Non-oriented electrical steel sheet and method of manufacturing the same

Abstract

The present application relates to a magnetic core material including 0.1-1.6 wt% of silicon (Si), 0.1-0.6 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), 0.03 wt% or less of tin (Sn), 0.025 wt% or less of niobium (Nb), 0.03 wt% or less of molybdenum (Mo), and the balance of iron (Fe) and other inevitable elements, thereby reducing iron loss without increasing production costs.

Description

Technical Field

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

[0002] An electric motor is a device that uses electrical energy to generate the driving force required for machinery. Its energy efficiency is a very important technical factor, enabling the motor to run for a longer period of time while consuming the same amount of energy. The energy efficiency of an electric motor is affected by the magnetic and mechanical properties of the non-oriented electrical steel sheet used as the core material of the motor.

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

[0004] Magnetic flux density refers to the number of magnetic field lines induced in a material under a specific magnetic field. It is usually assessed by the value induced in a magnetic field of 5000 A / m (B50), and the unit is Tesla (T). Iron loss refers to the loss generated in the material of electrical steel sheet during the magnetization process, which is the sum of hysteresis loss, eddy current loss, and abnormal loss.

[0005] To improve the iron loss of electrical steel sheets, methods include adding alloying elements such as silicon (Si), manganese (Mn), and aluminum (Al) to increase resistivity, or reducing eddy current losses by thinning the material. However, adding large amounts of elements that increase resistivity may lead to problems such as reduced magnetic flux density and rollability due to the increased content of these alloying elements.

[0006] In addition, the main alloying elements and additives combine to form precipitates. These fine precipitates can hinder the movement of magnetic domains, thus leading to a deterioration of magnetic properties.

[0007] Therefore, a technology is needed to reduce iron loss in non-oriented electrical steel sheets.

[0008] Existing technical documents Patent documents Existing document 1: Korean Patent No. 10-1901313. Summary of the Invention

[0009] Technical issues The present invention aims to solve the above problems. The purpose of the present invention is to provide a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet. By controlling the alloy composition, manufacturing process and CSL grain boundary formation ratio, iron loss is reduced without increasing production costs, thereby achieving excellent magnetic properties.

[0010] The technical problems of this invention are not limited to those described above. Other technical problems not mentioned will be clearly understood by those skilled in the art through the following description.

[0011] Technical solution The non-oriented electrical steel sheet of one embodiment of the present invention comprises 0.1 to 1.6 weight percent silicon (Si), 0.1 to 0.6 weight percent manganese (Mn), 0.4 to 1.5 weight percent aluminum (Al), less than 0.005 weight percent sulfur (S), less than 0.005 weight percent titanium (Ti), less than 0.03 weight percent tin (Sn), less than 0.025 weight percent niobium (Nb), less than 0.03 weight percent molybdenum (Mo), and the balance iron (Fe) and other unavoidable elements.

[0012] Furthermore, the following equation 1 can be satisfied.

[0013] [Formula 1] 2.75 <logT<4.0 (In Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], where [S], [Ti], [Sn], [Nb] and [Mo] represent the contents of S, Ti, Sn, Nb and Mo in ppm, respectively.) Furthermore, the volume fraction of the second phase with a diameter of 1.0 µm or more can be 45% or more.

[0014] Furthermore, it may include CSL (Coincidence Site Lattice Boundary), which may include ∑3 type grain boundaries, ∑5 type grain boundaries, ∑7 type grain boundaries and ∑9 type grain boundaries.

[0015] Furthermore, the CSL grain boundary formation ratio of grains present per unit area can satisfy the following equation 2.

[0016] [Equation 2]

[0017] Furthermore, iron loss (W 15 / 50 It can be below 6W / kg.

[0018] Furthermore, it may also contain less than 0.005% by weight of carbon (C), less than 0.02% by weight of phosphorus (P), and less than 0.005% by weight of nitrogen (N).

[0019] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: a first step of preparing steel, wherein the steel comprises 0.1 to 1.6 weight percent silicon (Si), 0.1 to 0.6 weight percent manganese (Mn), 0.4 to 1.5 weight percent aluminum (Al), less than 0.005 weight percent sulfur (S), less than 0.005 weight percent titanium (Ti), less than 0.03 weight percent tin (Sn), less than 0.025 weight percent niobium (Nb), less than 0.03 weight percent molybdenum (Mo), and the balance iron (Fe) and other unavoidable elements; a second step of hot rolling the steel to form a hot-rolled steel sheet; a third step of hot rolling annealing the hot-rolled steel sheet; a fourth step of cold rolling the hot-rolled steel sheet after the third step to form a cold-rolled steel sheet; and a fifth step of cold rolling annealing the cold-rolled steel sheet.

[0020] Furthermore, the second step may include reheating the steel to 1100–1250°C.

[0021] Furthermore, the steel can satisfy the following formula 1.

[0022] [Formula 1] 2.75 <logT<4.0 (In Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], where [S], [Ti], [Sn], [Nb] and [Mo] represent the contents of S, Ti, Sn, Nb and Mo in ppm, respectively.) Furthermore, the steel may also contain less than 0.005% by weight of carbon (C), less than 0.02% by weight of phosphorus (P), and less than 0.005% by weight of nitrogen (N).

[0023] The effects of the invention According to one embodiment of the present invention, a non-oriented electrical steel sheet with reduced iron loss and excellent magnetic properties can be produced without increasing production costs, as well as a method for manufacturing the non-oriented electrical steel sheet.

[0024] The effects of this invention are not limited to those described above, and those skilled in the art will clearly understand other effects not mentioned from the description of the scope of the invention. Attached Figure Description

[0025] Figure 1 A flowchart illustrating the general sequence of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention. Detailed Implementation

[0026] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily implement the present invention. However, the present invention is not limited to or restricted to the following embodiments.

[0027] Furthermore, when the relationship between a structural element (or region, layer, part, etc.) and another structural element is mentioned as "above", "connected", or "combined", it means that it can be directly set / connected / combined to another structural element or a third structural element can be set between them.

[0028] Terms such as “including” or “having” should be understood as indicating the presence of features, figures, steps, actions, structural elements, components or combinations thereof described in the specification, without precluding the presence or additional possibility of more than one other feature or figure, step, action, structural element, component or combination thereof.

[0029] To clearly illustrate the present invention, detailed descriptions of relevant well-known technologies that are not related to the description or may unnecessarily obscure the spirit of the present invention have been omitted. In this specification, when structural elements of the various figures are assigned reference numerals, the same or similar structural elements throughout the specification are assigned the same or similar reference numerals.

[0030] Furthermore, the terms or words used in this specification and the scope of the invention claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that inventors may appropriately define the concepts of terms in order to best illustrate their invention, they should be interpreted as meanings and concepts consistent with the technical ideas of this invention.

[0031] Unless otherwise specified, for the numerical values ​​A and B, the expression "A~B" means "above A and below B". In this expression, if the unit is only marked for the numerical value B, then that unit also applies to the numerical value A.

[0032] Furthermore, unless otherwise specified, 1 ppm is 0.0001 weight percentage.

[0033] Non-oriented electrical steel sheet The non-oriented electrical steel sheet of one embodiment of the present invention comprises 0.1 to 1.6 weight percent silicon (Si), 0.1 to 0.6 weight percent manganese (Mn), 0.4 to 1.5 weight percent aluminum (Al), less than 0.005 weight percent sulfur (S), less than 0.005 weight percent titanium (Ti), less than 0.03 weight percent tin (Sn), less than 0.025 weight percent niobium (Nb), less than 0.03 weight percent molybdenum (Mo), and the balance iron (Fe) and other unavoidable elements.

[0034] The following will provide a detailed description of the role and content of each alloying element contained in a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0035] Silicon (Si) Silicon (Si) is a major additive element in electrical steel sheets, which reduces iron loss by increasing the steel's resistivity. If too little silicon is added, the improvement in iron loss may be insufficient. On the other hand, if too much silicon is added, the magnetic flux density may decrease, and cold rollability may be reduced due to increased brittleness. Therefore, the silicon content needs to be adjusted appropriately.

[0036] If the silicon content is less than 0.1% by weight, the above-mentioned effect cannot be expected; if the silicon content is greater than 1.6% by weight, problems such as decreased magnetic flux density and increased brittleness may occur. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain 0.1 to 1.6% by weight of silicon.

[0037] Manganese (Mn) Like silicon (Si), manganese (Mn) is an element that improves magnetic properties by increasing resistivity and reducing iron loss. Furthermore, manganese is added to increase the fraction of elements that contribute to the magnetic texture. In addition, manganese can combine with sulfur (S) present in steel to form sulfides such as MnS.

[0038] If the manganese content is less than 0.1% by weight, fine MnS precipitates are formed, thereby inhibiting grain growth. If the manganese content is greater than 0.6% by weight, coarse MnS precipitates are formed, thereby reducing magnetic flux density. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain 0.1 to 0.6% by weight of manganese.

[0039] Aluminum (Al) Like silicon (Si) and manganese (Mn), aluminum (Al) is an element that reduces iron loss by increasing electrical resistance and is a major additive element in electrical steel sheets. Aluminum can reduce magnetic deviation by reducing magnetic anisotropy.

[0040] If the aluminum content is less than 0.4% by weight, the increase in resistivity is insufficient, which may lead to increased high-frequency iron losses and the formation of fine nitrides, thereby increasing the deviation in magnetic properties. Conversely, if the aluminum content is greater than 1.5% by weight, excessive nitride formation will occur, thereby reducing magnetic flux density and potentially reducing cold rollability. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain 0.4 to 1.5% by weight of aluminum.

[0041] Sulfur (S) Sulfur (S) is an unavoidable impurity element in the manufacturing process, and excessive addition may lead to increased brittleness. Furthermore, it can combine with manganese (Mn) to form MnS precipitates, thereby increasing iron loss. Therefore, it is preferable to add it in the lowest possible amount. An embodiment of the non-oriented electrical steel sheet of the present invention may contain less than 0.005% by weight of sulfur.

[0042] Titanium (Ti) Titanium (Ti) is an element with a strong tendency to form precipitates in steel, combining with carbon (C) or nitrogen (N) to form precipitates such as TiC and TiN. These precipitates inhibit grain growth. As the amount of titanium added increases, the proportion of precipitates also increases, forming a texture that is unfavorable to magnetization, thereby leading to a deterioration of magnetic properties. Therefore, it is preferable to add it in the lowest possible amount. In one embodiment of the present invention, the non-oriented electrical steel sheet may contain less than 0.005% by weight of titanium.

[0043] Tin (Sn) Tin (Sn) can prevent surface oxygen and nitrogen from penetrating into the steel and causing iron loss degradation. Tin is a grain boundary segregation element; if the tin content is too high, exceeding 0.07% by weight, it will inhibit grain growth, thereby degrading the magnetic properties. Therefore, its content needs to be controlled. In one embodiment of the present invention, the non-oriented electrical steel sheet may contain less than 0.03% by weight of tin. Preferably, it may contain more than 0% by weight and less than or equal to 0.03% by weight of tin.

[0044] Niobium (Nb) Niobium (Nb) can combine with carbon (C) or nitrogen (N) to form precipitates such as NbC within the crystal. These precipitates inhibit grain growth and domain wall movement, leading to deterioration of iron losses. Furthermore, excessive addition may increase production costs; therefore, from an economic perspective, its content needs to be controlled. Thus, in one embodiment of the present invention, the non-oriented electrical steel sheet may contain less than 0.025% by weight of niobium.

[0045] Molybdenum (Mo) Molybdenum (Mo) is a strong carbonitride-forming element. If its content is too high, it will form fine carbides, leading to increased iron loss and potentially impairing magnetic properties; therefore, its addition is preferred to be avoided as much as possible. Furthermore, excessive addition can lead to problems such as increased production costs, so its content needs to be appropriately controlled. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain less than 0.03% by weight of molybdenum.

[0046] The non-oriented electrical steel sheet of one embodiment of the present invention may further contain less than 0.005% by weight of carbon (C), less than 0.02% by weight of phosphorus (P), and less than 0.005% by weight of nitrogen (N).

[0047] Carbon (C) Carbon can combine with titanium (Ti), niobium (Nb), etc., to form carbides such as TiC and NbC, thereby increasing iron loss. If the carbon content is higher than 0.005% by weight, it may cause magnetic aging, leading to deterioration of magnetic properties. Therefore, the non-oriented electrical steel sheet of one embodiment of the present invention may contain less than 0.005% by weight of carbon.

[0048] Phosphorus (P) Phosphorus is a grain boundary segregation element. If added in excess, it can lead to problems such as inhibited grain growth, deterioration of magnetic properties, and reduced cold rollability due to the segregation effect. Therefore, it is preferable to add it in the lowest possible amount. In one embodiment of the present invention, the non-oriented electrical steel sheet may contain less than 0.02% by weight of phosphorus.

[0049] Nitrogen (N) Nitrogen (N) can combine with aluminum (Al) or titanium (Ti) to form precipitates such as AlN and TiN, thereby increasing iron loss and inhibiting grain growth. Therefore, it is preferable to add it in the lowest possible amount. An embodiment of the non-oriented electrical steel sheet of the present invention may contain less than 0.005% by weight of nitrogen.

[0050] In addition to the steel composition described above, the remaining components may contain Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets; since this is well known in the art, a detailed description of it is omitted.

[0051] In one embodiment of the present invention, the addition of elements other than the alloy composition described above is not excluded, and these elements can be included in various ways without hindering the technical concept of the present invention. If additional elements are included, they can be used in place of the remaining iron.

[0052] Furthermore, the non-oriented electrical steel sheet of one embodiment of the present invention can satisfy the following formula 1.

[0053] [Formula 1] 2.75 <logT<4.0 In Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], where [S], [Ti], [Sn], [Nb] and [Mo] represent the contents of S, Ti, Sn, Nb and Mo in ppm, respectively.

[0054] The above-mentioned logT is a formula relating the alloy composition of a non-oriented electrical steel sheet according to an embodiment of the present invention to additive elements other than silicon (Si), manganese (Mn), and aluminum (Al). The additive elements may include grain boundary strengthening elements added to form precipitates, and grain boundary embrittlement elements whose addition amounts need to be controlled because they would reduce the magnetic properties or mechanical strength of the electrical steel sheet.

[0055] In Equation 1 above, the coefficients before the elements are weights assigned to grain boundary strengthening elements and grain boundary embrittlement elements, respectively. More specifically, the weights are assigned based on the bond energy corresponding to the sublimation heat of each element, with iron (Fe) as the reference.

[0056] Therefore, by using the logarithm of the product obtained by multiplying the contents of sulfur (S), titanium (Ti), phosphorus (P), niobium (Nb) and molybdenum (Mo) by the weights of their respective elements, alloy composition design that improves magnetic properties and mechanical strength can be achieved.

[0057] Preferably, according to Formula 1 above, the logT of the non-oriented electrical steel sheet in an embodiment of the present invention can be greater than 2.75 and less than 4.0. If the above logT is less than 2.75, the texture improvement effect brought about by the added elements is reduced, making it difficult to obtain excellent magnetic properties and high-strength non-oriented electrical steel sheets. Conversely, if the above logT is greater than 4.0, the element content is unnecessarily high for improving magnetic properties, which may lead to deterioration of magnetic properties.

[0058] A non-oriented electrical steel sheet having the above alloy composition and manufactured by the method for manufacturing non-oriented electrical steel sheets described later can form a second phase. The second phase can refer to inclusions or precipitates that re-precipitate after solid solution in the steel. In this case, the second phase may include oxides, nitrides, etc.

[0059] Furthermore, in the second phase of the non-oriented electrical steel sheet according to one embodiment of the present invention, the volume fraction of the second phase with a diameter of 1.0 µm or more can be 45% or more. If the volume fraction of the second phase with a diameter of 1.0 µm or more is less than 45%, the volume fraction of the fine second phase with a particle size of less than 1.0 µm may increase relatively. When the volume fraction of the fine second phase increases, it hinders the movement of magnetic domains, leading to deterioration of iron losses.

[0060] An embodiment of the non-oriented electrical steel sheet of the present invention may include CSL grain boundaries (Coincidence Site Lattice boundary), which may include ∑3 type grain boundaries, ∑5 type grain boundaries, ∑7 type grain boundaries and ∑9 type grain boundaries.

[0061] Regarding the selective growth of Goss grains, according to the CSL (coincidence site lattice boundary) theory proposed by Harase et al., it is known that in non-oriented electrical steel sheets, there are relatively more CSL grain boundaries around grains that grow into secondary recrystallized grains. These special grain boundaries are believed to move faster than other grain boundaries. CSL grain boundaries refer to special grain boundaries in high-angle grain boundaries that satisfy the coincidence site condition due to the special orientation relationship between grains.

[0062] In a tetragonal crystal system, whether a grain boundary is a special grain boundary is determined by the following formula.

[0063] N=U 2 +V 2 +W 2

[0064] In the above formula, x and y are integers greater than or equal to 0, and U, V and W are Miller indices, representing the crystal orientation of the rotation axis shared by the two particles.

[0065] For example, a ∑1 type grain boundary refers to a low-angle grain boundary where the atomic arrangement of two grains differs by less than 15 degrees. A ∑3 type grain boundary refers to a case where the atomic arrangement is offset by 60°. In this case, one lattice site coincides for every three atoms. A ∑5 type grain boundary has one lattice site coincident for every five atoms, and a ∑7 type grain boundary has one lattice site coincident for every seven atoms. The larger the value, the fewer lattices coincide in terms of angle.

[0066] CSL grain boundaries can be measured using electron backscatter diffraction (EBSD) analysis, and the detailed measurement method will be described later.

[0067] In a non-oriented electrical steel sheet according to an embodiment of the present invention, the CSL grain boundary formation ratio of grains present per unit area can satisfy the following formula 2.

[0068] [Equation 2]

[0069] In Equation 2 above, ∑3, ∑5, ∑7 and ∑9 represent ∑3 type grain boundaries, ∑5 type grain boundaries, ∑7 type grain boundaries and ∑9 type grain boundaries, respectively.

[0070] When Equation 2 above is satisfied, it can have excellent magnetic properties. This is related to the movement of magnetic domains, which is affected by the grain boundary energy between grains.

[0071] For ∑5 and ∑9 grain boundaries with high boundary energies, the movement of magnetic domains may be hindered, leading to a deterioration in magnetic properties. For ∑3 and ∑7 grain boundaries, which have relatively low boundary energies, the movement of magnetic domains is smoother compared to ∑5 and ∑9 grain boundaries, which may have a positive impact on magnetic properties.

[0072] Therefore, when the CSL grain boundary formation ratio satisfies Equation 2 above, the magnetic domains move more freely during magnetization, thereby improving magnetic properties. Conversely, when Equation 2 is not satisfied, the grain boundary energy is high, which is detrimental to the movement of magnetic domains and may lead to deterioration of magnetic properties.

[0073] The non-oriented electrical steel sheet of one embodiment of the present invention can have excellent magnetic properties and can have magnetic properties suitable for motors used in household motors or household appliances. Preferably, the iron loss (W) 15 / 50 The iron loss (W) can be below 6 W / kg, more preferably, the iron loss (W) 15 / 50 It can be below 5.7 W / kg.

[0074] The following will describe in detail a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0075] Manufacturing method of non-oriented electrical steel sheet The following will refer to Figure 1 A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention is described.

[0076] Figure 1 A flowchart illustrating the general sequence of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0077] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: a first step (S1) of preparing steel having the above-mentioned 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 after 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.

[0078] The steps of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail below.

[0079] The first step (S1) of preparing steel with the aforementioned alloy composition is a step of preparing a semi-finished product for manufacturing a non-oriented electrical steel sheet as the final product. More specifically, this step may be a step of manufacturing a semi-finished product by designing the alloy composition according to the alloy composition range of an embodiment of the present invention. The semi-finished product may be a slab, but is not necessarily limited to this. Furthermore, the slab may be manufactured by processes known in the art, such as steelmaking processes and continuous casting processes.

[0080] Furthermore, the content of the alloy components has already been explained above, so it will not be repeated here. During the manufacturing process described later, the content of the alloy components remains essentially unchanged; therefore, the alloy composition of the steel is substantially the same as that of the non-oriented electrical steel sheet, the final product.

[0081] In a method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention, after the first step (S1), a second step (S2) can be performed to hot roll the steel 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.

[0082] First, the reheating step is performed before the hot rolling step and can be used to reheat the steel for subsequent processes. Specifically, this step can be to load the steel into a heating furnace and uniformly heat the steel to make it easier for plastic deformation to occur.

[0083] If the reheating temperature is below 1100℃, the rolling load increases, potentially reducing rollability. Conversely, if the reheating temperature is above 1250℃, precipitates formed from carbon (C), sulfur (S), nitrogen (N), etc., in the steel will re-dissolve, resulting in fine precipitates during subsequent rolling and annealing processes. These fine precipitates inhibit grain growth and lead to magnetic degradation.

[0084] Therefore, in the reheating step of one embodiment of the present invention, the steel can be reheated to 1100-1250°C.

[0085] Next, a hot rolling step can be performed to form a hot-rolled steel sheet. This hot rolling step may include roughing and finishing rolling. Roughing may involve rolling the steel into a rolled material with a suitable shape, thickness, and width, while finishing rolling may involve adjusting the steel to a specified thickness and width and rolling it to a good surface and shape at a final rolling temperature that meets the requirements of the application.

[0086] At this point, the final rolling temperature of the hot rolling step can be 800–900°C. If the final rolling temperature is below 800°C, rolling will occur in the two-phase region, which may result in an uneven microstructure. If the final rolling temperature is above 900°C, it may lead to a sharp decrease in strength.

[0087] Next, a winding step can be performed. The winding temperature is preferably 500–700°C. If the winding temperature is below 500°C, the grain size will be too small, resulting in insufficient grain growth even after annealing. If the winding temperature is above 700°C, fine precipitates will be generated, thereby reducing magnetic properties.

[0088] The thickness of the hot-rolled steel sheet formed in the second step (S2) is preferably 1.6 to 2.6 mm. If the thickness of the hot-rolled steel sheet is too thin, less than 1.6 mm, the thickness obtained after cold rolling will be insufficient, which may lead to poor shape in product application. Conversely, if the thickness of the hot-rolled steel sheet is greater than 2.6 mm, the cold rolling reduction rate will increase, the fraction of texture that is unfavorable to magnetic properties will increase, and thus lead to deterioration of magnetic properties.

[0089] In a method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention, after the second step (S2), a third step (S3) may be performed to hot-roll anneal the hot-rolled steel sheet. The third step (S3) may be a hot-roll annealing step, which is performed to ensure the uniformity of the microstructure and cold rollability of the hot-rolled steel.

[0090] The hot rolling annealing can be carried out at a temperature capable of removing the elongated as-cast structure and forming a uniform microstructure. Preferably, the heat treatment can be performed in the temperature range of 940–1110°C. In this case, the heating rate can be 20°C / s or higher, and the cooling rate can also be 20°C / s or higher.

[0091] If the hot-rolling annealing temperature is below 940℃, elongated as-cast structures will remain after hot rolling, resulting in uneven microstructure. Furthermore, the elongated as-cast structures inhibit grain growth, forming smaller grains, which then become an obstacle during cold rolling. Conversely, if the hot-rolling annealing temperature is above 1110℃, it will lead to an unbalanced texture in the final product and reduce its magnetic properties.

[0092] The hot rolling annealing can be carried out for 30 to 180 seconds at various temperature conditions to form a suitable grain size.

[0093] Between the third step (S3) and the fourth step (S4) described later, an acid pickling process may also be performed. This acid pickling process can be a process of removing the oxide layer formed on the surface using an acid pickling solution, and can be performed using processes known in the art.

[0094] Subsequently, the non-oriented electrical steel sheet of one embodiment of the present invention can undergo a fourth step (S4), in which the hot-rolled steel sheet that has undergone the third step (S3) is cold-rolled to form a cold-rolled steel sheet. The fourth step (S4) can be a process of rolling the hot-rolled steel sheet below the recrystallization temperature to further reduce the thickness of the steel sheet. More specifically, this step can be a process of rolling the hot-rolled steel sheet to a thickness and width conforming to the final product specifications.

[0095] At this point, the fourth step (S4) can perform a final cold rolling on the hot-rolled steel sheet to reduce its thickness to below 0.65 mm. The final reduction rate can be 50-96%. Furthermore, the fourth step (S4) can be performed using a warm rolling method, raising the steel sheet temperature to 100-200°C to facilitate rolling.

[0096] Following the fourth step (S4), the non-oriented electrical steel sheet of one embodiment of the present invention can undergo a fifth step (S5) to perform cold rolling annealing. The cold rolling annealing can be performed at a temperature that yields the optimal grain size to improve magnetic and mechanical properties. The optimal grain size can be 35–200 µm.

[0097] If the cold rolling annealing temperature is below 900℃, the grain size will be small, which may lead to a deterioration in magnetic flux density and iron loss. Conversely, if the cold rolling annealing temperature is above 1100℃, the precipitates may redissolve to produce fine precipitates, and excessive grain growth may lead to a decrease in strength.

[0098] Therefore, the cold rolling annealing temperature of the present invention can be 900–1100°C. At this temperature, the heating rate during cold rolling annealing can be 10°C / s or higher, and the cooling rate can be 20°C / s or higher. Furthermore, heat treatment can be performed at various temperature conditions for 30–120 seconds to obtain the optimal grain size.

[0099] In a method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention, a coating step may be included after the fifth step (S5). The coating step may be performed to ensure the insulation and improve the stamping properties of the non-oriented electrical steel sheet, and may refer to forming an insulating film on the surface of the cold-rolled steel sheet after the fifth step (S5). The coating step may be performed using processes known in the art.

[0100] The non-oriented electrical steel sheet manufactured by the manufacturing method of the non-oriented electrical steel sheet according to an embodiment of the present invention can have excellent magnetic properties and can have magnetic properties suitable for motors used in household motors or household appliances. Preferably, the iron loss (W) 15 / 50 The iron loss (W) can be below 6 W / kg, more preferably, the iron loss (W) 15 / 50 It can be below 5.8 W / kg.

[0101] Furthermore, it can possess both excellent magnetic properties and excellent mechanical strength. Preferably, the yield strength (YS) can be 250 MPa or higher, and the tensile strength (TS) can be 350 MPa or higher.

[0102] This allows for the production of non-oriented electrical steel sheets with excellent magnetic properties that reduce iron loss, while also exhibiting outstanding mechanical strength.

[0103] Experimental Example The structure and function of the present invention will be illustrated below through experimental examples. However, these are merely examples provided to aid in understanding the present invention and are not intended to limit the invention.

[0104] Table 1 below shows the content of the main alloy components in the experimental examples. Furthermore, Table 2 below shows some of the process conditions for manufacturing the experimental examples from steel with the alloy composition described in Table 1, whether Equation 1 is satisfied, the volume fraction of the second phase, whether Equation 2 is satisfied, and the iron loss value.

[0105] In this experimental example, steel having the alloy composition listed in Table 1 was manufactured according to the manufacturing method of non-oriented electrical steel sheet according to an embodiment of the present invention. Other process conditions not listed in Table 2 were controlled as control variables and were controlled under the same conditions within the range described in the manufacturing method of non-oriented electrical steel sheet according to an embodiment of the present invention.

[0106] In this experiment, according to the IEC 60404-2 international standard and based on the Epstein frame test to measure the magnetic properties of non-oriented electrical steel sheets, a test piece with a length of 300 mm and a width of 30 mm was prepared and measured.

[0107] In addition, the CSL (coincidence site lattice) boundary of this experimental example was measured by electron backscatter diffraction (EBSD) analysis, and the data was analyzed using OIM Analysis 8 software to obtain the result value.

[0108] In Table 2 below, W 15 / 50 This represents the iron loss (W) under conditions of 1.5T and 50Hz. 15 / 50 ).

[0109] Table 1

[0110] Table 2

[0111] Referring to Tables 1 and 2 above, Experimental Examples 2, 4, 6, 9, 11, 13, 15, 16, 18, 19, 22, 23, 25, 27, 28, and 30 are examples that satisfy the alloy composition range and reheating temperature range of an embodiment of the present invention. Furthermore, it can be confirmed that they satisfy Equation 1 above and the condition that the volume fraction of the second phase with a diameter of 1.0 µm or more is 45% or more, and also satisfy Equation 2 above. At this time, it can be confirmed that they satisfy the iron loss (W) requirement. 15 / 50 The value (i.e., the target value of the present invention) is 6 W / kg or less.

[0112] Conversely, Experimental Examples 1, 7, 8, 20, and 21 are comparative examples that do not satisfy the alloy composition range of one embodiment of the present invention, and it can be confirmed that they do not satisfy Equation 1 above. Furthermore, it can be confirmed that they do not satisfy the condition that the volume fraction of the second phase with a diameter of 1.0 µm or more is 45% or more, and they do not satisfy Equation 2 above. In this case, it can be confirmed that they do not satisfy the iron loss (W) requirement. 15 / 50 The value (i.e., the target value of the present invention) is 6 W / kg or less.

[0113] Experimental Examples 5, 12, 14, 24, 26, and 29 are comparative examples of alloy composition ranges that do not meet the requirements of this invention, and it can be confirmed that they do not satisfy Equation 1 above. Furthermore, it can be confirmed that the volume fraction of the second phase with a diameter of 1.0 µm or more is less than 45%, and it does not satisfy Equation 2 above. In this case, it can be confirmed that it does not satisfy the iron loss (W) requirement. 15 / 50 The value (i.e., the target value of the present invention) is 6 W / kg or less.

[0114] Experimental Example 17 is a comparative example that meets the alloy composition range of an embodiment of the present invention but does not meet Formula 1 above. Furthermore, it can be confirmed that the volume fraction of the second phase with a diameter of 1.0 µm or more is less than 45%, and it does not meet Formula 2 above. In this case, it can be confirmed that this experimental example does not meet the iron loss (W) requirement. 15 / 50 (The condition is below 6W / kg.)

[0115] Experimental Example 10 is a comparative example exceeding the reheating temperature range of one embodiment of the present invention. Furthermore, it can be confirmed that it does not meet the condition that the volume fraction of the second phase with a diameter of 1.0 µm or more is 45% or more. In this case, it can be confirmed that it does not meet the requirement of iron loss (W). 15 / 50 The value (i.e., the target value of the present invention) is 6 W / kg or less.

[0116] As described above, preferred embodiments of the present invention have been presented. Besides the embodiments described above, the present invention can be implemented in other specific ways without departing from its spirit or scope, which will be apparent to those skilled in the art. Therefore, the above embodiments should be considered exemplary embodiments, not limiting embodiments. Thus, the present invention is not limited to the above description, and various modifications can be made within the scope of the appended claims and their equivalents.

Claims

1. A non-oriented electrical steel sheet, characterized in that, It contains 0.1 to 1.6 wt% silicon (Si), 0.1 to 0.6 wt% manganese (Mn), 0.4 to 1.5 wt% aluminum (Al), less than 0.005 wt% sulfur (S), less than 0.005 wt% titanium (Ti), less than 0.03 wt% tin (Sn), less than 0.025 wt% niobium (Nb), less than 0.03 wt% molybdenum (Mo), and the balance iron (Fe) and other unavoidable elements.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that, Satisfy the following equation 1: [Formula 1] 2.75 <logT<4.0 In Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], where [S], [Ti], [Sn], [Nb] and [Mo] represent the contents of S, Ti, Sn, Nb and Mo in ppm, respectively.

3. The non-oriented electrical steel sheet according to claim 1, characterized in that, The volume fraction of the second phase with a diameter of 1.0 µm or more is 45% or more.

4. The non-oriented electrical steel sheet according to claim 1, characterized in that, Including CSL grain boundaries at overlapping locations, The CSL grain boundaries include ∑3 type grain boundaries, ∑5 type grain boundaries, ∑7 type grain boundaries and ∑9 type grain boundaries.

5. The non-oriented electrical steel sheet according to claim 4, characterized in that, The CSL grain boundary formation ratio of grains per unit area satisfies the following equation 2: [Equation 2] 。 6. The non-oriented electrical steel sheet according to claim 1, characterized in that, Iron loss W 15 / 50 It is below 6W / kg.

7. The non-oriented electrical steel sheet according to any one of claims 1 to 6, characterized in that, It also contains less than 0.005% by weight of carbon (C), less than 0.02% by weight of phosphorus (P), and less than 0.005% by weight of nitrogen (N).

8. A method for manufacturing a non-oriented electrical steel sheet, characterized in that, include: The first step is to prepare steel, which contains 0.1 to 1.6 wt% silicon (Si), 0.1 to 0.6 wt% manganese (Mn), 0.4 to 1.5 wt% aluminum (Al), less than 0.005 wt% sulfur (S), less than 0.005 wt% titanium (Ti), less than 0.03 wt% tin (Sn), less than 0.025 wt% niobium (Nb), less than 0.03 wt% molybdenum (Mo), and the balance iron (Fe) and other unavoidable elements. The second step is to hot-roll the steel to form a hot-rolled steel plate; The third step is to perform hot rolling annealing on the hot-rolled steel sheet; The fourth step is to cold roll the hot-rolled steel sheet that has undergone the third step to form a cold-rolled steel sheet; as well as The fifth step is to perform cold rolling annealing on the cold-rolled steel sheet.

9. The method for manufacturing non-oriented electrical steel sheet according to claim 8, characterized in that, The second step includes reheating the steel to 1100–1250°C.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 8, characterized in that, The steel material satisfies the following formula 1: [Formula 1] 2.75 <logT<4.0 In Equation 1, T = 5*[S] + 12*[Ti] + 5*[Sn] + 17*[Nb] + 17*[Mo], where [S], [Ti], [Sn], [Nb] and [Mo] represent the contents of S, Ti, Sn, Nb and Mo in ppm, respectively.

11. The method for manufacturing non-oriented electrical steel sheet according to any one of claims 8 to 10, characterized in that, The steel also contains less than 0.005% by weight of carbon (C), less than 0.02% by weight of phosphorus (P), and less than 0.005% by weight of nitrogen (N).

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