Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises 1.8-2.8 wt% of silicon (Si), 0.1-0.8 wt% of manganese (Mn), 0.4-1.5 wt% of aluminum (Al), 0.005 wt% or less of sulfur (S), 0.005 wt% or less of titanium (Ti), 0.07 wt% or less of tin (Sn), 0.065 wt% or less of niobium (Nb), 0.076 wt% or less of molybdenum (Mo), and the balance of iron (Fe) and other inevitable elements, and thus iron loss can be reduced.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

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

[0002] Interest in industrial electric motors is growing, driven by recent trends in electrification and automation within the manufacturing industry. Electric motors are devices that use electricity to generate the driving force required for machinery. Energy efficiency, which allows longer operation times using the same amount of energy, is a crucial technological element. This energy efficiency of electric motors is influenced by the magnetic and mechanical properties of the non-oriented electrical steel used as the core material.

[0003] Specifically, non-oriented electrical steel is a material that has uniform magnetic properties in all directions regardless of the rolling direction, and it is necessary to reduce iron loss and increase magnetic flux density to improve energy efficiency.

[0004] Magnetic flux density refers to the number of magnetic force lines induced in a material under a specific magnetic field. It is generally evaluated as the value (B50) induced under a magnetic field of 5000 A / m, and its unit is Tesla (T). Iron loss refers to the loss that occurs during the magnetization process of the electrical steel material, and is the sum of hysteresis loss, eddy current loss, and anomalous loss.

[0005] To improve the core loss of electrical steel sheets, methods include adding alloying elements that increase resistivity, such as silicon (Si), manganese (Mn), and aluminum (Al), or thinning the material to reduce eddy current loss. However, adding large amounts of elements that increase resistivity can cause problems such as reduced magnetic flux density and rollability due to the increased amount of alloying elements. Furthermore, the main alloying elements and the additive elements combine to form precipitates. Fine precipitates can impede the movement of magnetic domains, thereby degrading magnetic properties.

[0006] Therefore, there is a need for a technology that can reduce iron loss in non-oriented electrical steel sheets.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] Prior Document 1: Korean Patent Publication No. 10-2022-0054871

[0010] 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 having excellent magnetic properties and a method for manufacturing a non-oriented electrical steel sheet by reducing iron loss by controlling alloy components, manufacturing process, and CSL grain boundary formation ratio.

[0011] 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.

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 1.8 to 2.8 wt% of silicon (Si), 0.1 to 0.8 wt% of manganese (Mn), 0.4 to 1.5 wt% of aluminum (AL), 0.005 wt% or less of sulfur (S), 0.005 wt% or less of titanium (Ti), 0.07 wt% or less of tin (Sn), 0.065 wt% or less of niobium (Nb), 0.076 wt% or less of molybdenum (Mo), and the remainder being iron (Fe) and other unavoidable elements.

[0013] In addition, the following equation 1 can be satisfied.

[0014] [Formula 1]

[0015] 2.75 < logT < 4.40

[0016] (However, in Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], and [S], [Ti], [Sn], [Nb], and [Mo] represent the contents of S, Ti, Sn, Nb, and Mo in ppm, respectively.)

[0017] Additionally, the volume fraction of the secondary phase having a diameter of 1.0㎛ or more may be 45% or more.

[0018] In addition, it includes a CSL grain boundary (Coincidence Site Lattice Boundary), and the CSL grain boundary may include a ∑3 type grain boundary, a ∑5 type grain boundary, a ∑7 type grain boundary, and a ∑9 type grain boundary.

[0019] In addition, the CSL grain boundary formation ratio of crystal grains existing within a unit area can satisfy the following equation 2.

[0020] [Formula 2]

[0021]

[0022] Also, iron loss (W 15 / 50 ) may be less than 3.4 W / kg.

[0023] Additionally, it may further include 0.005 wt% or less of carbon (C), 0.02 wt% or less of phosphorus (P), and 0.005 wt% or less of nitrogen (N).

[0024] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a first step of preparing a steel material containing 1.8 to 2.8 wt% of silicon (Si), 0.1 to 0.8 wt% of manganese (Mn), 0.4 to 1.5 wt% of aluminum (AL), 0.005 wt% or less of sulfur (S), 0.005 wt% or less of titanium (Ti), 0.07 wt% or less of tin (Sn), 0.065 wt% or less of niobium (Nb), 0.076 wt% or less of molybdenum (Mo), and the remainder iron (Fe) and other unavoidable elements, a second step of hot-rolling the steel material 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 on which the third step has been performed to form a cold-rolled steel sheet, and a fifth step of cold-rolling and annealing the cold-rolled steel sheet.

[0025] Additionally, the second step may include a step of reheating the steel to 1100 to 1200°C.

[0026] In addition, the above steel material can satisfy the following equation 1.

[0027] [Formula 1]

[0028] 2.75 < logT < 4.40

[0029] (However, in Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], and [S], [Ti], [Sn], [Nb], and [Mo] represent the contents of S, Ti, Sn, Nb, and Mo in ppm%, respectively.)

[0030] Additionally, the steel may further include carbon (C) 0.005 wt% or less, phosphorus (P) 0.02 wt% or less, and nitrogen (N) 0.005 wt% or less.

[0031] According to one embodiment of the present invention, a non-oriented electrical steel sheet having excellent magnetic properties with reduced iron loss and a method for manufacturing a non-oriented electrical steel sheet can be implemented.

[0032] 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.

[0033] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 be applied to numerical value A as well.

[0040] Also, unless otherwise stated, 1 ppm is 0.0001 wt%.

[0041]

[0042] Non-oriented electrical steel sheet

[0043] A non-oriented electrical steel sheet according to one embodiment of the present invention contains 1.8 to 2.8 wt% of silicon (Si), 0.1 to 0.8 wt% of manganese (Mn), 0.4 to 1.5 wt% of aluminum (AL), 0.005 wt% or less of sulfur (S), 0.005 wt% or less of titanium (Ti), 0.07 wt% or less of tin (Sn), 0.065 wt% or less of niobium (Nb), 0.076 wt% or less of molybdenum (Mo), and the remainder being iron (Fe) and other unavoidable elements.

[0044] Hereinafter, the role and content of alloy elements included in a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0045]

[0046] Silicon (Si)

[0047] Silicon (Si) is a key additive in electrical steel, increasing the steel's resistivity and reducing core loss. If silicon is added insufficiently, the core loss improvement effect may be insufficient. However, excessive silicon addition can reduce magnetic flux density and, due to increased brittleness, deteriorate cold-rollability. Therefore, appropriate silicon content control is essential.

[0048] If the silicon content is less than 1.8 wt%, the above-described effect cannot be expected, and if the silicon content exceeds 2.8 wt%, problems such as a decrease in magnetic flux density and an increase in brittleness may occur. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 1.8 to 2.8 wt% of silicon.

[0049]

[0050] manganese (Mn)

[0051] Manganese (Mn), like silicon (Si), is an element that improves magnetic properties by increasing resistivity and reducing iron loss. It is also added to enhance the fraction of textures with favorable magnetic properties. Furthermore, manganese can combine with sulfur (S) present in steel to form sulfides such as MnS.

[0052] When the manganese content is less than 0.1 wt%, fine MnS precipitates are formed to inhibit grain growth, and when the manganese content exceeds 0.8 wt%, coarse MnS precipitates are formed to reduce the magnetic flux density. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain manganese in an amount of 0.1 to 0.8 wt%.

[0053]

[0054] Aluminum (Al)

[0055] Aluminum (Al), along with silicon (Si) and manganese (Mn), increases resistivity and reduces iron loss, making it a key additive in electrical steel. Aluminum can also play a role in reducing magnetic anisotropy, thereby reducing magnetic deviation.

[0056] When the aluminum content is less than 0.4 wt%, the increase in resistivity is not sufficient, which may increase high-frequency iron loss, and may increase the deviation of magnetic properties by forming fine nitrides. On the other hand, when the aluminum content exceeds 1.5 wt%, the formation of excessive nitrides may reduce the magnetic flux density, and may cause a decrease in cold rolling properties. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain 0.4 to 1.5 wt% of aluminum.

[0057]

[0058] Yellow (S)

[0059] Sulfur (S) is an impurity element that is inevitably contained during the manufacturing process, and adding large amounts can cause brittleness. Furthermore, it can increase iron loss by combining with manganese (Mn) to form MnS precipitates. Therefore, it is desirable to add as little S as possible. A non-oriented electrical steel sheet according to one embodiment of the present invention may contain sulfur in an amount of 0.005 wt% or less.

[0060]

[0061] Titanium (Ti)

[0062] Titanium (Ti) is an element with a strong tendency to form precipitates in steel, and combines with carbon (C) or nitrogen (N) to form precipitates such as TiC and TiN. These precipitates can inhibit grain growth. As the amount of titanium added increases, the fraction of precipitates increases, and this can form a texture that is unfavorable to magnetization, thereby deteriorating magnetic properties. Therefore, it is preferable to add as little as possible, and 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.

[0063]

[0064] Sn

[0065] Tin (Sn) can prevent oxygen and nitrogen from penetrating the surface of the steel and lowering the iron loss. Tin is a grain boundary segregation element, and if the content of tin is excessively added exceeding 0.07 wt%, it can inhibit grain growth and lower the magnetism. Therefore, there is a need to control the content, and the non-oriented electrical steel sheet according to one embodiment of the present invention can contain tin in an amount of 0.07 wt% or less. Preferably, it can contain tin in an amount exceeding 0 wt% and 0.07 wt% or less.

[0066]

[0067] niobium (Nb)

[0068] Niobium (Nb) can combine with carbon (C) or nitrogen (N) to form precipitates such as NbC within the grains. At this time, the precipitates may inhibit grain growth and domain wall movement, resulting in poor iron loss. Therefore, a non-oriented electrical steel sheet according to an embodiment of the present invention may contain niobium in an amount of 0.065 wt% or less.

[0069]

[0070] molybdenum (Mo)

[0071] Molybdenum (Mo) is a strong carbonitride-forming element. Excessive content can lead to the formation of fine carbides, increasing iron loss and detrimental to magnetic properties, so it is preferable to avoid adding it if possible. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention may contain molybdenum in an amount of 0.076 wt% or less.

[0072]

[0073] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 wt% or less of carbon (C), 0.02 wt% or less of phosphorus (P), and 0.005 wt% or less of nitrogen (N).

[0074]

[0075] carbon (C)

[0076] Carbon can increase iron loss by combining with titanium (Ti), niobium (Nb), etc., to form carbides such as TiC and NbC. If the carbon content exceeds 0.005 wt%, it can cause self-aging, which can deteriorate magnetic properties. Therefore, the non-oriented electrical steel sheet according to one embodiment of the present invention can contain carbon in an amount of 0.005 wt% or less.

[0077]

[0078] Person (P)

[0079] Phosphorus is a grain boundary segregation element, and if added excessively, problems such as grain growth inhibition, deterioration of magnetic properties, and reduction in cold rolling properties may occur due to the segregation effect. Therefore, it is preferable to add as little as possible, and the non-oriented electrical steel sheet according to one embodiment of the present invention may contain phosphorus at 0.02 wt% or less.

[0080]

[0081] Nitrogen (N)

[0082] Nitrogen (N) can combine with aluminum (Al) or titanium (Ti) to form precipitates such as AlN and TiN, which can increase iron loss and inhibit grain growth. Therefore, it is desirable to add as little as possible. The non-oriented electrical steel sheet according to one embodiment of the present invention may contain nitrogen in an amount of 0.005 wt% or less.

[0083]

[0084] 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.

[0085] 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.

[0086]

[0087] In addition, a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0088] [Formula 1]

[0089] 2.75 < logT < 4.40

[0090] However, in Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], and [S], [Ti], [Sn], [Nb], and [Mo] represent the contents of S, Ti, Sn, Nb, and Mo in ppm, respectively.

[0091] The above logT 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 include grain boundary strengthening elements added to form precipitates and grain boundary embrittlement elements that lower the magnetic properties or mechanical strength of the electrical steel sheet and thus require control of the amount added.

[0092] In the above equation 1, the coefficients in front of the elements are weights assigned to the grain boundary strengthening elements and grain boundary embrittlement elements, respectively. More specifically, the weights are assigned based on the bond energy according to the heat of sublimation of each element with iron (Fe) as the standard.

[0093] Through this, it is possible to design alloy components that improve magnetic properties and mechanical strength by utilizing the logarithmic value obtained by multiplying the contents of sulfur (S), titanium (Ti), phosphorus (P), niobium (Nb), and molybdenum (Mo) and the weights for those elements.

[0094] Preferably, the non-oriented electrical steel sheet according to one embodiment of the present invention may have a logT greater than 2.75 and less than 4.40 according to the above equation 1. When the logT is 2.75 or less, the texture improvement effect by the added elements is reduced, making it difficult to have excellent magnetic properties, and it may be difficult to obtain a high-strength non-oriented electrical steel sheet. On the other hand, when the logT is 4.40 or more, the content of elements unnecessary for improving the magnetic properties is excessive, which may result in inferior magnetic properties.

[0095] A non-oriented electrical steel sheet having the above-described alloy composition and manufactured using the non-oriented electrical steel sheet manufacturing method described below can form a secondary phase. Here, the secondary phase may refer to inclusions or precipitates that are dissolved in the steel and then re-precipitated. In this case, the secondary phase may include oxides, nitrides, etc.

[0096] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention may have a volume fraction of a secondary phase having a diameter of 1.0 ㎛ or more among the secondary phases at 45% or more. When the volume fraction of the secondary phase having a diameter of 1.0 ㎛ or more is less than 45%, the volume fraction of the fine secondary phase having a particle diameter of less than 1.0 ㎛ may relatively increase. When the volume fraction of the fine secondary phases increases, the movement of magnetic domains may be hindered, resulting in poor iron loss.

[0097] A non-oriented electrical steel sheet according to one embodiment of the present invention may include a CSL grain boundary (Coincidence Site Lattice boundary), and the CSL grain boundary may include a ∑3 type grain boundary, a ∑5 type grain boundary, a ∑7 type grain boundary, and a ∑9 type grain boundary.

[0098] According to the coincidence site lattice boundary (CSL) theory proposed by Harase et al. regarding the selective growth of Goss grains, there are relatively many CSL grain boundaries around grains that grow into secondary recrystallized grains in non-oriented electrical steel sheets, and it is known that these special grain boundaries move faster than other grain boundaries. A CSL grain boundary is a special grain boundary in a low-energy state that satisfies the coincidence site condition due to the special orientation relationship between grains among high-angle grain boundaries.

[0099] In a tetragonal crystal system, whether a grain boundary is a special grain boundary is determined by the following equation.

[0100] N = U 2 + V 2 + W 2

[0101]

[0102] In the above equation, x and y are integers greater than or equal to 0, and U, V, and W are Miller indices indicating the crystal orientation of the rotation axis common to both particles.

[0103] For example, a ∑1-type grain boundary refers to a low-angle grain boundary where the angle difference between the atomic arrangements of two grains is less than 15 degrees. A ∑3-type grain boundary is when the atomic arrangements are misaligned by 60 degrees. In this case, the lattice sites overlap one for every three atoms. As the number increases, the number of lattices that overlap in terms of angle decreases, such as one for every five atoms for a ∑5-type grain boundary and one for every seven atoms for a ∑7-type grain boundary.

[0104] CSL grain boundaries can be measured through EBSD (Electron Backscatter Diffraction) analysis, and the detailed measurement method will be described later.

[0105] According to one embodiment of the present invention, a non-oriented electrical steel sheet can have a CSL grain boundary formation ratio of crystal grains existing within a unit area that satisfies the following equation 2.

[0106] [Formula 2]

[0107]

[0108] However, in the above equation 2, ∑3, ∑5, ∑7 and ∑9 represent ∑3-type grain boundaries, ∑5-type grain boundaries, ∑7-type grain boundaries and ∑9-type grain boundaries, respectively.

[0109] When the above equation 2 is satisfied, the magnetic properties can be excellent. This is related to the movement of magnetic domains, and the movement of magnetic domains is affected by the boundary energy between crystal grains.

[0110] In the case of ∑5-type grain boundaries and ∑9-type grain boundaries with high boundary energy, the movement of magnetic domains can be hindered, which can deteriorate the magnetic properties. In the case of ∑3-type grain boundaries and ∑7-type grain boundaries, they have relatively low boundary energy, and the movement of magnetic domains is smoother than that of ∑5-type grain boundaries and ∑9-type grain boundaries, which can have a positive effect on the magnetic properties.

[0111] Therefore, if the CSL grain boundary formation ratio satisfies the above equation 2, the magnetic properties can be improved because the magnetic domains can move freely during magnetization. However, if the above equation 2 is not satisfied, the boundary energy between grains is high, which makes the movement of the magnetic domains unfavorable, and the magnetic properties can be inferior.

[0112]

[0113] A non-oriented electrical steel sheet according to one embodiment of the present invention can have excellent magnetic properties and can have magnetic properties suitable for a motor used in a servo motor or a general electric motor due to reduced iron loss. Preferably, the iron loss (W 15 / 50 ) may be less than or equal to 3.4 W / kg, and more preferably the iron loss (W 15 / 50 ) may be less than 3 W / kg.

[0114] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0115]

[0116] Method for manufacturing non-oriented electrical steel sheet

[0117] 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.

[0118] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0119] 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 steel having the above-described alloy composition, a second step (S2) of hot-rolling the steel 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.

[0120] 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.

[0121] The first step (S1) of preparing steel having the above-described alloy composition is a step for preparing a semi-finished product for manufacturing a non-oriented electrical steel sheet, which is the final product. More specifically, this may be a step for manufacturing a semi-finished product by designing the alloy components within the alloy composition range according to one embodiment of the present invention. The semi-finished product may be a slab, but is not necessarily limited thereto. In addition, 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.

[0122] Furthermore, since the content of the alloy components has been previously explained, a redundant description will be omitted. Since the content of the alloy components does not substantially change during the manufacturing process described below, the alloy composition of the above steel and the alloy composition of the final product, the non-oriented electrical steel sheet, are substantially identical.

[0123] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may, after the first step (S1), perform a second step (S2) of hot-rolling the steel material to form a hot-rolled steel sheet. More specifically, the second step (S2) may include a reheating step, a hot-rolling step, and a coiling step.

[0124] First, the reheating step may be performed prior to the hot rolling step, reheating the steel for subsequent processing. Specifically, this step may involve loading the steel into a heating furnace and uniformly heating the steel to facilitate plastic deformation.

[0125] At this time, if the reheating temperature is below 1100℃, the rolling load may increase, which may reduce the rollability. On the other hand, if the reheating temperature exceeds 1200℃, the precipitates formed by carbon (C), sulfur (S), nitrogen (N), etc. in the steel may be re-dissolved, resulting in the generation of fine precipitates during the subsequent rolling and annealing processes. These fine precipitates may inhibit grain growth and reduce the magnetic properties.

[0126] Therefore, the reheating step according to one embodiment of the present invention can reheat the steel to 1100 to 1200°C.

[0127] Next, a hot rolling step may be performed to form a hot-rolled steel plate. The hot rolling step may include rough rolling and finishing rolling. Here, rough rolling may refer to forming the steel into a rolled material having an appropriate shape, thickness, and width, while finishing rolling may refer to adjusting the steel to a specified thickness and width and rolling it at a finishing temperature appropriate for the intended use to obtain a good surface and shape.

[0128] At this time, the finishing temperature of the hot rolling step may be 800 to 900°C. If the finishing temperature is less than 800°C, rolling may be performed in a two-phase region, resulting in the formation of an uneven texture. If the finishing temperature exceeds 900°C, a problem of rapid deterioration in strength may occur.

[0129] 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 the magnetic properties.

[0130] The thickness of the hot-rolled steel sheet formed through the above 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. On the other hand, if the thickness of the hot-rolled steel sheet exceeds 2.6 mm, the cold rolling reduction ratio increases, and the fraction of aggregate structures unfavorable to magnetic properties increases, which may result in inferior magnetic properties.

[0131] 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 hot-rolling annealing the hot-rolled steel sheet after the second step (S2). The third step (S3) may be a hot-rolling annealing step in which annealing is performed to secure microstructural uniformity and cold-rollability of the hot-rolled steel material.

[0132] The above hot rolling annealing can be performed at a temperature that removes the elongated cast structure and forms a uniform microstructure. Preferably, the heat treatment can be performed at a temperature range of 940 to 1110°C. At this time, the heating rate can be 20°C / s or higher, and the cooling rate can be 20°C / s or higher.

[0133] If the hot-rolling annealing temperature is below 940°C, the elongated cast structure may remain after hot rolling, causing microstructural heterogeneity. Furthermore, the elongated cast structure inhibits grain growth, resulting in the formation of small grains, which can interfere with cold rolling. Conversely, if the hot-rolling annealing temperature exceeds 1110°C, it can cause grain structure imbalance in the final product and reduce magnetic properties.

[0134] The above hot rolling annealing can be performed for 30 to 180 seconds to form an appropriate grain size at each temperature condition.

[0135] An additional pickling process may be performed between the third step (S3) described above and the fourth step (S4) described below. The pickling process may be a process of removing an oxide layer formed on the surface using a pickling solution, and may be performed using a process known in the relevant technical field.

[0136] Thereafter, a non-oriented electrical steel sheet according to an embodiment of the present invention may be subjected to 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 at a temperature below the recrystallization temperature to further thin the steel sheet. More specifically, it may be a process of rolling the hot-rolled steel sheet to a thickness and width that meet the specifications of the final product.

[0137] At this time, the fourth step (S4) may perform final cold rolling so that the hot-rolled steel sheet has a thickness of 0.35 mm or less. At this time, the final reduction ratio may be 50 to 96%. In addition, the fourth step (S4) may be performed as warm rolling in which the temperature of the plate is increased to 100 to 200°C to facilitate rolling.

[0138] According to one embodiment of the present invention, a non-oriented electrical steel sheet may be subjected to a fifth step (S5) of cold rolling annealing the cold rolled steel sheet after the fourth step (S4). The differential cold rolling annealing may be performed at a temperature that produces an optimal grain size for improving magnetic and mechanical properties. Here, the optimal grain size may be 35 to 200 μm.

[0139] At this time, if the cold rolling annealing temperature is below 900℃, the crystal grain size may be formed small, which may result in inferior magnetic flux density and iron loss. On the other hand, if the cold rolling annealing temperature exceeds 1100℃, the precipitates may be re-dissolved, resulting in the generation of fine precipitates, and the crystal grains may grow excessively, which may cause a decrease in strength.

[0140] Accordingly, the cold rolling annealing temperature according to the present invention may be 900 to 1100°C. At this time, the temperature increase rate during cold rolling annealing may be 10°C / s or higher, and the cooling rate may be 20°C / s or higher. In addition, heat treatment may be performed for 30 to 120 seconds to derive the optimal crystal grain size under each temperature condition.

[0141] 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 of the non-oriented electrical steel sheet and improve the punchability, 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. The coating step may be performed using a process known in the art.

[0142] The non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic properties and can have magnetic properties suitable for use in a servo motor or a general electric motor. Preferably, the iron loss (W 15 / 50 ) may be less than or equal to 3.4 W / kg, and more preferably the iron loss (W 15 / 50) may be less than 3 W / kg.

[0143] In addition, it can have excellent magnetic properties and excellent mechanical strength at the same time. Preferably, the yield strength (YS) can be 270 MPa or more, and the tensile strength (TS) can be 380 MPa or more.

[0144] As a result, it is possible to manufacture a non-oriented electrical steel sheet having excellent magnetic properties with reduced iron loss and, at the same time, excellent mechanical strength.

[0145]

[0146] Experimental example

[0147] Below, the composition and operation of the present invention will be explained through experimental examples. However, these examples are provided to aid understanding of the present invention and are not intended to limit the present invention.

[0148] Table 1 below shows the contents of major alloy components of the experimental examples. In addition, Table 2 below shows some process conditions of the experimental examples manufactured with steel having the alloy composition of Table 1 below, satisfaction of Equation 1 above, volume fraction of secondary phases, satisfaction of Equation 2 above, and iron loss values.

[0149] In this experimental example, steel having an alloy composition described in Table 1 below was manufactured according to a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention. Other process conditions not described in Table 2 below were controlled variables and were identically controlled within the range described in the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0150] In this experiment, the magnetic properties of non-oriented electrical steel sheets were measured based on the Epstein frame test according to the international standard IEC 60404-2, and specimens measuring 300 mm in length and 30 mm in width were manufactured and measured.

[0151] In addition, the CSL grain boundary (Coincidence Site Lattice Boundary) of this experimental example was measured through EBSD (Electron Backscatter Diffraction) analysis, and the results of data interpretation using OIM Analysis 8, a measurement result interpretation software, were used.

[0152] W in Table 2 below 15 / 50 is the iron loss (W) at 1.5 T and 50 Hz 15 / 50 ) means.

[0153] Alloy compositionMajor elements (wt%)Added elements (ppm)SiMnAlCNSTiPSnNbMoA11.820.410.9326132323130244532690A21.850.330.931416221243354028A31.860.160.4812112916102366690821A41.870.280.722924181968401444306A51.920.331.3811152124148781723526A61.960.201.181010192447617470572A71.980.730.922 79272898405363813A82.070.190.402523282441335130615A92.100.240 .82281920277186659836A102.150.751.4129172524135710632659A112.1 60.760.50182311284891535511A122.190.301.142413242563341190469A 132.200.241.071520161865192579275A142.240.111.4512212929447116 65302A152.270.511.0118201312105243553654A162.290.491.07292427 2450416682262A172.320.121.202126262458266311258A182.330.231.35 272226185655147718A192.330.190.681191324120681608746A202.340.6 30.51271517144548896523A212.420.241.101126182164429234136A222. 420.390.7027232019100748664597A232.450.150.851417202778537765 537A242.480.691.3829172325122387274564A252.510.541.01242411261 076335095A262.580.411.47131015105836651765A272.610.141.3816121 328135241358425A282.630.221.321026249116786694298A292.640.730.901114232641210103190A302.660.250.471818121598419544261A312.73 0.161.1416282111118706325723A322.740.221.102225131350284460728.

[0154] Experimental alloy composition reheating [Formula 1] Secondary phase [Formula 2] W 15 / 50(W / kg)Temperature (℃)Satisfaction logTSatisfaction Diameter 1.0㎛ or more Volume fraction (%)Satisfied∑3×∑7 / 4×∑5×∑9Satisfied1A11130O4.35O58.6O0.89O2.982A21150 O3.19O62.0O0.72O2.953A31110O4.44X41.6X1.89X4.344A41180O4.1 8O51.7O0.23O2.895A51100O4.41X36.8X2.35X4.596A61155O4.32O58 .2O1.23O2.917A71180O4.35O43.9X1.68X4.218A81190O4.17O57.5O0. 51O2.859A91150O4.42X43.5X2.44X4.4810A101120O4.41X36.8X2.18 X4.3611a1111180O 3.5913A131105O4.20O55.9O0.45O2.7414A141165O4.31O34.9X2.94X 4.1815A151130O4.34O59.0O0.95O2.8916A161100O4.27O44.1X1.52X4 .1117A171110O4.06O52.1O0.40O2.6418A181130O4.21O59.2O0.92O2 .7119A191100O4.43X44.6X1.53X4.0920A201125O4.12O46.3O0.96O2 .5121A211195O3.95O61.7O0.58O2.6222A221180O4.41X33.9X2.12X3 .9423A231155O4.40X44.0X1.98X3.8824A241125O4.22O59.6O0.50O2. 4825A251190O3.78O62.3O0.88O2.3926A261120O4.39O38.8X1.56X3. 7127A271190O4.17O55.3O0.71O2.3528A281170O4.32O41.0X1.63X3.7 629A291150O3.81O51.1O0.88O2.4130A301200O4.21O56.6O0.76O2.3 931A311100O4.33O44.9X1.52X3.4932A321130O4.34O59.7O0.23O2.25

[0155]

[0156] Referring to Tables 1 and 2 above, Experimental Examples 1, 2, 4, 6, 8, 11, 13, 15, 17, 18, 20, 21, 24, 25, 27, 29, 30 and 32 are examples that satisfy the alloy composition range according to one embodiment of the present invention. In addition, it can be confirmed that the above Equation 1 is satisfied, the volume fraction of the secondary phase having a diameter of 1.0 ㎛ or more is 45% or more, and the above Equation 2 is all satisfied. At this time, the iron loss (W 15 / 50 ) It can be confirmed that the value satisfies 3.4 W / kg or less.

[0157] On the other hand, in the case of Experimental Examples 3, 5, 9, 10, 22 and 23, it can be confirmed that the fraction of the secondary phase having a diameter of 1.0 ㎛ or more does not satisfy the alloy composition range according to one embodiment of the present invention, and does not satisfy Equation 2 above, and at this time, the iron loss (W) targeted in the present invention 15 / 50 ) It can be confirmed that the value of 3.4 W / kg or less is not satisfied.

[0158] Experimental examples 7, 14, 16, 26, 28 and 30 are comparative examples that do not satisfy the alloy composition range according to one embodiment of the present invention. In addition, it can be confirmed that the volume fraction of the secondary phase with a diameter of 1.0 ㎛ or more does not satisfy 45% or more and does not satisfy the above equation 2. At this time, the iron loss (W 15 / 50 ) It can be confirmed that the value does not satisfy more than 3.4 W / kg.

[0159] In the case of Experimental Example 19, it is a comparative example that satisfies the alloy composition range according to one embodiment of the present invention, but does not satisfy the above Formula 1. In addition, it can be confirmed that the volume fraction of the secondary phase having a diameter of 1.0 ㎛ or more is less than 45%, and does not satisfy the above Formula 2. At this time, the iron loss (W) targeted in the present invention 15 / 50) It can be confirmed that the value of 3.4 W / kg or less is not satisfied.

[0160] In the case of Experimental Example 12, it is a comparative example that does not satisfy the reheating temperature range according to one embodiment of the present invention. At this time, it can be confirmed that the volume fraction of the secondary phase with a diameter of 1.0 ㎛ or more does not satisfy 45% or more, and the iron loss (W 15 / 50 ) It can be confirmed that the value does not satisfy 3.4 W / kg or less.

[0161] 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. A non-oriented electrical steel sheet containing 1.8 to 2.8 wt% of silicon (Si), 0.1 to 0.8 wt% of manganese (Mn), 0.4 to 1.5 wt% of aluminum (AL), 0.005 wt% or less of sulfur (S), 0.005 wt% or less of titanium (Ti), 0.07 wt% or less of tin (Sn), 0.065 wt% or less of niobium (Nb), 0.076 wt% or less of molybdenum (Mo), and the remainder being iron (Fe) and other unavoidable elements.

2. In paragraph 1, A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] 2.75 < logT < 4.40 (Wherein, in Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], and [S], [Ti], [Sn], [Nb], and [Mo] represent the contents of S, Ti, Sn, Nb, and Mo in ppm, respectively.) 3. In paragraph 1, Non-oriented electrical steel sheet having a volume fraction of secondary phases with a diameter of 1.0 ㎛ or greater of 45% or greater.

4. In paragraph 1, Contains a Coincidence Site Lattice Boundary (CSL), The above CSL boundary is, Non-oriented electrical steel sheet containing ∑3-type grain boundaries, ∑5-type grain boundaries, ∑7-type grain boundaries, and ∑9-type grain boundaries.

5. In paragraph 4, A non-oriented electrical steel sheet in which the CSL grain boundary formation ratio of crystal grains existing within a unit area satisfies the following equation 2. [Formula 2] 6. In paragraph 1, Iron Hand(W 15 / 50 ) Non-oriented electrical steel sheet having a strength of 3.4 W / kg or less.

7. In any one of paragraphs 1 to 6, Non-oriented electrical steel sheet further containing carbon (C) of 0.005 wt% or less, phosphorus (P) of 0.02 wt% or less, and nitrogen (N) of 0.005 wt% or less.

8. A first step of preparing a steel material containing 1.8 to 2.8 wt% of silicon (Si), 0.1 to 0.8 wt% of manganese (Mn), 0.4 to 1.5 wt% of aluminum (AL), 0.005 wt% or less of sulfur (S), 0.005 wt% or less of titanium (Ti), 0.07 wt% or less of tin (Sn), 0.065 wt% or less of niobium (Nb), 0.076 wt% or less of molybdenum (Mo), and the remainder being iron (Fe) and other unavoidable elements; 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 plate; A fourth step of cold rolling the hot rolled steel sheet that has undergone the third step to form a cold rolled steel sheet; and A method for manufacturing a non-oriented electrical steel sheet, comprising a fifth step of cold-rolling and annealing the cold-rolled steel sheet.

9. In paragraph 8, The second step above is, A method for manufacturing a non-oriented electrical steel sheet, comprising the step of reheating the above steel to 1100 to 1200°C.

10. In paragraph 8, The above steel is a method for manufacturing a non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] 2.75 < logT < 4.40 (Wherein, in Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], and [S], [Ti], [Sn], [Nb], and [Mo] represent the contents of S, Ti, Sn, Nb, and Mo in ppm%, respectively.) 11. In any one of paragraphs 8 to 10, A method for manufacturing a non-oriented electrical steel sheet, wherein the steel further contains carbon (C) of 0.005 wt% or less, phosphorus (P) of 0.02 wt% or less, and nitrogen (N) of 0.005 wt% or less.

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