Non-oriented electrical steel sheet, sra heat treated non-oriented electrical steel sheet and manufacturing methods therefor

Abstract

The present invention relates to a non-oriented electrical steel sheet and a manufacturing method therefor. One aspect of the present invention is to provide a non-oriented electrical steel sheet having excellent strength characteristics after final annealing, and a manufacturing method therefor. Another aspect of the present invention is to provide a non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics after SRA heat treatment, and a manufacturing method therefor.

Description

Technical Field

[0001] The present disclosure relates to a non-oriented electrical steel sheet, a SRA heat-treated non-oriented electrical steel sheet, and a manufacturing method thereof.Background Art

[0002] Recently, with increasing demand for energy savings in electrical devices, excellent magnetic properties are required for non-oriented electrical steel sheets used in the iron cores (motor cores) of rotating machines.

[0003] Motor cores may be divided into stator cores and rotor cores, and recently, in order to satisfy the demand for miniaturization and high output for HEV driving motors, etc., excellent magnetic properties, such as high magnetic flux density and low iron loss, have been strongly required for non-oriented electrical steel sheets used in stator cores.

[0004] To achieve miniaturization and high output of HEV driving motors, etc., the rotation speed of motors has tended to increase, but since HEV driving motors have a large outer diameter, a large amount of centrifugal force is applied to rotor cores and a very narrow portion (1 to 2 mm) known as a rotor core bridge portion exists depending on the structure, so non-oriented electrical steel sheets used in the rotor cores is required to have higher strength than before.

[0005] Therefore, as for the characteristics of non-oriented electrical steel sheets used in motor cores, it is ideal to have excellent magnetic properties, as well as high strength for rotor cores, and higher magnetic flux density and low iron loss for stator cores. In this manner, even the non-oriented electrical steel sheets used in the same motor core are required to have significantly different characteristics for rotor cores and stator cores, but in manufacturing the motor cores, from the viewpoint of increasing the material yield, etc., it is desirable to simultaneously collect a rotor core material and a stator core material from the same steel sheet and then laminate each core material to assemble it into a rotor core or a stator core.

[0006] Meanwhile, in the case of rotors, if the strength is high, it is advantageous for fracture during rotation, and in particular, it is advantageous for the design of motors if the strength is high in all directions rather than in a specific direction. This is because rotors are manufactured in a circular shape and rotate, so rotors receives tensile force in all directions. Therefore, if rotors are designed by considering only strength in a specific direction, the strength thereof in other directions may be weak during rotation, causing fracture.

[0007] In addition, when manufacturing rotors, a punching process using a mold is used, but if a difference in the strength of a steel plate in each direction is significant, a difference in the workability in each direction appears during the punching. This causes difficulties in mass-production.Summary of InventionTechnical Problem

[0008] An aspect of the present disclosure is to provide a non-oriented electrical steel sheet having excellent strength characteristics after final annealing and a manufacturing method thereof.

[0009] Another aspect of the present disclosure is to provide an SRA heat-treated non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics after SRA heat treatment and a manufacturing method thereof.Solution to Problem

[0010] According to an aspect of the present disclosure, a non-oriented electrical steel sheet includes, in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities and satisfies Relational Expression 1 below, and an average grain size is 5 to 25 µm. B / 10.81 + Bi / 208.98 ≤ 0.00007

[0011] A sum of Sn and Sb may be 0.1% or less.

[0012] The non-oriented electrical steel sheet may have a thickness of 0.15 to 0.25 mm.

[0013] The non-oriented electrical steel sheet may have a yield strength of 490 to 570 MPa.

[0014] According to another aspect of the present disclosure, an SRA heat-treated non-oriented electrical steel sheet includes: in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities and satisfies Relational Expression 1 below, and an average grain size is 70 to 110 µm. B / 10.81 + Bi / 208.98 ≤ 0.00007

[0015] A sum of Sn and Sb may be 0.1% or less.

[0016] The non-oriented electrical steel sheet may have a thickness of 0.15 to 0.25 mm.

[0017] 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 steel sheet) Tesla or more.

[0018] The non-oriented electrical steel sheet may have a core loss (W10 / 400) of 7.15 + 15.8 × t + 0.0015 × (d-91.7) 2< (t: thickness of steel sheet, d: average grain size) W / Kg or less.

[0019] According to another aspect of the present disclosure, a method of manufacturing a non-oriented electrical steel sheet includes: heating a slab including, in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities; finishing hot-rolling the heated slab to obtain a hot-rolled sheet; hot-rolled sheet annealing the hot-rolled sheet; pickling the hot-rolled sheet annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; and finally annealing the cold-rolled sheet at 710 to 830°C, wherein Relational Expression 2 is satisfied during the final annealing. B / 10.81 + Bi / 208.98 ≤ 0.00007

[0020] A sum of Sn and Sb may be 0.1% or less.

[0021] The slab heating temperature may be 1100 to 1160°C.

[0022] The finishing hot rolling temperature may be 870 to 950°C.

[0023] The hot-rolled sheet annealing temperature may be 950 to 1150°C.

[0024] The pickling temperature may be 65 to 92°C.

[0025] The cold rolling may be performed at a cold reduction ratio of 70 to 92%.

[0026] The final annealing may be performed for 50 to 120 seconds.

[0027] According to another aspect of the present disclosure, a method of manufacturing an SRA heat-treated non-oriented electrical steel sheet includes: heating a slab including, in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities; finishing hot-rolling the heated slab to obtain a hot-rolled sheet; hot-rolled sheet annealing the hot-rolled sheet; pickling the hot-rolled sheet annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; finally annealing the cold-rolled sheet at 710 to 830°C; and SRA heat-treating the finally annealed cold-rolled sheet at 750 to 850°C for 40 to 120 minutes, wherein Relational Expression 2 is satisfied during the final annealing. B / 10.81 + Bi / 208.98 ≤ 0.00007

[0028] A sum of Sn and Sb may be 0.1% or less.

[0029] The slab heating temperature may be 1100 to 1160°C.

[0030] The finishing hot rolling temperature may be 870 to 950°C.

[0031] The hot-rolled sheet annealing temperature may be 950 to 1150°C.

[0032] The pickling temperature may be 65 to 92°C.

[0033] The cold rolling may be performed at a cold reduction ratio of 70 to 92%.

[0034] The final annealing may be performed for 50 to 120 seconds.Advantageous Effects of Invention

[0035] According to an aspect of the present disclosure, the non-oriented electrical steel sheet having excellent strength characteristics after final annealing and a manufacturing method thereof may be provided.

[0036] According to another aspect of the present disclosure, the SRA heat-treated non-oriented electrical steel sheet having excellent high-frequency iron loss characteristics after SRA heat treatment and the manufacturing method thereof may be provided.Best Mode for Invention

[0037] Hereinafter, a non-oriented electrical steel sheet and SRA heat-treated non-oriented electrical steel sheet according to an embodiment of the present disclosure will be described. First, an alloy composition will be described. The content of the alloy composition described below refers to wt % unless otherwise specified.Si: 2.8 to 4.0%

[0038] Silicon (Si) plays a role in increasing the resistivity of a material to lower iron loss. If the content of Si is less than 2.8%, the effect of improving iron loss may be insufficient. If the content of Si exceeds 4.0%, brittleness of the material may increase, causing plate break during coiling and cold rolling, which may drastically reduce rolling productivity. Therefore, the content of Si is preferably in the range of 2.8 to 4.0%. A lower limit of the content of Si is more preferably 2.9%, and even more preferably 3.0%. An upper limit of the content of Si is more preferably 3.9%, and even more preferably 3.8%.Mn: 0.05 to 1.2%

[0039] Manganese (Mn) plays a role in increasing the resistivity of the material to improve iron loss and form sulfides. If the content of Mn is less than 0.05%, sulfides may be minutely precipitated, which may reduce magnetism. If the content of Mn exceeds 1.2%, the formation of {111} texture, which is unfavorable to magnetism, may be promoted to thus reduce the magnetic flux density. Therefore, the content of Mn is preferably in the range of 0.05 to 1.2%. A lower limit of the content of Mn is more preferably 0.1%, and even more preferably 0.2%. An upper limit of the content of Mn is more preferably 1.1%, and even more preferably 1.0%.Al: 0.1 to 1.2%

[0040] Aluminum (Al) plays a role in increasing the resistivity of the material to lower iron loss and has the effect of improving the rolling properties or improving the workability during cold rolling. If the content of Al is less than 0.1%, it may not be effective in reducing the high-frequency iron loss and a precipitation temperature of AlN may be lowered to minutely form nitrides are, which may lower the magnetism. If the content of Al exceeds 1.2%, nitrides may be formed excessively to deteriorate the magnetism and cause problems in all processes, such as steelmaking and continuous casting, which may significantly lower productivity. Therefore, the content of Al is preferably in the range of 0.1 to 1.2%. A lower limit of the content of Al is more preferably 0.2%, and even more preferably 0.3%. An upper limit of the content of Al is more preferably 1.1%, and even more preferably 1.0%.C: 0.005% or less (excluding 0%)

[0041] Carbon (C) is an element suppressing ferrite grain growth during annealing to excessively deteriorate magnetism during processing and combined with Ti, etc. to reduce magnetism. If the content of C exceeds 0.005%, magnetism may be excessively reduced. Therefore, the content of C is preferably in the range of 0.005% or less (excluding 0%). The content of C is more preferably 0.004% or less, and even more preferably 0.003% or less.S: 0.003% or less (excluding 0%)

[0042] Sulfur (S) is an element suppressing grain growth by forming fine sulfides inside a parent material, thereby weakening iron loss. If the content of S exceeds 0.003%, it may combine with Mn, etc. to suppress grain growth or excessively reduce magnetism after processing. Therefore, the content of S is preferably in the range of 0.003% or less (excluding 0%). The content of S is more preferably 0.002% or less.N: 0.005% or less (excluding 0%)

[0043] Nitrogen (N) is an element not only forming fine and long precipitates inside the parent material by combining with Al, Ti, etc. but also forming fine nitrides by combining with other impurities, thereby suppressing grain growth and worsening iron loss. If the content of N exceeds 0.005%, magnetism may be excessively reduced. Therefore, the content of N is preferably in the range of 0.005% or less (excluding 0%). The content of the N is more preferably 0.004% or less, and even more preferably 0.003% or less.Ti: 0.005% or less (excluding 0%)

[0044] Titanium (Ti) is an element having a very strong tendency to form precipitates in steel and is an element forming fine carbides or nitrides inside the parent material to suppress grain growth. If the content of Ti exceeds 0.005%, a lot of carbides and nitrides may be formed, which worsens iron loss and deteriorates magnetism. Therefore, the content of Ti is preferably in the range of 0.005% or less (excluding 0%). The content of the Ti is more preferably 0.004% or less, and even more preferably 0.003% or less.B: 0.0005% or less (excluding 0%)

[0045] Boron (B) is an element having a very strong tendency to form segregation precipitates in steel, and even a small amount of addition thereof causes segregation at grain boundaries to suppress grain growth. In particular, since the degree of segregation is stronger near an SRA heat treatment temperature, boron (B) has to be extremely suppressed. If the content of B exceeds 0.0005%, magnetism may be excessively reduced. Therefore, the content of B is preferably in the range of 0.0005% or less (excluding 0%).Bi: 0.005% or less (excluding 0%)

[0046] Bismuth (Bi) is an element having a very strong tendency to segregate in steel, and even a small amount of addition thereof causes segregation at grain boundaries to suppress grain growth. In particular, since the degree of segregation is stronger near the SRA heat treatment temperature, Bi has to be extremely suppressed. Therefore, the content of Bi is preferably in the range of 0.005% or less (excluding 0%). The content of Bi is more preferably 0.004% or less.One or more of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%Sn: 0.001 to 0.08%

[0047] Tin (Sn) is an element improving the texture of the steel sheet by segregating at grain boundaries and the surface and suppressing surface oxidation, thereby improving magnetism. If the content of Sn is less than 0.001%, it may be difficult to sufficiently obtain the aforementioned effect. If the content of Sn exceeds 0.08%, grain boundary segregation may become severe, deteriorating surface quality and increasing hardness to cause the cold-rolled sheet to fracture, thereby lowering the rollability. Therefore, the content of Sn is preferably in the range of 0.001 to 0.08%. A lower limit of the content of Sn is more preferably 0.01%. An upper limit of the content of Sn is more preferably 0.07%.Sb: 0.001 to 0.08%

[0048] Antimony (Sb) is an element improving the texture of the steel sheet by segregating at grain boundaries and the surface and suppressing surface oxidation, thereby improving magnetism. If the content of Sb is less than 0.001%, it may be difficult to sufficiently obtain the aforementioned effect. If the content of Sb exceeds 0.08%, grain boundary segregation may become severe, deteriorating the surface quality and increasing hardness to cause the cold-rolled sheet to fracture, thereby reducing the rollability. Therefore, the content of Sb is preferably in the range of 0.001 to 0.08%. A lower limit of the content of Sb is more preferably 0.01%. An upper limit of the content of Sb is more preferably 0.07%.

[0049] The sum of Sn and Sb may be 0.1% or less. If the sum of Sn and Sb exceeds 0.1%, the degree of segregation may become severe, which may deteriorate the surface quality and inhibit crystal growth to deteriorate the magnetism.

[0050] The remaining component is iron (Fe). However, since unintended impurities may inevitably be mixed in from raw materials or the surrounding environment during the general manufacturing process, the unintended impurities cannot be ruled out. Since these impurities may be known to anyone skilled in the general manufacturing process, not all of the contents are specifically mentioned in this specification.

[0051] The non-oriented electrical steel sheet of the present disclosure preferably satisfies Relational Expression 1 below.

[0052] B / 10.81 + Bi / 208.98 ≤ 0.00007

[0053] If Relational Expression 1 is not satisfied, the degree of grain boundary segregation may become severe, which inhibits crystal growth, and accordingly, it may be difficult to secure appropriate magnetic properties before / after SRA.

[0054] The non-oriented electrical steel sheet according to an embodiment of the present disclosure, that is, the non-oriented electrical steel sheet before SRA heat treatment after final annealing, preferably has an average grain size of 5 to 25 µm. If the average grain size is less than 5 µm, sufficient initial recrystallization structure cannot be secured, which may result in a disadvantage in that the magnetic properties are inferior after SRA heat treatment. If the average grain size exceeds 25 µm, there is a disadvantage in that the strength is reduced.

[0055] As described above, the non-oriented electrical steel sheet of the present disclosure may have a thickness of 0.15 to 0.25 mm. In addition, the yield strength may be 490 to 570 MPa.

[0056] The SRA heat-treated non-oriented electrical steel sheet, i.e., the non-oriented electrical steel sheet after SRA heat treatment according to another embodiment of the present disclosure, preferably has an average grain size of 70 to 110 µm. If the average grain size is less than 70 µm, there may be a disadvantage that the iron loss is inferior. If the average grain size exceeds 110 µm, there may be a disadvantage that the high-frequency iron loss is inferior.

[0057] As described above, the SRA heat-treated non-oriented electrical steel sheet of the present disclosure may have a thickness of 0.15 to 0.25 mm. In addition, a magnetic flux density (B50) may be 1.544 + 0.28×t + 0.0014 / t (t: thickness of the steel plate) Tesla, and the iron loss (W10 / 400) may be 7.15 + 15.8×t + 0.0015×(d-91.7) 2< (t: thickness of the steel plate, d: average grain size)W / Kg or less. In the present disclosure, since a higher magnetic flux density (B50) is advantageous, and therefore, an upper limit thereof is not particularly limited. However, the upper limit of the magnetic flux density (B50) may be, for example, 1.8T. In addition, in the present disclosure, a lower the iron loss (W10 / 400) is advantageous, and therefore, a lower limit thereof is not particularly limited. However, the lower limit of the iron loss (W10 / 400) may be, for example, 7W / Kg.

[0058] Hereinafter, a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present disclosure will be described.

[0059] First, a slab satisfying the aforementioned alloy composition is heated. A slab heating temperature may be 1100 to 1160°C. If the slab heating temperature is less than 1100°C, there may be a disadvantage that hot rolling is difficult due to high hot rolling resistance. If the slab heating temperature exceeds 1180°C, there may be a disadvantage that fine precipitates may increase and iron loss may deteriorate. Therefore the slab heating temperature is preferably in the range of 1100 to 1180°C.

[0060] Thereafter, the heated slab is subjected to finishing hot rolling to obtain a hot-rolled sheet. The finishing hot-rolling temperature may be 870 to 950°C. If the finishing hot-rolling temperature is less than 870°C, there may be a disadvantage that the strength of the sheet increases, causing defects, such as shape defects, when coiling. If the finishing hot rolling temperature exceeds 950°C, a rolling rate has to be increased, which makes hot rolling itself difficult.

[0061] Thereafter, the hot-rolled sheet is annealed. The hot-rolled sheet annealing temperature may be 950 to 1150°C. If the hot-rolled sheet annealing temperature is lower than 950°C, there may be a disadvantage that the hot-rolled sheet cannot be sufficiently recrystallized. If the hot-rolled sheet annealing temperature exceeds 1150°C, the grain size may become excessively large, which may make cold rolling difficult. Therefore, the hot-rolled sheet annealing temperature may have a range of 950 to 1150°C. A lower limit of the hot-rolled sheet annealing temperature is more preferably 970°C, even more preferably 990°C, and most preferably 1000°C or higher. An upper limit of the hot-rolled sheet annealing temperature is more preferably 1130°C, and even more preferably 1110°C.

[0062] Thereafter, the annealed hot-rolled sheet is pickled. The pickling temperature may be 65 to 92°C. If the pickling temperature is less than 65°C, there may be a disadvantage that an oxide layer formed after the hot-rolled sheet annealing is not sufficiently removed. If the pickling temperature exceeds 92°C, there may be a disadvantage that the amount of evaporation of hydrochloric acid and water increases, which worsens the working environment. Therefore, the pickling temperature may have a range of 65 to 92°C.

[0063] Thereafter, the pickled hot-rolled sheet is cold-rolled to obtain a cold-rolled plate. The cold rolling may be performed at a cold reduction ratio of 70 to 92%. If the cold reduction ratio is less than 70%, the thickness of the steel plate has to be thinned after the hot rolling, which may make hot rolling difficult or the thickness of the steel plate after the cold rolling may become thicker. If the cold reduction ratio exceeds 92%, there may be a disadvantage that the magnetism becomes poor due to the high reduction ratio. Therefore, the cold rolling reduction ratio may have a range of 70 to 92%.

[0064] Thereafter, the cold rolled sheet is finally annealed at 710 to 830°C. If the final annealing temperature is less than 710°C, there may be a disadvantage that it is difficult to secure sufficient initial recrystallization. If the final annealing temperature exceeds 830°C, there may be a disadvantage that the grains become excessively large and the strength decreases. Therefore, the final annealing temperature may have a range of 710 to 830°C. A lower limit of the final annealing temperature is more preferably 730°C, and even more preferably 750°C. An upper limit of the final annealing temperature is more preferably 820°C. The final annealing may be performed for 50 to 120 seconds. If the final annealing time is less than 50 seconds, there may be a disadvantage that it is difficult to secure sufficient initial recrystallization. If the final annealing time exceeds 120 seconds, there may be a disadvantage that the grains become excessively large and the strength decreases. Therefore, the final annealing time may range from 50 to 120 seconds. An upper limit of the final annealing time is more preferably 100 seconds.

[0065] It is preferable that Relational Expression 2 is satisfied during the final annealing.

[0066] Relational Expression 2 is an expression related to a grain boundary segregation behavior index for the annealing temperature of the cold rolled sheet. If the value of Relational Expression 2 is less than 0.077, the annealing temperature may be too low, making it difficult to recrystallize, resulting in a disadvantage in that a smaller grain size is obtained compared to a target grain size during the final annealing. If the value of Relational Expression 2 exceeds 0.17, the content of B and Bi is too high or the annealing temperature is too high, making it difficult to secure the target grain size during the final annealing.

[0067] Hereinafter, a method of manufacturing an SRA heat-treated non-oriented electrical steel sheet according to an embodiment of the present disclosure will be described.

[0068] After the aforementioned manufacturing process, the finally 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, there may be a disadvantage that the grain size becomes smaller after the SRA heat treatment, resulting in poor iron loss. If the SRA heat treatment temperature exceeds 850°C, there may be a disadvantage that the grain size becomes larger after the SRA heat treatment, resulting in poor magnetic flux density and high-frequency iron loss. Therefore, the SRA heat treatment temperature may have a range of 750 to 850°C. The SRA heat treatment may be performed for 40 to 120 minutes. The SRA heat treatment time begins to offset from the time when an atmosphere temperature of an annealing furnace or a plate temperature inside the annealing furnace reaches a target temperature. If the SRA heat treatment time is less than 40 minutes, sufficient grain growth may not be secured, which has the disadvantage of poor iron loss. If the SRA heat treatment time exceeds 120 minutes, there may be a disadvantage of excessive grain growth, which has the disadvantage of poor magnetic flux density. Therefore, the SRA heat treatment time may be in the range of 40 to 120 minutes.Mode for Invention

[0069] Hereinafter, the present disclosure will be described more specifically through examples. However, it should be noted that the following examples are only intended to illustrate the present disclosure in more detail and are not intended to limit the scope of the present disclosure. This is because the scope of the present disclosure is determined by the matters described in the claims and matters reasonably inferred therefrom.(Example)

[0070] A slab having the alloy composition of Table 1 below was heated at 1150°C, and the heated slab was subjected to finishing hot rolling at 920°C to obtain a hot-rolled sheet having a thickness of 1.8 mm. Thereafter, the hot-rolled sheet was annealed under the conditions described in Table 2 below and then pickled at 85°C. Thereafter, the hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet having a thickness of 0.15 to 0.25 mm. Thereafter, a final annealing was performed for 80 seconds under the conditions described in Table 2 below to manufacture a non-oriented electrical steel sheet. Thereafter, SRA heat treatment was performed under the conditions described in Table 3 below to manufacture a non-oriented electrical steel sheet. Meanwhile, the final annealing and SRA heat treatment conditions described in Tables 2 and 3 below were based on the atmosphere temperature of the annealing furnace.

[0071] Mechanical / electrical properties of the non-oriented electrical steel sheets manufactured in this manner after final annealing and the non-oriented electrical steel sheets after SRA heat treatment were measured, and the results are illustrated in Tables 2 and 3 below, respectively.

[0072] Yield strength was measured through a tensile test after manufacturing a specimen according to the JIS 13-A standard.

[0073] The number of specimens processed to a size of 305 mm × 30 mm in a rolling direction and a vertical rolling direction was adjusted so that the weight of the specimens was 400 to 450 g, and the magnetic flux density (B50) and iron loss (W10 / 400) were measured using the Epstein measurement method and an average value was calculated [Table 1]Steel gradeAlloy composition (wt%)SiMnAlSnSbSn+S bCSNTiBBiRelatio nal Express ion 1Inven tive Steel 13. 20.90.80.0 30.040.070.001 50.001 30.001 50.001 70.000 30.003 20.00004 3Compa rativ e Steel 13. 50.80.80.0 2-0.020.001 80.001 80.001 40.001 60.000 80.002 70.00008 7Compa rativ e Steel 23. 40.60.50.0 30.050.080.002 10.001 40.002 50.001 00.000 50.005 40.00007 2Inven tive Steel 23. 30.50.9-0.030.030.001 70.001 60.001 90.001 90.000 40.003 80.00005 5Inven tive Steel 33. 70.50.40.0 2-0.020.001 10.001 60.001 70.001 20.000 50.001 50.00005 3Inven tive Steel 43. 50.40.70.0 6-0.060.001 30.001 40.001 60.001 50.000 30.001 40.00003 4Inven tive Steel 53. 10.90.80.0 30.040.070.001 90.001 30.001 50.002 00.000 40.002 50.00004 9[Relational Expression 1] B / 10.81 + Bi / 208.98 [Table 2] Classi ficati onSteel gradeAnneali ng tempera ture of hot-rolled sheet (°C)Thickne ss (mm)Final annealin g temperat ure (°C)Relation al Expressi on 2Size of average grain after final annealing (µm)Yield strength after final annealing (MPa)Invent ive Exampl e 1Invent ive Steel 110200.257600.0869558Invent ive Exampl e 2Invent ive Steel 110200.257800.10511547Invent ive Exampl e 3Invent ive Steel 110200.258000.12814535Invent ive Exampl e 4Invent ive Steel 110200.258200.15722531Compar ative Exampl e 1Compar ative Steel 110200.208000.2592601Compar ative Exampl e 2Compar ative Steel 110400.208000.2594593Compar ative Exampl e 3Compar ative Steel 110600.208000.2593586Compar ative Exampl e 4Compar ative Steel 110800.208000.2594589Compar ative Exampl e 5Compar ative Steel 210200.257800.1764588Compar ative Exampl e 6Compar ative Steel 210400.257800.1763592Compar ative Exampl e 7Compar ative Steel 210600.257800.1762579Compar ative Exampl e 8Compar ative Steel 210800.257800.1764583Invent ive Exampl e 5Invent ive Steel 210400.257600.11012527Invent ive Exampl e 6Invent ive Steel 210400.207600.11010536Invent ive Exampl e 7Invent ive Steel 210400.207600.11010536Invent ive Exampl e 8Invent ive Steel 210400.157600.1107541Invent ive Exampl e 9Invent ive Steel 310500.157800.12914562Invent ive Exampl e 10Invent ive Steel 310500.157800.12914562Invent ive Exampl e 11Invent ive Steel 310500.157800.12914562Invent ive Exampl e 12Invent ive Steel 310500.157800.12914562Invent ive Exampl e 13Invent ive Steel 410800.258000.10116524Invent ive Exampl e 14Invent ive Steel 410800.258000.10116524Invent ive Exampl e 15Invent ive Steel 410800.258000.10116524Refere nce Exampl e 1Invent ive Steel 410800.258000.10116524Compar ative Exampl e 9Invent ive Steel 511000.207000.0543582Invent ive Exampl e 16Invent ive Steel 511000.207500.0898551Invent ive Exampl e 17Invent ive Steel 511000.208000.14612539Compar ative Exampl e 10Invent ive Steel 511000.208500.24134465Refere nce Exampl e 2Invent ive Steel 110200.258000.12814535Refere nce Exampl e 3Invent ive Steel 110200.258000.12814535Refere nce Exampl e 4Invent ive Steel 210400.157600.1107541Refere nce Exampl e 5Invent ive Steel 210400.157300.1107541[Relational Expression 2] 0.077 ≤ (B / 10.81 + Bi / 208.98)×e (final annealing temperature / 100)< ≤ 0.17 [Table 3] Classif icationSteel gradeSRA heat treatmen t temperat ure (°C)SRA heat treatmen t time (min.)Average grain size after 8RA heat treatment (µm)Magnetic flux density (B50) after 8RA heat treatment (Tesla)Iron ross (W10 / 400) after 8RA heat treatment (W / Kg)Inventi ve Example 1Inventi ve Steel 180060741.63411.3Inventi ve Example 2Inventi ve Steel 180060851.64111.1Inventi ve Example 3Inventi ve Steel 180060811.63811.2Inventi ve Example 4Inventi ve Steel 180060841.64311.1Compara tive Example 1Compara tive Steel 182060591.60512.1Compara tive Example 2Compara tive Steel 182060621.60311.7Compara tive Example 3Compara tive Steel 182060561.60112.3Compara tive Example 4Compara tive Steel 182060571.60412.2Compara tive Example 5Compara tive Steel 284060621.62712.5Compara tive Example 6Compara tive Steel 284060691.63012.0Compara tive Example 7Compara tive Steel 284060681.62412.1Compara tive Example 8Compara tive Steel 284060651.61512.3Inventi ve Example 5Inventi ve Steel 282060931.64111.0Inventi ve Example 6Inventi ve Steel 280060841.63510.1Inventi ve Example 7Inventi ve Steel 282060921.6249. 8Inventi ve Example 8Inventi ve Steel 282060811.6209.3Inventi ve Example 9Inventi ve Steel 378060731.6219.6Inventi ve Example 10Inventi ve Steel 380060811.6169.2Inventi ve Example 11Inventi ve Steel 382060841.6119.1Inventi ve Example 12Inventi ve Steel 384060961.6088.9Inventi ve Example 13Inventi ve Steel 480060791.63511.2Inventi ve Example 14Inventi ve Steel 482060831.63011.2Inventi ve Example 15Inventi ve Steel 484060981.62411.0Referen ce Example 1Inventi ve Steel 4860601131.60311.9Compara tive Example 9Inventi ve Steel 582060721.59811.1Inventi ve Example 16Inventi ve Steel 582060931.6269.9Inventi ve Example 17Inventi ve Steel 5820601051.61310.2Compara tive Example 10Inventi ve Steel 5820601381.60211.8Referen ce Example 2Inventi ve Steel 180030521.64814.7Referen ce Example 3Inventi ve Steel 18001501241.60512.7Referen ce Example 4Inventi ve Steel 273030641.62110.9Referen ce Example 5Inventi ve Steel 2880601421.59213.4

[0074] As can be seen from Tables 1 to 3 above, in the case of Inventive Examples 1 to 17 satisfying the alloy composition and manufacturing conditions proposed by the present disclosure, the average grain sizes intended to be obtained in the present disclosure are secured, and thus, the yield strength and magnetism targeted by the present disclosure are secured.

[0075] In the case of Comparative Examples 1 to 8 not satisfying the alloy composition proposed by the present disclosure, the yield strength is out of the range of the present disclosure and the magnetism is inferior because the average grain size targeted by the present disclosure is not secured.

[0076] In the case of Comparative Examples 9 and 10 not satisfying the manufacturing conditions proposed by the present disclosure, the yield strength is out of the range of the present disclosure and the magnetism is inferior.

[0077] In the case of Reference Examples 1 to 5 satisfying the alloy composition and manufacturing conditions up to final annealing proposed by the present disclosure, the yield strength targeted by the present disclosure is secured by securing the average grain size intended to be obtained in the present disclosure. However, it can be seen that the magnetism is at a low level because the average grain size after SRA is not secured as the SRA heat treatment conditions are not satisfied.

Claims

1. A non-oriented electrical steel sheet comprising: in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities, wherein the non-oriented electrical steel sheet satisfies Relational Expression 1 below and an average grain size is 5 to 25 µm. B / 10.81 + Bi / 208.98 ≤ 0.000072. The non-oriented electrical steel sheet of claim 1, wherein a sum of Sn and Sb is 0.1% or less.

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

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

5. An SRA heat-treated non-oriented electrical steel sheet comprising: in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities, wherein the SRA heat-treated non-oriented electrical steel sheet satisfies Relational Expression 1 below and an average grain size is 70 to 110 µm. B / 10.81 + Bi / 208.98 ≤ 0.000076. The SRA heat-treated non-oriented electrical steel sheet of claim 5, wherein a sum of Sn and Sb is 0.1% or less.

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

8. The SRA heat-treated non-oriented electrical steel sheet of 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 steel sheet) Tesla or more.

9. The SRA heat-treated non-oriented electrical steel sheet of claim 5, wherein the non-oriented electrical steel sheet has a core loss (W10 / 400) of 7.15 + 15.8 × t + 0.0015 × (d-91.7)2 (t: thickness of steel sheet, d: average grain size) W / Kg or less.

10. A method of manufacturing a non-oriented electrical steel sheet, the method comprising: heating a slab including, in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities; finishing hot-rolling the heated slab to obtain a hot-rolled sheet; hot-rolled sheet annealing the hot-rolled sheet; pickling the hot-rolled sheet annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; and finally annealing the cold-rolled sheet at 710 to 830°C, wherein Relational Expression 2 is satisfied during the final annealing, B / 10.81 + Bi / 208.98 ≤ 0.00007 11. The method of claim 10, wherein a sum of Sn and Sb is 0.1% or less.

12. The method of claim 10, wherein the slab heating temperature is 1100 to 1160°C.

13. The method of claim 10, wherein the finishing hot rolling temperature is 870 to 950°C.

14. The method of claim 10, wherein the hot-rolled sheet annealing temperature is 950 to 1150°C.

15. The method of claim 10, wherein the pickling temperature is 65 to 92°C.

16. The method of claim 10, wherein the cold rolling is performed at a cold reduction ratio of 70 to 92%.

17. The method of claim 10, wherein the final annealing is performed for 50 to 120 seconds.

18. A method of manufacturing an SRA heat-treated non-oriented electrical steel sheet, the method comprising: heating a slab including, in wt%, 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%), and at least one of Sn: 0.001 to 0.08% and Sb: 0.001 to 0.08%, and a remainder of Fe and inevitable impurities; finishing hot-rolling the heated slab to obtain a hot-rolled sheet; hot-rolled sheet annealing the hot-rolled sheet; pickling the hot-rolled sheet annealed hot-rolled sheet; cold-rolling the pickled hot-rolled sheet to obtain a cold-rolled sheet; finally annealing the cold-rolled sheet at 710 to 830°C; and SRA heat-treating the finally annealed cold-rolled sheet at 750 to 850°C for 40 to 120 minutes, wherein Relational Expression 2 is satisfied during the final annealing. B / 10.81 + Bi / 208.98 ≤ 0.00007 19. The method of claim 18, wherein a sum of Sn and Sb is 0.1% or less.

20. The method of claim 18, wherein the slab heating temperature is 1100 to 1160°C.

21. The method of claim 18, wherein the finishing hot rolling temperature is 870 to 950°C.

22. The method of claim 18, wherein the hot-rolled sheet annealing temperature is 950 to 1150°C.

23. The method of claim 18, wherein the pickling temperature is 65 to 92°C.

24. The method of claim 18, wherein the cold rolling is performed at a cold reduction ratio of 70 to 92%.

25. The method of claim 18, wherein the final annealing is performed for 50 to 120 seconds.

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