Core comprising non-oriented electrical steel sheets and method of manufacturing thereof

Abstract

A core according to one embodiment of the present application includes a laminate stacked from a plurality of non-oriented electrical steel sheets containing, in mass %, Si: 1.5 to 5.0 %, Al: 0.1 to 2.5 %, and Mn: 0.1 to 2.5 %, with the balance containing Fe and unavoidable impurities, the non-oriented electrical steel sheets having a nitrogen diffusion layer present at a depth of 30 μm in a direction from a side of the laminate inward, the nitrogen diffusion layer having a nitrogen content of 0.005 to 0.020 mass %.

Description

Technical Field

[0001] One embodiment of the present invention relates to an iron core comprising non-oriented electrical steel sheets and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to an iron core comprising non-oriented electrical steel sheets and a method for manufacturing the same, wherein the strength is improved by adjusting the atmosphere conditions during stress-relief annealing (SRA) to allow nitrogen gas to partially permeate to the side surfaces of the steel sheet laminate. Background Technology

[0002] Non-oriented electrical steel sheets are mainly used in motors that convert electrical energy into mechanical energy. To achieve high efficiency in the energy conversion process, non-oriented electrical steel sheets need to have excellent magnetic properties. In particular, with the increasing attention paid to environmentally friendly vehicles powered by electric motors rather than internal combustion engines, the demand for non-oriented electrical steel sheets as materials for drive motor cores is increasing. Therefore, non-oriented electrical steel sheets with excellent magnetic properties and strength are required.

[0003] The magnetic properties of non-oriented electrical steel sheets are primarily evaluated using iron loss and magnetic flux density. Iron loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization achieved under a specific magnetic field. Lower iron loss allows for the manufacture of more energy-efficient motors under the same conditions; higher magnetic flux density enables motor miniaturization or reduces copper losses. Therefore, by using non-oriented electrical steel sheets with low iron loss and high magnetic flux density, drive motors with excellent efficiency and torque can be manufactured, thereby improving the driving range and output power of environmentally friendly vehicles.

[0004] Depending on the operating conditions of the motor, the characteristics of the non-oriented electrical steel sheet to be considered will also change. To evaluate the characteristics of non-oriented electrical steel sheets used in motors, a widely adopted standard is the iron loss (W15 / 50) under a 1.5T magnetic field at a commercial frequency of 50Hz. However, in non-oriented electrical steel sheets with a thickness of less than 0.35mm used in environmentally friendly automotive drive motors, since low magnetic fields of 1.0T or lower and magnetic characteristics at high frequencies above 400Hz are often very important, the iron loss W is typically used instead. 10 / 400 This is used to evaluate the properties of non-oriented electrical steel sheets. Furthermore, due to the increased rotational speed, previously neglected strength characteristics have become important evaluation indicators.

[0005] Therefore, considering the recent energy efficiency improvement policies and the application direction of non-oriented electrical steel sheets, the development technology of non-oriented electrical steel sheets with low high-frequency iron loss, high magnetic flux density and excellent strength is essential.

[0006] The most basic and effective method for reducing iron loss, a crucial magnetic property of non-oriented electrical steel sheets, is to increase the amount of high resistivity elements such as Si, Al, and Mn, or to reduce the thickness of the steel sheet. Increasing the amount of Si, Al, and Mn increases the resistivity of the steel, reducing eddy current losses in the iron loss of non-oriented electrical steel sheets, thus effectively reducing iron loss. For high-frequency iron loss, eddy current losses account for a larger proportion, making this method particularly effective in reducing high-frequency iron loss. However, the effect varies depending on the addition ratio, and the magnetic flux density deteriorates with increasing alloying element addition. Therefore, to ensure excellent iron loss and magnetic flux density, the addition amount and the ratio of Si, Al, and Mn must be appropriately controlled. Reducing the thickness is also a method to significantly reduce eddy current losses and is very effective in reducing iron loss, but thinner steel sheets have disadvantages such as poor productivity and machinability.

[0007] Various techniques have been reported to improve magnetic flux density while reducing iron loss in non-oriented electrical steel sheets. These include improving texture and magnetic properties using special additives such as REM, or introducing additional manufacturing processes like warm rolling, double rolling, and double annealing. However, these techniques all lead to increased manufacturing costs or difficulties in mass production. Therefore, it is necessary to develop techniques that offer excellent magnetic properties and are easy to commercially produce. Furthermore, while techniques have been developed to suppress and control inclusion formation by drastically reducing the amount of impurities added and by adding elements such as Ca, these techniques also increase manufacturing costs and make it difficult to ensure the desired results.

[0008] The strength of steel plates tends to increase with increasing alloy content. However, elements such as Si and Al are brittle and have different effects on strength; therefore, the composition and proportion must be optimized to ensure high strength. On the other hand, finer grain size leads to higher strength, but since there is an optimal grain size that minimizes iron loss, techniques for appropriately controlling grain size are needed to simultaneously ensure low iron loss and high strength.

[0009] On the other hand, when using non-oriented electrical steel sheets to manufacture motors, the required characteristics for the motor rotor and stator are different. That is, for the stator, mechanical properties are not critical indicators other than magnetic properties, but for the rotor, the temperature rises and mechanical properties deteriorate during high-speed rotation, therefore, mechanical properties are required in addition to magnetic properties. Although the required characteristics for the stator and rotor are different, in order to improve the yield rate when manufacturing motors, it is still necessary to use the same type of non-oriented electrical steel sheet to manufacture both the stator and rotor. Summary of the Invention

[0010] (a) Technical problems to be solved One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an iron core comprising a non-oriented electrical steel sheet and a method for manufacturing the same, wherein the strength is improved by adjusting the atmosphere conditions during stress-relief annealing (SRA) to allow nitrogen gas to partially penetrate to the side surfaces of the steel sheet laminate.

[0011] (II) Technical Solution According to one embodiment of the present invention, the iron core comprises a laminate composed of multiple non-oriented electrical steel sheets, wherein the non-oriented electrical steel sheets comprise, by weight%, 1.5 to 5.0% Si, 0.1 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities. The non-oriented electrical steel sheets have a nitrogen diffusion layer extending 30 μm from the side of the laminate inward, and the nitrogen content in the nitrogen diffusion layer is 0.005 to 0.020% by weight.

[0012] Non-oriented electrical steel sheets may also contain one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; S: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; and N: less than 0.020% by weight and excluding 0%.

[0013] Non-oriented electrical steel sheets may also contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

[0014] Non-oriented electrical steel sheets may also contain one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0015] Non-oriented electrical steel sheets may also contain one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

[0016] Non-oriented electrical steel sheets can satisfy the following formula 1.

[0017] [Formula 1] 0.45 ≤ (VA+VB+VC) / (VD+VE+VF) ≤ 1.45 In Equation 1, VA, VB, VC, VD, VE and VF represent the area fraction (%) of textures having an orientation within 15° from (001)[0-10], (001)[-1-10], (100)

[025] , (223)[1-10], (111)[3-41] and (112)[1-10], respectively.

[0018] Non-oriented electrical steel sheets can satisfy the following formula 2.

[0019] [Equation 2] 0.35 ≤ VC / VE ≤ 1.35 In Equation 2, VC and VE represent the area fraction (%) of textures having an orientation within 15° from (100)

[025] and (111)[3-41], respectively.

[0020] A method for manufacturing an iron core according to an embodiment of the present invention includes: a step of preparing a non-oriented electrical steel sheet, wherein the non-oriented electrical steel sheet comprises, by weight %, Si: 1.5 to 5.0%, Al: 0.1 to 2.5% and Mn: 0.1 to 2.5%, with the balance comprising Fe and unavoidable impurities; a step of punching and stacking the non-oriented electrical steel sheet to manufacture a laminate; and a step of annealing the laminate in an atmosphere containing nitriding gas.

[0021] The atmosphere can contain 0.7 to 95% by volume of nitride gas.

[0022] The atmosphere may contain a balance of nitrogen and hydrogen.

[0023] The stress-relief annealing step can be performed at a temperature of 530 to 920°C for 550 seconds to 60 minutes.

[0024] Non-oriented electrical steel sheets can satisfy the following formula 1.

[0025] [Formula 1] 0.45 ≤ (VA+VB+VC) / (VD+VE+VF) ≤ 1.45 In Equation 1, VA, VB, VC, VD, VE and VF represent the area fraction (%) of textures having an orientation within 15° from (001)[0-10], (001)[-1-10], (100)

[025] , (223)[1-10], (111)[3-41] and (112)[1-10], respectively.

[0026] Non-oriented electrical steel sheets can satisfy the following formula 2.

[0027] [Equation 2] 0.35 ≤ VC / VE ≤ 1.35 In Equation 2, VC and VE represent the area fraction (%) of textures having an orientation within 15° from (100)

[025] and (111)[3-41], respectively.

[0028] The steps for preparing non-oriented electrical steel sheets include: hot rolling a slab to produce a hot-rolled steel sheet, wherein the slab comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities; cold rolling the hot-rolled steel sheet to produce a cold-rolled sheet; and annealing the cold-rolled sheet.

[0029] The hot-rolled steel plate manufacturing process includes a roughing rolling process and a finishing rolling process. The finishing rolling process is carried out in n passes with n = 2 or more, and satisfies the following equation 3.

[0030] [Formula 3] R1 / (R1+R2+……+Rn) ≥ 0.2 In Equation 3, R1 to Rn represent the reduction rate (%) from the first to the nth pass, respectively.

[0031] The finishing rolling process satisfies the following equation 4.

[0032] [Formula 4] R1 / Rn ≤ 8 In Equation 4, R1 and Rn represent the reduction rate (%) of the first and nth passes, respectively.

[0033] A method for manufacturing non-oriented electrical steel sheet includes: a step of hot rolling a slab to manufacture a hot-rolled steel sheet, wherein the slab comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities; a step of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and a step of annealing the cold-rolled sheet.

[0034] The hot-rolled steel plate manufacturing process includes a roughing rolling process and a finishing rolling process. The finishing rolling process is carried out in n passes with n = 2 or more, and satisfies Equation 3.

[0035] [Formula 3] R1 / (R1+R2+……+Rn) ≥ 0.2 In Equation 3, R1 to Rn represent the reduction rate (%) from the first to the nth pass, respectively.

[0036] The slab may also contain one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; S: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; and N: less than 0.005% by weight and excluding 0%.

[0037] The slab may also contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

[0038] The slab may also contain one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, and Zn: less than 0.01 wt% and excluding 0%.

[0039] The slab may also contain one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; Co: less than 0.05% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

[0040] (III) Beneficial Effects According to one embodiment of the present invention, the strength of the iron core is increased due to the infiltration of nitrogen during stress-relief annealing, and the magnetism is improved during stress-relief annealing. Therefore, it can perform excellently when used as a motor rotor.

[0041] According to one embodiment of the present invention, the texture of the non-oriented electrical steel sheet of the core is improved, while having excellent magnetic flux density, iron loss and yield strength, and can improve the efficiency of the motor.

[0042] Ultimately, the iron core according to one embodiment of the present invention can help manufacture environmentally friendly automotive motors, high-efficiency home appliance motors, and ultra-high-end electric motors. Detailed Implementation

[0043] The terms “first,” “second,” and “third” are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another. Therefore, without departing from the scope of the invention, a “first” part, component, region, layer, or section as described below may be referred to as a “second” part, component, region, layer, or section.

[0044] The technical terms used herein are for describing specific embodiments only and are not intended to limit the invention. Unless otherwise expressly stated herein, the singular forms used also include the plural forms. The word "comprising" as used in the specification is intended to describe the presence of a particular feature, region, integer, step, operation, element, and / or component, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0045] When referring to a part as "above" or "on top of" another part, it can be directly above or on top of the other part, or there can be other parts in between. Conversely, when referring to a part as "directly above" another part, there are no other parts in between.

[0046] In addition, unless otherwise specified, % refers to weight, 1 ppm is 0.0001 weight.

[0047] In one embodiment of the invention, further including an additional element means replacing the iron (Fe) in the balance with an equal amount of the corresponding additional element.

[0048] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries shall be interpreted as having meanings consistent with relevant technical literature and current disclosure, and shall not be interpreted as having ideal or overly formal meanings unless otherwise defined.

[0049] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different ways and is not limited to the embodiments described.

[0050] According to one embodiment of the present invention, the iron core comprises a laminate composed of multiple sheets of non-oriented electrical steel, wherein the non-oriented electrical steel sheets comprise, by weight percent, 1.5 to 5.0% Si, 0.1 to 2.5% Al and 0.1 to 2.5% Mn, with the balance comprising Fe and unavoidable impurities, and the non-oriented electrical steel sheets comprising a nitrogen diffusion layer in the direction from the side of the laminate toward the interior.

[0051] In one embodiment of the invention, the iron core refers to an iron core used in an electric motor, which can be used for stator or rotor applications. More specifically, it can be a stator iron core.

[0052] In one embodiment of the present invention, the iron core may be an integral stamped iron core or a segmented iron core, and more specifically, it may be an integral stamped iron core.

[0053] The iron core can be in the form of two or more layers of non-oriented electrical steel sheets, and there may be an insulating film between the non-oriented electrical steel sheets.

[0054] By weight percent, non-oriented electrical steel sheet contains Si: 1.5 to 5.0%, Al: 0.1 to 2.5% and Mn: 0.1 to 2.5%, with the balance containing Fe and unavoidable impurities.

[0055] The following explanation will begin with the reasons for the compositional restrictions on non-oriented electrical steel sheets.

[0056] Si: 1.50 to 5.00% by weight Silicon (Si) serves to increase the resistivity of materials to reduce iron loss and improve strength through solid solution strengthening. Insufficient Si addition may result in inadequate improvement in iron loss and strength. Excessive Si addition can lead to a significant decrease in magnetic flux density and potentially deteriorate rollability due to increased brittleness. Therefore, Si can be present in quantities of 1.5 to 5.0% by weight. More specifically, it can be present in quantities of 2.50 to 4.50% by weight. More specifically, it can be present in quantities of 2.70 to 3.85% by weight.

[0057] Al: 0.10 to 2.50% by weight The role of aluminum (Al) is to increase the resistivity of the material to reduce iron loss and improve rollability, and to reduce magnetic anisotropy to minimize magnetic deviation between the rolling direction and the direction perpendicular to rolling. If too little Al is added, it may be difficult to achieve the desired reduction in high-frequency iron loss. If too much Al is added, excessive nitride formation may occur, potentially leading to magnetic degradation. Therefore, Al can be present in quantities from 0.10 to 2.50% by weight. More specifically, it can be present in quantities from 0.50 to 2.50% by weight. More specifically, it can be present in quantities from 0.60 to 2.30% by weight.

[0058] Mn: 0.10 to 2.50% by weight The role of manganese (Mn) is to increase the resistivity of the material to improve iron loss and texture. If too little Mn is added, fine sulfide formation occurs, leading to magnetic degradation; if too much Mn is added, it may negatively affect magnetic flux density. Therefore, Mn can be present in quantities from 0.10 to 2.50% by weight. More specifically, it can be present in quantities from 0.2 to 1.8% by weight. More specifically, it can be present in quantities from 0.50 to 2.50% by weight.

[0059] In one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet at 25°C can be 63.0 μΩ·cm or higher. The iron loss of the non-oriented electrical steel sheet is divided into hysteresis loss and eddy current loss. By adding elements such as Si, Al, and Mn to increase the resistivity of the steel, eddy current loss can be significantly reduced. In particular, as the frequency increases, the proportion of eddy current loss in the total iron loss increases; therefore, it is necessary to control the resistivity of the steel at a certain level to obtain excellent high-frequency iron loss. Through the present invention, excellent characteristics can be obtained when the resistivity (ρ) of the steel is 63 μΩ·cm or higher. More specifically, the resistivity (ρ) can be from 64.0 to 90.0 μΩ·cm.

[0060] In one embodiment of the present invention, resistivity can be measured using methods such as the four-terminal method, the van der Pauw method, the four-point probe method, and the eddy current method.

[0061] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; S: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; and N: less than 0.020% by weight and excluding 0%.

[0062] P: less than 0.1% by weight Phosphorus (P) is a grain boundary and surface segregation element that improves the texture of steel. However, excessive P addition inhibits grain growth, leading to reduced iron loss, and grain boundary segregation deteriorates rollability, potentially reducing productivity. More specifically, P may be present in amounts from 0.0001 to 0.0500% by weight. More specifically, P may be present in amounts from 0.0020 to 0.0200% by weight.

[0063] C: less than 0.0050% by weight Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, thereby hindering grain boundary or magnetic wall movement and potentially leading to deterioration of magnetic properties. More specifically, C may contain 0.0005 to 0.0035% by weight.

[0064] S: less than 0.0050% by weight Sulfur (S) forms fine precipitates such as MnS and CuS, which degrade magnetic properties and may also worsen hot workability. More specifically, S may contain 0.0005 to 0.0040% by weight.

[0065] Ti: less than 0.0050% by weight Titanium (Ti) has a very strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides within the base material. This inhibits grain growth and magnetic wall movement, potentially leading to iron loss degradation. More specifically, Ti may contain 0.0005 to 0.0035% by weight.

[0066] N: less than 0.0200% by weight Nitrogen (N) not only forms fine AlN precipitates within the base material, but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and magnetic wall movement, potentially leading to worsened iron losses. More specifically, after annealing of slabs and cold-rolled sheets, N may contain 0.0005 to 0.0040% by weight. In one embodiment of the invention, during stress-relief annealing, N can partially permeate through the nitriding gas in the atmosphere. However, due to the small amount permeating to the side of the steel sheet, the N content may not change substantially when considering the overall composition of the steel sheet. Specifically, after stress-relief annealing, N may contain less than 0.0200% by weight. More specifically, it may contain 0.0010 to 0.0100% by weight.

[0067] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

[0068] Sn Tin (Sn) segregates at grain boundaries and on the surface, improving the texture of the material and inhibiting surface oxidation. Therefore, Sn can be added to enhance magnetic properties. However, excessive Sn addition can lead to severe grain boundary segregation, resulting in deteriorated surface quality and increased hardness, causing cold-rolled sheet fracture and potentially reducing rollability. Specifically, Sn may further comprise 0.005 to 0.200% by weight. More specifically, it may further comprise 0.010 to 0.080% by weight.

[0069] Sb Antimony (Sb) segregates at grain boundaries and on the surface, improving the texture of the material and inhibiting surface oxidation. Therefore, Sb can be further added to enhance magnetic properties. However, excessive Sb addition can lead to severe grain boundary segregation, resulting in deteriorated surface quality and increased hardness, causing cold-rolled sheet fracture and potentially reducing rollability. Specifically, Sb may further comprise 0.005 to 0.200% by weight. More specifically, it may further comprise 0.010 to 0.080% by weight.

[0070] Bi, Pb, Ge and As When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are added, these elements segregate at grain boundaries, thereby alleviating stress concentration at the grain boundaries during cold rolling and suppressing stress during subsequent recrystallization annealing processes. <111> / / Recrystallization of ND-oriented grains, thereby increasing magnetic flux density. When these elements are added in appropriate amounts, the above effects can be further obtained, but if the content is too high, a large amount of segregation will occur, thereby inhibiting grain growth and potentially leading to a deterioration in magnetic flux density and iron loss.

[0071] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0072] Cu: 0.005 to 0.200% by weight The role of copper (Cu) is to form sulfides with Mn. If too little Cu is added, (Cu·Mn)S will precipitate finely, potentially leading to magnetic degradation. If too much Cu is added, high-temperature brittleness occurs, which may cause cracking during continuous casting or hot rolling. More specifically, Cu can be present in amounts from 0.01 to 0.10% by weight.

[0073] Cr: 0.01 to 0.50% by weight Chromium (Cr) is added to increase resistivity, thereby improving iron loss. If too little Cr is added, the resistivity increase may be insufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr can be present in amounts ranging from 0.050 to 0.20% by weight.

[0074] Ni: less than 0.05% by weight Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, Ni may contain 0.001 to 0.03% by weight.

[0075] Zn: less than 0.01% by weight If the zinc (Zn) content is too high, it will act as an impurity and may lead to magnetic degradation. Therefore, Zn can be added further within the aforementioned range. More specifically, Zr can contain 0.001 to 0.005% by weight.

[0076] Co: less than 0.05% by weight Although cobalt (Co) does not form fine-sized precipitates that reduce the magnetism of steel sheets, it increases high-temperature strength and may lead to poor shape of hot-rolled steel coils.

[0077] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of the following: Mo: less than 0.03 wt% and excluding 0%; B: less than 0.0050 wt% and excluding 0%; V: less than 0.0050 wt% and excluding 0%; Ca: less than 0.0050 wt% and excluding 0%; Nb: less than 0.0050 wt% and excluding 0%; Zr: less than 0.0050 wt% and excluding 0%; Te: less than 0.0100 wt% and excluding 0%; and Mg: less than 0.0050 wt% and excluding 0%.

[0078] Mo: less than 0.030% by weight If excessive molybdenum (Mo) is added, it suppresses the segregation of segregating elements, which may reduce the texture improvement effect. Therefore, Mo can be contained in amounts below 0.03 wt%, with no particular lower limit, but since it segregates at the surface and grain boundaries and has a texture-improving effect, Mo can be contained in amounts above 0.001 wt%. More specifically, Mo can be contained in amounts from 0.001 to 0.010 wt%. More specifically, Mo can be contained in amounts from 0.005 to 0.010 wt%.

[0079] B: Less than 0.0050% by weight If excessive boron (B) is added, inclusions will form in the steel, which may lead to deterioration of its magnetic properties. Therefore, B can be contained in amounts up to 0.005% by weight, with no particular lower limit, but considering the cost of steelmaking, it can be set to 0.0001% by weight. More specifically, B can be contained in amounts from 0.0001 to 0.0030% by weight.

[0080] V: less than 0.0050% by weight Vanadium (V) has a strong tendency to form precipitates in steel, creating fine carbides or nitrides within the base metal. This inhibits grain growth and magnetic wall movement, leading to deterioration of iron losses. Therefore, the V content can be below 0.0050% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0003% by weight. That is, V can contain 0.0003 to 0.0050% by weight. More specifically, V can contain 0.0003 to 0.0030% by weight.

[0081] Ca: less than 0.0050% by weight Calcium (Ca) has a strong tendency to form precipitates in steel, forming fine sulfides inside the base material, thereby inhibiting grain growth and magnetic wall movement, leading to iron loss deterioration.

[0082] Nb: less than 0.0050% by weight Niobium (Nb) has a strong tendency to form precipitates in steel, creating fine carbides or nitrides within the base metal. This inhibits grain growth and magnetic wall movement, leading to deterioration of iron losses. Therefore, the Nb content can be below 0.0050% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0003% by weight. That is, Nb can be present from 0.0003 to 0.0050% by weight. More specifically, Nb can be present from 0.0003 to 0.0030% by weight.

[0083] Zr: less than 0.0050% by weight If excessive zirconium (Zr) is added, inclusions will form in the steel, which may lead to deterioration of its magnetic properties. Therefore, Zr can be contained at less than 0.005% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0001% by weight. That is, Zr can be contained from 0.0001 to 0.0050% by weight. More specifically, it can be contained from 0.0005 to 0.0030% by weight.

[0084] Te: less than 0.0100% by weight Tellurium (Te) diffuses into the oxide layer on the surface of hot-rolled steel coils, thereby increasing the coefficient of friction between the oxide layer and the rolling mill rolls. It also accumulates in the lower part of the oxide layer, increasing hardness. Therefore, tellurium (Te) can be added to allow the oxide layer, which breaks off during rolling, to detach rather than be pressed into the base material. If too little Te is added, the effect may be negligible. If too much Te is added, the oxide layer is more likely to detach, and the base material will directly contact the rolling mill rolls, thus weakening the aforementioned effect. Furthermore, during cold rolling, excessive deformation bands may form inside the steel sheet, potentially leading to the development of a texture that is detrimental to magnetism. More specifically, tellurium can be present in amounts from 0.0001 to 0.007% by weight.

[0085] Mg: less than 0.0050% by weight Magnesium (Mg) is an element that primarily combines with sulfur to form sulfides, which can affect the oxide layer on the surface of the base iron. Therefore, Mg can be contained in amounts up to 0.0050% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0001% by weight. That is, Mg can be contained from 0.0001 to 0.0050% by weight. More specifically, Mg can be contained from 0.0005 to 0.0030% by weight.

[0086] The balance includes Fe and unavoidable impurities. Regarding unavoidable impurities, these are impurities introduced during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets, which are well known in the art and therefore omitted in detail. In one embodiment of the invention, the addition of other elements besides the above-described alloy components is not excluded, and multiple elements may be included without impairing the technical concept of the invention. In cases where additional elements are further included, the corresponding amount replaces the iron (Fe) in the balance.

[0087] As previously mentioned, in one embodiment of the present invention, strength and magnetism can be improved simultaneously by developing a specific texture in the non-oriented electrical steel sheet.

[0088] Specifically, non-oriented electrical steel sheets satisfy the following formula 1.

[0089] [Formula 1] 0.45 ≤ (VA+VB+VC) / (VD+VE+VF) ≤ 1.45 In Equation 1, VA, VB, VC, VD, VE and VF represent the area fraction (%) of textures having an orientation within 15° from (001)[0-10], (001)[-1-10], (100)

[025] , (223)[1-10], (111)[3-41] and (112)[1-10], respectively.

[0090] In one embodiment of the present invention, while the fractions of the (001) and (111) planes parallel to the rolling surface, which have been the main focus of research on textures that primarily affect magnetism, are important, the (223) and (112) planes, which have similar textures, are equally important. In one embodiment of the present invention, the magnetism can be improved because the fractions and concentrations of the (001)[0-10], (001)[-1-10], and (100)

[025] textures, which are conducive to magnetization, are enhanced, while the fractions and concentrations of the (223)[1-10], (111)[3-41], and (112)[1-10] textures, which are unfavorable to magnetization, are reduced. If the value of Equation 1 is too small, magnetization will deteriorate, which may lead to an increase in iron loss. Even if the value of Equation 1 is larger, the magnetism will not be further improved, and the process to achieve this may become more complicated. More specifically, the value of Equation 1 can be from 0.50 to 1.40. In Equation 1, (hkl) is used as the unit of measurement. <uvw>The texture orientation referred to here is the texture orientation in the Miller index notation. Miller indices are a notation used in crystallography to represent lattice directions and planes, where (hkl) refers to the plane in the measured texture parallel to the rolling surface of the steel sheet. Furthermore, vector... <uvw>It refers to the direction parallel to the rolling direction in the measurement of the texture.

[0091] In one embodiment of the present invention, the value of Equation 1 can be observed and analyzed by electron backscatter diffraction (EBSD) measurement, and the texture fraction can be calculated based on the result. To ensure the reliability of the data, the measurement must include at least 5000 grains. The tolerance angle can be set to 15° or less.

[0092] In addition, non-oriented electrical steel sheets can satisfy the following formula 2.

[0093] [Equation 2] 0.35 ≤ VC / VE ≤ 1.35 In Equation 2, VC and VE represent the area fraction (%) of textures having an orientation within 15° from (100)

[025] and (111)[3-41], respectively.

[0094] Equation 2 is a formulaic expression of the relationship that (100)

[025] has a more favorable effect on magnetism and (111)[3-41] has a more unfavorable effect on magnetism in the texture. If the value of Equation 2 is too small, the magnetization process cannot proceed smoothly, which may lead to a significant deterioration of iron loss. Even if the value of Equation 2 is larger, the magnetism will not be further improved, and the process to achieve this goal may become more complicated. More specifically, the value of Equation 2 can be from 0.35 to 1.30.

[0095] In one embodiment of the present invention, the texture of the aforementioned non-oriented electrical steel sheet is determined by cold rolling annealing, and the texture characteristics are not substantially changed by subsequent punching and stress-relief annealing.

[0096] As previously stated, in one embodiment of the present invention, strength and magnetism can be simultaneously improved by developing a specific texture. Specifically, in a non-oriented electrical steel sheet according to an embodiment of the present invention, the iron loss (W10 / 400) can be below 12.0 W / kg, and the magnetic flux density (B50) can be above 1.60 T. The thickness reference can be 0.20 mm. More specifically, the iron loss (W10 / 400) can be 9.0 to 11.0 W / kg, and the magnetic flux density (B50) can be 1.61 to 1.70 T. The iron loss (W10 / 400) is the iron loss when excited to a magnetic flux density of 1.0 T at a frequency of 400 Hz. The magnetic flux density (B50) refers to the magnetic flux density induced under a magnetic field of 5000 A / m. The iron loss (W10 / 400) and magnetic flux density (B50) can be measured using a single sheettester in the rolling direction and the direction perpendicular to the rolling, and the average value is taken.

[0097] Furthermore, one embodiment of the present invention also exhibits excellent mechanical strength. More specifically, the yield strength can be above 480 MPa and below 570 MPa. The yield strength can be measured using the 0.2% off-set method during a tensile test. The aforementioned properties of the non-oriented electrical steel sheet can be measured by separating the non-oriented electrical steel sheet from the core.

[0098] In one embodiment of the present invention, the core is formed by laminating the aforementioned non-oriented electrical steel sheets, thus exhibiting high efficiency and excellent strength. A nitrided diffusion layer is present from the side of the laminate inwards, thereby further enhancing its strength.

[0099] The nitrogen content in the nitrogen diffusion layer extending 30 μm inward from the side of the laminate can be from 0.005 to 0.020% by weight. If the nitrogen content in the nitrogen diffusion layer is too low, the strength may not be adequately improved. Furthermore, if the nitrogen content in the nitrogen diffusion layer extending inward from the side of the laminate is too high, it hinders magnetic domain movement and may negatively affect magnetism. In one embodiment of the invention, only the rotor core may have the aforementioned characteristics. For the stator core, the strength characteristics are relatively less important and may not have the aforementioned characteristics. More specifically, the nitrogen content in the nitrogen diffusion layer extending 30 μm inward from the side of the laminate can be from 0.010 to 0.015% by weight.

[0100] The side surface of a laminate refers to the surface parallel to the thickness direction of the non-oriented electrical steel sheet (i.e., the lamination direction of the laminate). When the non-oriented electrical steel sheet is punched into a cylindrical shape, the circumferential surface is the side surface. The nitrogen content from the side surface to 30 μm can be measured using methods such as combustion analysis, energy dispersive X-ray spectroscopy, and glow discharge spectrometry. The nitrogen content refers to the average nitrogen content within 30 μm of the side surface.

[0101] A method for manufacturing an iron core according to an embodiment of the present invention includes: a step of preparing a non-oriented electrical steel sheet, wherein the non-oriented electrical steel sheet comprises, by weight %, Si: 1.5 to 5.0%, Al: 0.1 to 2.5% and Mn: 0.1 to 2.5%, with the balance comprising Fe and unavoidable impurities; a step of punching and stacking the non-oriented electrical steel sheet to manufacture a laminate; and a step of annealing the laminate in an atmosphere containing nitriding gas.

[0102] First, prepare the non-oriented electrical steel sheet. Since the steel composition and texture characteristics of the non-oriented electrical steel sheet have already been explained in the section concerning the non-oriented electrical steel sheet within the iron core, a repetition is omitted. As mentioned earlier, the steel composition and microstructure characteristics of the non-oriented electrical steel sheet within the iron core are substantially unchanged from those of the non-oriented electrical steel sheet before core manufacturing.

[0103] Non-oriented electrical steel sheets can be manufactured as follows. Specifically, it may include: hot rolling a slab to produce a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet to produce a cold-rolled sheet; and annealing the cold-rolled sheet.

[0104] Each step is explained in detail below.

[0105] First, the slab is hot-rolled.

[0106] The alloy composition of the slab has already been described in the section on the alloy composition of non-oriented electrical steel sheets, so it will not be repeated here. During the manufacturing process of non-oriented electrical steel sheets, the alloy composition remains essentially unchanged; therefore, the alloy composition of non-oriented electrical steel sheets and slabs is substantially the same.

[0107] Specifically, by weight percent, the slab contains Si: 1.5 to 5.0%, Al: 0.1 to 2.5% and Mn: 0.1 to 2.5%, with the balance including Fe and unavoidable impurities.

[0108] Other additional elements have already been described in the alloy composition of non-oriented electrical steel sheets, so they will not be repeated here.

[0109] Before hot rolling, the slab can be heated. The heating temperature of the slab is not limited, but it can be heated to below 1200°C. If the slab is heated to too high a temperature, precipitates such as AlN and MnS present in the slab will re-dissolve and may precipitate finely during subsequent hot rolling and annealing, thereby inhibiting grain growth and reducing magnetism.

[0110] Next, the slab is hot-rolled to produce hot-rolled plates.

[0111] In one embodiment of the invention, it was found that, in order to improve the texture, precise control of conditions is required starting from the hot rolling step. Specifically, it was found that the reduction rate of each pass in the finishing rolling process needs to be adjusted.

[0112] In one embodiment of the present invention, the hot-rolled steel plate manufacturing process includes a rough rolling step and a finish rolling step.

[0113] The roughing rolling step is a process of initially rolling the slab sent from the casting machine into the shape of a steel plate to produce an intermediate bar, consisting of 3 to 4 rolling mills; the finishing rolling step is a process of rolling the rough-rolled steel plate (intermediate bar) into the final hot-rolled target thickness to produce a hot-rolled steel coil, consisting of continuous multi-stage rolling mills.

[0114] The finishing rolling process is carried out in n passes of n = 2 or more, and satisfies Equation 3.

[0115] [Formula 3] R1 / (R1+R2+……+Rn) ≥ 0.20 In Equation 3, R1 to Rn represent the reduction rate (%) from the first to the nth pass, respectively.

[0116] In one embodiment of the present invention, the reduction rate of each step of the finishing mill and the reduction rate of the first pass have a significant impact on the texture formation. As shown in Equation 3, when the reduction rate of each pass is appropriately adjusted, the α-fiber texture and γ-fiber texture can be weakened, thereby improving the magnetism. R1 refers to the first pass, and the number of passes can be determined based on the number of times the work rolls pass through. Furthermore, the nth pass is the last pass, and R1+R2+……+Rn refers to the sum of the reduction rates of all passes. The reduction rate can be obtained by (thickness of steel plate before the pass - thickness of steel plate after the pass) / (thickness of steel plate before the pass)×100 (%). In Equation 3, R1+R2+……+Rn refers to the cumulative sum of the reduction rates (%) from the first pass to the last pass of the finishing mill.

[0117] In one embodiment of the invention, the finishing rolling can be 3 to 7 passes (i.e., n is 3 to 7). If the number of passes is too few, the rolling load will be too high, which may make operation difficult. If the number of passes is too many, it may lead to a decrease in productivity.

[0118] If the reduction rate R1 in the first pass of finishing rolling is too large and does not satisfy Equation 3, the γ-fiber texture will be significantly enhanced, and the magnetism may deteriorate. More specifically, the value of Equation 3 can be between 0.21 and 0.45.

[0119] The finishing rolling step can satisfy the following equation 4.

[0120] [Formula 4] R1 / Rn ≤ 8.0 In Equation 4, R1 and Rn represent the reduction rate (%) of the first and nth passes, respectively.

[0121] If the reduction rate Rn of the final pass of finishing rolling is too small and does not satisfy Equation 4, the improvement effect of the (001)[0-10], (001)[-1-10], and (100)

[025] textures in the easy magnetization direction may be insufficient. More specifically, the value of Equation 4 can be from 1.5 to 7.5.

[0122] In the finishing rolling process, the reduction rate (R1) of the first pass can be 40% to 80%. More specifically, it can be 42% to 80%.

[0123] In the finishing rolling process, the reduction rate (Rn) of the final pass can be 7% to 35%. More specifically, it can be 10% to 30%.

[0124] The thickness of hot-rolled steel sheets can range from 1.0 to 4.5 mm. In the hot-rolling process, the finishing temperature can be above 800°C, specifically 800 to 1000°C. Hot-rolled steel sheets can be coiled at temperatures below 700°C. More specifically, the thickness of hot-rolled steel sheets can range from 1.5 to 4.3 mm.

[0125] After manufacturing the hot-rolled steel sheet, a hot-rolled sheet annealing step can be further included. In this case, the soaking temperature can be between 850 and 1100°C. If the annealing temperature is too low, recrystallization will fail to form or grains will grow finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, the magnetic properties will decrease, and the deformation of the sheet shape may lead to poor rolling operability. More specifically, the temperature range can be between 830 and 1080°C. The soaking time can be between 10 and 300 seconds. The hot-rolled sheet annealing step can also be omitted.

[0126] Next, the hot-rolled steel sheet is cold-rolled to produce cold-rolled sheet. At this stage, cold rolling can be performed with a reduction rate of 40% to 85%. If the reduction rate is too low, the accumulated deformation energy in the rolled steel sheet is small, making recrystallization difficult in subsequent annealing processes. This results in residual rolled microstructure, potentially causing problems in improving magnetic flux density and iron loss. On the other hand, if the reduction rate is too high, it hinders the subsequent annealing process from promoting... <111> / / Recrystallization of ND-oriented grains, resulting in finer grains, may lead to deterioration of magnetic flux density and increased iron loss. More specifically, the reduction rate can be 60% to 75%. For the cold rolling step, a tandem cold rolling mill using multiple mill stands for continuous cold rolling of the steel sheet can be used, or a reversible rolling mill using 12 or more rolls for discontinuous cold rolling can be used. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0127] The manufacturing process of cold-rolled steel sheets can be performed once or more than twice, including intermediate annealing.

[0128] Next, in the annealing step of the cold-rolled sheet, the cold-rolled sheet is annealed. There are no particularly strict limitations on the annealing temperature in the cold-rolled sheet annealing process; the temperature typically used for non-oriented electrical steel sheets is sufficient. The iron loss of non-oriented electrical steel sheets is closely related to the grain size. The iron loss of non-oriented electrical steel sheets can be divided into hysteresis loss and eddy current loss. Hysteresis loss decreases as the grain size increases, while eddy current loss increases with increasing grain size. Therefore, there exists an optimal grain size that minimizes the sum of hysteresis loss and eddy current loss. Thus, it is important to derive and apply the annealing temperature that ensures the optimal grain size; the suitable annealing temperature is 850 to 1100°C. If the annealing temperature is too low, the grains will be too fine, leading to increased hysteresis loss; if it is too high, the grains will be too coarse, leading to increased eddy current loss and deterioration of iron loss. In addition, the annealing time is suitable to be between 10 and 300 seconds. In order to prevent magnetic degradation caused by the formation of an oxide layer, annealing can be carried out in a mixed atmosphere of hydrogen, argon, and nitrogen.

[0129] During the annealing process of cold-rolled sheet, all (i.e., more than 99%) of the processed structures formed in the cold rolling step can undergo recrystallization.

[0130] After annealing, cold-rolled steel sheets can form an insulating coating. The insulating coating can be processed into an organic, inorganic, or organic-inorganic composite coating, or it can be processed using other coating agents with insulating capabilities.

[0131] Non-oriented electrical steel sheets manufactured in this way have the aforementioned steel composition and texture characteristics.

[0132] Returning to the explanation of the core manufacturing method, non-oriented electrical steel sheets are punched and stacked to create a laminate. Punching refers to cutting the non-oriented electrical steel sheets into the shape of the motor core, which can be punched into a ring. Stacking refers to stacking the electrical steel sheets along the thickness direction.

[0133] Next, in the stress-relief annealing step, the laminate is annealed in an atmosphere containing nitriding gas. In one embodiment of the invention, nitriding gas is added to the atmosphere during stress-relief annealing, and a nitrogen diffusion layer can be formed from the side of the laminate toward the interior through nitriding treatment.

[0134] For nitriding gases, any gas capable of nitriding the sides of the laminate during stress-relief annealing can be used without restriction. However, although nitrogen (N2) contains nitrogen, it is excluded from the list of nitriding gases because of its weak reactivity; it does not actually undergo nitriding. Specifically, any gas that can dissociate nitrogen at temperatures above room temperature and diffuse into the steel to achieve nitriding, such as ammonia or cyanide, can be used as a nitriding gas. More specifically, ammonia can be included.

[0135] The atmosphere may contain 0.7 to 95 vol% nitride gas. If too little nitride gas is contained, the strength may not be sufficiently improved. If too much nitride gas is contained, a large amount of nitride will form on the sides, which may negatively affect the magnetism. More specifically, the atmosphere may contain 1.0 to 15.0 vol% nitride gas.

[0136] The atmosphere may contain nitrogen (N2) and hydrogen (H2) in the balance. Specifically, it may contain 5 to 15% by volume of hydrogen and the balance of nitrogen. More specifically, it may contain less than 90% by volume of nitrogen.

[0137] The soaking temperature for the stress-relief annealing step can be between 530 and 920°C. If the soaking temperature is too low, residual stress will remain during punching, which may negatively affect the magnetism. If the soaking temperature is too high, it may negatively affect the strength. More specifically, the soaking temperature can be between 550 and 900°C. The soaking time can be between 550 seconds and 60 minutes. More specifically, the soaking time can be between 10 minutes and 30 minutes.

[0138] The present invention will be further described in detail below by way of examples. However, these examples are only for illustration and the present invention is not limited to the following examples.

[0139] Example 1 A slab containing the composition shown in Table 1, with the balance being Fe and unavoidable impurities, was manufactured. This slab was heated to 1170°C and hot-rolled to a thickness of 2.2 mm, then coiled at 680°C. The finishing rolling process consisted of 7 passes, with reduction rates for each pass as shown in Table 2. The hot-rolled steel sheet was then hot-rolled and annealed at 1000°C for 50 seconds. The annealed and pickled sample was then cold-rolled to a thickness of 0.2 mm, and finally cold-rolled and annealed. This cold-rolled annealing was performed at 1000°C for 50 seconds.

[0140] For texture analysis, the steel plate was cut along the rolling direction to obtain a sample, which was then analyzed using EBSD. The tolerance angle was set to 15°.

[0141] Subsequently, the manufacturing of the stator core was simulated by stress-relief annealing at 750°C in an atmosphere of 90% nitrogen and 10% hydrogen for 1800 seconds.

[0142] In addition, the manufacturing of the simulated rotor core was carried out under stress-relief annealing at the temperatures, times, and ammonia-containing atmospheres shown in Table 3 below. The atmosphere consisted of ammonia, 10% hydrogen by volume, and the balance nitrogen, as shown in Table 3 below.

[0143] For yield strength, the tensile test was conducted using the 0.2% off-set method.

[0144] Iron loss (W10 / 400) and magnetic flux density (B50) were measured using a single sheet tester.

[0145] The nitrogen content in the nitrogen diffusion layer from the rotor side to 30 μm was measured by energy-dispersive X-ray spectroscopy (EDS).

[0146] Table 1 Table 2 Table 3 Table 4 As shown in Tables 1 to 4, when the steel composition and finishing rolling reduction are properly adjusted, and the SRA conditions are properly adjusted, the characteristics of both the stator and rotor are excellent, and in particular, it can be confirmed that the strength of the rotor is improved.

[0147] On the other hand, as with steel grades 16 to 30, when the steel composition or electrical steel sheet manufacturing process conditions are not properly adjusted and a specific texture is not developed, it can be confirmed that the characteristics of both the stator and rotor deteriorate.

[0148] Furthermore, for steel grades 1 to 5, 9, and 13 to 15, due to improper SRA process conditions of the rotor, nitrogen failed to properly penetrate into the nitrogen diffusion layer on the side of the rotor, confirming that the strength improvement of the rotor was insufficient.

[0149] This invention is not limited to the embodiments described above, and can be manufactured in many different ways. Those skilled in the art should understand that other specific methods can be used without changing the technical concept or essential features of the invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.< / uvw> < / uvw>

Claims

1. A type of iron core, wherein, The core comprises a laminate composed of multiple sheets of non-oriented electrical steel, wherein, by weight percent, the non-oriented electrical steel sheets comprise 1.5 to 5.0% Si, 0.1 to 2.5% Al and 0.1 to 2.5% Mn, with the balance comprising Fe and unavoidable impurities. The non-oriented electrical steel sheet has a nitrogen diffusion layer extending 30 μm from the side of the laminate inward, and the nitrogen content in the nitrogen diffusion layer is 0.005 to 0.020 by weight.

2. The iron core according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; S: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; and N: less than 0.0% by weight and excluding 0%.

3. The iron core according to claim 1, wherein, The non-oriented electrical steel sheet further contains one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

4. The iron core according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

5. The iron core according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

6. The iron core according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following formula 1. [Formula 1] 0.45 ≤ (VA+VB+VC) / (VD+VE+VF) ≤ 1.45 In Equation 1, VA, VB, VC, VD, VE and VF represent the area fraction (%) of textures having an orientation within 15° from (001)[0-10], (001)[-1-10], (100)[025], (223)[1-10], (111)[3-41] and (112)[1-10], respectively.

7. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following formula 1. [Equation 2] 0.35 ≤ VC / VE ≤ 1.35 In Equation 2, VC and VE represent the area fraction (%) of textures having an orientation within 15° from (100)[025] and (111)[3-41], respectively.

8. A method for manufacturing an iron core, comprising: The steps for preparing non-oriented electrical steel sheets, in weight percent, are as follows: the non-oriented electrical steel sheets contain Si: 1.5 to 5.0%, Al: 0.1 to 2.5% and Mn: 0.1 to 2.5%, with the balance containing Fe and unavoidable impurities; The steps of punching and laminating the non-oriented electrical steel sheet to manufacture a laminate; and The laminate is subjected to a stress-relief annealing step in an atmosphere containing nitriding gas.

9. The method for manufacturing an iron core according to claim 8, wherein, The atmosphere contains 0.7 to 95% by volume of nitride gas.

10. The method for manufacturing an iron core according to claim 8, wherein, The atmosphere contains a balance of nitrogen and hydrogen.

11. The method for manufacturing an iron core according to claim 8, wherein, The stress-relief annealing step is performed at a temperature of 530 to 920°C for 550 seconds to 60 minutes.

12. The method for manufacturing an iron core according to claim 8, wherein, The non-oriented electrical steel sheet satisfies the following formula 1. [Formula 1] 0.45 ≤ (VA+VB+VC) / (VD+VE+VF) ≤ 1.45 In Equation 1, VA, VB, VC, VD, VE and VF represent the area fraction (%) of textures having an orientation within 15° from (001)[0-10], (001)[-1-10], (100)[025], (223)[1-10], (111)[3-41] and (112)[1-10], respectively.

13. The method for manufacturing an iron core according to claim 8, wherein, The non-oriented electrical steel sheet satisfies the following formula 2. [Equation 2] 0.35 ≤ VC / VE ≤ 1.35 In Equation 2, VC and VE represent the area fraction (%) of textures having an orientation within 15° from (100)[025] and (111)[3-41], respectively.

14. The method for manufacturing an iron core according to claim 8, wherein, The steps for preparing non-oriented electrical steel sheets include: The step of hot rolling a slab to produce a hot-rolled steel sheet, wherein the slab comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.5% Al and 0.1 to 2.5% Mn, with the balance comprising Fe and unavoidable impurities; The steps of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and The annealing step for the cold-rolled sheet.

15. The method for manufacturing an iron core according to claim 14, wherein, The hot-rolled steel plate manufacturing process includes rough rolling and finish rolling. The finishing rolling step is performed in n passes where n is 2 or more, and satisfies the following equation 3. [Formula 3] R1 / (R1+R2+……+Rn) ≥ 0.2 In Equation 3, R1 to Rn represent the reduction rate (%) from the first to the nth pass, respectively.

16. The method for manufacturing an iron core according to claim 15, wherein, The finishing rolling step satisfies the following equation 4. [Formula 4] R1 / Rn ≤ 8 In Equation 4, R1 and Rn represent the reduction rate (%) of the first and nth passes, respectively.

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