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 having excellent iron loss and magnetic anisotropy under high magnetic flux and high frequency conditions; 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 to replace 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 essential. 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, for the high 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 tooth (Teeth) part and yoke part 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, in the process of manufacturing electrical steel sheets, specific resistance elements such as Si, Al, Mn, etc. are added in large amounts and the grain size is reduced to reduce eddy current loss. In addition, since eddy currents only pass 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 having excellent iron loss and magnetic anisotropy under high magnetic flux and high-frequency conditions 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 being 3 area % or less, and the density of inclusions in the region from the surface to t / 50 (t: the thickness of the steel sheet) in the thickness direction being equal to or less than the density of inclusions in the region outside thereof.

[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 (excluding 0%), N: 0.005% or less (excluding 0%), O: 0.005% or less (excluding 0%), and Ti: 0.01% or less (excluding 0%).

[0011] The non-oriented electrical steel sheet may further comprise 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%).

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

[0013] The non-oriented electrical steel sheet may further comprise one or more of Bi, Pb, Ge, and As, each having a content of 0.20% or less (excluding 0%) or a total content of 0.20% or less (excluding 0%).

[0014] The non-oriented electrical steel sheet may satisfy the following relational expression 1.

[0015] [Relational expression 1] Si > Al + Mn

[0016] The Goss orientation fraction in the entire region in the thickness direction of the non-oriented electrical steel sheet may be 5 area % or less.

[0017] The iron loss (W15 / 1000L) of the non-oriented electrical steel sheet can be 150 W / kg or less, and the iron loss (W15 / 1000C) can be 150 W / kg or less.

[0018] In the non-oriented electrical steel sheet, 2×(W15 / 1000C - W15 / 1000L) / (W15 / 1000C + W15 / 1000L) can be < 0.1.

[0019] 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 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; 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 at 600 - 1150 °C for 10 - 300 seconds, wherein, during the cold rolling, the following [Relationship 2] is satisfied, and during the heating, the heating rate in the temperature range of 300 - 500 °C is 5 - 150 °C / second (s), and by volume%, the gas atmosphere in the temperature range of 500 - 750 °C during the final annealing consists of hydrogen: 15 - 99.99%, oxygen: 0.0001 - 0.0030%, and the balance being an inert gas, and the oxygen content in the gas atmosphere in the temperature range of 800 - 1100 °C during the final annealing is 1 to 1.5 times the oxygen content in the temperature range of 500 - 750 °C.

[0020] [Relationship 2] The highest temperature on the surface of the cold rolled sheet during cold rolling < 200×cold rolling reduction rate / 100 + 40

[0021] The slab may further contain one or more of P: 0.005 - 0.08% and Sn: 0.01 - 0.2%.

[0022] The slab 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%).

[0023] The slab may further contain one or more of Mo: not more than 0.1% (except 0%), B: not more than 0.0050% (except 0%), V: not more than 0.050% (except 0%), Ca: not more than 0.010% (except 0%), Nb: not more than 0.0050% (except 0%), and Mg: not more than 0.0050% (except 0%).

[0024] The slab may further contain one or more of Sb: not more than 0.1% (except 0%), Ni: not more than 0.05% (except 0%), Cu: 0.005 - 0.2%, and Zn: not more than 0.01% (except 0%).

[0025] The slab may further contain one or more of Bi, Pb, Ge, and As with a content of not more than 0.20% (except 0%) respectively or a total content of not more than 0.20% (except 0%).

[0026] The slab may satisfy the following relational expression 1.

[0027] [Relational expression 1] Si > Al + Mn

[0028] The hot finish rolling may be carried out at 700 - 1050 °C.

[0029] The cold rolling may be carried out with a cold reduction rate of 35 - 98%.

[0030] During the cold rolling, the maximum rolling speed in one or more passes of the first pass and the second pass may be 3 m / s or more.

[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 excellent iron loss and magnetic anisotropy under high magnetic flux and high frequency conditions and a manufacturing method thereof. Embodiment

[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 significantly reduced. Therefore, the content of Al preferably has a range of 0.0005 - 3.5%. The lower limit of the Al content is more preferably 0.15%. The upper limit of the Al content 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, which 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 Mn content is more preferably 0.2%. The upper limit of the Mn content 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 iron loss. At the same time, if the cold rolling conditions and final annealing conditions are appropriately controlled, Cr can be enriched on the surface to 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 detrimental to magnetism. When Cr exceeds 5%, Cr will be evenly distributed throughout the thickness and will not be enriched on the surface, resulting in a decrease in the magnetic flux density throughout the steel sheet. 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 formed 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 S content is more preferably 0.001%. The upper limit of the S content is more preferably 0.015%, further preferably 0.005%, and most preferably 0.0035%.

[0044] The remaining component is iron (Fe). However, in the usual 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 is enriched on the surface and plays a role in controlling the proportion 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 P content 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, reducing toughness, and productivity will decrease compared to improving magnetic properties. Therefore, the content of Sn preferably has a range of 0.01 - 0.2%. The lower limit of the Sn content is more preferably 0.02%. The upper limit of the Sn content 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 has an adverse effect on magnetism. Therefore, the upper limit of Mo is restricted 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 has an adverse effect on magnetism. Therefore, the upper limit of B is restricted 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 has an adverse effect on magnetism. Therefore, the upper limit of V is restricted 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 has an adverse effect on magnetism. Therefore, the upper limit of Ca is restricted 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 has an adverse effect on magnetism. Therefore, the upper limit of Nb is restricted 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 has an adverse effect on magnetism. Therefore, the upper limit of Mg is restricted 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 can inhibit the diffusion of nitrogen at grain boundaries, suppress the {111} texture that is detrimental to magnetism, and increase the favorable {100} texture, thereby improving 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: less than 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: less than 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 with a content of less than 0.20% (except 0%) respectively or a total content of less than 0.20% (except 0%).

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

[0083] The non-oriented electrical steel sheet of the present invention can satisfy the following relational expression 1.

[0084] [Relational expression 1] Si > Al + Mn

[0085] When the relational expression 1 is not satisfied, the magnetic anisotropy index as a physical property of the steel sheet cannot be sufficiently reduced, and thus the magnetic anisotropy at high frequencies may increase significantly.

[0086] The Gaussian orientation fraction in the region from the surface to t / 10 (t: 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. The Gaussian orientation fraction can be the area fraction of grains with an orientation within 10° of the Gaussian orientation. The magnetic properties in the rolling direction of the Gaussian orientation are very excellent, but the Gaussian 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 with the Gaussian orientation. In particular, as the frequency increases, the influence of the surface layer on the overall iron loss increases. When the Gaussian orientation fraction in the region from the surface to t / 10 (t: 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. In addition, the measurement method of the Gaussian orientation fraction is to use the usual 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 a grain boundary with an orientation error angle of 3° or more from the surrounding grains within the measurement area is at least 5000 or more. In the case of grains measured in a cut shape within the measurement area, the fraction is calculated including its cut area.

[0087] The Gaussian orientation fraction in the entire region in the thickness direction of the non-oriented electrical steel sheet of the present invention can be 5 area% or less. When the Gaussian 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.

[0088] In the non-oriented electrical steel sheet of the present invention, the density of inclusions in the region from the surface to t / 50 (t: the thickness of the steel sheet) in the thickness direction is preferably equal to or less than the density of inclusions in the region other than that. The surface layer portion is particularly important for ensuring low high-frequency iron loss and has a great influence on the movement of magnetic domains. Therefore, a low density of inclusions in the surface layer portion is important for reducing iron loss. At this time, the density of inclusions in the surface layer portion being lower than the density of inclusions in the region other than that means that the formation of inclusions does not proceed well on the surface, and thus the high-frequency iron loss perpendicular to the rolling direction can be significantly improved. The density of the inclusions can be measured using an electron microscope, or corresponding equipment (SIMS - secondary ion mass spectrometry, AFM - atomic force microscopy, EPMA - Electron Probe X-ray Micro Analyzer, etc.) can be used for measurement. For the electron microscope, both a scanning electron microscope and a transmission electron microscope can be used to measure the value for an area of 1 mm × 1 mm or more as the measurement area of the inclusions or for an area of 1 mm × 1 mm × sample thickness (mm), and the measurement methods for the surface layer portion and the central portion are the same, so their density values can be compared regardless of the unit. At this time, the measurement region does not include the insulating coating. For the number of inclusions, at least when converted into a diameter by the spherical equivalent area method, inclusions with a size of 20 nm or more are counted. In the case of complex inclusions, even if they are irregular in shape and in a segmented connection form, as long as the parts caused by components other than steel are connected to each other, they are counted as one inclusion and not additionally counted. The maximum size of the inclusions is set to 5 μm or less, and even if there are larger inclusions, they should be excluded during counting and the density should be calculated. However, even if the area occupied by coarse inclusions in the measurement region is excluded, the reference area should reach 1 mm × 1 mm or more during measurement.

[0089] The iron loss (W15 / 1000L) of the non-oriented electrical steel sheet of the present invention provided as described above can be 150 W / kg or less, and the iron loss (W15 / 1000C) can be 150 W / kg or less. When the above conditions are not satisfied, the iron loss difference at high magnetic flux density is large, so it is difficult to achieve the object of the present invention for high power and high efficiency of the motor. It is known that the iron loss perpendicular to the rolling direction is closely related to the circumferential magnetic field characteristics of the yoke of the steel sheet. The lower the iron loss value, the more advantageous. Therefore, in the present invention, the lower limits of the iron loss (W15 / 1000L) and the iron loss (W15 / 1000C) are not particularly limited. However, the lower limits of the iron loss (W15 / 1000L) and the iron loss (W15 / 1000C) can be 50 W / kg and 50 W / kg, respectively. In addition, the maximum magnetic flux of W15 / 1000 is 1.5 T, and it represents the iron loss measured by the Epstein method under the condition of 1000 Hz. L represents the rolling direction, and C represents the direction perpendicular to the rolling direction.

[0090] In addition, for the non-oriented electrical steel sheet of the present invention, 2×(W15 / 1000C - W15 / 1000L) / (W15 / 1000C + W15 / 1000L) can be < 0.1. When the above conditions are not satisfied, the magnetic anisotropy at high frequency is high, so it is difficult to achieve the object of the present invention for high power and high efficiency of the motor. The magnetic anisotropy at high frequency may affect the increase in loss during high-speed rotation of the motor. The lower the value of 2×(W15 / 1000C - W15 / 1000L) / (W15 / 1000C + W15 / 1000L), the more advantageous. Therefore, in the present invention, the lower limit of 2×(W15 / 1000C - W15 / 1000L) / (W15 / 1000C + W15 / 1000L) is not particularly limited. However, the lower limit of 2×(W15 / 1000C - W15 / 1000L) / (W15 / 1000C + W15 / 1000L) can be -0.1.

[0091] The non-oriented electrical steel sheet of the present invention can have a thickness of 0.03 - 0.35 mm.

[0092] Hereinafter, a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention will be described.

[0093] First, a slab having the above alloy composition is heated at 1050-1220°C. When the slab heating temperature is lower than 1050°C, the temperature difference between the surface and interior of the slab during hot rolling is large, resulting in poor passability during hot rolling and insufficient reduction during hot rolling. When the slab heating temperature exceeds 1220°C, precipitates may redissolve and finely precipitate after hot rolling. The lower limit of the slab heating temperature is more preferably 1080°C, and even more preferably 1100°C. The upper limit of the slab heating temperature is more preferably 1200°C, and even more preferably 1180°C.

[0094] Afterwards, the slab is subjected to hot finishing rolling to obtain a hot-rolled plate. The hot finishing rolling can be carried out at 700-1050°C. When the hot finishing rolling temperature is lower than 700°C, the shape of the hot-rolled plate deteriorates, and the deformation is concentrated on the surface, making it impossible to hot-roll the steel plate, and there are disadvantages such as an increase in Gaussian similar orientation on the surface. When the hot finishing rolling temperature exceeds 1050°C, the friction between the roll and the plate surface increases, the Gaussian similar orientation increases, and problems such as poor plate shape caused by high-temperature deformation may occur. The lower limit of the hot finishing rolling temperature is more preferably 730°C, further preferably 750°C, and most preferably 780°C. The upper limit of the hot finishing rolling temperature is more preferably 1000°C, further preferably 960°C, and most preferably 930°C. In addition, the thickness of the hot-rolled plate can be 0.8-3mm.

[0095] The hot-rolled sheet is then annealed at 850-1150°C for 30-300 seconds. If the annealing temperature is below 850°C, the microstructure may not grow or may grow finely. If the annealing temperature exceeds 1150°C, the magnetic properties may decrease, and the sheet shape may be deformed, which may deteriorate the rolling workability. The lower limit of the hot-rolled sheet annealing temperature is more preferably 900°C, and even more preferably 950°C. The upper limit of the hot-rolled sheet annealing temperature is more preferably 1135°C, and even more preferably 1110°C. If the annealing time is less than 30 seconds, the Gaussian fraction of the surface portion of the final electrical steel sheet may increase significantly due to the difference in grain size growth between the surface and interior grains. If the annealing time exceeds 300 seconds, the grains may become coarse, and the Gaussian fraction of the final electrical steel sheet throughout the entire sheet thickness may increase significantly. The lower limit of the hot-rolled sheet annealing time is more preferably 60 seconds, and even more preferably 80 seconds. The upper limit of the hot-rolled sheet annealing time is more preferably 180 seconds, and even more preferably 150 seconds. The hot-rolled sheet annealing may be performed as needed to increase orientation favorable for magnetic properties, or may be omitted.

[0096] Then, the hot-rolled sheet annealed by the hot-rolled sheet is cold-rolled to obtain a cold-rolled sheet. The cold rolling preferably satisfies the following [Relationship 2].

[0097] [Relationship 2] During the cold rolling process, the maximum temperature on the surface of the cold-rolled sheet < 200 × cold reduction rate / 100 + 40

[0098] The temperature of the steel sheet may increase due to the waste heat during the steps 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 supply from the outside. When the maximum temperature on the surface of the cold-rolled sheet during the cold rolling process is 200 × cold reduction rate / 100 + 40 or higher, a large thrust is applied during material deformation, and the fraction of grains with a Gaussian orientation in the steel sheet increases significantly.

[0099] The cold rolling can be performed at a cold reduction rate of 35 - 98%. When the cold reduction rate is less than 35%, recrystallization does not occur in the characteristics of the steel that consumes the energy stored by processing to generate recrystallization during cold rolling, so there is a disadvantage that the magnetic properties deteriorate even after annealing. When the cold reduction rate exceeds 98%, a highly processed fine microstructure formed by rolling is formed, resulting in an increase in iron loss in both the rolling direction and the direction perpendicular to the rolling direction even after final annealing. The lower limit of the cold reduction rate is more preferably 55%, further preferably 65%, and most preferably 73%. The upper limit of the cold reduction rate is more preferably 93%, further preferably 88%, and most preferably 83%. In addition, the cold rolling can be single-pass cold rolling or multi-pass cold rolling with intermediate annealing between them.

[0100] The maximum rolling speed in one or more passes among the first pass and the second pass during the cold rolling can be 3 m / s or more. When the maximum rolling speed in one or more passes among the first pass and the second pass during the cold rolling is less than 3 m / s, a strong thrust is applied to the surface of the steel sheet during rolling, and more nucleation of the Gaussian orientation occurs, and the fraction of grains with a Gaussian orientation on the surface of the steel sheet may increase during final annealing. In the present invention, the faster the maximum rolling speed in one or more passes among the first pass and the second pass during the cold rolling, the more advantageous it is, so no particular limitation is imposed on its upper limit. However, the upper limit of the maximum rolling speed in one or more passes among the first pass and the second pass during the cold rolling can be 20 m / s.

[0101] Thereafter, 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 / second. When the heating rate in the temperature range of 300 - 500°C during the heating is less than 5°C / second, the recrystallization of grains with an orientation unfavorable to magnetism is promoted. When the heating rate in the temperature range exceeding 300°C to below 500°C during the heating exceeds 150°C / second, the recrystallization of grains with a Goss orientation unfavorable to magnetism perpendicular to the rolling direction is greatly promoted. The lower limit of the heating rate is more preferably 7°C / second, further preferably 10°C / second. The upper limit of the heating rate is more preferably 120°C / second, further preferably 100°C / second, and most preferably 50°C / second.

[0102] Thereafter, the heated cold-rolled sheet is subjected to final annealing. The final annealing can be carried out at 600 - 1150°C for 10 - 300 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 a Goss fraction in the overall sheet thickness increases significantly. When the final annealing time exceeds 300 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 240 seconds, further preferably 180 seconds, and most preferably 150 seconds.

[0103] In terms of volume percentage, the gas atmosphere in the temperature range of 500 - 750 °C during the final annealing 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 state on the steel plate surface can be substantially obtained. When the fraction of hydrogen is less than 15%, due to insufficient reduction ability, there is a drawback that the surface of the inventive material 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 plate 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 a Gaussian orientation on the surface is promoted, so there is a drawback of an increase in the surface fraction. In the present invention, the type of the inert gas is not particularly limited, and all types used in the technical field can be utilized. For example, nitrogen or argon can be used.

[0104] The oxygen content in the gas atmosphere in the temperature range of 800 - 1100 °C during the final annealing is preferably 1 to 1.5 times the oxygen content in the temperature range of 500 - 750 °C. By the control as described above, the growth of grains with a Gaussian orientation may not be induced. When the above conditions are not satisfied, there are drawbacks of forming an oxide layer in a wide area on the surface and the formation of oxides combined with oxygen to a deeper thickness.

[0105] In addition, after the final annealing, a step of forming an insulating layer may be further 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 Description of the Invention

[0106] Hereinafter, the present invention will be described in more detail by way of examples. However, it should be noted that the following examples are only used to illustrate the present invention for more detailed description and are not used to limit the scope of the rights of the present invention. This is because the scope of the rights of the present invention is determined by the content recorded in the claims and the content reasonably deduced therefrom.

[0107] (Examples)

[0108] 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.

[0109] The Goss orientation fraction, inclusion density, and electrical properties of the non-oriented electrical steel sheet manufactured as described above were measured, and the results are shown in Table 5 below.

[0110] The Goss orientation fraction in the surface layer (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 Goss 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 planes were 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 Goss orientation fraction of t / 10.

[0111] The density of inclusions in the surface layer (the region from the surface to t / 50 (t: the thickness of the steel sheet) in the thickness direction) and the region outside thereof was measured by SEM on the surface of the steel sheet. EDS was measured at the points with the presence contrast in the SEM image, and the points with composition values significantly higher than those of Fe and the composition of the steel sheet were regarded as inclusions, regardless of the size of the region forming the contrast. At this time, the points with oxygen of 5% or more were regarded as oxides, the points with N of 1% or more were regarded as nitrides, the points with C of 1% or more were regarded as carbides, the points with S of 1% or more were regarded as sulfides, etc., and their total amounts were measured.

[0112] The iron losses (W15 / 1000L) and iron losses (W15 / 1000C) were measured using the Epstein measurement method commonly used for quantitative measurement of electrical steel sheets. The samples were 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.

[0113] [Table 1]

[0114]

[0115] [Table 2]

[0116]

[0117] [Table 3]

[0118]

[0119] [Table 4]

[0120]

[0121] [Table 5]

[0122]

[0123] As can be seen from Table 1 to Table 5, in the case of Invention Examples 1 to 14 that satisfy the alloy composition and manufacturing conditions of the present invention, since the Gaussian orientation fraction and inclusion characteristics desired to be obtained by the present invention are satisfied, the iron loss and magnetic anisotropy have excellent levels.

[0124] In the case of Comparative Examples 1 to 10, since the manufacturing conditions of the present invention are not satisfied and the Gaussian orientation fraction or inclusion characteristics desired to be obtained by the present invention are not satisfied, the iron loss is good but the magnetic anisotropy is at a poor level.

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 in the thickness direction is 3 area% or less, where t is the thickness of the steel sheet, The density of inclusions in the region from the surface to t / 50 along the thickness direction is equal to or less than the density of inclusions in the region outside thereof, where t is the thickness of the steel sheet.

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: 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%.

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: 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%.

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: 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%.

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, each having a content of not more than 0.20% and excluding 0% or a total content of not more than 0.20% and excluding 0%.

7. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following relational expression 1, [Relational expression 1] Si > Al + Mn.

8. The non-oriented electrical steel sheet according to claim 1, wherein, The Gaussian orientation fraction in the entire region along the thickness direction of the non-oriented electrical steel sheet is 5 area % or less.

9. The non-oriented electrical steel sheet according to claim 1, wherein, The iron loss (W15 / 1000L) of the non-oriented electrical steel sheet is 150 W / Kg or less, and the iron loss (W15 / 1000C) is 150 W / Kg or less.

10. The non-oriented electrical steel sheet according to claim 1, wherein, In the non-oriented electrical steel sheet, 2×(W15 / 1000C - W15 / 1000L) / (W15 / 1000C + W15 / 1000L) < 0.

1.

11. A method for manufacturing a non-oriented electrical steel sheet, which comprises the following steps: Heating a slab at 1050 - 1220 °C, by weight %, the slab 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; 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 by the hot rolled sheet annealing to obtain a cold rolled sheet; Heat the cold-rolled sheet; and Perform final annealing on the heated cold-rolled sheet at 600 - 1150 °C for 10 - 300 seconds, wherein, the following [Relationship 2] is satisfied during cold rolling, During heating, the heating rate in the temperature range of 300 - 500 °C is 5 - 150 °C / second, By volume%, the gas atmosphere in the temperature range of 500 - 750 °C during final annealing consists of hydrogen: 15 - 99.99%, oxygen: 0.0001 - 0.0030%, and the balance of inert gas, During final annealing, the oxygen content in the gas atmosphere in the temperature range of 800 - 1100 °C is 1 to 1.5 times the oxygen content in the temperature range of 500 - 750 °C, [Relationship 2] The maximum temperature on the surface of the cold-rolled sheet during cold rolling < 200 × cold reduction rate / 100 + 40.

12. The manufacturing method of the non-oriented electrical steel sheet according to claim 11, wherein, The slab further contains one or more of P: 0.005 - 0.08% and Sn: 0.01 - 0.2%.

13. The method for manufacturing a non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of C: below 0.005% and excluding 0%, N: below 0.005% and excluding 0%, O: below 0.005% and excluding 0%, and Ti: below 0.01% and excluding 0%.

14. The manufacturing method of the non-oriented electrical steel sheet according to claim 12, wherein, The slab further contains one or more of Mo: below 0.1% and excluding 0%, B: below 0.0050% and excluding 0%, V: below 0.050% and excluding 0%, Ca: below 0.010% and excluding 0%, Nb: below 0.0050% and excluding 0%, and Mg: below 0.0050% 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 Sb: below 0.1% and excluding 0%, Ni: below 0.05% and excluding 0%, Cu: 0.005 - 0.2%, and Zn: below 0.01% and excluding 0%.

16. The method for manufacturing a non-oriented electrical steel sheet according to claim 11, wherein, The slab further contains one or more of Bi, Pb, Ge, and As with a content of below 0.20% and excluding 0% respectively or a total content of below 0.20% and excluding 0%.

17. The manufacturing method of the non-oriented electrical steel sheet according to claim 11, wherein, The slab satisfies the following Relationship 1, [Relationship 1] Si > Al + Mn.

18. The manufacturing method of the non-oriented electrical steel sheet according to claim 11, wherein, The hot finish rolling is performed at 700 - 1050 °C.

19. The manufacturing method of the non-oriented electrical steel sheet according to claim 11, wherein, The cold rolling is performed with a cold reduction rate of 35 - 98%.

20. The manufacturing method of the non-oriented electrical steel sheet according to claim 11, wherein, During 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.

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