Non-oriented electrical steel sheet 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 in which the iron loss perpendicular to the rolling direction at high frequencies is lower than the iron loss in the rolling direction; and a method for manufacturing the non-oriented electrical steel sheet.

Description

Technical Field

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Background Art

[0002] In order to reduce greenhouse gas emissions, electric vehicles and electric-powered transportation means are used instead of internal combustion engines. Currently, more than 50% of the total generated electric energy is consumed by electric motors to provide power. In order to replace internal combustion engines with electric motors in the future, it is very important to use electric power efficiently. In particular, with the high performance, miniaturization, and lightweight of electric motors, motors that form magnetic flux in the axial direction have also attracted much attention. These motors are used to eliminate the space limitations of various electric motors and improve performance, including existing electric vehicles, electric motorcycles, electric airplanes, and electric ships. Therefore, improving efficiency is absolutely necessary. In addition, with the development of technology and market changes, the attention to the high functionality and high efficiency of motors such as high-efficiency motors for household appliances, motors for robots, or industrial motors has been increasing continuously. Therefore, it can be said that the attention to the efficient use of electric energy is higher than ever.

[0003] In addition, in order to improve the efficiency of electric motors, optimization in all fields from material selection to design, assembly, and control is very important. In particular, in terms of materials, the magnetic properties of electrical steel sheets are the most important. Therefore, higher requirements are placed on low iron loss and high magnetic flux density. For automotive drive motors or motors for air-conditioning compressors that need to be driven in the commercial frequency region and high-frequency region, high-frequency low iron loss characteristics are very important. In addition, in the case of small high-power motors with a narrow yoke width, in order to obtain high torque during motor operation, high magnetic flux is also formed in the teeth and yoke parts of the motor. Therefore, it is important to improve the iron loss in the high magnetic flux at high frequencies for improving the motor efficiency.

[0004] Generally, a large amount of specific resistance elements such as Si, Al, and Mn are added during the manufacturing process of electrical steel sheets and the grain size is reduced, thereby reducing eddy current loss. In addition, since eddy current only passes through the surface layer of the steel sheet as the frequency increases, the high-frequency iron loss can be improved by increasing the specific resistance elements in the surface layer. However, this general manufacturing method is effective for controlling the iron loss when the magnetic flux is about 1.0 T, and there is no known method for reducing the iron loss under high magnetic flux. Summary of the Invention

[0005] (I) Technical Problem to be Solved

[0006] An object of one aspect of the present invention is to provide a non-oriented electrical steel sheet in which the iron loss perpendicular to the rolling direction is lower than the iron loss in the rolling direction at high frequencies and a method for manufacturing the same.

[0007] (II) Technical Solution

[0008] One embodiment of the present invention provides a non-oriented electrical steel sheet, which, by weight %, comprises: Si: 1.5 - 6.5%, Al: 0.0005 - 3.5%, Mn: 0.01 - 3.0%, Cr: 0.005 - 5.0%, S: 0.0005 - 0.03%, the balance being Fe and other inevitable impurities, the Goss orientation fraction in the region from the surface to t / 10 (t: the thickness of the steel sheet) in the thickness direction is 3 area % or less, and the Goss orientation fraction in the entire region in the thickness direction is 5 area % or less.

[0009] The non-oriented electrical steel sheet may further comprise one or more of P: 0.005 - 0.08% and Sn: 0.01 - 0.2%.

[0010] The non-oriented electrical steel sheet may further comprise one or more of C: 0.005% or less (except 0%), N: 0.005% or less (except 0%), O: 0.005% or less (except 0%), and Ti: 0.01% or less (except 0%).

[0011] The non-oriented electrical steel sheet may further comprise one or more of Mo: 0.1% or less (except 0%), B: 0.0050% or less (except 0%), V: 0.050% or less (except 0%), Ca: 0.010% or less (except 0%), Nb: 0.0050% or less (except 0%), and Mg: 0.0050% or less (except 0%).

[0012] The non-oriented electrical steel sheet may further comprise one or more of Sb: 0.1% or less (except 0%), Ni: 0.05% or less (except 0%), Cu: 0.005 - 0.2%, and Zn: 0.01% or less (except 0%).

[0013] The non-oriented electrical steel sheet may further comprise one or more of Bi, Pb, Ge, and As, and the contents of Bi, Pb, Ge, and As are each 0.20% or less (except 0%) or the total amount is 0.20% or less (except 0%).

[0014] The iron loss (W10 / 600C) of the non-oriented electrical steel sheet may be 28 W / kg or less, the iron loss (W10 / 800C) may be 43 W / kg or less, and the iron loss (W10 / 1200C) may be 75 W / kg or less.

[0015] The iron loss (W10 / 600L) of the non-oriented electrical steel sheet may be 30 W / kg or less, the iron loss (W10 / 800L) may be 48 W / kg or less, and the iron loss (W10 / 1200L) may be 85 W / kg or less.

[0016] The iron loss (W15 / 600C) of the non-oriented electrical steel sheet may be 65 W / kg or less, the iron loss (W15 / 800C) may be 95 W / kg or less, and the iron loss (W15 / 1200C) may be 175 W / kg or less.

[0017] The iron loss (W15 / 600L) of the non-oriented electrical steel sheet may be 75 W / kg or less, the iron loss (W15 / 800L) may be 105 W / kg or less, and the iron loss (W15 / 1200L) may be 190 W / kg or less.

[0018] The non-oriented electrical steel sheet may satisfy the following relational expression 1.

[0019] [Relational expression 1] Iron loss (W10 / 600C) + Iron loss (W10 / 800C) + Iron loss (W10 / 1200C) < Iron loss (W10 / 600L) + Iron loss (W10 / 800L) + Iron loss (W10 / 1200L)

[0020] 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 at 1050 - 1220 °C, and by weight%, the slab includes: Si: 1.5 - 6.5%, Al: 0.0005 - 3.5%, Mn: 0.01 - 3.0%, Cr: 0.005 - 5.0%, S: 0.0005 - 0.03%, the balance being Fe and other inevitable impurities; hot finish rolling the slab to obtain a hot rolled sheet; annealing the hot rolled sheet at 850 - 1150 °C for 30 - 300 seconds; cold rolling the hot rolled sheet annealed to obtain a cold rolled sheet; heating the cold rolled sheet; and finally annealing the cold rolled sheet heated, wherein, during the cold rolling, the following [Relational expression 2] is satisfied, the heating rate in the temperature range of 300 - 500 °C during the heating is 5 - 150 °C / second, and by volume%, the gas atmosphere during the final annealing consists of hydrogen: 15 - 99.99%, oxygen: 0.0001 - 0.0030%, and the balance being an inert gas.

[0021] [Relational expression 2] The highest temperature on the surface of the cold rolled sheet during the cold rolling process < 200 × cold rolling reduction rate / 100 + 60

[0022] The slab may further include one or more of P: 0.005 - 0.08% and Sn: 0.01 - 0.2%.

[0023] The slab may further contain one or more of C: less than 0.005% (except 0%), N: less than 0.005% (except 0%), O: less than 0.005% (except 0%), and Ti: less than 0.01% (except 0%).

[0024] The slab may further contain one or more of Mo: less than 0.1% (except 0%), B: less than 0.0050% (except 0%), V: less than 0.050% (except 0%), Ca: less than 0.010% (except 0%), Nb: less than 0.0050% (except 0%), and Mg: less than 0.0050% (except 0%).

[0025] The slab may further contain one or more of Sb: less than 0.1% (except 0%), Ni: less than 0.05% (except 0%), Cu: 0.005 - 0.2%, and Zn: less than 0.01% (except 0%).

[0026] The slab may further contain one or more of Bi, Pb, Ge, and As, and the contents of Bi, Pb, Ge, and As are each less than 0.20% (except 0%) or the total amount is less than 0.20% (except 0%).

[0027] The hot finish rolling may be carried out at 700 - 1050°C.

[0028] The cold rolling may be carried out at a cold rolling reduction rate of 35 - 98%.

[0029] During the cold rolling, the maximum rolling speed in one or more passes among the first pass and the second pass may be 3 m / s or more.

[0030] During the final annealing, it may be carried out at 600 - 1150°C for 10 - 500 seconds.

[0031] (III) Beneficial effects

[0032] According to one aspect of the present invention, it is possible to provide a non-oriented electrical steel sheet having an iron loss perpendicular to the rolling direction lower than the iron loss in the rolling direction at high frequencies and a manufacturing method thereof. Optimal implementation mode

[0033] Hereinafter, a non-oriented electrical steel sheet according to an embodiment of the present invention will be described. First, the alloy composition will be described. Unless otherwise specified, the contents of the alloy compositions described below represent weight %.

[0034] Si: 1.5 - 6.5%

[0035] Si plays a role in increasing the specific resistance of the material and reducing iron loss. When the content of Si is less than 1.5%, the improvement effect of high-frequency iron loss is insufficient. When the content of Si exceeds 6.5%, the hardness increases, and the productivity and blanking property deteriorate. Therefore, the content of Si preferably has a range of 1.5 - 6.5%. The lower limit of the content of Si is more preferably 1.8%, and further preferably 2.0%. The upper limit of the content of Si is more preferably 6.0%, further preferably 5.0%, and most preferably 4.0%.

[0036] Al: 0.0005 - 3.5%

[0037] Al plays a role in increasing the specific resistance of the material and reducing iron loss. When the content of Al is less than 0.0005%, since the amount of Al used to remove oxygen during steelmaking is small, a large amount of inclusions are formed in the steel, so it has no effect on reducing high-frequency iron loss, and fine nitrides are formed on the surface, so the magnetism may be reduced. When the content of Al exceeds 3.5%, problems will occur in all processes such as steelmaking and continuous casting, so the productivity may be greatly reduced. Therefore, the content of Al preferably has a range of 0.0005 - 3.5%. The lower limit of the content of Al is more preferably 0.15%. The upper limit of the content of Al is more preferably 3.0%, further preferably 2.5%, and most preferably 2.0%.

[0038] Mn: 0.01 - 3.0%

[0039] Mn plays a role in improving iron loss by increasing the specific resistance of the material, forming sulfides, and stabilizing austenite. When the content of Mn is less than 0.01%, fine sulfides represented by MnS precipitate in the steel, so the magnetism may be reduced. When the content of Mn exceeds 3.0%, the range of annealing temperature for obtaining an appropriate grain size to obtain low high-frequency iron loss is limited. In addition, the saturation magnetic flux of the material is reduced, and in particular, the formation of the {111} texture that is unfavorable to the magnetism of the steel is promoted, so the magnetic flux density may be reduced. Therefore, the content of Mn preferably has a range of 0.01 - 3.0%. The lower limit of the content of Mn is more preferably 0.2%. The upper limit of the content of Mn is more preferably 2.5%, further preferably 2.0%, and most preferably 1.5%.

[0040] Cr: 0.005 - 5.0%

[0041] Cr plays a role in increasing the specific resistance of the material and reducing the iron loss. At the same time, if the cold rolling conditions and the final annealing conditions are appropriately controlled, Cr can be enriched on the surface and form a Cr-enriched layer. When the content of Cr is less than 0.005%, the effect of Cr in increasing the specific resistance is very small, and Cr combines with C, etc. to form carbides, which may be disadvantageous to magnetism. When Cr exceeds 5%, Cr will be evenly distributed throughout the thickness and will not be enriched on the surface, and the magnetic flux density of the entire steel sheet will decrease. Therefore, the content of Cr preferably has a range of 0.005 - 5.0%. In terms of surface enrichment, the lower limit of Cr is more preferably 0.04%. In terms of preventing the decrease in magnetic flux density, the upper limit of Cr is more preferably 3.0%, further preferably 1.0%, and most preferably 0.3%.

[0042] S: 0.0005 - 0.03%

[0043] S is a strongly segregating element and an element that forms precipitates. When added in an appropriate amount, S segregates in the surface part and reacts with oxygen in the atmosphere during annealing, thereby suppressing the growth of Goss grains in the surface part. When the content of S is less than 0.0005%, the segregation effect on the surface is insufficient. When the content of S exceeds 0.03%, an FeS-enriched layer is generated on the surface, and thus the surface quality deteriorates significantly. Therefore, the content of S preferably has a range of 0.0005 - 0.03%. The lower limit of the content of S is more preferably 0.001%. The upper limit of the content of S is more preferably 0.015%, further preferably 0.005%, and most preferably 0.0035%.

[0044] The remaining component is iron (Fe). However, in the normal manufacturing process, it is inevitable to mix in undesirable impurities from raw materials or the surrounding environment, so these impurities cannot be completely excluded. For those skilled in the art of ordinary manufacturing processes, these impurities are well known, so all of their contents are not particularly mentioned in this specification.

[0045] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.005 - 0.08% and Sn: 0.01 - 0.2%.

[0046] P: 0.005 - 0.08%

[0047] P plays a role in enriching on the surface and controlling the fraction of the internal oxide layer. When the content of 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%, the melting point of the Si-based oxide fluctuates, and an internal oxide layer may be rapidly formed. Therefore, the content of P preferably has a range of 0.005 - 0.08%. The upper limit of the content of P is more preferably 0.07%.

[0048] Sn: 0.01 - 0.2%

[0049] Sn segregates at the surface and grain boundaries of the steel sheet, inhibits surface oxidation during annealing, and plays a role in improving the texture. When the content of Sn is less than 0.01%, the above effects may not be fully obtained. When the content of Sn exceeds 0.2%, it segregates at the grain boundaries, the toughness decreases, and the productivity decreases compared with improving the magnetic properties. Therefore, the content of Sn preferably has a range of 0.01 - 0.2%. The lower limit of the content of Sn is more preferably 0.02%. The upper limit of the content of Sn is more preferably 0.15%, further preferably 0.1%, and most preferably 0.07%.

[0050] The non-oriented electrical steel sheet of the present invention may further contain one or more of C: 0.005% or less (except 0%), N: 0.005% or less (except 0%), O: 0.005% or less (except 0%), and Ti: 0.01% or less (except 0%).

[0051] C: 0.005% or less (except 0%)

[0052] C reacts with N, Ti, Nb, V, etc. to form fine carbides, hindering grain growth and magnetic domain movement, and the upper limit of C is limited to 0.005%.

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

[0054] N combines with Ti, Nb, V, etc. to form nitrides, reducing grain growth, so the upper limit of N is limited to 0.005%.

[0055] O: 0.005% or less (except 0%)

[0056] O reacts with Fe, Ti, Al, Mn, Cr, Si, V, etc. to form fine oxides, hindering grain growth and magnetic domain movement, so the upper limit of O is limited to 0.005%.

[0057] Ti: 0.01% or less (except 0%)

[0058] Ti combines with C, N, O, etc. to form fine nitrides or oxides, hindering magnetic domain movement, so the upper limit of Ti is limited to 0.01%.

[0059] In addition, the non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.1% or less (except 0%), B: 0.0050% or less (except 0%), V: 0.050% or less (except 0%), Ca: 0.010% or less (except 0%), Nb: 0.0050% or less (except 0%), and Mg: 0.0050% or less (except 0%).

[0060] Mo: less than 0.1% (except 0%)

[0061] Mo reacts with C, O, N, etc. to form fine carbides or nitrides, etc., which have an adverse effect on magnetism. Therefore, the upper limit of Mo is limited to 0.1%.

[0062] B: less than 0.0050% (except 0%)

[0063] B reacts with C, O, N, etc. to form fine carbides or nitrides, etc., which have an adverse effect on magnetism. Therefore, the upper limit of B is limited to 0.0050%.

[0064] V: less than 0.050% (except 0%)

[0065] V reacts with C, O, N, etc. to form fine carbides or nitrides, etc., which have an adverse effect on magnetism. Therefore, the upper limit of V is limited to 0.050%.

[0066] Ca: less than 0.010% (except 0%)

[0067] Ca reacts with C, O, N, etc. to form fine carbides or nitrides, etc., which have an adverse effect on magnetism. Therefore, the upper limit of Ca is limited to 0.010%.

[0068] Nb: less than 0.0050% (except 0%)

[0069] Nb reacts with C, O, N, etc. to form fine carbides or nitrides, etc., which have an adverse effect on magnetism. Therefore, the upper limit of Nb is limited to 0.0050%.

[0070] Mg: less than 0.0050% (except 0%)

[0071] Mg reacts with C, O, N, etc. to form fine carbides or nitrides, etc., which have an adverse effect on magnetism. Therefore, the upper limit of Mg is limited to 0.0050%.

[0072] The non-oriented electrical steel sheet of the present invention may further contain one or more of Sb: less than 0.1% (except 0%), Ni: less than 0.05% (except 0%), Cu: 0.005 - 0.2%, and Zn: less than 0.01% (except 0%).

[0073] Sb: less than 0.1% (except 0%)

[0074] Sb is an element that segregates at grain boundaries. Adding Sb inhibits the diffusion of nitrogen through grain boundaries, suppresses the {111} texture that is detrimental to magnetism, increases the favorable {100} texture, and improves magnetic properties. When the content of Sb exceeds 0.1%, it hinders grain growth, reduces magnetism, and deteriorates rollability. More specifically, the content of Sb can be 0.001 - 0.1%. More specifically, the content of Sb can be 0.005 - 0.08%.

[0075] Ni: below 0.05% (except 0%)

[0076] Ni reacts with impurity elements to form fine sulfides, carbides, and nitrides, which have an adverse effect on magnetism. Therefore, the upper limit of Ni is restricted to 0.05%. More specifically, the content of Ni can be 0.0001 - 0.050%. More specifically, the content of Ni can be 0.001 - 0.030%.

[0077] Cu: 0.005 - 0.2%

[0078] Cu plays a role in forming sulfides together with Mn. When the content of Cu is less than 0.005%, fine (Cu·Mn)S precipitates, and the magnetism may deteriorate. When the content of Cu exceeds 0.2%, high-temperature brittleness occurs, and cracks may form during continuous casting or hot rolling. More specifically, the content of Cu can be 0.010 - 0.1%.

[0079] Zn: below 0.01% (except 0%)

[0080] Zn, as an impurity, can reduce magnetism. Therefore, the upper limit of Zn is restricted to 0.01%. More specifically, the content of Zn can be 0.0001 - 0.01%. More specifically, the content of Zn can be 0.001 - 0.008%.

[0081] The non-oriented electrical steel sheet of the present invention may further contain one or more of Bi, Pb, Ge, and As, and the contents of Bi, Pb, Ge, and As are respectively below 0.20% (except 0%) or the total amount is below 0.20% (except 0%).

[0082] When the above elements are further added, they segregate at grain boundaries, relieve stress concentration at grain boundaries during cold rolling, and inhibit the recrystallization of <111> / ND-oriented grains during subsequent recrystallization annealing, thereby increasing the magnetic flux density. If these elements are added appropriately, the above effects can be further obtained. However, when an excessive amount of these elements is included, a large amount of segregation occurs, grain growth is inhibited, and the magnetic flux density and iron loss may deteriorate instead. More specifically, one or more of Bi, Pb, Ge, and As can be included, and the contents of Bi, Pb, Ge, and As can be 0.0001 - 0.20% respectively or the total amount can be 0.0001 - 0.20%. More specifically, one or more of Bi, Pb, Ge, and As can be included, and the contents of Bi, Pb, Ge, and As can be 0.001 - 0.10% respectively or the total amount can be 0.001 - 0.10%.

[0083] The Goss orientation fraction in the region from the surface to t / 10 (t: the thickness of the steel sheet) in the thickness direction of the non-oriented electrical steel sheet of the present invention is preferably 3 area% or less, and the Goss orientation fraction in the entire region in the thickness direction is preferably 5 area% or less. The Goss orientation fraction can be the area fraction of grains having an orientation within 10° of the Goss orientation. The magnetic properties in the rolling direction of the Goss orientation are very excellent, but the Goss orientation has a significant adverse effect on the magnetic properties perpendicular to the rolling direction. Therefore, in order to improve the magnetic properties perpendicular to the rolling direction, it is very important to reduce the fraction of grains having the Goss orientation. In particular, as the frequency increases, the influence of the surface layer on the overall iron loss increases. When the Goss orientation fraction in the region from the surface to t / 10 (t: the thickness of the steel sheet) in the thickness direction exceeds 3 area%, it has a significant adverse effect on the magnetic properties perpendicular to the rolling direction. When the Goss orientation fraction in the entire region in the thickness direction exceeds 5 area%, it may have an adverse effect on the magnetic properties perpendicular to the rolling direction. The Goss orientation has very excellent magnetic properties in the rolling direction but has a significant adverse effect on the magnetic properties perpendicular to the rolling direction. Therefore, in order to improve the magnetic properties perpendicular to the rolling direction, it is important to reduce the fraction of grains having the Goss orientation. In particular, as the frequency increases, the influence of the surface layer on the overall iron loss becomes larger, so it is very important to reduce the Goss orientation fraction. In addition, the measurement method of the Goss orientation fraction is to use a normal EBSD to measure the cross-section of the steel sheet. To ensure statistical significance, the number of grains with a minimum grain size exceeding 5 μm and having a grain boundary with an orientation error angle of 3° or more from the surrounding grains in the measurement area is at least 5000 or more. In the case of grains measured in a cut shape in the measurement area, the fraction including its cut area is calculated.

[0084] As described above, the iron loss (W10 / 600C) of the non-oriented electrical steel sheet of the present invention can be 28 W / kg or less, the iron loss (W10 / 800C) can be 43 W / kg or less, and the iron loss (W10 / 1200C) can be 75 W / kg or less. In addition, the iron loss (W10 / 600L) can be 30 W / kg or less, the iron loss (W10 / 800L) can be 43 W / kg or less, and the iron loss (W10 / 1200L) can be 85 W / kg or less. In addition, the iron loss (W15 / 600C) can be 65 W / kg or less, the iron loss (W15 / 800C) can be 95 W / kg or less, and the iron loss (W15 / 1200C) can be 175 W / kg or less. In addition, the iron loss (W15 / 600L) can be 75 W / kg or less, the iron loss (W15 / 800L) can be 105 W / kg or less, and the iron loss (W15 / 1200L) can be 190 W / kg or less. When the above conditions are not satisfied, the high magnetic flux density iron loss is not excellent, so it is difficult to achieve the object of the present invention for high power and high efficiency of the motor. The lower the iron loss value, the more advantageous. Therefore, in the present invention, there is no particular limitation on the lower limit of the iron loss. However, the lower limits of the iron loss (W10 / 600C), the iron loss (W10 / 800C), and the iron loss (W10 / 1200C) can be 6 W / Kg, 8 W / Kg, and 15 W / Kg, respectively. In addition, the lower limits of the iron loss (W10 / 600L), the iron loss (W10 / 800L), and the iron loss (W10 / 1200L) can be 6.5 W / Kg, 9 W / Kg, and 17 W / Kg, respectively. In addition, the lower limits of the iron loss (W15 / 600C), the iron loss (W15 / 800C), and the iron loss (W15 / 1200C) can be 12 W / Kg, 12 W / Kg, and 25 W / Kg, respectively. In addition, the lower limits of the iron loss (W15 / 600L), the iron loss (W15 / 800L), and the iron loss (W15 / 1200L) can be 13 W / Kg, 13 W / Kg, and 27 W / Kg, respectively. In addition, W10 / 600, W10 / 800, and W10 / 1200 respectively represent the iron loss measured by the Epstein method under the conditions of a maximum magnetic flux of 1.0 T, 600 Hz, 800 Hz, and 1200 Hz. W15 / 600, W15 / 800, and W15 / 1200 respectively represent the iron loss measured by the Epstein method under the conditions of a maximum magnetic flux of 1.5 T, 600 Hz, 800 Hz, and 1200 Hz. L represents the rolling direction, and C represents the direction perpendicular to the rolling direction.

[0085] The non-oriented electrical steel sheet of the present invention preferably satisfies the following relational expression 1.

[0086] [Relationship 1] Iron loss (W10 / 600°C) + Iron loss (W10 / 800°C) + Iron loss (W10 / 1200°C) < Iron loss (W10 / 600L) + Iron loss (W10 / 800L) + Iron loss (W10 / 1200L)

[0087] By satisfying the above Relationship 1, the high-frequency iron loss perpendicular to the rolling direction is superior to that in the rolling direction. Therefore, when manufacturing an electric motor with the magnetic flux perpendicular to the rolling direction, the motor can be driven with high efficiency even at high speeds of rotation.

[0088] The non-oriented electrical steel sheet of the present invention may have a thickness of 0.03 - 0.35 mm.

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

[0090] First, a slab having the above alloy composition is heated at 1050 - 1220°C. When the heating temperature of the slab is lower than 1050°C, the temperature difference between the surface and the inside of the slab during hot rolling is large, the passability of the slab during hot rolling becomes poor, and there is a drawback that the reduction ratio during hot rolling is insufficient. When the heating temperature of the slab exceeds 1220°C, precipitates may redissolve and precipitate finely after hot rolling. The lower limit of the heating temperature of the slab is more preferably 1080°C, and further preferably 1100°C. The upper limit of the heating temperature of the slab is more preferably 1200°C, and further preferably 1180°C.

[0091] After that, the slab is hot finish-rolled to obtain a hot-rolled sheet. The hot finish-rolling can be carried out at 700 - 1050°C. When the hot finish-rolling temperature is lower than 700°C, the shape of the hot-rolled sheet deteriorates, and the deformation is concentrated on the surface, making it impossible to perform hot rolling on the steel sheet, and there is a drawback that the Goss-like orientation in the surface portion increases. When the hot finish-rolling temperature exceeds 1050°C, the frictional force between the roll and the sheet surface increases, the Goss-like orientation increases, and there are drawbacks such as poor sheet shape due to high-temperature deformation. The lower limit of the hot finish-rolling temperature is more preferably 730°C, further preferably 750°C, and most preferably 780°C. The upper limit of the hot finish-rolling temperature is more preferably 1000°C, further preferably 960°C, and most preferably 930°C. In addition, the thickness of the hot-rolled sheet can be 0.8 - 3 mm.

[0092] Thereafter, the hot-rolled sheet is subjected to hot-rolled sheet annealing at 850 - 1150 °C for 30 - 300 seconds. When the annealing temperature of the hot-rolled sheet is lower than 850 °C, the structure may not grow or may grow microscopically. When the annealing temperature of the hot-rolled sheet exceeds 1150 °C, the magnetic properties may decrease instead, and due to the deformation of the sheet shape, the rolling workability may deteriorate. The lower limit of the annealing temperature of the hot-rolled sheet is more preferably 900 °C, and further preferably 950 °C. The upper limit of the annealing temperature of the hot-rolled sheet is more preferably 1135 °C, and further preferably 1110 °C. When the annealing time of the hot-rolled sheet is less than 30 seconds, due to the difference in the growth of the grain size on the surface and inside, there is a drawback that the fraction of Goss in the surface part of the final electrical steel sheet increases significantly. When the annealing time of the hot-rolled sheet exceeds 300 seconds, the grains become coarser, and there is a drawback that the fraction of Goss in the overall sheet thickness of the finally obtained electrical steel sheet increases significantly. The lower limit of the annealing time of the hot-rolled sheet is more preferably 60 seconds, and further preferably 80 seconds. The upper limit of the annealing time of the hot-rolled sheet is more preferably 180 seconds, and further preferably 150 seconds. In order to increase the orientation favorable for magnetism, the hot-rolled sheet annealing can be carried out as needed, and the hot-rolled sheet annealing can also be omitted.

[0093] Thereafter, the hot-rolled sheet annealed with the hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet. It is preferable to satisfy the following [Relationship 2] during the cold rolling.

[0094] [Relationship 2] The maximum temperature on the surface of the cold-rolled sheet during cold rolling < 200 × cold rolling reduction rate / 100 + 60

[0095] The temperature of the steel sheet may increase due to the residual heat during the step of obtaining the hot-rolled sheet or the hot-rolled sheet annealing step, the heating caused by the mechanical friction of the steel sheet during rolling, or the heat supplied from the outside, etc. When the maximum temperature on the surface of the cold-rolled sheet during cold rolling is 200 × cold rolling reduction rate / 100 + 60 or more, a large thrust is received during material deformation, and the fraction of grains with Goss orientation in the steel sheet increases significantly.

[0096] The cold rolling can be carried out at a cold rolling reduction rate of 35 - 98%. When the cold rolling reduction rate is less than 35%, the energy stored by processing is consumed during cold rolling, and due to the characteristics of the steel that undergoes recrystallization, recrystallization does not occur, so there is a drawback that the magnetic properties after annealing also deteriorate. When the cold rolling reduction rate exceeds 98%, a highly processed fine structure formed by rolling is formed, and there is a problem of increased iron loss in the rolling direction and the direction perpendicular to the rolling direction even after the final annealing. The lower limit of the cold rolling reduction rate is more preferably 55%, further preferably 65%, and most preferably 73%. The upper limit of the cold rolling reduction rate is more preferably 93%, further preferably 88%, and most preferably 83%. In addition, the cold rolling can be a single cold rolling or multiple cold rollings with intermediate annealing between them.

[0097] The maximum rolling speed in one or more passes during the cold rolling can be 3 m / s or more. When the maximum rolling speed in one or more passes during the cold rolling is less than 3 m / s, a strong thrust is applied to the surface of the steel sheet during rolling, more nucleation of the Goss orientation occurs, and the fraction of grains with the Goss orientation on the surface of the steel sheet may increase during the final annealing. In the present invention, the faster the maximum rolling speed in one or more passes during the cold rolling, the more advantageous it is, so there is no particular limitation on its upper limit. However, the upper limit of the maximum rolling speed in one or more passes during the cold rolling can be 20 m / s.

[0098] After that, the cold-rolled sheet is heated to the final annealing temperature. The heating rate in the temperature range of 300 - 500 °C during the heating is preferably 5 - 150 °C / s. When the heating rate in the temperature range of 300 - 500 °C during the heating is less than 5 °C / s, the recrystallization of grains with an orientation unfavorable to magnetism is promoted. When the heating rate in the temperature range of 300 - 500 °C during the heating exceeds 150 °C / s, the recrystallization of grains with the Goss orientation, which is unfavorable to magnetism perpendicular to the rolling direction, is significantly promoted. The lower limit of the heating rate is more preferably 7 °C / s, further preferably 10 °C / s. The upper limit of the heating rate is more preferably 120 °C / s, further preferably 100 °C / s, and most preferably 50 °C / s.

[0099] After that, the cold-rolled sheet heated as described above is subjected to final annealing. The final annealing can be carried out at 600 - 1150 °C for 10 - 500 seconds. When the final annealing temperature is lower than 600 °C, there is a drawback that the Goss fraction inside the steel sheet increases significantly during recrystallization. When the final annealing temperature exceeds 1150 °C, coarse grains are formed, and there is a drawback that the high-frequency iron loss in the C direction deteriorates. The lower limit of the final annealing temperature is more preferably 700 °C, further preferably 730 °C, and most preferably 750 °C. The upper limit of the final annealing temperature is more preferably 1120 °C, further preferably 1100 °C, and most preferably 1050 °C. When the final annealing time is less than 10 seconds, there is a drawback that the fraction of grains with the Goss fraction in the overall plate thickness increases significantly. When the final annealing time exceeds 500 seconds, due to excessive grain growth, there is a drawback that the high-frequency iron loss increases significantly. The lower limit of the final annealing time is more preferably 20 seconds, further preferably 30 seconds, and most preferably 35 seconds. The upper limit of the final annealing time is more preferably 400 seconds, further preferably 300 seconds, and most preferably 200 seconds.

[0100] In terms of volume percentage, the gas atmosphere during the final annealing preferably consists of hydrogen: 15 - 99.99%, oxygen: 0.0001 - 0.0030%, and the balance being an inert gas. By controlling as described above, effects such as an oxygen-free surface on the steel sheet can be substantially obtained. When the fraction of hydrogen is less than 15%, due to insufficient reducing ability, there is a drawback that the surface of the material of the invention is oxidized. It is ideal for the fraction of hydrogen to be substantially 100%, but it is extremely difficult to utilize industrially, so the fraction of hydrogen is limited to 99.99%. When the fraction of oxygen is less than 0.0001%, a very small part of the steel sheet surface may combine with oxygen to form a local oxide layer, resulting in surface non-uniformity. When the fraction of oxygen exceeds 0.0030%, a wide oxide layer is formed on the surface part, the magnetic property deteriorates, and the nucleation of grains with Gaussian orientation on the surface is promoted, so there is a drawback of an increase in the surface fraction. In the present invention, there is no particular limitation on the type of the inert gas, and all types used in the technical field can be utilized. For example, nitrogen or argon can be used.

[0101] In addition, after the final annealing, a step of forming an insulating layer may further be included. Since the method of forming an insulating layer is well known in the technical field of non-oriented electrical steel sheets, detailed description is omitted. Detailed implementation mode

[0102] 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 do not 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.

[0103] (Example)

[0104] Slabs having the alloy compositions described in Tables 1 and 2 below were prepared, and then non-oriented electrical steel sheets were manufactured using the manufacturing conditions described in Tables 3 and 4 below. In addition, during the final annealing, the balance of the gas atmosphere in the temperature range of 500 to 750 was nitrogen.

[0105] The Gaussian orientation fraction and electrical properties of the non-oriented electrical steel sheets manufactured as described above were measured, and the results are shown in Tables 4 to 6 below.

[0106] The Gaussian orientation fraction in the surface layer part (the region from the surface to t / 10 (t: the thickness of the steel sheet) in the thickness direction) and the entire region in the thickness direction was measured using EBSD. To confirm the Gaussian orientation fraction according to the thickness, the RD-ND plane was observed, and for the upper and lower surfaces of 1 / 10 of the total thickness, the EBSD measurement plane was separated and analyzed. To ensure statistical reliability, the cross-sections of 100 samples were measured, and the texture according to the thickness was measured and averaged during the measurement of each sample, and it was evaluated as the Gaussian orientation fraction of t / 10.

[0107] 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 for quantitative measurement of ordinary electrical steel sheets. The sample was cut with a cutting machine so that the sample in the L direction was 305 mm in the L direction and 30 mm in the C direction. The sample in the C direction was 305 mm in the C direction and 30 mm in the L direction.

[0108] [Table 1]

[0109]

[0110] [Table 2]

[0111]

[0112] [Table 3]

[0113]

[0114] [Table 4]

[0115]

[0116] [Table 5]

[0117]

[0118] [Table 6]

[0119]

[0120] As can be seen from Tables 1 to 6, in the cases of Invention Examples 1 to 17, the alloy composition and manufacturing conditions of the present invention are satisfied, and since the fine structure expected to be obtained by the present invention is ensured, it can be seen that excellent magnetism is ensured.

[0121] In the case of Comparative Example 1 and Comparative Example 2, the alloy composition of the present invention is not satisfied, and since the fine structure expected to be obtained by the present invention cannot be ensured, it is known that excellent magnetic properties are ensured.

[0122] In the case of Comparative Example 3 to Comparative Example 6, the manufacturing conditions of the present invention are not satisfied, and since the fine structure expected to be obtained by the present invention cannot be ensured, it is known that excellent magnetic properties are ensured.

Claims

1. An non-oriented electrical steel sheet, by weight %, the non-oriented electrical steel sheet comprises: Si: 1.5 - 6.5%, Al: 0.0005 - 3.5%, Mn: 0.01 - 3.0%, Cr: 0.005 - 5.0%, S: 0.0005 - 0.03%, the balance Fe and other inevitable impurities, The Gaussian orientation fraction in the region from the surface to t / 10 along the thickness direction is 3 area % or less, where t is the thickness of the steel sheet, The Gaussian orientation fraction in the entire region along the thickness direction is 5 area % or less.

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

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

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

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

6. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Bi, Pb, Ge, and As, and the contents of Bi, Pb, Ge, and As are respectively 0.20% or less and excluding 0% or the total amount is 0.20% or less and excluding 0%.

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

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

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

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

11. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following relational expression 1, [Relationship 1] Iron loss (W10 / 600°C) + Iron loss (W10 / 800°C) + Iron loss (W10 / 1200°C) < Iron loss (W10 / 600L) + Iron loss (W10 / 800L) + Iron loss (W10 / 1200L).

12. A method for manufacturing a non-oriented electrical steel sheet, comprising the following steps: Heating a slab at 1050 - 1220°C, wherein, by weight%, the slab contains: Si: 1.5 - 6.5%, Al: 0.0005 - 3.5%, Mn: 0.01 - 3.0%, Cr: 0.005 - 5.0%, S: 0.0005 - 0.03%, the balance being Fe and other inevitable impurities; Performing hot finish rolling on the slab to obtain a hot rolled sheet; Annealing the hot rolled sheet at 850 - 1150°C for 30 - 300 seconds; Performing cold rolling on the hot rolled sheet annealed as described above to obtain a cold rolled sheet; Heating the cold rolled sheet; and Performing final annealing on the cold rolled sheet heated as described above, wherein, during the cold rolling, the following [Relationship 2] is satisfied, During the heating, the heating rate in the temperature range of 300 - 500°C is 5 - 150°C / second, By volume%, during the final annealing, the gas atmosphere consists of hydrogen: 15 - 99.99%, oxygen: 0.0001 - 0.0030%, and the balance being an inert gas, [Relationship 2] The maximum temperature on the surface of the cold rolled sheet during cold rolling < 200 × cold rolling reduction rate / 100 + 60.

13. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of P: 0.005 - 0.08% and Sn: 0.01 - 0.2%.

14. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of C: not more than 0.005% and excluding 0%, N: not more than 0.005% and excluding 0%, O: not more than 0.005% and excluding 0%, and Ti: not more than 0.01% and excluding 0%.

15. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of Mo: not more than 0.1% and excluding 0%, B: not more than 0.0050% and excluding 0%, V: not more than 0.050% and excluding 0%, Ca: not more than 0.010% and excluding 0%, Nb: not more than 0.0050% and excluding 0%, and Mg: not more than 0.0050% and excluding 0%.

16. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of Sb: not more than 0.1% and excluding 0%, Ni: not more than 0.05% and excluding 0%, Cu: 0.005 - 0.2%, and Zn: not more than 0.01% and excluding 0%.

17. The method for manufacturing an non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of Bi, Pb, Ge, and As, and the contents of Bi, Pb, Ge, and As are respectively not more than 0.20% and excluding 0% or the total amount is not more than 0.20% and excluding 0%.

18. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, The hot finish rolling is performed at 700 - 1050°C.

19. The method for manufacturing an non-oriented electrical steel sheet according to claim 12, wherein, The cold rolling is performed at a cold rolling reduction rate of 35 - 98%.

20. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, During the cold rolling, the maximum rolling speed in one or more passes among the first pass and the second pass is 3 m / second or more.

21. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, During the final annealing, it is performed at 600 - 1150°C for 10 - 500 seconds.

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