Non-oriented electrical steel sheet and method for manufacturing same

Abstract

The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing same. According to the non-oriented electrical steel sheet and the method for manufacturing same of the present application, deformation of the steel sheet during heat treatment can be minimized to suppress an increase in iron loss, and thus excellent magnetic properties can be achieved.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] This application relates to a non-oriented electrical steel sheet and a method for manufacturing the same.

[0002] Due to recent policies to reduce CO2 emissions to combat global warming, conventional internal combustion engine vehicles are rapidly being replaced by eco-friendly vehicles such as hybrid vehicles (HEVs) and, especially, electric vehicles (EVs). In response to this growing demand for EVs, the energy conversion efficiency of EV drive motors is being improved. This requires superior magnetic properties of non-oriented electrical steel, the core material for motors.

[0003] In particular, non-oriented electrical steel sheets with low high-frequency (400 Hz) iron loss are required to improve motor efficiency, particularly in high-speed driving where energy loss is significant. To meet this demand, non-oriented electrical steel sheets are being developed with increased silicon content or thinner thicknesses.

[0004] As the required thickness decreases, the manufacturing difficulty of non-oriented electrical steel sheets increases. Furthermore, this thin-rolling process causes sheet fractures, reducing production yields, and the thin steel sheets become deformed during heat treatment, increasing iron loss.

[0005] To address this issue, Patent Document 1 (Korean Patent Publication No. 2015-0185060) proposed a method for reducing the tension applied to a steel sheet by controlling the velocity difference between the inlet and outlet of the steel sheet passing through the final annealing furnace. However, even if the tension was reduced by controlling the velocity difference between the inlet and outlet of the steel sheet passing through the final annealing furnace, it was not possible to suppress significant deformation during crystallization. Therefore, there is a need for a non-oriented electrical steel sheet with excellent magnetic properties and a manufacturing method thereof that addresses these issues.

[0006] The object of the present application is to provide a non-oriented electrical steel sheet with excellent magnetic properties and a method for manufacturing the same by minimizing deformation of the steel sheet during heat treatment and suppressing an increase in iron loss.

[0007] In order to solve the above problem, the non-oriented electrical steel sheet of the present application comprises, in wt%, Si: 3.0% or more and 3.8% or less, Mn: 0.2% or more and 0.5% or less, and Al: 0.5% or more and 1.5% or less, and the remainder including Fe and other inevitable impurities, and is a non-oriented electrical steel sheet manufactured by reheating a slab and then performing hot rolling, cold rolling, and final annealing, wherein when the crystal orientation is measured in an area of ​​1000 ㎛ × 1000 ㎛ or more using electron backscatter diffraction (EBSD), the average value of the Kernel Average Misorientation (KAM) values ​​of each measuring point existing within the measuring area is 0.4° or less.

[0008] The above final annealing may be performed while the cold-rolled cold-rolled steel sheet is moved through a hearth roll having a surface roughness (Ra) of 0.1 ㎛ or more and 0.2 ㎛ or less.

[0009] In addition, the final annealing may be performed while the cold-rolled cold-rolled steel sheet is moved through a hearth roll having a friction coefficient of 0.05 or more and 0.2 or less.

[0010] Additionally, the final annealing may be performed while the cold-rolled steel sheet is moved under a tension of 10 MPa or less.

[0011] In addition, the slab may further include one or more selected from the group consisting of Sn: 0.04% or less, Sb: 0.04% or less, C: 0.003% or less, S: 0.002% or less, P: 0.015% or less, N: 0.002% or less, and Ti: 0.002% or less in wt%.

[0012] In addition, the above non-oriented electrical steel sheet has a core loss of W 15 / 50 is less than 2.0 W / kg, and W 10 / 400is less than 12.0 W / kg, and the magnetic flux density (B 50 ) may be greater than 1.63 T.

[0013] In addition, the method for manufacturing a non-oriented electrical steel sheet of the present application includes the steps of reheating and hot-rolling a slab containing, in wt%, Si: 3.0% or more and 3.8% or less, Mn: 0.2% or more and 0.5% or less, and Al: 0.5% or more and 1.5% or less, and the remaining Fe and other inevitable impurities; the step of cold-rolling to manufacture a cold-rolled steel sheet; and the step of final annealing the cold-rolled steel sheet, wherein when a crystal orientation is measured in an area of ​​1000 ㎛ × 1000 ㎛ or more using electron backscatter diffraction (EBSD), the average value of the Kernel Average Misorientation (KAM) values ​​of each measuring point existing within the measuring area is 0.4° or less.

[0014] In addition, the final annealing step can be performed by moving the cold rolled steel sheet through a hearth roll having a surface roughness (Ra) of 0.1 ㎛ or more and 0.2 ㎛ or less.

[0015] In addition, the final annealing step can be performed while moving the cold rolled steel sheet through a hearth roll having a friction coefficient of 0.05 or more and 0.2 or less.

[0016] Additionally, the tension applied to the cold rolled steel sheet in the final annealing step may be 10 MPa or less.

[0017] According to the non-oriented electrical steel sheet of the present application and the manufacturing method thereof, deformation of the steel sheet during heat treatment can be minimized, thereby suppressing an increase in iron loss, and thus providing a non-oriented electrical steel sheet with excellent magnetic properties.

[0018] FIG. 1 is a drawing exemplarily showing a process in which a cold-rolled steel sheet passes through a final annealing furnace to explain a final annealing step according to one embodiment of the present application.

[0019] The present application relates to a non-oriented electrical steel sheet, which is a core material used in a motor that converts electrical energy into mechanical energy. The non-oriented electrical steel sheet comprises, in wt%, Si: 3.0% or more and 3.8% or less, Mn: 0.2% or more and 0.5% or less, and Al: 0.5% or more and 1.5% or less, and the remainder including Fe and other inevitable impurities, and is manufactured by reheating a slab and then performing hot rolling, cold rolling, and final annealing, wherein when a crystal orientation is measured in an area of ​​1000 ㎛ × 1000 ㎛ or more using electron backscatter diffraction (EBSD) and analyzed using OIM software, the average value of the Kernel Average Misorientation (KAM) values ​​of each measuring point existing within the measuring area is 0.4° or less. Specifically, the average value of the KAM values ​​of each measuring point evaluated by the aforementioned method may be 0.39° or less. At this time, the KAM value of the target measurement point means the average value of the crystal orientation difference between the target measurement point and the surroundings of the target measurement point. The average value of the crystal orientation difference between the target measurement point and the surroundings of the target measurement point means the average value of the orientation difference between 6 pixels (first approximation) adjacent to a certain hexagonal pixel (target measurement point) among the measurement data, 12 pixels (second approximation) outside the pixel, and 18 pixels (third approximation) outside the pixel. In one embodiment, the average value of the KAM values ​​evaluated by the above-described method can be evaluated as the third approximation.

[0020] According to the non-oriented electrical steel sheet of the present application, deformation of the steel sheet during heat treatment can be minimized to suppress an increase in iron loss, and thus the magnetic properties can be excellent.

[0021] For example, the above non-oriented electrical steel sheet has a core loss of W 15 / 50 is less than 2.0 W / kg, and W 10 / 400 is less than 12.0 W / kg, and the magnetic flux density (B 50) may be 1.63 T or more. Specifically, the non-oriented electrical steel sheet has a core loss of W 15 / 50 1.99 W / kg or less or 1.98 W / kg or less, W 10 / 400 It can be 11.9 W / kg or less or 11.8 W / kg or less. The above non-oriented electrical steel sheet has a core loss W 15 / 50 and W 10 / 400 The lower the iron loss W, the better the magnetic properties. 15 / 50 and W 10 / 400 The lower limit of is not particularly limited, but may be, for example, more than 0 W / kg and 5 W / kg or more, respectively. In addition, the non-oriented electrical steel sheet has a magnetic flux density (B 50 ) is higher, the higher the magnetic flux density (B) is, the better the magnetic properties are. 50 ) is not particularly limited, but may be, for example, 1.75 T or less. The non-oriented electrical steel sheet may have excellent magnetic properties by having an average value of the above-mentioned KAM values. The iron loss W 15 / 50 is the low-frequency iron loss when a magnetic flux density of 1.5 T is induced at a low frequency of 50 Hz, and the iron loss W 10 / 400 is the high-frequency iron loss when a magnetic flux density of 1.0 T is induced at a high frequency of 400 Hz, and the magnetic flux density (B 50 ) means the magnetic flux density induced in a magnetic field of 5000 A / m. At this time, the iron loss and magnetic flux density were measured according to the IEC 60404 2 standard.

[0022] The components of the slab used in the manufacture of the above non-oriented electrical steel sheet are described below.

[0023] Si: 3.0 wt% or more and 3.8 wt% or less

[0024] Silicon (Si) is an element that increases the resistivity of a material and reduces iron loss. If the silicon content in the slab is less than the lower limit of the aforementioned range, the iron loss reduction effect may be insufficient. Furthermore, if the silicon content in the slab exceeds the upper limit of the aforementioned range, cold-rollability and punchability may be deteriorated. Therefore, the silicon content in the slab may be 3.0 wt% or more and 3.8 wt% or less, and specifically, 3.0 wt% or more and 3.5 wt% or less.

[0025] Mn: 0.2 wt% or more and 0.5 wt% or less

[0026] Manganese (Mn) is an element that increases resistivity, lowers iron loss, and forms sulfur (S) and MnS sulfides. If the manganese is included in the slab in an amount exceeding the upper limit of the aforementioned range, the MnS may be finely precipitated, increasing iron loss. Therefore, the manganese may be included in the slab in an amount of 0.2 wt% to 0.5 wt%, and specifically, in an amount of 0.2 wt% to 0.4 wt%.

[0027] Al: 0.5 wt% or more and 1.5 wt% or less

[0028] The above aluminum (Al) is an element that increases resistivity to lower iron loss and forms AlN nitride with nitrogen (N). If the aluminum is included in the slab in an amount less than the lower limit of the aforementioned range, the resistivity may be insufficient, thereby increasing iron loss. In addition, if the aluminum is included in the slab in an amount exceeding the upper limit of the aforementioned range, problems such as nozzle clogging may occur during the continuous casting process. Therefore, the aluminum may be included in the slab in an amount of 0.5 wt% or more and 1.5 wt% or less, and specifically, 0.6 wt% or more and 1.3 wt% or less, 0.7 wt% or more and 1.1 wt% or less, or 0.8 wt% or more and 1.0 wt% or less.

[0029] The remaining Fe and other unavoidable impurities

[0030] The above-mentioned inevitable impurities are impurities mixed in during the steelmaking and manufacturing processes of non-oriented electrical steel sheets, and as such, detailed descriptions are omitted. In addition to the components of the steel sheet substrate described above in one embodiment of the present application, additional elements may be added, and various elements may be included within a scope that does not impair the technical spirit of the present application. If additional elements are included, they may be included to replace the remaining iron (Fe).

[0031] For example, the above-mentioned inevitable impurities may be boron (B) and / or zirconium (Zr), and the steel plate material may include B: 0.002 wt% or less and / or Zr: 0.005 wt% or less.

[0032] In one example, the slab may further include one or more selected from the group consisting of Sn: 0.04% or less, Sb: 0.04% or less, C: 0.003% or less, S: 0.002% or less, P: 0.015% or less, N: 0.002% or less, and Ti: 0.002% or less, in wt%.

[0033] Sn: 0.04 wt% or less

[0034] Tin (Sn) is a surface precipitate element that is concentrated on the surface of the steel plate, thereby suppressing nitrogen adsorption and nitride formation, thereby reducing iron loss. If the tin content in the slab exceeds the upper limit of the aforementioned range, grain boundaries may become brittle, resulting in reduced fatigue resistance. Therefore, the tin content in the slab may be 0.04 wt% or less.

[0035] Sb: 0.04 wt% or less

[0036] Antimony (Sb) is a surface precipitated element that is concentrated on the surface of the steel plate, thereby suppressing nitrogen adsorption and nitride formation, thereby reducing iron loss. If the antimony content in the slab exceeds the upper limit of the aforementioned range, grain boundaries may become brittle, resulting in reduced fatigue resistance. Therefore, the antimony content in the slab may be 0.04 wt% or less.

[0037] C: 0.003 wt% or less

[0038] Carbon (C) is an element that can combine with other unavoidable impurities to form carbides, adversely affecting magnetic properties. Therefore, carbon may be included in the slab in an amount of 0.003 wt% or less.

[0039] S: 0.002 wt% or less

[0040] Sulfur (S) is an element that can combine with other unavoidable impurities to form sulfides, which can adversely affect magnetic properties. Therefore, the sulfur may be included in the slab in an amount of 0.002 wt% or less.

[0041] P: 0.015 wt% or less

[0042] Phosphorus (P) is an element that not only increases the resistivity of a material, but also improves the texture by segregating at grain boundaries, thereby increasing the resistivity and reducing the iron loss. However, if it is included in the slab in excess of the upper limit of the aforementioned range, it may cause the formation of a texture that is unfavorable to magnetism, thereby rendering the texture improvement ineffective. In addition, it may segregate excessively at grain boundaries, thereby reducing the rollability and workability, making production difficult. Therefore, the phosphorus may be included in an amount of 0.015 wt% or less.

[0043] N: 0.002 wt% or less

[0044] Nitrogen (N) is an element that can combine with other unavoidable impurities to form nitrides, adversely affecting magnetic properties. Therefore, nitrogen may be included in the slab in an amount of 0.002 wt% or less.

[0045] Ti: 0.002 wt% or less

[0046] Titanium (Ti) is an element that has a strong tendency to form precipitates in non-oriented electrical steel sheets, and deteriorates iron loss by forming fine carbides, nitrides, or sulfides within the non-oriented electrical steel sheet, thereby inhibiting grain growth. Therefore, the titanium may be included in the slab in an amount of 0.002 wt% or less.

[0047] In one example, the non-oriented electrical steel sheet may further include a coating layer. The coating layer is a coating formed on the surface of the non-oriented electrical steel sheet and may be referred to as an insulating film. Since the insulating film is widely known, a detailed description thereof will be omitted. For example, the coating layer may be formed by applying a chromium-free coating solution, i.e., an organic-inorganic composite coating solution that does not contain chromium, to the surface of the final annealed steel sheet and then baking it. At this time, the coating layer may be formed to a thickness of 0.1 ㎛ to 5 ㎛. The non-oriented electrical steel sheet further includes a coating layer formed on the surface, thereby maintaining insulation between upper and lower non-oriented electrical steel sheets when a plurality of non-oriented electrical steel sheets are stacked, thereby reducing eddy current loss.

[0048] The present application also relates to a method for manufacturing a non-oriented electrical steel sheet.

[0049] The method for manufacturing a non-oriented electrical steel sheet of the present application includes a hot rolling step, a cold rolled steel sheet manufacturing step, and a final annealing step. The non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet of the present application has a crystal orientation measured in an area of ​​1000 ㎛ × 1000 ㎛ or more using electron backscatter diffraction (EBSD) and analyzed using OIM software, and the average value of the KAM values ​​of each measurement point existing within the measurement area is 0.4° or less.

[0050] According to the method for manufacturing a non-oriented electrical steel sheet of the present application, deformation of the steel sheet during heat treatment can be minimized, thereby suppressing an increase in iron loss, and thus a non-oriented electrical steel sheet with excellent magnetic properties can be manufactured.

[0051] The above hot rolling step is a step for manufacturing a slab into a hot-rolled steel sheet, and is performed by reheating the slab and then hot rolling it. Specifically, reheating the slab is performed before hot rolling the slab to make the slab at a temperature at which it can be rolled. The reheating temperature of the slab is not particularly limited, but may be, for example, 1000°C to 1150°C. If the reheating temperature of the slab is below the lower limit of the above-mentioned range, it is not easy to perform hot rolling, and if it exceeds the upper limit of the above-mentioned range, coarsely precipitated aluminum nitride (AlN) may be re-dissolved and finely re-precipitated in a subsequent process, thereby increasing iron loss.

[0052] In one example, the slab may contain, in wt%, Si: 3.0% or more and 3.8% or less, Mn: 0.2% or more and 0.5% or less, and Al: 0.5% or more and 1.5% or less, and may contain the remainder of Fe and other unavoidable impurities. A specific description of the composition of the slab is the same as that described for the non-oriented electrical steel sheet, and therefore will be omitted.

[0053] In another example, the slab may further include one or more selected from the following in wt%: Sn: 0.04% or less, Sb: 0.04% or less, C: 0.003% or less, S: 0.002% or less, P: 0.015% or less, N: 0.002% or less, and Ti: 0.002% or less. A specific description of the composition of the slab is the same as that described for the non-oriented electrical steel sheet, and thus will be omitted.

[0054] The above hot rolling is performed to manufacture the reheated slab into a hot-rolled steel sheet. The thickness of the hot-rolled steel sheet may be 1.6 mm to 2.3 mm. In addition, the finishing rolling temperature during the hot rolling may be 800°C to 1000°C, and specifically 800°C to 900°C. The hot rolling may be performed under the above-described conditions, thereby being advantageous in terms of sheetability and grain structure control.

[0055] In one example, the method for manufacturing the non-oriented electrical steel sheet may further include a coiling step. The coiling step may be performed by coiling the hot-rolled steel sheet obtained by the hot rolling at 600°C or lower, and specifically, may be performed by coiling at 500°C to 600°C. If the coiling temperature of the hot-rolled steel sheet is lower than the lower limit of the aforementioned range, the brittleness may increase, resulting in plate breakage during coiling. In addition, if the coiling temperature of the hot-rolled steel sheet exceeds the upper limit of the aforementioned range, fine AlN may be formed during cooling, which may increase iron loss.

[0056] In another example, the method for manufacturing the non-oriented electrical steel sheet may further include a step of annealing the hot-rolled steel sheet. The step of annealing the hot-rolled steel sheet is a step for increasing an orientation favorable to magnetism, and may be performed by heating the hot-rolled steel sheet to 900°C to 1100°C at a heating rate of 10°C / s or higher in an atmosphere of 80% or more nitrogen, maintaining the temperature in this range for 30 to 90 seconds, and then cooling the hot-rolled steel sheet at a cooling rate of 20°C / s or higher. If the temperature and time conditions during annealing of the hot-rolled steel sheet are below the lower limit of the above-mentioned condition range, the structure may not grow or may grow finely, making it difficult to obtain a texture favorable to magnetism during annealing after cold rolling. In addition, if the temperature and time conditions during annealing of the hot-rolled steel sheet exceed the upper limit of the above-mentioned condition range, the self-crystalline grains may grow excessively and the surface defects of the sheet may become excessive. Thereafter, the annealed hot-rolled steel sheet may be further pickled.

[0057] The step of manufacturing the above cold-rolled steel sheet is a step for manufacturing the hot-rolled steel sheet into a cold-rolled steel sheet, and is performed through cold rolling. The thickness of the cold-rolled steel sheet may be 0.10 mm to 0.30 mm, specifically, 0.15 mm to 0.30 mm. In addition, the reduction ratio during the cold rolling may be 80% or more, specifically, 84% to 94%.

[0058] Hereinafter, the final annealing step is described with reference to the attached drawings. The attached drawings are exemplary, and the final annealing step is not limited to the attached drawings.

[0059] The final annealing step is a step for securing magnetic properties by growing crystal grains to a specific size, and is performed by heat treating the cold-rolled steel sheet. FIG. 1 is a drawing exemplarily showing a process of a cold-rolled steel sheet passing through a final annealing furnace to explain the final annealing step according to one embodiment of the present application. As shown in FIG. 1, the final annealing step may be performed by passing the cold-rolled cold-rolled steel sheet (10) through a final annealing furnace (20) while moving it through a hearth roll (21). For example, the final annealing may be performed by heating the cold-rolled steel sheet (10) to 950°C to 1100°C at a heating rate of 10°C / s or more, maintaining it for 30 to 90 seconds, and then cooling it at a cooling rate of 10°C / s or more. The final annealing step is performed at the heating rate, temperature, time, and cooling rate within the aforementioned ranges, thereby reducing iron loss and deriving an optimal grain size considering mechanical properties. In contrast, in the final annealing step, if the temperature and time exceed the upper limits of the aforementioned ranges, the grain size may become coarser, resulting in increased eddy current loss. Furthermore, in the final annealing step, if the heating rate, temperature, time, and cooling rate are below the lower limits of the aforementioned ranges, the grain size may become fine, resulting in increased hysteresis loss.

[0060] At this time, the final annealing can be performed in an atmosphere containing 80% or more hydrogen and the remainder nitrogen. By performing the final annealing under the aforementioned atmosphere, oxidation and nitriding of the surface of the non-oriented electrical steel sheet can be prevented. In contrast, if the atmosphere during the final annealing is below the aforementioned hydrogen fraction range, nitrogen can penetrate the surface of the cold-rolled steel sheet to form nitrides, thereby increasing iron loss.

[0061] In one example, the final annealing step may be performed while moving the cold rolled steel sheet through a hearth roll having a surface roughness (Ra) of 0.1 ㎛ or more and 0.2 ㎛ or less. Specifically, the surface roughness (Ra) of the hearth roll may be 0.1 ㎛ or more and 0.18 ㎛ or less. The final annealing step is performed while moving the cold rolled steel sheet through the hearth roll having the above-described surface roughness (Ra), whereby the tension applied to the cold rolled steel sheet being moved during the final annealing can be reduced, and crystal deformation of the steel sheet can be suppressed, so that the non-oriented electrical steel sheet manufactured accordingly can have excellent magnetic properties. In contrast, when the surface roughness (Ra) of the hearth roll is less than the lower limit of the above-described range, the cold rolled steel sheet may not move and slip may occur, making it impossible to produce a non-oriented electrical steel sheet. In addition, when the surface roughness (Ra) of the above-mentioned hearth roll exceeds the upper limit of the above-mentioned range, the tension applied to the cold-rolled steel sheet may increase, thereby increasing the iron loss of the manufactured non-oriented electrical steel sheet.

[0062] In another example, the final annealing step may be performed while moving the cold rolled steel sheet through a hearth roll having a friction coefficient of 0.05 or more and 0.2 or less, specifically, 0.06 or more and 0.19 or less. If the friction coefficient of the hearth roll is less than the lower limit of the above-mentioned range, the cold rolled steel sheet may not move and slip may occur, making it impossible to produce a non-oriented electrical steel sheet. In addition, if the friction coefficient of the hearth roll exceeds the upper limit of the above-mentioned range, the tension applied to the cold rolled steel sheet may increase, thereby increasing the iron loss of the manufactured non-oriented electrical steel sheet. Specifically, the hearth roll may have the above-mentioned surface roughness (Ra) and the above-mentioned friction coefficient at the same time. The above final annealing step is performed while moving the cold rolled steel sheet through a hearth roll having the surface roughness (Ra) and coefficient of friction described above, so that the tension applied to the cold rolled steel sheet being moved during the final annealing can be reduced, and crystal deformation of the steel sheet can be suppressed, so that the non-oriented electrical steel sheet manufactured accordingly can have excellent magnetic properties.

[0063] For example, the tension applied to the cold rolled steel sheet in the final annealing step may be 10 MPa or less. Specifically, the tension applied to the cold rolled steel sheet in the final annealing step may be 9.5 MPa or less. In addition, the lower limit of the tension applied to the cold rolled steel sheet in the final annealing step may be 4 MPa or more, specifically, 5 MPa or more. By applying the aforementioned tension to the cold rolled steel sheet in the final annealing step, the non-oriented electrical steel sheet produced may have excellent magnetic properties.

[0064] In one example, the method for manufacturing the non-oriented electrical steel sheet may further include a step of forming a coating layer. The step of forming the coating layer may be performed on the surface of the steel sheet that has undergone the final annealing, and specifically, may be performed by forming the coating layer on the surface of the steel sheet that has undergone the heat treatment during the final annealing. A detailed description of the coating layer is the same as that described for the non-oriented electrical steel sheet, and therefore will be omitted.

[0065]

[0066] Hereinafter, the present application will be described in more detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the examples presented below.

[0067]

[0068] Example 1

[0069] Manufacturing of non-oriented electrical steel sheets

[0070] A slab was manufactured by steelmaking and continuous casting using the components shown in Table 1 below, the remaining Fe, and other unavoidable impurities, and after reheating at a temperature of 1100°C, hot rolling was performed at a finishing temperature of 850°C to manufacture a hot-rolled steel plate having a thickness of 2 mm.

[0071] Afterwards, the hot-rolled steel sheet was coiled at a coiling temperature of 580°C.

[0072] Afterwards, the hot-rolled steel sheet was annealed by heating it to 1000°C at a heating rate of 20°C / s in an atmosphere of 100% nitrogen, maintaining it at this temperature for 60 seconds, and then cooling it at a cooling rate of 30°C / s.

[0073] Afterwards, the annealed hot-rolled steel plate was cold-rolled at a reduction ratio of 87.5% to manufacture a cold-rolled steel plate with a thickness of 0.25 mm.

[0074] Thereafter, the cold rolled steel sheet was moved through the hearth rolls shown in Table 1 below and passed through a final annealing furnace, where it was heated to 1050°C at a heating rate of 20°C / s in an atmosphere of 100% hydrogen, maintained at this temperature for 60 seconds, and then cooled at a cooling rate of 20°C / s to produce a non-oriented electrical steel sheet by final annealing.

[0075] Slab composition (wt%)SiMnAlSnCSPNTi3.30.30.90.03500.00210.00170.00820.00170.0015

[0076] Examples 2 to 6 and Comparative Examples 1 to 2

[0077] Manufacturing of non-oriented electrical steel sheets

[0078] A non-oriented electrical steel sheet was manufactured in the same manner as in Example 1, except that the hearth roll was changed as shown in Table 2 below during the final annealing.

[0079] Final thickness of non-oriented electrical steel sheet (mm) Surface roughness of hearth roll (Ra) Coefficient of friction of hearth roll Example 10.25 0.10.1 Example 20.13 0.1 Example 30.18 0.1 Example 40.13 0.06 Example 50.13 0.15 Example 60.13 0.19 Comparative example 10.22 0.1 Comparative example 20.13 0.22

[0080] Evaluation Example 1. Tension Evaluation

[0081] In each of the examples and comparative examples, the degree of warpage of the cold-rolled steel sheet passing through the final annealing furnace was measured during the final annealing to evaluate the tension applied to the cold-rolled steel sheet, and the results are shown in Table 3 below.

[0082]

[0083] Evaluation Example 2. Evaluation of the average KAM value

[0084] The crystal orientation was measured in an area of ​​1000 ㎛ × 1000 ㎛ or more for the non-oriented electrical steel sheets manufactured in each of the examples and comparative examples using electron backscatter diffraction (EBSD), and the average value of the KAM value of each measurement point existing within the measured area analyzed using OIM software was evaluated, and the results are shown in Table 3 below.

[0085]

[0086] Evaluation Example 3. Iron loss and magnetic flux density evaluation

[0087] The iron loss and magnetic flux density were measured for the non-oriented electrical steel sheets manufactured in the examples and comparative examples, respectively, according to the method described in IEC 60404 2, and the average values ​​are shown in Table 3 below. At this time, W 15 / 50 is the low-frequency iron loss when a magnetic flux density of 1.5 T is induced at a low frequency of 50 Hz, and W 10 / 400 is the high-frequency iron loss when a magnetic flux density of 1.0 T is induced at a high frequency of 400 Hz, and B 50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0088] Average value of tension KAM values ​​(°)W 15 / 50 (W / kg)W 10 / 400 (W / kg)B 50 Example 15.20.211.9111.41.65 Example 26.20.301.9511.51.64 Example 38.10.391.9511.81.63 Example 45.80.241.9311.51.65 Example 57.90.351.9511.61.65 Example 69.20.391.9811.71.65 Comparative Example 111.50.492.1012.31.62 Comparative Example 210.90.452.0812.21.63

[0089] As shown in Table 3 above, it was confirmed that the non-oriented electrical steel sheets manufactured in each of Examples 1 to 6 had a small tension applied to the hot-rolled steel sheet during final annealing, and thus had a small average KAM value, low iron loss, and high magnetic flux density.

[0090] In contrast, it was confirmed that the non-oriented electrical steel sheets manufactured in Comparative Examples 1 and 2 each had a large tension applied to the hot-rolled steel sheet during final annealing, and thus had a large average KAM value, high iron loss, and low magnetic flux density.

[0091] <Explanation of symbols>

[0092] 10: Cold rolled steel sheet

[0093] 20: Final annealing furnace

[0094] 21: Hearth Roll

[0095] A: Direction of cold rolled steel sheet

Claims

1. A non-oriented electrical steel sheet manufactured by reheating a slab containing Si: 3.0% or more and 3.8% or less, Mn: 0.2% or more and 0.5% or less, and Al: 0.5% or more and 1.5% or less, and the remainder containing Fe and other inevitable impurities, and then through hot rolling, cold rolling, and final annealing. A non-oriented electrical steel sheet in which the average value of the Kernel Average Misorientation (KAM) of each measuring point within a measuring area of ​​1000 ㎛ × 1000 ㎛ or more, when measuring the crystal orientation using electron backscatter diffraction (EBSD), is 0.4° or less.

2. In paragraph 1, The above final annealing is performed on a non-oriented electrical steel sheet while the cold rolled steel sheet is moved through a hearth roll having a surface roughness (Ra) of 0.1 ㎛ or more and 0.2 ㎛ or less.

3. In paragraph 1, The above final annealing is performed on a non-oriented electrical steel sheet while the cold rolled steel sheet is moved through a hearth roll having a friction coefficient of 0.05 or more and 0.2 or less.

4. In paragraph 1, A non-oriented electrical steel sheet in which the final annealing is performed while the cold rolled steel sheet is moved under a tension of 10 MPa or less.

5. In paragraph 1, The above slab is a non-oriented electrical steel sheet further comprising at least one selected from the group consisting of Sn: 0.04% or less, Sb: 0.04% or less, C: 0.003% or less, S: 0.002% or less, P: 0.015% or less, N: 0.002% or less, and Ti: 0.002% or less in weight %.

6. In paragraph 1, Iron Hand W 15 / 50 is less than 2.0 W / kg, and W 10 / 400 is less than 12.0 W / kg, and the magnetic flux density (B 50 ) Non-oriented electrical steel sheet having a strength of 1.63 T or higher.

7. A step of hot rolling after reheating a slab containing Si: 3.0% or more and 3.8% or less, Mn: 0.2% or more and 0.5% or less, and Al: 0.5% or more and 1.5% or less in wt%, and the remainder including Fe and other unavoidable impurities; A step for manufacturing a cold rolled steel sheet by cold rolling; and It includes a step of final annealing of the above cold rolled steel sheet, A method for manufacturing a non-oriented electrical steel sheet, wherein when crystal orientation is measured over an area of ​​1000 ㎛ × 1000 ㎛ or more using electron backscatter diffraction (EBSD), the average value of the Kernel Average Misorientation (KAM) values ​​of each measuring point within the measuring area is 0.4° or less.

8. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the final annealing step is performed by moving the cold rolled steel sheet through a hearth roll having a surface roughness (Ra) of 0.1 ㎛ or more and 0.2 ㎛ or less.

9. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the final annealing step is performed by moving the cold rolled steel sheet through a hearth roll having a friction coefficient of 0.05 or more and 0.2 or less.

10. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the tension applied to the cold rolled steel sheet in the final annealing step is 10 MPa or less.

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