Non-oriented electrical steel sheet, SRA heat-treated non-oriented electrical steel sheet, and their manufacturing method

Abstract

Provided are a non-oriented electrical steel sheet having excellent strength characteristics after final annealing, an SRA heat-treated non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics after SRA heat treatment, and a method for manufacturing the same. [Solution] The alloy contains, by weight, 2.8 to 4.0% Si, 0.05 to 1.2% Mn, 0.1 to 1.2% Al, 0.005% or less (excluding 0%) C, 0.003% or less (excluding 0%) S, 0.005% or less (excluding 0%) N, 0.005% or less (excluding 0%) Ti, 0.005% or less (excluding 0%) B, 0.0005% or less (excluding 0%) Bi, one or more of 0.001 to 0.08% Sn and 0.001 to 0.08% Sb, with the balance being Fe and other unavoidable impurities, The non-oriented electrical steel sheet satisfies the following relational expression 1, has an average crystal grain size of 5 to 25 μm, and contains 0.1% or less of the total of Sn and Sb. The non-oriented electrical steel sheet has a thickness of 0.15 to 0.25 mm and a yield strength of 490 to 570 MPa. [Relationship 1] B / 10.81 + Bi / 208.98≦0.00007

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet, a non-oriented electrical steel sheet that has been subjected to SRA heat treatment (stress relief annealing), and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet that has excellent high-frequency iron loss characteristics after SRA heat treatment, a non-oriented electrical steel sheet that has been subjected to SRA heat treatment, and a manufacturing method thereof. [Background technology]

[0002] Recently, as demand for energy conservation in electrical equipment has increased, there has been a demand for better magnetic properties in the non-oriented electrical steel sheets used in the iron cores (motor cores) of rotating machines.

[0003] Motor cores are divided into stator cores and rotor cores, and in recent years, to meet the demand for smaller size and higher output for drive motors for HEVs (Hybrid Electric Vehicles), there has been a strong demand for non-oriented electrical steel sheets used in stator cores to have excellent magnetic properties such as high magnetic flux density and low iron loss.

[0004] As a means of achieving the miniaturization and high output of HEV drive motors and the like, there is a trend toward increasing motor rotation speeds. However, because HEV drive motors have large outer diameters, large centrifugal forces act on the rotor core, and depending on the structure, there are extremely narrow sections (1 to 2 mm) called rotor core bridges. For these reasons, the non-oriented electrical steel sheets used in rotor cores are required to be stronger than ever before.

[0005] Therefore, the ideal properties of non-oriented electrical steel sheets used in motor cores are not only excellent magnetic properties, but also high strength for rotor cores and higher magnetic flux density and lower iron loss for stator cores.Thus, even when using the same non-oriented electrical steel sheets for motor cores, the required properties for rotor cores and stator cores are significantly different.However, from the perspective of increasing material yield, when manufacturing motor cores, it is preferable to simultaneously extract the rotor core material and the stator core material from the same steel sheet, and then stack the respective core materials to assemble them into the rotor core or stator core.

[0006] On the other hand, in the case of rotors, high strength is advantageous in preventing fracture during rotation, and in particular, high strength in all directions, rather than in a specific direction, is advantageous in motor design. This is because rotors are made circular and rotate, so they are subjected to tensile forces in all directions. Therefore, if a rotor is designed with only consideration for strength in a specific direction, the strength in other directions during rotation will be weak, and fracture may occur.

[0007] Furthermore, when manufacturing rotors, a punching process using a die is used, and if the strength of the steel sheet varies greatly in different directions, differences in workability in different directions will appear during punching, which will cause difficulties in mass production. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a non-oriented electrical steel sheet having excellent strength properties after final annealing, and a method for producing the same.

[0009] The present invention provides an SRA heat-treated non-oriented electrical steel sheet that is excellent in high-frequency iron loss characteristics after SRA heat treatment, and a method for manufacturing the same. [Means for solving the problem]

[0010] The non-oriented electrical steel sheet of the present invention is characterized by containing, by weight%, 2.8 to 4.0% Si, 0.05 to 1.2% Mn, 0.1 to 1.2% Al, 0.005% or less (excluding 0%) C, 0.003% or less (excluding 0%) S, 0.005% or less (excluding 0%) N, 0.005% or less (excluding 0%) Ti, 0.0005% or less (excluding 0%) B, 0.0005% or less (excluding 0%) Bi, one or more of 0.001 to 0.08% Sn and 0.001 to 0.08% Sb, with the balance being Fe and other unavoidable impurities, satisfying the following relational expression 1, and having an average crystal grain size of 5 to 25 μm.

[0011] [Equation 1] B / 10.81+Bi / 208.98≦0.00007

[0012] The total content of Sn and Sb may be 0.1% or less.

[0013] The non-oriented electrical steel sheet may have a thickness of 0.15 to 0.25 mm.

[0014] The non-oriented electrical steel sheet may have a yield strength of 490 to 570 MPa.

[0015] The non-oriented electrical steel sheet of the present invention is characterized by having, by weight%, Si: 2.8 to 4.0%, Mn: 0.05 to 1.2%, Al: 0.1 to 1.2%, C: 0.005% or less (excluding 0%), S: 0.003% or less (excluding 0%), N: 0.005% or less (excluding 0%), Ti: 0.005% or less (excluding 0%), B: 0.0005% or less (excluding 0%), Bi: 0.005% or less (excluding 0%), one or more of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and the balance being Fe and other unavoidable impurities, satisfying the following relational expression 1, and having an average crystal grain size of 70 to 110 μm, having been subjected to SRA heat treatment.

[0016] [Equation 1] B / 10.81+Bi / 208.98≦0.00007

[0017] The total content of Sn and Sb may be 0.1% or less.

[0018] The non-oriented electrical steel sheet may have a thickness of 0.15 to 0.25 mm.

[0019] The non-oriented electrical steel sheet may have a magnetic flux density (B50) of 1.544+0.28×t+0.0014 / t (t: thickness of the steel sheet) Tesla or more.

[0020] The iron loss (W10 / 400) of the above non-oriented electrical steel sheet is 7.15 + 15.8 × t + 0.0015 × (d - 91.7) 2 (t: thickness of steel sheet, d: average grain size) W / Kg or less.

[0021] The method for producing a non-oriented electrical steel sheet of the present invention contains, by weight, Si: 2.8 to 4.0%, Mn: 0.05 to 1.2%, Al: 0.1 to 1.2%, C: 0.005% or less (excluding 0%), S: 0.003% or less (excluding 0%), N: 0.005% or less (excluding 0%), Ti: 0.005% or less (excluding 0%), B: 0.0005% or less (excluding 0%), Bi: 0.005% or less (excluding 0%), Sn: 0.001 to 0.08%, and Sb: 0.001 to 0.0 8% or more, with the remainder being Fe and other inevitable impurities, and the method includes the steps of heating a slab that satisfies the following relational expression 1; finish hot rolling the heated slab to obtain a hot-rolled sheet; hot-rolling the hot-rolled sheet; pickling the hot-rolled annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; and final annealing the cold-rolled sheet at 710 to 830°C, wherein the method is characterized in that the following relational expression 2 is satisfied during the final annealing.

[0022] [Equation 1] B / 10.81+Bi / 208.98≦0.00007

[0023] [Equation 2] 0.077≦(B / 10.81+Bi / 208.98)×e (最終焼鈍温度 / 100) ≦0.17

[0024] The total content of Sn and Sb may be 0.1% or less.

[0025] The slab heating temperature may be 1100 to 1160°C.

[0026] The finish hot rolling temperature may be 870 to 950°C.

[0027] The annealing temperature of the hot-rolled sheet may be 950 to 1150°C.

[0028] The pickling temperature may be 65 to 92°C.

[0029] The cold rolling may be performed at a cold reduction rate of 70 to 92%.

[0030] The final annealing may be performed for 50 to 120 seconds.

[0031] The method for producing a non-oriented electrical steel sheet of the present invention contains, by weight%, Si: 2.8 to 4.0%, Mn: 0.05 to 1.2%, Al: 0.1 to 1.2%, C: 0.005% or less (excluding 0%), S: 0.003% or less (excluding 0%), N: 0.005% or less (excluding 0%), Ti: 0.005% or less (excluding 0%), B: 0.0005% or less (excluding 0%), Bi: 0.005% or less (excluding 0%), one or more of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and the balance being Fe and other unavoidable elements. The method includes the steps of heating a pure slab that satisfies the following relational expression 1, finish hot rolling the heated slab to obtain a hot-rolled sheet, hot-annealing the hot-rolled sheet, pickling the hot-annealed hot-rolled sheet, cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet, final annealing the cold-rolled sheet at 710 to 830°C, and SRA heat treatment of the final-annealed cold-rolled sheet at 750 to 850°C for 40 to 120 minutes, wherein the final annealing is an SRA heat treatment that satisfies the following relational expression 2:

[0032] [Equation 1] B / 10.81+Bi / 208.98≦0.00007

[0033] [Equation 2] 0.077≦(B / 10.81+Bi / 208.98)×e (最終焼鈍温度 / 100) ≦0.17

[0034] The total content of Sn and Sb may be 0.1% or less.

[0035] The slab heating temperature may be 1100 to 1160°C.

[0036] The finish hot rolling temperature may be 870 to 950°C.

[0037] The hot-rolled sheet annealing temperature may be 950 to 1150°C.

[0038] The pickling temperature may be 65 to 92°C.

[0039] The cold rolling may be performed at a cold reduction rate of 70 to 92%.

[0040] The final annealing may be performed for 50 to 120 seconds. [Effects of the Invention]

[0041] According to the present invention, it is possible to provide a non-oriented electrical steel sheet having excellent strength properties after final annealing, and a method for producing the same.

[0042] Furthermore, according to the present invention, it is possible to provide an SRA heat-treated non-oriented electrical steel sheet that is excellent in high-frequency iron loss characteristics after SRA heat treatment, and a method for manufacturing the same. DETAILED DESCRIPTION OF THE INVENTION

[0043] The non-oriented electrical steel sheet and the SRA heat-treated non-oriented electrical steel sheet of the present invention will be described below. First, the alloy composition will be described. The contents of the alloy compositions described below are in weight percent unless otherwise specified.

[0044] Si: 2.8 to 4.0% Silicon (Si) plays a role in increasing the resistivity of the material and reducing iron loss. If the Si content is less than 2.8%, the effect of improving iron loss may be insufficient. If the Si content exceeds 4.0%, the brittleness of the material increases, and sheet breakage may occur during coiling and cold rolling, resulting in a rapid decrease in rolling productivity. Therefore, the Si content is preferably in the range of 2.8 to 4.0%. The lower limit of the Si content is more preferably 2.9%, and even more preferably 3.0%. The upper limit of the Si content is more preferably 3.9%, and even more preferably 3.8%.

[0045] Mn: 0.05 to 1.2% Manganese (Mn) increases the resistivity of the material, improves core loss, and plays a role in forming sulfides. If the Mn content is less than 0.05%, fine sulfides may precipitate, reducing magnetic properties. If the Mn content exceeds 1.2%, it may promote the formation of a {111} texture, which is unfavorable to magnetic properties, resulting in a decrease in magnetic flux density. Therefore, the Mn content is preferably in the range of 0.05 to 1.2%. The lower limit of the Mn content is more preferably 0.1%, and even more preferably 0.2%. The upper limit of the Mn content is more preferably 1.1%, and even more preferably 1.0%.

[0046] Al: 0.1 to 1.2% Aluminum (Al) increases the resistivity of the material, reducing iron loss, improving rollability, and improving workability during cold rolling. If the Al content is less than 0.1%, the effect of reducing high-frequency iron loss is not achieved, and the precipitation temperature of AlN is lowered, resulting in the formation of fine nitrides, which may reduce magnetic properties. If the Al content exceeds 1.2%, excessive nitrides are formed, reducing magnetic properties and causing problems in all processes, including steelmaking and continuous casting, and significantly reducing productivity. Therefore, the Al content is preferably in the range of 0.1 to 1.2%. The lower limit of the Al content is more preferably 0.2%, and even more preferably 0.3%. The upper limit of the Al content is more preferably 1.1%, and even more preferably 1.0%.

[0047] C: 0.005% or less (excluding 0%) Carbon (C) is an element that suppresses the growth of ferrite crystal grains during annealing, excessively degrades magnetic properties during processing, and bonds with Ti and other elements to reduce magnetic properties. If the C content exceeds 0.005%, magnetic properties may be excessively reduced. Therefore, the C content is preferably 0.005% or less (excluding 0%). The C content is more preferably 0.004% or less, and even more preferably 0.003% or less.

[0048] S: 0.003% or less (excluding 0%) Sulfur (S) is an element that inhibits grain growth by forming fine sulfides inside the base material, thereby worsening iron loss. If the S content exceeds 0.003%, it may combine with Mn and other elements to inhibit grain growth or may result in excessive deterioration of magnetic properties after processing. Therefore, the S content is preferably 0.003% or less (excluding 0%). It is more preferable that the S content be 0.002% or less.

[0049] N: 0.005% or less (excluding 0%) Nitrogen (N) is an element that not only combines with Al, Ti, etc. to form fine, elongated precipitates inside the base material, but also combines with other impurities to form fine nitrides, which inhibit grain growth and worsen iron loss. If the N content exceeds 0.005%, magnetic properties may be excessively reduced. Therefore, the N content is preferably 0.005% or less (excluding 0%). The N content is more preferably 0.004% or less, and even more preferably 0.003% or less.

[0050] Ti: 0.005% or less (excluding 0%) Titanium (Ti) is an element that has a strong tendency to form precipitates in steel, forming fine carbides or nitrides within the matrix, thereby inhibiting grain growth. If the Ti content exceeds 0.005%, a large amount of carbides and nitrides is formed, which deteriorates iron loss and other magnetic properties. Therefore, the Ti content is preferably 0.005% or less (excluding 0%). The Ti content is more preferably 0.004% or less, and even more preferably 0.003% or less.

[0051] B: 0.0005% or less (excluding 0%) Boron (B) is an element that has a strong tendency to form segregated precipitates in steel, and even a small amount of addition can segregate at grain boundaries and inhibit grain growth. Since the degree of segregation is particularly pronounced near the SRA heat treatment temperature, it must be minimized. If the B content exceeds 0.0005%, magnetic properties may be excessively reduced. Therefore, the B content is preferably 0.0005% or less (excluding 0%).

[0052] Bi: 0.005% or less (excluding 0%) Bismuth (Bi) is an element with a strong tendency to segregate within steel, and even a small amount of addition segregates at grain boundaries and inhibits grain growth. Since the degree of segregation is particularly pronounced near the SRA heat treatment temperature, it must be minimized. Therefore, the Bi content is preferably 0.005% or less (excluding 0%). It is more preferable that the Bi content be 0.004% or less.

[0053] One or more of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%

[0054] Sn: 0.001 to 0.08% Tin (Sn) is an element that segregates at grain boundaries and surfaces to improve the texture of steel sheets and inhibit surface oxidation, thereby enhancing magnetic properties. If the Sn content is less than 0.001%, it may be difficult to fully achieve the above-mentioned effects. If the Sn content exceeds 0.08%, the grain boundary segregation becomes severe, deteriorating surface quality and increasing hardness, which may cause breakage of the cold-rolled sheet and reduce rollability. Therefore, the Sn content is preferably in the range of 0.001 to 0.08%. The lower limit of the Sn content is more preferably 0.01%. The upper limit of the Sn content is more preferably 0.07%.

[0055] Sb: 0.001 to 0.08% Antimony (Sb) is an element that segregates at grain boundaries and surfaces to improve the texture of steel sheets and inhibit surface oxidation, thereby enhancing magnetic properties. If the Sb content is less than 0.001%, it may be difficult to fully achieve the above-mentioned effects. If the Sb content exceeds 0.08%, the grain boundary segregation becomes severe, deteriorating surface quality and increasing hardness, which may cause breakage of the cold-rolled sheet and reduce rollability. Therefore, the Sb content is preferably in the range of 0.001 to 0.08%. The lower limit of the Sb content is more preferably 0.01%. The upper limit of the Sb content is more preferably 0.07%.

[0056] The total content of Sn and Sb may be 0.1% or less. If the total content of Sn and Sb exceeds 0.1%, the degree of segregation becomes severe, which may cause problems such as deterioration of surface quality, impeding crystal growth, and deteriorating magnetic properties.

[0057] The remaining component is iron (Fe). However, in a normal manufacturing process, unintentional impurities may be inevitably mixed in from the raw materials or the surrounding environment, and this cannot be excluded. These impurities are known to any engineer in a normal manufacturing process, and therefore, the contents of all of them will not be specifically mentioned in this specification.

[0058] The non-oriented electrical steel sheet of the present invention preferably satisfies the following relational expression 1.

[0059] [Equation 1] B / 10.81+Bi / 208.98≦0.00007

[0060] If the above relational expression 1 is not satisfied, the degree of grain boundary segregation becomes severe, inhibiting crystal growth, and as a result, it becomes difficult to ensure appropriate magnetic properties before and after SRA.

[0061] The non-oriented electrical steel sheet according to one embodiment of the present invention, i.e., the non-oriented electrical steel sheet after final annealing and before SRA heat treatment, preferably has an average crystal grain size of 5 to 25 μm. If the average crystal grain size is less than 5 μm, a sufficient initial recrystallized structure cannot be ensured, resulting in a disadvantage that the magnetic properties after SRA heat treatment deteriorate. If the average crystal grain size is more than 25 μm, there is a disadvantage that the strength decreases.

[0062] The non-oriented electrical steel sheet of the present invention provided as described above may have a thickness of 0.15 to 0.25 mm and a yield strength of 490 to 570 MPa.

[0063] The SRA heat-treated non-oriented electrical steel sheet according to another embodiment of the present invention, i.e., the non-oriented electrical steel sheet after the SRA heat treatment, preferably has an average grain size of 70 to 110 μm. If the average grain size is less than 70 μm, there is a drawback in that iron loss deteriorates. If the average grain size is more than 110 μm, there is a drawback in that high-frequency iron loss deteriorates.

[0064] The SRA heat-treated non-oriented electrical steel sheet of the present invention provided as described above may have a thickness of 0.15 to 0.25 mm, a magnetic flux density (B50) of 1.544 + 0.28 × t + 0.0014 / t (t: thickness of steel sheet) Tesla, and an iron loss (W10 / 400) of 7.15 + 15.8 × t + 0.0015 × (d: 91.7). 2 (t: thickness of the steel sheet, d: average crystal grain size) W / Kg or less. In the present invention, the higher the magnetic flux density (B50), the more advantageous it is, so there is no particular restriction on its upper limit. However, as an example, the upper limit of the magnetic flux density (B50) may be 1.8 T. In the present invention, the lower the iron loss (W10 / 400), the more advantageous it is, so there is no particular restriction on its lower limit. However, as an example, the lower limit of the iron loss (W10 / 400) may be 7 W / Kg.

[0065] The method for producing a non-oriented electrical steel sheet according to the present invention will be described below.

[0066] First, a slab satisfying the above-mentioned alloy composition is heated. The slab heating temperature may be 1100 to 1160°C. If the slab heating temperature is less than 1100°C, there is a drawback that the hot deformation resistance is high and hot rolling becomes difficult. If the slab heating temperature is more than 1180°C, there is a drawback that fine precipitates increase and iron loss deteriorates. Therefore, the slab heating temperature is preferably in the range of 1100 to 1180°C.

[0067] The heated slab is then finish hot-rolled to obtain a hot-rolled sheet. The finish hot-rolling temperature may be 870 to 950°C. If the finish hot-rolling temperature is less than 870°C, the strength of the sheet increases, which can lead to defects such as poor shape during coiling. If the finish hot-rolling temperature exceeds 950°C, the rolling speed must be increased, which can make hot-rolling difficult.

[0068] Thereafter, the hot-rolled sheet is annealed. The annealing temperature may be 950 to 1150°C. If the annealing temperature is less than 950°C, there is a drawback that the hot-rolled sheet is not sufficiently recrystallized. If the annealing temperature is more than 1150°C, there is a drawback that the crystal grain size becomes excessively large, making cold rolling difficult. Therefore, the annealing temperature may be in the range of 950 to 1150°C. The lower limit of the annealing temperature of the hot-rolled sheet is more preferably 970°C, even more preferably 990°C, and most preferably 1000°C or higher. The upper limit of the annealing temperature of the hot-rolled sheet is more preferably 1130°C, even more preferably 1110°C.

[0069] Thereafter, the hot-rolled sheet annealed is pickled. The pickling temperature may be 65 to 92°C. If the pickling temperature is less than 65°C, there is a drawback that the oxide layer generated after the hot-rolled sheet annealing is not sufficiently removed. If the pickling temperature is more than 92°C, there is a drawback that the amount of evaporation of hydrochloric acid and water increases, deteriorating the working environment. Therefore, the pickling temperature may be in the range of 65 to 92°C.

[0070] The pickled hot-rolled sheet is then cold-rolled to obtain a cold-rolled sheet. The cold rolling can be performed at a cold reduction of 70 to 92%. If the cold reduction is less than 70%, the thickness of the steel sheet after hot rolling must be thinned, which can result in difficulties in hot rolling or an excessively thick steel sheet after cold rolling. If the cold reduction is more than 92%, the magnetic properties can be degraded due to the high reduction. Therefore, the cold reduction can be in the range of 70 to 92%.

[0071] The cold-rolled sheet is then final annealed at 710 to 830°C. If the final annealing temperature is less than 710°C, it is difficult to ensure sufficient initial recrystallization. If the final annealing temperature is more than 830°C, it is difficult to ensure sufficient initial recrystallization. Therefore, the final annealing temperature can be in the range of 710 to 830°C. The lower limit of the final annealing temperature is more preferably 730°C, and even more preferably 750°C. The upper limit of the final annealing temperature is more preferably 820°C. The final annealing can be performed for 50 to 120 seconds. If the final annealing time is less than 50 seconds, it is difficult to ensure sufficient initial recrystallization. If the final annealing time is more than 120 seconds, it is difficult to ensure sufficient initial recrystallization. Therefore, the final annealing time can be in the range of 50 to 120 seconds. The upper limit of the final annealing time is more preferably 100 seconds.

[0072] During the final annealing, it is preferable that the following relational expression 2 is satisfied.

[0073] [Equation 2] 0.077≦(B / 10.81+Bi / 208.98)×e (最終焼鈍温度 / 100) ≦0.17

[0074] The above-mentioned relational expression 2 relates the grain boundary segregation behavior index to the annealing temperature of the cold-rolled sheet. If the value of the relational expression 2 is less than 0.077, the annealing temperature becomes too low, making recrystallization difficult and resulting in a grain size smaller than the target grain size in the final annealing. If the value of the relational expression 2 exceeds 0.17, the B and Bi contents become too high or the annealing temperature becomes too high, making it difficult to achieve the target grain size in the final annealing.

[0075] The method for producing the SRA heat-treated non-oriented electrical steel sheet of the present invention will be described below.

[0076] After the above-mentioned manufacturing process, the final-annealed cold-rolled sheet is subjected to SRA heat treatment at 750 to 850°C for 40 to 120 minutes. The SRA heat treatment temperature may be 750 to 850°C. If the SRA heat treatment temperature is less than 750°C, the crystal grain size after the SRA heat treatment is reduced, resulting in a deterioration in core loss. If the SRA heat treatment temperature is more than 850°C, the crystal grain size after the SRA heat treatment is increased, resulting in a deterioration in magnetic flux density and high-frequency core loss. Therefore, the SRA heat treatment temperature may be in the range of 750 to 850°C. The SRA heat treatment may be performed for 40 to 120 minutes. The SRA heat treatment time is estimated based on the time it takes for the ambient temperature of the annealing furnace or the sheet temperature in the annealing furnace to reach the target temperature. If the SRA heat treatment time is less than 40 minutes, sufficient crystal grain growth cannot be ensured, resulting in a deterioration in core loss. If the SRA heat treatment time exceeds 120 minutes, the crystal grains grow excessively, resulting in a decrease in magnetic flux density. Therefore, the SRA heat treatment time may be in the range of 40 to 120 minutes. [Example]

[0077] The present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are intended to illustrate and explain the present invention in more detail, and are not intended to limit the scope of the present invention. The scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0078] (Example) A slab having the alloy composition shown in Table 1 below was heated at 1150°C, and then the heated slab was finish hot-rolled at 920°C to obtain a hot-rolled sheet with a thickness of 1.8 mm. The hot-rolled sheet was then annealed under the conditions shown in Table 2 below, and then pickled at 85°C. The hot-rolled sheet was then cold-rolled to obtain a cold-rolled sheet with a thickness of 0.15 to 0.25 mm. A non-oriented electrical steel sheet was then manufactured by final annealing for 80 seconds under the conditions shown in Table 2 below. A non-oriented electrical steel sheet was then manufactured by SRA heat treatment under the conditions shown in Table 3 below. The conditions for final annealing and SRA heat treatment shown in Tables 2 and 3 below were based on the atmospheric temperature of the annealing furnace.

[0079] The mechanical and electrical properties of the non-oriented electrical steel sheets after final annealing and the non-oriented electrical steel sheets after SRA heat treatment were measured, and the results are shown in Tables 2 and 3 below, respectively.

[0080] The yield strength was measured by a tensile test after preparing a test piece according to JIS 13-A standard.

[0081] The magnetic flux density (B50) and iron loss (W10 / 400) were measured by the Epstein measurement method using test pieces processed to a size of 305 mm x 30 mm in the rolling direction and the direction perpendicular to the rolling, and the number of pieces was adjusted so that the weight was 400 to 450 g, and the average values ​​were calculated.

[0082] [Table 1]

[0083] [Table 2]

[0084] [Table 3]

[0085] As shown in Tables 1 to 3 above, in the case of Examples 1 to 17, which satisfy the alloy composition and manufacturing conditions proposed by the present invention, the average crystal grain size that the present invention aims to achieve is secured, and therefore it is clear that the yield strength and magnetic properties targeted by the present invention are secured.

[0086] In the case of Comparative Examples 1 to 8, which do not satisfy the alloy composition proposed by the present invention, it is found that the average crystal grain size that the present invention aims to achieve cannot be secured, the yield strength is outside the range of the present invention, and the magnetic properties are at an inferior level.

[0087] In the case of Comparative Examples 9 and 10, which do not satisfy the manufacturing conditions proposed by the present invention, the yield strength is outside the range of the present invention, and it is clear that the magnetic properties are at a deteriorated level.

[0088] In the case of Reference Examples 1 to 5, which satisfy the alloy composition and manufacturing conditions up to the final annealing proposed by the present invention, the average grain size that the present invention aims to achieve is secured, and it is clear that the yield strength targeted by the present invention is secured. However, since the SRA heat treatment conditions are not satisfied, it is clear that the average grain size after SRA cannot be secured, and the magnetic properties are at a low level.

Claims

1. In weight percent, the alloy contains 2.8 to 4.0% Si, 0.05 to 1.2% Mn, 0.1 to 1.2% Al, 0.005% or less (excluding 0%) C, 0.003% or less (excluding 0%) S, 0.005% or less (excluding 0%) N, 0.005% or less (excluding 0%) Ti, 0.005% or less (excluding 0%) B, 0.0005% or less (excluding 0%) Bi, and one or more of 0.001 to 0.08% Sn and 0.001 to 0.08% Sb, with the balance being Fe and other inevitable impurities; The following relational expression 1 is satisfied: A non-oriented electrical steel sheet characterized in that the average crystal grain size is 5 to 25 μm. [Relationship 1] B / 10.81+Bi / 208.98≦0.00007

2. 2. The non-oriented electrical steel sheet according to claim 1, wherein the total content of Sn and Sb is 0.1% or less.

3. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has a thickness of 0.15 to 0.25 mm.

4. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has a yield strength of 490 to 570 MPa.

5. In weight percent, the alloy contains 2.8 to 4.0% Si, 0.05 to 1.2% Mn, 0.1 to 1.2% Al, 0.005% or less (excluding 0%) C, 0.003% or less (excluding 0%) S, 0.005% or less (excluding 0%) N, 0.005% or less (excluding 0%) Ti, 0.005% or less (excluding 0%) B, 0.0005% or less (excluding 0%) Bi, and one or more of 0.001 to 0.08% Sn and 0.001 to 0.08% Sb, with the balance being Fe and other inevitable impurities; The following relational expression 1 is satisfied: A non-oriented electrical steel sheet characterized by being subjected to SRA heat treatment and having an average crystal grain size of 70 to 110 μm. [Relationship 1] B / 10.81+Bi / 208.98≦0.00007

6. 6. The SRA heat-treated non-oriented electrical steel sheet according to claim 5, wherein the total of Sn and Sb is 0.1% or less.

7. The SRA heat-treated non-oriented electrical steel sheet according to claim 5, wherein the non-oriented electrical steel sheet has a thickness of 0.15 to 0.25 mm.

8. 6. The non-oriented electrical steel sheet according to claim 5, wherein the non-oriented electrical steel sheet has a magnetic flux density (B50) of 1.544 + 0.28 × t + 0.0014 / t (t: thickness of the steel sheet) Tesla or more.

9. The non-oriented electrical steel sheet has an iron loss (W10 / 400) of 7.15 + 15.8 × t + 0.0015 × (d - 91.7) ２ 6. The non-oriented electrical steel sheet according to claim 5, which has been subjected to an SRA heat treatment in which the SRA heat treatment satisfies the following: (t: thickness of the steel sheet, d: average grain size) W / Kg or less.

10. heating a slab containing, in weight percent, 2.8 to 4.0% Si, 0.05 to 1.2% Mn, 0.1 to 1.2% Al, 0.005% or less (excluding 0%) C, 0.003% or less (excluding 0%) S, 0.005% or less (excluding 0%) N, 0.005% or less (excluding 0%) Ti, 0.0005% or less (excluding 0%) B, 0.0005% or less (excluding 0%) Bi, one or more of 0.001 to 0.08% Sn and 0.001 to 0.08% Sb, with the balance being Fe and other unavoidable impurities; finish hot rolling the heated slab to obtain a hot-rolled sheet; annealing the hot-rolled sheet; pickling the annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; and final annealing of the cold-rolled sheet at 710 to 830°C; A method for producing a non-oriented electrical steel sheet, characterized in that the following relational expression 2 is satisfied during the final annealing: [Relationship 1] B / 10.81+Bi / 208.98≦0.00007 [Relationship 2] 0.077≦(B / 10.81+Bi / 208.98)×e （最終焼鈍温度／１００） ≦0.17

11. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the total of Sn and Sb is 0.1% or less.

12. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the slab heating temperature is 1100 to 1160°C.

13. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the finish hot rolling temperature is 870 to 950°C.

14. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the hot-rolled sheet annealing temperature is 950 to 1150°C.

15. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the pickling temperature is 65 to 92°C.

16. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the cold rolling is performed at a cold reduction rate of 70 to 92%.

17. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the final annealing is performed for 50 to 120 seconds.

18. heating a slab containing, in weight percent, 2.8 to 4.0% Si, 0.05 to 1.2% Mn, 0.1 to 1.2% Al, 0.005% or less (excluding 0%) C, 0.003% or less (excluding 0%) S, 0.005% or less (excluding 0%) N, 0.005% or less (excluding 0%) Ti, 0.0005% or less (excluding 0%) B, 0.0005% or less (excluding 0%) Bi, one or more of 0.001 to 0.08% Sn and 0.001 to 0.08% Sb, with the balance being Fe and other unavoidable impurities; finish hot rolling the heated slab to obtain a hot-rolled sheet; annealing the hot-rolled sheet; pickling the annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; Final annealing the cold-rolled sheet at 710 to 830°C; subjecting the final annealed cold-rolled sheet to an SRA heat treatment at 750 to 850°C for 40 to 120 minutes; The method for producing a non-oriented electrical steel sheet, wherein the final annealing is performed using an SRA heat treatment that satisfies the following relational expression 2: [Relationship 1] B / 10.81+Bi / 208.98≦0.00007 [Relationship 2] 0.077≦(B / 10.81+Bi / 208.98)×e （最終焼鈍温度／１００） ≦0.17

19. The method for manufacturing a non-oriented electrical steel sheet according to claim 18, wherein the total amount of Sn and Sb is 0.1% or less after the SRA heat treatment.

20. The method for manufacturing a non-oriented electrical steel sheet according to claim 18, wherein the slab is subjected to SRA heat treatment at a heating temperature of 1100 to 1160°C.

21. The method for manufacturing a grain-oriented electrical steel sheet according to claim 18, wherein the finish hot rolling is performed at a temperature of 870 to 950°C using an SRA heat treatment.

22. The method for manufacturing a non-oriented electrical steel sheet according to claim 18, wherein the hot-rolled sheet is subjected to SRA heat treatment at an annealing temperature of 950 to 1150°C.

23. The method for manufacturing a non-oriented electrical steel sheet according to claim 18, wherein the pickling temperature is an SRA heat treatment of 65 to 92°C.

24. The method for manufacturing a non-oriented electrical steel sheet according to claim 18, wherein the cold rolling is performed at a cold reduction rate of 70 to 92% and the steel sheet is subjected to SRA heat treatment.

25. The method for manufacturing a non-oriented electrical steel sheet according to claim 18, wherein the final annealing is an SRA heat treatment performed for 50 to 120 seconds.

Images