Non-oriented electromagnetic steel sheet and method for manufacturing the same

Abstract

A method for manufacturing a non-oriented electromagnetic steel sheet according to an embodiment of the present invention includes a step of performing first hot rolling on a first steel material and a second steel material containing silicon (Si), manganese (Mn), and aluminum (Al), respectively; a step of forming a first laminated structure in which the first steel material and the second steel material that have been first hot rolled are laminated; a step of performing second hot rolling on the first laminated structure to form a second laminated structure; a step of performing cold rolling on the second laminated structure to form a third laminated structure; and a step of performing cold rolling annealing treatment on the third laminated 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 excellent high-frequency iron loss and a method for manufacturing the same.

Background Art

[0002] Electrical steel sheets can be classified into oriented electrical steel sheets and non-oriented electrical steel sheets according to their magnetic properties. Oriented electrical steel sheets are manufactured so that magnetization is easy in the rolling direction of the steel sheet and have particularly excellent magnetic properties in the rolling direction. Therefore, they are mainly used as cores for large, medium, and small transformers that require low iron loss and high magnetic permeability. On the contrary, non-oriented electrical steel sheets have uniform magnetic properties regardless of the direction of the steel sheet, and thus are widely used as core materials for small motors, small power transformers, ballasts, etc. As a prior art document, there is Korean Patent Publication No. 10-2015-0001467.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The technical problem to be achieved by the present invention is to provide a non-oriented electrical steel sheet having excellent high-frequency iron loss and a method for manufacturing the same.

[0004] However, such problems are exemplary and do not limit the scope of the present invention.

Means for Solving the Problems

[0005] According to one aspect of the present invention for solving the above problems, a method for manufacturing a non-oriented electromagnetic steel sheet includes a step of hot-rolling a first steel material and a second steel material containing silicon (Si), manganese (Mn), and aluminum (Al) respectively for the first time, a step of forming a first laminated structure by laminating the first steel material and the second steel material hot-rolled for the first time, a step of hot-rolling the first laminated structure for the second time to form a second laminated structure, a step of cold-rolling the second laminated structure to form a third laminated structure, and a step of annealing the third laminated structure by cold rolling.

[0006] The method for manufacturing the non-oriented electromagnetic steel sheet may further include a step of removing a scale layer formed on the surfaces of the first steel material and the second steel material hot-rolled for the first time after the step of hot-rolling for the first time and before the step of forming the first laminated structure.

[0007] In the method for manufacturing the non-oriented electromagnetic steel sheet, the step of hot-rolling for the first time may include a step of rough rolling under the conditions of a reheat temperature (SRT): 1000 to 1200 °C and a finish rough rolling temperature (RDT): 800 to 900 °C.

[0008] In the method for manufacturing the non-oriented electromagnetic steel sheet, the step of hot-rolling for the second time may include a step of hot-rolling under the conditions of a reheat temperature (SRT): 1100 to 1200 °C, a finish rolling temperature (FDT): 800 to 1000 °C, and a coiling temperature (CT): 560 to 600 °C.

[0009] In the method for manufacturing the non-oriented electromagnetic steel sheet, the thicknesses of the first steel material and the second steel material hot-rolled for the first time may be 100 to 150 mm respectively, the thickness of the second laminated structure hot-rolled for the second time may be 1.6 to 2.6 mm, and the thickness of the third laminated structure cold-rolled may be 0.25 to 0.60 mm.

[0010] In the method for manufacturing the non-oriented electromagnetic steel sheet, the cold rolling and annealing treatment step may include an annealing step performed under the conditions of a heating rate of 10 °C / s or more, an annealing start temperature of 900 to 1100 °C, and a holding time of 30 to 90 seconds, and a cooling step performed under the condition of a cooling rate of 30 °C / s or more.

[0011] In the method for manufacturing the non-oriented electromagnetic steel sheet, the first steel material and the second steel material may each contain silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): more than 0 and 0.5% by weight or less, aluminum (Al): 0.5 to 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities.

[0012] In the method for manufacturing the non-oriented electromagnetic steel sheet, the cold-rolled and annealed third laminate may have an iron loss (W 10 / 400 ) of 14.0 W / kg or less and a magnetic flux density (B 50 ) of 1.6 T or more.

Advantages of the Invention

[0013] According to an embodiment of the present invention, a method for manufacturing a non-oriented electromagnetic steel sheet excellent in high-frequency iron loss and a non-oriented electromagnetic steel sheet using the same can be provided.

[0014] Of course, the scope of the present invention is not limited by such effects.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] The method for manufacturing an isotropic electromagnetic steel sheet according to an embodiment of the present invention will be described in detail. The terms described below are terms appropriately selected in consideration of the functions in the present invention, and the definitions of such terms must be made based on the content throughout this specification.

[0017] Generally, electromagnetic steel sheets are classified into oriented electromagnetic steel sheets and isotropic electromagnetic steel sheets. In the case of oriented electromagnetic steel sheets, they are mainly used for static devices such as transformers, and in the case of isotropic electromagnetic steel sheets, they are often used for rotating machines that rotate like motors. The characteristics of electromagnetic steel sheets can be evaluated by magnetic flux density and iron loss. The magnetic flux density is mainly B 50 , and in the case of iron loss, generally W 15 / 50 is evaluated, but when high-frequency characteristics are required as in the case of electric vehicles, it is evaluated by W 10 / 400 . B 50 indicates the magnetic flux density at 5000 A / m, W 15 / 50 indicates the iron loss at 50 Hz and 1.5 T, and W 10 / 400 indicates the iron loss at 400 Hz and 1.0 T.

[0018] Due to the CO₂ emission reduction policy for preventing global warming, existing internal combustion engine vehicles are being rapidly replaced by environmentally friendly vehicles (hybrid electric vehicles (HEVs), electric vehicles (EVs)), especially electric vehicles (EVs). In line with the increasing demand for such electric vehicles (EVs), the energy conversion efficiency of drive motors for electric vehicles is being improved, and for this purpose, excellent magnetic properties of the motor core material are required. The non-oriented electrical steel sheet used as the motor core material plays a role in converting electrical energy into mechanical energy in rotating equipment, and for energy savings, it is important to have its magnetic properties, that is, low iron loss and high magnetic flux density. In particular, for the high efficiency of the motor during high-speed driving where energy loss is large, a non-oriented electrical steel sheet with low high-frequency (400 Hz) iron loss is required. In response to such needs, the development of non-oriented electrical steel sheet products has been carried out by adding elements such as silicon (Si), manganese (Mn), and aluminum (Al) to improve the specific resistance or to enable the thinning of the material. However, when the alloying elements such as silicon (Si), manganese (Mn), and aluminum (Al) increase, rolling becomes difficult, the cold rolling recovery rate decreases, thinning becomes difficult, and when thinning the thickness of the electrical steel sheet, there is a problem that the production unit price increases and the productivity decreases.

[0019] In the present invention, two slabs that have been roughly rolled are laminated and subjected to double hot rolling, and by generating shear strain up to the central layer, a method for manufacturing a non-oriented electrical steel sheet with excellent magnetic flux density is provided even when the preliminary annealing process is omitted.

[0020] FIG. 1 is a flowchart showing a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention, and FIG. 2 is a diagram schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0021] Referring to FIGS. 1 and 2, a method for manufacturing a non-oriented electromagnetic steel sheet according to an embodiment of the present invention includes a step (S10) of performing first hot rolling on a first steel material 11 and a second steel material 12 containing silicon (Si), manganese (Mn), and aluminum (Al), respectively; a step (S20) of forming a first laminated structure 10 by laminating the first hot-rolled first steel material 11 and the second steel material 12; a step (S30) of performing second hot rolling on the first laminated structure 10 to form a second laminated structure 20; a step (S40) of performing cold rolling on the second laminated structure 20 to form a third laminated structure 30; and a step (S50) of performing cold rolling annealing treatment on the third laminated structure 30.

[0022] First hot rolling step (S10)

[0023] The first steel material 11 and the second steel material 12 input into the first hot rolling process are steel materials for manufacturing a non-oriented electromagnetic steel sheet. For example, silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): more than 0 and 0.5 wt% or less, aluminum (Al): 0.5 to 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, and the balance of iron (Fe) and other inevitable impurities are included respectively.

[0024] Hereinafter, the roles and contents of exemplary components to which the method for manufacturing a non-oriented electromagnetic steel sheet according to the technical idea of the present invention can be applied will be described. However, the method for manufacturing a non-oriented electromagnetic steel sheet according to the technical idea of the present invention is not limited by such an example of the composition range, and can be extended to any composition range capable of performing the function of the non-oriented electromagnetic steel sheet.

[0025] Silicon (Si): 2.8 to 3.8 wt%

[0026] Silicon (Si) is a component that increases the resistivity and reduces the iron loss (eddy current loss), and it is a major additive element. When the addition amount of silicon is less than 2.8% by weight, it is difficult to obtain the desired high-frequency low iron loss value, and as the addition amount increases, the permeability and magnetic flux density tend to decrease. Also, when the addition amount of silicon exceeds 3.8% by weight, the brittleness increases, making cold rolling difficult and reducing productivity.

[0027] Manganese (Mn): more than 0 and 0.5 wt% or less

[0028] Manganese (Mn) increases the resistivity together with silicon and improves the structure. When manganese is added in an amount exceeding 0.5% by weight, the magnetic properties deteriorate, such as the formation of coarse MnS precipitates and a decrease in magnetic flux density. Furthermore, when the manganese content exceeds 0.5% by weight, the reduction in iron loss is small compared to the addition amount, while the decrease in cold rollability becomes significant. Moreover, when the manganese content is less than 0.2% by weight, it can form fine MnS precipitates and suppress the growth of crystal grains. More strictly, the composition range of manganese can also be adjusted to 0.2 - 0.5% by weight.

[0029] Aluminum (Al): 0.5 to 1.2 wt%

[0030] Aluminum (Al) is a component that increases the resistivity together with silicon and reduces the iron loss (eddy current loss), and it is a major additive element. Aluminum plays a role in reducing magnetic anisotropy and magnetic deviation. Aluminum reacts with nitrogen to induce the precipitation of AlN. When the aluminum content is less than 0.5% by weight, it is difficult to expect the above-mentioned effects, and it may form fine nitrides and increase the deviation of magnetic properties. When the aluminum content exceeds 1.2% by weight, the cold rollability decreases, excessive nitrides are formed, the magnetic flux density decreases, and the magnetic properties deteriorate.

[0031] Carbon (C): more than 0 and 0.002 wt% or less

[0032] Carbon (C) is an element that forms carbides such as TiC and NbC and increases iron loss. The less of it, the more preferable, and it is limited to 0.002 wt% or less. When the carbon content exceeds 0.002 wt%, magnetic aging occurs and magnetic properties deteriorate, while when it is 0.002 wt% or less, the magnetic aging phenomenon is suppressed.

[0033] Phosphorus (P): more than 0 and 0.015 wt% or less

[0034] Phosphorus (P) is an element that segregates at grain boundaries and promotes the development of the microstructure. When the phosphorus content exceeds 0.015 wt%, the growth of grains is suppressed due to the segregation effect, magnetic properties deteriorate, and cold rolling properties decrease.

[0035] Sulfur (S): more than 0 and 0.002 wt% or less

[0036] Sulfur (S) forms precipitates such as MnS and CuS, increasing iron loss and suppressing the growth of crystal grains. Therefore, it is added as low as possible and limited to 0.002 wt% or less. When the sulfur content exceeds 0.002 wt%, the problem of increased iron loss occurs.

[0037] Nitrogen (N): more than 0 and 0.002 wt% or less

[0038] Nitrogen (N) forms precipitates such as AlN, Tin, and NbN, increasing iron loss and suppressing the growth of crystal grains. Therefore, it is added as low as possible and limited to 0.002 wt% or less. When the nitrogen content exceeds 0.002 wt%, the problem of increased iron loss occurs.

[0039] Titanium (Ti): more than 0 and 0.002 wt% or less

[0040] Titanium (Ti) forms fine precipitates such as TiC and TiN, suppressing the growth of crystal grains. Since the more titanium is added, the more inferior the magnetic properties become, it is added as low as possible and limited to 0.002 wt% or less. When the titanium content exceeds 0.002 wt%, the problem of deteriorated magnetic properties occurs.

[0041] The first steel material 11 and the second steel material 12 having the above-described composition each undergo a first hot rolling process. The step (S10) of hot rolling the steel material in the first hot rolling process is a rough rolling step, and may include a step of hot rolling under the conditions of a reheating temperature (SRT): 1000 to 1200°C and a finish rough rolling temperature (RDT): 800 to 900°C.

[0042] When the slab reheating temperature exceeds 1200°C, precipitates such as C, S, and N in the slab redissolve, and fine precipitates may occur in subsequent rolling and annealing processes, suppressing the growth of crystal grains and possibly deteriorating the magnetic properties. When the slab reheating temperature is less than 1000°C, the rolling load increases, and there may be a problem that the iron loss becomes high in the final product.

[0043] The step (S10) of hot rolling the first steel material 11 and the second steel material 12 includes, for example, a step of hot rolling a slab having a thickness of 200 to 300 mm with a reduction ratio of 50 to 65% to produce a bar having a thickness of 100 to 150 mm.

[0044] First laminated structure forming step (S20)

[0045] Referring to FIG. 2(a), a first laminated structure 10 in which the first hot-rolled first steel material 11 and the second steel material 12 are laminated can be formed. The respective thicknesses t1 of the first steel material 11 and the second steel material 12 constituting the first laminated structure 10 may have a thickness of, for example, 100 to 150 mm.

[0046] After the step (S10) of hot rolling in the first pass, before the step (S20) of forming the first laminated structure, a step of removing the scale layer formed on the surface of the first hot-rolled first steel material 11 and / or the second steel material 12 can be performed. The scale layer may include an oxide layer formed on the surface portion of the first steel material 11 and / or the second steel material 12 during the process of hot rolling the first steel material 11 and / or the second steel material 12 in the first pass.

[0047] By performing the first laminated structure forming step (S20) after removing the scale layer, the interface between the first steel material 11 and the second steel material 12 constituting the first laminated structure 10 can be an interface formed by the steel materials with the oxide layer removed coming into contact with each other.

[0048] Second hot rolling to form the second laminated structure step (S30)

[0049] Referring to FIG. 2(b), the first laminated structure 10 can be second hot-rolled to form a second laminated structure 20.

[0050] The step (S30) of the second hot rolling can include a step of hot rolling under the conditions of a reheating temperature (SRT): 1100 to 1200 °C, a finish rolling temperature (FDT): 800 to 1000 °C, and a coiling temperature (CT): 560 to 600 °C.

[0051] The step (S30) of the second hot rolling can include a step (S30) of rolling the first laminated structure 10 to a thickness t2 of 1.6 to 2.6 mm to form the second laminated structure 20.

[0052] FIG. 3 is a scanning electron micrograph of a cross section of the second laminated structure taken after the second hot rolling in the method for manufacturing a non-oriented electromagnetic steel sheet according to an embodiment of the present invention.

[0053] Referring to FIG. 3, the interface F between the first steel material 11 and the second steel material 12 constituting the second laminated structure 20 can be confirmed, and it can be confirmed that the first steel material 11 and the second steel material 12 are joined after the second hot rolling.

[0054] On the other hand, by generating shear strain up to the center of the laminated structure during the above-described double hot rolling, since the driving force for dynamic recrystallization is sufficient, a recrystallized hot-rolled structure appears after hot rolling, so a separate preliminary annealing process is not required before cold rolling.

[0055] Cold rolling to form the third laminated structure step (S40)

[0056] Referring to FIG. 2(c), the second laminate structure 20 can be cold-rolled to form a third laminate structure 30.

[0057] The cold-rolling step may include a step (S40) of rolling the second laminate structure 20 to a thickness t3 of 0.25 to 0.60 mm to form the third laminate structure 30. The reduction ratio of cold rolling may be 60 to 82%.

[0058] Cold rolling annealing treatment step (S50)

[0059] The third laminate structure 30 can be subjected to cold rolling and annealing treatment. The cold rolling and annealing treatment step (S50) may include a step of annealing under the conditions of a heating rate of 10°C / s or more, an annealing temperature of 900 to 1100°C, a holding time of 30 to 90 seconds, and a cooling rate of 30°C / s or more.

[0060] Cold rolling and annealing are performed on the cold-rolled sheet obtained after cold rolling. Considering the improvement of iron loss and mechanical properties, the temperature for deriving the optimum grain size is applied. In order to prevent surface oxidation and nitridation during cold rolling and annealing, heating is performed under the conditions of a mixed atmosphere. The surface state is further smoothed through a mixed atmosphere of nitrogen and hydrogen. If the cold rolling and annealing temperature is less than 900°C, the grain size is fine, so the hysteresis loss may increase. If the cold rolling and annealing temperature exceeds 1100°C, the grain size becomes coarse and the eddy current loss increases.

[0061] Referring to FIG. 2(d), after final annealing, a coating process can be performed to form the insulating coating layer 15. By forming the insulating coating layer 15, the punching property can be improved and the insulation can be ensured. The thickness of the insulating coating layer 15 formed on the upper part of the third laminate structure 30 is about 1 to 2 μm, and the thickness of the insulating coating layer 15 formed on the lower part of the third laminate structure 30 can also be about 1 to 2 μm.

[0062] The final thickness of the laminated structure is 0.25 to 0.6 mm, and the iron loss (W 10 / 400 ) is 14.0 W / kg or less and the magnetic flux density (B 50 ) can be 1.6 T or more (strictly 1.65 T or more).

[0063] The non-oriented electromagnetic steel sheet embodied by the above-described manufacturing method includes a laminated structure of a steel material containing silicon (Si), manganese (Mn), and aluminum (Al). The laminated structure is characterized in that after laminating a first hot-rolled first steel material and a second steel material, second hot rolling, cold rolling, and cold rolling annealing treatments are sequentially performed.

[0064] The first steel material and the second steel material can each contain silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): more than 0 and 0.5% by weight or less, aluminum (Al): 0.5 to 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities.

[0065] According to the present invention, it is possible to embody a non-oriented electromagnetic steel sheet having a similar iron loss value as compared with a product having a normal process (including single-plate hot rolling and preliminary annealing) at the same thickness, but having an improved magnetic flux density. That is, by performing double hot rolling so that shear strain acts internally due to the asymmetric rolling effect, the preliminary annealing process can be omitted through double hot rolling, and excellent high-frequency iron loss can be ensured. Furthermore, since the preliminary annealing process can be omitted, an increase in production cost can be suppressed. Compared with the prior art, the manufacturing process of the double-layer product can be simplified, and it is possible to manufacture a non-oriented electromagnetic steel sheet having a similar iron loss value as a product manufactured by a normal process (single-plate hot rolling and preliminary annealing), but having an improved magnetic flux density.

[0066] Experimental example

[0067] The following presents preferred experimental examples to facilitate the understanding of the present invention. However, the following experimental examples are merely for assisting in the understanding of the present invention, and the present invention is not limited by the following experimental examples.

[0068] 1. Composition of test piece

[0069] In this experimental example, a test piece having the composition of alloying elements in Table 1 (unit: wt%) is provided.

[0070]

Table 1

[0071] Referring to Table 1, the composition of the non-oriented electrical steel sheet according to the experimental example satisfies silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): more than 0 and 0.5 wt% or less, aluminum (Al): 0.5 to 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, and the balance being iron (Fe).

[0072] 2. Process conditions and evaluation of physical properties

[0073] Table 2 shows the process conditions, iron loss, and magnetic flux density of this experimental example.

[0074] Among the hot rolling methods disclosed in Table 2, the item of double hot rolling means sequentially performing the first hot rolling and the second hot rolling disclosed in the manufacturing method of the non-oriented electromagnetic steel sheet according to an embodiment of the present invention described with reference to FIGS. 1 and 2. The item of single-plate hot rolling means performing hot rolling on one slab in an existing manner without introducing a laminated structure. Further, the item of hot-rolled thickness means the thickness of the material to be rolled after the final hot rolling. The item of APL application means whether or not a preliminary annealing (APL) treatment is applied after hot rolling and before cold rolling. The steps of the preliminary annealing treatment may include an annealing step at a heating rate of 10 ° C / s or more, an annealing temperature of 900 to 1100 ° C, and a holding time of 30 to 90 seconds, and a cooling step at a cooling rate of 20 ° C / s or more. The preliminary annealing treatment was applied only in Experimental Example 2. The item of final thickness means the thickness of the material to be rolled after cold rolling. The item of annealing temperature means the temperature in the cold rolling annealing treatment after the cold rolling process. The cold rolling annealing treatment includes an annealing step at a heating rate of 10 ° C / s or more, an annealing start temperature of 900 to 1100 ° C, and a holding time of 30 to 90 seconds, and a cooling step at a cooling rate of 30 ° C / s or more.

[0075]

Table 2

[0076] Referring to Table 2, in the case of Experimental Examples 1 and 4 in which the preliminary annealing process was omitted for the hot-rolled material subjected to single-plate hot rolling, it can be confirmed that the iron loss (W 10 / 400 ) value exceeds 14.0 W / kg. On the contrary, in the case of Experimental Example 2 in which the hot-rolled material subjected to single-plate hot rolling was subjected to preliminary annealing treatment, it can be confirmed that the iron loss (W 10 / 400 ) value is 14.0 W / kg or less. In the case of Experimental Examples 3 and 5 to which the manufacturing method of the non-oriented electromagnetic steel sheet according to the embodiment of the present application described with reference to FIGS. 1 and 2 was applied, although the double hot rolling process was applied, the preliminary annealing process was omitted, but the iron loss (W 10 / 400 ) is 14.0 W / kg or less and the magnetic flux density (B 50It can be confirmed that it has . In particular, compared with Experimental Example 1 and Experimental Example 4 where the preliminary annealing was omitted, the reason for the improvement in magnetic flux density is that the asymmetric rolling effect occurs due to double hot rolling, and shear strain acts on the internal structure of the hot-rolled material, improving the magnetic flux density by dynamic recrystallization.

[0077] According to Experimental Example 3 and Experimental Example 5, it was confirmed that a manufacturing method of a non-oriented electromagnetic steel sheet with excellent magnetic flux density can be realized even if the preliminary annealing process is omitted by laminating two rough-rolled slabs and performing double hot rolling to generate shear strain up to the central layer.

[0078] Figure 4 is an image of the hot-rolled structure analyzed after hot rolling in Experimental Example 3 to which the manufacturing method of the non-oriented electromagnetic steel sheet according to the embodiment of the present invention was applied. (a) in Figure 4 is an image of the cross-section of the steel sheet cut in the longitudinal direction parallel to the casting direction, analyzing the hot-rolled structure, and (b) in Figure 4 is an image of the cross-section of the steel sheet cut in the thickness direction perpendicular to the casting direction, analyzing the hot-rolled structure. The area indicated by the red dotted line in (a) of Figure 4 is the area showing the internal structure of the central layer of the first steel material and the second steel material, respectively.

[0079] Referring to Figure 4, by generating shear strain up to the center of the laminated structure during double hot rolling, since the driving force for dynamic recrystallization is sufficient, it can be confirmed that a recrystallized hot-rolled structure appears after hot rolling. Therefore, it can be understood that a separate preliminary annealing process is not necessary.

[0080] Figure 5 is an image of the hot-rolled structure analyzed after hot rolling in Experimental Example 1 to which the manufacturing method of the non-oriented electromagnetic steel sheet according to the comparative example of the present invention was applied. (a) in Figure 5 is an image of the cross-section of the steel sheet cut in the longitudinal direction parallel to the casting direction, analyzing the hot-rolled structure, and (b) in Figure 5 is an image of the cross-section of the steel sheet cut in the thickness direction perpendicular to the casting direction, analyzing the hot-rolled structure. The area indicated by the red dotted line in (a) of Figure 5 is the area showing the internal structure of the central layer of a single steel material (single plate).

[0081] Referring to Fig. 5, when performing single-plate hot rolling by a normal process, shear strain occurs only in the surface layer due to symmetrical rolling, while only plane strain is applied in the internal structure, and the driving force for dynamic recrystallization is insufficient. Therefore, it can be confirmed that the cast structure extended to the central layer remains. Thus, it can be understood that a preliminary annealing process is necessary to eliminate such a cast structure.

[0082] The single-plate hot-rolled material (normal process) performs preliminary annealing to develop the {100} plane in order to obtain a dynamic recrystallized structure in the internal structure. However, for the hot-rolled material (example) subjected to double hot rolling, dynamic recrystallization occurs in the internal structure of the central layer of the laminated structure due to double hot rolling, so the preliminary annealing can be omitted.

[0083] In the final product, it was confirmed that although it has an iron loss similar to that of the single-plate product obtained by preliminary annealing, the product manufactured according to the present invention has a magnetic flux density improved compared to that of the product from which the preliminary annealing (APL) was omitted. Therefore, it has the advantageous effect that the multi-layer configured in a double layer can be manufactured more simply than in the prior art, and the preliminary annealing process can be omitted.

[0084] In the above, the embodiments of the present invention have been mainly described, but various changes and modifications can be made at the level of those skilled in the art. As long as such changes and modifications do not depart from the scope of the present invention, it can be said that they belong to the present invention. Therefore, the scope of the rights of the present invention must be determined by the appended claims.

Claims

1. A step of performing first hot rolling on a first steel material and a second steel material containing silicon (Si), manganese (Mn), and aluminum (Al) respectively; A step of forming a first laminated structure by laminating the first steel material and the second steel material that have been first hot rolled; A step of performing second hot rolling on the first laminated structure to form a second laminated structure; A step of performing cold rolling on the second laminated structure to form a third laminated structure; A method for manufacturing a non-oriented electrical steel sheet, comprising a step of performing cold rolling annealing treatment on the third laminated structure.

2. After the step of performing the first hot rolling, and before the step of forming the first laminated structure, the method further includes a step of removing a scale layer formed on the surfaces of the first steel material and the second steel material that have been first hot rolled, according to the method for manufacturing a non-oriented electrical steel sheet described in Claim 1.

3. The step of performing the first hot rolling includes a step of performing rough rolling under the conditions of reheating temperature (SRT): 1000 - 1200 °C, finish rough rolling temperature (RDT): 800 - 900 °C, according to the method for manufacturing a non-oriented electrical steel sheet described in Claim 1.

4. The step of performing the second hot rolling includes a step of performing hot rolling under the conditions of reheating temperature (SRT): 1100 - 1200 °C, finish rolling temperature (FDT): 800 - 1000 °C, coiling temperature (CT): 560 - 600 °C, according to the method for manufacturing a non-oriented electrical steel sheet described in Claim 1.

5. The thicknesses of the first steel material and the second steel material that have been first hot rolled are each 100 - 150 mm, The thickness of the second laminated structure that has been second hot rolled is 1.6 - 2.6 mm, The thickness of the third laminated structure that has been cold rolled is 0.25 - 0.60 mm, according to the method for manufacturing a non-oriented electrical steel sheet described in Claim 1.

6. The step of performing cold rolling annealing treatment includes a step of annealing under the conditions of heating rate: 10 °C / s or more, annealing start temperature: 900 - 1100 °C, holding time: 30 - 90 seconds, and a step of cooling under the condition of cooling rate: 30 °C / s or more, according to the method for manufacturing a non-oriented electrical steel sheet described in Claim 1.

7. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the first steel material and the second steel material each contain silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): more than 0 and 0.5% by weight or less, aluminum (Al): 0.5 to 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities.

8. The cold-rolled and annealed third laminate has an iron loss (W １０／４００ ), and a magnetic flux density (B ５０ ) of 1.6 T or more, and is characterized by the method for manufacturing a non-oriented electrical steel sheet according to claim 1.

9. A non-oriented electrical steel sheet comprising a laminated structure of steel materials containing silicon (Si), manganese (Mn), and aluminum (Al), wherein the laminated structure is realized by laminating a first hot-rolled first steel material and a second steel material, and then sequentially performing a second hot rolling, a cold rolling, and a cold rolling annealing treatment.

10. The non-oriented electrical steel sheet according to claim 9, wherein the first steel material and the second steel material each contain silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): more than 0 and 0.5% by weight or less, aluminum (Al): 0.5 to 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities.

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