Non-oriented electrical steel sheet, non-oriented electrical steel sheet subjected to SRA heat treatment, and method for producing same

Abstract

The invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof. The purpose of one aspect of the present invention is to provide: a non-oriented electrical steel sheet having excellent strength characteristics after final annealing; and a method for producing the non-oriented electrical steel sheet. Another purpose of the present invention 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 method for producing the same.

Description

Technical Field

[0001] The present invention relates to a non-oriented electrical steel sheet, a non-oriented electrical steel sheet subjected to SRA heat treatment, and methods for manufacturing the same. Background Art

[0002] In recent years, with the growing demand for energy conservation in electrical equipment, there has been a need for non-oriented electrical steel sheets for cores (motor cores) of rotating machines to have more excellent magnetic properties.

[0003] Motor cores can be divided into stator cores and rotor cores. In recent years, in order to meet the requirements for miniaturization and high power of HEV drive motors and the like, non-oriented electrical steel sheets for stator cores are strongly required to have excellent magnetic properties such as high magnetic flux density and low iron loss.

[0004] As a means of achieving miniaturization and high power of the HEV drive motor and the like, the rotational speed of the motor tends to increase. However, since the outer diameter of the HEV drive motor is large, the rotor core is subjected to a large centrifugal force, and there are very narrow portions (1 - 2 mm), such as what is called a rotor core bridge, depending on the structure. Therefore, the non-oriented electrical steel sheet for the rotor core has higher strength than in the past.

[0005] Therefore, the ideal properties of non-oriented electrical steel sheets for motor cores are, in addition to excellent magnetic properties, high strength when used for rotor cores, and higher magnetic flux density and low iron loss when used for stator cores. As described above, even for non-oriented electrical steel sheets for the same motor core, there are significant differences in the required properties between the rotor core and the stator core. However, in the process of manufacturing a motor core, from the perspective of improving the material yield rate and the like, it is preferably possible to simultaneously take out the rotor core material and the stator core material from the same steel sheet, and then stack and assemble each core material into a rotor core or a stator core.

[0006] In addition, in the case of the rotor, high strength is beneficial for preventing breakage during rotation. In particular, for motor design, it is more advantageous to have high strength in all directions rather than in a specific direction. This is because the rotor is made circular and rotates, so it is subjected to tensile forces in all directions. Therefore, when designing the rotor considering only the strength in a specific direction, the strength in other directions during rotation is weak, and thus breakage may occur.

[0007] Furthermore, when manufacturing the rotor, a blanking process using a die is employed. When the difference in strength in each direction of the steel sheet is large, differences in workability are shown in each direction during blanking. Therefore, there are difficulties in mass production. Summary of the Invention

[0008] (I) Technical Problems to be Solved

[0009] An object of one aspect of the present invention is to provide a non-oriented electrical steel sheet having excellent strength characteristics after final annealing and a method for manufacturing the same.

[0010] An object of other aspects of the present invention is to provide a non-oriented electrical steel sheet subjected to SRA heat treatment having excellent high-frequency iron loss characteristics after SRA heat treatment and a method for manufacturing the same.

[0011] (II) Technical Solution

[0012] One embodiment of the present invention provides a non-oriented electrical steel sheet, which, by weight%, comprises: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: 0.005% or less (except 0%); S: 0.003% or less (except 0%); N: 0.005% or less (except 0%); Ti: 0.005% or less (except 0%); B: 0.0005% or less (except 0%); Bi: 0.005% or less (except 0%); one or more of Sn: 0.001 - 0.08% and Sb: 0.001 - 0.08%, the balance Fe and other inevitable impurities, and the non-oriented electrical steel sheet satisfies the following relational expression 1, and the average grain size is 5 - 25 μm.

[0013] [Relational Expression 1] B / 10.81 + Bi / 208.98 ≤ 0.00007

[0014] The total content of the Sn and the Sb may be 0.1% or less.

[0015] The non-oriented electrical steel sheet may have a thickness of 0.15 - 0.25 mm.

[0016] The yield strength of the non-oriented electrical steel sheet may be 490 - 570 MPa.

[0017] Another embodiment of the present invention provides a non-oriented electrical steel sheet subjected to SRA heat treatment, which, by weight%, comprises: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: 0.005% or less (except 0%); S: 0.003% or less (except 0%); N: 0.005% or less (except 0%); Ti: 0.005% or less (except 0%); B: 0.0005% or less (except 0%); Bi: 0.005% or less (except 0%); one or more of Sn: 0.001 - 0.08% and Sb: 0.001 - 0.08%, the balance Fe and other inevitable impurities, and the non-oriented electrical steel sheet satisfies the following relational expression 1, and the average grain size is 70 - 110 μm.

[0018] [Relationship 1] B / 10.81 + Bi / 208.98 ≤ 0.00007

[0019] The total content of the Sn and the Sb may be 0.1% or less.

[0020] The non-oriented electrical steel sheet may have a thickness of 0.15 - 0.25 mm.

[0021] The magnetic flux density (B50) of the non-oriented electrical steel sheet may be 1.544 + 0.28 × t + 0.0014 / t (t: thickness of the steel sheet) Tesla or more.

[0022] The iron loss (W10 / 400) of the non-oriented electrical steel sheet may be 7.15 + 15.8 × t + 0.0015 × (d - 91.7) 2 (t: thickness of the steel sheet, d: average grain size) W / Kg or less.

[0023] Another embodiment of the present invention provides a method for manufacturing a non-oriented electrical steel sheet, the manufacturing method including the following steps: heating a slab, which, by weight%, contains: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: 0.005% or less (except 0%); S: 0.003% or less (except 0%); N: 0.005% or less (except 0%); Ti: 0.005% or less (except 0%); B: 0.0005% or less (except 0%); Bi: 0.005% or less (except 0%); Sn: one or more of 0.001 - 0.08% and Sb: 0.001 - 0.08%, the balance of Fe and other inevitable impurities, the slab satisfying the following Relationship 1; hot finish 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 finally annealing the cold rolled sheet at 710 - 830 °C, wherein the following Relationship 2 is satisfied during the final annealing.

[0024] [Relationship 1] B / 10.81 + Bi / 208.98 ≤ 0.00007

[0025] [Relationship 2] 0.077 ≤ (B / 10.81 + Bi / 208.98) × e (最终退火温度 / 100) ≤ 0.17

[0026] The total content of the Sn and the Sb may be 0.1% or less.

[0027] The heating temperature of the slab may be 1100 - 1160 °C.

[0028] The temperature of the hot finish rolling can be 870 - 950 °C.

[0029] The temperature of the annealing of the hot rolled sheet can be 950 - 1150 °C.

[0030] The temperature of the pickling can be 65 - 92 °C.

[0031] The cold rolling can be carried out at a cold reduction rate of 70 - 92%.

[0032] The final annealing can be carried out for 50 - 120 seconds.

[0033] Another embodiment of the present invention provides a method for manufacturing a non-oriented electrical steel sheet subjected to SRA heat treatment, the manufacturing method comprising the following steps: heating a slab which, by weight, comprises: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: less than 0.005% (except 0%); S: less than 0.003% (except 0%); N: less than 0.005% (except 0%); Ti: less than 0.005% (except 0%); B: less than 0.0005% (except 0%); Bi: less than 0.005% (except 0%); one or more of Sn: 0.001 - 0.08% and Sb: 0.001 - 0.08%, the balance of Fe and other inevitable impurities, the slab satisfying the following relational expression 1; hot finish rolling the heated slab to obtain a hot rolled sheet; annealing the hot rolled sheet; pickling the hot rolled sheet after the annealing of the hot rolled sheet; cold rolling the pickled hot rolled sheet to obtain a cold rolled sheet; finally annealing the cold rolled sheet at 710 - 830 °C; and subjecting the cold rolled sheet after the final annealing to SRA heat treatment at 750 - 850 °C for 40 - 120 minutes, wherein the following relational expression 2 is satisfied during the final annealing.

[0034] [Relational expression 1] B / 10.81 + Bi / 208.98 ≤ 0.00007

[0035] [Relational expression 2] 0.077 ≤ (B / 10.81 + Bi / 208.98) × e (最终退火温度 / 100) ≤ 0.17

[0036] The total content of the Sn and the Sb can be 0.1% or less.

[0037] The heating temperature of the slab can be 1100 - 1160 °C.

[0038] The temperature of the hot finish rolling can be 870 - 950 °C.

[0039] The annealing temperature of the hot-rolled sheet can be 950 - 1150 °C.

[0040] The pickling temperature can be 65 - 92 °C.

[0041] The cold rolling can be carried out at a cold reduction rate of 70 - 92%.

[0042] The final annealing can be carried out for 50 - 120 seconds.

[0043] (III) Advantageous Effects

[0044] According to one aspect of the present invention, it is possible to provide a non-oriented electrical steel sheet having excellent strength characteristics after final annealing and a method for manufacturing the same.

[0045] According to another aspect of the present invention, it is possible to provide a non-oriented electrical steel sheet subjected to SRA heat treatment having excellent high-frequency iron loss characteristics after SRA heat treatment and a method for manufacturing the same. Best Mode for Carrying Out the Invention

[0046] Hereinafter, a non-oriented electrical steel sheet and a non-oriented electrical steel sheet subjected to SRA heat treatment according to an embodiment of the present invention will be described. First, the alloy composition will be described. Unless otherwise specified, the content of the alloy composition described below represents weight %.

[0047] Si: 2.8 - 4.0%

[0048] Silicon (Si) serves to increase the specific resistance of the material and reduce iron loss. When the content of the Si is less than 2.8%, the iron loss improvement effect may be insufficient. When the content of the Si exceeds 4.0%, the brittleness of the material increases, and plate fracture occurs during coiling and cold rolling, and the rolling productivity may be sharply reduced. Therefore, the content of the Si preferably has a range of 2.8 - 4.0%. The lower limit of the Si content is more preferably 2.9%, and further preferably 3.0. The upper limit of the Si content is more preferably 3.9%, and further preferably 3.8%.

[0049] Mn: 0.05 - 1.2%

[0050] Manganese (Mn) serves to increase the specific resistance of the material, improve iron loss, and form sulfides. When the content of the Mn is less than 0.05%, fine sulfides precipitate, and the magnetic properties may be reduced. When the content of the Mn exceeds 1.2%, the formation of the {111} texture, which is unfavorable for magnetic properties, is promoted, and thus the magnetic flux density may be reduced. Therefore, the content of the Mn preferably has a range of 0.05 - 1.2%. The lower limit of the Mn content is more preferably 0.1%, and further preferably 0.2%. The upper limit of the Mn content is more preferably 1.1%, and further preferably 1.0%.

[0051] Al: 0.1 - 1.2%

[0052] Aluminum (Al) serves to increase the specific resistance of the material and reduce iron loss, and has the effect of improving the rollability or the workability during cold rolling. When the content of the Al is less than 0.1%, it has no effect on reducing the high-frequency iron loss, and the precipitation temperature of AlN decreases, thus forming fine nitrides, so the magnetism may decrease. When the content of the Al exceeds 1.2%, excessive nitrides are formed, resulting in poor magnetism and causing problems in all processes such as steelmaking and continuous casting, so the productivity may be significantly reduced. Therefore, the content of the Al preferably has a range of 0.1 - 1.2%. The lower limit of the content of the Al is more preferably 0.2%, and further preferably 0.3%. The upper limit of the content of the Al is more preferably 1.1%, and further preferably 1.0%.

[0053] C: 0.005% or less (except 0%)

[0054] Carbon (C) is an element that inhibits the growth of ferrite grains during annealing and causes excessive deterioration of magnetism during processing, and combines with Ti etc. to reduce magnetism. When the content of the C exceeds 0.005%, the magnetism may be excessively reduced. Therefore, the content of the C preferably has a range of 0.005% or less (except 0%). The content of the C is more preferably 0.004% or less, and further preferably 0.003% or less.

[0055] S: 0.003% or less (except 0%)

[0056] Sulfur (S) is an element that inhibits grain growth by forming fine sulfides inside the base material, thereby reducing iron loss. When the content of the S exceeds 0.003%, it combines with Mn etc. to inhibit grain growth or the magnetism may be excessively reduced after processing. Therefore, the content of the S preferably has a range of 0.003% or less (except 0%). The content of the S is more preferably 0.002% or less.

[0057] N: 0.005% or less (except 0%)

[0058] Nitrogen (N) is an element that deteriorates iron loss. For example, nitrogen (N) combines with Al, Ti etc. to form fine and long precipitates inside the base material, and combines with other impurities to form fine nitrides, thereby inhibiting grain growth etc. When the content of the N exceeds 0.005%, the magnetism may be excessively reduced. Therefore, the content of the N preferably has a range of 0.005% or less (except 0%). The content of the N is more preferably 0.004% or less, and further preferably 0.003% or less.

[0059] Ti: 0.005% or less (except 0%)

[0060] Titanium (Ti) is an element that has a very strong tendency to form precipitates in steel, and is an element that inhibits grain growth by forming fine carbides or nitrides inside the base material. When the Ti content exceeds 0.005%, a large amount of carbides and nitrides are formed, which deteriorates the magnetic properties, for example, worsens the iron loss, etc. Therefore, the Ti content preferably has a range of 0.005% or less (except 0%). The Ti content is more preferably 0.004% or less, and further preferably 0.003% or less.

[0061] B: 0.0005% or less (except 0%)

[0062] Boron (B) is an element that easily forms segregated precipitates in steel. Even if added in a small amount, it will cause segregation at the grain boundary, thereby inhibiting grain growth. In particular, since its segregation degree is more obvious near the SRA heat treatment temperature, it must be suppressed as much as possible. When the content of the B exceeds 0.0005%, the magnetic properties may be excessively reduced. Therefore, the content of the B is preferably in the range of 0.0005% or less (except 0%).

[0063] Bi: 0.005% or less (except 0%)

[0064] Bismuth (Bi) is an element that is very easy to segregate in steel. Even if it is added in a small amount, it will segregate at the grain boundary and inhibit grain growth. In particular, since its segregation degree is more obvious near the SRA heat treatment temperature, it must be suppressed as much as possible. Therefore, the Bi content is preferably in the range of 0.005% or less (except 0%). The Bi content is more preferably 0.004% or less.

[0065] Sn: 0.001-0.08% and Sb: 0.001-0.08% or more

[0066] Sn: 0.001-0.08%

[0067] Tin (Sn) is an element that improves the texture of the steel sheet by segregating at the grain boundaries and the surface, and improves the magnetism by inhibiting surface oxidation. When the Sn content is less than 0.001%, it may be difficult to fully obtain the above-mentioned effects. When the Sn content exceeds 0.08%, the grain boundary segregation becomes serious, the surface quality deteriorates, the hardness increases, and the cold-rolled sheet breaks, so the rolling property may be reduced. Therefore, the Sn content preferably has a range of 0.001-0.08%. The lower limit of the Sn content is more preferably 0.01%. The upper limit of the Sn content is more preferably 0.07%.

[0068] Sb: 0.001-0.08%

[0069] Antimony (Sb) is an element that plays a role in improving the texture of the steel sheet by segregating at grain boundaries and surfaces, and enhancing magnetism by suppressing surface oxidation. When the content of Sb is less than 0.001%, it may be difficult to fully obtain the above effects. When the content of Sb exceeds 0.08%, grain boundary segregation becomes severe, the surface quality deteriorates, and the hardness increases, resulting in fracture of the cold-rolled sheet, so the rollability may decrease. Therefore, the content of Sb preferably has a range of 0.001 - 0.08%. The lower limit of the content of Sb is more preferably 0.01%. The upper limit of the content of Sb is more preferably 0.07%.

[0070] The total content of the Sn and the Sb may be 0.1% or less. When the total content of the Sn and the Sb exceeds 0.1%, the degree of segregation intensifies, the surface quality deteriorates, and crystal growth is hindered, so the problem of deteriorated magnetism may occur.

[0071] The remaining component is iron (Fe). However, in the normal manufacturing process, unnecessary impurities inevitably mix in from raw materials or the surrounding environment, so these impurities cannot be completely excluded. These impurities are well-known to those skilled in the normal manufacturing process, so all of their contents are not particularly mentioned in this specification.

[0072] The non-oriented electrical steel sheet of the present invention preferably satisfies the following relational expression 1.

[0073] [Relational expression 1] B / 10.81 + Bi / 208.98 ≤ 0.00007

[0074] When the relational expression 1 is not satisfied, the degree of grain boundary segregation intensifies, hindering crystal growth, so it is difficult to ensure appropriate magnetic properties before and after SRA.

[0075] The non-oriented electrical steel sheet according to an embodiment of the present invention, that is, the average grain size of the non-oriented electrical steel sheet before SRA heat treatment after final annealing is preferably 5 - 25 μm. When the average grain size is less than 5 μm, a sufficient initial recrystallized structure cannot be ensured, and there is a disadvantage that the magnetic properties deteriorate after SRA heat treatment. When the average grain size exceeds 25 μm, there is a disadvantage of reduced strength.

[0076] The non-oriented electrical steel sheet of the present invention provided as above may have a thickness of 0.15 - 0.25 mm. In addition, the yield strength may be 490 - 570 MPa.

[0077] The SRA heat-treated non-oriented electrical steel sheet according to another embodiment of the present invention, that is, the average grain size of the non-oriented electrical steel sheet after SRA heat treatment is preferably 70 - 110 μm. When the average grain size is less than 70 μm, there is a disadvantage of deteriorated iron loss. When the average grain size exceeds 110 μm, there is a disadvantage of deteriorated high-frequency iron loss.

[0078] The SRA heat-treated non-oriented electrical steel sheet of the present invention provided as described above may have a thickness of 0.15 - 0.25 mm. In addition, the magnetic flux density (B50) may be 1.544 + 0.28×t + 0.0014 / t (t: thickness of the steel sheet) 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 sheet, d: average grain size) W / Kg or less. In the present invention, the larger the magnetic flux density (B50), the more advantageous it is, and thus there is no particular limitation on its upper limit. However, the upper limit of the magnetic flux density (B50) may be, for example, 1.8 T. In addition, in the present invention, the smaller the iron loss (W10 / 400), the more advantageous it is, and thus there is no particular limitation on its lower limit. However, the lower limit of the iron loss (W10 / 400) may be, for example, 7 W / Kg.

[0079] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described.

[0080] First, a slab satisfying the above alloy composition is heated. The heating temperature of the slab may be 1100 - 1160 °C. When the heating temperature of the slab is lower than 1100 °C, there is a disadvantage of high hot deformation resistance and difficulty in hot rolling. When the heating temperature of the slab exceeds 1180 °C, fine precipitates increase, and there is a disadvantage of deteriorated iron loss. Therefore, the heating temperature of the slab preferably has a range of 1100 - 1180 °C.

[0081] After that, the heated slab is hot finish-rolled to obtain a hot-rolled sheet. The hot finish-rolling temperature may be 870 - 950 °C. When the hot finish-rolling temperature is lower than 870 °C, the strength of the sheet increases, and there is a disadvantage of causing defects such as poor shape when coiling the rolled sheet. When the hot finish-rolling temperature exceeds 950 °C, it is necessary to increase the rolling speed, and thus there is a disadvantage that hot rolling itself is difficult to perform.

[0082] After that, the hot-rolled sheet is annealed. The annealing temperature of the hot-rolled sheet can be 950 - 1150 °C. When the annealing temperature of the hot-rolled sheet is lower than 950 °C, there is a disadvantage that the hot-rolled sheet cannot be fully recrystallized. When the annealing temperature of the hot-rolled sheet exceeds 1150 °C, there is a disadvantage that the grain size is too large and it is difficult to perform cold rolling. Therefore, the annealing temperature of the hot-rolled sheet can be in the range of 950 - 1150 °C. The lower limit of the annealing temperature of the hot-rolled sheet is more preferably 970 °C, further preferably 990 °C, and most preferably 1000 °C or above. The upper limit of the annealing temperature of the hot-rolled sheet is more preferably 1130 °C, further preferably 1110 °C.

[0083] After that, the hot-rolled sheet annealed by the above is pickled. The pickling temperature can be 65 - 92 °C. When the pickling temperature is lower than 65 °C, there is a disadvantage that the oxide layer generated after annealing of the hot-rolled sheet cannot be fully removed. When the pickling temperature exceeds 92 °C, the evaporation amounts of hydrochloric acid and water increase, and there is a disadvantage that the operating environment deteriorates. Therefore, the pickling temperature can be in the range of 65 - 92 °C.

[0084] After that, the pickled hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet. The cold rolling can be carried out at a cold reduction rate of 70 - 92%. When the cold reduction rate is less than 70%, the thickness of the steel sheet must be reduced after hot rolling, so there are disadvantages that it is difficult to perform hot rolling or the thickness of the cold-rolled steel sheet becomes thick. When the cold reduction rate exceeds 92%, due to the high cold reduction rate, there is a disadvantage that the magnetic property deteriorates. Therefore, the cold reduction rate can be in the range of 70 - 92%.

[0085] After that, the cold-rolled sheet is finally annealed at 710 - 830 °C. When the final annealing temperature is lower than 710 °C, there is a disadvantage that it is difficult to ensure sufficient initial recrystallization. When the final annealing temperature exceeds 830 °C, the grains are too large and there is a disadvantage that the strength decreases. Therefore, the final annealing temperature can be in the range of 710 - 830 °C. The lower limit of the final annealing temperature is more preferably 730 °C, further preferably 750 °C. The upper limit of the final annealing temperature is more preferably 820 °C. The final annealing can be carried out for 50 - 120 seconds. When the final annealing time is less than 50 seconds, there is a disadvantage that it is difficult to ensure sufficient initial recrystallization. When the final annealing time exceeds 120 seconds, the grains are too large and there is a disadvantage that the strength decreases. Therefore, the final annealing time can be in the range of 50 - 120 seconds. The upper limit of the final annealing time is more preferably 100 seconds.

[0086] Preferably, the following relational expression 2 is satisfied during the final annealing.

[0087] [Relational expression 2] 0.077 ≤ (B / 10.81 + Bi / 208.98) × e(最终退火温度 / 100) ≤0.17

[0088] The relational expression 2 is related to the grain boundary segregation behavior index of the annealing temperature of the cold-rolled sheet. When the value of the relational expression 2 is less than 0.077, the annealing temperature is too low and recrystallization is difficult, having the drawback of obtaining a grain size smaller than the target grain size during final annealing. When the value of the relational expression 2 exceeds 0.17, the contents of B and Bi are too high or the annealing temperature is too high, and it is difficult to ensure the target grain size during final annealing.

[0089] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet heat-treated by SRA according to an embodiment of the present invention will be described.

[0090] After the above manufacturing process, the cold-rolled sheet subjected to the final annealing is subjected to SRA heat treatment at 750 - 850 °C for 40 - 120 minutes. The temperature of the SRA heat treatment can be 750 - 850 °C. When the temperature of the SRA heat treatment is lower than 750 °C, the grain size becomes smaller after the SRA heat treatment, and there is a drawback of poor iron loss. When the temperature of the SRA heat treatment exceeds 850 °C, the grain size after the SRA heat treatment becomes larger, having drawbacks of poor magnetic flux density and high-frequency iron loss. Therefore, the temperature of the SRA heat treatment can have a range of 750 - 850 °C. The SRA heat treatment can be performed for 40 minutes to 120 minutes. The SRA heat treatment time is calculated from the time when the atmosphere temperature of the annealing furnace or the plate temperature in the annealing furnace reaches the target temperature. When the SRA heat treatment time is less than 40 minutes, sufficient grain growth cannot be ensured, and there is a drawback of poor iron loss. When the SRA heat treatment time exceeds 120 minutes, the grains grow excessively, and there is a drawback of poor magnetic flux density. Therefore, the SRA heat treatment time can have a range of 40 - 120 minutes. Detailed Description of the Invention

[0091] Hereinafter, the present invention will be described in more detail by way of examples. However, it should be noted that the following examples are only used to illustrate the present invention for more detailed description and are not used to limit the scope of the rights of the present invention. This is because the scope of the rights of the present invention is determined by the content recorded in the claims and the content reasonably deduced therefrom.

[0092] (Examples)

[0093] A slab having the alloy composition shown in Table 1 below was heated at 1150°C, and then the heated slab was hot finish rolled at 920°C to obtain a hot rolled sheet with a thickness of 1.8 mm. Thereafter, the hot rolled sheet was subjected to hot rolled sheet annealing 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 with a thickness of 0.15 - 0.25 mm. Thereafter, it was finally annealed for 80 seconds under the conditions described in Table 2 below to manufacture a non-oriented electrical steel sheet. Thereafter, it was subjected to SRA heat treatment under the conditions described in Table 3 below to manufacture a non-oriented electrical steel sheet. In addition, the final annealing and SRA heat treatment conditions described in Table 2 and Table 3 below are based on the atmosphere temperature of the annealing furnace.

[0094] After measuring the mechanical / electrical physical properties of the non-oriented electrical steel sheet after final annealing and the non-oriented electrical steel sheet after SRA heat treatment manufactured as described above, the results are shown in Table 2 and Table 3 below, respectively.

[0095] After making a test piece according to JIS13 - A standard, the yield strength was measured by a tensile test.

[0096] The number of test pieces processed to a size of 305 mm × 30 mm was adjusted in the rolling direction and the direction perpendicular to rolling so that the weight was 400 - 450 g, and the magnetic flux density (B50) and iron loss (W10 / 400) were measured by the Epstein measurement method, and the average value was calculated.

[0097] [Table 1]

[0098]

[0099] [Table 2]

[0100]

[0101] [Table 3]

[0102]

[0103] As can be seen from Tables 1 to 3 above, in the case of Invention Examples 1 to 17 that satisfy the alloy composition and manufacturing conditions proposed by the present invention, since the average grain size desired by the present invention is ensured, the yield strength and magnetic properties desired by the present invention can be ensured.

[0104] In the case of Comparative Examples 1 to 8 that do not satisfy the alloy composition proposed by the present invention, it can be seen that since the average grain size desired by the present invention cannot be ensured, the yield strength deviates from the scope of the present invention, and the magnetic properties are at a poor level.

[0105] In Comparative Example 9 and Comparative Example 10 where the manufacturing conditions proposed by the present invention are not satisfied, it can be seen that the yield strength deviates from the scope of the present invention and the magnetic properties are at a poor level.

[0106] In the case of Reference Examples 1 to 5 where the alloy composition proposed by the present invention and the manufacturing conditions up to the final annealing are satisfied, it can be seen that since the average grain size desired to be obtained by the present invention is ensured, the yield strength desired by the present invention can be ensured. However, it can be seen that since the SRA heat treatment conditions are not satisfied, the average grain size after SRA cannot be ensured, and thus the magnetic properties are at a poor level.

Claims

1. An non-oriented electrical steel sheet, by weight %, the non-oriented electrical steel sheet comprises: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: less than or equal to 0.005% excluding 0%; S: less than or equal to 0.003% excluding 0%; N: less than or equal to 0.005% excluding 0%; Ti: less than or equal to 0.005% excluding 0%; B: less than or equal to 0.0005% excluding 0%; Bi: less than or equal to 0.005% excluding 0%; one or more of Sn: 0.001 - 0.08% and Sb: 0.001 - 0.08%, balance Fe and other inevitable impurities, The non-oriented electrical steel sheet satisfies the following relational expression 1, The average grain size is 5 - 25 μm, [Relational expression 1] B / 10.81 + Bi / 208.98 ≤ 0.00007.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The total content of the said Sn and the said 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 - 0.25 mm.

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

5. An SRA heat-treated non-oriented electrical steel sheet, by weight %, the non-oriented electrical steel sheet contains: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: less than or equal to 0.005% excluding 0%; S: less than or equal to 0.003% excluding 0%; N: less than or equal to 0.005% excluding 0%; Ti: less than or equal to 0.005% excluding 0%; B: less than or equal to 0.0005% excluding 0%; Bi: less than or equal to 0.005% excluding 0%; one or more of Sn: 0.001 - 0.08% and Sb: 0.001 - 0.08%, balance Fe and other inevitable impurities, The non-oriented electrical steel sheet satisfies the following relational expression 1, The average grain size is 70 - 110 μm, [Relational expression 1] B / 10.81 + Bi / 208.98 ≤ 0.00007.

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

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

8. The non-oriented electrical steel sheet heat-treated by SRA according to claim 5, wherein, The magnetic flux density (B50) of the non-oriented electrical steel sheet is 1.544 + 0.28×t + 0.0014 / t tesla or more, where t is the thickness of the steel sheet.

9. The non-oriented electrical steel sheet heat-treated by SRA according to claim 5, wherein, The iron loss (W10 / 400) of the non-oriented electrical steel sheet is 7.15 + 15.8×t + 0.0015×(d - 91.7) 2 W / Kg or less, where t is the thickness of the steel sheet and d is the average grain size.

10. A method for manufacturing a non-oriented electrical steel sheet, which includes the following steps: Heating a slab, by weight%, the slab contains: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: less than or equal to 0.005% excluding 0%; S: less than or equal to 0.003% excluding 0%; N: less than or equal to 0.005% excluding 0%; Ti: less than or equal to 0.005% excluding 0%; B: less than or equal to 0.0005% excluding 0%; Bi: less than or equal to 0.005% excluding 0%; one or more of Sn: 0.001 - 0.08% and Sb: 0.001 - 0.08%, balance Fe and other inevitable impurities; Hot finish rolling the heated slab to obtain a hot rolled sheet; Annealing the hot rolled sheet; Pickling the hot rolled sheet after the annealing of the 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 - 830 °C, wherein, 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 (最终退火温度 / 100) ≤ 0.

17.

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

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

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

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

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

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

17. The manufacturing method of the non-oriented electrical steel sheet according to claim 10, wherein, The final annealing is carried out for 50 - 120 seconds.

18. A method for manufacturing a non-oriented electrical steel sheet subjected to SRA heat treatment, which comprises the following steps: Heating a slab, which, by weight%, contains: Si: 2.8 - 4.0%; Mn: 0.05 - 1.2%; Al: 0.1 - 1.2%; C: 0.005% or less and excluding 0%; S: 0.003% or less and excluding 0%; N: 0.005% or less and excluding 0%; Ti: 0.005% or less and excluding 0%; B: 0.0005% or less and excluding 0%; Bi: 0.005% or less and excluding 0%; Sn: 0.001 - 0.08% and Sb: one or more of 0.001 - 0.08%, the balance of Fe and other inevitable impurities; Subjecting the heated slab to hot finish rolling to obtain a hot rolled sheet; Annealing the hot rolled sheet; Pickling the hot rolled sheet after the annealing of the hot rolled sheet; Subjecting the pickled hot rolled sheet to cold rolling to obtain a cold rolled sheet; Subjecting the cold rolled sheet to final annealing at 710 - 830 °C; and Subjecting the cold rolled sheet after the final annealing to SRA heat treatment at 750 - 850 °C for 40 - 120 minutes, wherein, the following relationship 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 (最终退火温度 / 100) ≤ 0.

17.

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

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

21. The method for manufacturing an SRA heat-treated non-oriented electrical steel sheet according to claim 18, wherein, The temperature of the hot finish rolling is 870 - 950 °C.

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

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

24. The manufacturing method of the non-oriented electrical steel sheet heat-treated by SRA according to claim 18, wherein, The cold rolling is carried out at a cold reduction rate of 70 - 92%.

25. The method for manufacturing a non-oriented electrical steel sheet heat-treated by SRA according to claim 18, wherein, The final annealing is carried out for 50 - 120 seconds.

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