Iron core comprisng non-oriented electrical steel sheet and method for manufacturing same

Abstract

An iron core according to an embodiment of the present invention comprises: a laminate having stacked therein a plurality of non-oriented electrical steel sheets comprising, by wt%, 1.5-4.5% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, and the remainder being Fe and inevitable impurities, wherein the non-oriented electrical steel sheets have an area fraction of 7% or more of crystal grains having an orientation of 15° or less from the {100}<025>.

Description

Iron core including non-oriented electrical steel sheet and method for manufacturing the same

[0001] One embodiment of the present invention relates to a core including a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a method for controlling the pressing conditions for a laminate during stress relief annealing (SRA), thereby forming {100} <025> The present invention relates to an iron core including a non-oriented electrical steel sheet having improved magnetism by forming a plurality of fractions, and a method for manufacturing the same.

[0002] Non-oriented electrical steel is primarily used in motors that convert electrical energy into mechanical energy. This process requires excellent magnetic properties to achieve high efficiency. In particular, with the recent rise in eco-friendly vehicles powered by motors instead of internal combustion engines, demand for non-oriented electrical steel, used as a drive motor core material, is increasing. This demand is driven by the need for non-oriented electrical steel with both superior magnetic properties and strength.

[0003] The magnetic properties of non-oriented electrical steel are primarily assessed by core loss and magnetic flux density. Core loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density represents the degree of magnetization achieved under a specific magnetic field. Lower core loss allows for more energy-efficient motors under similar conditions, while higher flux density allows for smaller motors and reduced copper loss. Therefore, non-oriented electrical steel with low core loss and high flux density can be used to create drive motors with superior efficiency and torque, thereby improving the driving range and power output of eco-friendly vehicles.

[0004] The characteristics of non-oriented electrical steel sheets that must be considered also vary depending on the operating conditions of the motor. The general standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors is widely used as W15 / 50, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, in the case of non-oriented electrical steel sheets with a thickness of 0.35mm or less used in eco-friendly vehicle drive motors, magnetic characteristics are often important at low fields of 1.0T or less and high frequencies of 400Hz or higher, so W 10 / 400 The properties of non-oriented electrical steel sheets are often evaluated by iron loss.

[0005] Additionally, during high-speed rotation, the motor temperature increases to around 200°C, which causes deterioration of mechanical characteristics. Therefore, maintaining mechanical characteristics at these temperatures is important for increasing motor efficiency.

[0006] One embodiment of the present invention provides a core including a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a core including a non-oriented electrical steel sheet and a method for manufacturing the same. In particular, the core is formed by controlling the pressing conditions for a laminate during stress relief annealing (SRA), thereby forming a {100} <025> Provided are an iron core including a non-oriented electrical steel sheet with improved magnetism by forming a plurality of fractions, and a method for manufacturing the same.

[0007] According to one embodiment of the present invention, a core comprises a laminate in which a plurality of non-oriented electrical steel sheets are laminated, including Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities, and the non-oriented electrical steel sheets are {100} <025> The area fraction of crystal grains having an orientation of 15° or less from the center is 7% or more.

[0008] The non-oriented electrical steel sheet may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0009] The non-oriented electrical steel sheet may further contain 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0010] The non-oriented electrical steel sheet may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0011] The non-oriented electrical steel sheet may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0012]

[0013] A method for manufacturing an iron core according to one embodiment of the present invention comprises the steps of preparing a non-oriented electrical steel sheet containing, by weight %, 1.5 to 4.5% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, and the remainder Fe and unavoidable impurities; the step of forming and laminating the non-oriented electrical steel sheet to manufacture a laminate; and the step of annealing the laminate while applying pressure at a pressure of 0.1 to 2 MPa, a stress relief annealing step.

[0014] In the step of preparing a non-oriented electrical steel sheet, the non-oriented electrical steel sheet may contain unrecrystallized portions of 3 area% or more.

[0015] In the step of preparing a non-oriented electrical steel sheet, the average grain size of the non-oriented electrical steel sheet may be 30㎛ or less.

[0016] The cracking temperature of the stress relief annealing step can be 750 to 850°C.

[0017] The stress relief annealing step can be annealed to satisfy the following equation 1.

[0018] [Formula 1]

[0019] Pressure ≥ average grain size × unrecrystallized fraction × 5 / SRA temperature

[0020] (In Equation 1, the unit of pressure is MPa, the unit of average grain size is ㎛, the unit of unrecrystallized fraction is area%, and the unit of SRA temperature is ℃.)

[0021] The step of preparing a non-oriented electrical steel sheet may include a step of hot-rolling a slab containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder including Fe and inevitable impurities, to produce a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0022] The slab may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0023] The slab may further contain 0.005 to 0.200 wt% of each or a combination of one or more of Sn, Sb, Bi, Pb, Ge and As.

[0024] The slab may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0025] The slab may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), Co: 0.05 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0026] The method further includes a step of heating the cold-rolled sheet before the cold-rolled sheet annealing step, wherein the heating rate in the range of 300 to 500°C may be 40°C / sec or more, and the heating rate in the range of 500 to 700°C may be 20 to 38°C / sec.

[0027] In the cold rolled sheet annealing step of annealing the cold rolled sheet, the cracking temperature may be 850℃ or lower.

[0028] According to one embodiment of the present invention, the iron core is {100} <025> Because there are many crystal grains, the isotropy of iron loss is excellent.

[0029] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the manufacture of eco-friendly automobile motors, high-efficiency home appliance motors, and super-premium-grade electric motors.

[0030] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0032] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0033] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0034] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0035] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0036] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0037]

[0038] According to one embodiment of the present invention, a core comprises a laminate in which a plurality of non-oriented electrical steel sheets are laminated, including Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities, and the non-oriented electrical steel sheets are {100} <025> The area fraction of crystal grains having an orientation of 15° or less from the center is 7% or more.

[0039] In one embodiment of the present invention, the iron core refers to an iron core used in a motor and can be used for a stator or a rotor. More specifically, it can be an iron core for a stator.

[0040] In one embodiment of the present invention, the core may be an integral punched core or a split core, and more specifically, may be an integral punched core.

[0041] The core may be formed by laminating two or more non-oriented electrical steel sheets, and an insulating film may exist between the non-oriented electrical steel sheets.

[0042] The non-oriented electrical steel sheet contains, in weight %, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities.

[0043] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0044]

[0045] Si: 1.5 to 4.5 wt%

[0046] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and increases strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects may be insufficient. If too much Si is added, the material becomes brittle, which drastically reduces rolling productivity and may form a surface oxide layer and oxides that are harmful to magnetism. Therefore, Si may be included in an amount of 1.5 to 4.5 wt%. More specifically, it may be included in an amount of 2.0 to 4.3 wt%. More specifically, it may be included in an amount of 2.5 to 3.9 wt%. More specifically, it may be included in an amount of 3.15 to 3.85 wt%.

[0047]

[0048] Al: 0.1 to 2.0 wt%

[0049] Aluminum (Al) increases the resistivity of the material, thereby reducing iron loss, and enhances strength through solid solution strengthening. If too little Al is added, fine nitrides may form, making it difficult to achieve the effect of improving magnetism. If too much Al is added, excessive nitrides may form, deteriorating magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. Therefore, Al may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.2 to 2.0 wt%. Even more specifically, it may be included in an amount of 0.5 to 1.9 wt%.

[0050]

[0051] Mn: 0.1 to 2.0 wt%

[0052] Manganese (Mn) improves iron loss by increasing the resistivity of the material and plays a role in forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration, and if too much Mn is added, fine MnS is excessively precipitated and promotes the formation of {111} texture, which is unfavorable for magnetism, resulting in a rapid decrease in magnetic flux density. Therefore, Mn may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.2 to 1.8 wt%. More specifically, it may be included in an amount of 0.3 to 1.5 wt%.

[0053]

[0054] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0055] P: 0.1 wt% or less

[0056] Phosphorus (P) is a grain boundary segregation element that can improve magnetic flux density, but if added in too large a quantity, it increases the brittleness of the steel plate, resulting in poor weldability. More specifically, P may be included in an amount of 0.0001 to 0.0500 wt%.

[0057] C: 0.005 wt% or less

[0058] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, thereby hindering grain boundary or domain wall movement and deteriorating magnetic properties. More specifically, C can be included in an amount of 0.0001 to 0.003 wt%.

[0059] S: 0.005 wt% or less

[0060] Sulfur (S) can form fine precipitates, MnS and CuS, which can deteriorate magnetic properties and hot workability. More specifically, S can be included in an amount of 0.0001 to 0.0030 wt%.

[0061] Ti: 0.005 wt% or less

[0062] Titanium (Ti) has a strong tendency to form precipitates within the steel, and can deteriorate iron loss by forming fine carbides, nitrides, or sulfides within the parent material, thereby inhibiting grain growth and domain wall migration. More specifically, it can contain 0.0001 to 0.003 wt% of Ti.

[0063] N: 0.005 wt% or less

[0064] 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 domain wall migration, thereby worsening iron loss. More specifically, N may be included in an amount of 0.0001 to 0.0030 wt%.

[0065]

[0066] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0067] Sn and Sb

[0068] Tin (Sn) and antimony (Sb) play a role in suppressing the development of {111} orientation, which segregates at the grain boundary in the early stage of final recrystallization annealing and worsens magnetism. If too much Sn and Sb are added, the recovery and growth of coarse stretched band structure may be hindered and the surface quality may be worsened. Therefore, at least one of Sn and Sb may be further added within the above-mentioned range. More specifically, Sn may be included in an amount of 0.005 to 0.200 wt% or Sb may be included in an amount of 0.005 to 0.200 wt%. More specifically, Sn may be included in an amount of 0.01 to 0.060 wt% or Sb may be included in an amount of 0.005 to 0.040 wt%. More specifically, Sn may be included in an amount of 0.01 to 0.060 wt% and Sb may be included in an amount of 0.005 to 0.040 wt%.

[0069] Bi, Pb, Ge, and As

[0070] When added, bismuth (Bi), lead (Pb), germanium (Ge) and arsenic (As) segregate at grain boundaries, thereby relieving stress concentration at grain boundaries during cold rolling, and thus reducing stress concentration in the subsequent recrystallization annealing process. <111> / ND By suppressing the recrystallization of the grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained. However, if they are included in excessive amounts, segregation may occur in large quantities, inhibiting grain growth and lowering the magnetic flux density and iron loss.

[0071]

[0072] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0073] Cu: 0.005 to 0.200 wt%

[0074] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu · Mn)S may occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement may occur, leading to cracks during rolling or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.10 wt%.

[0075] Cr: 0.01 to 0.50 wt%

[0076] Chromium (Cr) increases resistivity and improves iron loss. If too little Cr is added, the resistivity-enhancing effect may not be sufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr may be included in an amount of 0.050 to 0.20 wt%.

[0077] Ni: 0.05 wt% or less

[0078] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, it can contain 0.001 to 0.03 wt% of Ni.

[0079] Zn: 0.01 wt% or less

[0080] Zinc (Zn) can act as an impurity and degrade magnetism if the content is excessive. Therefore, Zn may be added further within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 wt%.

[0081] Co: 0.05 wt% or less

[0082] Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it can increase high-temperature strength and cause poor coil shape after hot rolling.

[0083]

[0084] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.0050 wt% or less (excluding 0%), Te: 0.0100 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0085] Mo: 0.030 wt% or less

[0086] When molybdenum (Mo) is added in excessive amounts, it may suppress segregation of segregating elements, thereby reducing the effect of improving the texture. Therefore, Mo may be included in an amount of 0.03 wt% or less. The lower limit is not particularly limited, but since it plays a role in improving the texture by segregating on the surface and grain boundaries, it may be included in an amount of 0.001 wt% or more. More specifically, Mo may be included in an amount of 0.001 to 0.010 wt%. More specifically, Mo may be included in an amount of 0.005 to 0.010 wt%.

[0087] B: 0.0050 wt% or less

[0088] Excessive addition of boron (B) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, B may be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. More specifically, B may be included in an amount of 0.0001 to 0.0030 wt%.

[0089] V: 0.0050 wt% or less

[0090] Vanadium (V) has a very strong tendency to form precipitates within the steel, and forms fine carbides or nitrides within the base metal, thereby inhibiting grain growth and domain wall migration, thereby deteriorating iron loss. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not particularly limited, but may be 0.0003 wt% due to steelmaking costs. That is, V may be included in an amount of 0.0003 to 0.0050 wt%. More specifically, V may be included in an amount of 0.0003 to 0.0030 wt%.

[0091] Ca: 0.0050 wt% or less

[0092] Calcium (Ca) has a strong tendency to form precipitates within the steel, and forms fine sulfides within the parent material, which inhibits grain growth and domain wall movement, thereby deteriorating iron loss.

[0093] Nb: 0.0050 wt% or less

[0094] Niobium (Nb) has a very strong tendency to form precipitates in steel, and forms fine carbides or nitrides inside the base metal, which inhibits grain growth and domain wall migration, thereby deteriorating iron loss. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not particularly limited, but may be 0.0003 wt% due to steelmaking costs. That is, Nb may be included in an amount of 0.0003 to 0.0050 wt%. More specifically, Nb may be included in an amount of 0.0003 to 0.0030 wt%.

[0095] Zr: 0.0050 wt% or less

[0096] Excessive addition of zirconium (Zr) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, Zr can be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. That is, Zr can be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it can be included in an amount of 0.0005 to 0.0030 wt%.

[0097] Te: 0.0100 wt% or less

[0098] Tellurium (Te) diffuses into the oxide layer on the surface of a hot-rolled coil, increases the coefficient of friction between the oxide layer and the rolling work rolls, and concentrates under the oxide layer to improve hardness. Therefore, it can be added to prevent the fractured oxide layer during rolling from being pressed into the base metal and to be removed. If the amount of Te added is too small, the effect may be minimal. If too much Te is added, the oxide layer is easily removed, and the base metal comes into direct contact with the work rolls, reducing the effect. In addition, deformation bands may be excessively generated in the steel sheet during cold rolling, which may lead to the development of a {111} / ND texture that is unfavorable for magnetism. More specifically, tellurium may be included in an amount of 0.0001 to 0.007 wt%.

[0099] Mg: 0.0050 wt% or less

[0100] Magnesium (Mg) is an element that mainly combines with sulfur to form sulfides, and can affect the surface oxide layer of the steel base. Therefore, Mg may be included in an amount of 0.0050 wt% or less. The lower limit is not particularly limited, but may be set to 0.0001 wt% due to steelmaking costs. That is, Mg may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 to 0.0030 wt%.

[0101]

[0102] The remainder comprises iron (Fe) and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. When additional elements are included, they are included in place of the remainder, iron (Fe).

[0103]

[0104] In one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet may be 55 μΩ·cm or more. The resistivity is better the larger it is for reducing eddy current loss in a high-frequency rotating machine, but if it is too large, the magnetic flux density may be inferior. In one embodiment of the present invention, the resistivity can be estimated from the equation 13.25+11.3×([Si]+[Al]+[Mn] / 2+[Cu] / 2+[Cr] / 2). More specifically, the resistivity may be 58 to 80 μΩ·cm.

[0105]

[0106] In one embodiment of the present invention, {100} in a non-oriented electrical steel sheet <025> Grains having an orientation of 15° or less from {100} <025> The anisotropy of the core can be improved by increasing the ratio of {100} (also called crystal grains). <025> As the crystal grain fraction increases, the fraction of textures with {100} / ND increases, which improves the anisotropy of iron loss. Specifically, {100} in non-oriented electrical steel sheets <025> The area fraction of grains having an orientation of 15° or less from may be 7.0% or more. More specifically, it may be 8.0 to 15.0%. More specifically, it may be 8.5 to 13.0%. The grain fraction may be analyzed by separating the laminated non-oriented electrical steel sheets one by one and using SEM-EBSD for a thickness region of 1 / 2 to 1 / 4 of the total thickness in the ND direction. At this time, the tolerance angle may be within 15°.

[0107] As described above, in one embodiment of the present invention, by appropriately controlling the steel component and appropriately forming the aggregate structure, the magnetism can be improved. Specifically, the circumferential iron loss (W) of the non-oriented electrical steel sheet based on a thickness of 0.25 mm 10 / 400 ) may be less than 17.0 W / Kg. In addition, the magnetic flux density (B 50 ) can be 1.65T or more. Iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. The iron loss in the circumferential direction can be measured with a ring core measuring instrument or obtained by measuring the magnetism in each direction and averaging it.

[0108]

[0109] A method for manufacturing an iron core according to one embodiment of the present invention comprises the steps of preparing a non-oriented electrical steel sheet containing, by weight %, 1.5 to 4.5% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, and the remainder Fe and unavoidable impurities; the step of forming and laminating the non-oriented electrical steel sheet to manufacture a laminate; and the step of annealing the laminate while applying pressure at a pressure of 0.1 to 2 MPa, a stress relief annealing step.

[0110] First, a non-oriented electrical steel sheet containing 1.5 to 4.5 wt% of Si, 0.1 to 2.0 wt% of Al, and 0.1 to 2.0 wt% of Mn, with the remainder being Fe and unavoidable impurities, is prepared. The components of the non-oriented electrical steel sheet have been described above, so a redundant description will be omitted. The steel components do not substantially change during the laminate manufacturing and stress-relief annealing steps.

[0111] In the step of preparing a non-oriented electrical steel sheet, the non-oriented electrical steel sheet may contain more than 3 area% of non-recrystallized matter. If some non-recrystallized matter exists, it is {100} recrystallized during SRA under pressure. <025> It helps in grain formation and can improve the mechanical strength of the steel core. Non-recrystallized refers to rolled grains that have not undergone recrystallization when measuring the cross-section of non-oriented electrical steel sheets. More specifically, non-recrystallized grains can be included in an area% of 3 to 50%. More specifically, they can be included in an area% of 4 to 9%.

[0112] In the step of preparing a non-oriented electrical steel sheet, the average grain size of the non-oriented electrical steel sheet may be 30 ㎛ or less. By forming the grains in this way to be small, the grains can grow under pressure during SRA to form {100} <025> It helps in grain formation and can improve the mechanical strength of the steel core. The grain size can be measured on the cross-section in the TD direction and can be calculated as the diameter of a circle with the same area. More specifically, the average grain size can be 3 to 30 ㎛. More specifically, it can be 10 to 25 ㎛.

[0113] The step of preparing a non-oriented electrical steel sheet may include a step of hot-rolling a slab containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder including Fe and inevitable impurities, to produce a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0114] First, the slab is hot rolled.

[0115] The alloy composition of the slab has been described in the alloy composition of the previously mentioned non-oriented electrical steel sheet, so a duplicate description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab are substantially identical.

[0116] Specifically, the slab contains Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, with the remainder being Fe and unavoidable impurities.

[0117] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0118] Slabs can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1200℃ or lower. If the slab heating temperature is too high, precipitates such as AlN and MnS present within the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, inhibiting grain growth and reducing magnetism.

[0119] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 1.0 to 4.5 mm. In the step of producing the hot-rolled sheet, the finishing rolling temperature can be 800°C or higher. Specifically, it can be 800 to 1000°C. The hot-rolled sheet can be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled sheet can be 1.5 to 4.3 mm.

[0120] After manufacturing a hot-rolled steel sheet, an additional step of annealing the hot-rolled sheet may be included. At this time, the soaking temperature may be 800 to 1100°C. If the annealing temperature is too low, the recrystallized structure may not be formed or may grow finely, thereby reducing the effect of increasing the magnetic flux density. If the annealing temperature is too high, the magnetic properties may deteriorate, and the rolling workability may deteriorate due to deformation of the plate shape. More specifically, the temperature range may be 830 to 1080°C. The soaking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may be omitted.

[0121] Next, the hot rolled steel sheet is cold rolled to produce a cold rolled sheet. At this time, cold rolling can be performed at a reduction ratio of 40 to 85%. If the reduction ratio is too low, the accumulated strain energy in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which can cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it can cause problems in the subsequent annealing process. <111> / ND The recrystallization of the grains in the direction of orientation is promoted, and the grains become finer, which can cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 60 to 75%. The cold rolling step can be performed using a tandem cold rolling mill that continuously cold rolls the steel sheet using multiple rolling stands, or a reverse rolling mill that discontinuously cold rolls the steel sheet using 12 or more rolling rolls. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0122] The process of manufacturing cold rolled sheets can be performed once or twice or more with intermediate annealing in between.

[0123] Next, before annealing the cold-rolled sheet, the cold-rolled sheet is heated. The heating rate in the range of 300 to 500°C is 40°C / sec or more, and the heating rate in the range of 500 to 700°C may be 20 to 38°C / sec. The heating rate in the range of 300 to 500°C needs to be high. By increasing the heating rate at this time, a thin and dense oxide layer can be formed on the surface, thereby preventing additional oxidation and further improving magnetism. In addition, {100} <025> It also helps to generate a large number of crystal grains. More specifically, the heating rate in the range of 300 to 500°C can be 43 to 70°C / sec.

[0124] The heating rate in the range of 500 to 700℃ can be relatively low. However, if it is too low or too high, {111} / ND orientation develops, resulting in {100} <025> It may interfere with the formation of a large number of crystal grains. More specifically, the heating rate in the range of 500 to 700°C may be 21 to 37°C / sec.

[0125] Next, the cold-rolled sheet is annealed. At this time, the soaking temperature may be 850°C or lower. If the soaking temperature is too high, the grains may not grow sufficiently, increasing hysteresis loss and deteriorating iron loss. More specifically, annealing may be performed at a temperature of 750 to 850°C. The soaking time may be 10 to 300 seconds.

[0126] After cold-rolled sheet annealing, an insulating film can be formed. The insulating film can be treated with organic, inorganic, or organic-inorganic composite films, and can also be treated with other insulating film agents.

[0127] Returning to the description of the core manufacturing method, a laminate is manufactured by stamping and laminating non-oriented electrical steel sheets. Stamping refers to cutting non-oriented electrical steel sheets into the shape of the motor core, which can be stamped into a ring shape. Lamination refers to stacking electrical steel sheets along their thickness, and can be stacked to a height of 20 mm to 300 mm, as needed.

[0128] Next, in the stress relief annealing step, the laminate is annealed while being pressed. Stress relief annealing is a process of removing the stress applied to the steel plate during punching. In one embodiment of the present invention, during stress relief annealing, pressure is applied to the laminate to apply tensile stress in all directions perpendicular to the core surface, thereby {100} <025> and improves the anisotropy of iron loss. Specifically, the pressure applied to the laminate is 0.10 to 2.00 MPa. If the pressure is too small, it is difficult to achieve the aforementioned purpose. If the pressure is too large, the {111} / ND orientation develops and {100} <025> This is formed less. More specifically, the pressure can be 0.50 to 1.75 MPa.

[0129] The soaking temperature of the stress-relief annealing step may be between 750 and 850°C. If the soaking temperature is too low, residual stress may remain during the punching process, which may adversely affect the magnetism. If the soaking temperature is too high, an oxide layer may develop, which may lead to a deterioration in the magnetism. More specifically, the soaking temperature may be between 775 and 825°C. The soaking time may be between 30 minutes and 6 hours. The atmosphere may be a nitrogen atmosphere.

[0130] The stress relief annealing step can be annealed to satisfy the following equation 1.

[0131] [Formula 1]

[0132] Pressure ≥ average grain size × unrecrystallized fraction × 5 / SRA temperature

[0133] (In Equation 1, the unit of pressure is MPa, the unit of average grain size is ㎛, the unit of unrecrystallized fraction is area%, and the unit of SRA temperature is ℃.)

[0134] That is, the lower the SRA cracking temperature and the larger the crystal grains, the higher the pressure must be {100} <025> can be produced in large quantities.

[0135]

[0136] The present invention will be described in more detail below through examples. However, these examples are intended only to illustrate the present invention and are not intended to limit the present invention.

[0137]

[0138] Example

[0139] A slab containing the following Table 1 and other impurities was manufactured. C, S, N, and Ti were all controlled to 0.0030% or less. This was heated to 1150°C and hot-rolled at a finishing temperature of 850°C to manufacture a hot-rolled sheet having a thickness of 2.0 mm. The hot-rolled hot-rolled sheet was annealed at 1100°C for 4 minutes and pickled. Thereafter, it was cold-rolled to produce a thickness of 0.25 mm. Cold-rolled sheet annealing was performed under the conditions shown in Table 2 below. After cold-rolled sheet annealing, the unrecrystallized fraction and average grain size of the non-oriented electrical steel sheet were measured and summarized in Table 2 below.

[0140] Cold-rolled, annealed, non-oriented electrical steel sheets were punched into rings with an outer diameter of 100 mm and an inner diameter of 80 mm, stacked to a height of 30 mm, and pressure was applied using a jig to perform SRA to finally manufacture the core. The SRA soaking time was 1 hour, and the atmosphere was nitrogen.

[0141] Method for measuring unrecrystallized fraction: The fraction of elongated grains was obtained through EBSD. Specifically, it was determined that the Grain Orienation Spread (GOS) was 2° or more.

[0142] Method for measuring average grain size: The grain size was obtained from the number of grains per unit area using an optical microscope.

[0143] {100} <025> Grain fraction measurement method: The non-oriented electrical steel sheet present in the core was separated, polished in the ND direction, and a 1 / 2t-thick region was observed using EBSD to obtain the fraction. At this time, the tolerance angle was set to 15°.

[0144] Circumferential iron loss (W10 / 400) measurement method: The circumferential iron loss was measured by winding a Cu wire around a ring-shaped non-oriented electrical steel plate.

[0145] Steel grade (weight%)SiAlMnSnSbResistivity (μΩ·cm)13.60.80.80.0500.0306723.40.50.50.0300.0106033.40.51.00.0500.0206343.21.01.50.0300.0306953.31.00.70.0500.0406663.20.51.10.0500.0406173.30.50.90.0500.040618 3.50.70.50.0100.0106493.50.70.80.0250.02565103.80.50.70.0200.02066113.80.41.20.0150.01569123.60.51.20.0500.01066133.60.50.80.0500.05064143.61.71.10.0150.03079153.41.70.90.0050.00576

[0146] Steel gradeHeating rate (300 to 500℃ section, ℃ / sec)Heating rate (500 to 700℃ section, ℃ / sec)Cracking temperature (℃)Unrecrystallized fraction (area %)Average grain size (㎛)145248005182482279051535225810435435278305215453385031665636785515751327956128652881061995037900138107018770817115945835315124135745155134530760109144432720355154928770227

[0147] Steel grade (weight%) SRA temperature (℃) Jig pressure (MPa) Equation 1 Right-hand side value {100} <025> Fraction (area %) Circumferential iron loss (W / kg) 17751.500.5811.315.827801.200.489.715.738000.900.886.518.748100.750.655.319.558302.500.296.018.768250.700.459.716.478350.950.439.815.187901.20 0.728.715.498001.100.243.520.1108200.900.836.019.5118300.750.276.518.6128600.450.446.018.7138100.750.566.517.9147750.351.135.718.4157901.250.974.518.1

[0148] As shown in Tables 1 to 3, the steel components are appropriately controlled and the process conditions are appropriately controlled, {100} <025> When these multiples are formed, it can be confirmed that the circumferential iron loss is excellent.

[0149] On the other hand, if the steel component is not properly controlled or the process conditions are not properly controlled, {100} <025> It can be confirmed that this exists in small quantities and that the circumferential iron loss is inferior.

[0150]

[0151] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A laminate comprising a plurality of non-oriented electrical steel sheets, each of which contains 1.5 to 4.5 wt% of Si, 0.1 to 2.0 wt% of Al, and 0.1 to 2.0 wt% of Mn, with the remainder being Fe and unavoidable impurities. The above non-oriented electrical steel sheet is {100} <025> A core having an area fraction of crystal grains having an orientation of 15° or less from the core of 7% or more.

2. In paragraph 1, The above non-oriented electrical steel sheet is an iron core further comprising at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

3. In paragraph 1, The above non-oriented electrical steel sheet is an iron core further containing 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As.

4. In paragraph 1, The above non-oriented electrical steel sheet is an iron core further comprising at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

5. In paragraph 1, The above non-oriented electrical steel sheet is an iron core further comprising at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

6. A step for preparing a non-oriented electrical steel sheet containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities; A step of manufacturing a laminate by punching and laminating the above non-oriented electrical steel sheets; and A method for manufacturing a steel core, comprising a stress relief annealing step of annealing the laminate while applying pressure of 0.1 to 2 MPa.

7. In paragraph 6, A method for manufacturing a core, wherein the non-oriented electrical steel sheet is prepared in a step of preparing the non-oriented electrical steel sheet, wherein the non-oriented electrical steel sheet contains 3 area% or more of unrecrystallized material.

8. In paragraph 6, A method for manufacturing a core in which, in the step of preparing the non-oriented electrical steel sheet, the non-oriented electrical steel sheet has an average grain size of 30 ㎛ or less.

9. In paragraph 6, A method for manufacturing a steel core, wherein the cracking temperature of the stress relief annealing step is 750 to 850°C.

10. In paragraph 6, A method for manufacturing a steel core in which the stress relief annealing step satisfies the following equation 1. [Formula 1] Pressure ≥ average grain size × unrecrystallized fraction × 5 / SRA temperature (In Equation 1, the unit of pressure is MPa, the unit of average grain size is ㎛, the unit of unrecrystallized fraction is area%, and the unit of SRA temperature is ℃.) 11. In paragraph 6, The steps for preparing the above non-oriented electrical steel sheet are A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities; A step of manufacturing a cold rolled sheet by cold rolling the hot rolled steel sheet above, and A method for manufacturing an iron core, comprising: a cold rolled sheet annealing step of annealing the cold rolled sheet.

12. In paragraph 11, A method for manufacturing a core, wherein the above slab further includes at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

13. In paragraph 11, A method for manufacturing an iron core, wherein the above slab further contains 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As.

14. In paragraph 11, A method for manufacturing an iron core, wherein the above slab further includes at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

15. In paragraph 11, A method for manufacturing an iron core, wherein the above slab further includes at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

16. In paragraph 11, The method further comprises a step of heating the cold rolled sheet prior to the cold rolled sheet annealing step of annealing the cold rolled sheet, A method for manufacturing an iron core, wherein the heating rate in the range of 300 to 500°C is 40°C / sec or more, and the heating rate in the range of 500 to 700°C is 20 to 38°C / sec.

17. In paragraph 11, A method for manufacturing an iron core, wherein in the cold rolled sheet annealing step of annealing the cold rolled sheet, the cracking temperature is 850°C or lower.