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

Abstract

The non-oriented electrical steel sheet according to one embodiment of the present application contains, in terms of weight %, Si: 3.3 to 4.0 %, Al: 0.4 to 1.5 %, Mn: 0.2 to 1.0 %, C: 0.0015 to 0.0040 %, N: 0.0005 to 0.0020 %, S: 0.0005 to 0.0025 %, Mo: 0.005 to 0.01 %, Ti: 0.0005 to 0.0020 %, Nb: 0.0005 to 0.0020 %, and V: 0.0005 to 0.0020 %, with the balance containing Fe and inevitable impurities.

Description

Technical Field

[0001] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same by appropriately adding Mo, Ti, Nb, and V, and controlling the cooling process after final annealing within a specific temperature range for a specified time to suppress the formation of fine carbonitrides. This relates to a non-oriented electrical steel sheet with excellent magnetic properties and strength, and a method for manufacturing the same. Background Technology

[0002] Electric motors, which convert electrical energy into mechanical energy, primarily use non-oriented electrical steel sheets. To achieve high efficiency in the energy conversion process, the properties of electrical steel sheets need further improvement.

[0003] In particular, with the recent surge in attention to environmentally friendly electric vehicles that replace internal combustion engines, the demand for non-oriented electrical steel sheets, used as core materials for electric motor drives, has been steadily increasing. Consequently, methods to simultaneously improve the magnetic properties and strength of non-oriented electrical steel sheets have attracted considerable attention.

[0004] The magnetic properties of non-oriented electrical steel are mainly evaluated using iron loss and magnetic flux density. Iron loss refers to the energy loss that occurs at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization achieved under a specific magnetic field. Lower iron loss allows for the manufacture of more energy-efficient motors under the same conditions, while higher magnetic flux density allows for smaller motors or reduced copper losses. Therefore, manufacturing non-oriented electrical steel sheets with low iron loss and high magnetic flux density is important. By using non-oriented electrical steel sheets with these properties, drive motors with excellent efficiency and torque can be manufactured, thereby improving the driving range and output power of environmentally friendly vehicles.

[0005] On the other hand, the properties of non-oriented electrical steel sheets should also take into account the operating conditions of the electric motor. As a common standard for evaluating the properties of non-oriented electrical steel sheets used in electric motors, the iron loss W15 / 50 under a 1.5T magnetic field at a commercial frequency of 50Hz is widely adopted. However, for non-oriented electrical steel sheets with a thickness of less than 0.35mm used in drive motors for environmentally friendly vehicles, the magnetic properties under low magnetic fields below 1.0T and high frequencies above 400Hz are often important. In many cases, the properties of non-oriented electrical steel sheets are evaluated using the W10 / 400 iron loss.

[0006] Furthermore, the high-efficiency non-oriented electrical steel sheet used in electric motors for environmentally friendly vehicles needs to possess excellent strength and magnetism. The drive motors for environmentally friendly vehicles are primarily designed with permanent magnets inserted into the rotor. To ensure the superior performance of permanent magnet insertion motors, the permanent magnets should be located outside the rotor, so that they are as close as possible to the stationary element.

[0007] However, if the strength of the electrical steel sheet is low, the permanent magnets inserted into the rotor may detach due to centrifugal force when the motor rotates at high speed. Therefore, high-strength electrical steel sheets are required to ensure the performance and durability of the motor.

[0008] A common method to simultaneously improve the magnetic properties and strength of non-oriented electrical steel sheets is to add alloying elements such as Si, Al, or Mn. By adding these alloying elements to increase the resistivity of the steel, eddy current losses can be reduced, thereby reducing total iron losses.

[0009] In addition, alloying elements are used as substitutes in iron and dissolved in solid solution to produce a strengthening effect and increase strength.

[0010] On the other hand, with the increase of alloying elements such as Si, Al, and Mn, there are disadvantages such as decreased magnetic flux density and increased brittleness. If the amount added exceeds a certain level, cold rolling is impossible, making commercial production impossible. In particular, the thinner the electrical steel sheet, the better the high-frequency iron loss, and the brittleness-induced deterioration of rollability becomes a fatal problem.

[0011] Depending on the design intent of the electric motor, electrical steel sheets with improved strength may be used even if magnetic properties are reduced. Methods for manufacturing electrical steel sheets for this purpose include methods utilizing interstitial element precipitation and methods refining the grain size.

[0012] In order to increase the speed by miniaturizing the motor or to enhance the effect of the permanent magnets inserted into the rotor, a rotor made of electrical steel sheet with significantly increased strength is used, although the magnetic properties of the electrical steel sheet are slightly reduced.

[0013] At this point, when fine precipitates containing interstitial solid solution elements such as C, N, and S are formed, although the strength increase is good, the iron loss deteriorates rapidly, which will reduce the efficiency of the motor. The disadvantage of the method of reducing grain size is that the inclusion of non-recrystallized parts increases the inhomogeneity of the steel plate material, thereby increasing the quality deviation of mass-produced products.

[0014] To address the aforementioned issues, a method exists for manufacturing non-oriented electrical steel sheets that simultaneously improve both magnetism and strength by controlling the cooling rate of the final annealing process. However, the steel sheets produced by this method suffer from material inhomogeneity due to the presence of unrecrystallized portions, making them unsuitable for mass production processes.

[0015] Furthermore, most previously proposed techniques for simultaneously improving magnetism and strength have been overlooked due to increased manufacturing costs, decreased productivity and yield, or poor improvement results. Summary of the Invention

[0016] (a) Technical problems to be solved

[0017] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same by appropriately adding Mo, Ti, Nb, and V, and controlling the cooling process after final annealing within a specific temperature range for a period of time to suppress the formation of fine carbonitrides.

[0018] (II) Technical Solution

[0019] According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight percent, 3.3 to 4.0% Si, 0.4 to 1.5% Al, 0.2 to 1.0% Mn, 0.0015 to 0.0040% C, 0.0005 to 0.0020% N, 0.0005 to 0.0025% S, 0.005 to 0.01% Mo, 0.0005 to 0.0020% Ti, 0.0005 to 0.0020% Nb, and 0.0005 to 0.0020% V, with the balance comprising Fe and unavoidable impurities.

[0020] It satisfies the following equation 1.

[0021] [Formula 1]

[0022] 1.75≤([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≤4.00

[0023] (In Formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (by weight%) of Mo, Ti, Nb, V, C, and N, respectively.)

[0024] According to an embodiment of the present invention, a non-oriented electrical steel sheet,

[0025] According to one embodiment of the present invention, the non-oriented electrical steel sheet has an average grain diameter of 55 to 80 μm.

[0026] According to one embodiment of the present invention, the distribution density of at least one of carbides, nitrides, and carbonitrides with a particle size of less than 50 nm in the non-oriented electrical steel sheet is 0.5 particles / mm². 2 the following.

[0027] The value calculated using Equation 2 below is between 500 and 2000.

[0028] [Equation 2]

[0029] [Average grain diameter (μm)] 2 ×[Distribution density (pcs / mm) of at least one of carbides, nitrides, and carbonitrides with a grain diameter of less than 50 nm] 2 )]

[0030] According to one embodiment of the present invention, the non-oriented electrical steel sheet further comprises at least one of Sn: 0.015 to 0.1 wt%, Sb: 0.015 to 0.1 wt%, and P: 0.005 to 0.05 wt%.

[0031] According to one embodiment of the present invention, the non-oriented electrical steel sheet further comprises at least one of Cu: less than 0.05 wt%, B: less than 0.002 wt%, Mg: less than 0.005 wt%, and Zr: less than 0.005 wt%.

[0032] According to one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet is 50 μΩ·cm or higher.

[0033] According to one embodiment of the present invention, the non-oriented electrical steel sheet has a density of 7.55 g / cm³. 3 above.

[0034] According to an embodiment of the present invention, a non-oriented electrical steel sheet with a 0.2% offset yield strength (R p0.2 )440MPa or above.

[0035] According to an embodiment of the present invention, a non-oriented electrical steel sheet with a 0.2% offset yield strength (R p0.2 ) is the upper yield strength (R) eH More than 98.5% of them.

[0036] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the step of manufacturing a slab, wherein the slab comprises, by weight percent, Si: 3.3 to 4.0%, Al: 0.4 to 1.5%, Mn: 0.2 to 1.0%, C: 0.0015 to 0.0040%, N: 0.0005 to 0.0020%, S: 0.0005 to 0.0025%, Mo: 0.005 to 0.01%, Ti: 0.0005 to 0.0020%, Nb: 0.0005 to 0.0020%, and V: 0.0005 to 0.0020%, with the balance comprising Fe and unavoidable impurities, satisfying Formula 1; the step of hot rolling the slab to manufacture a hot-rolled sheet; the step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and the step of final annealing the cold-rolled sheet.

[0037] [Formula 1]

[0038] 1.75≤([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≤4.00

[0039] (In Formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (by weight%) of Mo, Ti, Nb, V, C, and N, respectively.)

[0040] The final annealing step includes a homogenization step at a homogenization temperature of 910 to 1000°C, and a cooling step of cooling from the homogenization temperature to 600°C within 25 seconds.

[0041] The process further includes, after the step of manufacturing the hot-rolled sheet, an annealing step at a temperature of 850 to 1150°C.

[0042] The final annealing step is performed in an atmosphere of mixed hydrogen (H2) and nitrogen (N2).

[0043] (III) Beneficial Effects

[0044] According to one embodiment of the present invention, by providing a non-oriented electrical steel sheet that simultaneously improves magnetism and strength, it is helpful to improve the performance of the drive motor of an environmentally friendly vehicle. Attached Figure Description

[0045] Figure 1 This is a temperature diagram of the final annealing process in one embodiment of the present invention.

[0046] Figure 2 This is a TEM image of the cross-section measured using steel grade B1.

[0047] Figure 3 This is a TEM image of the cross-section measured using steel grade B3. Detailed Implementation

[0048] 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.

[0049] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in the specification can specifically refer to a particular 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, components, and / or groups.

[0050] 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.

[0051] Additionally, unless otherwise specified, % indicates weight, and 1 ppm is 0.0001 wt%.

[0052] 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.

[0053] 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.

[0054] Embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0055] According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight percent, 3.3 to 4.0% Si, 0.4 to 1.5% Al, 0.2 to 1.0% Mn, 0.0015 to 0.0040% C, 0.0005 to 0.0020% N, 0.0005 to 0.0025% S, 0.005 to 0.01% Mo, 0.0005 to 0.0020% Ti, 0.0005 to 0.0020% Nb, and 0.0005 to 0.0020% V, with the balance comprising Fe and unavoidable impurities.

[0056] The reasons for the compositional restrictions on non-oriented electrical steel sheets are explained below.

[0057] Si: 3.3 to 4.0% by weight

[0058] Silicon (Si) increases the resistivity of materials, reduces iron loss, and improves strength through solid solution strengthening. If the amount of Si added is too small, the effect on improving iron loss and strength may be insufficient. When the amount of Si added is too large, rolling productivity drops rapidly due to increased brittleness of the material, and there is a problem of forming oxide layers and surface oxides that are detrimental to magnetism. Therefore, 3.3 to 4.0 wt% Si may be included. More specifically, 3.4 to 3.6 wt% Si may be included.

[0059] Al: 0.40 to 1.50% by weight

[0060] Aluminum (Al) plays a crucial role in increasing resistivity and reducing iron loss, and also enhances strength through solid solution strengthening. If too little Al is added, the improvement in magnetic properties will 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 may occur, potentially degrading the magnetism and causing problems in all processes, including steelmaking and continuous casting, thus reducing productivity. Therefore, 0.4 to 1.5% by weight of Al may be included. More specifically, 0.5 to 1.0% by weight may be included.

[0061] Mn: 0.20 to 1.00% by weight

[0062] Manganese (Mn) improves iron loss by increasing resistivity and forms sulfides. If too little Mn is added, fine MnS forms, causing magnetic degradation; if too much Mn is added, excessive fine MnS precipitates, promoting the formation of an unfavorable {111} texture and leading to a rapid decrease in magnetic flux density. Therefore, it may contain 0.2% to 1.0% by weight of Mn. More specifically, it may contain 0.30% to 0.70% by weight.

[0063] C: 0.0015 to 0.0040% by weight

[0064] Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, which reduces magnetism, hinders dislocation slip, and plays a role in improving strength.

[0065] If too little carbon is added, the strength improvement effect will be insufficient. If the carbon content is too high, the magnetic properties will deteriorate due to the increase of fine carbides.

[0066] Therefore, it may contain 0.0015 to 0.0040% by weight of C. More specifically, it may contain 0.0020 to 0.0038% by weight.

[0067] N: 0.0005 to 0.0020% by weight

[0068] Nitrogen (N) not only forms fine AlN precipitates within the steel sheet, but also combines with other impurities to form fine precipitates that inhibit grain growth and worsen iron loss. On the other hand, it also increases strength. If too little nitrogen is added, the strength may not be sufficiently improved. If too much nitrogen is added, the fine nitrides increase, causing a sharp deterioration in iron loss. Therefore, it may contain 0.0005 to 0.0020% by weight of N. Specifically, it may contain 0.0008 to 0.0018% by weight.

[0069] S: 0.0005 to 0.0025% by weight

[0070] Sulfur (S) forms fine precipitates called MnS, which degrade magnetic properties and hot workability; therefore, its content is best kept low. However, if too little S is added, the magnetic flux density may decrease. Therefore, it may contain 0.0005 to 0.0025% by weight of S. Specifically, it may contain 0.0010 to 0.0023% by weight.

[0071] Mo: 0.0050 to 0.0100 wt%

[0072] Molybdenum (Mo) segregates at grain boundaries during annealing to suppress the development of {111} textures that are detrimental to magnetism, and increases strength by forming fine carbides during cooling.

[0073] If too little Mo is added, its effect is minimal; if too much Mo is added, it promotes carbide formation and degrades the magnetism. Therefore, it may contain 0.005 to 0.01% by weight of Mo. Specifically, it may contain 0.0060 to 0.0090% by weight.

[0074] Ti, Nb, V: 0.0005 to 0.0020 wt%, respectively.

[0075] Titanium (Ti), niobium (Nb), and vanadium (V) have a strong tendency to precipitate in steel.

[0076] Iron loss is degraded by inhibiting grain growth and domain wall movement through the formation of fine carbides, nitrides, or sulfides within the base material. Therefore, the upper limits for Ti, Nb, and V need to be appropriately adjusted. On the other hand, if their content is too low, the strength of the electrical steel sheet may be significantly reduced. Therefore, 0.0005 to 0.0020 wt% Ti, Nb, and V may be included, respectively. Specifically, 0.0007 to 0.0018 wt% may be included.

[0077] Ti+Nb+V: 0.0030 to 0.0050 wt%

[0078] As mentioned above, Ti, Nb, and V play a role in improving strength, and therefore are preferably contained in amounts of 0.0030% by weight or more. When their content is excessive, fine carbides, nitrides, or sulfides are formed, which inhibit grain growth and domain wall movement, thereby deteriorating iron loss.

[0079] According to an embodiment of the present invention, the non-oriented electrical steel sheet satisfies the following formula 1.

[0080] [Formula 1]

[0081] 1.75≤([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≤4.00

[0082] (In Formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (by weight%) of Mo, Ti, Nb, V, C, and N, respectively.)

[0083] When Equation 1 is satisfied, the formation of fine carbonitrides can be minimized. That is, in the range of 1.75 to 4.00, the formation of fine carbonitrides is suppressed, the distribution density of carbonitrides can be minimized, and therefore it can be managed within this range. If the value of Equation 1 is too low, there may be problems with strength.

[0084] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain at least one of Sn: 0.015 to 0.1 wt%, Sb: 0.015 to 0.1 wt%, and P: 0.005 to 0.05 wt%.

[0085] Sn, Sb: 0.015 to 0.100% by weight each

[0086] Tin (Sn) and antimony (Sb) segregate on the surface and at grain boundaries of the steel sheet to suppress surface oxidation during annealing. They also hinder element diffusion through grain boundaries, preventing recrystallization of the {111} / / ND orientation and improving texture. If too little Sn and Sb are added, the above effects may be insufficient. When too much Sn and Sb are added, increased grain boundary segregation leads to decreased toughness, which may reduce productivity compared to improved magnetism. Therefore, each may further contain 0.015 to 0.100 wt% Sn and Sb. Specifically, each contains 0.020 to 0.075 wt%.

[0087] P: 0.005 to 0.050% by weight

[0088] Phosphorus (P) segregates on the surface and at grain boundaries of the steel sheet to suppress surface oxidation during annealing. It also hinders element diffusion across grain boundaries, preventing recrystallization of the {111} / / ND orientation and improving texture. If too little P is added, the above effects may be insufficient. If too much P is added, hot workability may decrease, and productivity may decrease compared to the improvement in magnetic properties. Therefore, 0.005 to 0.050 wt% P may be included. Specifically, 0.0007 to 0.045 wt% P may be included.

[0089] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain at least one of Cu: less than 0.05 wt%, B: less than 0.002 wt%, Mg: less than 0.005 wt%, and Zr: less than 0.005 wt%.

[0090] Cu: less than 0.05% by weight

[0091] Copper (Cu) is an element that can form sulfides at high temperatures. When added in large quantities, it can cause surface defects during the manufacturing of slabs.

[0092] Therefore, when further comprising Cu, it may contain less than 0.05% by weight of Cu. Specifically, it may contain 0.001 to 0.05% by weight.

[0093] B: less than 0.002% by weight, Mg: less than 0.005% by weight, and Zr: less than 0.005% by weight.

[0094] B, Mg, and Zr are elements that have an adverse effect on magnetism, and their content may be further included within the range mentioned above.

[0095] The balance includes Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking process and the manufacturing process of grain-oriented electrical steel sheets; these impurities are well-known in the art and therefore omitted in detail. In one embodiment of the invention, the addition of other elements besides the aforementioned alloy composition is not excluded, and various elements may be included without affecting the technical concept of the invention. When additional elements are further included, they replace a portion of the Fe in the balance.

[0096] According to one embodiment of the invention, the average grain diameter of the non-oriented electrical steel sheet is 55 to 80 μm. If the average grain diameter is too small, the iron loss may deteriorate. If the average grain diameter is too large, the strength may weaken. More specifically, the average grain diameter may be 58 to 75 μm.

[0097] According to one embodiment of the present invention, the density of at least one of carbides, nitrides, and carbonitrides with a particle size of less than 50 nm in the non-oriented electrical steel sheet is 0.5 particles / mm². 2 the following.

[0098] In one embodiment of the invention, the density of carbides, nitrides, or carbonitrides (hereinafter collectively referred to as "carbonitrides") can be reduced as much as possible by controlling the content of Mo, Ti, Nb, V, C, and N to a certain amount or more, appropriately adding Mo, Ti, Nb, and V relative to the C and N content, and adjusting the cooling time in the final annealing process.

[0099] The lower limit for carbonitride particle size is 5 nm. Carbonitride particles smaller than this size may not have a substantial effect on magnetism. The grain diameter can be the grain diameter of the circle described below. This circle refers to an imaginary circle with an area assumed to be the same as the area of ​​the carbonitride when observing the steel sheet. The measurement surface for carbonitrides can be a surface (ND surface) or a cross-section (TD surface, RD surface). Carbonitrides can be observed using TEM. Carbonitrides refer to particulate fractions with a high C and / or N content relative to the base material of the steel sheet.

[0100] The distribution density of carbonitrides can be 0.5 particles / mm². 2 Specifically, the number can be from 0.05 to 0.50 per mm. 2 More specifically, it can be 0.10 to 0.40 per mm. 2 When carbides, nitrides, or carbonitrides are present simultaneously, the distribution density is the sum of their components.

[0101] According to one embodiment of the present invention, the value of the non-oriented electrical steel sheet calculated by the following formula 2 is 500 to 2000.

[0102] [Equation 2]

[0103] [Average grain diameter (μm)] 2 ×[Distribution density (pcs / mm) of at least one of carbides, nitrides, and carbonitrides with a grain diameter of less than 50 nm] 2 )]

[0104] When the value of Equation 2 is between 500 and 2000, the strength can be increased while improving the magnetism.

[0105] According to one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet is 50 μΩ·cm or higher. Specifically, it is 53 μΩ·cm or higher. More specifically, it is 58 μΩ·cm or higher. Although there is no particular upper limit, it can be 100 μΩ·cm or lower.

[0106] According to one embodiment of the present invention, the density of the non-oriented electrical steel sheet can be 7.55 g / cm³. 3 That's all. In one embodiment of the invention, improved strength can be obtained while maintaining a suitable density. Specifically, the density can be from 7.55 to 8.00 g / cm³. 3 .

[0107] According to one embodiment of the present invention, a non-oriented electrical steel sheet possesses both excellent strength and magnetic properties. Specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention can have a 0.2% offset yield strength (R0.2) of 440 MPa or higher. p0.2When an electric motor rotates at high speed, it experiences significant stress along the direction from the inside out. This is particularly true in the case of permanent magnet insertion motors, where arranging the permanent magnets at the ends of the rotor can improve efficiency. However, when using electrical steel sheets with low yield strength, the permanent magnets inserted into the rotor can deform and break at the rotor ends due to centrifugal force during motor rotation, potentially leading to durability issues. Therefore, the mechanical properties of the steel sheet are important, which can be controlled by adjusting the yield strength by 0.2% (R0.2). p0.2 To confirm. More specifically, 0.2% offset yield strength (R) p0.2 The pressure can be 440 to 460 MPa.

[0108] In addition, in one embodiment of the present invention, the reduction in yield strength is less even when tension is applied compared to before tension is applied, so the strength of the motor can be maintained even when the motor rotates at high speed.

[0109] Specifically, 0.2% offset yield strength (R p0.2 ) can be the upper yield strength (R) eH More than 98.5% of the yield strength. More specifically, 0.2% offset yield strength (R p0.2 ) can be the upper yield strength (R) eH The yield strength is 98.5% to 99.9% of the total yield strength. The yield strength can be measured according to ISO 6892 by performing a tensile test on a specimen with a parallel section length of 80 mm and measuring the yield strength under 0.2% tension or no tension.

[0110] According to one embodiment of the present invention, the non-oriented electrical steel sheet may have a magnetic flux density (B50) of 1.66 T or more. Here, B50 represents the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, the magnetic flux density (B50) may be 1.67 to 1.70 T.

[0111] According to one embodiment of the present invention, the iron loss (W10 / 400) of the non-oriented electrical steel sheet can be 12.0 W / kg or less. W10 / 400 refers to the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. More specifically, the iron loss (W10 / 400) can be 10.5 to 11.5 W / kg. The standard thickness for measuring iron loss can be 0.30 mm.

[0112] A method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention includes: a step of manufacturing 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.

[0113] The following is a detailed explanation of each step.

[0114] First, the slab is manufactured.

[0115] Regarding the alloy composition of the slab, the alloy composition of the non-oriented electrical steel sheet has already been described, so a repeat description is omitted. The alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet; therefore, the alloy composition of the non-oriented electrical steel sheet and the slab is actually the same.

[0116] Specifically, by weight percent, the slab comprises Si: 3.3 to 4.0%, Al: 0.4 to 1.5%, Mn: 0.2 to 1.0%, C: 0.0015 to 0.0040%, N: 0.0005 to 0.0020%, S: 0.0005 to 0.0025%, Mo: 0.005 to 0.01%, Ti: 0.0005 to 0.0020%, Nb: 0.0005 to 0.0020%, and V: 0.0005 to 0.0020%, with the balance comprising Fe and unavoidable impurities, satisfying the following formula 1.

[0117] [Formula 1]

[0118] 1.75≤([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≤4.00

[0119] (In Formula 1, [Mo], [Ti], [Nb], [V], [C], and [N] represent the contents (by weight%) of Mo, Ti, Nb, V, C, and N, respectively.)

[0120] The slab manufacturing process can be performed using processes known in the art.

[0121] The slab manufacturing process can be carried out using processes known in the art.

[0122] After the slab is manufactured, it can be heated.

[0123] Specifically, the slab can be placed in a heating furnace and heated to a temperature below 1200℃. When the slab is heated to too high a temperature, precipitates such as AlN and MnS present in the slab will dissolve again and precipitate out finely during hot rolling and annealing, inhibiting grain growth and causing magnetic degradation.

[0124] Next, hot-rolled sheets are manufactured by hot rolling the slab. The thickness of the hot-rolled sheet can be 2 to 2.3 mm. In the manufacturing process of the hot-rolled sheet, the final rolling temperature can be above 800°C. Specifically, it can be 800–1000°C. The hot-rolled sheet can be coiled at a temperature below 700°C.

[0125] After 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 be very small, making it difficult to obtain a magnetically favorable texture during cold rolling followed by annealing.

[0126] If the annealing temperature is too high, the grains may overgrow and the surface defects of the plate may become excessive. Annealing of hot-rolled plates is performed as needed to improve the orientation favorable to magnetism and can be omitted. The annealed hot-rolled plate can be pickled. More specifically, the annealing temperature for hot-rolled plates can be from 950 to 1150°C.

[0127] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. At this stage, the reduction rate can be adjusted to 70% to 85%. Depending on the requirements, the cold rolling step may include one cold rolling step or two or more cold rolling steps with intermediate annealing interspersed. The intermediate annealing temperature can be 850 to 1150°C. The thickness of the cold-rolled sheet can be 0.10 to 0.35 mm.

[0128] Next, the cold-rolled sheet undergoes final annealing. During the annealing process, there are no particular restrictions on the annealing temperature, as long as the temperature is generally applicable to non-oriented electrical steel sheets.

[0129] The iron loss of non-oriented electrical steel sheets is closely related to the grain diameter, therefore it can be kept within a soaking temperature range of 910 to 1000℃ (T max Annealing is performed at a temperature of 100 seconds or less. At this temperature, the soaking temperature refers to a state where there is almost no temperature fluctuation. Alternatively, annealing can be performed with a short soaking time of less than 100 seconds.

[0130] Then, within 25 seconds (t), from the homogenization temperature (T) max Cooled to 600°C. By cooling in such a short time, the formation of fine carbonitrides can be suppressed to the maximum extent, thus inhibiting irregular grain growth. More specifically, the temperature is reduced from the homogenization temperature (T) to 600°C within 15 to 23 seconds (t). max Cool to 600℃.

[0131] Figure 1 This is a schematic diagram of the heat spreader temperature and cooling time (t) according to an embodiment of the present invention.

[0132] The final annealing step can be performed in an atmosphere containing a mixture of hydrogen (H2) and nitrogen (N2). Specifically, annealing can be performed in an atmosphere containing 5 to 40 vol% hydrogen and 60% to 95 vol% nitrogen. Annealing in the above atmosphere has the advantage of preventing the formation of fine oxides at high temperatures that are detrimental to magnetism.

[0133] During the final annealing process, the average grain diameter formed can be 55 to 80 μm, and all the processed structures formed in the previous cold rolling steps (i.e., more than 99%) can be recrystallized.

[0134] After final annealing, an insulating film can be formed. This insulating film can be treated with organic, inorganic, or organic / inorganic composite film layers, or with other insulating films.

[0135] The invention will be described in more detail below by way of examples. However, these examples are merely illustrative and the invention is not limited to the examples described herein.

[0136] Example 1

[0137] Slabs were prepared according to Table 1 and the composition including Fe and unavoidable impurities.

[0138] The slab was heated to 1,150°C and hot-rolled at a finishing temperature of 880°C to prepare a hot-rolled sheet with a thickness of 2.0 mm. The hot-rolled sheet was annealed at 1020°C for 100 seconds and then cold-rolled to a thickness of 0.25 mm. It was then subjected to a final annealing at the temperatures specified in Table 2 for 100 seconds.

[0139] The calculated values ​​of Equation 1 for each sample, the cooling time from the homogenization temperature to 600°C during final annealing, the distribution density of (Mo, Ti, Nb, V) and (C, N) precipitates with diameters less than 50 nm, the average grain diameter, and the upper yield strength (R) eH ), 0.2% offset yield strength (R p0.2 ), R p0.2 / R eH The magnetic properties are shown in Table 2.

[0140] The content of each component was determined by ICP wet method.

[0141] The cooling time from the highest temperature to 600°C was measured by directly measuring the plate temperature with TC attached to the sample surface.

[0142] TEM samples were prepared using a replication method and observed at high magnification at a depth of 0.5 mm. 2 The above area, when a carbide or nitride with a diameter of less than 50 nm and containing one of Mo, Ti, Nb and V is found, is used to calculate the distribution density by dividing its quantity by the observed area.

[0143] The grain diameter is calculated by polishing and etching the cross-section of the sample in the rolling direction, and photographing the area containing more than 1500 grains using an optical microscope, and then calculating (measured area ÷ number of grains)^0.5.

[0144] Yield strength, conforming to ISO 6892 standard, is determined by tensile testing using specimens with a parallel section length of 80 mm, and the results are displayed.

[0145] Magnetic properties such as magnetic flux density and iron loss were measured by cutting each sample into 5 pieces (60mm wide × 60mm long). The magnetic flux density and iron loss were measured in the rolling direction and perpendicular direction using a single sheet tester.

[0146] Table 1

[0147]

[0148] Table 2

[0149]

[0150] Table 3

[0151]

[0152] As shown in Tables 1 to 3, the invention example, by appropriately adjusting the alloy composition and shortening the cooling time during final annealing, achieved excellent magnetic properties with high Rp0.2 (above 440 MPa) and superior magnetic properties due to proper control of carbonitride distribution and particle size.

[0153] It was also confirmed that in A1 and D2, the strength characteristics were poor because the value of Equation 1 was too small.

[0154] When the factor 1 values ​​of B2 and C2 are too large, a large amount of carbonitrides are generated, resulting in a decrease in magnetic properties.

[0155] It can be confirmed that due to the excessively long cooling time, B1 and C1 generated a large amount of carbonitrides, resulting in a decrease in magnetic properties.

[0156] It can be confirmed that A2 has poor strength properties due to its excessively high homogenization temperature, large grain size, and poor strength characteristics.

[0157] It can be confirmed that the soaking temperature of D1 is too low, the grains are too small, and the strength and magnetism are both poor.

[0158] It can be confirmed that D5 and D6 have low Mo, Ti, Nb, and V contents, resulting in poor strength and magnetism.

[0159] This invention can be implemented in various ways and is not limited to the embodiments described above. 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, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

Claims

1. A non-oriented electrical steel sheet, wherein, The non-oriented electrical steel sheet, by weight percent, comprises Si: 3.3 to 4.0%, Al: 0.4 to 1.5%, Mn: 0.2 to 1.0%, C: 0.0015 to 0.0040%, N: 0.0005 to 0.0020%, S: 0.0005 to 0.0025%, Mo: 0.005 to 0.01%, Ti: 0.0005 to 0.0020%, Nb: 0.0005 to 0.0020%, and V: 0.0005 to 0.0020%, with the balance comprising Fe and unavoidable impurities. Satisfy the following equation 1, The average grain diameter is 55 to 80 μm. The total distribution density of carbides, nitrides, and carbonitrides with a particle size of less than 50 nm is 0.5 particles / mm. 2 the following, [Formula 1] 1.75≤([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≤4.00 In Formula 1, [Mo], [Ti], [Nb], [V], [C] and [N] represent the weight % content of Mo, Ti, Nb, V, C and N, respectively.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The value calculated using Equation 2 below is between 500 and 2000. [Equation 2] [Average grain diameter, μm] 2 ×[Total distribution density of carbides, nitrides, and carbonitrides with a particle size of less than 50 nm, particles / mm] 2 ].

3. The non-oriented electrical steel sheet according to claim 1, wherein, It further comprises at least one 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 at least one of Cu: less than 0.05 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 density is 7.55 g / cm³. 3 above.

7. The non-oriented electrical steel sheet according to claim 1, wherein, 0.2% offset yield strength (R) p0.2 ) 440MPa and above.

8. The non-oriented electrical steel sheet according to claim 1, wherein, 0.2% offset yield strength (R) p0.2 ) is the upper yield strength (R) eH More than 98.5% of them.

9. A method for manufacturing a non-oriented electrical steel sheet, wherein, The manufacturing method includes the step of manufacturing a slab, wherein the slab, by weight percent, comprises Si: 3.3 to 4.0%, Al: 0.4 to 1.5%, Mn: 0.2 to 1.0%, C: 0.0015 to 0.0040%, N: 0.0005 to 0.0020%, S: 0.0005 to 0.0025%, Mo: 0.005 to 0.01%, Ti: 0.0005 to 0.0020%, Nb: 0.0005 to 0.0020%, and V: 0.0005 to 0.0020%, with the balance comprising Fe and unavoidable impurities, satisfying the following formula 1. The steps of hot rolling a slab to manufacture a hot-rolled plate; The steps of cold rolling hot-rolled sheet to manufacture cold-rolled sheet; as well as The final annealing step is performed on the cold-rolled sheet. The final annealing step includes a homogenization process at a homogenization temperature of 910 to 1000°C, followed by a cooling process from the homogenization temperature to 600°C within 25 seconds. [Formula 1] 1.75≤([Mo]+[Ti]+[Nb]+[V]) / ([C]+[N])≤4.00 In Formula 1, [Mo], [Ti], [Nb], [V], [C] and [N] represent the weight % content of Mo, Ti, Nb, V, C and N, respectively.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The process further includes, after the step of manufacturing the hot-rolled sheet, an annealing step at a temperature of 850 to 1150°C.

11. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The final annealing step is performed in an atmosphere of mixed hydrogen (H2) and nitrogen (N2).

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