Non-oriented electrical steel sheet, manufacturing method for manufacturing non-oriented electrical steel sheet, hearth roll, and annealing line

Abstract

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet, comprising: a hot rolling step of manufacturing a hot-rolled sheet by hot rolling a slab comprising, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities; a hot rolling annealing step of manufacturing a hot-rolled annealed sheet by hot rolling the hot-rolled sheet; and a cold rolling step of manufacturing a cold-rolled sheet by cold rolling the hot-rolled annealed sheet. A method for manufacturing a non-oriented electrical steel sheet is provided, comprising: a cold rolling annealing step of manufacturing a cold rolling annealed sheet by cold rolling annealing the cold rolling sheet; wherein the average KAM value of the non-oriented electrical steel sheet measured by EBSD is 0.4˚ or less.

Description

Technology Field

[0001] The present invention relates to a non-oriented electrical steel sheet, a method for manufacturing a non-oriented electrical steel sheet, a hearth roll, and an annealing facility. Background Technology

[0002] Due to policies aimed at reducing carbon dioxide (CO2) emissions to prevent global warming, existing internal combustion engine vehicles are being rapidly replaced by eco-friendly vehicles (hybrid vehicles (HEV), electric vehicles (EV), etc.), particularly electric vehicles (EV).

[0003] In line with the increasing demand for electric vehicles (EVs), the energy conversion efficiency of drive motors for EVs is being improved, and to this end, excellent magnetic properties of motor core materials are required.

[0004] Non-oriented electrical steel sheets used as motor core materials play a crucial role in converting electrical energy into mechanical energy in rotating machinery; to achieve energy savings, it is essential to possess magnetic properties, specifically low iron loss and high magnetic flux density. To meet these requirements, silicon (Si) content, product thickness, grain size, texture, and precipitates must be appropriately controlled.

[0005] The magnetic properties of non-oriented electrical steel sheets can deteriorate due to residual stress. If residual stress develops in non-oriented electrical steel sheets due to stress during the production process, transportation, or core processing, iron loss may increase and magnetic flux density may decrease.

[0006] Since non-oriented electrical steel sheets are thin (e.g., with a thickness of 0.62 mm), there is a high possibility that residual stress will occur during the production process. In particular, when heat treatment is performed using a continuous heat treatment method during the final heat treatment process, residual stress is applied during the movement of the steel sheet, which may cause the magnetic properties of the non-oriented electrical steel sheets to deteriorate. The problem to be solved

[0007] Embodiments of the present invention can provide a non-oriented electrical steel sheet with improved magnetic properties and a method for manufacturing the same. means of solving the problem

[0008] One embodiment of the present invention is a method for manufacturing a non-oriented electrical steel sheet, comprising: a hot rolling step of manufacturing a hot-rolled sheet by hot rolling a slab comprising, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities; and a hot rolling annealing step of manufacturing a hot-rolled annealed sheet by hot rolling annealing the hot-rolled sheet. A method for manufacturing a non-oriented electrical steel sheet is provided, comprising: a cold rolling step of manufacturing a cold-rolled sheet by cold rolling the hot-rolled annealed sheet; and a cold rolling annealing step of manufacturing a cold-rolled annealed sheet by cold rolling the cold-rolled sheet; wherein the average KAM value of the non-oriented electrical steel sheet measured by EBSD is 0.4˚ or less.

[0009] In this embodiment, the cold rolling annealing step for manufacturing a cold rolling annealed plate by cold rolling annealing the cold rolling plate can be performed under conditions of a heating rate of 10℃ / s or more, a cold rolling annealing temperature of 900℃ to 1050℃, a cold rolling annealing time of 30s to 90s, and a cooling rate of 10℃ / s or more.

[0010] In the present embodiment, the cold rolling annealing step is performed in an annealing furnace, and the cold rolled plate can be transported by a hearth roll provided in the annealing furnace.

[0011] In this embodiment, the surface roughness (Ra) of the hearth roll may be 0.1 μm to 0.2 μm.

[0012] In this embodiment, the friction coefficient of the hearth roll may be 0.05 to 0.20.

[0013] In this embodiment, the tension applied to the cold-rolled plate in the annealing furnace may be 10 MPa or less.

[0014] In this embodiment, the slab may further contain 0.005 wt% to 0.05 wt% of tin (Sn) and antimony (Sb) in total.

[0015] In this embodiment, the silicon content included in the non-oriented electrical steel sheet and the average KAM value can satisfy the relationship 1 ([Si] / [KAM] ≥ 6.0).

[0016] One embodiment of the present invention provides a non-oriented electrical steel sheet comprising, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities, wherein the average KAM value of the non-oriented electrical steel sheet measured by EBSD is 0.4˚ or less.

[0017] In this embodiment, the non-oriented electrical steel sheet may further contain 0.005 wt% to 0.05 wt% of tin (Sn) and antimony (Sb) in total.

[0018] In this embodiment, the silicon content included in the non-oriented electrical steel sheet and the average KAM value can satisfy the relationship 2 ([Si] / [KAM] ≥ 6.0).

[0019] One embodiment of the present invention provides a hearth roll that is provided in an annealing furnace and conveys a steel plate, wherein the surface roughness (Ra) of the hearth roll is 0.1 μm to 0.2 μm.

[0020] In this embodiment, the friction coefficient of the hearth roll may be 0.05 to 0.20.

[0021] In this embodiment, the tension applied to the steel plate may be 10 MPa or less.

[0022] One embodiment of the present invention provides an annealing facility comprising: an annealing furnace for heat-treating a steel plate; and a hearth roll provided inside the annealing furnace for conveying the steel plate, wherein the surface roughness (Ra) of the hearth roll is 0.1 μm to 0.2 μm.

[0023] In this embodiment, the friction coefficient of the hearth roll may be 0.05 to 0.20.

[0024] In this embodiment, the tension applied to the steel plate may be 10 MPa or less.

[0025] Other aspects, features, and advantages other than those described above will become clear from the following specific details, claims, and drawings for implementing the invention. Effects of the invention

[0026] According to one embodiment of the present invention as described above, the magnetic properties of a non-oriented electrical steel sheet can be improved. Of course, the scope of the present invention is not limited by this effect. Brief explanation of the drawing

[0027] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating an annealing facility used in a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. Specific details for implementing the invention

[0028] The present invention is capable of various modifications and may have various embodiments; specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, and the methods for achieving them, will become clear by referring to the embodiments described below in detail together with the drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various forms.

[0029] In the following embodiments, terms such as first, second, etc. are used not in a limiting sense, but for the purpose of distinguishing one component from another component.

[0030] In the following examples, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0031] In the following embodiments, terms such as "include" or "have" mean that the features or components described in the specification are present, and do not preclude the possibility that one or more other features or components may be added.

[0032] In the drawings, the size of components may be exaggerated or reduced for convenience of explanation. For example, the size and thickness of each component shown in the drawings are depicted arbitrarily for convenience of explanation, and therefore the present invention is not necessarily limited to what is illustrated.

[0033] Where an embodiment can be implemented differently, a specific process sequence may be performed differently from the order described. For example, two processes described consecutively may be performed substantially simultaneously or proceed in the reverse order of the description.

[0034] In this specification, "A and / or B" indicates the case where it is A, B, or both A and B. And, "at least one of A and B" indicates the case where it is A, B, or both A and B.

[0035] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. When describing with reference to the drawings, identical or corresponding components are given the same reference numerals, and redundant descriptions thereof will be omitted.

[0036] FIG. 1 is a flowchart schematically illustrating a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0037] Referring to FIG. 1, a method for manufacturing a non-oriented electrical steel sheet may include a hot rolling step (S100), a hot rolling annealing step (S200), a cold rolling step (S300), and a cold rolling annealing step (S400).

[0038] In the hot rolling step (S100), the slab may be reheated, then hot-rolled at a predetermined finishing rolling temperature, and then cooled and coiled. At this time, in the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, the semi-finished product subject to hot rolling may be a slab. The slab in the semi-finished product state can be obtained through a continuous casting process after obtaining molten steel of a predetermined composition through a steelmaking process.

[0039] In one embodiment, the slab may contain silicon (Si), manganese (Mn), aluminum (Al), carbon (C), phosphorus (P), sulfur (S), nitrogen (N), titanium (Ti), the remainder being iron (Fe) and unavoidable impurities. Additionally, the slab may contain at least one of tin (Sn) and antimony (Sb).

[0040] Specifically, the slab may contain, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities. Additionally, the slab may contain, in wt%, a total of 0.005 wt% to 0.05 wt% of tin (Sn) and antimony (Sb).

[0041] Silicon (Si) can be an element that increases the resistivity of the manufactured non-oriented electrical steel sheet, thereby lowering iron loss. Silicon (Si) may be included in an amount of 1.8 wt% to 2.7 wt%. If the silicon (Si) content is less than 1.8 wt%, the reduction in iron loss may be insufficient. In other words, if the silicon (Si) content is less than 1.8 wt%, it may be difficult to achieve low iron loss. On the other hand, as the silicon (Si) content increases, the permeability and magnetic flux density may decrease. If the silicon (Si) content exceeds 2.7 wt%, brittleness increases, reducing rollability and making cold rolling at room temperature impossible. For example, if the silicon (Si) content exceeds 2.7 wt%, warm rolling at 80°C to 200°C is required, which may increase process costs and consequently lower productivity.

[0042] Manganese (Mn) can increase the resistivity of non-oriented electrical steel sheets manufactured together with silicon and lower iron loss, and can form sulfur (S) and sulfide inclusions (e.g., MnS). Manganese (Mn) may be included in an amount of 0.1 wt% to 0.5 wt%. If manganese (Mn) is included in an amount less than 0.1 wt%, it may be difficult to obtain the above-mentioned effects. If manganese (Mn) is included in an amount greater than 0.5 wt%, sulfide inclusions (e.g., MnS) may precipitate finely, which may increase iron loss.

[0043] Aluminum (Al) can increase the resistivity of non-oriented electrical steel sheets manufactured together with silicon, thereby lowering iron loss, and can form nitrogen (N) and nitride inclusions (e.g., AlN). Aluminum (Al) may be included in an amount of 0.1 wt% to 0.5 wt%. If the content of aluminum (Al) is less than 0.1 wt%, the amount of aluminum (Al) added is low, resulting in insufficient resistivity and potentially increasing iron loss. On the other hand, if the content of aluminum (Al) exceeds 0.5 wt%, a large amount of nitride inclusions (e.g., AlN) may be formed, which may increase magnetic flux density.

[0044] Carbon (C) is an element that increases iron loss by forming carbides such as TiC, so it may be desirable to have a lower carbon content in the slab (or non-oriented electrical steel sheet). Carbon may be included in an amount greater than 0 and less than or equal to 0.003 wt%. If carbon is included in an amount greater than 0.003 wt%, self-aging may occur, which can degrade the magnetic properties of the manufactured non-oriented electrical steel sheet. If carbon is included in an amount less than or equal to 0.003 wt%, the self-aging phenomenon may be suppressed.

[0045] Sulfur (S) can be a component that increases iron loss and inhibits grain growth by forming precipitates such as MnS and TiS. Therefore, it may be desirable to have a low sulfur (S) content in the slab. Sulfur (S) may be included in an amount greater than 0 and less than or equal to 0.002 wt%. If sulfur (S) is included in an amount greater than 0.002 wt%, precipitates such as MnS and TiS may be formed, which may increase iron loss and inhibit grain growth.

[0046] Phosphorus (P) is a grain boundary segregation element and may be a component that develops texture. Phosphorus (P) may be included in an amount greater than 0 and less than or equal to 0.015 wt%. If phosphorus (P) is included in an amount greater than 0.015 wt%, grain growth may be inhibited due to the segregation effect, magnetic properties may be degraded, and cold rolling performance may be reduced.

[0047] Nitrogen (N) can form precipitates such as AlN and TiN, which can increase iron loss and inhibit grain growth. Therefore, it may be desirable to have a low nitrogen content in the slab. Nitrogen (N) may be included in an amount greater than 0 and less than or equal to 0.002 wt%. If nitrogen (N) is included in an amount greater than 0.002 wt%, precipitates such as AlN and TiN may be formed, which can increase iron loss and inhibit grain growth.

[0048] Titanium (Ti) can inhibit grain growth by forming fine precipitates such as TiC, TiN, and TiS. Since magnetic properties deteriorate as titanium (Ti) is added, it may be desirable to add titanium (Ti) as low as possible. Titanium (Ti) may be included in an amount greater than 0 and less than or equal to 0.002 wt%. If titanium is included in an amount greater than 0.002 wt%, it can inhibit grain growth by forming fine precipitates such as TiC, TiN, and TiS, and magnetic properties may deteriorate.

[0049] Tin (Sn) and antimony (Sb) can serve as surface precipitation elements that concentrate in the surface layer of the steel sheet to inhibit nitrogen adsorption and nitride formation, thereby reducing iron loss. Tin (Sn) and antimony (Sb) may be included in a total amount of 0.005 wt% to 0.05 wt%. If the sum of the contents of tin (Sn) and antimony (Sb) is less than 0.005 wt%, the effect of inhibiting the formation of the nitride layer may be negligible. If the sum of the contents of tin (Sn) and antimony (Sb) exceeds 0.05 wt%, the grain boundaries may become embrittled, raising concerns about fracture during cold rolling, and fatigue properties may deteriorate, potentially causing the core to fail during motor operation.

[0050] In the hot rolling step (S100), the slab can be reheated, and then the reheated slab can be hot-rolled to produce a hot-rolled plate. For example, the slab on which the hot rolling step (S100) is performed can be called a hot-rolled plate.

[0051] In the hot rolling step (S100), the slab may be reheated. Specifically, in the hot rolling step (S100), a slab having a width of 900 mm or more and a thickness of 200 mm to 300 mm may be reheated. The slab reheating temperature in the hot rolling step (S100) may be 1160°C to 1200°C. If the slab reheating temperature is less than 1160°C, it may be difficult to perform hot rolling. On the other hand, if the slab reheating temperature exceeds 1200°C, AlN may melt and finely reprecipitate in subsequent processes, which may increase iron loss. Therefore, if the slab reheating temperature in the hot rolling step (S100) satisfies 1160°C to 1200°C, a decrease in rollability can be prevented and a deterioration in magnetic properties can be prevented.

[0052] The hot rolling step (S100) can finish rolling the slab at a predetermined finish rolling temperature. At this time, the finish rolling temperature may be 850℃ to 950℃.

[0053] In addition, the hot rolling step (S100) may cool the hot-rolled slab to a predetermined coiling temperature (CT) and coil it. At this time, the coiling temperature may be 550°C to 650°C. If the coiling temperature is below 550°C, brittleness increases, and plate breakage may occur during coiling. On the other hand, if the coiling temperature exceeds 650°C, fine AlN may be formed during coiling, which may increase iron loss.

[0054] The thickness of the hot-rolled plate produced through the hot rolling step (S100) may be 1.8 mm to 2.5 mm. At this time, if the thickness of the hot-rolled plate exceeds 2.5 mm, the cold rolling reduction rate increases, which may result in a deterioration of the texture.

[0055] A hot rolling annealing step (S200) may be performed after the hot rolling step (S100). A hot-rolled plate in which the hot rolling annealing step (S200) has been performed may be called a hot-rolled annealed plate. The hot rolling annealing step (S200) may be performed under conditions where the heating rate is 10℃ / s or higher, the holding temperature (e.g., hot rolling annealing temperature) is 900℃ to 1100℃, the holding time (e.g., hot rolling annealing time) is 30s to 120s, and the cooling rate is 20℃ / s or higher. Specifically, in the hot rolling annealing step (S200), the hot rolling plate is heated at a heating rate of 10°C / s or more, the heated hot rolling plate is maintained at a temperature of 900°C to 1100°C (e.g., hot rolling annealing temperature) for a period of 30 s to 120 s (e.g., annealing), and can be cooled at a cooling rate of 20°C / s or more. At this time, the hot rolling annealing step (S200) can be performed in an atmosphere where the nitrogen fraction is 80% to 100% and the remainder is atmospheric.

[0056] A cold rolling step (S300) may be performed after the hot rolling annealing step (S200). The hot-rolled annealed plate after the cold rolling step (S300) may be called a cold-rolled plate. In the cold rolling step (S300), the hot-rolled annealed plate may be cold-rolled with a reduction rate of 72% to 86%. The thickness of the cold-rolled plate after the cold rolling step (S300) may be 0.35mm to 0.50mm.

[0057] A cold rolling annealing step (S400) may be performed after the cold rolling step (S300). A cold rolled plate in which the cold rolling annealing step (S400) has been performed may be called a cold rolling annealing plate. The cold rolling annealing step (S400) may be performed under conditions where the heating rate is 10℃ / s or higher, the holding temperature (e.g., cold rolling annealing temperature) is 900℃ to 1050℃, the holding time (e.g., cold rolling annealing time) is 30s to 90s, and the cooling rate is 10℃ / s or higher. Specifically, in the cold rolling annealing step (S400), the cold rolled plate is heated at a heating rate of 10°C / s or more, the heated cold rolled plate is maintained at a temperature of 900°C to 1050°C (e.g., cold rolling annealing temperature) for a time of 30 s to 90 s (e.g., annealing), and can be cooled at a cooling rate of 10°C / s or more. At this time, the cold rolling annealing step (S400) can be performed in an atmosphere in which the hydrogen fraction is 20% or more and the remainder is nitrogen. If the hydrogen fraction is less than 20%, nitrogen (N) may penetrate to the surface and form nitrides, which may increase iron loss.

[0058] FIG. 2 is a schematic diagram illustrating an annealing facility used in a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. Specifically, FIG. 2 is a schematic diagram illustrating an annealing facility used in a cold rolling annealing step (S400) in a method for manufacturing a non-oriented electrical steel sheet.

[0059] Referring to FIG. 2, the annealing facility (1) is for manufacturing non-oriented electrical steel sheets and may include an annealing furnace (100, e.g., a continuous heat treatment furnace) for heat treating a steel sheet (10, e.g., a cold-rolled sheet), a hearth roll (200) installed inside the annealing furnace (100) for transporting the steel sheet (10), and tension reels (300) respectively provided at the inlet and outlet sides of the annealing furnace (100).

[0060] The annealing furnace (100) is for heat treating a steel plate (10) and may be equipped with a heating zone (110), a cracking zone (120), and a cooling zone (130) according to the direction of travel (SD) of the steel plate (10). In the heating zone (110), the steel plate (10) can be heated to a cold-rolled annealing temperature at a heating rate of 10°C / s or more, in the cracking zone (120), the steel plate (10) can be maintained at the cold-rolled annealing temperature for 30 to 90 seconds, and in the cooling zone (130), the steel plate (10) can be cooled at a cooling rate of 10°C / s or more.

[0061] A hearth roll (200) for moving a steel plate (10) may be provided inside the annealing furnace (100). A plurality of hearth rolls (200) may be provided, and each hearth roll (200) may be spaced apart at a predetermined interval along the direction of travel (SD) of the steel plate (10).

[0062] In one embodiment, the surface roughness (Ra) of the hearth roll (200) may be 0.1 μm to 0.2 μm. If the surface roughness (Ra) of the hearth roll (200) is less than 0.1 μm, the steel plate (10) may not move within the annealing furnace (100) and slipping may occur, which may reduce productivity. If the surface roughness (Ra) of the hearth roll (200) is greater than 0.2 μm, the tension applied to the steel plate (10) increases, and the iron loss of the manufactured non-oriented electrical steel plate may increase. Therefore, if the surface roughness (Ra) of the hearth roll (200) satisfies 0.1 μm to 0.2 μm, slipping may be prevented, and the increase in iron loss of the manufactured non-oriented electrical steel plate may be prevented.

[0063] In one embodiment, the friction coefficient of the hearth roll (200) may be 0.05 to 0.20. If the friction coefficient of the hearth roll (200) is less than 0.05, the steel plate (10) may not move within the annealing furnace (100) and slipping may occur, which may reduce productivity. If the friction coefficient of the hearth roll (200) is greater than 0.20, the tension applied to the steel plate (10) increases, and the iron loss of the manufactured non-oriented electrical steel plate may increase. Therefore, if the friction coefficient of the hearth roll (200) satisfies 0.05 to 0.20, slipping may be prevented, and the increase in iron loss of the manufactured non-oriented electrical steel plate may be prevented.

[0064] In one embodiment, a hearth roll (200) made of a material such as ceramic or carbon may be used, or the surface condition of the hearth roll (200) may be made slippery through processing so that the hearth roll (200) has a surface roughness (Ra) of 0.1 μm to 0.2 μm and a friction coefficient of 0.05 to 0.20.

[0065] In one embodiment, the tension applied to the steel plate (10) in the annealing furnace (100) may be 10 MPa or less. If the tension applied to the steel plate (10) exceeds 10 MPa, the iron loss of the manufactured non-oriented electrical steel plate may increase. The tension applied to the steel plate (10) in the annealing furnace (100) may be measured through an annealing facility.

[0066] In one embodiment, a tension reel (300) may be provided at the inlet and outlet sides of the annealing furnace (100), respectively.

[0067] In one embodiment, a cold rolling annealing step (S400) may be performed using the annealing facility shown in FIG. 2. For example, the cold rolling annealing step (S400) may be performed in an annealing furnace (e.g., a continuous heat treatment furnace). As described above, a hearth roll (200, FIG. 2) for moving a steel plate (10, FIG. 2) may be provided inside the annealing furnace (100, FIG. 2). A plurality of hearth rolls (200) may be provided, and each hearth roll (200) may be spaced apart at a predetermined interval along the direction of travel (SD) of the steel plate (10). The surface roughness (Ra) of the hearth roll (200) may be 0.1 μm to 0.2 μm. The friction coefficient of the hearth roll (200) may be 0.05 to 0.20. The tension applied to the steel plate (10) in the annealing furnace (100) may be 10 MPa or less.

[0068] When the tension applied to a steel sheet (e.g., cold-rolled sheet) increases during heat treatment in an annealing furnace (e.g., continuous heat treatment furnace), the residual stress of the steel sheet increases, which may degrade the magnetic properties of the manufactured non-oriented electrical steel sheet. In the present invention, by controlling the surface roughness and friction coefficient of the hearth roll of the annealing furnace to minimize the tension applied to the steel sheet at high temperatures during heat treatment in the annealing furnace, the residual stress of the steel sheet can be reduced, thereby lowering the iron loss of the manufactured non-oriented electrical steel sheet and increasing the magnetic flux density.

[0069] In one embodiment, a non-oriented electrical steel sheet can be manufactured through a hot rolling step (S100) to a cold rolling annealing step (S400). Additionally, although not illustrated, a coating step for forming an insulating coating layer on the non-oriented electrical steel sheet can be performed after the cold rolling annealing step (S400). By forming an insulating coating layer on the non-oriented electrical steel sheet through the coating step, punchability can be improved and insulation can be ensured.

[0070] The non-oriented electrical steel sheet produced by the above-described manufacturing method may contain silicon (Si), manganese (Mn), aluminum (Al), carbon (C), phosphorus (P), sulfur (S), nitrogen (N), titanium (Ti), the remainder being iron (Fe) and unavoidable impurities. Additionally, the non-oriented electrical steel sheet may contain at least one of tin (Sn) and antimony (Sb).

[0071] Specifically, the non-oriented electrical steel sheet may contain, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities. Additionally, the non-oriented electrical steel sheet may contain, in wt%, a total of 0.005 wt% to 0.05 wt% of tin (Sn) and antimony (Sb).

[0072] In one embodiment, the non-oriented electrical steel sheet has an iron loss (W) of 3.5 W / kg or less. 15 / 50 It may have a standard. In this case, iron loss can be measured according to the IEC 60404-2 standard.

[0073] The uniformity of the microstructure of non-oriented electrical steel can vary depending on the internal residual stress. For example, if the internal residual stress of the non-oriented electrical steel decreases, the uniformity of the microstructure may increase, and if the residual stress increases, the uniformity of the microstructure may decrease.

[0074] In addition, the uniformity of the microstructure can be represented using the average KAM value. For example, if the uniformity of the microstructure increases, the average KAM value may decrease, and if the uniformity of the microstructure decreases, the average KAM value may increase.

[0075] When the internal residual stress of non-oriented electrical steel decreases, the microstructural uniformity may increase, and when microstructural uniformity increases, the average KAM value may decrease. When the internal residual stress of non-oriented electrical steel increases, the microstructural uniformity may decrease, and when microstructural uniformity decreases, the average KAM value may increase.

[0076] If the internal residual stress of the non-oriented electrical steel sheet decreases, the average KAM value may decrease, and if the internal residual stress of the non-oriented electrical steel sheet increases, the average KAM value may increase.

[0077] In the present invention, residual stress in non-oriented electrical steel sheets was indirectly quantitatively analyzed using the average KAM value obtained through EBSD measurement.

[0078] In one embodiment, the non-oriented electrical steel sheet may have an average Kernel Average Misorientation (KAM) value of 0.4° or less as measured by Electron Back Scattering Diffraction (EBSD). If the average KAM value exceeds 0.4°, the non-oriented electrical steel sheet has an iron loss (W) of 3.5 W / kg or more. 15 / 50 ) can have. In this case, the average KAM value is measured by EBSD for a non-oriented electrical steel sheet over an area of ​​1000 µm X 1000 µm or more, and the condition for calculating the orientation difference between adjacent pixels can be calculated by the third approximation.

[0079] KAM (Kernel Average Misorientation) is an EBSD OIM TMAs an analysis method provided by the software, it is the average value of the amount of crystal rotation (crystallization orientation difference) between the target measurement point and surrounding measurement points, and the larger the average KAM value, the more deformation exists within the crystal. In other words, the average KAM value represents the distribution of deformation based on local orientation changes. KAM is calculated for each pixel by averaging the orientation difference between a regular hexagonal pixel in the EBSD data and the 6 adjacent pixels (first approx.), 12 pixels further outward (second approx.), or 18 pixels further outward (third approx.), and taking that value as the value of the center pixel.

[0080] The higher the silicon (Si) content, the lower the iron loss of the non-oriented electrical steel sheet can be. For example, if the silicon (Si) content is high, the iron loss of the non-oriented electrical steel sheet can be small even if residual stress exists within the non-oriented electrical steel sheet. However, even if the silicon content of the non-oriented electrical steel sheet satisfies 1.8 wt% to 2.7 wt%, the non-oriented electrical steel sheet may have a large iron loss if there is a lot of residual stress within the non-oriented electrical steel sheet.

[0081] In one embodiment, the silicon content of the non-oriented electrical steel sheet and the average KAM value of the non-oriented electrical steel sheet can satisfy the relationship 1 below.

[0082] <Relation Equation 1>

[0083] [Si] / [KAM] ≥ 6.0

[0084] In Equation 1, [Si] represents the silicon content (wt%) contained in the non-oriented electrical steel sheet, and [KAM] represents the average KAM value (°). For example, if the silicon content is 2.0 wt%, [Si] is 2.0, and if the average KAM value is 0.3°, [KAM] may be 0.3.

[0085] If the value of Equation 1 is less than 6.0, the silicon content contained in the non-oriented electrical steel is low or the residual stress present in the non-oriented electrical steel is high, so the iron loss (W) of the non-oriented electrical steel exceeds 3.5 W / kg. 15 / 50 ) can have. Therefore, if the silicon content contained in the non-oriented electrical steel sheet satisfies 1.8 wt% to 2.7 wt%, the average KAM value satisfies 0.4˚ or less, and the value of Equation 1 satisfies 6.0 or more, the non-oriented electrical steel sheet has an iron loss (W) of 3.5 W / kg or less. 15 / 50 Can have ).

[0086] Experimental Example

[0087] The present invention will be explained in more detail below through experimental examples. However, the following experimental examples are intended to explain the present invention more specifically, and the scope of the present invention is not limited by the following experimental examples. The following experimental examples may be appropriately modified or changed by those skilled in the art within the scope of the present invention.

[0088] Table 1 below shows the composition of the steel grades used in the experimental examples of the present invention. Steel grades A to E may be provided with the compositions listed in Table 1, and steel grades A to E may each contain the remainder of iron (Fe) and unavoidable impurities.

[0089] The non-oriented electrical steel sheets of Examples 1 to 12 and Comparative Examples 1 to 15 below were manufactured by the following method.

[0090] A slab having the composition shown in Table 1 was prepared. Subsequently, the slab was hot-rolled to produce a hot-rolled plate with a thickness of 1.9 mm. At this time, the hot rolling was performed under conditions of a reheat temperature of 1180°C, a finish rolling temperature of 900°C, and a coiling temperature of 550°C.

[0091] The obtained hot-rolled plate was hot-rolled and annealed to produce a hot-rolled annealed plate. At this time, the hot-rolled annealing was performed under conditions of heating rate: 15℃ / s, hot-rolled annealing temperature: 950℃, holding time (e.g., hot-rolled annealing time): 50s, and cooling rate: 20℃ / s.

[0092] The obtained hot-rolled annealed plate was cold-rolled to produce a cold-rolled plate with a thickness of 0.40 mm. At this time, the cold rolling was performed under conditions of a reduction rate of 80%.

[0093] Subsequently, the obtained cold-rolled sheet was subjected to cold-roll annealing and coating to produce a final product (e.g., non-oriented electrical steel sheet). At this time, the cold-roll annealing was performed under conditions of a heating rate of 10°C / s, a cold-roll annealing temperature of 950°C, a holding time (e.g., cold-roll annealing time) of 40s, and a cooling rate of 10°C / s. The cold-roll annealing was carried out in a mixed atmosphere of 60% hydrogen and 40% nitrogen. In addition, the surface roughness (Ra) and friction coefficient of the hearth roll during cold-roll annealing were controlled as described in Tables 2 and 3 below to control the tension applied to the steel sheet (e.g., cold-rolled sheet). At this time, the tension corresponds to the tension value measured through the annealing equipment.

[0094] Average KAM value

[0095] For the manufactured specimens, an area of ​​1000 µm X 1000 µm or larger was measured using EBSD, and the average KAM value was derived through a third approximation using the measured data.

[0096] [Si] / [KAM]

[0097] [Si] represents the silicon content (wt%) contained in non-oriented electrical steel sheets, and [KAM] represents the average KAM value. For example, when the silicon content is 2.0 wt%, [Si] is 2.0, and when the average KAM value is 0.3°, [KAM] is 0.3, so [Si] / [KAM] can be 6.0.

[0098] Iron hand

[0099] After measuring iron loss using the Epstein test according to IEC60404-2 standards, the average was presented.

[0100] Gangjong Ingredients (wt%) Si Mn Al C S P N Ti A 1.7 0.3 0.3 0.0021 0.0017 0.0082 0.0017 0.0015 B 1.9 0.3 0.3 0.0021 0.0017 0.0082 0.0017 0.0015 C 2.3 0.3 0.3 0.0021 0.0017 0.0082 0.0017 0.0015 D 2.6 0.3 0.3 0.0021 0.0017 0.0082 0.0017 0.0015 E 2.9 0.3 0.3 0.0021 0.0017 0.0082 0.0017 0.0015

[0101] division Gangjong Hearth roll surface roughness (Ra, μm) Hersroll coefficient of friction Tension (MPa) Average KAM value (˚) [Si] / [KAM] Iron loss (W 15 / 50 ,W / kg) Example 1 B 0.1 0.06 5.2 0.2 9.5 3.38 Example 2 B 0.13 0.06 6.2 0.25 7.6 3.48 Example 3 B 0.1 0.06 5.2 0.2 9.5 3.38 Example 4 C 0.1 0.06 5.4 0.21 11.0 3.12 Example 5 C 0.13 0.06 6.6 0.27 8.5 3.25 Example 6 C 0.18 0.06 9 0.37 6.2 3.47 Example 7 C 0.1 0.06 5.4 0.21 11.0 3.12 Example 8 C 0.1 0.15 8.2 0.35 6.6 3.42 Example 9 D 0.1 0.06 5.6 0.22 11.8 2.91 Example 10 D 0.18 0.06 9.2 0.4 6.5 3.31 Example 11 D 0.1 0.06 5.6 0.22 11.8 2.91 Example 12 D 0.1 0.19 9.0 0.39 6.7 3.39

[0102] division Gangjong Hearth roll surface roughness (Ra, μm) Hersroll coefficient of friction Tension (MPa) Average KAM value (˚) [Si] / [KAM] Iron loss (W 15 / 50 ,W / kg) Comparative Example 1 A 0.1 0.06 5 0.19 8.9 3.52 Comparative Example 2 A 0.13 0.06 6.2 0.25 6.8 3.63 Comparative Example 3 B 0.08 0.06 Continuous heat treatment impossible due to slip Comparative Example 4 B 0.18 0.06 8.6 0.37 5.1 3.71 Comparative Example 5 B 0.22 0.06 10.8 0.49 3.9 3.91 Comparative Example 6 B 0.1 0.15 7.8 0.32 5.9 3.68 Comparative Example 7 B 0.1 0.19 9.2 0.39 4.9 3.81 Comparative Example 8 B 0.1 0.22 10.5 0.45 4.2 3.91 Comparative Example 9 C 0.1 0.03 Continuous heat treatment impossible due to slip Comparative Example 10 C 0.22 0.06 11.2 0.51 4.5 3.65 Comparative Example 11 C 0.1 0.19 9.6 0.40 5.8 3.55 Comparative Example 12 C 0.1 0.22 10.9 0.48 4.8 3.65 Comparative Example 13 D 0.22 0.06 11.4 0.52 5.0 3.52 Comparative Example 14 D 0.1 0.22 11.1 0.49 5.3 3.51 Comparative Example 15 E Plate fracture during cold rolling

[0103] Referring to Tables 1, 2, and 3, it can be confirmed that when the roughness of the hearth roll during the cold rolling annealing stage satisfies 0.1 μm to 0.2 μm and the coefficient of friction of the hearth roll satisfies 0.05 to 0.20, the tension applied to the steel sheet (e.g., cold-rolled sheet) is 10 MPa or less. When the tension applied to the steel sheet (e.g., cold-rolled sheet) is 10 MPa or less, the residual stress of the steel sheet decreases, and it can be confirmed that the average KAM value is 0.4˚ or less. Furthermore, when the average KAM value is 0.4˚ or less and the [Si] / [KAM] value is 6.0 or higher, the iron loss (W) is 3.5 W / kg or less. 15 / 50 It can be confirmed that it has a standard.

[0104] Accordingly, when the component content of the slab (or non-oriented electrical steel sheet) satisfies Silicon (Si): 1.8 wt% to 2.7 wt%, Manganese (Mn): 0.1 wt% to 0.5 wt%, Aluminum (Al): 0.1 wt% to 0.5 wt%, Carbon (C): greater than 0 and less than or equal to 0.003 wt%, Sulfur (S): greater than 0 and less than or equal to 0.002 wt%, Phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, Nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, and Titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the roughness of the hearth roll during the cold rolling annealing stage satisfies 0.1 μm to 0.2 μm and the coefficient of friction of the hearth roll satisfies 0.05 to 0.20, the manufactured non-oriented electrical steel sheet has an iron loss (W) of 3.5 W / kg or less. 15 / 50 Can have a standard.

[0105] Comparative Examples 1 and 2 are cases where the silicon (Si) content contained in the slab (or, non-oriented electrical steel sheet) is less than 1.8 wt%, wherein, when the silicon (Si) content contained in the slab (or, non-oriented electrical steel sheet) is less than 1.8 wt%, the silicon content is too low, so the non-oriented electrical steel sheet has an iron loss (W) exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0106] Comparative Example 3 is a case where the surface roughness of the hearth roll is less than 0.1 μm. When the surface roughness of the hearth roll is less than 0.1 μm, the steel sheet (e.g., cold-rolled sheet) cannot move within the annealing furnace and slip occurs, making continuous heat treatment impossible.

[0107] Referring to Comparative Example 4, in the case where the [Si] / [KAM] value is less than 6.0, the silicon content is low relative to the average KAM value, so the non-oriented electrical steel sheet has an iron loss (W) exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0108] Comparative Example 5 is a case where the surface roughness (Ra) of the hearth roll exceeds 0.2 μm, wherein when the surface roughness (Ra) of the hearth roll exceeds 0.2 μm, the tension applied to the steel sheet may exceed 10 MPa, the average KAM value may exceed 0.4˚, and the [Si] / [KAM] value becomes less than 6.0, resulting in an iron loss (W) of the non-oriented electrical steel sheet exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0109] Comparative Examples 6 and 7 are cases where the [Si] / [KAM] value is less than 6.0, and when the [Si] / [KAM] value is less than 6.0, the silicon content is low relative to the average KAM value, so the non-oriented electrical steel sheet has an iron loss (W) exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0110] Comparative Example 8 is a case where the friction coefficient of the hearth roll exceeds 0.2, wherein when the friction coefficient of the hearth roll exceeds 0.2, the tension applied to the steel sheet may exceed 10 MPa, the average KAM value may exceed 0.4˚, and the [Si] / [KAM] value becomes less than 6.0, resulting in an iron loss (W) of the non-oriented electrical steel sheet exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0111] Comparative Example 9 is a case where the friction coefficient of the hearth roll is less than 0.05. When the friction coefficient of the hearth roll is less than 0.05, the steel sheet (e.g., cold-rolled sheet) cannot move within the annealing furnace and slip occurs, making continuous heat treatment impossible.

[0112] Comparative Example 10 is a case where the surface roughness (Ra) of the hearth roll exceeds 0.2 μm, wherein when the surface roughness (Ra) of the hearth roll exceeds 0.2 μm, the tension applied to the steel sheet may exceed 10 MPa, the average KAM value may exceed 0.4˚, and the [Si] / [KAM] value becomes less than 6.0, so that the non-oriented electrical steel sheet has an iron loss (W) exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0113] Comparative Example 11 is a case where the [Si] / [KAM] value is less than 6.0, wherein the silicon content is low relative to the average KAM value, and the non-oriented electrical steel sheet has an iron loss (W) exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0114] Comparative Example 12 is a case where the friction coefficient of the hearth roll exceeds 0.2, wherein when the friction coefficient of the hearth roll exceeds 0.2, the tension applied to the steel sheet may exceed 10 MPa, the average KAM value may exceed 0.4˚, and the [Si] / [KAM] value becomes less than 6.0, resulting in an iron loss (W) of the non-oriented electrical steel sheet exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0115] Comparative Example 13 is a case where the surface roughness (Ra) of the hearth roll exceeds 0.2 μm, wherein when the surface roughness (Ra) of the hearth roll exceeds 0.2 μm, the tension applied to the steel sheet may exceed 10 MPa, the average KAM value may exceed 0.4˚, and the [Si] / [KAM] value becomes less than 6.0, so that the non-oriented electrical steel sheet has an iron loss (W) exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0116] Comparative Example 14 is a case where the friction coefficient of the hearth roll exceeds 0.2, wherein when the friction coefficient of the hearth roll exceeds 0.2, the tension applied to the steel sheet may exceed 10 MPa, the average KAM value may exceed 0.4˚, and the [Si] / [KAM] value becomes less than 6.0, resulting in an iron loss (W) of the non-oriented electrical steel sheet exceeding 3.5 W / kg. 15 / 50 Can have a standard.

[0117] Comparative Example 15 is a case where the silicon (Si) content in the slab (or, non-oriented electrical steel sheet) exceeds 2.7 wt%, and when the silicon (Si) content in the slab (or, non-oriented electrical steel sheet) exceeds 2.7 wt%, the silicon content is too high and sheet breakage occurs during cold rolling.

[0118] The present invention has been described with reference to the embodiments illustrated in the drawings, but this is merely illustrative, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible therefrom. Accordingly, the true technical scope of protection of the present invention should be determined by the technical spirit of the appended claims. Explanation of the symbols

[0119] 1: Annealing Equipment 10: Steel plate 100: Annealing furnace 110: Heating plate 120: Rift Zone 130: Cooling plate 200: Hearthstone

Claims

Claim 1 A method for manufacturing a non-oriented electrical steel sheet comprises: a hot rolling step of manufacturing a hot-rolled sheet by hot rolling a slab containing, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities; a hot rolling annealing step of manufacturing a hot-rolled annealed sheet by hot rolling the hot-rolled sheet; and a cold rolling step of manufacturing a cold-rolled sheet by cold rolling the hot-rolled annealed sheet. A method for manufacturing a non-oriented electrical steel sheet, comprising: a cold rolling annealing step of cold rolling annealing the cold rolled sheet to produce a cold rolled annealed sheet; wherein the cold rolling annealing step is performed in an annealing furnace, the cold rolled sheet is conveyed by a hearth roll provided in the annealing furnace, the surface roughness (Ra) of the hearth roll is 0.1㎛ to 0.2㎛, the average KAM value of the non-oriented electrical steel sheet measured by EBSD is 0.4˚ or less, and the silicon content and the average KAM value contained in the non-oriented electrical steel sheet satisfy the following Equation 1. <Equation 1> [Si] / [KAM] ≥ 6.0 In the above Equation 1, [Si] means the silicon content (wt%) contained in the slab, and [KAM] means the average KAM value (°). Claim 2 A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the cold rolling annealing step of manufacturing a cold rolling annealed sheet by cold rolling annealing the cold rolled sheet is performed under conditions of a heating rate of 10℃ / s or more, a cold rolling annealing temperature of 900℃ to 1050℃, a cold rolling annealing time of 30s to 90s, and a cooling rate of 10℃ / s or more. Claim 3 delete Claim 4 delete Claim 5 A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the friction coefficient of the hearth roll is 0.05 to 0.

20. Claim 6 A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the tension applied to the cold-rolled sheet in the annealing furnace is 10 MPa or less. Claim 7 A method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the slab further comprises 0.005 wt% to 0.05 wt% of tin (Sn) and antimony (Sb) in total. Claim 8 delete Claim 9 A non-oriented electrical steel sheet comprising, in wt%, silicon (Si): 1.8 wt% to 2.7 wt%, manganese (Mn): 0.1 wt% to 0.5 wt%, aluminum (Al): 0.1 wt% to 0.5 wt%, carbon (C): greater than 0 and less than or equal to 0.003 wt%, sulfur (S): greater than 0 and less than or equal to 0.002 wt%, phosphorus (P): greater than 0 and less than or equal to 0.015 wt%, nitrogen (N): greater than 0 and less than or equal to 0.002 wt%, titanium (Ti): greater than 0 and less than or equal to 0.002 wt%, and the remainder being iron (Fe) and unavoidable impurities, wherein the average KAM value of the non-oriented electrical steel sheet measured by EBSD is 0.4˚ or less, and the silicon content and the average KAM value contained in the non-oriented electrical steel sheet satisfy the following Equation 1. <Equation 1> [Si] / [KAM] ≥ 6.0 In the above relationship 1, [Si] represents the silicon content (wt%) contained in the non-oriented electrical steel sheet, and [KAM] represents the average KAM value (°). Claim 10 In claim 9, the non-oriented electrical steel sheet further comprises 0.005 wt% to 0.05 wt% of tin (Sn) and antimony (Sb) in total. Claim 11 delete Claim 12 delete Claim 13 delete Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 delete

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