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

Abstract

The non-oriented electrical steel sheet according to an embodiment of the present application, the steel sheet comprising, in weight %, Si: 2.0 to 3.8 %, Al: 0.1 to 2.5 %, Mn: 0.1 to 2.5 %, Mo: 0.01 to 0.08 %, Ti: 0.0010 to 0.0050 %, Nb: 0.0010 to 0.0050 %, C: 0.0020 to 0.0060 %, N: 0.0010 to 0.0050 %, the balance comprising Fe and inevitable impurities.

Description

Technical Field

[0001] This invention discloses a non-oriented electrical steel sheet and its manufacturing method according to an embodiment. Specifically, one embodiment of the invention involves adding appropriate amounts of Mo, Ti, and Nb to produce a non-oriented electrical steel sheet and its manufacturing method that suppresses the formation of fine carbonitrides during the molten steel process through bubbling. Ultimately, this invention improves the magnetization properties of the non-oriented electrical steel sheet by enhancing the cleanliness of the steel and promoting domain wall movement. Background Technology

[0002] Energy conservation, dust reduction, and greenhouse gas emission reduction through efficient use of electricity are becoming key issues in improving the global environment. Since electric motors consume over 50% of all electricity generated, their high efficiency is crucial for efficient power utilization. Recently, with the rapid development of environmentally friendly vehicles (hybrid, plug-in hybrid, electric, and fuel cell vehicles), interest in high-efficiency drive motors is increasing rapidly. Furthermore, with growing awareness of efficiency in household appliances and heavy-duty motors, coupled with government regulations, the demand for efficient electricity utilization is higher than ever before.

[0003] On the other hand, optimizing all aspects from material selection to design, assembly, and control is crucial for improving motor efficiency. Particularly in terms of materials, the magnetic properties of electrical steel sheets are paramount, with high requirements for low iron loss and high magnetic flux density. High-frequency, low-iron-loss characteristics are critical for automotive drive motors or air conditioning compressor motors, which must operate not only within the commercial frequency range but also at high frequencies. To achieve this high-frequency, low-iron-loss characteristic, it is essential to increase the initial permeability, a necessary characteristic for achieving high-frequency, low-iron-loss performance because magnetization is rapid even under relatively low magnetizing forces.

[0004] In the manufacturing process of this type of electrical steel sheet, it is necessary to add a large amount of non-resistive elements such as Si, Al, and Mn to actively control inclusions and fine precipitates within the steel sheet and prevent them from interfering with domain wall movement. However, to control the formation of inclusions and fine precipitates, high-quality raw materials must first be used to refine impurity elements such as C, S, N, Ti, Nb, and V in steelmaking to extremely low levels. Furthermore, two refining processes require a significant amount of time, thus reducing productivity. Therefore, current research focuses on how to add large amounts of non-resistive elements such as Si, Al, and Mn to control impurity elements at extremely low levels, but the practical application results are not significant. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] According to an embodiment of the present invention, a non-oriented electrical steel sheet and a method for manufacturing the same are provided. Specifically, in one embodiment of the present invention, a non-oriented electrical steel sheet and a method thereof are provided by inhibiting the formation of micro-carbonitrides by bubbling during the production of molten steel through the appropriate addition of Mo, Ti, and Nb.

[0007] (II) Technical Solution

[0008] According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, 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%, with the balance comprising Fe and unavoidable impurities, satisfying the following formula 1.

[0009] [Formula 1]

[0010] 0.02≤([Ti]+[Nb])×[Mo] / ([C]+[N])≤ 0.05

[0011] In Formula 1, [Ti], [Nb], [Mo], [C] and [N] represent the contents (by weight) of Ti, Nb, Mo, C and N, respectively.

[0012] The non-oriented electrical steel sheet of one embodiment of the present invention may further contain carbides, nitrides and carbonitrides with a particle size of 0.1 μm or smaller, and the density of one or more of them may be 100 particles / mm². 2 Or smaller.

[0013] The total amount of Ti, Nb, C and N can be from 0.003 to 0.015 wt%.

[0014] The non-oriented electrical steel sheet of one embodiment of the present invention may further contain one or more of Sn: 0.015 to 0.1 wt%, Sb: 0.015 to 0.1 wt%, and P: 0.005 to 0.05 wt%.

[0015] The non-oriented electrical steel sheet of one embodiment of the present invention may further contain one or more of the following: Cu: less than 0.01 wt%, S: less than 0.005 wt%, B: less than 0.002 wt%, Mg: less than 0.005 wt%, and Zr: 0.005 wt%.

[0016] An embodiment of the present invention provides a non-oriented electrical steel sheet with a resistivity of 50 μΩ·cm or higher.

[0017] An embodiment of the present invention provides a non-oriented electrical steel sheet with an average particle size of 50 to 100 μm.

[0018] An embodiment of the present invention provides a non-oriented electrical steel sheet that can have a magnetic permeability of over 5000 at 30 A / m.

[0019] An embodiment of the present invention discloses a method for manufacturing a non-oriented electrical steel sheet, comprising the following steps: manufacturing molten steel, wherein the molten steel comprises, 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%, with the balance being Fe and unavoidable impurities, and satisfying Formula 1; bubbling the molten steel for 5 to 10 minutes; manufacturing a slab by continuous casting of the molten steel; hot rolling the slab to manufacture a hot-rolled plate; cold rolling the hot-rolled plate to manufacture a cold-rolled plate; and finally annealing the cold-rolled plate.

[0020] [Formula 1]

[0021] 0.02≤([Ti]+[Nb])×[Mo] / ([C]+[N])≤ 0.05

[0022] In Formula 1, [Ti], [Nb], [Mo], [C] and [N] represent the contents (by weight%) of Ti, Nb, Mo, C and N, respectively.

[0023] Inert gas can be used at 5 Nm 3 Bubbling is performed at the above flow rates.

[0024] The grain growth property is calculated to be 10 to 15 using Equation 2 below.

[0025] [Equation 2]

[0026] Grain growth = Final annealing soaking temperature (°C) × Final annealing soaking time (minutes) / Average grain size (μm)

[0027] (III) Beneficial Effects

[0028] According to one embodiment of the invention, Ti and Nb are added in a constant ratio to suppress the formation of fine carbonitrides, thereby improving the cleanliness of the steel, promoting domain wall movement, and enhancing magnetization properties. This results in increased initial permeability, thus also effective against iron losses in the high-frequency region. Therefore, by providing a technology for manufacturing non-oriented electrical steel sheets suitable for high-speed rotation, this contributes to the manufacture of environmentally friendly automotive motors, high-efficiency household appliance motors, and ultra-high-end motors. Detailed Implementation

[0029] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0030] The terminology used herein is for reference only in specific embodiments and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular form used herein is intended to include the plural form as well. The word "comprising" as used in the specification can specifically refer to a feature, domain, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, and / or components.

[0031] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, there are no other parts in between.

[0032] In addition, unless otherwise specified, % means weight, 1ppm is 0.0001 weight.

[0033] In one embodiment of the present invention, the inclusion of additional elements refers to the replacement of a portion of the remaining iron (Fe) by additional elements, the replacement amount being equivalent to the amount of additional elements added.

[0034] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0035] The embodiments of the present invention will be described in detail below to enable those skilled in the art to practice the invention. However, although the invention is practiced in various different ways, it is not limited to the embodiments described herein.

[0036] An embodiment of the non-oriented electrical steel sheet of the present invention, by weight%, comprises Si: 2.0 to 3.8%, Al: 0.1 to 2.5%, Mn: 0.1 to 2.5%, Mo: 0.01 to 0.08%, Ti: 0.0010 to 0.0050%, Nb: 0.0010 to 0.0050%, C: 0.0020 to 0.0060%, N: 0.0010 to 0.0050%, with the balance comprising Fe and unavoidable impurities.

[0037] The reasons for the compositional restrictions on non-oriented electrical steel sheets are described below.

[0038] Si: 2.00 to 3.80% by weight

[0039] The role of silicon (Si) is to reduce iron loss by increasing the resistivity of the material. If too little Si is added, the improvement in iron loss may be insufficient. If too much Si is added, the productivity and stamping performance will be relatively reduced due to the increased hardness of the material. Therefore, Si can be contained in the form of 2.0 to 3.8% by weight. More specifically, it can be contained in the form of 2.3 to 3.7% by weight. More specifically, it can be contained in the form of 3.5 to 3.3% by weight.

[0040] Al: 0.10 to 2.50% by weight

[0041] The role of aluminum (Al) is to increase the resistivity of the material to reduce iron loss. If too little Al is added, the magnetic improvement effect may be difficult to achieve due to the formation of fine nitrides or the inability to form a dense surface oxide layer. If too much Al is added, excessive nitride formation will lead to magnetic degradation, causing problems in all processes such as steelmaking and continuous casting, potentially significantly reducing productivity. Therefore, Al can be contained in quantities of 0.1 to 2.5% by weight. More specifically, it can be contained in quantities of 0.2 to 2.0% by weight. More specifically, it can be contained in quantities of 0.5 to 1.5% by weight.

[0042] Mn: 0.10 to 2.50% by weight

[0043] Manganese (Mn) improves iron loss and forms sulfides by increasing the resistivity of the material. If too little Mn is added, fine MnS formation leads to magnetic degradation; if too much Mn is added, it promotes the formation of {111} textures that are detrimental to magnetism, potentially causing a sharp decrease in magnetic flux density. Therefore, Mn can be present in quantities from 0.1 to 2.5 wt%. More specifically, it can be present in quantities from 0.15 to 2.0 wt%. More specifically, it can be present in quantities from 0.2 to 1.5 wt%.

[0044] Mo: 0.010 to 0.080 wt%

[0045] The role of molybdenum (Mo) is to suppress the formation of (Nb, Ti)C,N by reacting with Nb and Ti to achieve complete solution, and to reduce the distribution density by coarsening carbonitrides. If too little Mo is added, complete solid solution cannot be achieved, reducing the inhibition of carbide and nitride formation. If too much Mo is added, Si compounds may form in the steel sheet, inhibiting grain growth throughout the steel sheet and leading to poor magnetism. Therefore, Mo can be contained in 0.01 to 0.08% by weight. More specifically, it can be contained in 0.02 to 0.07% by weight. More specifically, it can be contained in 0.03 to 0.05% by weight.

[0046] Nb, Ti: 0.0010 to 0.0050 wt% each

[0047] Niobium (Nb) and titanium (Ti) combine with C and N to form fine carbides and nitrides, and therefore their respective concentrations should be limited to below 0.0050%. However, when Mo is added, the Ti combines with the Niobium and either dissolves completely or exists in the form of coarse carbonitrides, which reduces its ability to inhibit domain wall movement.

[0048] Furthermore, when adding Mo, an amount of 0.0010% by weight or more is required to suppress the formation of Si compounds. Therefore, Nb and Ti can each contain 0.0010 to 0.0050% by weight. More specifically, they can each contain 0.0015 to 0.0040% by weight. More specifically, they can each contain 0.0020 to 0.0040% by weight.

[0049] C: 0.0020 to 0.0060% by weight

[0050] The role of carbon (C) is to induce magnetic aging and combine with Ti, Nb, etc., to form carbides, thus weakening magnetism. Therefore, the lower the carbon (C) content, the better. However, in one embodiment of the present invention, the addition of Mo during the steelmaking process maximally suppresses carbide formation through bubbling. Even if it contains more than 0.0020% by weight, it will not have a significant impact on magnetism. To control carbon below 0.0020% by weight, the additional cost required for the decarburization process is too high, which may lead to increased costs. Therefore, C can be contained in 0.0020 to 0.0060% by weight. More specifically, it can be contained in 0.0025 to 0.0050% by weight. More specifically, it can be contained in 0.0025 to 0.0040% by weight.

[0051] N: 0.0010 to 0.0050% by weight

[0052] Nitrogen (N) not only forms fine AlN precipitates within the base metal, but also combines with Ti, Nb, etc., to form fine nitrides, thereby inhibiting grain growth and worsening iron loss. Therefore, the lower the nitrogen (N) content, the better. However, in one embodiment of the present invention, by adding Mo during the steelmaking process, carbide formation is suppressed as much as possible through bubbling, and even if it contains 0.0010% by weight or more, it will not have a significant impact on magnetism. To control nitrogen below 0.0010% by weight, the management costs of the purity of the molten iron alloy and the purity of the molten iron may be too high, leading to increased costs. Therefore, N can be contained in 0.0010 to 0.0050% by weight. More specifically, it can be contained in 0.0015 to 0.0045% by weight. More specifically, it can be contained in 0.0015 to 0.0040% by weight.

[0053] Ti+Nb+C+N: 0.0030 to 0.0150 wt%

[0054] Mo combines completely with Ti and Nb in a solid solution. However, if the total amount of impurities such as Ti and Nb is too high, the bubbling time in steelmaking increases, leading to a decrease in productivity. Therefore, the upper limit of the total amount can be limited to 0.015% by weight. Simultaneously, the lower limit can be limited to 0.003% by weight to suppress the formation of intermetallic compounds through the reaction of Mo with Si. More specifically, the total amount of Ti, Nb, C, and N can range from 0.0050% to 0.0150% by weight.

[0055] According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 1.

[0056] [Formula 1]

[0057] 0.02≤([Ti]+[Nb])×[Mo] / ([C]+[N])≤ 0.05

[0058] In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the contents (by weight%) of Ti, Nb, Mo, C, and N, respectively.

[0059] When Equation 1 is satisfied, the formation of fine carbonitrides can be minimized. That is, if the value is in the range of 0.020 to 0.050, the formation of fine carbonitrides is suppressed, the distribution density of carbonitrides becomes minimal, and therefore can be managed within this range. More specifically, the value of Equation 1 can be between 0.030 and 0.060.

[0060] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Sn: 0.015 to 0.1 wt%, Sb: 0.015 to 0.1 wt%, and P: 0.005 to 0.05 wt%.

[0061] Sn, Sb: each representing 0.015 to 0.100% by weight.

[0062] Tin (Sn) and antimony (Sb) segregate on the surface and grain boundaries of the steel sheet, inhibiting surface oxidation during annealing, hindering element diffusion through grain boundaries, and impeding recrystallization of the {111} / / ND orientation, thus contributing to improved texture. If too little Sn and Sb are added, the effects may be insufficient. If too much Sn and Sb are added, increased grain boundary segregation leads to decreased toughness, potentially reducing productivity compared to improved magnetism. Therefore, Sn and Sb can each be contained in amounts from 0.015 to 0.100% by weight. More specifically, they can each be contained in amounts from 0.020 to 0.075% by weight.

[0063] P: 0.005 to 0.050% by weight

[0064] Phosphorus (P) segregates on the surface and grain boundaries of the steel sheet, inhibiting surface oxidation during annealing, hindering element diffusion across grain boundaries, impeding recrystallization of the {111} / / ND orientation, and improving texture. If too little P is added, the effect may be insufficient. If too much P is added, hot workability may decrease, and productivity may be reduced compared to the improvement in magnetic properties. Therefore, P can be contained in amounts from 0.005 to 0.050% by weight. More specifically, it can be further contained in amounts from 0.007 to 0.045% by weight.

[0065] According to one embodiment of the present invention, the non-oriented electrical steel sheet contains Cu: less than 0.01 wt%, S: less than 0.005 wt%, B: less than 0.002 wt%, Mg: less than 0.005 wt%, and Zr: less than 0.005 wt%, and may also contain more.

[0066] Cu: less than 0.01% by weight

[0067] Copper (Cu) is an element that can form sulfides at high temperatures, and its addition in large quantities can cause surface defects during slab manufacturing. Therefore, when Cu is added, it can be present in amounts of less than 0.01% by weight. More specifically, it can be present in amounts of 0.001 to 0.01% by weight.

[0068] S: less than 0.005% by weight

[0069] Sulfur (S) forms fine precipitates such as MnS, CuS, and (Mn,Cu)S, which degrade magnetic properties and hot workability; therefore, it is best to control its level at low levels. Thus, when S is added, it can be present in amounts of 0.005% by weight or less. More specifically, it can be present in amounts of 0.0001 to 0.005% by weight. More specifically, it can be present in amounts of 0.0005 to 0.0035% by weight.

[0070] B: less than 0.002% by weight, Mg: less than 0.005% by weight, Zr: less than 0.005% by weight

[0071] B, Mg, and Zr are elements that have an adverse effect on magnetism, and their content can be controlled within the specified range.

[0072] The balance includes Fe and unavoidable impurities. These unavoidable impurities are those introduced during the steelmaking process and the manufacturing process of the grain-oriented electrical steel sheet. These impurities are well-known in the art and therefore will not be specifically described. In one embodiment of the invention, the addition of elements other than the stated alloy composition is not excluded, and various elements may be included without prejudice to the spirit of the invention. When additional elements are further included, they replace a portion of the Fe in the balance.

[0073] According to an embodiment of the present invention, the density of one or more of carbides, nitrides, and carbonitrides with a particle size of less than 0.1 μm in the non-oriented electrical steel sheet can be 100 particles / mm². 2 the following.

[0074] According to one embodiment of the present invention, Mo is added in appropriate amounts relative to the contents of Ti and Nb, while containing a certain amount of Ti, Nb, C and N. During the steelmaking process, Mo reacts with Nb and Ti through bubbling. Through this process, the density of carbides, nitrides or carbonitrides (hereinafter collectively referred to as "carbonitrides") can be reduced as much as possible.

[0075] The lower limit for carbonitride particle size can be 0.02 μm. Carbonitride particles smaller than this size may not have a substantial effect on magnetism. Particle size can refer to the particle size of an imaginary circle with the same area as the carbonitride when observing the steel plate.

[0076] According to one embodiment of the invention, the measuring surface of the carbonitrides includes a certain amount of Ti, Nb, C, and N. Furthermore, during the steelmaking process, Mo is completely dissolved through the effect of Nb and Ti via bubbling, which can minimize the density of the carbides, nitrides, or carbonitrides (hereinafter also referred to as "carbonitrides"). A section perpendicular to the rolling direction (TD plane) can also be used. The carbonitrides can be observed using SEM.

[0077] The density of carbonitrides can be 100 per mm. 2 More specifically, it can contain 50 to 100 per mm. 2 .

[0078] According to an embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet can reach 50 μΩ·cm or higher. More specifically, it can reach 53 μΩ·cm or higher. More specifically, it can reach 58 μΩ·cm or higher. Although this is a particularly limited upper limit, it is 100 μΩ·cm or lower.

[0079] The non-oriented electrical steel sheet according to an embodiment of the present invention has improved magnetic permeability and is suitable for high-speed rotation. Therefore, when applied to the motors of environmentally friendly vehicles, it can help increase driving range. Specifically, the non-oriented electrical steel sheet according to an embodiment of the present invention can have a magnetic permeability of over 5000 at 30 A / m.

[0080] According to an embodiment of the present invention, the non-oriented electrical steel sheet may have an average grain size of 50 to 100 μm. Within this range, high-frequency iron loss is excellent. More specifically, the average grain size is 75 to 95 μm.

[0081] As described above, in one embodiment of the invention, magnetism can be improved by presenting an optimal alloy composition and minimizing carbonitrides. Specifically, the iron loss (W) of the non-oriented electrical steel sheet... 10 / 400 The magnetic flux density (B) can be below 12.5 W / kg. 50 The value is above 1.65T. Iron loss (W) 10 / 400 The term "iron loss" refers to the iron loss when a magnetic flux density of 1.0 T is applied at a frequency of 400 Hz. Magnetic flux density (B0) 50 ) is the magnetic flux density induced under a magnetic field of 5000 A / m. More specifically, the iron loss (W) of non-oriented electrical steel sheets 10 / 400 The flux density (B) can be 11.0 to 12.5 W / kg. 50 The capacity can be 1.65 to 1.70T.

[0082] A method for manufacturing non-oriented electrical 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 manufacturing a slab by continuous casting of molten steel; a step of hot rolling the slab into a hot-rolled plate; a step of cold rolling the hot-rolled plate into a cold-rolled plate; and a step of finally annealing the cold-rolled plate.

[0083] The steps are explained in detail below.

[0084] First, molten steel is produced.

[0085] Since the alloy composition of the steel used in manufacturing non-oriented electrical steel sheets has already been described previously, a repetition of that description is omitted. During the manufacturing process of non-oriented electrical steel sheets, the alloy composition does not undergo substantial changes; therefore, the alloy composition of non-oriented electrical steel sheets and molten steel is essentially the same.

[0086] Specifically, by weight percent, the molten steel contains 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 balance including Fe and unavoidable impurities, satisfying the following formula 1.

[0087] [Formula 1]

[0088] 0.02≤([Ti]+[Nb])×[Mo] / ([C]+[N])≤0.05

[0089] In Formula 1, [Ti], [Nb], [Mo], [C] and [N] represent the contents (by weight) of Ti, Nb, Mo, C and N, respectively.

[0090] The casting process of 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 Mo ferroalloys, Ti ferroalloys, Nb ferroalloys, etc.

[0091] Next, the molten steel will be bubbled for 5 to 10 minutes.

[0092] The bubbling at this point is achieved by adding raw materials such as Mo ferroalloy, Ti ferroalloy, and Nb ferroalloy to adjust all alloy compositions, which is different from the bubbling during deoxidation or desulfurization processes.

[0093] In addition, during the bubbling process after adding raw materials such as Mo ferroalloy, Ti ferroalloy, and Nb ferroalloy, an inert gas was used at a concentration of 5 Nm. 3 The above flow rate input differs from the bubbling processes used in existing steelmaking processes, such as deoxidation or desulfurization. The inert gas can be Ar. The flow rate can be 5 to 15 Nm³. 3 .

[0094] Bubbling can be performed for 5 to 10 minutes. Through bubbling, Mo reacts fully with Ti and Nb to achieve complete dissolution, minimizing the density of carbonitrides in the final manufactured electrical steel sheet. If the bubbling time is too short, the bubbling effect may be minimal. Even with extended bubbling times, Mo struggles to react with Ti and Nb, leading to increased costs due to reduced productivity.

[0095] When there is no bubbling in the molten steel, the carbonitrides of Ti and Nb exist in the molten steel in a fine form. They are redissolved in the slab reheating process and precipitated as even finer particles during the hot rolling process. Therefore, they are not removed during the hot-rolled plate annealing and final annealing processes, but are retained as is, leading to the deterioration of the magnetic properties of the final manufactured steel plate.

[0096] The next step is to manufacture slabs from continuously cast steel.

[0097] The slab manufacturing process can be performed using processes known in the art.

[0098] After the slab is manufactured, it can be heated. Specifically, the slab can be placed in a heating furnace and heated to a temperature between 1100°C and 1250°C. When the slab is heated to too high a temperature, precipitates such as AlN and MnS present in the slab will redissolve and precipitate finely during hot rolling and annealing, inhibiting grain growth and reducing magnetism.

[0099] The next step is to manufacture hot-rolled plates by hot rolling the slabs.

[0100] The thickness of hot-rolled steel sheets can be 2 to 2.3 mm. In the manufacturing process of hot-rolled steel sheets, the final rolling temperature can be above 800°C, specifically between 800 and 1000°C. Hot-rolled steel sheets can be wound at temperatures of 700°C or lower.

[0101] Following the manufacturing process of the hot-rolled sheet, an annealing step may be included. In this case, the annealing temperature can be between 850 and 1150°C. If the annealing temperature is too low, the microstructure will not grow or will grow very finely, making it difficult to obtain a magnetically favorable texture during post-annealing. If the annealing temperature is too high, excessive grain growth will occur, and surface defects will become excessive. Annealing of the hot-rolled sheet is performed to increase the magnetically favorable orientation as needed, and may be omitted. The annealed hot-rolled sheet may be pickled. More specifically, the annealing temperature can be between 950 and 1150°C.

[0102] The next step is to cold roll the hot-rolled sheet to produce cold-rolled sheet.

[0103] At this point, the reduction can be adjusted by changing the reduction ratio to 70% to 85%. If necessary, the cold rolling step may include one or two or more cold rolling steps with intermediate annealing interspersed therebetween. In this case, the intermediate annealing temperature may be between 850 and 1150°C.

[0104] The next step is to perform final annealing on the cold-rolled sheet.

[0105] In the degradation process of cold-rolled steel sheets, there are no major restrictions on the annealing temperature; any temperature commonly used for non-oriented electrical steel sheets is acceptable. Since the iron loss of non-oriented electrical steel sheets is closely related to grain size, a suitable annealing temperature is 8500 to 1000℃. Furthermore, the annealing time can be less than 100 seconds, allowing for short-time annealing.

[0106] In the final annealing process, the average grain size can be 50 to 100 μm, and the processed structure formed in the previous cold rolling step (i.e., 99% or more) can be recrystallized.

[0107] After final annealing, an insulating film can be formed. The insulating film can be organic film, inorganic film, or organic and inorganic composite film, and can also be treated with other insulating film-forming agents.

[0108] The invention will be described in more detail below by way of examples. However, the following examples are only illustrative and the invention is not limited to them.

[0109] Example 1

[0110] Table 1, S: 0.002 wt%, balance includes Fe and unavoidable impurities in the composition of cast steel. Based on the time summarized in Table 2, through 10 Nm... 3 Ar was added at a flow rate to cause it to bubble and prepare a slab. The slab was heated to 1150°C and hot-rolled at 850°C to produce a hot-rolled sheet with a thickness of 2.0 mm. The hot-rolled sheet was annealed at 1100°C for 4 minutes and then pickled. It was then cold-rolled to a thickness of 0.25 mm and finally annealed at the temperatures shown in Table 2 to produce a non-oriented electrical steel sheet. The initial permeability of 30 A / m was determined by cutting 5 specimens (60 mm wide × 60 mm long) using a single-sheet tester, and by averaging the values ​​in the rolling direction and perpendicular direction using a single-sheet tester, as summarized in Table 2 below.

[0111] For the carbonitride density, the number of carbonitride particles with a diameter less than 0.1 μm was observed on the TD surface of the sample using SEM, and the results were summarized. The average grain size was observed using electron microscopy, and the results are summarized in Table 2 below.

[0112] For grain growth, the final annealing temperature (°C) × final annealing time (minutes) / average grain size (μm) was calculated and summarized in Table 2 below.

[0113] Table 1

[0114]

[0115] Table 2

[0116]

[0117] As shown in Tables 1 and 2, it can be seen that, compared with Ti and Nb, the example of appropriate addition of Mo and bubbling of molten steel shows that less carbonitride is formed, and the magnetic permeability, magnetic flux density and iron loss are excellent.

[0118] On the other hand, it can be seen that steel grade 4 does not satisfy equation 1 due to the excessive addition of Mo. Mo and Si form compounds, resulting in a large number of fine carbonitrides, which have poor permeability and magnetism.

[0119] Steel grades 5 and 6 do not satisfy Equation 1 due to insufficient Mo addition, which confirms the formation of a large amount of carbonitrides, resulting in poor magnetic permeability and magnetism.

[0120] Grade 7 steel, with appropriate addition of alloying elements, but with excessively long bubbling time, caused oxides in the slag to re-oxidize and enter the molten steel, forming a large number of fine carbonitrides, resulting in poor magnetic permeability and magnetism.

[0121] In steel grade 9, excessive Nb was added and the bubbling time was too short, resulting in the formation of a large amount of carbonitrides, which leads to poor magnetic permeability and magnetism.

[0122] Steel grades 10 to 12 do not satisfy equation 1, resulting in the formation of a large number of carbonitrides, and thus poor magnetic permeability and magnetism.

[0123] Steel grade 14, with excessive N addition forming a large amount of carbonitrides, has poor magnetic permeability and magnetic properties.

[0124] Steel grade 15 has low Nb and C content, resulting in the formation of a large amount of Mo-Si compounds and numerous fine carbonitrides, leading to poor magnetic permeability and magnetism.

[0125] This invention is not limited to the embodiments described, and can be implemented and manufactured in various different ways. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, the embodiments described should be understood as exemplary in all respects and not restrictive.

Claims

1. A non-oriented electrical steel sheet, wherein, The steel plate, by weight percent, comprises Si: 2.0 to 3.8%, Al: 0.1 to 2.5%, Mn: 0.1 to 2.5%, Mo: 0.01 to 0.08%, Ti: 0.0010 to 0.0050%, Nb: 0.0010 to 0.0050%, C: 0.0020 to 0.0060%, and N: 0.0010 to 0.0050%, with the balance comprising Fe and unavoidable impurities, and satisfies the following formula 1. The total density of carbides, nitrides, and carbonitrides with a particle size of less than 0.1 μm is 100 particles / mm². 2 or smaller, [Formula 1] 0.02≤([Ti]+[Nb])×[Mo] / ([C]+[N])≤0.05 In Formula 1, [Ti], [Nb], [Mo], [C], and [N] represent the weight percentage of Ti, Nb, Mo, C, and N, respectively.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The total amount of Ti, Nb, C and N is 0.003 to 0.015 by weight.

3. The non-oriented electrical steel sheet according to claim 1, wherein, It further comprises one or more of Sn: 0.015 to 0.1 wt%, Sb: 0.015 to 0.1 wt%, and P: 0.005 to 0.05 wt%.

4. The non-oriented electrical steel sheet according to claim 1, wherein, It further comprises one or more of Cu: less than 0.01 wt%, S: less than 0.005 wt%, B: less than 0.002 wt%, Mg: less than 0.005 wt%, and Zr: less than 0.005 wt%.

5. The non-oriented electrical steel sheet according to claim 1, wherein, The resistivity is above 50 μΩ·cm.

6. The non-oriented electrical steel sheet according to claim 1, wherein, The average grain size is 50 to 100 μm.

7. The non-oriented electrical steel sheet according to claim 1, wherein, The permeability measured at 30 A / m is above 5000.

8. A method for manufacturing a non-oriented electrical steel sheet, comprising: The step of producing molten steel, by weight percent, wherein the molten steel comprises Si: 2.0 to 3.8%, Al: 0.1 to 2.5%, Mn: 0.1 to 2.5%, Mo: 0.01 to 0.08%, Ti: 0.0010 to 0.0050%, Nb: 0.0010 to 0.0050%, C: 0.0020 to 0.0060% and N: 0.0010 to 0.0050%, the balance comprising Fe and unavoidable impurities, and satisfying the following formula 1; The step of bubbling the molten steel for 5 to 10 minutes; The step of manufacturing slabs by continuous casting of the molten steel; The step of hot rolling the slab to produce a hot-rolled plate; The step of cold rolling the hot-rolled sheet to produce a cold-rolled sheet; as well as The final annealing step is performed on 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 weight % content of Ti, Nb, Mo, C and N, respectively.

9. The method for manufacturing non-oriented electrical steel sheet according to claim 8, wherein, The bubbling process involves using an inert gas at a concentration of 5 Nm. 3 The above traffic imports.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 8, wherein, The grain growth rate, calculated using Equation 2, is 10 to 15. [Equation 2] Grain growth = final annealing temperature × final annealing time / average grain size. The unit of the soaking temperature in the final annealing step is ℃, the unit of the soaking time in the final annealing step is minutes, and the unit of the average grain size is μm.

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