Non-oriented electrical steel sheet and method for producing same

Abstract

The invention provides a non-oriented electrical steel plate. The non-oriented electrical steel sheet includes: 2.8 wt% to 3.8 wt% of silicon (Si), 0.2 wt% to 0.5 wt% of manganese (Mn), 0.5 wt% to 1.2 wt% of aluminum (Al), 0 wt% (excluding) to 0.002 wt% of carbon (C), 0 wt% (excluding) to 0.015 wt% of phosphorus (P), 0 wt% (excluding) to 0.002 wt% of sulfur (S), 0 wt% (excluding) to 0.002 wt% of nitrogen (N), 0 wt% (excluding) to 0.002 wt% of titanium (Ti), and the balance being steel. And the remainder being iron (Fe) and other unavoidable impurities, in which in a final microstructure, crystal grains having a {111} / / ND orientation have a volume fraction of 30% or less and an average misalignment angle of 23 DEG or more, and crystal grains having a {001} / / ND orientation have a volume fraction of 15% or more and an average misalignment angle of 48 DEG or more.

Description

Technical Field

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

[0002] Electrical steel sheets can be divided into oriented electrical steel sheets and non-oriented electrical steel sheets according to their magnetic properties. Oriented electrical steel sheets exhibit excellent magnetic properties particularly in the rolling direction of the steel sheets (because they are produced to be easily magnetized in the rolling direction), and are therefore mostly used as cores for large, medium and small transformers requiring low core loss and high magnetic permeability. On the other hand, non-oriented electrical steel sheets have uniform magnetic properties regardless of the direction of the steel sheets, and are therefore generally used as core materials for small motors, small power transformers, stabilizers, etc.

[0003] Related documents include Korean Patent Publication No. 2015-0001467A. Summary of the invention

[0004] Technical issues

[0005] The present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, wherein the non-oriented electrical steel sheet can achieve low core loss and uniform magnetic properties at high frequency.

[0006] However, the above description is an example, and the scope of the present invention is not limited thereto.

[0007] Technical Solution

[0008] According to one aspect of the present invention, there is provided a non-oriented electrical steel sheet, comprising silicon (Si): 2.8 wt% to 3.8 wt%, manganese (Mn): 0.2 wt% to 0.5 wt%, aluminum (Al): 0.5 wt% to 1.2 wt%, carbon (C): greater than 0 wt% and not greater than 0.002 wt%, phosphorus (P): greater than 0 wt% and not greater than 0.015 wt%, sulfur (S): greater than 0 wt% and not greater than 0.002 wt%, Nitrogen (N): greater than 0 wt% and not more than 0.002 wt%, titanium (Ti): greater than 0 wt% and not more than 0.002 wt%, and the balance of iron (Fe) and inevitable impurities, wherein, in the final microstructure, grains having a {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and grains having a {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more.

[0009] The non-oriented electrical steel sheet may have a core loss (W 10 / 400 ) and core loss standard deviation of 0.725W / kg or less.

[0010] The average grain size of the non-oriented electrical steel sheet may be 80 μm to 150 μm.

[0011] According to another aspect of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet, the method comprising providing a steel material, the steel material comprising silicon (Si): 2.8 wt% to 3.8 wt%, manganese (Mn): 0.2 wt% to 0.5 wt%, aluminum (Al): 0.5 wt% to 1.2 wt%, carbon (C): greater than 0 wt% and not greater than 0.002 wt%, phosphorus (P): greater than 0 wt% and not greater than 0.015 wt%, sulfur (S): greater than 0 wt% and not greater than 0.002 wt%, nitrogen (N): greater than 0 wt% and not greater than 0.002 wt%, titanium (Ti): greater than 0 wt% and not greater than 0.002 wt%, and the balance of iron (Fe) and inevitable impurities; hot rolling the steel material; and subjecting the hot rolled steel material to a first calcination. Annealing; cold rolling the steel material annealed for the first time, and annealing the cold rolled steel material for the second time, wherein the hot rolling is performed under the following conditions: slab reheating temperature (SRT): 1100°C to 1200°C, finishing outlet temperature (FDT): 800°C to 1000°C, coiling temperature (CT): 560°C to 600°C, the first annealing is performed under the following conditions: heating rate: 10°C / s or more, annealing start temperature: 900°C to 1050°C, annealing holding time: 30 seconds to 90 seconds, cooling rate: 20°C / s or less, and the second annealing is performed under the following conditions: heating rate: 10°C / s or more, annealing start temperature: 900°C to 1100°C, annealing holding time: 30 seconds to 90 seconds, cooling rate: 30°C / s or more.

[0012] After the first annealing, the average grain size may be 140 μm to 250 μm, and the intermediate layer may have <110> / / The volume fraction of RD-oriented grains may be 20% or less.

[0013] Cold rolling can be performed under the following conditions: Reduction rate: 81% to 92%.

[0014] After hot rolling, the thickness of the steel material may be 1.6 mm to 2.6 mm, and after cold rolling, the thickness of the steel material may be 0.1 mm to 0.3 mm.

[0015] Beneficial effects

[0016] According to an embodiment of the present invention, a non-oriented electrical steel sheet and a method for manufacturing the same can be provided, the non-oriented electrical steel sheet being capable of achieving low core loss and uniform magnetic properties at high frequency. For example, a non-oriented electrical steel sheet can be provided, the non-oriented electrical steel sheet being capable of achieving low average core loss and standard deviation by controlling the conditions of preliminary annealing after hot rolling. The increase in production cost can be suppressed by limiting the temperature and grain size in the preliminary annealing. By manufacturing a non-oriented electrical steel sheet having a uniform microstructure and texture, uniform magnetic properties can be ensured.

[0017] However, the scope of the present invention is not limited to the above-mentioned effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. 4 is a flow chart of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0019] Figure 2 Included are electron backscatter diffraction (EBSD) inverse pole figure (IPF) scanning images of the nonoriented electrical steel sheet according to Embodiment 1 in the test examples of the present invention.

[0020] Figure 3 An EBSDIPF scanning image of the non-oriented electrical steel sheet according to Comparative Example 2 is included in the test examples of the present invention. DETAILED DESCRIPTION

[0021] Now, a method for manufacturing a nonoriented electrical steel sheet according to an embodiment of the present invention will be described in detail. The terms used herein are appropriately selected according to their functions in the present invention, and the definitions of these terms should be based on the entire contents of this specification.

[0022] Electrical steel sheets are generally divided into oriented electrical steel sheets and non-oriented electrical steel sheets. Oriented electrical steel sheets are mostly used in stationary machines (such as transformers), while non-oriented electrical steel sheets are generally used in rotating machines (such as motors and generators). Currently, in order to cope with global environmental issues, existing internal combustion engine vehicles are rapidly being replaced by hybrid electric vehicles (HEVs), electric vehicles (EVs) and hydrogen-powered vehicles.

[0023] Non-oriented electrical steel sheets, which are used as motor core materials, are used to convert electrical energy into mechanical energy in rotating machines, and magnetic properties, namely low core loss and high magnetic flux density, are essential for energy conservation. Core loss refers to the energy loss that occurs during magnetization, while magnetic flux density refers to the force that generates power. Magnetic flux density is mainly expressed in B 50 Evaluation, core loss is usually measured in W 15 / 50 evaluation, but when high frequency characteristics are required in electric vehicles, the core loss is measured in W 10 / 400 Evaluate. B 50Indicates the magnetic flux density at 5000A / m, W 15 / 50 represents the core loss at 50Hz and 1.5T, W 10 / 400 Represents the core loss at 400Hz and 1.0T.

[0024] In order to meet the required properties, it is necessary to properly control the silicon (Si) content, product thickness, grain size, texture, precipitates, etc. Increasing the Si content and reducing the product thickness are effective in reducing core loss, but they also reduce the magnetic flux density. To compensate for this, it is essential to control the grain size, texture and precipitates in the manufacturing process of non-oriented electrical steel sheets. Since magnetic properties (e.g., core loss and magnetic flux density) are very sensitive to grain size, texture and precipitates, deviations in the manufacturing process may lead to deviations in magnetic properties.

[0025] The motor core is a structure in which tens to hundreds of non-oriented electrical steel sheets are laminated. When the motor core is produced using non-oriented electrical steel sheets having large magnetic property deviations, problems may occur during motor operation.

[0026] According to the present invention, a non-oriented electrical steel sheet for a vehicle drive motor is subjected to primary annealing after hot rolling and before cold rolling to achieve low core loss and high magnetic flux density. The primary annealing is different from the final annealing performed after cold rolling.

[0027] Related studies have proposed a method of cold rolling and final annealing by increasing the grain size to 400 μm or more after preliminary annealing. However, this method may lead to deviations in magnetic properties due to the inhomogeneity of microstructure and texture. Other studies have proposed a method of ensuring productivity and improving texture by controlling the grain size to 150 μm or more after preliminary annealing. However, this method does not set a limit on the grain size after preliminary annealing, and does not consider the deviation in magnetic properties caused by the subsequent inhomogeneity of microstructure / texture.

[0028] The present invention provides a non-oriented electrical steel sheet capable of realizing uniform microstructure and texture after cold rolling and final annealing by limiting appropriate grain size and texture after preliminary annealing, and a method for manufacturing the same.

[0029] Figure 1 FIG. 4 is a flow chart of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0030] refer to Figure 1, a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes providing a steel material containing silicon (Si), manganese (Mn) and aluminum (Al) (S10); hot rolling the steel material (S20); performing a first annealing on the hot-rolled steel material (S30); cold rolling the first annealed steel material (S40) and performing a second annealing on the cold-rolled steel material (S50).

[0031] Provide steel (S10)

[0032] The steel material provided for the hot rolling process is a steel material for manufacturing a non-oriented electrical steel sheet, and contains, for example, Si: 2.8 wt% to 3.8 wt%, Mn: 0.2 wt% to 0.5 wt%, Al: 0.5 wt% to 1.2 wt%, carbon (C): greater than 0 wt% and not more than 0.002 wt%, phosphorus (P): greater than 0 wt% and not more than 0.015 wt%, sulfur (S): greater than 0 wt% and not more than 0.002 wt%, nitrogen (N): greater than 0 wt% and not more than 0.002 wt%, titanium (Ti): greater than 0 wt% and not more than 0.002 wt%, and the balance of iron (Fe) and inevitable impurities.

[0033] Functions and contents of exemplary components applicable to the method for manufacturing a nonoriented electrical steel sheet according to technical features of the present invention will now be described.

[0034] Si: 2.8 wt% to 3.8 wt%

[0035] Si is a main element added as a component for increasing resistivity and reducing core loss (or eddy current loss). When the content of Si is less than 2.8 wt%, it is not easy to achieve the low core loss value required at high frequency, and when the content increases, the magnetic permeability and magnetic flux density decrease. When the content of Si is more than 3.8 wt%, brittleness increases, resulting in difficulty in cold rolling and reduced productivity.

[0036] Mn: 0.2 wt% to 0.5 wt%

[0037] Mn and Si together increase resistivity and improve texture. When more than 0.5 wt % of Mn is added, coarse MnS precipitates are formed, thereby deteriorating magnetic properties, such as reduced magnetic flux density. In addition, when the content of Mn is greater than 0.5 wt %, the reduction in core loss is small compared to the amount added, and cold rolling performance is significantly deteriorated. Since when the content of Mn is less than 0.2 wt %, fine MnS precipitates may be formed and grain growth may be inhibited, the composition of Mn can be controlled to 0.2 wt % to 0.5 wt %.

[0038] Al: 0.5 wt% to 1.2 wt%

[0039] Al is a main element added together with Si as a component for increasing resistivity and reducing core loss (or eddy current loss). Al is used to reduce magnetic deviation by reducing magnetic anisotropy. When Al is combined with N, AlN precipitation is induced. When the content of Al is less than 0.5 wt%, the above effect may not be easily expected, and fine nitrides may be formed, thereby increasing the deviation of magnetic properties, and when the content of Al is more than 1.2 wt%, cold rolling properties deteriorate, and excessive nitride formation occurs, thereby reducing magnetic flux density and deteriorating magnetic properties.

[0040] C: more than 0 wt% and not more than 0.002 wt%

[0041] C is an element for forming carbides such as TiC and NbC to increase core loss, and the less the better. The content of C is limited to 0.002 wt% or less. When the content of C is more than 0.002 wt%, magnetic aging occurs, thereby deteriorating magnetic properties, while when the content of C is 0.002 wt% or less, magnetic aging is suppressed.

[0042] P: more than 0 wt% and not more than 0.015 wt%

[0043] P is a grain boundary segregation element and an element for forming a texture. When the content of P is more than 0.015 wt%, grain growth is inhibited, magnetic properties are deteriorated, and cold rolling properties are reduced due to segregation effects.

[0044] S: more than 0 wt% and not more than 0.002 wt%

[0045] S forms precipitates such as MnS and CuS to increase core loss and inhibit grain growth, so the less the better. The S content is limited to 0.002 wt% or less. When the S content is more than 0.002 wt%, the core loss increases.

[0046] N: more than 0 wt% and not more than 0.002 wt%

[0047] N forms precipitates such as AlN, TiN, and NbN to increase core loss and inhibit grain growth, so the less the better. The content of N is limited to 0.002 wt% or less. When the content of N is more than 0.002 wt%, the core loss increases.

[0048] Ti: more than 0 wt% and not more than 0.002 wt%

[0049] Ti forms fine precipitates such as TiC and TiN and inhibits grain growth. Ti deteriorates magnetic properties, so the less the better. The content of Ti is limited to 0.002 wt% or less. When the content of Ti is greater than 0.002 wt%, magnetic properties deteriorate.

[0050] Hot rolling (S20)

[0051] The steel material having the above composition is hot rolled. The hot rolling (S20) of the steel material can be performed under the following conditions: slab reheating temperature (SRT): 1100°C to 1200°C, finishing outlet temperature (FDT): 800°C to 1000°C, and coiling temperature (CT): 560°C to 600°C.

[0052] When the SRT is higher than 1200°C, precipitates such as C, S and N in the slab may be redissolved, and fine precipitates may appear during subsequent rolling and annealing, thereby inhibiting grain growth and deteriorating magnetic properties. When the SRT is lower than 1100°C, the rolling load may increase and the final product may have high core loss.

[0053] After hot rolling the steel (S20), the thickness of the hot rolled sheet may be, for example, 1.6 mm to 2.6 mm. Since the cold rolling reduction rate increases and the texture deteriorates when the hot rolled sheet is thick, the thickness may be controlled to be 2.6 mm or less.

[0054] The hot rolled steel can be coiled under the following conditions: CT: 560°C to 600°C. When CT is below 560°C, the annealing effect of the steel does not occur, so the grains do not grow, while when CT is above 600°C, oxidation may increase during cooling, so pickling properties may deteriorate.

[0055] First annealing (S30)

[0056] The hot rolled steel material may be subjected to a first annealing (S30). The first annealing is an annealing and pickling line (APL) process for annealing and pickling the hot rolled plate, and may be understood as preliminary annealing or thermal annealing.

[0057] The first annealing (S30) includes an annealing process in which the temperature is increased at a heating rate of 10°C / s or more, annealing is started at a temperature of 900°C to 1050°C, and maintained for 30 seconds to 90 seconds. After annealing, the steel material may be cooled at a cooling rate of 20°C / s or more. After cooling, pickling may be further performed.

[0058] After hot rolling, the hot rolled sheet is annealed to ensure uniformity of microstructure and cold rollability. The first annealing temperature is controlled between 900°C and 1050°C to form a uniform microstructure by eliminating elongated cast structures. When the first annealing temperature is too low (below 900°C), after hot rolling, the elongated cast structure may remain, resulting in microstructural inhomogeneity, and smaller grains may be formed, thereby reducing cold rollability. On the other hand, when the first annealing temperature is too high (above 1050°C), texture imbalance may occur in the final product, resulting in anisotropic properties.

[0059] After the first annealing, the average grain size may be 140 μm to 250 μm, and the intermediate layer may have <110> / / The volume fraction of RD-oriented grains may be greater than 0% and not greater than 20%. In this article, RD refers to the rolling direction, and the middle layer refers to the middle portion of the steel excluding the portion corresponding to t / 4 of the thickness t of the steel from the top and bottom surfaces (ranging from 1 / 4 to 3 / 4 of the thickness).

[0060] Cold rolled (S40)

[0061] The steel material after the first annealing is cold rolled (S40). The cold rolling reduction ratio may be 81% to 92%, and the thickness of the cold rolled steel material may be 0.1 mm to 0.3 mm. In order to improve rollability, the plate temperature may be increased to 100° C. to 200° C. for warm rolling.

[0062] Second annealing (S50)

[0063] The cold rolled steel may be subjected to a second annealing. The second annealing is an annealing coating line (ACL) process for final annealing of the cold rolled sheet and may be understood as cold annealing. The second annealing (S50) may include annealing under the following conditions: heating rate: 10°C / s or more, annealing temperature: 900°C to 1100°C, holding time: 30 seconds to 90 seconds, and cooling under the following conditions: cooling rate: 30°C / s or more.

[0064] The cold-rolled sheet obtained after cold rolling is subjected to secondary annealing. A temperature that enables an optimum grain size to be achieved is applied in consideration of core loss reduction and mechanical properties. In the cold annealing, heating is performed under mixed atmosphere conditions to prevent surface oxidation and nitration. The surface is further smoothed in a mixed atmosphere of nitrogen and hydrogen. When the cold annealing temperature is lower than 900°C, fine grains may be formed, thereby increasing hysteresis loss, and when the cold annealing temperature is higher than 1100°C, coarse grains may be formed, thereby increasing eddy current loss.

[0065] Meanwhile, after the final cold annealing, a coating process may be performed to form an insulating coating. By forming the insulating coating, stampability may be improved and insulation may be ensured. The thickness of the insulating coating formed above and below the cold-rolled material may be about 1 μm to 2 μm.

[0066] The nonoriented electrical steel sheet manufactured using the above method is a nonoriented electrical steel sheet comprising Si: 2.8 wt% to 3.8 wt%, Mn: 0.2 wt% to 0.5 wt%, Al: 0.5 wt% to 1.2 wt%, C: greater than 0 wt% and not greater than 0.002 wt%, P: greater than 0 wt% and not greater than 0.015 wt%, S: greater than 0 wt% and not greater than 0.002 wt%, N: greater than 0 wt% and not greater than 0.002 wt%, Ti: greater than 0 wt% and not greater than 0.002 wt%, and the balance of iron Fe and inevitable impurities. In the final microstructure, grains having a {111} / / ND orientation have a volume fraction greater than 0% and no greater than 30% and an average misorientation angle of 23° or greater (e.g., 23° or greater and 40° or less), and grains having a {001} / / ND orientation have a volume fraction of 15% or greater (e.g., 15% or greater and 50% or less) and an average misorientation angle of 48° or greater (e.g., 48° or greater and 60° or less).

[0067] Herein, ND is a direction perpendicular to the rolling direction RD and the top surface of the steel plate. Grains with a {111} / / ND orientation include grains whose sample surface is parallel to the {111} plane, and grains with a {001} / / ND orientation include grains whose sample surface is parallel to the {001} plane.

[0068] Steel is made up of many grains, each with a different orientation. The distribution of these orientations is called texture. Adjacent grains have their own orientation. The difference in orientation angles between adjacent grains is called the misorientation angle.

[0069] A larger average misorientation angle (which indicates that grains with similar orientations are not close together) indicates a uniform microstructure. In contrast, a smaller average misorientation angle (which indicates that grains with similar orientations are close together) indicates an inhomogeneous microstructure. The misorientation angle varies depending on the orientation and the material.

[0070] In the final microstructure, the average grain size may be 80 μm to 150 μm. The final manufactured non-oriented electrical steel sheet may have a core loss (W 10 / 400 ) and core loss standard deviation of 0.725W / kg or less.

[0071] According to the embodiments of the present invention, based on the non-oriented electrical steel sheet and the manufacturing method thereof, a non-oriented electrical steel sheet capable of achieving low average core loss and standard deviation by controlling the conditions of the preliminary annealing after hot stamping can be provided. The increase in production cost can be suppressed by limiting the temperature and grain size in the preliminary annealing. By manufacturing a non-oriented electrical steel sheet having a uniform microstructure and texture, uniform magnetic properties can be ensured.

[0072] Test Example

[0073] Test Examples will now be described to better understand the present invention. However, the following test examples are only used to facilitate understanding of the present invention, and the present invention is not limited thereto.

[0074] 1. Sample composition

[0075] The samples provided in this test example have the alloy element composition shown in Table 1 (unit: weight %).

[0076] [Table 1]

[0077] Si Mn Al C P S N Ti margin 3.3 0.3 0.9 0.002 0.0052 0.0014 0.0018 0.0011 Fe

[0078] Referring to Table 1, the composition of the nonoriented electrical steel sheet according to the test example satisfies Si: 2.8 wt% to 3.8 wt%, Mn: 0.2 wt% to 0.5 wt%, Al: 0.5 wt% to 1.2 wt%, C: greater than 0 wt% and not greater than 0.002 wt%, P: greater than 0 wt% and not greater than 0.015 wt%, S: greater than 0 wt% and not greater than 0.002 wt%, N: greater than 0 wt% and not greater than 0.002 wt%, Ti: greater than 0 wt% and not greater than 0.002 wt%, and the balance of iron Fe. A hot rolled sheet having a thickness of 2.0 mm was produced by reheating a slab having the above composition to a temperature of 1130° C. and hot rolling under the condition of an FDT of 850° C. The hot-rolled sheet was subjected to the first annealing (i.e., preliminary annealing) under the following conditions: heating rate: 15°C / s, annealing holding time: 50 seconds, cooling rate: 30°C / s, cold rolling, and then subjected to the second annealing (i.e., final annealing) under the following conditions: heating rate: 20°C / s, annealing start temperature: 1000°C, annealing holding time: 50 seconds, cooling rate: 30°C / s. Then, the final product was obtained through a coating process. The final annealing was carried out in a mixed atmosphere of 30% hydrogen-70% nitrogen.

[0079] 2. Process conditions and performance evaluation

[0080] Table 2 shows the process conditions (e.g., preliminary annealing temperature) of this test example and the property evaluation results based on the conditions. In the test example of Table 2, the same final annealing temperature of 975°C was applied. 2 The core loss was measured more than 10 times at different positions on samples of 100 mm or larger.

[0081] at the same time, Figure 2 comprising an electron backscatter diffraction (EBSD) inverse pole figure (IPF) scanning image of the non-oriented electrical steel sheet according to Example 1 in a test example of the present invention, and Figure 3 The EBSD IPF scanning image of the non-oriented electrical steel sheet according to Comparative Example 2 is included in the test examples of the present invention. Figure 2 and Figure 3 , (a) is an image showing the texture after preliminary annealing (ie, the first annealing), and (b) is an image showing the texture after final annealing (ie, the second annealing).

[0082] [Table 2]

[0083]

[0084] Referring to Table 2, in Examples 1 to 3, the first annealing was performed under the following conditions: heating rate: 10°C / s or more, annealing start temperature: 900°C to 1050°C, annealing holding time: 30 seconds to 90 seconds, cooling rate: 20°C / s or more. After the first annealing, the average grain size was 140 μm to 250 μm, and the intermediate layer had <110> The volume fraction of grains with / / RD orientation satisfies the range of 20% or less. In the final microstructure after final annealing (i.e., second annealing), grains with {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and grains with {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more. Core loss (W 10 / 400 ) is 13.5 W / kg or less, and the core loss standard deviation is 0.725 W / kg or less. According to Examples 1 to 3, a texture that is beneficial to magnetic properties is implemented to achieve a low average core loss value and produce a uniform microstructure / texture, thereby controlling the standard deviation to 0.725 W / kg or less. Figure 2 , showing the creation of a uniform microstructure / texture.

[0085] On the other hand, in Comparative Example 1, the preliminary annealing (i.e., the first annealing) temperature is lower than and does not satisfy the annealing start temperature range of 900° C. to 1050° C. Therefore, after the first annealing, the average grain size is less than and does not satisfy the range of 140 μm to 250 μm, and the intermediate layer has <110> The volume fraction of grains with a / / RD orientation is greater than and does not satisfy the range of 20% or less. In the final microstructure after final annealing (i.e., the second annealing), the volume fraction of grains with a {111} / / ND orientation is greater than and does not satisfy the range of 30% or less, the volume fraction of grains with a {001} / / ND orientation is less than and does not satisfy the range of 15% or more, and the core loss (W 10 / 400 ) does not meet the range of 13.5W / kg or less.

[0086] In Comparative Example 2, the preliminary annealing (i.e., the first annealing) temperature is higher than and does not satisfy the annealing start temperature range of 900°C to 1050°C. Therefore, after the first annealing, the average grain size is greater than and does not satisfy the range of 140μm to 250μm. In the final microstructure after the final annealing (i.e., the second annealing), the average misorientation angle of the grains with the {111} / / ND orientation is less than and does not satisfy the range of 23° or greater, and the average misorientation angle of the grains with the {001} / / ND orientation is less than and does not satisfy the range of 48° or greater. Although the core loss (W) of 13.5W / kg or less is satisfied, 10 / 400 ), but the core loss standard deviation does not satisfy the range of 0.725 W / kg or less. According to Comparative Example 2, a texture beneficial to magnetic properties is implemented to achieve a low average core loss value, but an uneven microstructure / texture is generated, exceeding the standard deviation of 0.725 W / kg. Figure 3 , showing the creation of an inhomogeneous microstructure / texture.

[0087] In Comparative Example 3, the preliminary annealing (i.e., the first annealing) temperature is lower than and does not satisfy the annealing start temperature range of 900° C. to 1050° C. Therefore, after the first annealing, the average grain size is less than and does not satisfy the range of 140 μm to 250 μm, and the intermediate layer has <110> The volume fraction of grains with a / / RD orientation is greater than and does not satisfy the range of 20% or less. In the final microstructure after final annealing (i.e., the second annealing), the volume fraction of grains with a {111} / / ND orientation is greater than and does not satisfy the range of 30% or less, the volume fraction of grains with a {001} / / ND orientation is less than and does not satisfy the range of 15% or more, and the core loss (W 10 / 400 ) does not meet the range of 13.5W / kg or less.

[0088] In Comparative Example 4, the preliminary annealing (i.e., the first annealing) temperature is higher than and does not satisfy the annealing start temperature range of 900°C to 1050°C. Therefore, after the first annealing, the average grain size is greater than and does not satisfy the range of 140 μm to 250 μm. In the final microstructure after the final annealing (i.e., the second annealing), the average misorientation angle of the grains having the {001} / / ND orientation is less than and does not satisfy the range of 48° or more. Although the core loss (W) of 13.5 W / kg or less is satisfied, 10 / 400 ), but the core loss standard deviation does not satisfy the range of 0.725 W / kg or less. According to Comparative Example 4, a texture beneficial to magnetic properties is implemented to achieve a low average core loss value, but an uneven microstructure / texture is generated, exceeding the standard deviation of 0.725 W / kg.

[0089] While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.

Claims

1. A nonoriented electrical steel sheet comprising silicon (Si): 2.8 wt% to 3.8 wt%, manganese (Mn): 0.2 wt% to 0.5 wt%, aluminum (Al): 0.5 wt% to 1.2 wt%, carbon (C): greater than 0 wt% and not greater than 0.002 wt%, phosphorus (P): greater than 0 wt% and not greater than 0.015 wt%, sulfur (S): greater than 0 wt% and not greater than 0.002 wt%, nitrogen (N): greater than 0 wt% and not greater than 0.002 wt%, titanium (Ti): greater than 0 wt% and not greater than 0.002 wt%, and the balance of iron (Fe) and inevitable impurities, in, In the final microstructure, grains having a {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and grains having a {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more.

2. The non-oriented electrical steel sheet according to claim 1, wherein: The non-oriented electrical steel sheet has a core loss (W 10 / 400 ) and core loss standard deviation of 0.725W / kg or less.

3. The non-oriented electrical steel sheet according to claim 1, wherein: The non-oriented electrical steel sheet has an average grain size of 80 μm to 150 μm.

4. A method for manufacturing a non-oriented electrical steel sheet, the method comprising: Provided is a steel material, comprising 2.8 to 3.8 wt% silicon (Si), 0.2 to 0.5 wt% manganese (Mn), 0.5 to 1.2 wt% aluminum (Al), more than 0 wt% to 0.002 wt% carbon (C), more than 0 wt% to 0.015 wt% phosphorus (P), more than 0 wt% to 0.002 wt% sulfur (S), more than 0 wt% to 0.002 wt% nitrogen (N), more than 0 wt% to 0.002 wt% titanium (Ti), and the balance of iron (Fe) and unavoidable impurities; hot rolling the steel; Performing the first annealing on the hot rolled steel; Cold rolling the steel that has undergone the first annealing; as well as The cold rolled steel is annealed for the second time. The hot rolling is carried out under the following conditions: slab reheating temperature (SRT): 1100°C to 1200°C, finishing outlet temperature (FDT): 800°C to 1000°C, coiling temperature (CT): 560°C to 600°C, The first annealing is performed under the following conditions: heating rate: 10°C / s or more, annealing start temperature: 900°C to 1050°C, annealing holding time: 30 seconds to 90 seconds, cooling rate: 20°C / s or more, and The second annealing is performed under the following conditions: heating rate 10° C. / s or more, annealing start temperature: 900° C. to 1100° C., annealing holding time: 30 seconds to 90 seconds, cooling rate: 30° C. / s or more.

5. The method according to claim 4, wherein: After the first annealing, the average grain size is 140 μm to 250 μm, and the intermediate layer has <110> / / The volume fraction of RD-oriented grains is 20% or less.

6. The method according to claim 4, wherein: The cold rolling was performed at a reduction ratio of 81% to 92%.

7. The method according to claim 4, wherein: After hot rolling, the thickness of the steel material is 1.6 mm to 2.6 mm, and after cold rolling, the thickness of the steel material is 0.1 mm to 0.3 mm.

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