates such as NbC may form, thereby inhibiting grain growth and reducing magnetic properties. When converting the niobium (Nb) content to ppm, the niobium (Nb) content can range from 0 ppm (excluding) to 30 ppm.

[0053] Copper (Cu) can form sulfides with manganese. Furthermore, the resulting precipitates can inhibit grain growth. The copper (Cu) content can range from 0% by weight (excluding) to 0.02% by weight. When the copper (Cu) content exceeds 0.02% by weight, high-temperature brittleness may occur, leading to cracking during continuous casting or hot rolling. When converting the copper (Cu) content to ppm, the copper (Cu) content can range from 0 ppm (excluding) to 200 ppm.

[0054] In the implementation scheme, the contents of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) in the slab can satisfy the following relationship 1.

[0055] <Relation 1> 2.75≤log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu])≤3.70 In Equation 1, [S], [N], [Ti], [Zr], [Nb], [P], and [Cu] can represent the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the slab, respectively. For example, when the sulfur (S) content in the slab is 5 ppm, [S] can be 5.

[0056] When the value of Equation 1 is less than 2.75, the ratio of burr length to the thickness of the non-oriented electrical steel sheet may be greater than 3.5%. Therefore, shape defects, stress, and reduced insulation properties may occur during the lamination process of the manufactured non-oriented electrical steel sheet. In addition, when the value of Equation 1 is greater than 3.70, the proportion of fracture surface may be greater than 55%, which may lead to cracks.

[0057] Therefore, when the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the slab satisfy Equation 1, the ratio of burr length to the thickness of the non-oriented electrical steel sheet formed in the stamping process can be 3.5% or less, and the occurrence of cracks can be prevented or minimized. This will be described in more detail below.

[0058] In the implementation scheme, the content of silicon (Si), manganese (Mn) and aluminum (Al) in the slab can satisfy the following relationship 2.

[0059] <Relation 2> 1.55≤log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al]))≤1.80 In Equation 2, [Si], [Mn], and [Al] can represent the contents (in weight %) of silicon (Si), manganese (Mn), and aluminum (Al) in the slab, respectively. For example, when the silicon (Si) content in the slab is 2.0 weight %, [Si] can be 2.0.

[0060] When the value of Equation 2 is less than 1.55, the iron loss of the manufactured non-oriented electrical steel sheet may be greater than 3.0 W / kg. On the other hand, when the value of Equation 2 is greater than 1.80, the iron loss can be excellent, but the cold rollability may deteriorate, thus potentially leading to cracking or sheet breakage. Therefore, when the value of Equation 2 is between 1.55 and 1.80, the manufactured non-oriented electrical steel sheet can have an iron loss of 3.0 W / kg or less, and can prevent or minimize cracking and / or sheet breakage in the steel sheet during cold rolling. This will be described in more detail below.

[0061] In hot rolling operation S100, the slab can be reheated, and then the reheated slab can be hot rolled to produce hot-rolled sheet. For example, the steel sheet produced by hot rolling operation S100 can be referred to as hot-rolled sheet.

[0062] First, in the hot rolling operation S100, the slab can be reheated. The slab reheating temperature can be from 1000°C to 1250°C. When the slab reheating temperature is below 1000°C, the rolling load during hot rolling (e.g., roughing and / or finishing rolling) may increase, thus potentially reducing rollability. On the other hand, when the slab reheating temperature is above 1250°C, precipitates such as C, S, or N in the slab may redissolve, potentially forming fine precipitates during subsequent rolling and annealing operations, which may inhibit grain growth and reduce magnetic properties.

[0063] In hot rolling operation S100, the slab can be rolled at a specific final rolling temperature. In this case, the final rolling temperature can be between 850°C and 950°C.

[0064] Alternatively, in the hot rolling operation S100, the hot-rolled steel sheet can be cooled to a certain winding temperature (CT) before being wound. In this case, the winding temperature can be between 550°C and 680°C.

[0065] The thickness of hot-rolled sheet produced by hot rolling operation S100 can range from 1.8 mm to 2.6 mm. In this case, when the thickness of the hot-rolled sheet is greater than 2.6 mm, the cold rolling reduction rate may increase, and therefore the texture may deteriorate.

[0066] The hot annealing operation S200 can be performed after the hot rolling operation S100. In the hot annealing operation S200, the hot-rolled sheet can be annealed to produce a hot-annealed sheet. For example, a steel sheet that has undergone the hot annealing operation S200 can be referred to as a hot-annealed sheet.

[0067] In hot annealing operation S200, the hot-rolled sheet can be heated to the hot annealing temperature at a heating rate (or heating rate) of 20°C / s or greater, then annealed at the hot annealing temperature for 30 to 150 seconds, and then cooled at a cooling rate of 20°C / s or greater. In this case, the hot annealing temperature can be from 950°C to 1100°C. When the hot annealing temperature is below 950°C, grain growth may be insufficient, which may lead to the formation of fine grains, thereby reducing the magnetism of the manufactured non-oriented electrical steel sheet. In addition, when the hot annealing temperature is below 950°C, fine inclusions such as carbides and nitrides may form from the surface layer, and these inclusions may not grow sufficiently, thereby reducing the magnetism of the manufactured non-oriented electrical steel sheet. On the other hand, when the hot annealing temperature is above 1100°C, grains may overgrow, increasing grain size deviation, and significant oxidation may occur, which will adversely affect the manufactured non-oriented electrical steel sheet.

[0068] The cutting operation S300 can be performed after the hot annealing operation S200. In the cutting operation S300, the wound steel sheet (e.g., a hot-annealed sheet or a hot-rolled sheet) can be unwound, and then the steel sheet (e.g., a hot-annealed sheet or a hot-rolled sheet) can be cut using a cutting tool or the like, and then the cut steel sheet (e.g., a hot-annealed sheet or a hot-rolled sheet) can be wound.

[0069] In the implementation scheme, during the cutting operation S300, the steel plate (e.g., a hot-annealed sheet or a hot-rolled sheet) can be cut using a cutting tool or the like. For example, during the cutting operation S300, the steel plate (e.g., a hot-annealed sheet or a hot-rolled sheet) can be divided into three equal parts in the width direction, or it can be divided into four equal parts in the width direction. Alternatively, during the cutting operation S300, two edge portions of the steel plate (e.g., a hot-annealed sheet or a hot-rolled sheet) can be cut.

[0070] The cold rolling operation S400 can be performed after the cutting operation S300. In the cold rolling operation S400, the cut and hot-annealed sheet material can be cold-rolled to produce cold-rolled sheet material. For example, a steel sheet that has undergone the cold rolling operation S400 can be referred to as cold-rolled sheet material.

[0071] Prior to the cold rolling operation S400, an acid pickling solution can be used to remove the oxide layer formed on the surface of the heat-annealed sheet.

[0072] In cold rolling operation S400, hot-annealed sheet metal can be cold-rolled to a thickness of 0.5 mm or less. In this case, to provide rollability, the sheet temperature can be raised to 150°C to 200°C, followed by warm rolling. The reduction rate in cold rolling operation S400 can be 50% or greater. The final reduction rate in cold rolling operation S400 can be 70% to 95%.

[0073] The cold annealing operation S500 can be performed after the cold rolling operation S400. In the cold annealing operation S500, the cold-rolled sheet can be annealed to prepare a cold-annealed sheet. For example, a steel sheet that has undergone the cold annealing operation S500 can be referred to as a cold-annealed sheet.

[0074] In the cold annealing operation S500, the cold-rolled sheet can be heated to the cold annealing temperature (e.g., the target temperature) at a heating rate of 5°C / s to 30°C / s, then annealed at the cold annealing temperature for 40 to 300 seconds, and then cooled at a cooling rate of 20°C / s or greater. In this case, the cold annealing temperature can be from 800°C to 1100°C. When the cold annealing temperature is below 800°C, the grain size may become finer, and therefore hysteresis losses may increase. On the other hand, when the cold annealing temperature is above 1100°C, the grain size may become coarser, and therefore eddy current losses may increase.

[0075] To prevent surface oxidation and nitration, a cold annealing operation S500 can be performed in a mixed atmosphere. For example, a mixed atmosphere of nitrogen and hydrogen can be used to further smooth the surface condition.

[0076] The coating operation S600 can be performed after the cold annealing operation S500. In the coating operation S600, a coating can be formed on the cold-annealed sheet material. Forming a coating through the coating operation S600 can improve stampability and ensure insulation properties.

[0077] In the implementation plan, non-oriented electrical steel sheets can be manufactured through hot rolling operation S100 to coating operation S600.

[0078] According to embodiments of the present invention, the non-oriented electrical steel sheet may contain silicon (Si), aluminum (Al), manganese (Mn), carbon (C), sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), copper (Cu), the balance iron (Fe), and unavoidable impurities.

[0079] Specifically, non-oriented electrical steel sheets may contain 2.0% to 3.8% silicon (Si), 0.1% to 1.3% aluminum (Al), 0.1% to 0.5% manganese (Mn), 0% (excluding) to 0.003% carbon (C), 0% (excluding) to 0.003% sulfur (S), 0% (excluding) to 0.003% nitrogen (N), 0% (excluding) to 0.003% titanium (Ti), 0% (excluding) to 0.003% zirconium (Zr), 0% (excluding) to 0.003% niobium (Nb), 0.001% to 0.015% phosphorus (P), 0% (excluding) to 0.02% copper (Cu), the balance iron (Fe), and unavoidable impurities.

[0080] The average grain size of the non-oriented electrical steel sheet manufactured by the method for manufacturing non-oriented electrical steel sheets according to embodiments of the present invention can be from 50 µm to 150 µm. Furthermore, the non-oriented electrical steel sheet manufactured by the method for manufacturing non-oriented electrical steel sheets according to embodiments of the present invention can have an iron loss of 3.0 W / kg or less (based on W). 15 / 50 ) and magnetic flux density of 1.60 T or greater (based on B) 50 Furthermore, the non-oriented electrical steel sheet manufactured by the method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention can have a yield strength (YP) of 200 MPa or greater and a tensile strength (TS) of 350 MPa or greater.

[0081] Figure 2 The cross-section of a non-oriented electrical steel sheet after a stamping process is schematically shown according to an embodiment of the present invention.

[0082] Reference Figure 2 When the non-oriented electrical steel sheet 100 according to an embodiment of the present invention is subjected to a stamping process, a shear surface 110, a fracture surface 120 and burrs 130 may be formed on the non-oriented electrical steel sheet 100.

[0083] In an embodiment, the shear surface 110 may be a surface extending in the thickness direction of the non-oriented electrical steel sheet 100 or extending at an angle relative to the thickness direction. The shear surface 110 may have a smooth surface. Alternatively, when analyzed from the stamped side, the shear surface 110 may be formed as a straight line within the thickness range of the material and may have a low roughness when viewed from the front.

[0084] In an embodiment, the fracture surface 120 may be the surface formed when the non-oriented electrical steel sheet 100 fractures. The fracture surface 120 may be irregular compared to the shear surface 110. The fracture surface 120 may have an irregular surface. Alternatively, when analyzed from the stamped side, the fracture surface 120 may be formed diagonally within the thickness of the material and may have a rough surface when viewed from the front.

[0085] In the implementation, burr 130 may be formed on the non-oriented electrical steel sheet 100 during the stamping process. Alternatively, burr 130 may refer to a portion formed outside the thickness range of the material when analyzed from the side after stamping.

[0086] Additionally, in the implementation scheme, a flip can be formed on the non-oriented electrical steel sheet 100. As the stamping process proceeds, the compressive stress generated during stamping may cause plastic deformation of the material, and flipping may occur due to the pressure generated as the material bends due to this plastic deformation. Flipping may be affected by material quality or gap conditions.

[0087] In the implementation scheme, the shear surface ratio (%) can be 45% to 100% (or 45% to 100% (excluding)). In this case, the shear surface ratio (%) can be calculated as L1 / TH*100. In this case, TH can be the thickness of the non-oriented electrical steel sheet 100, and L1 can be the length of the shear surface 110 in the thickness direction of the non-oriented electrical steel sheet 100. That is, the shear surface ratio (%) can refer to the ratio of the shear surface 110 to the thickness of the non-oriented electrical steel sheet 100. In addition, the thickness TH of the non-oriented electrical steel sheet 100 and the length L1 of the shear surface 110 in the thickness direction of the non-oriented electrical steel sheet 100 can be measured using an optical microscope (OM).

[0088] In the implementation scheme, the fracture surface percentage (%) can be from 0% to 55% (or from 0% (excluding) to 55%). In this case, the fracture surface percentage (%) can be calculated as L2 / TH*100. In this case, TH can be the thickness of the non-oriented electrical steel sheet 100, and L2 can be the length of the fracture surface 120 in the thickness direction of the non-oriented electrical steel sheet 100. That is, the fracture surface percentage (%) can refer to the ratio of the fracture surface 120 to the thickness of the non-oriented electrical steel sheet 100. In addition, the thickness TH of the non-oriented electrical steel sheet 100 and the length L2 of the fracture surface 120 in the thickness direction of the non-oriented electrical steel sheet 100 can be measured using an optical microscope (OM). When the fracture surface percentage (%) is greater than 55%, the magnetic properties may deteriorate. Furthermore, when the fracture surface percentage (%) is greater than 55%, residual stress may increase, and it may be difficult to form a good laminated surface during the lamination process.

[0089] In the implementation scheme, the ratio of the length of the burr 130 to the thickness of the non-oriented electrical steel sheet 100 can be 3.5% or less. In this case, the ratio of the length of the burr 130 to the thickness TH of the non-oriented electrical steel sheet 100 can be calculated as L3 / TH*100. In this case, L3 can be the length of the burr 130 in the thickness direction of the non-oriented electrical steel sheet 100, and TH can be the thickness of the non-oriented electrical steel sheet 100 in the thickness direction. When the ratio of the length L3 of the burr 130 to the thickness TH of the non-oriented electrical steel sheet 100 is greater than 3.5%, shape defects, stress, and reduced insulation properties may occur during the lamination process of the non-oriented electrical steel sheet 100.

[0090] In the implementation plan, the contents of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) in the non-oriented electrical steel sheet can satisfy the following relationship 3.

[0091] <Relationship 3> 2.75≤log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu])≤3.70 In Equation 3, [S], [N], [Ti], [Zr], [Nb], [P], and [Cu] can represent the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the non-oriented electrical steel sheet, respectively. For example, when the sulfur (S) content in the non-oriented electrical steel sheet is 5 ppm, [S] can be 5.

[0092] When the value of Equation 3 is less than 2.75, the length of burrs formed during the stamping process may increase, potentially leading to shape defects, stress, and reduced insulation properties during the lamination of non-oriented electrical steel sheets. Specifically, when the value of Equation 3 is less than 2.75, the ratio of the length L3 of the burr 130 to the thickness TH of the non-oriented electrical steel sheet 100 may be greater than 3.5%, again potentially causing shape defects, stress, and reduced insulation properties during the lamination of non-oriented electrical steel sheets. Furthermore, when the value of Equation 3 is greater than 3.70, the fracture surface area may exceed 55%, potentially leading to cracks.

[0093] Therefore, when the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the slab satisfy Equation 3, the ratio of the length L3 of the burr 130 to the thickness TH of the non-oriented electrical steel sheet 100 can be 3.5% or less. This can prevent or minimize the occurrence of shape defects, stress, and reduced insulation properties during the lamination process of the non-oriented electrical steel sheet 100, and can also prevent or minimize the occurrence of cracks. This will be described in more detail below.

[0094] In the implementation plan, the content of silicon (Si), manganese (Mn) and aluminum (Al) in the non-oriented electrical steel sheet can satisfy the following relationship 4.

[0095] <Relation 4> 1.55≤log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al]))≤1.80 In Equation 4, [Si], [Mn], and [Al] can represent the content (in weight %) of silicon (Si), manganese (Mn), and aluminum (Al) in the non-oriented electrical steel sheet, respectively. For example, when the silicon (Si) content in the non-oriented electrical steel sheet is 2.0 weight %, [Si] can be 2.0.

[0096] When the value of Equation 4 is less than 1.55, the iron loss of the non-oriented electrical steel sheet 100 may be greater than 3.0 W / kg. On the other hand, when the value of Equation 4 is greater than 1.80, the iron loss can be excellent, but the cold rollability may deteriorate, thus potentially leading to cracking or sheet breakage. Therefore, when the value of Equation 4 is between 1.55 and 1.80, the non-oriented electrical steel sheet 100 can have an iron loss of 3.0 W / kg or less, and can prevent or minimize the occurrence of cracks and / or sheet breakage in the steel sheet during cold rolling. This will be described in more detail below.

[0097] Experimental Examples The present invention will be described in more detail below through experimental examples. However, the following experimental examples are intended to further illustrate the invention, and the scope of the invention is not limited to the following experimental examples. Those skilled in the art can make appropriate modifications or changes to the following experimental examples within the scope of the invention.

[0098] [Table 1] [Table 2] [Table 3] Examples 1 to 6 and Comparative Examples 1 to 6 can be samples of slabs containing the components shown in Table 1, the balance of iron (Fe), and unavoidable impurities, manufactured under the process conditions shown in Table 2. In this case, all samples are manufactured to the same dimensions of 80 mm in width and 150 mm in length.

[0099] Examples 1 to 6 and Comparative Examples 1 to 6 were manufactured under the same process conditions but with different component contents.

[0100] The thickness, length of sheared surfaces, length of fracture surfaces, and length of burrs of a sample (e.g., a non-oriented electrical steel sheet) are measured by observing the side and front surfaces of the sample (e.g., a non-oriented electrical steel sheet) using an optical microscope (OM) at magnifications of 100 to 300.

[0101] In Table 3, the value of relation 1 corresponds to the value of log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu]), and the value of relation 2 corresponds to the value of log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al])).

[0102] Referring to Examples 1 to 6, it can be seen that the value of Equation 1 is 2.75 to 3.70, and the value of Equation 2 is 1.55 to 1.80. Furthermore, it can be seen that when the value of Equation 1 is 2.75 to 3.70, the ratio of burr length to the thickness of the non-oriented electrical steel sheet (or sample) is 3.5% or less, and the fracture surface area percentage (%) is 0% to 55% (or 0% (excluding) to 55%). Additionally, it can be seen that when the value of Equation 2 is 1.55 to 1.80, the iron loss is 3.0 W / kg or less.

[0103] Comparative Example 1 corresponds to the case where the value of Relation 2 is less than 1.55, and it can be seen that the iron loss of Comparative Example 1 is greater than 3.0 W / kg. Therefore, when the value of Relation 2 is less than 1.55, the iron loss of the manufactured non-oriented electrical steel sheet may be greater than 3.0 W / kg.

[0104] Comparative Example 2 corresponds to the case where the value of Relation 1 is less than 2.75, and it can be seen that the ratio of the burr length to the thickness of the non-oriented electrical steel sheet in Comparative Example 2 is greater than 3.5%. In this case, when the ratio of the burr length to the thickness of the non-oriented electrical steel sheet is greater than 3.5%, shape defects, stress, and reduced insulation properties may occur during the lamination process of the non-oriented electrical steel sheet.

[0105] Comparative Example 3 corresponds to the case where the value of Relation 1 is less than 2.75, and it can be seen that the ratio of the burr length to the thickness of the non-oriented electrical steel sheet in Comparative Example 3 is greater than 3.5%. In this case, when the ratio of the burr length to the thickness of the non-oriented electrical steel sheet is greater than 3.5%, shape defects, stress, and reduced insulation properties may occur during the lamination process of the non-oriented electrical steel sheet.

[0106] Comparative Examples 4 and 5 correspond to cases where the value of Relation 1 is greater than 3.70, and it can be seen that the fracture surface percentage (%) in Comparative Examples 4 and 5 are 73.9% and 74.8%, respectively. When the fracture surface percentage (%) is greater than 55%, cracks may occur.

[0107] Comparative Example 6 can correspond to the case where the value of Relation 2 is greater than 1.80. When the value of Relation 2 is greater than 1.80, the iron loss can be 3.0 W / kg, but the cold rollability may be reduced, and therefore sheet fracture and / or cracks may occur.

[0108] Although the invention has been described with reference to embodiments shown in the accompanying drawings, these are merely examples, and those skilled in the art will understand that various modifications and other equivalent embodiments can be derived therefrom. Therefore, the spirit and scope of the invention should be defined by the appended claims.

Claims

1. A method for manufacturing non-oriented electrical steel sheet, the method comprising: A slab is hot-rolled to produce a hot-rolled sheet, wherein the slab comprises 2.0 wt% to 3.8 wt% silicon (Si), 0.1 wt% to 1.3 wt% aluminum (Al), 0.1 wt% to 0.5 wt% manganese (Mn), greater than 0 wt% to 0.003 wt% carbon (C), greater than 0 wt% to 0.003 wt% sulfur (S), greater than 0 wt% to 0.003 wt% nitrogen (N), greater than 0 wt% to 0.003 wt% titanium (Ti), greater than 0 wt% to 0.003 wt% zirconium (Zr), greater than 0 wt% to 0.003 wt% niobium (Nb), 0.001 wt% to 0.015 wt% phosphorus (P), greater than 0 wt% to 0.02 wt% copper (Cu), the balance being iron (Fe), and unavoidable impurities. The hot-rolled sheet is hot-annealed to produce a hot-annealed sheet. The heat-annealed sheet is cold-rolled to produce a cold-rolled sheet; and The cold-rolled sheet is cold-annealed to produce a cold-annealed sheet. The contents of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the slab satisfy the following relationship: 1 <Relation 1> 2.75≤log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu])≤3.70, Wherein, [S], [N], [Ti], [Zr], [Nb], [P] and [Cu] represent the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) in the slab.

2. The method according to claim 1, wherein, When the non-oriented electrical steel sheet is stamped, shear surfaces, fracture surfaces and burrs are formed in the non-oriented electrical steel sheet.

3. The method according to claim 2, wherein, The proportion of the shear surface is 45% to 100%, and the proportion of the fracture surface is 0% to 55%.

4. The method according to claim 2, wherein, The ratio of the length of the burr to the thickness of the non-oriented electrical steel sheet is 3.5% or less.

5. The method according to claim 1, wherein, The content of silicon (Si), manganese (Mn), and aluminum (Al) in the slab satisfies the following relationship: 2 <Relation 2> 1.55≤log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al]))≤1.80, Wherein, [Si], [Mn] and [Al] represent the contents of silicon (Si), manganese (Mn) and aluminum (Al) in the slab (in weight %), respectively.

6. The method according to claim 1, wherein, The average grain size of the non-oriented electrical steel sheet is 50 µm to 150 µm.

7. The method according to claim 1, wherein, The iron loss (based on W15 / 50) of the non-oriented electrical steel sheet is 3.0 W / kg or less.

8. A non-oriented electrical steel sheet, said non-oriented electrical steel sheet comprising... 2.0 wt% to 3.8 wt% silicon (Si), 0.1 wt% to 1.3 wt% aluminum (Al), 0.1 wt% to 0.5 wt% manganese (Mn), greater than 0 wt% to 0.003 wt% carbon (C), greater than 0 wt% to 0.003 wt% sulfur (S), greater than 0 wt% to 0.003 wt% nitrogen (N), greater than 0 wt% to 0.003 wt% titanium (Ti), greater than 0 wt% to 0.003 wt% zirconium (Zr), greater than 0 wt% to 0.003 wt% niobium (Nb), 0.001 wt% to 0.015 wt% phosphorus (P), greater than 0 wt% to 0.02 wt% copper (Cu), balance iron (Fe), and unavoidable impurities. in, The contents of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P), and copper (Cu) in the non-oriented electrical steel sheet satisfy the following relationship 3 <Relationship 3> 2.75≤log(5*[S]+21*[N]+11*[Ti]+12*[Zr]+18*[Nb]+6*[P]+11*[Cu])≤3.70, Wherein, [S], [N], [Ti], [Zr], [Nb], [P] and [Cu] represent the contents (in ppm) of sulfur (S), nitrogen (N), titanium (Ti), zirconium (Zr), niobium (Nb), phosphorus (P) and copper (Cu) contained in the non-oriented electrical steel sheet, respectively.

9. The non-oriented electrical steel sheet according to claim 8, wherein, When the non-oriented electrical steel sheet is stamped, shear surfaces, fracture surfaces and burrs are formed in the non-oriented electrical steel sheet.

10. The non-oriented electrical steel sheet according to claim 9, wherein, The proportion of the shear surface is 45% to 100%, and the proportion of the fracture surface is 0% to 55%.

11. The non-oriented electrical steel sheet according to claim 9, wherein, The ratio of the length of the burr to the thickness of the non-oriented electrical steel sheet is 3.5% or less.

12. The non-oriented electrical steel sheet according to claim 8, wherein, The silicon (Si), manganese (Mn), and aluminum (Al) content in the non-oriented electrical steel sheet satisfies the following relationship: 4 <Relation 4> 1.55≤log(10.1169+(11.75*[Si]+6.2*[Mn]+8.76*[Al]))≤1.80, Wherein, [Si], [Mn] and [Al] represent the contents (in weight %) of silicon (Si), manganese (Mn) and aluminum (Al) contained in the non-oriented electrical steel sheet, respectively.

13. The non-oriented electrical steel sheet according to claim 8, wherein, The average grain size of the non-oriented electrical steel sheet is 50 µm to 150 µm.

14. The non-oriented electrical steel sheet according to claim 8, wherein, The iron loss of the non-oriented electrical steel sheet (based on W) 15 / 50 The value is 3.0 W / kg or less.

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