Non-oriented electrical steel sheet and method for manufacturing same

Abstract

The present invention provides a non-oriented electrical steel sheet comprising: 3.0-3.8 wt% of silicon (Si); 0.2-0.4 wt% of manganese (Mn); 0.8-1.5 wt% of aluminum (Al); more than 0 but no more than 0.003 wt% of carbon (C); more than 0 but no more than 0.003 wt% of sulfur (S); more than 0 but no more than 0.003 wt% of nitrogen (N); more than 0 but no more than 0.003 wt% of titanium (Ti); 0.012-0.12 wt% of copper (Cu); and the balance of iron (Fe) and other inevitable impurities, wherein the non-oriented electrical steel sheet satisfies formula 1 below. Formula 1: 5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu] (wherein [Cu] represents a weight % value of copper, and [Mn] represents a weight % value of manganese).

Description

Non-oriented electrical steel sheet and manufacturing method thereof

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

[0002] Electrical steel sheets can be divided into grain-oriented and non-oriented electrical steel sheets based on their magnetic properties. Grain-oriented electrical steel sheets are manufactured to facilitate magnetization along the rolling direction, exhibiting particularly superior magnetic properties in that direction. Therefore, they are primarily used as cores for large, medium-sized, and small-sized transformers requiring low core loss and high magnetic permeability. In contrast, non-oriented electrical steel sheets exhibit consistent magnetic properties regardless of the sheet's orientation, making them widely used as core materials for small motors, power transformers, and stabilizers.

[0003] As a prior art document, there is Korean Patent Publication No. 2015-0001467A.

[0004] The technical problem to be achieved by the present invention is to provide a high-efficiency non-oriented electrical steel sheet and a method for manufacturing the same.

[0005] However, these tasks are exemplary and the scope of the present invention is not limited thereby.

[0006] According to one aspect of the present invention for solving the above problem, a non-oriented electrical steel sheet includes silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): 0 to 0.003 wt% or less, sulfur (S): 0 to 0.003 wt% or less, nitrogen (N): 0 to 0.003 wt% or less, titanium (Ti): 0 to 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt% and the remainder iron (Fe) and other unavoidable impurities, and satisfies the following equation 1.

[0007] Equation 1: 5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu]

[0008] (However, the above [Cu] is the weight% value of copper, and the above [Mn] is the weight% value of manganese)

[0009] The number density of CuS and Cu2S with an average diameter of 200 nm or less as copper sulfide precipitates in the final microstructure of the above non-oriented electrical steel sheet is an average of 1000 / mm in the cross section of the steel sheet. 2 It could be as follows:

[0010] In the final microstructure of the above non-oriented electrical steel sheet, the area fraction of CuS and Cu2S having an average diameter of 200 nm or less among the entire sulfides may be 3.6% or less.

[0011] The above non-oriented electrical steel sheet has a core loss (W) of 12.0 W / kg or less. 10 / 400 ) is characterized by having.

[0012] According to another aspect of the present invention for solving the above problem, a method for manufacturing a non-oriented electrical steel sheet comprises the steps of: providing a steel material including silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): 0 to 0.003 wt% or less, sulfur (S): 0 to 0.003 wt% or less, nitrogen (N): 0 to 0.003 wt% or less, titanium (Ti): 0 to 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt% and the remainder iron (Fe) and other unavoidable impurities, and satisfying the following formula 1; hot-rolling the steel material; performing a first annealing heat treatment on the hot-rolled steel material; cold-rolling the first annealing heat treatment-treated steel material; and a step of performing a second annealing heat treatment on the cold-rolled steel.

[0013] Equation 1: 5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu]

[0014] (However, the above [Cu] is the weight% value of copper, and the above [Mn] is the weight% value of manganese)

[0015] In the above method for manufacturing a non-oriented electrical steel sheet, the hot rolling step includes a step of coiling at a coiling temperature (CT): 500 to 700°C after hot rolling, the first annealing heat treatment step includes a step of heating at a rate of 30°C / s or more and less than 50°C / s, annealing at 900 to 1100°C, and cooling at a rate of 30°C or more and less than 50°C / s, and the second annealing heat treatment step includes a step of annealing at 900 to 1100°C.

[0016] In the above method for manufacturing a non-oriented electrical steel sheet, the hot rolling step can be performed under the conditions of a reheating temperature (SRT): 1100 to 1200°C and a finishing rolling temperature (FDT): 700 to 1000°C.

[0017] In the above method for manufacturing a non-oriented electrical steel sheet, the thickness of the hot-rolled steel may be 1.6 to 2.3 mm, and the thickness of the cold-rolled steel may be 0.15 to 0.5 mm.

[0018] In the method for manufacturing the above non-oriented electrical steel sheet, after performing the second annealing heat treatment step, the final microstructure is such that the number density of CuS and Cu2S having an average diameter of 200 nm or less as copper sulfide precipitates is an average of 1000 / mm in the cross section of the steel sheet. 2 Below, it can be characterized in that the area fraction of CuS and Cu2S having an average diameter of 200 nm or less among the entire sulfide is 3.6% or less.

[0019] According to an embodiment of the present invention, a high-efficiency non-oriented electrical steel sheet and a method for manufacturing the same can be provided.

[0020] Of course, the scope of the present invention is not limited by these effects.

[0021] Figure 1 is a flowchart showing a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0022] FIG. 2 is a drawing illustrating the composition range of manganese and copper constituting the steel sheet in a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0023] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail. The terms described below have been appropriately selected in consideration of their functions in the present invention, and their definitions should be based on the contents of this specification.

[0024] Electrical steel is generally divided into grain-oriented and non-oriented electrical steel. Grain-oriented electrical steel is primarily used in stationary equipment such as transformers, while non-oriented electrical steel is primarily used in rotating machinery such as motors and generators. Recently, in response to global environmental issues, there has been a rapid technological shift away from conventional internal combustion engines and toward hybrid vehicles (HEVs), electric vehicles (EVs), and hydrogen-powered vehicles.

[0025] All rotating machines, powered by electrical energy, generate mechanical energy by rotating an internal iron core. This iron core is formed by laminating multiple sheets of non-oriented electrical steel, stamped into the shapes of the stator and rotor. The magnetic properties of this electrical steel have a dominant influence on the performance of the motor core.

[0026] The magnetic properties of non-oriented electrical steel sheets are typically evaluated by magnetic flux density and iron loss. Magnetic flux density is B 50 , for iron loss, usually W 15 / 50 It is mainly evaluated for W, but in cases where high-frequency characteristics are required, such as electric vehicles, 10 / 400 It is evaluated as iron hand. B 50 represents the magnetic flux density at 5000 A / m, and W 15 / 50represents the iron loss at 50 Hz, 1.5 T, and W 10 / 400 represents the iron loss at 400 Hz and 1.0 T. The magnetic flux density is related to the motor's torque, and iron loss is the amount of energy lost as heat. Therefore, iron loss must be reduced to increase the motor's energy efficiency, and increasing the material's resistivity is particularly important for effectively reducing iron loss at high frequencies.

[0027] Resistivity is affected by the content of alloying elements contained in the steel sheet, and therefore silicon (Si), aluminum (Al), and manganese (Mn), which have a high resistivity increase rate per addition amount, are generally used as the main alloying elements. Copper (Cu) is also an element that has a high resistivity increase rate per addition amount, but when added in large quantities, it can form fine precipitates such as CuS and Cu2S in the material, which can hinder the movement of the domain walls during magnetization and adversely affect magnetism. In the case of manganese (Mn), it also forms MnS precipitates by combining with sulfur (S), but it is relatively coarse compared to CuS and Cu2S, so its effect on magnetism is small. If the ratio of added manganese (Mn) and copper (Cu) is adjusted, manganese (Mn) will preferentially combine with sulfur (S) to form coarse MnS precipitates, which can suppress the formation of CuS and Cu2S precipitates and prevent the deterioration of magnetism.

[0028] Therefore, the present invention proposes a non-oriented electrical steel sheet that can reduce high-frequency iron loss by increasing resistivity through addition of copper (Cu) element, and prevent deterioration of magnetism due to inclusions by suppressing the formation of CuS and Cu2S inclusions through addition of manganese (Mn).

[0029] Figure 1 is a flowchart showing a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0030] Referring to FIG. 1, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of: providing a steel material containing silicon (Si), manganese (Mn), aluminum (Al), and copper (Cu) (S10); hot rolling the steel material (S20); first annealing heat treatment on the hot-rolled steel material (S30); cold rolling the first annealing heat treatment-treated steel material (S40); and second annealing heat treatment on the cold-rolled steel material (S50).

[0031] Steel provision stage (S10)

[0032] The steel used in the hot rolling process is steel for manufacturing non-oriented electrical steel sheets, and includes, for example, silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): more than 0 and 0.003 wt% or less, sulfur (S): more than 0 and 0.003 wt% or less, nitrogen (N): more than 0 and 0.003 wt% or less, titanium (Ti): more than 0 and 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt% and the remainder iron (Fe) and other unavoidable impurities.

[0033] Below, the roles and contents of exemplary composition components to which the method for manufacturing a non-oriented electrical steel sheet according to the technical idea of ​​the present invention can be applied are described.

[0034] Silicon (Si): 3.0 to 3.8 wt%

[0035] Silicon (Si) is a key additive that increases resistivity and reduces iron loss (eddy current loss). If the silicon content is less than 3.0 wt%, it is difficult to achieve the desired high-frequency low iron loss value, resulting in insufficient iron loss improvement. If the silicon content exceeds 3.8 wt%, the increased alloying element composition reduces permeability and magnetic flux density, and increases brittleness, making cold rolling difficult and reducing productivity.

[0036] Manganese (Mn): 0.2 to 0.4 wt%

[0037] Manganese (Mn), together with silicon, increases resistivity and improves grain structure. At manganese contents below 0.2 wt%, the iron loss-improving effect is insufficient. However, at manganese contents exceeding 0.4 wt%, excessive MnS precipitates form, potentially increasing iron loss and significantly reducing cold-rollability.

[0038] Aluminum (Al): 0.8 to 1.5 wt%

[0039] Aluminum (Al) is a major additive element that, together with silicon, increases resistivity and reduces core loss (eddy current loss). Aluminum reduces magnetic anisotropy, thereby reducing magnetic deviation. Aluminum induces AlN precipitation when combined with nitrogen. If the aluminum content is less than 0.8 wt%, it is difficult to expect the above-mentioned effect, and fine nitrides may be formed, increasing the deviation in magnetic properties. If the aluminum content exceeds 1.5 wt%, it may react with nitrogen during the final annealing to form excessive nitrides, which may reduce the magnetic flux density, deteriorate the core loss, and cause a decrease in cold rolling properties.

[0040] Carbon (C): more than 0 and less than 0.003 wt%

[0041] Carbon (C) is an element that increases iron loss by forming carbides such as TiC and NbC, and is limited to 0.003 wt% or less. When the carbon content exceeds 0.003 wt%, self-aging occurs, reducing magnetic properties. When the carbon content is below 0.003 wt%, self-aging is suppressed.

[0042] Sulfur (S): more than 0 and less than 0.003 wt%

[0043] Sulfur (S) increases iron loss by forming precipitates such as MnS and CuS, and inhibits grain growth, so it is limited to 0.003 wt% or less. If the sulfur content exceeds 0.003 wt%, the problem of increased iron loss arises.

[0044] Nitrogen (N): More than 0 and less than 0.003 wt%

[0045] Nitrogen (N) increases iron loss by forming precipitates such as AlN, TiN, and NbN, and inhibits grain growth, so it is limited to 0.003 wt% or less. If the nitrogen content exceeds 0.003 wt%, the problem of increased iron loss arises.

[0046] Titanium (Ti): more than 0 and less than 0.003 wt%

[0047] Titanium (Ti) inhibits grain growth by forming fine precipitates such as TiC and TiN. As the amount of titanium increases, magnetic properties deteriorate, so its content is limited to 0.003 wt% or less. Exceeding 0.003 wt% titanium leads to deterioration of magnetic properties.

[0048] Copper (Cu): 0.012 to 0.12 wt%

[0049] Copper (Cu) is an element with a high resistivity increase relative to the amount added. Increasing the resistivity of the material is crucial for effectively reducing iron loss at high frequencies in non-oriented electrical steel sheets. However, if the copper content is below 0.012 wt%, the aforementioned effect is unlikely. However, if the copper content exceeds 0.12 wt%, the precipitates become excessively fine, potentially degrading magnetism. Therefore, copper (Cu) content is limited to 0.12 wt% or less.

[0050] The relationship between manganese (Mn) and copper (Cu)

[0051] Resistivity is affected by the content of alloying elements contained in the steel sheet, and therefore manganese (Mn), which has a high resistivity increase rate per addition amount, is generally used as the main alloying element. Copper (Cu) is also an element that has a high resistivity increase rate per addition amount, but when added in large quantities, it can form fine precipitates such as CuS and Cu2S in the material, which can hinder the movement of the domain walls during magnetization and adversely affect magnetism. In the case of manganese (Mn), it also forms MnS precipitates by combining with sulfur (S), but it is relatively coarse compared to CuS and Cu2S, so its effect on magnetism is small. If the ratio of added manganese (Mn) and copper (Cu) is adjusted, manganese (Mn) will preferentially combine with sulfur (S) to form coarse MnS precipitates, and thus the formation of CuS and Cu2S precipitates can be suppressed, preventing the deterioration of magnetism. In the present invention, a non-oriented electrical steel sheet is proposed that increases resistivity by adding copper (Cu) element to reduce high-frequency iron loss, and prevents deterioration of magnetism due to inclusions by suppressing the formation of CuS and Cu2S inclusions by adding manganese (Mn). In order to do this, Equation 1, which is a relationship between the contents of manganese (Mn) and copper (Cu), is provided as follows.

[0052] Equation 1:

[0053] 5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu]

[0054] (However, the above [Cu] is the weight% value of copper, and the above [Mn] is the weight% value of manganese)

[0055] The influences of the above [Cu] and the above [Mn] on the resistivity of the material are known to be 3.88 μΩ·cm and 6.20 μΩ·cm per 1.0 wt%, respectively. Since the resistivity directly affects the iron loss, the influence was given as a weight and the number density of sulfides according to (6.20·[Mn%]) / (3.88·[Cu%]) was subjected to linear regression analysis. Based on the derived linear regression equation, the area fraction of CuS and Cu2S having an average diameter of 200 nm or less among the entire sulfides was designed to be 3.6% or less, thereby deriving the above equation 1. If the area fraction of CuS and Cu2S having an average diameter of 200 nm or less among the entire sulfides exceeds 3.6%, the resistivity may increase, but a problem arises in that the fine sulfides increase too much. Therefore, in the non-oriented electrical steel sheet according to the embodiment of the present invention, the content of manganese and copper satisfies manganese (Mn): 0.2 to 0.4 wt%, copper (Cu): 0.012 to 0.12 wt%, and at the same time, corresponds to a composition range (area A shown in FIG. 2) that satisfies the above formula 1.

[0056] Hot rolling stage (S20)

[0057] The steel having the above-described composition undergoes a hot rolling process. The step (S20) of hot rolling the steel can be performed under conditions of a reheating temperature (SRT): 1100 to 1200°C and a finishing rolling temperature (FDT): 700 to 1000°C.

[0058] If the slab reheat temperature exceeds 1200℃, precipitates such as C, S, and N within the slab will be re-dissolved, causing fine precipitates to form during subsequent rolling and annealing processes, inhibiting grain growth and deteriorating magnetism. If the slab reheat temperature is lower than 1100℃, the rolling load increases, which can lead to increased iron loss in the final product.

[0059] After performing the step (S20) of hot rolling the above steel, the thickness of the hot-rolled sheet may be, for example, 1.6 to 2.3 mm. As the thickness of the hot-rolled sheet increases, the cold rolling reduction ratio increases, resulting in a deteriorated texture. Therefore, it is preferable to control the thickness to 2.3 mm or less.

[0060] The above hot-rolled steel can be coiled at a coiling temperature (CT) of 500 to 700°C. If the coiling temperature is lower than 500°C, the steel does not have an annealing effect, so grain growth does not occur. If the coiling temperature exceeds 700°C, oxidation may increase during cooling, which may result in poor pickling properties.

[0061] First annealing heat treatment step (S30)

[0062] A step (S30) of performing a first annealing heat treatment on hot-rolled steel may be performed. The first annealing heat treatment may be understood as a preliminary annealing treatment or a hot-rolled annealing treatment, as it is an APL (Annealing and Pickling Line) step of annealing and pickling a hot-rolled sheet.

[0063] The above first annealing heat treatment step (S30) includes an annealing process in which the temperature is increased at a rate of 30°C / s or more and less than 50°C / s, then annealing is started at a temperature of 900 to 1100°C and maintained for 30 to 180 seconds. After annealing, the steel material may be cooled at a rate of 30°C or more and less than 50°C / s. A pickling step may be further included after cooling.

[0064] After hot rolling, a hot-rolled sheet annealing process is performed to ensure uniformity of microstructure and cold rollability. The first annealing temperature is controlled at 900 to 1100°C to form a uniform microstructure by removing the elongated cast structure. If the first annealing temperature is too low, below 900°C, the elongated cast structure remaining after hot rolling may remain, causing microstructure inhomogeneity and forming small crystal grains, which may act as a factor interfering with cold rolling. On the other hand, if the first annealing temperature is too high, exceeding 1100°C, it may cause an imbalance in the texture of the final product, resulting in anisotropy of properties.

[0065] If the above steel is cooled at a cooling rate of less than 30°C / s after annealing, the average grain size of the final microstructure may exceed 200 μm and the total number of sulfides may increase, resulting in a problem of inferior mechanical properties of the non-oriented electrical steel sheet.

[0066] When the above steel is cooled at a cooling rate of 50°C / s or higher after annealing, it is difficult to secure time for manganese (Mn) to preferentially combine with sulfur (S) to form coarse MnS precipitates, so the formation of CuS and Cu2S precipitates becomes relatively easy, which may lead to a problem of deterioration in magnetism.

[0067] Cold rolling stage (S40)

[0068] The first annealed heat-treated steel is subjected to a cold rolling step (S40). Considering the thickness of the hot-rolled sheet and the target cold rolling thickness, the cold rolling reduction ratio may be 75 to 90%. The thickness of the steel after cold rolling may be 0.15 to 0.5 mm. To impart rollability, the sheet temperature may be increased to 150 to 300°C for warm rolling.

[0069] Second annealing heat treatment step (S50)

[0070] The above cold-rolled steel material can be subjected to a second annealing heat treatment. The second annealing heat treatment is an ACL (Annealing and Coating Line) step for final annealing of the cold-rolled sheet, and can be understood as a cold-rolled annealing treatment. The second annealing heat treatment step (S50) may include an annealing step under the conditions of a heating rate of 10°C / s or more, an annealing temperature of 900 to 1100°C, and a holding time of 30 to 120 seconds.

[0071] Secondary annealing heat treatment is performed on the cold-rolled sheet obtained after cold rolling. The temperature is selected to achieve the optimal grain size, considering iron loss and mechanical properties. To prevent surface oxidation and nitriding during cold annealing, the steel is heated under a mixed atmosphere. The mixed atmosphere of nitrogen and hydrogen further smoothes the surface. If the cold annealing temperature is below 900°C, the grain size becomes fine, which can increase hysteresis loss. If the cold annealing temperature exceeds 1100°C, the grain size becomes coarse, increasing eddy current loss.

[0072] Meanwhile, a coating process may be performed to form an insulating coating layer after the final cold-rolled annealing. Forming the insulating coating layer can improve punchability and ensure insulation. The insulating coating layer may be formed on at least one surface of the cold-rolled material. In this case, the thickness of the insulating coating layer may be approximately 1 to 2 μm. For example, the thickness of the insulating coating layer formed on each of one and the other surfaces of the cold-rolled material may be approximately 1 to 2 μm.

[0073] The non-oriented electrical steel sheet manufactured by the above-described manufacturing method is a non-oriented electrical steel sheet including silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): 0 to 0.003 wt% or less, sulfur (S): 0 to 0.003 wt% or less, nitrogen (N): 0 to 0.003 wt% or less, titanium (Ti): 0 to 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt% and the remainder iron (Fe) and other inevitable impurities, and satisfying Equation 1 (5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu]; wherein [Cu] is a weight% value of copper, and wherein [Mn] is a weight% value of manganese), and wherein the precipitate in the final microstructure is The number density of CuS and Cu2S with an average diameter of 200 nm or less as copper sulfide is 1000 / mm 2 Below, the area fraction of CuS and Cu2S with an average diameter of 200 nm or less among the entire sulfides is 3.6% or less, and the iron loss (W) is 12.0 W / kg or less. 10 / 400 ) has.

[0074] To aid understanding of the present invention, preferred experimental examples are presented below. However, the following experimental examples are provided solely to aid understanding of the present invention, and the present invention is not limited to the following experimental examples.

[0075] Experimental example

[0076] 1. Preparation of the sample

[0077] In this experimental example, specimens including the alloy element composition (unit: wt%) of Table 1 are provided. In addition to the alloy element composition disclosed in Table 1, the specimens have a composition of carbon (C): 0.002 wt%, sulfur (S): 0.002 wt%, nitrogen (N): 0.002 wt%, titanium (Ti): 0.002 wt%, and the remainder iron (Fe). In Table 1, the hot-rolled annealing cooling rate refers to the cooling rate of the process of cooling after annealing in the first annealing heat treatment step performed before cold rolling the hot-rolled steel. In this experimental example, the other process conditions for manufacturing the specimens were commonly applied to each same value within the range satisfying the process conditions described in the manufacturing method according to the technical idea of ​​the present invention described above. For example, in the hot rolling stage, the following conditions were commonly applied: reheating temperature (SRT): 1150°C, finishing rolling temperature (FDT): 850°C, coiling temperature (CT): 600°C, first annealing heat treatment annealing temperature: 1000°C, and second annealing heat treatment annealing temperature: 1000°C.

[0078] Experimental Example No. Si[wt%]Al[wt%]Mn[wt%]Cu[wt%][Mn] / [Cu] After hot rolling and annealing Cooling speed [℃ / s] Classification 13.310.9040.1890.01051840Comparative example 123.310.9040.1890.013314.2140Comparative example 233.310.9040.1890.05043.7540Comparative example 343.310.9040.1890.10981.7240Comparative example 453.310.9040.1890.13071.4540Comparative example 563.290.8980.2120.010819.6340Comparative example 673.290.8980.2120.012916.4340Invention example 183.290. 8980.2120.05014.2340Comparative Example 793.290.8980.2120.11041.9240Comparative Example 8103.290.8980.2120.12961.6440Comparative Example 9113.280.9020.3010.011226.8840Comparative Example 10123.280.9020.3010.013122.9840Invention Example 2-1133.280.9020.3010.04986.0440Invention Example 2-2143.280.9020.3010.11022.7340Comparative Example 11153.280.9020. 3010.13052.3140Comparative Example 12163.30.9010.3930.011135.4140Comparative Example 13173.30.9010.3930.012830.740Comparative Example 14183.30.9010.3930.05027.8328Comparative Example 15193.30.9010.3930.05027.8332Invention Example 3203.30.9010.3930.05027.8340Invention Example 4213.30.9010.3930.05027.8348Invention Example 5223.30.9010.3930.05027.835 2Comparative Example 16 233.30.90 10.39 30.109 63.5940Comparative Example 17 243.30.90 10.39 30.130 43.0140Comparative Example 18 253.310.899 0.408 0.0108 37.7840Comparative Example 19 263.310.8990.4080 013 131.1540Comparative Example 20 273.310.8990.4080 050 38.1140Comparative Example 21 283.310.8990.4080 110 23.740Comparative Example 22 293.310.8990.4080 129 53.1540Comparative Example 23

[0079] 2. Microstructure and magnetic evaluation

[0080] Table 2 shows the microstructure and magnetic properties of the specimens of this experimental example implemented by the composition and process of Table 1. In Table 2, item A is the number density (unit: number / mm) of copper sulfides (CuS and Cu2S) as precipitates observed in the cross-section of the final microstructure of the specimen. 2 ) and item B is the total sulfide number density (unit: number / mm) as precipitates observed in the cross-section of the final microstructure of the specimen. 2 ) means, and item C means the area fraction (=A / B) of CuS and Cu2S with an average diameter of 200 nm or less among the total sulfides observed in the cross-section of the final microstructure of the specimen.

[0081] The TD (Transverse Direction) surface of the non-oriented electrical steel sheet was analyzed using EDS (Energy Dispersive Spectrometer), and the analysis cross-sectional area was 160 mm. 2 In this way, the number density of CuS and Cu2S having an equivalent circle diameter (ECD) of 200 nm or less was measured. The equivalent circle diameter (ECD) is the diameter of a circle having the same area (2D) as the irregular inclusions actually observed.

[0082] The number density ratio (C) is 100 times the number density of fine CuS+Cu2S (A) divided by the number density of total sulfide (B).

[0083] Iron Loss (W 10 / 400 ) is the value measured under the conditions of 400 Hz frequency and 1.0 T magnetic flux density, and was measured in accordance with the international standard IEC 60404-2.

[0084] Experimental Example No. A: Number density of CuS+Cu2S particles with an average diameter of 200 nm or less (# / mm) 2 )B: Total sulfide number density (# / mm) 2)C: CuS+Cu2S ratio (%) with an average diameter of 200 nm or less W 10 / 400 (W / kg) Classification 110 174 811.35 12.28 Comparative Example 128 175 861.07 12.23 Comparative Example 23 44 88 97 84.99 12.17 Comparative Example 34 12 73 112 05 11.37 12.19 Comparative Example 45 160 81 19 89 13.4 112.21 Comparative Example 56 12 183 551.4 412.11 Comparative Example 67 66 84 340.78 11.98 Invention Example 18 436 98 294.4 312.02 Comparative Example 79 116 9 120 9 09.67 12.03 Comparative Example 8 10 14 7 0 128 10 11.47 12.08 Comparative Example 9 11 7 4 11 7 0 8 0.63 12.14 Comparative Example 10 12 11 7 11 7 7 9 11 1.98 Invention Example 2-11 3 4 6 8 13 15 5 3.56 11.82 Invention Example 2-2 14 11 2 4 15 4 2 07.29 12.05 Comparative Example 11 15 12 4 2 16 18 17.67 12 .07Comparative Example 12 16 7 9 15 15 4 0.5 2 12.05Comparative Example 13 17 7 5 15 2 18 0.4 9 12.04Comparative Example 14 18 6 8 2 18 9 5 4 3.6 12.02Comparative Example 15 19 5 3 1 1 8 3 7 6 2.8 9 11.93Invention Example 3 20 4 5 0 16 6 2 0 2.7 11 1.84Invention Example 4 2 14 3 5 15 3 2 2 2.8 4 11.89Invention Example 5 2 2 4 0 6 15 1 2 9 2.6 8 12.01Comparative Example 16 23906188484.8112.08Comparative Example 17241303196286.6412.18Comparative Example 182569157050.4412.44Comparative Example 1926136157910.8612.56Comparative Example 2027411171862.3912.15Comparative Example 21281048194335.3912.31Comparative Example 22291265201566.2812.35Comparative Example 23

[0085]

[0086] Referring to Table 1 and Table 2, Experimental Examples 7, 12, 13, 19, 20, and 21 are invention examples of the present invention, and satisfy the composition range of silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): 0 to 0.003 wt% or less, sulfur (S): 0 to 0.003 wt% or less, nitrogen (N): 0 to 0.003 wt% or less, titanium (Ti): 0 to 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt%, and the remainder iron (Fe), and satisfy Equation 1 (5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu]), and are performed before cold rolling a hot-rolled steel. 1. In the case where the cooling rate of the process of cooling after annealing in the annealing heat treatment step satisfies the range of 30℃ or more and less than 50℃ / s, the number density of CuS and Cu2S with an average diameter of 200 nm or less as copper sulfide precipitates in the final microstructure is 1000 / mm. 2 Below, the area fraction of CuS and Cu2S with an average diameter of 200 nm or less among the entire sulfides is 3.6% or less, and the iron loss (W) is 12.0 W / kg or less. 10 / 400 ) can be implemented.

[0087] In contrast, experimental examples 1, 6, 11, and 16 are comparative examples of the present invention, and the copper (Cu) content is too low, so the increase in resistivity is minimal, resulting in an iron loss (W) of 12.0 W / kg or less. 10 / 400 ) cannot be implemented. Experimental examples 2 and 3 are comparative examples of the present invention, and the manganese (Mn) content is less than 0.2%, so the increase in resistivity is minimal, resulting in an iron loss (W) of 12.0 W / kg or less. 10 / 400 ) cannot be implemented. Experimental examples 25, 26, 27, 28, and 29 are comparative examples of the present invention, in which the manganese (Mn) content exceeds 0.4%, resulting in excessive MnS precipitation, deteriorating magnetism, and causing an iron loss (W) of 12.0 W / kg or less. 10 / 400) cannot be implemented. Experimental examples 4, 5, 8, 17, and 23 are comparative examples of the present invention, and do not satisfy equation 1 (5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu]), resulting in a core loss (W) of 12.0 W / kg or less. 10 / 400 ) cannot be implemented. Experimental examples 9, 10, 14, 15, and 24 are comparative examples of the present invention, and the number density of CuS and Cu2S with an average diameter of 200 nm or less as copper sulfide precipitates in the final microstructure is 1000 / mm. 2 In case of exceeding , the iron loss (W) is less than 12.0 W / kg. 10 / 400 ) cannot be implemented. Experimental examples 18 and 22 are comparative examples of the present invention, and when the cooling rate of the process of cooling after annealing in the first annealing heat treatment step performed before cold rolling the hot-rolled steel is in the range of 30°C or more and less than 50°C / s, the iron loss (W) is 12.0 W / kg or less. 10 / 400 ) can be confirmed to be unable to be implemented.

[0088] The effect that can be obtained through the present invention is that the ratio of the content of Mn elements and Cu elements in the steel plate can be adjusted to suppress the formation of micro-precipitates that are unfavorable to magnetism, while maximizing the effect of increasing the resistivity.

[0089] By controlling the content of Mn according to the content of added Cu, the formation of fine CuS and Cu2S precipitates can be suppressed through the formation of coarse MnS precipitates, thereby maximizing the resistivity increasing effect of added Cu, and thus manufacturing a non-oriented electrical steel sheet with low iron loss.

[0090] In addition, the low iron loss non-oriented electrical steel sheet manufactured in this way can be applied to the core of an electric motor to manufacture a high-efficiency motor.

[0091] While the above description focuses on specific embodiments of the present invention, those skilled in the art will appreciate that various modifications and variations can be made. As long as such modifications and variations do not depart from the scope of the present invention, they are considered to be within the scope of the present invention. Therefore, the scope of the present invention should be determined by the claims set forth below.

Claims

1. A non-oriented electrical steel sheet containing silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): more than 0 and 0.003 wt% or less, sulfur (S): more than 0 and 0.003 wt% or less, nitrogen (N): more than 0 and 0.003 wt% or less, titanium (Ti): more than 0 and 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt% and the remainder iron (Fe) and other unavoidable impurities. Characterized in that it satisfies the following equation 1, Non-oriented electrical steel sheet. Equation 1: 5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu] (However, the above [Cu] is the weight% value of copper, and the above [Mn] is the weight% value of manganese) 2. In paragraph 1, The number density of CuS and Cu2S with an average diameter of 200 nm or less as copper sulfide precipitates in the final microstructure is 1000 / mm 2 Characterized by the following: Non-oriented electrical steel sheet.

3. In paragraph 1, In the final microstructure, the area fraction of CuS and Cu2S having an average diameter of 200 nm or less among the entire sulfides is characterized by being 3.6% or less. Non-oriented electrical steel sheet.

4. In paragraph 1, Iron loss (W) of 12.0 W / kg or less 10 / 400 ), characterized by having Non-oriented electrical steel sheet.

5. A step of providing a steel material, which comprises silicon (Si): 3.0 to 3.8 wt%, manganese (Mn): 0.2 to 0.4 wt%, aluminum (Al): 0.8 to 1.5 wt%, carbon (C): more than 0 and 0.003 wt% or less, sulfur (S): more than 0 and 0.003 wt% or less, nitrogen (N): more than 0 and 0.003 wt% or less, titanium (Ti): more than 0 and 0.003 wt% or less, copper (Cu): 0.012 to 0.12 wt% and the remainder iron (Fe) and other unavoidable impurities, but satisfies the following formula 1; A step of hot rolling the above steel; A step of performing a first annealing heat treatment on the hot-rolled steel material; A step of cold rolling the first annealed heat-treated steel; and A step of performing a second annealing heat treatment on the cold-rolled steel material; Method for manufacturing non-oriented electrical steel sheet. Equation 1: 5.26 [Cu] ≤ [Mn] ≤ 25.03 [Cu] (However, the above [Cu] is the weight% value of copper, and the above [Mn] is the weight% value of manganese) 6. In paragraph 5, The above hot rolling step includes a coiling step at a coiling temperature (CT): 500 to 700°C after hot rolling, The above first annealing heat treatment step includes a step of raising the temperature at a rate of 30°C / s or more and less than 50°C / s, annealing at 900 to 1100°C, and cooling at a rate of 30°C or more and less than 50°C / s, The second annealing heat treatment step includes an annealing step at 900 to 1100°C. Method for manufacturing non-oriented electrical steel sheet.

7. In paragraph 5, The above hot rolling step is performed under the conditions of reheating temperature (SRT): 1100 to 1200℃ and finishing rolling temperature (FDT): 700 to 1000℃. Method for manufacturing non-oriented electrical steel sheet.

8. In paragraph 5, The thickness of the hot-rolled steel is 1.6 to 2.3 mm, and the thickness of the cold-rolled steel is 0.15 to 0.5 mm. Method for manufacturing non-oriented electrical steel sheet.

9. In paragraph 5, After performing the second annealing heat treatment step, the number density of CuS and Cu2S with an average diameter of 200 nm or less as copper sulfide precipitates in the final microstructure is 1000 / mm 2 Below, it is characterized in that the area fraction of CuS and Cu2S having an average diameter of 200 nm or less among the entire sulfides is 3.6% or less. Method for manufacturing non-oriented electrical steel sheet.

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