Non-oriented electrical steel sheet and method for producing same

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention is a non-oriented electrical steel sheet comprising more than 0 wt% and 0.003 wt% or less of carbon (C), 2.0 wt% to 4.0 wt% of silicon (Si), 0.1 wt% to 0.5 wt% of manganese (Mn), 0.3 wt% to 0.9 wt% of aluminum (Al), more than 0 wt% and 0.015 wt% or less of phosphorus (P), and the balance of iron and unavoidable impurities. The present invention relates to a steel sheet having a final microstructure satisfying inequality 1, inequality 1: 0.00172 [A]-0.0266 [B] lt, and a final microstructure satisfying the inequality 1: 0.00172 [A]-0.0266 [B] lt, and a final microstructure satisfying the inequality 1: 0.00172 [A]-0.0266 [B] lt, and a final microstructure satisfying the inequality 1: 0.00172 [A]-0.0266 [B] lt, and a final microstructure satisfying the inequality 1: 0.00172 [A]-0.0266 [B] lt, and a final microstructure satisfying the inequality 1: 0.00172 [A]-0.0266 [B] lt. (In the formula, [A] represents the average number of secondary phase particles in a cross-section of a steel sheet having an area of 10 * 10mm2, and [B] represents the volume fraction (unit:%) of particles having an average size of 2 [mu] m or more among the secondary phase particles.

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 with improved magnetic properties 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 based on their magnetic properties. Oriented electrical steel sheets exhibit excellent magnetic properties, particularly in the rolling direction of the steel sheet, because they are manufactured to be easily magnetized in the rolling direction. Therefore, they are mostly used as core materials for large, medium, and small transformers, which require low iron loss and high magnetic permeability. On the other hand, non-oriented electrical steel sheets have uniform magnetic properties regardless of the orientation of the steel sheet and are therefore commonly used as core materials for small motors, small power transformers, stabilizers, and the like. Currently, in order to comply with the trend of improving the efficiency and reducing the size of electrical equipment to enhance energy conservation, research is underway to minimize the iron loss of non-oriented electrical steel sheets. For example, due to regulations aimed at reducing carbon dioxide (CO2) emissions to combat global warming, existing internal combustion engine vehicles are rapidly being replaced by electric vehicles (EVs). Since EVs generate high torque at low speeds or under acceleration conditions and operate at high speeds (e.g., 200 Hz or higher) when traveling at constant or high speeds, non-oriented electrical steel sheets used as motor core materials need to meet both high magnetic flux density and low iron loss.

[0003] Related art includes Korean Patent Publication No. 2015-0001467A. Summary of the Invention

[0004] Technical issues

[0005] The present invention provides a non-oriented electrical steel sheet that satisfies both high magnetic flux density and low iron loss.

[0006] However, the above description is only 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 nonoriented electrical steel sheet comprising: greater than 0 wt% and not more than 0.003 wt% of carbon (C), 2.0 wt% to 4.0 wt% of silicon (Si), 0.1 wt% to 0.5 wt% of manganese (Mn), 0.3 wt% to 0.9 wt% of aluminum (Al), greater than 0 wt% and not more than 0.015 wt% of phosphorus (P), greater than 0 wt% and not more than 0.003 wt% of sulfur (S), greater than 0 wt% and not more than 0.003 wt% of nitrogen (N), greater than 0 wt% and not more than 0.003 wt% of titanium (Ti), and the balance being iron (Fe) and other unavoidable impurities, wherein a final microstructure of the nonoriented electrical steel sheet satisfies Inequality 1.

[0009] Inequality 1: 0.00172[A]-0.0266[B]<2.0

[0010] (where [A] represents the area of ​​10×10mm 2 [B] represents the volume fraction of the secondary phase particles with an average size of 2 μm or more in the cross section of the steel plate.

[0011] The electrical steel sheet may have a thickness of 0.25 mm to 0.35 mm, a magnetic flux density (B 50 ) and iron loss of 12.5W / kg or less (W 10 / 400 ).

[0012] The non-oriented electrical steel sheet may have an average grain size of 80 to 150 micrometers.

[0013] According to another aspect of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet, the method comprising: (a) providing a steel material consisting of: greater than 0 wt% and not more than 0.003 wt% of carbon (C), 2.0 wt% to 4.0 wt% of silicon (Si), 0.1 wt% to 0.5 wt% of manganese (Mn), 0.3 wt% to 0.9 wt% of aluminum (Al), greater than 0 wt% and not more than 0.015 wt% of phosphorus (P), greater than 0 wt% and not more than 0.003 wt% of sulfur (S), more than 0 wt% and not more than 0.003 wt% of nitrogen (N), more than 0 wt% and not more than 0.003 wt% of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities; (b) hot rolling the steel; (c) performing primary annealing on the hot rolled steel in a coiled state without cooling to room temperature after coiling; (d) cold rolling the steel after the primary annealing; and (e) cold annealing the cold rolled steel.

[0014] (c) may include coiling at a coiling temperature (CT) of 550° C. to 650° C., and annealing at 850° C. to 950° C. for 10 hours to 30 hours.

[0015] The primary annealing can be performed in a batch annealing furnace (BAF) instead of an annealing and pickling line (APL).

[0016] The hot rolling may include reheating the steel at a slab reheating temperature (SRT) of 1110°C to 1150°C and hot rolling the steel at a finishing outlet temperature (FDT) of 860°C to 900°C.

[0017] The cold annealing 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 120 seconds, and cooling at a cooling rate of 20° C. / s or more.

[0018] The final microstructure obtained after performing (a) to (e) satisfies Inequality 1.

[0019] Inequality 1: 0.00172[A]-0.0266[B]<2.0

[0020] (where [A] represents the area of ​​10×10mm 2 [B] represents the volume fraction of the secondary phase particles with an average size of 2 μm or more in the cross section of the steel plate.

[0021] Beneficial effects

[0022] According to the embodiments of the present invention, a non-oriented electrical steel sheet satisfying both high magnetic flux density and low iron loss and a method for manufacturing the same can be provided.

[0023] However, the scope of the present invention is not limited to the above-mentioned effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] 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. DETAILED DESCRIPTION

[0025] The non-oriented electrical steel sheet and the method for manufacturing the same according to the embodiment of the present invention will now be described in detail. The terms used herein are selected according to their functions in the present invention, and the definitions of these terms should be taken in conjunction with the context of the entire specification.

[0026] Generally speaking, factors such as chemical composition, steel sheet thickness, microstructure, insulation coating, and texture all affect the magnetic properties of non-oriented electrical steel sheet. These various factors are influenced by the process conditions used to manufacture non-oriented electrical steel sheet. The manufacturing process for non-oriented electrical steel sheet is as follows: steelmaking / continuous casting → hot rolling → heat treatment → cold rolling → heat treatment and coating. These process conditions can be individually optimized to produce electrical steel sheet with excellent magnetic properties.

[0027] Non-oriented electrical steel sheets are commonly used as materials for transformers and rotating machinery (such as motors). Currently, due to environmental concerns, there is an increasing demand for environmental protection and improved energy efficiency. In particular, the automotive industry is transitioning from internal combustion engine vehicles to electric vehicles (EVs) and hybrid electric vehicles (HEVs). To improve the efficiency of EV motors, there is a growing demand for improved magnetic properties of non-oriented electrical steel sheets. Non-oriented electrical steel sheets are required to exhibit magnetic properties with high magnetic flux density and low iron loss.

[0028] In order to reduce the iron loss of non-oriented electrical steel sheets, the thickness of the steel sheets needs to be reduced or the resistivity of the steel sheets needs to be increased. In order to reduce the thickness of the steel sheets, advanced manufacturing technology is required, but this will lead to a decrease in productivity during the process. In addition, the cost of processing and lamination in the production of motor cores will also increase. In order to increase the resistivity of the steel sheets, high alloy elements such as silicon (Si), aluminum (Al) and manganese (Mn) can be added. However, the addition of such alloy elements complicates cold rolling. For example, in the ordinary electrical steel sheet process, when the Si content exceeds 3.5 wt%, fracture occurs during the cold rolling process, so component control is required. In the non-oriented electrical steel sheet process, when the Si content is greater than 3.5 wt%, the resistivity may not exceed 60 μΩ·cm.

[0029] To achieve the high magnetic flux density, low iron loss, and improved resistivity required for non-oriented electrical steel sheets for high-efficiency electric vehicles, optimal alloy control and advanced processing technology are required.

[0030] In terms of optimal alloy control, Si, Al, and Mn are the main alloying elements used to increase resistivity. In addition to these elements, elements that improve cold rollability, such as chromium (Cr), copper (Cu), and nickel (Ni), are also considered. However, these elements can alter magnetic and mechanical properties, making it difficult to find optimal conditions.

[0031] Regarding the manufacturing process of non-oriented electrical steel sheets, it is well known that achieving high magnetic flux density and low iron loss in non-oriented electrical steel sheets containing more than 3% Si requires the use of an annealing and pickling line (APL) process. Although the texture can be improved by controlling the heating rate, the magnetic properties deteriorate due to microstructural inhomogeneities. Therefore, microstructural control of the hot-rolled structure, starting with the APL process as an intermediate process, is crucial.

[0032] In the present invention, a non-oriented electrical steel sheet capable of achieving high magnetic flux density and low iron loss by controlling the microstructure of a thermally annealed material under process conditions that can be mass-produced and a method for manufacturing the same will be described.

[0033] A non-oriented electrical steel sheet having improved magnetic properties and a method of manufacturing the same will now be described in detail.

[0034] steel plate

[0035] The non-oriented electrical steel sheet according to the embodiment of the present invention contains: carbon (C) of greater than 0 wt% and not more than 0.003 wt%, silicon (Si) of 2.0 wt% to 4.0 wt%, manganese (Mn) of 0.1 wt% to 0.5 wt%, aluminum (Al) of 0.3 wt% to 0.9 wt%, phosphorus (P) of greater than 0 wt% and not more than 0.015 wt%, sulfur (S) of greater than 0 wt% and not more than 0.003 wt%, nitrogen (N) of greater than 0 wt% and not more than 0.003 wt%, titanium (Ti) of greater than 0 wt% and not more than 0.003 wt%, and the balance of iron (Fe) and other inevitable impurities. The functions and contents of the components contained in the non-oriented electrical steel sheet will now be described.

[0036] C: greater than 0 wt% and not more than 0.003 wt%

[0037] Carbon (C) is an element that increases iron loss by forming carbides such as TiC and NbC. The less C content, the better. The C content is limited to 0.003% by weight or less. When the C content exceeds 0.003% by weight, magnetic aging occurs, deteriorating magnetic properties. However, when the C content is 0.003% by weight or less, magnetic aging is suppressed.

[0038] Silicon: 2.0 wt% to 4.0 wt%

[0039] Si is a primary element added as a component to reduce eddy current loss by increasing resistivity. When the Si content is less than 2.0 wt%, achieving the desired low iron loss is difficult, and increasing the Si content reduces magnetic permeability and magnetic flux density. When the Si content exceeds 4.0 wt%, brittleness increases, making cold rolling difficult and reducing productivity.

[0040] Mn: 0.1 wt% to 0.5 wt%

[0041] Mn, along with Si, increases resistivity and improves texture. When the Mn content is less than 0.1% by weight, fine MnS precipitates form, inhibiting grain growth. However, when Mn is added in excess of 0.5% by weight, coarse MnS precipitates form, leading to deterioration in magnetic properties, such as reduced magnetic flux density. Furthermore, when the Mn content exceeds 0.5% by weight, the reduction in iron loss is minimal compared to the added amount, and cold rolling properties significantly deteriorate.

[0042] Al: 0.3 wt% to 0.9 wt%

[0043] Al is a major element added along with Si as a component that reduces eddy current loss by increasing resistivity. Al, when combined with N, induces the precipitation of AlN. When the Al content is less than 0.3% by weight, the aforementioned effects may be less likely to be expected. However, when the Al content exceeds 0.9% by weight, cold rolling properties deteriorate, and the magnetic flux density decreases, degrading magnetic properties.

[0044] P: greater than 0 wt% and not more than 0.015 wt%

[0045] P is an element that develops texture as a grain boundary segregation element. When the P content exceeds 0.015 wt%, grain growth is inhibited, magnetic properties deteriorate, and cold rolling properties are reduced due to segregation effects.

[0046] S: greater than 0 wt% and not more than 0.003 wt%

[0047] S increases iron loss and inhibits grain growth by forming precipitates such as MnS and CuS, so the less the better. The S content is limited to 0.002 wt% or less. When the S content exceeds 0.003 wt%, iron loss increases.

[0048] N: greater than 0 wt% and not more than 0.003 wt%

[0049] Nitrogen increases iron loss and inhibits grain growth by forming precipitates such as AlN, TiN, and NbN, so the less the better. The N content is limited to 0.003 wt% or less. When the N content exceeds 0.003 wt%, iron loss increases.

[0050] Ti: greater than 0 wt% and not more than 0.003 wt%

[0051] Ti inhibits grain growth by forming fine precipitates such as TiC and TiN. Ti deteriorates magnetic properties, so the less the better. The Ti content is limited to 0.003 wt% or less. When the Ti content exceeds 0.003 wt%, magnetic properties deteriorate.

[0052] The final microstructure of the non-oriented electrical steel sheet according to the embodiment of the present invention having the above-mentioned alloy element composition satisfies Inequality 1.

[0053] Inequality 1: 0.00172[A]-0.0266[B]<2.0,

[0054] Where [A] represents the area of ​​10×10mm 2 [B] represents the volume fraction (in %) of the secondary phase particles with an average size of 2 μm or larger in the steel plate cross section. In the final microstructure, the secondary phase particles may include inclusion particles and / or precipitate particles.

[0055] The non-oriented electrical steel sheet according to the embodiment of the present invention having the above-mentioned composition may have a thickness of 0.25 mm to 0.35 mm, a magnetic flux density (B 50 ) and an iron loss of 12.5W / kg or less (W 10 / 400 The non-oriented electrical steel sheet may have an average particle size of 80 μm to 150 μm. The non-oriented electrical steel sheet may also have the following mechanical properties: a yield point (YP) of 400 MPa or greater and a tensile strength (TS) of 500 MPa or greater.

[0056] A method of manufacturing the non-oriented electrical steel sheet according to an embodiment of the present invention having the above-mentioned composition and properties will now be described.

[0057] Method for manufacturing non-oriented electrical steel sheet

[0058] 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.

[0059] Reference Figure 1 , a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: (a) providing a steel material composed of: greater than 0 wt% and not more than 0.003 wt% of C, 2.0 wt% to 4.0 wt% of Si, 0.1 wt% to 0.5 wt% of Mn, 0.3 wt% to 0.9 wt% of Al, greater than 0 wt% and not more than 0.015 wt% of P, greater than 0 wt% and not more than 0.003 wt% of S, greater than 0 wt% and not more than 0.015 wt% of P, greater than 0 wt% and not more than 0.003 wt% of S, greater than 0 wt% and not more than 0.015 wt% of % and not more than 0.003 wt % of N, greater than 0 wt % and not more than 0.003 wt % of Ti, and the balance of Fe and other inevitable impurities (S10); (b) hot rolling the steel (S20); (c) performing primary annealing on the hot-rolled steel in a coiled state that has not been cooled to room temperature after coiling (S30); (d) cold rolling the steel after the primary annealing (S40); and (e) cold annealing the cold-rolled steel (S50).

[0060] In the step of providing the steel material (S10), the composition of the steel material has been described in detail above. The steel material may have a slab shape.

[0061] The step of hot rolling the steel ( S20 ) may include reheating the steel at a slab reheating temperature (SRT) of 1110° C. to 1150° C. and hot rolling the steel at a finishing outlet temperature (FDT) of 860° C. to 900° C.

[0062] When the SRT is higher than 1150°C, precipitates such as C, S, and N in the slab may redissolve, and fine precipitates may form during subsequent rolling and annealing processes, thereby inhibiting grain growth and deteriorating magnetic properties. When the SRT is lower than 1110°C, the rolling load may increase.

[0063] The steel material after hot rolling can have a thickness of 1.8 mm to 2.6 mm. Since the reduction rate of cold rolling increases and the texture deteriorates when the hot-rolled plate is thicker, the thickness can be controlled to 2.6 mm or less.

[0064] The step (S30) of performing a primary annealing on the hot-rolled steel material in a coiled state that has not been cooled to room temperature after coiling can include coiling at a coiling temperature (CT) of 550°C to 650°C and annealing at 850°C to 950°C for 10 to 30 hours. After annealing, the steel sheet is cooled to room temperature. Prior to the subsequent cold rolling process, an acid pickling solution is used to remove the oxide layer formed on the surface of the steel sheet that has been cooled to room temperature.

[0065] When CT is below 550°C, recovery and recrystallization are insufficient, resulting in excessive dislocation density and accumulated energy. However, when CT is above 650°C, excessive oxidation occurs during cooling due to high Si, Al, and Mn contents, potentially deteriorating pickling properties. Furthermore, recovery and recrystallization occur sufficiently, reducing dislocation density and accumulated energy, leading to poor microstructure and texture after APL.

[0066] When batch annealing (BAF) is performed after coiling and cooling to room temperature, a large amount of fine precipitates form at low temperatures during the cooling process to room temperature after coiling, which affects subsequent processes and deteriorates magnetic properties. Meanwhile, when BAF annealing is performed without cooling to room temperature after coiling, the ratio of coarse precipitates is expected to be high because annealing is performed before fine precipitates form.

[0067] Meanwhile, when the annealing temperature is lower than 850°C, or when the annealing temperature is within the appropriate range of 850°C to 950°C but the annealing time is shorter than 10 hours, fine inclusions such as carbides and nitrides form in the surface layer of the steel sheet, and the inclusions do not grow sufficiently, resulting in poor magnetic properties of the final product. Furthermore, insufficient grain growth leads to the formation of fine grains, which in turn deteriorates the magnetic properties of the final product.

[0068] On the other hand, when the annealing temperature is higher than 950°C or when the annealing temperature is within the appropriate range of 850°C to 950°C but the annealing time is longer than 30 hours, inclusions are unevenly distributed, grains grow excessively resulting in significant variations in grain size, and oxidation occurs extensively, thereby adversely affecting the final product.

[0069] Meanwhile, according to a comparative embodiment of the present invention, the APL process of annealing and pickling a hot-rolled plate may include annealing under conditions of a heating rate of 20° C. / s or more, an annealing temperature of 950° C. to 1100° C., and a holding time of 30 seconds to 120 seconds, cooling under conditions of a cooling rate of 30° C. / s or more, and pickling.

[0070] The method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention is characterized in that primary annealing is performed in a batch annealing furnace (BAF) rather than in a continuous annealing system of annealing and pickling (eg, APL).

[0071] In the BAF process, where the steel is inserted into a furnace and processed in a coiled state, the entire coil is heated simultaneously, which can lead to material inhomogeneities due to temperature differences between the inside and outside of the coil. Therefore, relatively long heat treatment times can be used to minimize these temperature differences. The BAF process can be performed in a 100% nitrogen atmosphere.

[0072] Meanwhile, the BAF process has the advantage that heat treatment conditions such as temperature and time during the heating, holding and cold annealing processes can be optimized according to the required properties, and production costs and steel plate oxidation can be reduced compared with continuous annealing processes such as APL or ACL.

[0073] The cold rolling step (S40) may include cold rolling at a reduction ratio of 80% to 85%, and the thickness of the cold-rolled steel may be 0.35 mm or less. The cold rolling process may include finally cold rolling the pickled hot-rolled sheet to a thickness of greater than or equal to 0.25 mm and less than or equal to 0.35 mm. To improve rollability, the sheet temperature may be raised to 150°C to 200°C for hot rolling.

[0074] The cold annealing step (S50) is an annealing and coating line (ACL) process for performing final annealing on the cold-rolled sheet, and may include annealing under the conditions of a heating rate of 10°C / s or greater, an annealing temperature of 900°C to 1100°C, and a holding time of 30 seconds to 120 seconds, and cooling under the conditions of a cooling rate of 20°C / s or greater.

[0075] The cold-rolled sheet obtained after cold rolling is cold annealed. A temperature that achieves the optimal grain size is selected, taking into account iron loss reduction and mechanical properties. Heating is performed under mixed atmosphere conditions to prevent surface oxidation and nitration during cold annealing. A mixed atmosphere of nitrogen and hydrogen is used to further smooth the surface. Cold annealing temperatures below 900°C may result in the formation of fine grains, increasing hysteresis loss, while temperatures above 1100°C may lead to the formation of coarse grains, increasing eddy current loss.

[0076] After the final annealing, a coating process may be performed to improve punchability and ensure insulation.

[0077] The final microstructure of the nonoriented electrical steel sheet manufactured by performing the above steps satisfies Inequality 1.

[0078] Inequality 1: 0.00172[A]-0.0266[B]<2.0,

[0079] Where [A] represents the area of ​​10×10mm 2 [B] represents the volume fraction (in %) of the secondary phase particles with an average size of 2 μm or larger in the steel plate cross section. In the final microstructure, the secondary phase particles may include inclusion particles and / or precipitate particles.

[0080] The non-oriented electrical steel sheet manufactured by performing the above steps may have a thickness of 0.25 mm to 0.35 mm, a magnetic flux density (B 50 ) and an iron loss of 12.5W / kg or less (W 10 / 400 The non-oriented electrical steel sheet may have an average grain size of 80 μm to 150 μm. The non-oriented electrical steel sheet may also have the following mechanical properties: YP of 400 MPa or greater and TS of 500 MPa or greater.

[0081] Test Examples

[0082] Test Examples will now be described for a better understanding of 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.

[0083] 1. Sample composition

[0084] The samples provided in this test example have the alloy element composition shown in Table 1 (unit: weight %).

[0085] [Table 1]

[0086] C Si Mn Al P S N Ti margin 0.0019 3.31 0.32 0.77 0.0055 0.0015 0.0017 0.0012 Fe

[0087] % and no more than 0.003 wt % of C, 2.0 to 4.0 wt % of Si, 0.1 to 0.5 wt % of Mn, 0.3 to 0.9 wt % of Al, more than 0 to 0.015 wt % of P, more than 0 to 0.003 wt % of S, more than 0 to 0.003 wt % of N, more than 0 to 0.003 wt % of Ti, and the balance of Fe.

[0088] 2. Process conditions and performance evaluation

[0089] Table 2 shows the process conditions and properties of a non-oriented electrical steel sheet produced in a test example according to the present invention. Slabs having the composition shown in Table 1 were reheated to 1140°C and hot rolled at an FDT of 880°C to produce hot-rolled sheets with a thickness of 2.0 mm. After hot rolling, heat treatment was performed continuously under the various temperature conditions shown in Table 2. Cold rolling was then performed to produce cold-rolled sheets with a thickness of 0.25 mm, followed by final annealing at 975°C for 50 seconds. A coating process was then performed to produce the final product. Final annealing was performed in a mixed atmosphere of 30% hydrogen and 70% nitrogen. In this example, a heating rate of 20°C / s and a cooling rate of 30°C / s were used. The distribution of inclusions in the final annealed material of each sample was observed. Iron loss and magnetic flux density values ​​in the L direction, parallel to the rolling direction, and the C direction, perpendicular to the rolling direction, were measured using a single sheet tester (SST) and averaged to obtain the magnetic properties of the final product.

[0090] In Table 2, the Z value is calculated as 0.00172×[A]-0.0266×[B], where [A] is an indicator of the total number of inclusions in the final annealed material and represents an area of ​​10×10 mm. 2 The average number of secondary phase particles in the cross section of the steel plate, [B] is an indicator of the volume fraction of coarse inclusions, and represents the volume fraction value (unit: %) of particles with an average size of 2 μm or larger in the secondary phase particles.

[0091] [Table 2]

[0092]

[0093]

[0094] Test Examples 4, 7 and 10 according to embodiments of the present invention were Figure 1 The BAF annealing step (S30) satisfies the annealing conditions of 850°C to 950°C and 10 hours to 30 hours. In this case, it is shown that the Z value is less than 2 and the iron loss (W 10 / 400 ) is 12.5W / kg or less.

[0095] On the other hand, Test Examples 1 and 2 Figure 1 The BAF annealing step (S30) is lower than and does not meet the annealing temperature range of 850°C to 950°C. In Test Example 12, Figure 1 The BAF annealing step (S30) of the embodiment 3, 6 and 9 exceeds and does not meet the annealing temperature range of 850°C to 950°C. Figure 1 The BAF annealing step (S30) satisfies the annealing temperature range of 850°C to 950°C, but is lower than and does not meet the annealing time of 10 hours to 30 hours. Figure 1 The BAF annealing step (S30) satisfies the annealing temperature range of 850° C. to 950° C., but exceeds and does not satisfy the annealing time of 10 hours to 30 hours.

[0096] In short, the average number of secondary phase particles was higher in Test Examples 1, 2, 3, 5, 6, 8, 9, 11, and 12 compared to the embodiment (i.e., Test Examples 4, 7, and 10). In addition, Test Examples 1, 2, and 12, which did not meet the annealing temperature range of 850° C. to 950° C., had a lower volume fraction of particles having an average size of 2.0 μm or more in the secondary phase particles than in the embodiment (i.e., Test Examples 4, 7, and 10).

[0097] According to the comparative examples of the present invention, test examples 1, 2, 3, 5, 6, 8, 9, 11 and 12 showed a Z value greater than 2 and an iron loss (W greater than 12.5 W / kg). 10 / 400 ).

[0098] For example, when comparing Test Example 8 with Test Example 10, it can be seen that even if [B] (which represents the volume fraction of particles with an average size of 2 μm or more in the secondary phase particles) is the same, when [A] (which is an indicator of the number of inclusions in the final annealed material and represents an area of ​​10×10 mm 2 When the average number of secondary phase particles in the cross section of the steel plate is low, the Z value will drop below 2, and the iron loss (W 10 / 400 )reduce.

[0099] Comparing Test Example 11 with Test Example 10, it can be seen that even if [A] (which is an indicator of the number of inclusions in the final annealed material and represents an area of ​​10×10 mm 2 However, when [B] (which is an indicator of the volume fraction of coarse inclusions and represents the volume fraction of secondary phase particles with an average size of 2 μm or more) is high, the Z value drops below 2 and the iron loss (W 10 / 400 )reduce.

[0100] The non-oriented electrical steel sheet and the method for manufacturing the same according to the technical features of the present invention have been described above. The above description shows that by performing the thermal annealing process in a BAF rather than a continuous annealing system (e.g., APL) and by appropriately controlling the temperature and holding time during the manufacturing process of the non-oriented electrical steel sheet, the microstructure can be controlled and the magnetic properties of the final annealed material can be improved.

[0101] 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 claims.

Claims

1. A nonoriented electrical steel sheet comprising: carbon (C) in an amount greater than 0 wt % and not more than 0.003 wt %, silicon (Si) in an amount ranging from 2.0 wt % to 4.0 wt %, manganese (Mn) in an amount ranging from 0.1 wt % to 0.5 wt %, aluminum (Al) in an amount ranging from 0.3 wt % to 0.9 wt %, phosphorus (P) in an amount greater than 0 wt % and not more than 0.015 wt %, sulfur (S) in an amount greater than 0 wt % and not more than 0.003 wt %, nitrogen (N) in an amount greater than 0 wt % and not more than 0.003 wt %, titanium (Ti) in an amount greater than 0 wt % and not more than 0.003 wt %, and the balance being iron (Fe) and other unavoidable impurities, in, The final microstructure of the non-oriented electrical steel sheet satisfies Inequality 1, Inequality 1: 0.00172[A]-0.0266[B]<2.0, (where [A] represents the area of ​​10×10mm 2 [B] represents the average number of secondary phase particles in the cross section of the steel plate, and [B] represents the volume fraction of particles with an average size of 2 μm or more in the secondary phase particles (unit: %)).

2. The non-oriented electrical steel sheet according to claim 1, wherein: The thickness of the electrical steel sheet is 0.25 mm to 0.35 mm, and the magnetic flux density (B 50 ) is 1.66T or greater, iron loss (W 10 / 400 ) is 12.5W / kg or less.

3. The non-oriented electrical steel sheet according to claim 1, wherein: The average particle size of the non-oriented electrical steel sheet is 80 micrometers to 150 micrometers.

4. A method for manufacturing a non-oriented electrical steel sheet, the method comprising: (a) providing a steel material composed of more than 0 wt% and not more than 0.003 wt% of carbon (C), 2.0 wt% to 4.0 wt% of silicon (Si), 0.1 wt% to 0.5 wt% of manganese (Mn), 0.3 wt% to 0.9 wt% of aluminum (Al), more than 0 wt% and not more than 0.015 wt% of phosphorus (P), more than 0 wt% and not more than 0.003 wt% of sulfur (S), more than 0 wt% and not more than 0.003 wt% of nitrogen (N), more than 0 wt% and not more than 0.003 wt% of titanium (Ti), and the balance of iron (Fe) and other inevitable impurities; (b) hot rolling the steel; (c) performing primary annealing on the hot-rolled steel material in a coiled state without cooling to room temperature after coiling; (d) cold rolling the steel after primary annealing; and (e) The cold-rolled steel is cold annealed.

5. The method according to claim 4, wherein: (c) comprising coiling at a coiling temperature (CT) of 550° C. to 650° C., and annealing at 850° C. to 950° C. for 10 hours to 30 hours.

6. The method according to claim 4, wherein: The primary annealing is carried out in a batch annealing furnace (BAF) rather than in an annealing and pickling line (APL).

7. The method according to claim 4, wherein: The hot rolling includes reheating the steel at a slab reheating temperature (SRT) of 1110° C. to 1150° C., and hot rolling the steel at a finishing outlet temperature (FDT) of 860° C. to 900° C.

8. The method according to claim 4, wherein: The cold annealing includes 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 120 seconds, and cooling at a cooling rate of 20° C. / s or more.

9. The method according to claim 4, wherein: The final microstructure obtained after performing (a) to (e) satisfies Inequality 1, Inequality 1: 0.00172[A]-0.0266[B]<2.0, (where [A] represents the area of ​​10×10mm 2 [B] represents the average number of secondary phase particles in the cross section of the steel plate, and [B] represents the volume fraction of particles with an average size of 2 μm or more in the secondary phase particles (unit: %)).

Images