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

Abstract

The present invention provides a non-oriented electrical steel sheet capable of improving the cleanliness within the steel and facilitating magnetic domain wall movement to improve magnetization characteristics, and a method for manufacturing the same. [Solution] The non-oriented electrical steel sheet of the present invention contains, by weight%, 2.0 to 3.8% Si, 0.1 to 2.5% Al, 0.1 to 2.5% Mn, 0.01 to 0.08% Mo, 0.0010 to 0.0050% Ti, 0.0010 to 0.0050% Nb, 0.0020 to 0.0060% C, and 0.0010 to 0.0050% N, with the remainder being Fe and unavoidable impurities, and satisfies formula 1, [Formula 1] 0.02≦([Ti]+[Nb])×[Mo] / ([C]+[N])≦0.05 (In formula 1, [Ti], [Nb], [Mo], [C] and [N] represent the contents (wt%) of Ti, Nb, Mo, C and N, respectively.) One or more of carbides, nitrides, and carbides with a particle size of 0.1 μm or less have a density of 100 pieces / mm 2 The present invention is characterized in that:

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet in which Mo, Ti, and Nb are appropriately added to suppress the formation of fine carbides by bubbling during the molten steel manufacturing process, and to a method for manufacturing the same. As a result, the internal cleanliness of the steel is improved, magnetic domain wall movement is facilitated, and magnetization properties are improved. [Background technology]

[0002] Efficient use of electrical energy is a major challenge for improving the global environment, including energy conservation, reduction of fine dust generation, and reduction of greenhouse gas emissions. Currently, more than 50% of all generated electrical energy is consumed by electric motors, so improving the efficiency of electric motors is essential for the efficient use of electricity. In recent years, with the rapid development of environmentally friendly automobiles (hybrid, plug-in hybrid, electric vehicles, fuel cell vehicles), interest in high-efficiency drive motors has surged. At the same time, awareness of high efficiency in areas such as high-efficiency motors for home appliances and super-premium motors for heavy electrical machinery, as well as government regulations, continues, and the demand for efficient use of electrical energy is higher than ever before.

[0003] On the other hand, optimizing all aspects, from material selection to design, assembly, and control, is crucial for increasing the efficiency of electric motors. In particular, the magnetic properties of electrical steel sheets are of paramount importance, with high demands for low iron loss and high magnetic flux density. For automotive drive motors and air conditioning compressor motors that must operate not only in the commercial frequency range but also in the high frequency range, high-frequency low iron loss characteristics are extremely important. To obtain such high-frequency low iron loss characteristics, it is important to improve the initial permeability, which is an essential characteristic for achieving high-frequency low iron loss because it allows for faster magnetization even under low magnetization force.

[0004] Such electrical steel sheets require the addition of large amounts of resistive elements such as Si, Al, and Mn during the manufacturing process, and the inclusions and fine precipitates present within the steel sheet must be actively controlled to prevent them from hindering magnetic domain wall movement. However, in order to control inclusions and fine precipitates, it is necessary to purify impurity elements such as C, S, N, Ti, Nb, and V to extremely low levels during steelmaking, which requires the use of high-grade raw materials, and furthermore, secondary refining takes a lot of time, resulting in a decrease in productivity. Therefore, although research is being conducted on methods for adding large amounts of resistive elements such as Si, Al, and Mn and controlling impurity elements to extremely low levels, there have been very few practical application results. [Overview of the project] [Problems that the invention aims to solve]

[0005] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. More specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, in which Mo, Ti, and Nb are appropriately added to suppress the formation of fine carbides by bubbling during the molten steel manufacturing process. [Means for solving the problem]

[0006] An embodiment of the present invention provides a non-oriented electrical steel sheet containing, by weight %, Si: 2.0-3.8%, Al: 0.1-2.5%, Mn: 0.1-2.5%, Mo: 0.01-0.08%, Ti: 0.0010-0.0050%, Nb: 0.0010-0.0050%, C: 0.0020-0.0060%, and N: 0.0010-0.0050%, with the remainder being Fe and unavoidable impurities, satisfying the following formula 1. [Formula 1] 0.02≦([Ti]+[Nb])×[Mo] / ([C]+[N])≦0.05 (In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the content (weight %) of Ti, Nb, Mo, C, and N, respectively.) One or more carbides, nitrides, and carbonized materials with a particle size of 0.1 μm or less have a density of 100 particles / mm³. 2The following characteristics apply:

[0007] The content of Ti, Nb, C, and N may be 0.003 to 0.015% by weight.

[0008] An embodiment of the present invention may further contain one or more of the following: Sn: 0.015-0.1% by weight, Sb: 0.015-0.1% by weight, and P: 0.005-0.05% by weight.

[0009] An embodiment of the present invention may further contain one or more of the following: Cu: 0.01% by weight or less, S: 0.005% by weight or less, B: 0.002% by weight or less, Mg: 0.005% by weight or less, and Zr: 0.005% by weight or less.

[0010] An unoriented electrical steel sheet according to one embodiment of the present invention may have a resistivity of 50 μΩ·cm or more.

[0011] The non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 100 μm.

[0012] An unoriented electrical steel sheet according to one embodiment of the present invention may have a magnetic permeability of 5000 or more at 30 A / m.

[0013] A method for manufacturing non-oriented electrical steel sheets according to one embodiment of the present invention is characterized by comprising the steps of: producing molten steel that contains, by weight %, Si: 2.0~3.8%, Al: 0.1~2.5%, Mn: 0.1~2.5%, Mo: 0.01~0.08%, Ti: 0.0010~0.0050%, Nb: 0.0010~0.0050%, C: 0.0020~0.0060%, and N: 0.0010~0.0050%, with the remainder being Fe and unavoidable impurities, and satisfying the following formula 1; bubbling the molten steel for 5~10 minutes; continuously casting the molten steel to produce a slab; hot rolling the slab to produce a hot-rolled sheet; cold rolling the hot-rolled sheet to produce a cold-rolled sheet; and final annealing of the cold-rolled sheet. [Formula 1] 0.02 ≤ ([Ti] + [Nb]) × [Mo] / ([C] + [N]) ≤ 0.05 (In Formula 1, [Ti], [Nb], [Mo], [C], and [N] respectively represent the contents (wt%) of Ti, Nb, Mo, C, and N.)

[0014] Bubbling can be carried out at 5 Nm 3 or more flow rate using an inert gas.

[0015] The grain growth property calculated by the following Formula 2 may be 10 to 15. [Formula 2] Grain growth property = Temperature (°C) at the final annealing stage Annealing × Time (min) at the final annealing stage Annealing / Average crystal grain diameter (μm)

Advantages of the Invention

[0016] According to an embodiment of the present invention, Mo is added in a certain ratio to Ti and Nb to suppress the formation of fine carbides, improve the cleanliness in the steel, facilitate magnetic wall movement, and improve the magnetization characteristics. As a result, the initial permeability is improved, which also has an effect on the iron loss in the high-frequency region. Therefore, it provides a technology capable of manufacturing a non-oriented electrical steel sheet suitable for high-speed rotation, and contributes to the manufacture of environmentally friendly automotive motors, high-efficiency household appliance motors, and super-premium class electric motors.

Modes for Carrying Out the Invention

[0017] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, the first part, component, region, layer, or section described below can be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0018] The terminology used herein is for the purpose of referring to particular embodiments only and is not intended to limit the present invention. The singular forms used herein include the plural forms as well, unless the context clearly dictates otherwise. As used in the specification, "comprising" means embodying a specific feature, region, integer, step, operation, element, and / or component, and does not preclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0019] When a part is referred to as being "on" or "above" another part, this may mean directly on the other part or may include intervening parts therebetween. On the other hand, when a part is referred to as being "directly above" another part, there are no intervening parts therebetween. Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0020] In one embodiment of the present invention, the meaning of further comprising an additional element means comprising the additional element in place of the remaining iron (Fe) by the amount of the additional element added. Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have meanings consistent with the relevant technical literature and the presently disclosed content, and are not to be interpreted in an idealized or overly formal sense unless defined otherwise.

[0021] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention belongs can easily implement them. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein.

[0022] An example of the present invention is a non-oriented electrical steel sheet containing, by weight percent, Si: 2.0-3.8%, Al: 0.1-2.5%, Mn: 0.1-2.5%, Mo: 0.01-0.08%, Ti: 0.0010-0.0050%, Nb: 0.0010-0.0050%, C: 0.0020-0.0060%, and N: 0.0010-0.0050%, with the remainder being Fe and unavoidable impurities. The following explains the reasons for limiting the composition of non-oriented electrical steel sheets.

[0023] Si:2.00~3.80wt% Silicon (Si) plays a role in increasing the resistivity of materials and reducing iron loss. If the amount of Si is too low, the effect of reducing iron loss may be insufficient. If too much Si is added, the hardness of the material may increase, and productivity and punching performance may be inferior. Therefore, the Si content can be 2.0 to 3.8% by weight. More specifically, it can be 2.3 to 3.7% by weight. Even more specifically, it can be 3.5 to 3.3% by weight.

[0024] Al: 0.10~2.50% by weight Aluminum (Al) plays a role in increasing the resistivity of the material and reducing iron loss. If there is too little Al, fine nitrides may form, or the surface oxide layer may not be densely formed, resulting in a lack of magnetic improvement. If there is too much Al, excessive nitrates will be formed, degrading the magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. Therefore, the Al content can be 0.1 to 2.5% by weight. More specifically, it can be 0.2 to 2.0% by weight. Even more specifically, it can be 0.5 to 1.5% by weight.

[0025] Mn:0.10~2.50wt% Manganese (Mn) plays a role in increasing the resistivity of the material, improving iron loss, and promoting sulfide formation. If there is too little Mn, fine MnS is formed, causing magnetic degradation. If there is too much Mn, it promotes the formation of a {111} texture unfavorable to magnetism, causing a rapid decrease in magnetic flux density. Therefore, the material can contain 0.1 to 2.5 wt% Mn. More specifically, it can contain 0.15 to 2.0 wt% Mn. Even more specifically, it can contain 0.2 to 1.5 wt% Mn.

[0026] Mo:0.010~0.080wt% Molybdenum (Mo) reacts with Nb and Ti to completely dissolve them, suppressing the formation of (Nb,Ti)C and N, and coarsening carbides to reduce their distribution density. If there is too little Mo, complete dissolution may not occur, and the ability to suppress the formation of carbide nitrides may decrease. If there is too much Mo, Si compounds may form within the steel sheet, suppressing the grain growth of the entire steel sheet and resulting in inferior magnetism. Therefore, the Mo content can be 0.01 to 0.08 wt%. More specifically, it can be 0.02 to 0.07 wt%. Even more specifically, it can be 0.03 to 0.05 wt%.

[0027] Nb, Ti: 0.0010-0.0050% by weight each Niobium (Nb) and titanium (Ti) combine with C and N to form fine carbides and nitrides, respectively, and therefore their amounts must be limited to 0.0050% or less. However, when Mo is added, it combines with the niobium to form a complete solid solution, or exists in the form of coarse carbides, reducing its role in suppressing magnetic field wall movement. Furthermore, when Mo is added, it is necessary to add at least 0.0010% by weight of each to suppress the formation of Si compounds. Therefore, Nb and Ti can each be contained in 0.0010 to 0.0050% by weight. More specifically, they can each be contained in 0.0015 to 0.0040% by weight. Even more specifically, they can each be contained in 0.0020 to 0.0040% by weight.

[0028] C:0.0020~0.0060wt% Carbon (C) causes magnetic aging and combines with Ti, Nb, etc. to form carbides, which degrade magnetic properties, so a lower amount is preferable. However, in one embodiment of the present invention, carbide formation is suppressed to the maximum extent by bubbling during the steelmaking process along with the addition of Mo, so even if it contains 0.0020% by weight or more, it does not have a significant effect on magnetism. Controlling the carbon content to less than 0.0020% by weight can result in excessively high additional costs for the decarburization process, leading to cost increases. Therefore, the C content can be 0.0020 to 0.0060% by weight. More specifically, it can be 0.0025 to 0.0050% by weight. Even more specifically, it can be 0.0025 to 0.0040% by weight.

[0029] N:0.0010~0.0050wt% Nitrogen (N) not only forms fine AlN precipitates within the base material, but also combines with Ti, Nb, etc. to form fine nitrides, suppressing grain growth and worsening iron loss; therefore, lower levels are preferable. However, in one embodiment of the present invention, carbide formation is suppressed to the maximum extent by bubbling during the steelmaking process along with the addition of Mo, so even if it contains 0.0010% by weight or more, it does not significantly affect magnetism. Controlling the nitrogen content to less than 0.0010% by weight can lead to excessive management costs for the purity of the molten steel alloy ferroalloy and molten iron, resulting in increased costs. Therefore, the N content can be 0.0010 to 0.0050% by weight. More specifically, it can be 0.015 to 0.0045% by weight. Even more specifically, it can be 0.0015 to 0.0040% by weight.

[0030] Ti+Nb+C+N:0.0030~0.0150wt% Mo reacts with Ti and Nb to form a complete solution, but if the total amount of impurities such as Ti and Nb is too high, the bubbling time in steelmaking increases and productivity decreases, so the upper limit of the total amount can be limited to 0.015% by weight. On the other hand, since Mo reacts with Si to suppress the formation of intermetallic compounds, the lower limit can be limited to 0.003% by weight. More specifically, the content of Ti, Nb, C, and N may be between 0.0050 and 0.0150% by weight.

[0031] A non-oriented electrical steel sheet according to one embodiment of the present invention satisfies the following formula 1. [Formula 1] 02≦([Ti]+[Nb])×[Mo] / ([C]+[N])≦0.05 (In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the content (weight %) of Ti, Nb, Mo, C, and N, respectively.)

[0032] When Equation 1 is satisfied, the formation of fine carbon deposits can be minimized. That is, within the range of 0.020 to 0.050, the formation of fine carbon deposits is suppressed and the distribution density of carbon deposits is minimized, so it can be controlled within this range. More specifically, the value of Equation 1 may be between 0.030 and 0.060.

[0033] An embodiment of the present invention may further contain one or more of the following: Sn: 0.015-0.1% by weight, Sb: 0.015-0.1% by weight, and P: 0.005-0.05% by weight.

[0034] Sn, Sb: 0.015-0.100% by weight, respectively. Tin (Sn) and antimony (Sb) segregate on the surface and grain boundaries of the steel sheet, suppressing surface oxidation during annealing, hindering elemental diffusion across grain boundaries, and improving texture by inhibiting recrystallization in the {111} / / ND orientation. If too little Sn and Sb are added, the aforementioned effects may not be sufficient. If too much Sn and Sb are added, the toughness may decrease due to increased grain boundary segregation, and the productivity relative to the improvement in magnetism may decrease. Therefore, an additional 0.015 to 0.100 wt% of Sn and Sb each can be included. More specifically, an additional 0.020 to 0.075 wt% of each can be included.

[0035] P:0.005~0.050wt% Phosphorus (P) segregates on the surface and grain boundaries of the steel sheet, suppressing surface oxidation during annealing, hindering elemental diffusion through grain boundaries, and improving texture by inhibiting recrystallization in the {111} / / ND orientation. If too little P is added, its effect may be insufficient. If too much P is added, the hot working properties may deteriorate, and the productivity relative to the improvement in magnetism may decrease. Therefore, an additional 0.005 to 0.050 wt% of P can be included. More specifically, an additional 0.007 to 0.045 wt% of P can be included.

[0036] An embodiment of the present invention may further contain one or more of the following: Cu: 0.01% by weight or less, S: 0.005% by weight or less, B: 0.002% by weight or less, Mg: 0.005% by weight or less, and Zr: 0.005% by weight or less.

[0037] Cu: 0.01% by weight or less, Copper (Cu) is an element that can form sulfides at high temperatures, and when added in large quantities, it can cause surface defects during slab manufacturing. Therefore, if Cu is to be included further, it can be included in amounts of 0.01% by weight or less. More specifically, it can be included in amounts of 0.001 to 0.01% by weight.

[0038] S: 0.005% by weight or less, Sulfur (S) forms fine precipitates such as MnS, CuS, and (Mn,Cu)S, which degrade magnetic properties and worsen hot workability, so it is best to keep its content low. Therefore, if S is further present, it can be included in amounts of 0.005% by weight or less. More specifically, it can be included in amounts of 0.0001 to 0.005% by weight. Even more specifically, it can be included in amounts of 0.0005 to 0.0035% by weight.

[0039] B: 0.002% by weight or less, Mg: 0.005% by weight or less, and Zr: 0.005% by weight or less B, Mg, and Zr are elements that adversely affect magnetism and may be further included within the ranges described above.

[0040] The remainder consists of Fe and unavoidable impurities. These unavoidable impurities are introduced during the steelmaking process and the manufacturing process of grain-oriented electrical steel sheets, and since this is widely known in the field, a detailed explanation is omitted. This embodiment of the present invention does not exclude the addition of elements other than the alloy components described above; a variety of elements can be included within the limits that do not impair the technical concept of the present invention. If additional elements are included, they are included in place of the remaining Fe.

[0041] An embodiment of the present invention provides a non-oriented electrical steel sheet having a density of 100 particles / mm² of one or more carbides, nitrides, and carbonized materials having a particle size of 0.1 μm or less. 2 The following is also acceptable.

[0042] In one embodiment of the present invention, by adding an appropriate amount of Mo relative to the Ti and Nb content while containing Ti, Nb, C, and N in a certain amount or more, and by completely dissolving Mo with Nb and Ti through bubbling in the steelmaking process, the density of carbides, nitrates, or carbonized materials (hereinafter sometimes collectively referred to as "carbonized materials") can be reduced to the maximum extent.

[0043] The lower limit of the carbide particle size may be 0.02 μm. Carbides smaller than the aforementioned particle size may have no substantial effect on magnetism. When observing a steel plate, the particle size can be defined as the particle size of a virtual circle with the same area as the carbide. The measurement surface for the carbide may be the cross-section perpendicular to the rolling direction (TD plane). Carbide can be observed using a scanning electron microscope (SEM).

[0044] The density of carbonized material is 100 particles / mm³. 2 It may also be 50-100 pieces / mm 2 That's fine.

[0045] An unoriented electrical steel sheet according to one embodiment of the present invention may have a resistivity of 50 μΩ·cm or more. More specifically, it may be 53 μΩ·cm or more. Even more specifically, it may be 58 μΩ·cm or more. There is no particular upper limit, but it may be 100 μΩ·cm or less.

[0046] The non-oriented electromagnetic steel sheet according to an embodiment of the present invention has an improved magnetic permeability and is suitable for high-speed rotation. As a result, when applied to an environmentally friendly automobile motor, it can contribute to an increase in the driving distance. Specifically, the non-oriented electromagnetic steel sheet according to an embodiment of the present invention has a magnetic permeability of 5000 or more at 30 A / m.

[0047] The non-oriented electromagnetic steel sheet according to an embodiment of the present invention has an average crystal grain size of 50 to 100 μm and is excellent in high-frequency iron loss within the above-described range. More specifically, the average crystal grain size is 75 to 95 μm.

[0048] As described above, an embodiment of the present invention presents an optimal alloy composition, minimizes carbides, and can improve magnetism. Specifically, the iron loss (W 10 / 400 ) of the non-oriented electromagnetic steel sheet is 12.5 W / kg or less, and the magnetic flux density (B 50 ) is 1.65 T or more. The iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 HZ. The magnetic flux density (B 50 ) is the magnetic flux density induced by a magnetic field of 5000 A / m. More specifically, the iron loss (W 10 / 400 ) of the non-oriented electromagnetic steel sheet is 11.0 to 12.5 W / kg, and the magnetic flux density (B 50 ) is 1.65 to 1.70 T.

[0049] The manufacturing method of the non-oriented electromagnetic steel sheet according to an embodiment of the present invention includes a step of manufacturing molten steel; a step of bubbling the molten steel for 5 to 10 minutes; a step of continuously casting the molten steel to manufacture a slab; a step of hot-rolling the slab to manufacture a hot-rolled sheet; a step of cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet, and a step of final annealing the cold-rolled sheet.

[0050] Hereinafter, each step will be specifically described.

[0051] First, molten steel is manufactured. The alloy composition of molten steel was explained in the section on the alloy composition of non-oriented electrical steel sheets mentioned above, so a redundant explanation will be omitted. Since the alloy composition does not substantially change during the manufacturing process of non-oriented electrical steel sheets, the alloy composition of non-oriented electrical steel sheets and molten steel are substantially the same.

[0052] Specifically, the molten steel contains, by weight percent, Si: 2.0-3.8%, Al: 0.1-2.5%, Mn: 0.1-2.5%, Mo: 0.01-0.08%, Ti: 0.0010-0.0050%, Nb: 0.0010-0.0050%, C: 0.0020-0.0060%, and N: 0.0010-0.0050%, with the remainder being Fe and unavoidable impurities, and satisfies the following formula 1. [Formula 1] 02≦([Ti]+[Nb])×[Mo] / ([C]+[N])≦0.05 (In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the content (by weight %) of Ti, Nb, Mo, C, and N, respectively.)

[0053] The process for producing molten steel can be carried out using processes known in the art. In one embodiment of the present invention, the main elements Mo, Ti, and Nb can be adjusted by adding iron alloys of Mo, iron alloys of Ti, iron alloys of Nb, etc.

[0054] Next, the molten steel is bubbling for 5-10 minutes. The bubbling in this case is the bubbling that occurs after all the alloy components have been adjusted by adding raw materials such as Mo ferroalloy, Ti ferroalloy, and Nb ferroalloy, and can be distinguished from bubbling during the deoxidation or desulfurization process. Furthermore, the bubbling process involves adding raw materials such as Mo ferroalloys, Ti ferroalloys, and Nb ferroalloys, and uses an inert gas at 5 Nm. 3 The above flow rate This method can be distinguished from conventional bubbling in molten steel production processes, such as deoxidation or desulfurization, by the way the gas is introduced. The inert gas can be Ar gas. flow rate 5~15Nm 3 It can be done this way.

[0055] Bubbling can be performed for 5 to 10 minutes. Bubbling allows Mo to react sufficiently with Ti and Nb to achieve complete solution, minimizing the density of carbides in the final manufactured electrical steel sheet. If the bubbling time is too short, the bubbling effect described above may be reduced. If the bubbling time is too long, Mo may not react further with Ti and Nb, which can lead to decreased productivity and increased costs.

[0056] If bubbling is not performed in the molten steel, Ti and Nb carbides exist in the molten steel in a fine form. These are remelted during the slab reheating stage and precipitated into even finer forms during the hot rolling process. As a result, they remain without being removed during the hot-rolled sheet annealing and final annealing processes, causing a degradation of magnetism in the final steel sheet.

[0057] Next, the molten steel is continuously cast to produce the slab. The slab manufacturing process can be carried out using processes known in the relevant art. After manufacturing the slab, it can be heated. Specifically, the slab can be placed in a heating furnace and heated to a temperature between 1,100°C and 1,250°C. If the slab heating temperature is too high, precipitates such as AlN and MnS present in the slab may be redissolved, and then finely precipitated during hot rolling and annealing, suppressing grain growth and reducing magnetism.

[0058] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 2 to 2.3 mm. During the production of the hot-rolled sheet, the finishing rolling temperature can be 800°C or higher. Specifically, it may be 800 to 1000°C. The hot-rolled sheet can be wound at a temperature of 700°C or lower.

[0059] The process may further include a step of annealing the hot-rolled sheet after the step of manufacturing the hot-rolled sheet. In this case, the hot-rolled sheet annealing temperature may be 850 to 1150°C. If the hot-rolled sheet annealing temperature is too low, the microstructure will not grow or will grow finely, making it difficult to obtain a magnetically favorable texture during annealing after cold rolling. If the annealing temperature is too high, magnetic crystal grains may grow excessively, resulting in an excessive number of surface defects in the sheet. Hot-rolled sheet annealing is performed as needed to increase the magnetically favorable orientation and can be omitted. The annealed hot-rolled sheet can be pickled. More specifically, the hot-rolled sheet annealing temperature is 950 to 1150°C.

[0060] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. At this time, the reduction ratio can be adjusted to 70-85%. The cold-rolling step, when necessary, may include one cold-rolling step or two or more cold-rolling steps with an intermediate annealing step in between. In this case, the intermediate annealing temperature is 850-1150°C.

[0061] Next, the cold-rolled sheet is subjected to final annealing. In the annealing process of the cold-rolled sheet, there are no major restrictions on the annealing temperature, as long as it is within the range typically used for non-oriented electrical steel sheets. Since the iron loss of non-oriented electrical steel sheets is closely related to the size of the crystal grains, a temperature of 8500 to 1000°C is appropriate. Furthermore, the annealing time can be as short as 100 seconds or less.

[0062] In the final annealing process, the average grain size becomes 50-100 μm, and all (i.e., more than 99%) of the structure formed in the preceding cold rolling stage can be recrystallized. After the final annealing, an insulating film can be formed. The insulating film can be an organic, inorganic, or mixed-inorganic film, or it can be treated with other insulating coating agents.

[0063] The present invention will be described in more detail below through examples. However, these examples are merely illustrative of the present invention and the invention is not limited thereto. [Examples]

[0064] Table 1 shows that molten steel was produced with a composition of S: 0.002 wt% and the remainder being Fe, and unavoidable impurities. This was then subjected to Ar for the durations summarized in Table 2 below, at a rate of 10 Nm³. 3 of flow rate The material was introduced and bubbling to produce a slab. The slab was heated to 1,150°C and hot-finished-rolled at 850°C to produce a hot-rolled sheet with a thickness of 2.0 mm. The hot-rolled sheet was annealed at 1,100°C for 4 minutes and then pickled. After that, it was cold-rolled to a thickness of 0.25 mm, and then final annealing was performed at the temperatures shown in Table 2 to produce non-oriented electrical steel sheets. The initial magnetic permeability of 30 A / m was determined by cutting 60 mm wide x 60 mm long x 5 pieces and using a Single Sheet tester to obtain the average values ​​in the rolling direction and perpendicular direction, and the results are summarized in Table 2 below.

[0065] The carbide density was determined by observing the number of carbides with a particle size of 0.1 μm or less relative to the TD plane of the specimen using SEM, and the results were summarized. The average crystal grain size was determined by observation using an electron microscope, and the results are summarized in Table 2 below.

[0066] The grain growth rate is determined at the final annealing stage. Annealing Temperature (°C) × Final annealing stage Annealing The calculations were performed using the formula time (minutes) / average crystal grain size (μm) and summarized in Table 2 below.

[0067] [Table 1]

[0068] [Table 2]

[0069] As shown in Tables 1 and 2, the examples in which Mo was appropriately added to Ti and Nb and the molten steel was properly bubbling showed that less carbide was formed and that the permeability, magnetic flux density, and iron loss were excellent. On the other hand, when steel type 4 has an excess of Mo added, it does not satisfy Equation 1, and it can be confirmed that Mo forms compounds with Si, resulting in the formation of a large amount of fine carbides, and thus inferior permeability and magnetism. Steel grades 5 and 6 have too little Mo added, failing to satisfy Equation 1, resulting in the formation of a large amount of carbides and inferior permeability and magnetism.

[0070] In steel grade 7, although the alloy components were added appropriately, the bubbling time was too long, causing oxides in the slag to re-oxidize in the molten steel, resulting in the formation of a large amount of fine carbides, which led to inferior permeability and magnetism. It can be confirmed that steel grade 9 has an excessive amount of Nb added, the bubbling time is too short, a large amount of carbides are formed, and its permeability and magnetism are inferior.

[0071] Steel grades 10 to 12 do not satisfy Equation 1, and it can be confirmed that a large amount of carbides are formed, resulting in inferior permeability and magnetism. Steel type 14 contains an excessive amount of nitrogen, resulting in the formation of a large amount of carbides, and it can be confirmed that its permeability and magnetism are inferior. Steel type 15 contains low amounts of Nb and C, forms a large amount of Mo-Si compounds, and forms a large amount of fine carbides, resulting in inferior magnetic permeability and magnetism.

[0072] The present invention is not limited to the embodiments described herein and can be manufactured in a variety of different forms. Those with ordinary skill in the art to which the present invention pertains will understand that the invention can be implemented in other specific forms without altering the technical idea or essential features of the invention. Therefore, the embodiments described above should be understood to be illustrative and not limiting in all respects.

Claims

1. In weight percent, it contains Si: 2.0–3.8%, Al: 0.1–2.5%, Mn: 0.1–2.5%, Mo: 0.01–0.08%, Ti: 0.0010–0.0050%, Nb: 0.0010–0.0050%, C: 0.0020–0.0060%, and N: 0.0010–0.0050%, with the remainder being Fe and unavoidable impurities. The following equation 1 is satisfied, The total density of carbides, nitrides, and carbonized materials having a particle size of 0.1 μm or less is 100 particles / mm². ２ A non-oriented electrical steel sheet characterized by the following: [Formula 1] 0.02≦([Ti]+[Nb])×[Mo] / ([C]+[N])≦0.05 (In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the content (by weight %) of Ti, Nb, Mo, C, and N, respectively.)

2. The non-oriented electrical steel sheet according to claim 1, characterized in that the content of Ti, Nb, C, and N is 0.005 to 0.015% by weight.

3. The non-oriented electrical steel sheet according to claim 1 or 2, further comprising one or more of the following: Sn: 0.015 to 0.1% by weight, Sb: 0.015 to 0.1% by weight, and P: 0.005 to 0.05% by weight.

4. The non-oriented electrical steel sheet according to any one of claims 1 to 3, further comprising one or more of the following: Cu: 0.01% by weight or less, S: 0.005% by weight or less, B: 0.002% by weight or less, Mg: 0.005% by weight or less, and Zr: 0.005% by weight or less.

5. A non-oriented electrical steel sheet according to any one of claims 1 to 4, characterized in that its resistivity is 50 μΩ·cm or more.

6. The non-oriented electrical steel sheet according to any one of claims 1 to 5, characterized in that the average grain size is 50 to 100 μm.

7. A non-oriented electrical steel sheet according to any one of claims 1 to 6, characterized in that the magnetic permeability at 30 A / m is 5000 or more.

8. A step in producing molten steel that, by weight percent, contains Si: 2.0-3.8%, Al: 0.1-2.5%, Mn: 0.1-2.5%, Mo: 0.01-0.08%, Ti: 0.0010-0.0050%, Nb: 0.0010-0.0050%, C: 0.0020-0.0060%, and N: 0.0010-0.0050%, with the remainder being Fe and unavoidable impurities, and satisfying the following formula 1. In the step of bubbling the molten steel for 5 to 10 minutes, In the step of manufacturing a slab by continuously casting the molten steel, In the step of hot-rolling the slab to produce a hot-rolled sheet, The steps of: cold rolling the hot-rolled sheet to produce a cold-rolled sheet, and A method for manufacturing non-oriented electrical steel sheets, characterized by including a step of final annealing of the cold-rolled sheet. [Formula 1] 0.02≦([Ti]+[Nb])×[Mo] / ([C]+[N])≦0.05 (In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the content (by weight %) of Ti, Nb, Mo, C, and N, respectively.)

9. A method for manufacturing a non-oriented electrical steel sheet according to claim 8, characterized in that the grain growth rate calculated by the following formula 2 is 10 to 15. [Formula 2] Grain growth = Annealing temperature in the final annealing stage (°C) × Annealing time in the final annealing stage (minutes) / Average grain size (μm)

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