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 2.8-3.8 wt% of silicon (Si), 0.2-0.5 wt% of manganese (Mn), 0.5-1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu) and the balance of iron (Fe) and other inevitable impurities, and has a secondary phase volume fraction, which is a particle size of 1.1 μm or more, of 50% or more, and thus can have excellent mechanical properties and magnetic properties.

Description

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

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet.

[0002] As environmental regulations have become increasingly stringent worldwide, conventional internal combustion engine vehicles are being replaced by eco-friendly vehicles such as hybrid, electric, and hydrogen-powered vehicles. As demand for eco-friendly vehicles grows, interest in the efficiency of their electric motors is also growing. This has led to a growing demand for high-quality non-oriented electrical steel sheets, used as core materials in electric motors.

[0003] In general, the quality of non-oriented electrical steel sheets is judged by their magnetic properties, and the magnetic properties can be evaluated mainly through magnetic flux density and iron loss.

[0004] First, the magnetic flux density represents the number of magnetic force lines induced in a material under a specific magnetic field, and is generally the value induced under a magnetic field of 5000 A / m (B 50 ) is evaluated. The higher the magnetic flux density, the more efficient it is because it can induce a larger magnetic field with the same energy. Factors that can improve the magnetic flux density include the composition of the alloy components, grain size, and texture.

[0005] Next, iron loss represents the energy loss that occurs during the magnetization process of a material, and can indicate energy loss occurring at a specific magnetic flux density and frequency. Iron loss can be divided into hysteresis loss, which occurs due to the magnetization phenomenon itself, and eddy current loss, which is formed by the eddy current induced during magnetization.

[0006] Representative methods for improving the aforementioned magnetic properties include increasing resistivity by adding elements such as silicon (Si), aluminum (Al), and manganese (Mn), and utilizing thinning of steel sheets. However, adding elements that increase resistivity, such as silicon (Si), aluminum (Al), and manganese (Mn), can reduce magnetic flux density and reduce rollability, making thinning difficult. Furthermore, thinning of steel sheets can lower productivity and lead to increased costs due to advanced production processes.

[0007] The present invention has been devised to solve the above problems, and the object of the present invention is to provide a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet having excellent mechanical and magnetic properties by controlling alloy components and a manufacturing process.

[0008] The tasks of the present invention are not limited to the tasks mentioned above, and other tasks not mentioned will be clearly understood by those skilled in the art from the description below.

[0009] An electrical steel sheet according to one embodiment of the present invention contains 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the remainder iron (Fe) and other unavoidable impurities, and the volume fraction of a secondary phase having a particle size of 1.1 μm or more is 50% or more.

[0010] In addition, the secondary phase may include nitrides and oxides, but the ratio of the number of nitrides and oxides excluding CaO per unit area may satisfy the following equation 1.

[0011] [Formula 1]

[0012] 0.5≤(Number of nitrides) / (Number of oxides excluding CaO)≤4.5

[0013] Additionally, the yield strength (YS) may be greater than 380 MPa.

[0014] Also, iron loss (W 10 / 400 ) may be less than 13.5 W / kg.

[0015] A method for manufacturing an electrical steel sheet according to one embodiment of the present invention includes a first step of preparing a semi-finished steel sheet, a second step of hot-rolling the steel sheet to form a hot-rolled steel sheet, a third step of hot-rolling and annealing the hot-rolled steel sheet, a fourth step of cold-rolling the hot-rolled steel sheet subjected to the third step to form a cold-rolled steel sheet, and a fifth step of cold-rolling and annealing the cold-rolled steel sheet, wherein the second step includes a step of reheating the steel sheet to 1100 to 1180°C.

[0016] Additionally, the fifth step may be performed by heat treatment at 925 to 1100°C.

[0017] In addition, the steel contains 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the remainder iron (Fe) and other unavoidable impurities, and the volume fraction of a secondary phase having a particle size of 1.1 μm or more may be 50% or more.

[0018] In addition, the secondary phase may include nitrides and oxides, but the ratio of the number of nitrides and oxides excluding CaO per unit area may satisfy the following equation 1.

[0019] [Formula 1]

[0020] 0.5≤(Number of nitrides) / (Number of oxides excluding CaO)≤4.5

[0021] According to one embodiment of the present invention, a high-strength and high-efficiency electrical steel sheet and a method for manufacturing the electrical steel sheet having excellent mechanical and magnetic properties can be realized.

[0022] The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

[0023] FIG. 1 is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention is not limited or restricted by the following embodiments.

[0025] Additionally, when a component (or region, layer, portion, etc.) is referred to as being "on," "connected to," or "coupled to" another component, it means that it can be directly placed / connected / coupled to the other component, or that a third component may be placed between them.

[0026] Terms such as "include" or "have" should be understood to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0027] In order to clearly explain the present invention, a detailed description of a part that is irrelevant to the description or a related known technology that may unnecessarily obscure the gist of the present invention has been omitted, and when adding reference signs to components of each drawing in this specification, the same or similar reference signs are attached to the same or similar components throughout the specification.

[0028] In addition, terms and words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0029] Unless otherwise specified, the notation 'A to B' for numerical values ​​A and B means 'A or more and B or less'. In such notation, if a unit is attached only to numerical value B, the unit shall also be applied to numerical value A.

[0030] Also, unless otherwise stated, 1 ppm is 0.0001 wt%.

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0032]

[0033] Non-oriented electrical steel sheet

[0034] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the remainder of iron (Fe) and other unavoidable impurities.

[0035] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention can form a secondary phase through the control of the alloy components described above and the manufacturing method described below. Here, the secondary phase may refer to inclusions or precipitates that are dissolved in the steel and then precipitated again, and may include oxides and nitrides.

[0036] More specifically, in the non-oriented electrical steel sheet according to one embodiment of the present invention, the volume fraction of the secondary phase having a particle size of 1.1 ㎛ or more among the formed secondary phases is 50% or more. Here, if the volume fraction of the secondary phase having a particle size of 1.1 ㎛ or more is less than 50%, conversely, the volume fraction of the fine secondary phase having a particle size of less than 1.1 ㎛ becomes relatively high, and the fine secondary phases may hinder the movement of magnetic domains, thereby deteriorating the magnetic properties of the electrical steel sheet.

[0037] Therefore, in an electrical steel sheet according to one embodiment of the present invention, by controlling the alloy components and the manufacturing method so that the volume fraction of secondary phases having a particle size of 1.1 ㎛ or more is 50% or more, the volume fraction occupied by relatively fine secondary phases having a particle size of 1.1 ㎛ or less can be reduced, thereby preventing the fine secondary phases from hindering the movement of magnetic domains and thereby lowering the magnetic properties of the electrical steel sheet.

[0038] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention can have a ratio of the number of oxides excluding nitride and CaO per unit area among secondary phases that satisfies the following [Formula 1].

[0039] [Formula 1]

[0040] 0.5≤(Number of nitrides) / (Number of oxides excluding CaO)≤4.5

[0041] Here, the number of nitrides may be the number of nitrides formed per unit area in the electrical steel sheet according to one embodiment of the present invention, and the number of oxides not including CaO may refer to the number of oxides other than CaO among the secondary oxides. In addition, in Equation 1, the nitrides and oxides are not necessarily limited to having a particle size of 1.1 μm or more.

[0042] If the ratio of the number of nitrides to the number of oxides not containing CaO is less than 0.5, the effect of improving the mechanical properties by precipitation strengthening may be minimal, and thus it may be difficult to secure high yield strength (YS) characteristics of the final product, the non-oriented electrical steel sheet. On the other hand, if the ratio of the number of nitrides to the number of oxides not containing CaO exceeds 4.5, it is advantageous for securing strength by precipitation strengthening, but may cause a decrease in rollability. The decrease in rollability may hinder the improvement of magnetic properties through thinning.

[0043] In addition, a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 2.

[0044] [Formula 2]

[0045] 3.0 < log T < 4.0

[0046] In the above equation 2, T = 5·[S] + 12·[Ti] + 6·[P] +5·[Sn] +15·[Ni] + 11·[Cu]. [S], [Ti], [P], [Sn], [Ni] and [Cu] represent the contents of S, Ti, P, Sn, Ni and Cu, respectively, and the unit of content of each alloy element is ppm.

[0047] The above log T is a relationship between additive elements excluding silicon (Si), manganese (Mn), and aluminum (Al) among the alloy components of a non-oriented electrical steel sheet according to one embodiment of the present invention. Here, the additive elements may refer to additive elements added to improve the strength of the non-oriented electrical steel sheet and form precipitates.

[0048] More specifically, log T can mean a relationship that uses the weights for each grain boundary strengthening element and embrittlement element as a coefficient and expresses the content of the added elements to be controlled for improving magnetic properties as a formula.

[0049] That is, the coefficient value multiplied in front of each element in T may be a weight given to each element by considering the heat of sublimation according to the bond energy based on iron (Fe).

[0050] According to one embodiment of the present invention, the non-oriented electrical steel sheet may have a log T greater than 3 and less than 4 in order to improve the magnetic properties of the non-oriented electrical steel sheet according to the above equation 2. When the log T is 3 or less, it is difficult to obtain the effect of improving the magnetic properties due to the effect of improving the texture by the added element. On the other hand, when the log T is 4 or more, the content of impurity elements may be too high, which may deteriorate the magnetic properties.

[0051] A non-oriented electrical steel sheet according to one embodiment of the present invention can have improved texture and enhanced magnetic properties by satisfying the above equation 2.

[0052] In addition, a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 3.

[0053] [Formula 3]

[0054] 0.3 < {[Si]+[Mn]+[Al]}-log T < 1.3

[0055] In Equation 3, [Si], [Mn], and [Al] represent the contents of Si, Mn, and Al, respectively, and the unit of the contents is weight%.

[0056] The {[Si]+[Mn]+[Al]}-log T in the above [Formula 3] is a relational expression representing the correlation between the sum of silicon (Si), manganese (Mn), and aluminum (Al) and log T, which is a relational expression of the above-described additive elements. More specifically, {[Si]+[Mn]+[Al]}-log T may mean a relational expression representing the relationship between silicon (Si), manganese (Mn), and aluminum (Al) and the above-described additive elements by formulating the content of each element with respect to the strength and rollability of a non-oriented electrical steel sheet.

[0057] According to one embodiment of the present invention, the non-oriented electrical steel sheet may have {[Si]+[Mn]+[Al]}-log T greater than 0.3 and less than 1.3 according to the above [Formula 3]. When {[Si]+[Mn]+[Al]}-log T is 0.3 or less, the effect of improving the strength of the final product, the non-oriented electrical steel sheet, may be small, making it difficult to realize high strength characteristics. On the other hand, when {[Si]+[Mn]+[Al]}-log T is 1.3 or more, the strength of the steel may increase excessively, thereby reducing the rollability. Due to the reduction in rollability, thin sheet rolling may be impossible, and thus, the reduction in rollability may hinder the improvement of magnetic properties through thinning.

[0058] An electrical steel sheet according to one embodiment of the present invention can have improved mechanical strength by satisfying the above formula 3, and more specifically, can secure high strength characteristics due to improved mechanical strength without excessively impeding rollability.

[0059] Hereinafter, the role and content of each alloy element included in a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0060]

[0061] Silicon (Si)

[0062] Silicon (Si) is a key additive in electrical steel, increasing the resistivity of steel and thereby reducing eddy current losses, thereby improving magnetic properties. If the silicon content is too low, the increase in resistivity may not be sufficient, resulting in insufficient improvement in core loss. Conversely, excessive silicon content can increase the material's brittleness, reducing cold-rollability. Furthermore, increasing silicon content increases brittleness, which can lead to poor cold-rollability and reduced productivity.

[0063] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 2.8 to 3.8 wt% of silicon, and more preferably 2.8 to 3.65 wt%.

[0064]

[0065] manganese (Mn)

[0066] Manganese (Mn), like silicon (Si), improves the magnetic properties of steel by increasing resistivity and thus reducing iron loss. Manganese can also be added to enhance the grain structure, which is beneficial for magnetic properties. Insufficient manganese content reduces the resistivity-enhancing effect, potentially leading to increased high-frequency iron loss.

[0067] Additionally, manganese can react with sulfur (S) to form sulfides such as MnS. When the manganese content is less than 0.2 wt%, fine MnS precipitates are formed, which can inhibit grain growth and deteriorate magnetic properties. On the other hand, when the manganese content exceeds 0.5 wt%, coarse MnS precipitates are formed, which can reduce the magnetic flux density and deteriorate magnetic properties.

[0068] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.2 to 0.5 wt% of manganese, and preferably 0.2 to 0.32 wt%.

[0069]

[0070] Aluminum (Al)

[0071] Aluminum (Al), along with silicon (Si) and manganese (Mn), is an element that improves magnetic properties by increasing resistivity and reducing iron loss. Furthermore, aluminum can reduce magnetic anisotropy, thereby reducing magnetic deviation. If the aluminum content is too low, it can form fine nitrides, increasing magnetic property deviation. Conversely, if the aluminum content is excessive, it can form excessive nitrides, reducing magnetic flux density.

[0072] Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.5 to 1.5 wt% of aluminum, and more preferably 0.5 to 0.98 wt%.

[0073]

[0074] Carbon (C)

[0075] Carbon (C) is an effective element for increasing strength. However, it can increase iron loss by combining with titanium (Ti) and niobium (Nb) to form carbides such as TiC and NbC. If the carbon content exceeds 0.005 wt%, self-aging may occur, degrading magnetic properties. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.005 wt% or less of carbon.

[0076]

[0077] Yellow (S)

[0078] Sulfur (S) is an unavoidable impurity element in steel that is inherently present during the manufacturing process. Adding it in large amounts can cause brittleness. Furthermore, it can form precipitates such as MnS and CuS, increasing iron loss and inhibiting grain growth. Therefore, it is desirable to keep the amount of S added as low as possible. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain sulfur at 0.005 wt% or less.

[0079]

[0080] Person (P)

[0081] Phosphorus (P) is an element that improves grain structure through grain boundary segregation, thereby increasing resistivity and reducing iron loss. However, when phosphorus is added in large amounts exceeding 0.015 wt%, excessive grain boundary segregation may occur, resulting in grain growth inhibition, deterioration of magnetic properties, and reduced cold-rollability. Therefore, a non-oriented electrical steel sheet according to an embodiment of the present invention may contain phosphorus in an amount of 0.015 wt% or less.

[0082]

[0083] Nitrogen (N)

[0084] Nitrogen (N) is an element that contributes to the strength and corrosion resistance of steel, and it is an element that stabilizes austenite and improves the toughness of steel. However, nitrogen in steel can combine with aluminum (Al) and titanium (Ti) to form precipitates such as AlN and TiN, which can increase iron loss. Furthermore, it inhibits grain growth, so it is desirable to add as little nitrogen (N) as possible. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain nitrogen (N) at 0.005 wt% or less.

[0085]

[0086] Titanium (Ti)

[0087] Titanium (Ti) is an element with a strong tendency to form precipitates within steel. It can combine with carbon (C) or nitrogen (N) to form fine precipitates such as TiC and TiN, which can inhibit grain growth. As titanium is added, the fraction of the precipitates increases, and a texture that is unfavorable for magnetization can be formed, thereby deteriorating magnetic properties. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain titanium in an amount of 0.005 wt% or less.

[0088]

[0089] Sn

[0090] Tin (Sn) is an element that helps form a grain structure favorable for magnetic properties. It also prevents surface oxygen and nitrogen from penetrating into the steel, thereby reducing iron loss. However, if the tin content exceeds 0.08 wt%, it can inhibit grain growth, reducing magnetism and reducing rollability. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain tin at 0.08 wt% or less.

[0091]

[0092] Nickel (Ni)

[0093] Nickel (Ni) is an element that can enhance strength and improve the texture. Furthermore, when added together with copper (Cu), it can inhibit the precipitation of sulfur (S) into fine CuS. However, if the nickel content exceeds 0.07 wt%, it can reduce the magnetic flux density and increase the production cost due to its high price. Therefore, a non-oriented electrical steel sheet according to an embodiment of the present invention may contain nickel at 0.07 wt% or less.

[0094]

[0095] copper (Cu)

[0096] Copper (Cu) is an element that is resistant to oxidation and corrosion and can improve the grain structure. However, if the copper content exceeds 0.07 wt%, it can form precipitates such as CuS, which can hinder grain growth and deteriorate iron loss. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain copper in an amount of 0.07 wt% or less.

[0097]

[0098] In addition to the aforementioned steel components, the remainder may contain iron and unavoidable impurities. Unavoidable impurities are impurities introduced during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the field, a detailed description will be omitted.

[0099] In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are included, they may be included to replace the remaining Fe.

[0100] A non-oriented electrical steel sheet including an alloy component according to one embodiment of the present invention may have excellent mechanical properties, and may have a yield strength (YS) of 380 MPa or more and a tensile strength (TS) of 480 MPa or more. Preferably, the yield strength (YS) may be 392 MPa or more.

[0101] In addition, a non-oriented electrical steel sheet including an alloy component according to one embodiment of the present invention can have excellent magnetic properties and has a low iron loss (W 10 / 400 ) may be less than or equal to 13.5 W / kg. More preferably, the iron loss (W 10 / 400 ) may be less than 13 W / kg.

[0102] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0103]

[0104] Method for manufacturing non-oriented electrical steel sheet

[0105] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described with reference to FIG. 1.

[0106] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first step (S1) of preparing a semi-finished steel sheet, a second step (S2) of hot-rolling the steel sheet to form a hot-rolled steel sheet, a third step (S3) of hot-rolling and annealing the hot-rolled steel sheet, a fourth step (S4) of cold-rolling the hot-rolled steel sheet that has undergone the third step (S3) to form a cold-rolled steel sheet, and a fifth step (S5) of cold-rolling and annealing the cold-rolled steel sheet.

[0107] Hereinafter, each step of a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0108] The first step (S1) of preparing a semi-finished steel product is a step of preparing steel having the above-described alloy composition range for manufacturing the final product, non-oriented electrical steel sheet. More specifically, this step may be a step of manufacturing a semi-finished product by designing the alloy components within the above-described alloy composition range. The semi-finished product may be a slab, but is not limited thereto. Furthermore, the manufacturing of the slab may be performed using a process known in the relevant technical field, such as a steelmaking process or a casting process.

[0109] In a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, the second step (S2) may form a hot-rolled steel sheet by hot-rolling the steel material that has undergone the first step (S1).

[0110] More specifically, the second stage (S2) may include a reheating stage, a hot rolling stage, and a coiling stage.

[0111] First, the reheating step may be performed prior to the hot rolling step, and may be used to reheat the steel for subsequent processing. Specifically, this may be a step of uniformly heating the steel by loading it into a heating furnace to facilitate plastic deformation.

[0112] At this time, if the reheating temperature (SRT, Slab Reheating Temperature) is less than 1100℃, the rolling load may increase during hot rolling, which may reduce the rollability. On the other hand, if the reheating temperature exceeds 1180℃, precipitates such as carbon (C), sulfur (S), and nitrogen (N) in the semi-finished product may be re-dissolved, and fine precipitates may be formed at the grains and grain boundaries during cooling. This may be advantageous for improving strength, but it may inhibit grain growth and deteriorate iron loss, thereby reducing magnetic properties. Therefore, in the reheating step according to one embodiment of the present invention, the reheating temperature may be 1100 to 1180℃.

[0113] Next, a hot rolling step may be performed. The hot rolling step may include rough rolling and finishing rolling. The rough rolling step may be used to form the steel into a rolled material having an appropriate shape, thickness, and width, while the finishing rolling step may be used to adjust the steel to a specified thickness and width and roll it at a finishing temperature suitable for the intended use to obtain a good surface and shape.

[0114] At this time, the finishing temperature of the hot rolling step may be 800 to 900°C. If the finishing rolling temperature is less than 800°C, rolling may be performed in the two-phase region, which may result in the formation of an uneven texture. On the other hand, if the finishing rolling temperature exceeds 900°C, a problem of rapid strength reduction may occur.

[0115] Afterwards, a coiling step can be performed. At this time, the coiling temperature is preferably 500 to 700°C. If the coiling temperature is lower than 500°C, the grain size may become too small, preventing sufficient grain growth even after annealing. If the coiling temperature exceeds 700°C, fine precipitates may be generated, which may deteriorate magnetic properties.

[0116] The thickness of the hot-rolled steel sheet that has undergone the above-described second step (S2) is preferably 1.6 to 2.6 mm. If the thickness of the hot-rolled steel sheet is excessively thin, less than 1.6 mm, the thickness obtained after cold rolling may be insufficient, which may cause shape defects during product application. Conversely, if the thickness of the hot-rolled steel sheet exceeds 2.6 mm, the cold rolling reduction ratio increases, which may deteriorate the texture.

[0117] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a third step (S3) of annealing the hot-rolled steel sheet after the second step (S2). More specifically, the third step (S3) may be a hot-rolling annealing step performed to ensure uniformity of the microstructure and cold-rollability of the hot-rolled steel material.

[0118] The above hot rolling annealing step can be performed at a temperature that removes the elongated cast structure and forms a uniform microstructure with an average diameter of 50 to 200 μm. More specifically, the heat treatment can be performed at 900 to 1110°C for 30 to 180 seconds. At this time, the heating rate can be 20°C / s or higher, and the cooling rate can be 20°C / s or higher.

[0119] If the hot-rolling annealing temperature is below 900°C, the elongated cast structure remaining after hot rolling may remain, causing microstructure changes. This may lead to small grain sizes, which may hinder cold rolling. On the other hand, if the annealing temperature exceeds 1110°C, it may cause an imbalance in the final product's texture, resulting in reduced magnetic properties. In addition, the hot-rolling annealing time may range from 30 to 180 seconds to ensure the formation of an appropriate grain size under each temperature condition.

[0120] Thereafter, the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention may perform a fourth step (S4) of cold rolling the hot-rolled steel sheet that has undergone the third step (S3) to form a cold-rolled steel sheet. The fourth step (S4) may be a process of rolling the hot-rolled steel sheet that has undergone the third step (S3) at a temperature below the recrystallization temperature to further thin the steel sheet. More specifically, the fourth step (S4) may be a process of rolling the hot-rolled steel sheet to a thickness and width that meet the specifications of the final product.

[0121] The above fourth step (S4) can be performed at a reduction ratio of 50 to 96%, and the thickness of the cold rolled steel sheet formed through the cold rolling can be 0.35 mm or less. In addition, if necessary, to facilitate rolling, the sheet temperature can be increased to 100 to 200°C, and warm rolling can be performed at a temperature below recrystallization.

[0122] Thereafter, the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention may perform a fifth step (S5) of cold-rolling annealing the cold-rolled steel sheet. The cold-rolling annealing step may be performed to soften the cold-rolled steel sheet that has been hardened through a cold rolling step by a recrystallization phenomenon. In addition, the cold-rolling annealing step may be performed at a temperature that derives an optimal grain size in consideration of iron loss reduction and mechanical properties. If the cold-rolling annealing temperature is below the standard, the grain size may be fine, which may increase hysteresis loss. On the other hand, if the cold-rolling annealing temperature exceeds the standard, the grain size becomes coarse, and the eddy current loss increases.

[0123] Accordingly, the fifth step (S5) according to one embodiment of the present invention may be performed by heating the cold-rolled steel sheet to 925 to 1100°C, maintaining the temperature for 30 to 120 seconds, and then cooling the cold-rolled steel sheet. At this time, the heating rate may be 10°C / s or higher, and the cooling rate may be 20°C / s or higher.

[0124] Additionally, the fifth step (S5) may be performed in a mixed atmosphere of nitrogen and hydrogen to prevent oxidation or nitriding of the surface of the cold-rolled steel sheet. This can improve the surface quality of the cold-rolled steel sheet.

[0125] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further include a coating step after the fifth step (S5). The coating step may be performed to secure the insulation properties and improve the punchability of the non-oriented electrical steel sheet, and may mean forming an insulating film on the surface of the cold-rolled steel sheet on which the fifth step (S5) has been performed.

[0126] A non-oriented electrical steel sheet manufactured by a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may have excellent mechanical properties, and may have a yield strength (YS) of 380 MPa or more and a tensile strength (TS) of 480 MPa or more. Preferably, the yield strength (YS) may be 392 MPa or more.

[0127] In addition, a non-oriented electrical steel sheet including an alloy component according to one embodiment of the present invention can have excellent magnetic properties and has a low iron loss (W 10 / 400 ) may be less than or equal to 13.5 W / kg. More preferably, the iron loss (W 10 / 400 ) may be less than 13 W / kg.

[0128] Accordingly, the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention can improve magnetic properties and mechanical strength by controlling the reheating temperature and cold rolling annealing temperature.

[0129] In addition, the present invention can provide a high-strength and high-efficiency non-oriented electrical steel sheet having high mechanical strength and excellent magnetic properties and a method for manufacturing the non-oriented electrical steel sheet.

[0130]

[0131] Comparative and experimental examples

[0132] Below, preferred comparative examples and experimental examples are presented to aid understanding of the present invention. However, the following comparative examples and experimental examples are provided solely to aid understanding of the present invention, and the present invention is not limited to the following experimental examples.

[0133] Table 1 shows the alloy element composition of comparative examples and experimental examples, and Table 2 shows the results of measuring the mechanical properties and magnetic properties according to the volume fraction of secondary phases having a size of 1.1㎛ or more in comparative examples and experimental examples, whether [Formula 1] is satisfied, reheating temperature, cold rolling annealing conditions, whether [Formula 2] is satisfied, and whether [Formula 3] is satisfied.

[0134] These comparative examples and experimental examples were manufactured using steel having the alloy compositions described in Table 1 below. In addition, the manufacturing processes of the comparative examples and experimental examples of the present invention, other than the process conditions described in Table 2 below, were controlled under the same conditions within the range described in the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention described above, as a control variable.

[0135] The mechanical properties of these comparative and experimental examples were measured in accordance with the ISO 6892-1 international standard. In addition, the magnetic properties of these comparative and experimental examples were measured using an Epstein steel strip measuring 300 mm in length and 30 mm in width, based on the Epstein frame test in accordance with the IEC 60404-2 international standard.

[0136] In the table below, the volume fraction of secondary phases having a size of 1.1 μm or more means the volume fraction of secondary phases having a size of 1.1 μm or more among the secondary phases generated in the non-oriented electrical steel sheet according to one embodiment of the present invention. In addition, in the table below, the iron loss is W 10 / 400 , and means iron loss at 400Hz, 1.0T, and the unit is W / kg. In addition, in Table 2 below, O in the satisfaction indicates that the formula is satisfied, and X indicates that the formula is not satisfied.

[0137]

[0138]

[0139]

[0140]

[0141] Referring to Tables 1 and 2 above, Comparative Examples 1 and 4 were manufactured with alloy compositions of A0 and A5, respectively, and satisfy the alloy composition according to one embodiment of the present invention. On the other hand, it can be confirmed that Comparative Examples 1 and 4 do not satisfy the volume fraction of secondary phases having a size of 1.1 μm or more of 50% or more, and are comparative examples that do not satisfy the above [Formula 1].

[0142] At this time, the above comparative examples 1 and 4 have iron loss (W) which is the magnetic characteristic value targeted in the present invention. 10 / 400 ) It can be confirmed that it does not satisfy 13.5 W / kg or less. In addition, it can be confirmed that in the case of the above comparative example 1, it does not satisfy the mechanical property value targeted in the present invention, which is a yield strength (YS) of 380 MPa or more.

[0143] Continuing with reference to Tables 1 and 2, Comparative Example 2 is a comparative example that is manufactured with an A2 alloy composition and satisfies the alloy composition according to an embodiment of the present invention and satisfies the above [Formula 1], but does not satisfy the volume fraction of a secondary phase having a size of 1.1 μm or more of 50% or more. In addition, Comparative Examples 3, 5, and 6 are comparative examples that satisfy the above [Formula 1], but do not satisfy the volume fraction of a secondary phase having a size of 1.1 μm or more of 50% or more. In addition, Comparative Examples 3, 5, and 6 are manufactured with an A4, A6, and A8 alloy composition, respectively, and do not satisfy the alloy composition according to an embodiment of the present invention.

[0144] At this time, Comparative Examples 2, 3, 5 and 6 have iron loss (W), which is the magnetic characteristic value targeted in the present invention. 10 / 400 ) It can be confirmed that it does not satisfy 13.5 W / kg or less.

[0145] Referring to Tables 1 and 2, Comparative Example 3 is a comparative example manufactured with an A4 alloy composition and does not satisfy the copper (Cu) content and reheating temperature range of the present invention. In addition, Comparative Example 4 is a comparative example manufactured with an A5 composition and satisfies the alloy composition range of the present invention, but does not satisfy the reheating temperature range.

[0146] As a result, the iron loss (W) of Comparative Example 3 10 / 400 ) is 14.8 W / kg, and the iron loss (W) of comparative example 4 10 / 400 ) is 13.9 W / kg, which is the iron loss (W) which is the magnetic characteristic value targeted in the present invention.10 / 400 ) It can be confirmed that it does not satisfy 13.5 W / kg or less.

[0147] Referring to Tables 1 and 2 above, Comparative Example 4 is a comparative example manufactured with an A5 alloy composition, which satisfies the alloy composition range of the present invention, but does not satisfy the cold rolling annealing temperature range of the present invention. In addition, Comparative Example 5 is a comparative example manufactured with an A6 alloy composition, which deviates from the copper (Cu) content of the present invention and deviates from the cold rolling annealing temperature range.

[0148] At this time, in the case of Comparative Examples 4 and 5, the iron loss (W) which is the magnetic characteristic value targeted in the present invention 10 / 400 ) It can be confirmed that it does not satisfy 13.5 W / kg or less.

[0149] Referring to Tables 1 and 2 above, Comparative Example 2 is a comparative example manufactured with an A2 alloy composition, which satisfies the alloy composition according to an embodiment of the present invention, but does not satisfy [Formula 2], which is a relationship according to the content of added elements. In addition, Comparative Examples 3 and 5 are comparative examples manufactured with an A4 and A6 alloy composition, respectively, which deviate from the copper (Cu) content according to an embodiment of the present invention and do not satisfy [Formula 2]. Comparative Example 6 is a comparative example manufactured with an A8 alloy composition, which deviates from the nickel (Ni) content of the present invention and does not satisfy [Formula 2].

[0150] As a result, Comparative Examples 2, 3, 5 and 6 have the iron loss (W) which is the magnetic characteristic value targeted in the present invention. 10 / 400 ) It can be confirmed that it does not satisfy 13.5 W / kg or less.

[0151] Continuing with reference to Tables 1 and 2 above, Comparative Examples 1 and 2 are comparative examples manufactured with A0 and A2 alloy compositions, respectively, which satisfy the alloy composition range according to one embodiment of the present invention, but do not satisfy [Formula 3], which is a relationship according to the content of added elements. In addition, Comparative Example 5 is a comparative example manufactured with A6 alloy composition, which deviates from the copper (Cu) content of the present invention, and does not satisfy [Formula 3]. Comparative Example 6 is a comparative example having an A8 alloy composition, and does not satisfy the nickel (Ni) content range and [Formula 3] above.

[0152] At this time, Comparative Examples 1, 2, 5 and 6 have iron loss (W), which is the magnetic characteristic value targeted in the present invention. 10 / 400 ) It can be confirmed that it does not satisfy 13.5 W / kg or less.

[0153] On the other hand, it can be confirmed that Experimental Examples 1 to 5 according to one embodiment of the present invention satisfy the target volume fraction of the secondary phase having a size of 1.1 ㎛ or more by 50% or more, and satisfy [Formula 1] above. In addition, it can be confirmed through Tables 1 and 2 above that both the reheating temperature range and the cold rolling annealing temperature range are satisfied.

[0154] As a result, Experimental Examples 1 to 5 can satisfy the mechanical properties targeted in the present invention, such as the yield strength (YS) of 380 MPa or more, and the magnetic properties targeted in the present invention, such as the iron loss (W 10 / 400 ) can satisfy all of 13.5 W / kg or less.

[0155] Through this, it can be confirmed that the non-oriented electrical steel sheet according to one embodiment of the present invention has high strength and excellent magnetic properties.

[0156] As described above, preferred embodiments of the present invention have been described. It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms, in addition to the embodiments described above, without departing from the spirit or scope thereof. Therefore, the above-described embodiments should be considered illustrative rather than restrictive, and accordingly, the present invention is not limited to the above description, but may be modified within the scope of the appended claims and their equivalents.

Claims

1. Contains 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the remainder of iron (Fe) and other unavoidable impurities. Electrical steel sheet having a volume fraction of secondary phases having a particle size of 1.1㎛ or larger of 50% or larger.

2. In paragraph 1, The above secondary award is, Including nitrides and oxides, An electrical steel sheet in which the ratio of the number of oxides excluding nitride and CaO per unit area satisfies the following equation 1. [Formula 1] 0.5≤(Number of nitrides) / (Number of oxides excluding CaO)≤4.5 3. In paragraph 1, Electrical steel sheet with a yield strength (YS) of 380 MPa or more.

4. In paragraph 1, Iron Loss (W 10 / 400 ) Electrical steel sheet having a strength of 13.5 W / kg or less.

5. The first step is to prepare semi-finished steel; A second step of hot rolling the above steel to form a hot-rolled steel plate; The third step of hot-rolling and annealing the above hot-rolled steel sheet; A fourth step of forming a cold rolled steel sheet by cold rolling the hot rolled steel sheet that has undergone the third step above, and Including a fifth step of cold rolling annealing the above cold rolled steel sheet, The second step above is, A method for manufacturing an electrical steel sheet, comprising a step of reheating the above steel to 1100 to 1180°C.

6. In paragraph 5, The fifth step above is, A method for manufacturing electrical steel sheets by performing heat treatment at 925 to 1100°C.

7. In paragraph 5, The above steel is, Contains 2.8 to 3.8 wt% of silicon (Si), 0.2 to 0.5 wt% of manganese (Mn), 0.5 to 1.5 wt% of aluminum (Al), 0.005 wt% or less of carbon (C), 0.005 wt% or less of sulfur (S), 0.015 wt% or less of phosphorus (P), 0.005 wt% or less of nitrogen (N), 0.005 wt% or less of titanium (Ti), 0.08 wt% or less of tin (Sn), 0.07 wt% or less of nickel (Ni), 0.07 wt% or less of copper (Cu), and the remainder of iron (Fe) and other unavoidable impurities. A method for manufacturing an electrical steel sheet having a volume fraction of a secondary phase having a particle size of 1.1㎛ or more of 50% or more.

8. In paragraph 7, The above secondary award is, Including nitrides and oxides, A method for manufacturing an electrical steel sheet in which the number ratio of oxides excluding nitride and CaO per unit area satisfies the following equation 1. [Formula 1] 0.5≤(Number of nitrides) / (Number of oxides excluding CaO)≤4.5

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