Non-oriented electrical steel sheet and method for producing same

Abstract

A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of: performing primary hot rolling on each of a first steel material and a second steel material containing silicon (Si), manganese (Mn), and aluminum (Al); forming a first laminated structure by laminating the first steel material and the second steel material after the primary hot rolling; forming a second laminate structure by secondary hot rolling of the first laminate structure; forming a third laminate structure by cold rolling the second laminate structure, and cold annealing the third laminate structure.

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 a non-oriented electrical steel sheet having low core loss at high frequencies 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, especially in the rolling direction of the steel sheets, because they are manufactured to be easily magnetized in the rolling direction, and are therefore mostly used as cores of large, medium and small transformers requiring low core loss and high magnetic permeability. In contrast, 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. Related literature includes Korean Patent Publication No. 2015-0001467A. Summary of the invention

[0003] Technical issues

[0004] The present invention provides a non-oriented electrical steel sheet having low core loss at high frequency and a method for manufacturing the same.

[0005] However, the above description is only an example, and the scope of the present invention is not limited thereto.

[0006] Technical Solution

[0007] According to one aspect of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet, the method comprising: performing primary hot rolling on each of a first steel material and a second steel material containing silicon (Si), manganese (Mn) and aluminum (Al); forming a first laminated structure by laminating the first steel material and the second steel material after the primary hot rolling; forming a second laminated structure by secondary hot rolling the first laminated structure; forming a third laminated structure by cold rolling the second laminated structure, and cold annealing the third laminated structure.

[0008] The method may further include removing an oxide scale layer formed on surfaces of the first steel material and the second steel material after the primary hot rolling and before forming the first laminated structure.

[0009] The primary hot rolling may include performing rough rolling under the conditions of a slab reheating temperature (SRT) of 1000°C to 1200°C and a rough rolling outlet temperature (RDT) of 800°C to 900°C.

[0010] The secondary hot rolling may include hot rolling under the conditions of a SRT of 1100°C to 1200°C, a finishing outlet temperature (FDT) of 800°C to 1000°C, and a coiling temperature (CT) of 560°C to 600°C.

[0011] The first and second steel materials after primary hot rolling may each have a thickness of 100 to 150 mm, the second laminated structure after secondary hot rolling may have a thickness of 1.6 to 2.6 mm, and the third laminated structure after cold rolling may have a thickness of 0.25 to 0.60 mm.

[0012] The cold annealing may include annealing at a heating rate of 10° C. / s or more, an annealing start temperature of 900° C. to 1100° C., and a holding time of 30 seconds to 90 seconds, and cooling at a cooling rate of 30° C. / s or more.

[0013] The first steel material and the second steel material may each contain 2.8 wt% to 3.8 wt% of Si, greater than 0 wt% and not more than 0.5 wt% of Mn, 0.5 wt% to 1.2 wt% of Al, greater than 0 wt% and not more than 0.002 wt% of carbon (C), greater than 0 wt% and not more than 0.015 wt% of phosphorus (P), greater than 0 wt% and not more than 0.002 wt% of sulfur (S), greater than 0 wt% and not more than 0.002 wt% of nitrogen (N), greater than 0 wt% and not more than 0.002 wt% of titanium (Ti), and the balance of iron (Fe) and unavoidable impurities.

[0014] The third laminate structure after cold annealing may have a core loss (W 10 / 400 ) and a magnetic flux density of 1.6T or greater (B 50 ).

[0015] Beneficial Effects

[0016] According to an embodiment of the present invention, a method for manufacturing a non-oriented electrical steel sheet having low core loss at a high frequency and a non-oriented electrical steel sheet manufactured using the method can be provided.

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

[0018] Figure 1 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 cross-sectional views for describing a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0020] Figure 3 is a cross-sectional scanning electron microscope (SEM) image of a second laminated structure after secondary hot rolling in the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0021] Figure 4 Included are microscopic images of a hot rolled structure after hot rolling using the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention in Test Example 2.

[0022] Figure 5 Included are microscopic images of a hot rolled structure after hot rolling using the method for manufacturing a non-oriented electrical steel sheet according to a comparative example of the present invention in Test Example 1. DETAILED DESCRIPTION

[0023] Now, a method for manufacturing a nonoriented electrical steel sheet according to an embodiment of the present invention will be described in detail. 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.

[0024] 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 machinery such as transformers, and non-oriented electrical steel sheets are often used in rotating machinery such as motors. The performance of electrical steel sheets can be evaluated based on magnetic flux density and core loss. Magnetic flux density is mostly measured by B 50 Evaluation, core loss is generally calculated in W 15 / 50 However, if high frequency characteristics are required in electric vehicles, W 10 / 400 Evaluate. B 50 Indicates the magnetic flux density at 5000A / m, W 15 / 50 represents the core loss at 50Hz and 1.5T, W 10 / 400 Indicates the core loss at 400 Hz and 1.0 T.

[0025] Due to regulations aimed at reducing CO2 emissions to combat global warming, existing internal combustion engine vehicles are being rapidly replaced by environmentally friendly vehicles such as hybrid electric vehicles (HEVs) and electric vehicles (EVs), more specifically, by electric vehicles. As the demand for electric vehicles increases, the energy conversion efficiency of electric vehicle drive motors continues to improve, so it is necessary for the motor core material to have excellent magnetic properties. Non-oriented electrical steel sheets used as motor core materials are used in rotating machinery to convert electrical energy into mechanical energy, and magnetic properties (i.e., low core loss and high magnetic flux density) are essential for energy saving. In particular, non-oriented electrical steel sheets with low core loss at high frequencies (e.g., 400 Hz) are required to improve the efficiency of the motor during high-speed operation with high energy loss. In order to meet these requirements, non-oriented electrical steel sheet products are currently being developed by adding elements such as silicon (Si), manganese (Mn) and aluminum (Al) to increase resistivity or reduce material thickness. However, when alloy elements such as Si, Mn and Al increase, the rolling process may not be properly performed, thereby reducing the cold rolling recovery rate and causing difficulty in thickness reduction, and when the thickness of the electrical steel sheet is reduced, the production cost increases and the productivity decreases.

[0026] The present invention provides a method for manufacturing a non-oriented electrical steel sheet, which can achieve high magnetic flux density without a preliminary annealing process by laminating two rough-rolled slabs and performing double-layer hot rolling to cause shear deformation of the middle layer of the steel sheet.

[0027] Figure 1 is a flow chart of a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention, Figure 2 Included are cross-sectional views for describing a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0028] Reference Figure 1 and Figure 2 , a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: performing primary hot rolling on each of a first steel material 11 and a second steel material 12 containing Si, Mn and Al (S10); forming a first laminated structure 10 by laminating the first steel material 11 and the second steel material 12 after the primary hot rolling (S20); forming a second laminated structure 20 by secondary hot rolling the first laminated structure 10 (S30); forming a third laminated structure 30 by cold rolling the second laminated structure 20 (S40), and cold annealing the third laminated structure 30 (S50).

[0029] First hot rolling (S10)

[0030] The first steel material 11 and the second steel material 12 provided to the primary hot rolling process are steel materials for manufacturing a non-oriented electrical steel sheet, and each of the first steel material 11 and the second steel material 12 contains, for example, 2.8 wt% to 3.8 wt% of Si, more than 0 wt% and not more than 0.5 wt% of Mn, 0.5 wt% to 1.2 wt% of Al, more than 0 wt% and not more than 0.002 wt% of carbon (C), more than 0 wt% and not more than 0.015 wt% of phosphorus (P), more than 0 wt% and not more than 0.002 wt% of sulfur (S), more than 0 wt% and not more than 0.002 wt% of nitrogen (N), more than 0 wt% and not more than 0.002 wt% of titanium (Ti), and the balance of iron (Fe) and inevitable impurities.

[0031] The functions and contents of exemplary components applicable to the method for producing a non-oriented electrical steel sheet according to the technical features of the present invention will now be described. However, the method for producing a non-oriented electrical steel sheet according to the technical features of the present invention is not limited to the following exemplary compositions, and can be extended to any composition capable of achieving the functions of the non-oriented electrical steel sheet.

[0032] Si: 2.8 wt% to 3.8 wt%

[0033] Si is a main element added as a component to increase resistivity and reduce 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 greater than 3.8 wt%, brittleness increases, making cold rolling difficult and reducing productivity.

[0034] Mn: greater than 0 wt% and not more than 0.5 wt%

[0035] Mn increases resistivity and improves structure together with Si. When Mn is added in excess of 0.5 wt%, 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 addition amount, and cold rolling performance is significantly deteriorated. Because when the content of Mn is less than 0.2 wt%, fine MnS precipitates can be formed and grain growth can be suppressed, the composition of Mn can be more strictly controlled to 0.2 wt% to 0.5 wt%.

[0036] Al: 0.5 wt% to 1.2 wt%

[0037] 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. Al induces AlN precipitation when combined with N. 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 to increase the deviation of magnetic properties, and when the content of Al is greater than 1.2 wt%, cold rolling properties deteriorate, nitrides are generated excessively, resulting in a decrease in magnetic flux density and deterioration of magnetic properties.

[0038] C: greater than 0 wt% and not more than 0.002 wt%

[0039] C is an element that forms carbides such as TiC and NbC and increases 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 and the magnetic properties deteriorate, while when the content of C is 0.002 wt% or less, magnetic aging is suppressed.

[0040] P: greater than 0 wt% and not more than 0.015 wt%

[0041] P is a grain boundary segregation element and an element that develops the structure. When the P content is more than 0.015 wt%, grain growth is inhibited, magnetic properties deteriorate, and cold rolling properties are reduced due to the segregation effect.

[0042] S: greater than 0 wt% and not more than 0.002 wt%

[0043] S forms precipitates such as MnS and CuS, increases core loss, and inhibits grain growth, so the less the better. The S content is limited to 0.002 wt% or less. When the S content is greater than 0.002 wt%, the core loss increases.

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

[0045] N forms precipitates such as AlN, TiN, and NbN, increases core loss, and inhibits grain growth, so the less the better. The N content is limited to 0.002 wt% or less. When the N content is greater than 0.002 wt%, the core loss increases.

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

[0047] 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.

[0048] The first steel material 11 and the second steel material 12 having the above composition are each subjected to primary hot rolling. The primary hot rolling (S10) is a rough rolling step and may include hot rolling at a slab reheating temperature (SRT) of 1000 to 1200°C and a rough rolling outlet temperature (RDT) of 800 to 900°C.

[0049] 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 1000°C, the rolling load may increase and the final product may have high core loss.

[0050] The primary hot rolling ( S10 ) of the first and second steel materials 11 and 12 includes, for example, forming bars having a thickness of 100 to 150 mm by performing hot rough rolling on slabs having a thickness of 200 to 300 mm at a reduction rate of 50% to 65%.

[0051] Forming a first laminate structure (S20)

[0052] Reference Figure 2 (a) The first laminated structure 10 may be formed by laminating the first steel material 11 and the second steel material 12 after primary hot rolling. The first steel material 11 and the second steel material 12 constituting the first laminated structure 10 may each have a thickness t1 of, for example, 100 mm to 150 mm.

[0053] After the primary hot rolling S10 and before forming the first laminated structure (S20), an oxide scale layer formed on the surface of the first steel material 11 and / or the second steel material 12 after the primary hot rolling may be removed. The oxide scale layer may include an oxide layer formed on the surface of the first steel material 11 and / or the second steel material 12 when the first steel material 11 and / or the second steel material 12 are primary hot rolled.

[0054] Since the formation ( S20 ) of the first laminated structure is performed after the oxide scale layer is removed, the interface between the first steel material 11 and the second steel material 12 constituting the first laminated structure 10 may be an interface where the steel materials from which the oxide scale layer has been removed are in contact with each other.

[0055] The second laminate structure is formed by performing secondary hot rolling (S30)

[0056] Reference Figure 2 (b) The second laminated structure 20 may be formed by subjecting the first laminated structure 10 to secondary hot rolling.

[0057] The secondary hot rolling ( S30 ) may include hot rolling under the conditions of a SRT of 1100° C. to 1200° C., a finishing outlet temperature (FDT) of 800° C. to 1000° C., and a coiling temperature (CT) of 560° C. to 600° C.

[0058] The secondary hot rolling ( S30 ) may include forming the second laminated structure 20 ( S30 ) by rolling the first laminated structure 10 to a thickness t2 of 1.6 mm to 2.6 mm.

[0059] Figure 3 is a cross-sectional scanning electron microscope (SEM) image of a second laminated structure after secondary hot rolling in the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0060] Reference Figure 3 , the interface F between the first steel material 11 and the second steel material 12 constituting the second laminated structure 20 shows that the first steel material 11 and the second steel material 12 are joined together after the secondary hot rolling.

[0061] Meanwhile, when double-layer hot rolling is performed as described above, since shear deformation occurs inside the laminated structure and the driving force for dynamic recrystallization is sufficient, a recrystallized hot-rolled structure is presented after hot rolling, and thus no preliminary annealing process is required before cold rolling.

[0062] The third laminate structure is formed by cold rolling (S40)

[0063] Reference Figure 2 (c) The third laminated structure 30 may be formed by cold rolling the second laminated structure 20 .

[0064] The cold rolling may include forming the third laminated structure 30 by rolling the second laminated structure 20 to a thickness t3 of 0.25 mm to 0.60 mm (S40). The reduction rate of the cold rolling may be 60% to 82%.

[0065] Cold annealing (S50)

[0066] The third laminate structure 30 may be cold annealed. The cold annealing (S60) may include annealing at a heating rate of 10°C / s or more, an annealing temperature of 900°C to 1100°C, and a holding time of 30 seconds to 90 seconds, and cooling at a cooling rate of 30°C / s or more.

[0067] The cold rolled steel sheet obtained after cold rolling is cold annealed. A temperature that can achieve an optimum grain size is applied in consideration of core loss reduction and mechanical properties. In cold annealing, heating is performed under mixed atmosphere conditions to prevent surface oxidation and nitration. The surface is further smoothed using a mixed atmosphere of nitrogen and hydrogen. When the cold annealing temperature is lower than 900°C, fine grains may be formed to increase hysteresis loss, and when the cold annealing temperature is higher than 1100°C, coarse grains may be formed to increase eddy current loss.

[0068] Reference Figure 2 (d), after the final annealing, a coating process may be performed to form an insulating coating layer 15. By forming the insulating coating layer 15, punchability may be improved and insulation may be ensured. The insulating coating layer 15 formed on the third laminate structure 30 may have a thickness of about 1 to 2 microns, and the insulating coating layer 15 under the third laminate structure 30 may also have a thickness of about 1 to 2 microns.

[0069] The laminate structure may have a final thickness of 0.25 mm to 0.6 mm, a core loss (W) of 14.0 W / kg or less, and a magnetic flux density (B) of 1.6 T or more, and more strictly, 1.65 T or more. 50 ).

[0070] The nonoriented electrical steel sheet manufactured using the above method includes a laminated structure of steel materials containing Si, Mn and Al, which is formed by laminating a first steel material and a second steel material after primary hot rolling, and then sequentially performing secondary hot rolling, cold rolling and cold annealing.

[0071] The first steel material and the second steel material may each contain 2.8 to 3.8 wt% of Si, greater than 0 to 0.5 wt% of Mn, 0.5 to 1.2 wt% of Al, greater than 0 to 0.002 wt% of C, greater than 0 to 0.015 wt% of P, greater than 0 to 0.002 wt% of S, greater than 0 to 0.002 wt% of N, greater than 0 to 0.002 wt% of Ti, and balance Fe and unavoidable impurities.

[0072] According to the present invention, the core loss value of the non-oriented electrical steel sheet is close to that of the product produced by the general process (including single-layer hot rolling and preliminary annealing) at the same thickness or the magnetic flux density is higher. That is, since shear deformation is applied to the inside due to the asymmetric rolling effect of the double-layer hot rolling, it is possible to ensure low core loss at high frequency without the need for the preliminary annealing process by the double-layer hot rolling. In addition, since the preliminary annealing process can be omitted, the increase in production cost can be suppressed. Compared with the existing method, the manufacturing process of the double-layer product can be simplified, and a non-oriented electrical steel sheet having a core loss value close to that of the product produced by the general process (single-layer hot rolling and preliminary annealing) and a higher magnetic flux density can be manufactured.

[0073] Test Example

[0074] Test examples will now be described in order 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.

[0075] 1. Sample composition

[0076] The samples provided in this test example have the alloy element composition shown in Table 1 (unit: weight %).

[0077] [Table 1]

[0078] Si Mn Al C P S N Ti Fe 3.3 0.2 1.2 0.0018 0.0055 0.0011 0.0019 0.0020 margin

[0079] 1, the composition of the nonoriented electrical steel sheet according to the test example satisfies Si: 2.8 wt% to 3.8 wt%, Mn: greater than 0 wt% and not more than 0.5 wt%, Al: 0.5 wt% to 1.2 wt%, C: greater than 0 wt% and not more than 0.002 wt%, P: greater than 0 wt% and not more than 0.015 wt%, S: greater than 0 wt% and not more than 0.002 wt%, N: greater than 0 wt% and not more than 0.002 wt%, Ti: greater than 0 wt% and not more than 0.002 wt%, and the balance is Fe.

[0080] 2. Process conditions and performance evaluation

[0081] Table 2 shows the process conditions, core loss and magnetic flux density of this test example.

[0082] In the hot rolling method shown in Table 2, the double-layer hot rolling item refers to the hot rolling method according to the above reference Figure 1 and Figure 2 The method of manufacturing the non-oriented electrical steel sheet of the embodiment of the present invention includes a method of sequentially performing primary hot rolling and secondary hot rolling, and the single-layer hot rolling item refers to a method of performing hot rolling on a single slab without adopting a laminated structure as in the existing method. The hot rolling thickness item refers to the thickness of the rolled steel plate after the final hot rolling. The APL application item refers to whether a preliminary annealing process (e.g., annealing and pickling line (APL)) is applied after hot rolling and before cold rolling, and the preliminary annealing process may include annealing under the conditions of a heating rate of 10°C / s or more, an annealing temperature of 900°C to 1100°C, and a holding time of 30 seconds to 90 seconds, and cooling under the conditions of a cooling rate of 30°C / s or more. The preliminary annealing process is only applicable to Test Example 2. The final thickness item indicates the thickness of the rolled steel plate after cold rolling. The annealing temperature item refers to the temperature when cold annealing is performed after cold rolling. The cold annealing includes annealing at a heating rate of 10° C. / s or more, an annealing start temperature of 900° C. to 1100° C., and a holding time of 30 seconds to 90 seconds, and cooling at a cooling rate of 30° C. / s or more.

[0083] [Table 2]

[0084]

[0085] Referring to Table 2, Test Examples 1 and 4 in which the preliminary annealing of the single-layer hot-rolled steel sheet was omitted showed a core loss (W 10 / 400 ) value. In contrast, Test Example 2, in which a single-layer hot-rolled steel sheet was preliminarily annealed, exhibited a core loss (W ) of 14.0 W / kg or less. 10 / 400 ) value. Based on the above reference Figure 1 and Figure 2 The method for manufacturing a non-oriented electrical steel sheet according to the embodiment of the present invention, Test Examples 3 and 5 in which double hot rolling was performed but preliminary annealing was omitted, showed a core loss (W 10 / 400 ) and a magnetic flux density (B 50 ). In particular, the reason why the magnetic flux density increases compared with Test Examples 1 and 4 in which the preliminary annealing is omitted is that an asymmetric rolling effect is generated due to the double-layer hot rolling process, and shear deformation is applied to the internal structure of the hot-rolled steel sheet, thereby improving the magnetic flux density through dynamic recrystallization.

[0086] According to Test Examples 3 and 5, it is shown that a method for manufacturing a non-oriented electrical steel sheet can be implemented by laminating two rough-rolled slabs and performing double hot rolling to shear-deform the middle layer of the steel sheet without a preliminary annealing process to achieve high magnetic flux density.

[0087] Figure 4 Included are microscopic images of a hot rolled structure after hot rolling using the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention in Test Example 2. Figure 4 (a) is a microscope image of the hot-rolled structure on a cross section of a steel plate cut along the length direction parallel to the casting direction, Figure 4 (b) is a microscope image of the hot rolled structure on a cross section of a steel plate cut along the thickness direction perpendicular to the casting direction. Figure 4 In (a), the area indicated by the red dotted line shows the internal structure of the intermediate layer between the first steel material and the second steel material.

[0088] Reference Figure 4 , which shows that when double-layer hot rolling is performed, due to the shear deformation generated inside the laminated structure and the sufficient driving force for dynamic recrystallization, a recrystallized hot-rolled structure is presented after hot rolling. Therefore, it can be understood that no preliminary annealing process is required.

[0089] Figure 5 Included are microscopic images of a hot rolled structure after hot rolling using the method for manufacturing a non-oriented electrical steel sheet according to a comparative example of the present invention in Test Example 1. Figure 5 (a) is a microscope image of the hot-rolled structure on a cross section of a steel plate cut along the length direction parallel to the casting direction, Figure 5 (b) is a microscope image of the hot-rolled structure on a cross section of a steel plate cut along the thickness direction perpendicular to the casting direction. Figure 5 In (a), the area indicated by the red dashed line shows the internal structure of the middle layer of a single steel material (single layer).

[0090] Reference Figure 5 , shows that when general single-layer hot rolling is performed, due to the symmetrical rolling process, shear deformation only occurs on the surface, and only plane deformation is applied to the internal structure, so the middle layer retains an elongated casting structure due to insufficient driving force for dynamic recrystallization. Therefore, it can be understood that a preliminary annealing process is required to prevent the above-mentioned casting structure.

[0091] For a single-layer hot-rolled steel sheet (general process), a {100} plane is formed by performing preliminary annealing, thereby obtaining a dynamic recrystallization structure in the internal structure. However, for a double-layer hot-rolled steel sheet (implementation), the preliminary annealing can be omitted because the double-layer hot rolling process causes dynamic recrystallization in the internal structure of the middle layer of the laminated structure.

[0092] It can be seen that the core loss of the final product manufactured according to the present invention is similar to that of a single-layer product obtained by performing preliminary annealing, and the magnetic flux density is also higher than that of a product produced by omitting preliminary annealing (such as APL). Therefore, compared with the existing method, a multi-layer (ie, double-layer) steel sheet can be manufactured more simply, and the preliminary annealing process can be omitted.

[0093] 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 without departing from the scope of the invention as defined by the following claims.

Claims

1. A method for manufacturing a non-oriented electrical steel sheet, the method comprising: performing primary hot rolling on each of a first steel material and a second steel material including silicon (Si), manganese (Mn), and aluminum (Al); forming a first laminated structure by laminating a first steel material and a second steel material after primary hot rolling; forming a second laminated structure by hot rolling the first laminated structure for a second time; forming a third laminated structure by cold rolling the second laminated structure; and The third laminate structure is cold annealed.

2. The method according to claim 1, further comprising: After the primary hot rolling and before forming the first laminated structure, the oxide scale layer formed on the surfaces of the first steel material and the second steel material after the primary hot rolling is removed.

3. The method according to claim 1, wherein: The primary hot rolling includes performing rough rolling under the conditions of a slab reheating temperature (SRT) of 1000°C to 1200°C and a rough rolling outlet temperature (RDT) of 800°C to 900°C.

4. The method according to claim 1, wherein: The secondary hot rolling includes hot rolling under the conditions of SRT of 1100° C. to 1200° C., finishing outlet temperature (FDT) of 800° C. to 1000° C., and coiling temperature (CT) of 560° C. to 600° C.

5. The method according to claim 1, wherein: The first steel material and the second steel material after the primary hot rolling each have a thickness of 100 mm to 150 mm, The second laminated structure after secondary hot rolling has a thickness of 1.6 mm to 2.6 mm, and The third laminated structure after cold rolling has a thickness of 0.25 mm to 0.60 mm.

6. The method according to claim 1, wherein: The cold annealing comprises: performing annealing under the conditions of a heating rate of 10° C. / s or more, an annealing start temperature of 900° C. to 1100° C., and a holding time of 30 seconds to 90 seconds; and The cooling is performed at a cooling rate of 30° C. / s or more.

7. The method according to claim 1, wherein: The first steel material and the second steel material each contain 2.8 wt% to 3.8 wt% of Si, greater than 0 wt% and not more than 0.5 wt% of Mn, 0.5 wt% to 1.2 wt% of Al, greater than 0 wt% and not more than 0.002 wt% of carbon (C), greater than 0 wt% and not more than 0.015 wt% of phosphorus (P), greater than 0 wt% and not more than 0.002 wt% of sulfur (S), greater than 0 wt% and not more than 0.002 wt% of nitrogen (N), greater than 0 wt% and not more than 0.002 wt% of titanium (Ti), and the balance of iron (Fe) and unavoidable impurities.

8. The method according to claim 1, wherein: The third laminate structure after cold annealing has a core loss (W) of 14.0 W / kg or less. 10 / 400 ) and a magnetic flux density of 1.6T or greater (B 50 ).

9. A non-oriented electrical steel sheet comprising a laminated structure of steel materials containing silicon (Si), manganese (Mn) and aluminum (Al), the laminated structure being formed by laminating a first steel material and a second steel material after primary hot rolling, and then sequentially performing secondary hot rolling, cold rolling and cold annealing.

10. The non-oriented electrical steel sheet according to claim 9, wherein: The first steel material and the second steel material each contain 2.8 wt% to 3.8 wt% of Si, greater than 0 wt% and not more than 0.5 wt% of Mn, 0.5 wt% to 1.2 wt% of Al, greater than 0 wt% and not more than 0.002 wt% of carbon (C), greater than 0 wt% and not more than 0.015 wt% of phosphorus (P), greater than 0 wt% and not more than 0.002 wt% of sulfur (S), greater than 0 wt% and not more than 0.002 wt% of nitrogen (N), greater than 0 wt% and not more than 0.002 wt% of titanium (Ti), and the balance of iron (Fe) and unavoidable impurities.

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