Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

The present invention relates to a non-oriented electrical steel sheet and a manufacturing method therefor. An aspect of the present invention is to provide: a non-oriented electrical steel sheet in which an iron loss in a direction perpendicular to a rolling direction at high frequency is less than that in the rolling direction; and a manufacturing method therefor.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a non-oriented electrical steel sheet and a method of manufacturing the same.BACKGROUND ART

[0002] Electric vehicles and electric-powered transportation have been used to replace internal combustion engines to reduce greenhouse gas emissions. Currently, 50% or more of all electrical energy generated may be consumed by electric motors for power, and efficient use of electricity may be important in order for internal combustion engines to be replaced by electric motors in the future. In particular, along with the improvement of electric performance, miniaturization and weight reduction have also been implemented, and motors forming magnetic flux in the axial direction may also draw attention. These electric motors may be used to resolve space constraints and improve performance of various electric devices including existing electric vehicles, electric two-wheeled vehicles, electric airplanes, ships, and electric and thus, high efficiency may be necessary. Also, interest in high-functioning and high-efficiency motors for home appliances, robots, and industrial motors has continued along with technological development and changes in the market and efficient use of electric energy may be higher than ever.

[0003] In order to improve the efficiency of an electric motor, optimization in all areas from material selection to design, assembly, and control may be important. In particular, in terms of material, magnetic properties of an electrical steel may be the most important, such that there has been high demand for low iron loss and high magnetic flux density. As for automobile drive motors or air conditioner compressor motors driven in the commercial frequency region and also in the high-frequency region, low iron loss properties at high frequencies may be important. Also, in the case of a small high-power motor having a yoke with a narrow width, high magnetic flux may be formed in the teeth area of the motor and also in the yoke area to obtain high torque when the motor is operated, and thus, improvement of iron loss at high magnetic flux at high frequencies may be important for improving motor efficiency.

[0004] Generally, as for electrical steel, eddy current loss may be reduced by adding a large amount of non-resistive elements such as Si, Al, and Mn and reducing the grain size during the manufacturing process. Since eddy current only passes through a surface layer of the steel sheet as the frequency increases, high-frequency iron loss may be improved by increasing a resistivity element of the surface layer. However, the general manufacturing method may be effective in controlling iron loss at a magnetic flux of around 1.0 T, and a method of reducing iron loss at high magnetic flux may not be known.DETAILED DESCRIPTION OF PRESENT DISCLOSURETechnical Problems to Solve

[0005] An aspect in the present disclosure is to provide a non-oriented electrical steel sheet in which iron loss in a rolling vertical direction may be lower than that in a rolling direction at a high frequency, and a method of manufacturing the same.Solution to Problem

[0006] According to an embodiment of the present disclosure, a non-oriented electrical steel sheet includes, by weight %, Si: 1.5 to 6.5%, Al: 0.0005 to 3.5%, Mn: 0.01 to 3.0%, Cr: 0.005 to 5.0%, S: 0.0005 to 0.03%, and a balance of Fe and inevitable impurities, wherein a Goss orientation fraction in a region from a surface to 1 / 10t (t: thickness of the steel sheet) in a thickness direction is 3 area % or less, and wherein a Goss orientation fraction in an entire region in the thickness direction is 5 area % or less.

[0007] The non-oriented electrical steel sheet may further include one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

[0008] The non-oriented electrical steel sheet may further include one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), 0:0.005% or less (excluding 0%) and Ti: 0.01% or less (excluding 0%).

[0009] The non-oriented electrical steel sheet may further include one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%) and Mg: 0.0050% or less (excluding 0%).

[0010] The non-oriented electrical steel sheet may further include one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2% and Zn: 0.01% or less (excluding 0%).

[0011] The non-oriented electrical steel sheet further includes 0.20% or less (excluding 0%) of one or more of Bi, Pb, Ge and As individually or in combination.

[0012] The non-oriented electrical steel sheet may have an iron loss (W10 / 600C) of 28 W / kg or lower, an iron loss (W10 / 800C) of 43 W / kg or lower, and an iron loss (W10 / 1200C) of 75 W / kg or lower.

[0013] The non-oriented electrical steel sheet may have an iron loss (W10 / 600L) of 30 W / kg or lower, an iron loss (W10 / 800L) of 48 W / kg or lower, and an iron loss (W10 / 1200L) of 85 W / kg or lower.

[0014] The non-oriented electrical steel sheet may have an iron loss (W15 / 600C) of 65 W / kg or lower, an iron loss (W15 / 800C) of 95 W / kg or lower, and an iron loss (W15 / 1200C) of 175 W / kg or lower.

[0015] The non-oriented electrical steel sheet may have an iron loss (W15 / 600L) of 75 W / kg or lower, an iron loss (W15 / 800L) of 105 W / kg or lower, and an iron loss (W15 / 1200L) of 190 W / kg or lower.

[0016] The non-oriented electrical steel sheet may satisfy relational expression 1 as below:iron loss (W10 / 600C)+iron loss (W10 / 800C)+iron loss (W10 / 1200C)<iron loss (W10 / 600L)+iron loss (W10 / 800L)+iron loss (W10 / 1200L)  [Relational expression 1]

[0017] According to another embodiment of the present disclosure, a method of manufacturing a non-oriented electrical steel sheet includes heating a slab including, by weight %, Si: 1.5 to 6.5%, Al: 0.0005 to 3.5%, Mn: 0.01 to 3.0%, Cr: 0.005 to 5.0%, S: 0.0005 to 0.03%, and a balance of Fe and inevitable impurities at 1050 to 1220° C.; finishing hot-rolling the slab and obtaining a hot-rolled sheet; hot-rolled sheet annealing the hot-rolled sheet for 30 to 300 seconds at 850 to 1150° C.; cold-rolling the hot-rolled sheet annealed hot-rolled sheet and obtaining a cold-rolled sheet; heating the cold-rolled sheet; and final annealing the heated cold-rolled sheet, wherein, in the cold-rolling, [Relational expression 2] is satisfied, wherein, in the heating, a heating rate in a temperature range of 300 to 500° C. is 5 to 150° C. / s, and wherein, in the final annealing, a gas atmosphere includes, by volume %, hydrogen: 15 to 99.99%, oxygen: 0.0001 to 0.0030%, and a remainder of inert gas.Highest temperature of cold-rolled sheet surface during cold-rolling<200×cold reduction ratio / 100+60  [Relational expression 2]

[0018] The slab may further include one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

[0019] The slab may further include one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), 0:0.005% or less (excluding 0%) and Ti: 0.01% or less (excluding 0%).

[0020] The slab may further include one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%) and Mg: 0.0050% or less (excluding 0%).

[0021] The slab may further include one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2% and Zn: 0.01% or less (excluding 0%).

[0022] The slab may further include 0.20% or less (excluding 0%) of one or more of Bi, Pb, Ge and As individually or in combination.

[0023] The finishing hot-rolling may be performed at 700 to 1050° C.

[0024] The cold-rolling may be performed with a cold reduction ratio of 35 to 98%.

[0025] In the cold rolling, a maximum rolling rate in one or more of first pass and second pass may be 3 m / s or higher.

[0026] The final annealing may be performed for 10 to 500 seconds at 600 to 1150° C.Advantageous Effects of Invention

[0027] According to an aspect of the present disclosure, a non-oriented electrical steel sheet in which iron loss in a rolling vertical direction may be lower than that in a rolling direction at a high frequency, and a method of manufacturing the same may be provided.BEST MODE FOR INVENTION

[0028] Hereinafter, a non-oriented electrical steel sheet according to an embodiment of the present invention may be described. First, an alloy composition may be described. The content of the alloy composition described below may be indicated in weight % unless otherwise indicated.Si: 1.5 to 6.5%

[0029] Si may increase resistivity of a material and may reduce iron loss. When the content of Si is less than 1.5%, the effect of improvement of high-frequency iron loss may be insufficient. When the content of Si exceeds 6.5%, hardness may increase and productivity and die-casting may deteriorate. Accordingly, the content of Si may preferably have a range of 1.5 to 6.5%. A lower limit of the content of Si may preferably be 1.8%, and more preferably 2.0%. An upper limit of the content of Si may preferably be 6.0%, more preferably 5.0%, and most preferably 4.0%.Al: 0.0005 to 3.5%

[0030] Al may increase resistivity of the material and may reduce iron loss. When the Al content is less than 0.0005%, the amount of Al to exclude oxygen during steel manufacturing may be small, and inclusions may be formed excessively in steel, which may not be effective in reducing high-frequency iron loss, and fine nitrides may be formed on the surface, which may reduce magnetism. When the Al content exceeds 3.5%, there may be problems in all processes such as steelmaking and continuous casting, which may significantly reduce productivity. Accordingly, the Al content may preferably have a range of 0.0005 to 3.5%. A lower limit of the Al content may be 0.15% more preferably. An upper limit of the Al content may preferably be 3.0%, more preferably 2.5%, and most preferably 2.0%.Mn: 0.01 to 3.0%

[0031] Mn may increase resistivity of the material, thereby improving iron loss and forming sulfides, and may stabilize austenite. When the content of the Mn is less than 0.01%, sulfides, which is MnS, may be finely precipitated in steel, which may reduce magnetism. When the content of the Mn exceeds 3.0%, the range of annealing temperatures in which an appropriate grain size for obtaining low high-frequency iron loss may be obtained may be limited. Also, saturation magnetic flux of the material may be lowered, and formation of {111} texture, which is particularly unfavorable to ferromagnetism, may be promoted, such that magnetic flux density may reduce. Accordingly, the content of Mn may preferably have a range of 0.01 to 3.0%. A lower limit of the Mn content may be more preferably 0.2%. An upper limit of the Mn content may be preferably 2.5%, more preferably 2.0%, and most preferably 1.5%.Cr: 0.005 to 5.0%

[0032] Cr may increase resistivity of the material and may reduce iron loss, and also, when the cold-rolling conditions and the final annealing conditions are properly controlled, Cr may be concentrated on the surface and may form a Cr-concentrated layer. When the Cr content is less than 0.005%, Cr may have a minimal effect on increasing resistivity and may form carbides by combining with C, or the like, which may be detrimental to magnetism. When Cr exceeds 5%, Cr may be evenly distributed throughout the entire thickness rather than concentrating on the surface, a decrease in magnetic flux density may occur throughout the steel sheet. Accordingly, the Cr content may preferably have a range of 0.005 to 5.0%. In terms of surface enrichment, a lower limit of Cr may more preferably be 0.04%. In terms of preventing the decrease in magnetic flux density, an upper limit of the Cr may preferably be 3.0%, more preferably 1.0%, and most preferably 0.3%.S: 0.0005 to 0.03%

[0033] S may be a strong segregating element and may form precipitates. When S is added in an appropriate amount, S may segregate on the surface and may react with oxygen in the atmosphere during annealing, thereby inhibiting growth of Goss grains on the surface. When the S content is less than 0.0005%, the surface segregation effect may not be sufficient. When the S content exceeds 0.03%, a FeS enriched layer may be formed on the surface, which may significantly deteriorate the surface quality. Accordingly, the S content may preferably have a range of 0.0005 to 0.03%. A lower limit of the S content may more preferably be 0.001%. An upper limit of the S content may preferably be 0.015%, more preferably 0.005%, and most preferably 0.0035%.

[0034] A remainder of the present disclosure is iron (Fe). However, in a general manufacturing process, inevitable impurities may be inevitably added from raw materials or an ambient environment, and thus, impurities may not be excluded. A person skilled in the art of a general manufacturing process may be aware of the impurities, and thus, the descriptions of the impurities may not be provided in the present disclosure.

[0035] The non-oriented electrical steel sheet of the present invention may further include one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.P: 0.005 to 0.08%

[0036] P may be concentrated on the surface and may control a fraction of the internal oxide layer. When the content of the P is less than 0.005%, it may be difficult to form a uniform internal oxide layer. When the content of P exceeds 0.08%, and a melting point of the Si-based oxide may change, an internal oxide layer may form rapidly. Accordingly, the content of the P may preferably have a range of 0.005 to 0.08%. An upper limit of the P content may more preferably be 0.07%.Sn: 0.01 to 0.2%

[0037] Sn may be segregated on the surface and grain system of the steel sheet, may suppress surface oxidation during annealing and may improving texture. When the Sn content is less than 0.01%, it may be difficult to sufficiently obtain the above-mentioned effect. When the Sn content exceeds 0.2%, Sn may be segregated on the grain system, and may lower toughness, such that productivity may degrade compared to improvement of magnetism. Accordingly, the Sn content may preferably have a range of 0.01 to 0.2%. A lower limit of Sn content may more preferably be 0.02%. An upper limit of Sn content may preferably be 0.15%, more preferably 0.1%, and most preferably 0.07%.

[0038] The non-oriented electrical steel sheet of the present invention may further include one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%) and Ti: 0.01% or less (excluding 0%).C: 0.005% or less (Excluding 0%)

[0039] C may react with N, Ti, Nb, V, or the like and may form fine carbides, which hinder grain growth and domain movement, and thus, an upper limit thereof may be limited to 0.005%.N: 0.005% or less (Excluding 0%)

[0040] N may combine with Ti, Nb, V, or the like, and may form nitrides, which may hinder grain growth, and thus, an upper limit thereof may be limited to 0.005%.0:0.005% or Less (Excluding 0%)

[0041] O may react with Fe, Ti, Al, Mn, Cr, Si, V, or the like, and may form fine oxides, which hinder grain growth and domain movement, and thus, an upper limit thereof may be limited to 0.005%.Ti: 0.01% or Less (Excluding 0%)

[0042] Ti may combine with C, N, O, or the like, and may form fine nitrides or oxides, which hinder domain movement, and thus, an upper limit thereof may be limited to 0.01%.

[0043] Also, the non-oriented electrical steel sheet of the present invention may further include one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%) and Mg: 0.0050% or less (excluding 0%).Mo: 0.1% or Less (Excluding 0%)

[0044] Mo may react with C, O, N, or the like, and may form fine carbides or nitrides, which adversely affect magnetism, and thus, an upper limit thereof may be limited to 0.1%.B: 0.0050% or Less (Excluding 0%)

[0045] B may react with C, O, N, or the like, and may form fine carbides or nitrides, which adversely affect magnetism, and thus, an upper limit thereof may be limited to 0.0050%.V: 0.050% or Less (Excluding 0%)

[0046] V may react with C, O, N, or the like, and may form fine carbides or nitrides, which adversely affect magnetism, and thus, an upper limit thereof may be limited to 0.050%.Ca: 0.010% or Less (Excluding 0%)

[0047] Ca may react with C, O, N, or the like, and may form fine carbides or nitrides, which adversely affect magnetism, and thus, an upper limit thereof may be limited to 0.010%.Nb: 0.0050% or Less (Excluding 0%)

[0048] Nb may react with C, O, N, or the like, and may form fine carbides or nitrides, which adversely affect magnetism, and thus, an upper limit thereof may be limited to 0.0050%.Mg: 0.0050% or Less (Excluding 0%)

[0049] Mg may react with C, O, N, or the like, and may form fine carbides or nitrides, which adversely affect magnetism, and thus, an upper limit thereof may be limited to 0.0050%.

[0050] The non-oriented electrical steel sheet of the present invention may further include one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2% and Zn: 0.01% or less (excluding 0%).Sb: 0.1% or Less (Excluding 0%)

[0051] Sb may segregate in the grain system, and may be added to suppress the diffusion of nitrogen through the grain system, to suppress the {111} texture (texture) detrimental to magnetism, and to increase the {100} texture advantageous to improve magnetic properties. When the content of Sb exceeds 0.1%, Sb may hinder grain growth, which may lower magnetism and may deteriorate rolling properties. More specifically, the content of Sb may be 0.001 to 0.1%. More specifically, the content of Sb may be 0.005 to 0.08%Ni: 0.05% or Less (Excluding 0%)

[0052] Ni may react with impurity elements and may form fine sulfides, carbides, and nitrides, which have a detrimental effect on magnetism, and thus, an upper limit thereof may be limited to 0.05%. More specifically, the content of Ni may be 0.0001 to 0.050%. More specifically, the content of Ni may be 0.001 to 0.030%.Cu: 0.005 to 0.2%

[0053] Cu may form sulfides together with Mn. When the content of Cu is less than 0.005%, (Cu Mn)S may be finely precipitated, which may deteriorate magnetism. When the content of Cu exceeds 0.2%, high-temperature embrittlement may occur, which may cause cracks during casting or hot rolling. More specifically, the content of Cu may be 0.010 to 0.1%.Zn: 0.01% or Less (Excluding 0%)

[0054] Zn may act as an impurity and may deteriorate magnetism, and thus, an upper limit thereof may be limited to 0.01%. More specifically, the content of Zn may be 0.0001 to 0.01%. More specifically, the content of Zn may be 0.001 to 0.008%.

[0055] The non-oriented electrical steel sheet of the present invention may further include 0.20% or less (excluding 0%) of one or more of Bi, Pb, Ge and As individually or in combination.

[0056] When the above-mentioned elements are additionally added, the elements may segregate in the grain system, and may relieve stress concentration in the grain system during cold rolling, thereby inhibiting recrystallization of <111> / / ND orientation grains in the subsequent recrystallization annealing process, and improving magnetic flux density. When the elements are added appropriately, the above-mentioned effect may be additionally obtained, but when the elements are included excessively, a large amount of segregation may occur, which may inhibit grain growth and may deteriorate magnetic flux density and iron loss. More specifically, one or more of Bi, Pb, Ge and As may be included in an amount of 0.0001 to 0.20% individually or in combination. More specifically, one or more of Bi, Pb, Ge and As may be included in an amount of 0.001 to 0.10% individually or in combination.

[0057] As for the non-oriented electrical steel sheet of the present invention, it may be preferable that a Goss orientation fraction in the region from the surface to 1 / 10t (t: thickness of the steel sheet) in the thickness direction may be 3 area % or less, and that a Goss orientation fraction in the entire region in the thickness direction may be 5 area % or less. The Goss orientation fraction may be an area fraction of grains having an orientation within 10° from the Goss orientation. The Goss orientation may have excellent magnetism in the rolling direction, but may have a great negative effect on the magnetism in the rolling vertical direction. Thus, it may be important to reduce the fraction of grains having the Goss orientation in order to improve magnetism in the rolling vertical direction. In particular, on the surface layer, as frequency increases, the effect on overall iron loss may increase. When the Goss orientation fraction in the region from the surface to 1 / 10t (t: thickness of steel sheet) in the thickness direction exceeds 3 area %, magnetism in the rolling vertical direction may be adversely affected. When the Goss orientation fraction in the entire region in the thickness direction exceeds 5 area %, magnetism in the rolling vertical direction may be adversely affected. The Goss orientation may have excellent magnetism in the rolling direction, but may have a significant adverse effect on the magnetism in the rolling vertical direction. Thus, it may be important to lower the fraction of grains having the Goss orientation in order to improve the magnetism in the rolling vertical direction. In particular, on the surface layer, the total iron loss may be greatly affected as the frequency increases, it may be very important to lower the Goss orientation fraction. A method of measuring the Goss orientation fraction may include measuring the cross-section of the steel sheet using the usual EBSD, and ensuring that the number of grains having a minimum grain size exceeding 5 μm and having a grain system having an orientation error angle of 3° or more from the surrounding grains is at least 5,000 or more within the measurement area, which may have statistical significance. In the case of grains measured in a cut form within the measurement area, the fraction may be calculated including the cut area.

[0058] As described above, the non-oriented electrical steel sheet of the present invention may have an iron loss (W10 / 600C) of 28 W / kg or lower, an iron loss (W10 / 800C) of 43 W / kg or lower, and an iron loss (W10 / 1200C) of 75 W / kg or lower. Also, iron loss (W10 / 600L) may be 30 W / kg or lower, iron loss (W10 / 800L) may be 43 W / kg or lower, and iron loss (W10 / 1200L) may be 85 W / kg or lower. Also, iron loss (W15 / 600C) may be 65 W / kg or lower, iron loss (W15 / 800C) may be 95 W / kg or lower, and iron loss (W15 / 1200C) may be 175 W / kg or lower. Also, iron loss (W15 / 600L) may be 75 W / kg or lower, iron loss (W15 / 800L) may be 105 W / kg or lower, and iron loss (W15 / 1200L) may be 190 W / kg or lower. When the condition is not satisfied, the high magnetic flux density iron loss may not be excellent, such that it may be difficult to achieve the purpose of the present invention, which is to be used for a high output and high efficiency of a motor. A lower value of iron loss may be advantageous, and thus, in the present invention, a lower limit of iron loss may not be specifically limit. However, a lower limit of iron loss (W10 / 600C), iron loss (W10 / 800C) and iron loss (W10 / 1200C) may be 6 W / Kg, 8 W / Kg and 15 W / Kg, respectively. Also, a lower limit of iron loss (W10 / 600L), iron loss (W10 / 800L) and iron loss (W10 / 1200L) may be 6.5 W / Kg, 9 W / Kg and 17 W / Kg, respectively. Also, a lower limit of iron loss (W15 / 600C), iron loss (W15 / 800C) and iron loss (W15 / 1200C) may be 12 W / Kg, 12 W / Kg and 25 W / Kg, respectively. Also, a lower limit of iron loss (W15 / 600L), iron loss (W15 / 800L) and iron loss (W15 / 1200L) may be 13 W / Kg, 13 W / Kg and 27 W / Kg, respectively. Meanwhile, the W10 / 600, W10 / 800, and W10 / 1200 may indicate iron loss measured by the Epstein method under the conditions of maximum magnetic flux of 1.0 T, 600 Hz, 800 Hz, and 1200 Hz, respectively. The W15 / 600, W15 / 800, and W15 / 1200 may indicate iron loss measured by the Epstein method under the conditions of maximum magnetic flux of 1.5 T and 600 Hz, 800 Hz, and 1200 Hz, respectively. L may indicate the rolling direction, and C may indicate the rolling vertical direction.

[0059] It may be preferable that the non-oriented electrical steel sheet of the present invention may satisfy relational expression 1 as below.iron loss (W10 / 600C)+iron loss (W10 / 800C)+iron loss (W10 / 1200C)<iron loss (W10 / 600L)+iron loss (W10 / 800L)+iron loss (W10 / 1200L)  [Relational expression 1]

[0060] By satisfying relational expression 1, the high-frequency iron loss in the rolling vertical direction may be superior than that in the rolling direction, and thus, when manufacturing a motor using the rolling vertical direction as a magnetic flux, a motor may be driven with high efficiency even at high speed rotation.

[0061] The non-oriented electrical steel sheet of the present invention may have a thickness of 0.03 to 0.35 mm.

[0062] Hereinafter, a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention may be described.

[0063] First, a slab having the aforementioned alloy composition may be heated at 1050 to 1220° C. When the slab heating temperature is lower than 1050° C., the temperature difference between the surface and the internal portion of the slab may increase during hot-rolling, passing ability may deteriorate during hot-rolling, and the reduction ratio may not be sufficient during hot-rolling. When the slab heating temperature exceeds 1220° C., precipitates may be re-dissolved and may be finely precipitated after hot-rolling. A lower limit of the slab heating temperature may be preferably 1080° C., and more preferably 1100° C. An upper limit of the slab heating temperature may be preferably 1200° C., and more preferably 1180° C.

[0064] Thereafter, the slab may be finishing hot-rolled and a hot-rolled sheet may be obtained. The finishing hot-rolling may be performed at 700 to 1050° C. When the finishing hot-rolling temperature is less than 700° C., the shape of the hot-rolled sheet may become poor, the deformation may be concentrated on the surface, such that it may be impossible to perform hot-rolling of the steel sheet, and the Goss-like orientation of the surface may increase. When the finishing hot-rolling temperature exceeds 1050° C., friction between the rolling roll and the sheet surface may increase, the Goss-like orientation may increase, and defects in the sheet shape due to high temperature deformation may occur. A lower limit of the finishing hot-rolling temperature may be preferably 730° C., more preferably 750° C., and most preferably 780° C. An upper limit of the finishing hot-rolling temperature may be preferably 1000° C., more preferably 960° C., and most preferably 930° C. Meanwhile, the thickness of the hot-rolled sheet may be 0.8 to 3 mm.

[0065] Thereafter, the hot-rolled sheet may be hot-rolled sheet annealed for 30 to 300 seconds at 850 to 1150° C. When the hot-rolled sheet annealing temperature is lower than 850° C., the structure may not grow or may grow finely. When the hot-rolled sheet annealing temperature exceeds 1150° C., magnetic properties may deteriorate, and rolling workability may deteriorate due to deformation of the sheet shape. A lower limit of the hot-rolled sheet annealing temperature may be preferably 900° C., and more preferably 950° C. An upper limit of the hot-rolled sheet annealing temperature may be preferably 1135° C., and more preferably 1110° C. When the hot-rolled sheet annealing time is less than 30 seconds, growth of the grain diameter on the surface and the grain diameter therein may be different, such that the Goss fraction on the surface of the final electrical steel sheet may significantly increase. When the hot-rolled sheet annealing time exceeds 300 seconds, the grains may become coarser, such that the Goss fraction in the entire sheet thickness of the final electrical steel sheet may significantly increase. A lower limit of the hot-rolled sheet annealing time may be preferably 60 seconds, and more preferably 80 seconds. An upper limit of the hot-rolled sheet annealing time may be preferably 180 seconds, and more preferably 150 seconds. The hot-rolled sheet annealing may be performed to increase the orientation which may be advantageous to magnetism if desired, or the hot-rolled sheet annealing may not be performed.

[0066] Thereafter, the hot-rolled sheet annealed may be cold-rolled and a cold-rolled sheet may be obtained. It may be preferable to satisfy [Relational expression 2] as below during the cold-rolling.Highest temperature of cold-rolled sheet surface during cold-rolling<200×cold reduction ratio / 100+60  [Relational expression 2]

[0067] The temperature of the steel sheet may be increased by residual heat during the obtaining the hot-rolled sheet or the hot-rolled sheet annealing, heating due to mechanical friction of the steel sheet during rolling, or heat supply from the outside. When the maximum temperature of the cold-rolled sheet surface during cold-rolling is 200×cold reduction ratio / 100+60 or higher, a shear force may act greatly when the material is deformed, and the fraction of grains having Goss orientation in the steel sheet may increase significantly.

[0068] The cold-rolling may be performed with a cold reduction ratio of 35 to 98%. When the cold reduction ratio is less than 35%, the energy stored by processing during cold-rolling may be consumed, and recrystallization may not occur due to the characteristics of steel in which recrystallization occurs, such that magnetism may be deteriorated even after annealing. When the cold reduction ratio exceeds 98%, a high-processing microstructure formed by rolling may be formed, such that iron loss may increase in both the rolling and rolling vertical directions even after the final annealing. A lower limit of the cold reduction ratio may be preferably 55%, more preferably 65%, and most preferably 73%. An upper limit of the cold reduction ratio may be preferably 93%, more preferably 88%, and most preferably 83%. Meanwhile, the cold-rolling may be a single cold-rolling or two or more cold-rollings with intermediate annealing therebetween.

[0069] The rolling maximum rate in one or more of the first pass and second pass during cold-rolling may be 3 m / s or higher. When the rolling maximum rate in one or more of the first pass and second pass during cold-rolling is less than 3 m / s, a strong shear force may be applied to the surface of the steel sheet during rolling, which may increase the nucleation of Goss orientation, and accordingly, the fraction of grains having Goss orientation on the surface of the steel sheet may increase during final annealing. In the present invention, a higher rolling maximum rate in one or more of the first pass and second pass during cold-rolling may be advantageous, and thus, there is no particular limitation on an upper limit thereof. However, an upper limit of the rolling maximum rate in one or more of the first pass and second pass during cold-rolling may be 20 m / s.

[0070] Thereafter, the cold-rolled sheet may be heated to the final annealing temperature. The heating rate in the temperature range of 300 to 500° C. during heating may preferably be 5 to 150° C. / s. When the heating rate in the temperature range of 300 to 500° C. during heating is less than 5° C. / s, recrystallization of grains having an orientation unfavorable to magnetism may be promoted. When the heating rate in the temperature range of 300 to 500° C. during heating exceeds 150° C. / s, recrystallization of grains having a Goss orientation unfavorable to magnetism in the rolling vertical direction may be greatly promoted. A lower limit of the heating rate may preferably be 7° C. / s, and more preferably 10° C. / s. An upper limit of the heating rate may preferably be 120° C. / s, more preferably 100° C. / s, and most preferably 50° C. / s.

[0071] Thereafter, the heated cold-rolled sheet may be final annealed. The final annealing may be performed at 600 to 1150° C. for 10 to 500 seconds. When the final annealing temperature is lower than 600° C., the Goss fraction in the steel sheet may increase significantly during recrystallization. When the final annealing temperature exceeds 1150° C., coarse grains may be formed and high-frequency iron loss in the C direction may be deteriorated. A lower limit of the final annealing temperature may be preferably 700° C., more preferably 730° C., and most preferably 750° C. An upper limit of the final annealing temperature may be preferably 1120° C., more preferably 1100° C., and most preferably 1050° C. When the final annealing time is less than 10 seconds, the fraction of grains having Goss fraction in the entire sheet thickness may increase significantly. When the final annealing time exceeds 500 seconds, the high-frequency iron loss may increase significantly due to grain overgrowth. A lower limit of the final annealing time may be preferably 20 seconds, more preferably 30 seconds, and most preferably 35 seconds. An upper limit of the final annealing time may be preferably 400 seconds, more preferably 300 seconds, and most preferably 200 seconds.

[0072] It may be preferable that the gas atmosphere during the final annealing may include, by volume %, hydrogen: 15 to 99.99%, oxygen: 0.0001 to 0.0030%, and a remainder of inert gas. By controlling as above, an effect similar to anoxia on the steel sheet surface may be practically obtained. When the hydrogen fraction is less than 15%, the surface of the material of the invention may be oxidized due to insufficient reduction ability. The hydrogen fraction may practically be 100% preferably, but it may be extremely difficult to be used industrially, such that the hydrogen fraction may be limited to 99.99%. When the oxygen fraction is less than 0.0001%, an extremely small portion of the steel sheet surface may combine with oxygen, such that a local oxide layer may be formed, which may create surface unevenness. When the oxygen fraction exceeds 0.0030%, a wide oxide layer may be formed on the surface, which may deteriorate magnetism and may promote the nucleation of grains having a Goss orientation on the surface, thereby increasing the surface fraction. In the present invention, the type of the inert gas may not be particularly limited, and all types used in the relevant technical field may be used. For example, nitrogen or argon may be used.

[0073] Forming an insulating layer may be further included after the final annealing. The method of forming the insulating layer may be widely known in the field of non-oriented electrical steel sheet technology, and thus, a detailed description thereof may not be provided.MODE FOR INVENTION

[0074] Hereinafter, the present disclosure may be described more specifically through embodiments. However, it should be noted that the embodiments below are merely intended to describe the present disclosure in greater detail based on embodiments, and are not intended to limit the scope of the rights of the present disclosure. This may be because the scope of rights of the present invention is determined by matters described in the claims and matters reasonably inferred therefrom.Embodiment

[0075] A slab having the alloy composition listed in Tables 1 and 2 below was prepared, and a non-oriented electrical steel sheet was manufactured using the manufacturing conditions listed in Tables 3 and 4 below. The remainder in the gas atmosphere in the temperature range of 500 to 750 during the final annealing was nitrogen.

[0076] The Goss orientation fraction and electrical properties of the non-oriented electrical steel sheet manufactured in this manner were measured, and the results are listed in Tables 4 to 6 below.

[0077] The Goss orientation fraction in the surface layer (the region from the surface to 1 / 10t (t: the thickness of the steel sheet) in the thickness direction) and the entire region in the thickness direction were measured using EBSD. In order to confirm the Goss orientation fraction according to thickness, the RD-ND plane was observed, and the EBSD measurement plane was separated and analyzed for the upper and lower surfaces, which are 1 / 10 of the total thickness. In order to ensure statistical reliability, the cross-sections of 100 samples were measured, and the texture according to thickness in each sample measurement was measured, averaged, and evaluated as the Goss orientation fraction of 1 / 10t.

[0078] Iron loss (W10 / 600C), iron loss (W10 / 800C), iron loss (W10 / 1200C), iron loss (W10 / 600L), iron loss (W10 / 800L), iron loss (W10 / 1200L), iron loss (W15 / 600C), iron loss (W15 / 800C), iron loss (W15 / 1200C), iron loss (W15 / 600L), iron loss (W15 / 800L) and iron loss (W15 / 1200L) were measured using the Epstein measurement method used for quantitative measurement of a general electrical steel sheet. The sample was cut with a cutter such that the L direction sample was 305 mm in the L direction and 30 mm in the C direction. The C direction sample was 305 mm in the C direction and 30 mm in the L direction.TABLE 1SteelAlloy composition (weight %)typeSiAlMnCrSPSnCInventive4.31.30.350.030.00090.0100.0300.0030steel 1Inventive2.51.30.350.030.00100.0100.0300.0030steel 2Inventive3.60.30.550.020.00150.0080.0600.0025steel 3Inventive3.61.90.550.020.00110.0090.0500.0024steel 4Inventive3.60.70.030.020.00100.0090.0500.0023steel 5Inventive3.60.71.500.020.00150.0110.0600.0014steel 6Inventive3.01.10.502.230.00120.0080.0300.0028steel 7Inventive3.01.10.503.320.00110.0110.0500.0025steel 8Inventive3.51.00.500.020.00050.0050.0100.0011steel 9Inventive3.51.00.500.020.01050.0050.0200.0012steel10Comparative3.60.30.550.020.00150.0250.0400.0025steel 1Inventive3.60.30.550.020.00150.0250.0200.0025steel11Inventive3.51.00.500.020.00050.0050.1200.0011steel12Inventive3.51.00.500.020.00050.0050.0100.0011steel13Comparative4.01.230.020.050.00200.0050.0100.0033steel 2Inventive4.00.241.330.050.00150.0050.0100.0031steel14Inventive5.52.181.370.010.0140.0050.0100.0039steel15Inventive3.10.80.500.020.00120.0080.0300.0020steel16Inventive3.10.80.500.020.00120.0080.0300.0020steel17Inventive3.10.80.500.020.00120.0080.0300.0020steel18Inventive3.10.80.500.020.00120.0080.0300.0020steel19Inventive3.10.80.500.020.00120.0080.0300.0020steel20Inventive3.10.80.500.020.00120.0080.0300.0020steelTABLE 2SteelAlloy composition (weight %)typeNOTiMcBVCaNbMgInventive0.00200.00090.00100.00500.00100.00050.00080.00100.0006steel 1Inventive0.00200.00070.00150.00400.00100.00060.00120.00100.0005steel 2Inventive0.00160.00040.00100.0010|0.00100.00030.00060.00100.0010steel 3Inventive0.00180.00030.00200.00200.00100.00040.00110.00100.0011steel 4Inventive0.00210.00030.00200.00100.00100.00090.00100.00120.0021steel 5Inventive0.00110.00030.00100.00100.00060.00050.00120.00200.0031steel 6Inventive0.00280.00070.00100.00100.00200.00370.00050.00290.0027steel 7Inventive0.00200.00150.00070.00100.00080.00270.00200.00250.0006steel 8Inventive0.00130.00040.00150.00100.00050.00030.00100.00100.0010steel 9Inventive0.00100.00030.00150.00100.00050.00050.00100.00100.0010steel10Comparative0.00160.00040.00100.00100.00100.00030.00060.00100.0010steel 1Inventive0.00160.00040.00100.00100.00100.00030.00060.00100.0010steel11Inventive0.00130.00040.00150.00100.00050.00030.00100.00100.0010steel12Inventive0.00130.00040.00150.00100.00050.00030.00100.00100.0010steel13Comparative0.00310.00030.00070.09640.00090.00360.00370.00170.0017steel 2Inventive0.00480.00030.00150.07840.00450.00100.00180.00500.0047steel14Inventive0.00170.00040.00100.02690.00030.00270.00590.00320.0040steel15Inventive0.00150.00050.00050.07000.00050.00050.00050.00050.0005steel16Inventive0.00150.00050.00050.00050.00300.00050.00050.00050.0005steel17Inventive0.00150.00050.00050.00050.00050.02500.00050.00050.0005steel18Inventive0.00150.00050.00050.00050.00050.00050.00700.00050.0005steel19Inventive0.00150.00050.00050.00050.00050.00050.00050.00050.0005steel20Inventive0.00150.00500.00500.00050.00050.00050.00050.00050.0005steel21TABLE 3Cold-rolledsheetHot-Hot-surfaceFinishingHot-rolledrolledCold-maximumSlabhot-rolledsheetsheetColdrolledtemperatureheatingrollingsheetannealingAnnealingrollingsheetinSteeltemperaturetemperaturethicknesstemperaturetimereductionthicknesscold-rollingClassificationtype(° C.)(° C.)(mm)(° C.)(min)(%)(mm)(° C.)InventiveInventive10508401.5110090870.20190examplesteel 11InventiveInventive110010392.095040900.20217examplesteel 22InventiveInventive10508921.5105070870.20215examplesteel 33InventiveInventive11408991.5102050870.20215examplesteel 44InventiveInventive113010331.0105090800.30181examplesteel 55InventiveInventive12008000.588070400.2090examplesteel 66InventiveInventive11308701.51130110870.20183examplesteel 77InventiveInventive12008021.5113040870.20208examplesteel 88InventiveInventive12007821.5104090870.25201examplesteel 99InventiveInventive11909701.5110050870.25213examplesteel1010ComparativeComparative12008581.51130120830.25192examplesteel 11InventiveInventive11907561.5980120830.25198examplesteel1111InventiveInventive11509001.5110040830.25208examplesteel1212InventiveInventive120010291.5108050830.25197examplesteel1313ComparativeComparative12007672.099050880.25213examplesteel 22InventiveInventive105010222.01100180880.25217examplesteel1414ComparativeInventive11407502.095080880.25185examplesteel315InventiveInventive10509061.595090830.25208examplesteel1516ComparativeInventive125010281.5108090830.25198examplesteel417InventiveInventive11308651.599060940.09225examplesteel1618ComparativeInventive11007361.5100060820.27203examplesteel519InventiveInventive11007442.0110080930.15225examplesteel1720ComparativeInventive115010202.0103060850.30191examplesteel621TABLE 4Firstpass andsecondpass, onor morof theHeatingrollingrate inSurfaceEntiremaximumtemperatureGas atmosphereportionregionrate inrangeFinalFinalduring finalGossGosscold-of 300 toannealingannealingannealingorientationorientationSteelrolling500° C.temperaturetime(volume %)fractionfractionClassificationtype(m / s)(° C. / s)(º C.)(min)HydrogenOxygenRemainder(area %)(area %)InventInvent6878090300.000669.99941.32.9examplesteel11InventiveInventive152975012099.990.00010.00991.13.0examplesteel22InventiveInventive255108060250.000874.99922.42.8examplesteel33InventiveInventive256100090300.001369.99872.53.examplesteel44InventiveInventive75850200500.000949.99910.21.4examplesteel55InventiveInventive55750360300.001069.99901.72.4examplesteel66InventiveInventive5572070300.000669.99940.82.0examplesteel77InventiveInventive136750200200.001979.99810.32.8examplesteel88InventiveInventive96104080250.001774.99831.12.0examplesteel99InventiveInventive195820240300.001169.99890.11.0examplesteel1010ComparativeComparative81598060100.000289.99985.47.2examplesteel11InventiveInventive117850150300.001869.99821.01.9examplesteel1111InventiveInventive2412100060500.000149.99990.61.5examplesteel1212InventiveInventive105850270500.000249.99980.93.3examplesteel1313ComparativeComparative175112050100.000889.99924.16.2examplesteel22InventiveInventive2511800130350.000964.99910.62.0examplesteel1414ComparativeInventive56800180100.000389.99973.15.7examplesteel315InventiveInventive235850200350.001064.99901.63.7examplesteel1516ComparativeInventive111488080100.000989.99911.84.1examplesteel417InventiveInventive151590080350.001764.99831.22.8examplesteel1618ComparativeInventive196800200120.000287.99983.65.4examplesteel519InventiveInventive204750250500.000449.99960.41.2examplesteel1720ComparativeInventive725100080100.001389.99878.110.3examplesteel621TABLE 5IronIronIronWhetherlosslossIron losslossIron lossIron lossrelational(W10 / 600C)(W10 / 800C)(W10 / 1200C)(W10 / 600L)(W10 / 800L)(W10 / 1200L)expression 1Classification(W / Kg)(W / Kg)(W / Kg)(W / Kg)(W / Kg)(W / Kg)satisfiedInventive14.324.143.815.424.344.5○example1Inventive19.632.553.52133.354.5○example2Inventive16.527.962.117.728.362.4○example3Inventive13.622.342.514.522.642.7○example4Inventive10.917.228.211.817.529○example5Inventive15.424.543.916.624.844.5○example6Inventive15.825.745.417.126.246.4○example7Inventive9.114.4199.814.719.6○example8Inventive11.218.939.512.119.240.2○example9Inventive11.517.325.112.617.625.8○example10Comparative25.240.989.823.440.388.4xexample1Inventive1728.356.418.428.757.5○example11Inventive17.129.865.518.630.267○example12Inventive10.918.730.611.71931.2○example13Comparative30.847.769.528.847.267.9xexample2Inventive25.23958.227.339.459.6○example14Comparative34.443.747.831.543.946.4xexample3Inventive16.428.250.317.528.751○example15Comparative3050.79128.349.889.9xexample4Inventive4.67.411.957.612.1○example16Comparative27.844.656.926.343.755.5xexample5Inventive6.49.9166.910.116.4○example17Comparative21.433.886.219.533.183.8xexample6iron loss (W10 / 600C) + iron loss (W10 / 800C) + iron loss (W10 / 1200C) < ironloss (W10 / 600L) + iron loss (W10 / 800L) + iron loss (W10 / 1200L)TABLE 6Iron lossIron lossIron lossIron lossIron lossIron loss(W15 / 600C)(W15 / 800C)(W15 / 1200C)(W15 / 600L)(W15 / 800L)(W15 / 1200L)Classification(W / Kg)(W / Kg)(W / Kg)(W / Kg)(W / Kg)(W / Kg)Inventive31.553.291.734.655.894.4example 1Inventive42.771.2108.747.074.8111.9example 2Inventive36.361.8132.740.064.8136.7example 3Inventive29.548.686.432.451.089.0example 4Inventive23.237.153.225.538.954.8example 5Inventive33.052.884.336.355.486.9example 6Inventive34.255.990.037.658.792.7example 7Inventive19.531.033.921.532.634.9example 8Inventive24.641.984.427.144.086.9example 9Inventive24.136.440.626.538.341.8example 10Comparative51.889.7192.957.094.2198.7example 1Inventive37.162.2117.540.865.3121.1example 11Inventive38.266.5143.942.069.7148.2example 12Inventive24.241.665.226.643.767.2example 13Comparative62.5103.0132.668.8108.2136.6example 2Inventive53.483.2102.158.787.4105.2example 14Comparative63.889.545.370.293.946.7example 3Inventive36.462.7108.440.065.8111.6example 15Comparative63.4111.5199.269.8117.0205.1example 4Inventive9.916.122.710.916.923.4example 16Comparative57.496.1110.363.1100.9113.6example 5Inventive13.521.128.814.822.129.6example 17Comparative43.073.3180.847.377.0186.3example 6As indicated in Tables 1 to 6, in inventive examples 1 to 17, the alloy composition and manufacturing conditions of the present invention were satisfied, such that the microstructure aimed to obtain in the present invention was ensured, and thus, excellent magnetism was ensured.In comparative examples 1 and 2, the alloy composition of the present invention was not satisfied, such that the microstructure aimed to be obtained in the present invention was not ensured, and thus, excellent magnetism was ensured.In comparative examples 3 to 6, the manufacturing conditions of the present invention were not satisfied, such that the microstructure aimed to be obtained in the present invention was not ensured, and thus, excellent magnetism was ensured.

Claims

1. A non-oriented electrical steel sheet, comprising:by weight %, Si: 1.5 to 6.5%, Al: 0.0005 to 3.5%, Mn: 0.01 to 3.0%, Cr: 0.005 to 5.0%, S: 0.0005 to 0.03%, and a balance of Fe and inevitable impurities,wherein a Goss orientation fraction in a region from a surface to 1 / 10t (t: thickness of the steel sheet) in a thickness direction is 3 area % or less, andwherein a Goss orientation fraction in an entire region in the thickness direction is 5 area % or less.

2. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet further includes one or more of P: 0.005 to 0.08% and Sn: 0.01 to 0.2%.

3. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet further includes one or more of C: 0.005% or less (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%) and Ti: 0.01% or less (excluding 0%).

4. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet further includes one or more of Mo: 0.1% or less (excluding 0%), B: 0.0050% or less (excluding 0%), V: 0.050% or less (excluding 0%), Ca: 0.010% or less (excluding 0%), Nb: 0.0050% or less (excluding 0%) and Mg: 0.0050% or less (excluding 0%).

5. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet further includes one or more of Sb: 0.1% or less (excluding 0%), Ni: 0.05% or less (excluding 0%), Cu: 0.005 to 0.2% and Zn: 0.01% or less (excluding 0%).

6. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet further includes 0.20% or less (excluding 0%) of one or more of Bi, Pb, Ge and As individually or in combination.

7. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W10 / 600C) of 28 W / kg or lower, an iron loss (W10 / 800C) of 43 W / kg or lower, and an iron loss (W10 / 1200C) of 75 W / kg or lower.

8. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W10 / 600L) of 30 W / kg or lower, an iron loss (W10 / 800L) of 48 W / kg or lower, and an iron loss (W10 / 1200L) of 85 W / kg or lower.

9. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W15 / 600C) of 65 W / kg or lower, an iron loss (W15 / 800C) of 95 W / kg or lower, and an iron loss (W15 / 1200C) of 175 W / kg or lower.

10. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet has an iron loss (W15 / 600L) of 75 W / kg or lower, an iron loss (W15 / 800L) of 105 W / kg or lower, and an iron loss (W15 / 1200L) of 190 W / kg or lower.

11. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet satisfies relational expression 1 as below:iron loss (W10 / 600C)+iron loss (W10 / 800C)+iron loss (W10 / 1200C)<iron loss (W10 / 600L)+iron loss (W10 / 800L)+iron loss (W10 / 1200L).  [Relational expression 1]12. A method of manufacturing a non-oriented electrical steel sheet, the method comprising:heating a slab including, by weight %, Si: 1.5 to 6.5%, Al: 0.0005 to 3.5%, Mn: 0.01 to 3.0%, Cr: 0.005 to 5.0%, S: 0.0005 to 0.03%, and a balance of Fe and inevitable impurities at 1050 to 1220° C.;finishing hot-rolling the slab and obtaining a hot-rolled sheet;hot-rolled sheet annealing the hot-rolled sheet for 30 to 300 seconds at 850 to 1150° C.;cold-rolling the hot-rolled sheet annealed hot-rolled sheet and obtaining a cold-rolled sheet;heating the cold-rolled sheet; andfinal annealing the heated cold-rolled sheet,wherein, in the cold-rolling, [Relational expression 2] is satisfied,wherein, in the heating, a heating rate in a temperature range of 300 to 500° C. is 5 to 150° C. / s, andwherein, in the final annealing, a gas atmosphere includes, by volume %, hydrogen: 15 to 99.99%, oxygen: 0.0001 to 0.0030%, and a remainder of inert gas.13-17. (canceled)18. The method of claim 12, wherein the finishing hot-rolling is performed at 700 to 1050° C.

19. The method of claim 12, wherein the cold-rolling is performed with a cold reduction ratio of 35 to 98%.

20. The method of claim 12, wherein, in the cold rolling, a maximum rolling rate in one or more of first pass and second pass is 3 m / s or higher.

21. The method of claim 12, wherein the final annealing is performed for 10 to 500 seconds at 600 to 1150° C.