Non-oriented electrical steel sheet and method for manufacturing same

Abstract

A non-oriented electrical steel sheet, according to one embodiment of the present invention, comprises, by weight%, Si: 1.5% to 5.0%, Al: 0.1% to 2.5%, and Mn: 0.1% to 2.5%, with the remainder being Fe and inevitable impurities, wherein an area ratio of crystal grains that are 30μm smaller than average crystal grains to crystal grains that are 30μm larger than the average crystal grains is 12% or more, an area ratio of crystal grains having a grain diameter of 20μm or less is 0.8% or less, and Formula 1 below is satisfied. [Formula 1] GSSTD / GSAVE ≤ 0.7 (In Formula 1, GSSTD refers to a standard deviation of crystal grains, and GSAVE refers to an average crystal grain diameter.)

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, which simultaneously improves strength and magnetism by appropriately forming grain sizes by controlling the reduction ratio and temperature of each pass in the finishing rolling process during the hot-rolled sheet manufacturing process.

[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 Iron loss is often used to evaluate the properties of non-oriented electrical steel sheets. Furthermore, with increasing rotational speeds, strength, previously considered unimportant, is now being evaluated as an important characteristic.

[0005] Therefore, reflecting the recent energy efficiency improvement policy and the direction of utilization of non-oriented electrical steel sheets, it can be said that 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 methods for reducing core loss, one of the important magnetic properties of non-oriented electrical steel, are increasing the content of high-resistivity elements such as Si, Al, and Mn, or thinning the steel sheet. Increasing the content of Si, Al, and Mn increases the resistivity of the steel, which in turn reduces eddy current loss among the core loss of non-oriented electrical steel, thereby reducing core loss. Since eddy current loss accounts for a larger proportion of high-frequency core loss, this method can be a very effective method for reducing high-frequency core loss. However, the effect varies depending on the addition ratio, and the magnetic flux density deteriorates as the content of alloying elements increases. Therefore, to secure excellent core loss and magnetic flux density, it is necessary to appropriately control the appropriate addition amount and the addition ratio between Si, Al, and Mn. Thinning the steel sheet is also very effective in reducing core loss by significantly reducing eddy current loss, but thin steel sheets have the disadvantage of poor productivity and workability.

[0007] Various technologies have been reported to improve the magnetic flux density while lowering the core loss of non-oriented electrical steel sheets. These include improving the texture by utilizing special additive elements such as REM to enhance magnetic properties, or introducing additional manufacturing processes such as warm rolling, double rolling, and double annealing. However, all of these technologies lead to increased manufacturing costs or difficulties in mass production. Therefore, it is necessary to develop technologies that are both excellent in magnetism and easy to produce commercially. In addition, technologies are being developed to suppress and control the formation of inclusions by minimizing the amount of impurities added and adding elements such as Ca. However, these also lead to increased manufacturing costs, and it is difficult to clearly secure their effects.

[0008] The strength of steel sheets tends to increase with increasing alloy content. However, elements such as silicon (Si) and aluminum (Al) are brittle and have different effects on strength. Therefore, optimizing the content and ratio of these elements is essential to ensure high strength. Furthermore, while finer grain sizes improve strength, there is an optimal grain size that minimizes iron loss. Therefore, technology to appropriately control grain size is essential to simultaneously achieve both low iron loss and high strength.

[0009] 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 a non-oriented electrical steel sheet and a method for manufacturing the same, which simultaneously improves strength and magnetism by appropriately forming grain sizes by controlling the reduction rate and temperature of each pass in the finishing rolling process during the hot-rolled sheet manufacturing process.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.5%, and Mn: 0.1 to 2.5%, the remainder being Fe and unavoidable impurities, and has an area ratio of grains that are 30 ㎛ smaller than the average grain size to 30 ㎛ larger than the average grain size of 12% or more, an area ratio of grains having a grain size of 20 ㎛ or less of 0.8% or less, and satisfies the following equation 1.

[0011] [Formula 1]

[0012] GS STD / GS AVE ≤ 0.7

[0013] (GS in Equation 1 STD means the standard deviation of the crystal grains, and GS AVE refers to the average grain size.)

[0014] GS STD may be 30 to 100㎛.

[0015] GS AVE may be 50 to 160㎛.

[0016] 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%).

[0017] 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.

[0018] 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%).

[0019] 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: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0020] A non-oriented electrical steel sheet according to one embodiment of the present invention may have a resistivity (ρ) of 63 μΩ·cm or more at 25°C.

[0021] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have a core loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more.

[0022] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, by weight %, 1.5 to 5.0% Si, 0.1 to 2.5% Al, and 0.1 to 2.5% Mn, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0023] The step of manufacturing a hot rolled steel sheet includes a rough rolling step and a finish rolling step, and the finish rolling step is performed through n passes, where n is 3 or more, and the reduction ratio (R) of an intermediate pass other than the first or last pass j ), the average of the pressure reduction ratios of all passes of the rolling process (R AVE ) and the largest absolute value of the difference in the pressure ratio of the intermediate pass is less than 40%.

[0024] The rolling process may have a difference between the rolling entry temperature (FET) and the rolling exit temperature (FDT) of 150°C or less.

[0025] 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%).

[0026] 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.

[0027] 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%).

[0028] 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%).

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention has grain sizes appropriately formed, and thus has excellent magnetic flux density, iron loss, and yield strength at the same time.

[0030] 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-class electric motors.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0035] 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.

[0036] 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.

[0037] 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.

[0038]

[0039] A non-oriented electrical steel sheet according to one embodiment of the present invention includes Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.5%, and Mn: 0.1 to 2.5%, with the remainder being Fe and unavoidable impurities.

[0040] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0041]

[0042] Si: 1.50 to 5.00 wt%

[0043] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and enhances 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 magnetic flux density may decrease significantly, and the rollability may deteriorate due to increased brittleness. Therefore, Si may be included in an amount of 1.5 to 5.0 wt%. More specifically, it may be included in an amount of 2.50 to 4.50 wt%. Even more specifically, it may be included in an amount of 2.70 to 3.85 wt%.

[0044]

[0045] Al: 0.10 to 2.50 wt%

[0046] Aluminum (Al) increases the resistivity of the material, thereby lowering iron loss and improving rollability, and reduces magnetic anisotropy, thereby reducing magnetic deviation in the rolling direction and the direction perpendicular to the rolling direction. If too little Al is added, it may be difficult to obtain the effect of reducing high-frequency iron loss. If too much Al is added, excessive nitride formation may occur, which may deteriorate magnetism. Therefore, Al may be included in an amount of 0.10 to 2.50 wt%. More specifically, it may be included in an amount of 0.50 to 2.50 wt%. More specifically, it may be included in an amount of 0.60 to 2.30 wt%.

[0047]

[0048] Mn: 0.10 to 2.50 wt%

[0049] Manganese (Mn) increases the resistivity of the material, improving iron loss and grain structure. If too little Mn is added, fine sulfides form, causing magnetic deterioration. However, if too much Mn is added, it can adversely affect magnetic flux density. Therefore, Mn may be included in an amount of 0.10 to 2.50 wt%, more specifically, 0.15 to 1.80 wt%.

[0050]

[0051] In one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet at 25℃ can be 63.0 μΩ·cm or more. 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, the resistivity of the steel increases, and the eddy current loss can be significantly reduced. In particular, as the frequency increases, the proportion of the total iron loss occupied by the eddy current loss increases, so in order to obtain excellent high-frequency iron loss, it is necessary to control the resistivity of the steel to a certain level or more. Through the present invention, when the resistivity (ρ) of the steel is 63 μΩcm or more, excellent characteristics can be secured. More specifically, the resistivity (ρ) can be 64.0 to 90.0 μΩ·cm.

[0052] In one embodiment of the present invention, resistivity can be measured using a 4-point method, etc.

[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: 0.100 wt% or less

[0056] Phosphorus (P) is an element that improves the grain structure of steel by segregating between grain boundaries and surfaces. However, if too much P is added, it can inhibit grain growth, thereby lowering iron loss, and reduce rollability due to grain boundary segregation, which can also reduce productivity. More specifically, P can be included in an amount of 0.0001 to 0.0500 wt%. Even more specifically, P can be included in an amount of 0.0010 to 0.0200 wt%.

[0057] C: 0.0050 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 0.0005 to 0.0045 wt%.

[0059] S: 0.0050 wt% or less

[0060] Sulfur (S) can form fine precipitates, MnS and CuS, which can worsen magnetic properties and hot workability. More specifically, S can be included in an amount of 0.0005 to 0.0045 wt%.

[0061] Ti: 0.0050 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 0.0005 to 0.0035 wt% of Ti.

[0063] N: 0.0050 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 0.0005 to 0.0045 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

[0068] Tin (Sn) can be added to improve magnetism because it improves the material's texture by segregating at grain boundaries and surfaces and plays a role in suppressing surface oxidation. If too much Sn is added, grain boundary segregation becomes severe, which deteriorates the surface quality and increases hardness, which can cause fracture of cold-rolled sheets and reduce rollability. Specifically, Sn can be further included in an amount of 0.005 to 0.200 wt%. More specifically, it can be further included in an amount of 0.010 to 0.080 wt%.

[0069] Sb

[0070] Antimony (Sb) can be additionally added to improve magnetism, as it improves the material's aggregate structure and suppresses surface oxidation by segregating at grain boundaries and surfaces. If too much Sb is added, grain boundary segregation becomes severe, deteriorating surface quality and increasing hardness, which can cause cold-rolled sheet fracture and reducing rollability. Specifically, Sb can be further included in an amount of 0.005 to 0.200 wt%. More specifically, it can be further included in an amount of 0.010 to 0.080 wt%.

[0071] Bi, Pb, Ge, and As

[0072] 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.

[0073]

[0074] 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%).

[0075] Cu: 0.005 to 0.200 wt%

[0076] 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%.

[0077] Cr: 0.01 to 0.50 wt%

[0078] 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%.

[0079] Ni: 0.05 wt% or less

[0080] 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.

[0081] Zn: 0.01 wt% or less

[0082] 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%.

[0083] Co: 0.05 wt% or less

[0084] 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.

[0085]

[0086] 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%).

[0087] Mo: 0.030 wt% or less

[0088] 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%.

[0089] B: 0.0050 wt% or less

[0090] 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%.

[0091] V: 0.0050 wt% or less

[0092] 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%.

[0093] Ca: 0.0050 wt% or less

[0094] 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.

[0095] Nb: 0.0050 wt% or less

[0096] 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%.

[0097] Zr: 0.0050 wt% or less

[0098] 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%.

[0099] Te: 0.0100 wt% or less

[0100] 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%.

[0101] Mg: 0.0050 wt% or less

[0102] 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%.

[0103]

[0104] 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).

[0105]

[0106] As described above, in one embodiment of the present invention, by appropriately forming the grain size of crystal grains, strength and magnetism can be improved simultaneously.

[0107] In one embodiment of the present invention, the non-oriented electrical steel sheet has an area ratio of grains having a grain size that is 30 ㎛ smaller than the average grain size to grains having a grain size that is 30 ㎛ larger than the average grain size of 12.0% or more. That is, in one embodiment of the present invention, by forming grains having a difference of ±30 ㎛ or less from the average grain size in various areas, the core loss can be reduced. The more fine grains there are, the more hysteresis loss increases, resulting in poor core loss, and if there are too many coarse grains, the eddy current loss increases, resulting in poor core loss. More specifically, the area ratio of grains having a grain size that is 30 ㎛ smaller than the average grain size to grains having a grain size that is 30 ㎛ larger than the average grain size can be 12.5 to 20.0%.

[0108] In one embodiment of the present invention, crystal grains can be measured based on a cross-section including the thickness direction of the steel sheet, more specifically, the TD plane. The crystal grain size can be obtained by observing the crystal grains with an optical microscope and assuming a circle with the same area as the crystal grains, and using the diameter of that circle as the basis. The specimen can be measured as a specimen that includes at least the entire thickness and has a longitudinal area of ​​10 mm, and the measurement can be performed at least three times.

[0109] The area ratio of crystal grains with a grain size of 20 ㎛ or less may be 0.80% or less. Fine crystal grains with a grain size of 20 ㎛ or less can be minimized by controlling the process from the hot rolling stage. As the iron loss deteriorates as fine crystal grains are formed, their occupied area can be minimized. More specifically, the area ratio of crystal grains with a grain size of 20 ㎛ or less may be 0.20 to 0.75%.

[0110] A non-oriented electrical steel sheet according to one embodiment of the present invention satisfies the following equation 1.

[0111] [Formula 1]

[0112] GS STD / GS AVE ≤ 0.70

[0113] (GS in Equation 1 STD means the standard deviation of the crystal grains, and GS AVE refers to the average grain size.)

[0114] The standard deviation of the crystal grains can be specifically the population standard deviation. More specifically, it can be calculated using the following formula for n crystal grains.

[0115]

[0116] GS i represents the grain size of the i-th crystal grain, and GSAVE represents the average grain size.

[0117] Equation 1 implies that the fine and coarse grains should be reduced to make the grain size uniform. More specifically, the value of Equation 1 can be between 0.30 and 0.67.

[0118] GS STD can be 30 to 100㎛. More specifically, GS STD may be 33 to 95㎛.

[0119] GS AVE can be 50 to 160㎛. More specifically, GS AVE may be 60 to 155㎛.

[0120] As described above, in one embodiment of the present invention, by appropriately forming the crystal grain size, strength and magnetism can be improved at the same time. Specifically, a non-oriented electrical steel sheet according to one embodiment of the present invention may have a core loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more. The thickness standard may be 0.20 mm. More specifically, the core loss (W10 / 400) may be 9.0 to 11.0 W / kg. The magnetic flux density (B50) may be 1.61 to 1.70 T. The core loss (W10 / 400) is the core loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. The magnetic flux density (B50) refers to a magnetic flux density induced in a magnetic field of 5000 A / m. Iron loss (10 / 400) and magnetic flux density (B50) can be measured with a single sheet tester in the rolling direction and the direction perpendicular to the rolling, and the average values ​​can be measured.

[0121] Additionally, one embodiment of the present invention also exhibits excellent mechanical strength. The yield strength may be 480 MPa or greater. More specifically, the yield strength may be 480 MPa or greater and 650 MPa or less. The yield strength can be measured using a 0.2% offset method during a tensile test.

[0122]

[0123] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet.

[0124]

[0125] Below, each step is explained in detail.

[0126] First, the slab is hot rolled.

[0127] 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.

[0128] Specifically, the slab contains Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.5%, Mn: 0.1 to 2.5%, and the remainder includes Fe and inevitable impurities.

[0129] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0130] 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.

[0131] Next, the slab is hot rolled to produce a hot-rolled plate.

[0132] In one embodiment of the present invention, it was discovered that precise control of conditions from the hot rolling stage is necessary to improve the aggregate structure. Specifically, it was discovered that the reduction rate and temperature of each pass in the sand rolling process need to be controlled.

[0133] In one embodiment of the present invention, the steps for manufacturing a hot-rolled steel sheet include a rough rolling step and a finishing rolling step. The rough rolling step is a process for first rolling a slab transferred from a casting machine into a bar shape and is comprised of three to four rolling mills. The finishing rolling step is a process for rolling the rough-rolled steel sheet to the final hot-rolling target thickness to make a hot-rolled coil and is comprised of a continuous multi-stage rolling mill.

[0134] The thought rolling step is performed through n passes, where n is 3 or more.

[0135] Pressure ratio (R) of intermediate passes other than the first or last pass j ), the average of the pressure reduction ratios of all passes of the rolling process (R AVE ) and the largest absolute value of the difference in the pressure ratio of the intermediate pass is less than 40%.

[0136] The average of the compression ratios of all passes of the rolling process (R AVE ) can be expressed as the following equation.

[0137]

[0138] At this time, R i means the compression ratio of the ith pass.

[0139] That is, the average of the pressure reduction rates of all passes of the thought rolling (R AVE ) can be expressed as (R1+R2+……+Rn) / n.

[0140] Meanwhile, R j is the first (R1) or last pass (R n ) of the intermediate pass, not the compression ratio (R j ) means the average of the pressure reduction ratios of all passes of the rolling process (R AVE ) and the absolute value of the difference in the pressure ratio of the intermediate pass is |(R AVE -R j )| can be expressed as, and the largest value of these can be less than or equal to 40%. That is, Max|(R AVE -R j )| can be expressed as ≤ 40.0%.

[0141] This means that the deviation between the reduction ratios of all passes in the rolling process is not large. If the above value is too large, a large number of coarse or fine grains are generated, which ultimately results in poor magnetic and yield strength. More specifically, the average reduction ratio of all passes in the rolling process (R AVE) and the largest absolute value of the difference in the compression ratio of the intermediate pass may be 20.0 to 39.5%.

[0142] In addition, the difference (FET-FDT) between the finish rolling entry temperature (FET) and the finish rolling exit temperature (FDT) in the finishing rolling step may be 150℃ or less. If this temperature difference is too large, the non-uniformity in the microstructure itself after rolling may increase, resulting in non-uniform microstructure in the final product. More specifically, the difference (FET-FDT) between the finish rolling entry temperature (FET) and the finish rolling exit temperature (FDT) may be 50 to 148℃. The finish rolling entry temperature may be based on the steel sheet temperature immediately before entering the finishing rolling mill, and the finish rolling exit temperature may be based on the steel sheet temperature immediately after exiting the finishing rolling mill.

[0143] In one embodiment of the present invention, the rolling process may be performed in three to seven passes (i.e., n is 3 to 7). If the number of passes is too small, the rolling load may be excessively large, making the process difficult. If the number of passes is too large, productivity may be reduced.

[0144] The thickness of the hot-rolled sheet may be 1.0 to 4.5 mm. The finishing rolling temperature during the manufacturing process of the hot-rolled sheet may be 800°C or higher. Specifically, it may be 800 to 1000°C. The hot-rolled sheet may be coiled at a temperature of 700°C or lower. More specifically, the thickness of the hot-rolled sheet may be 1.5 to 4.3 mm.

[0145] After manufacturing a hot-rolled steel sheet, an annealing step of the hot-rolled sheet may be further included. At this time, the soaking temperature may be 850 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 10 to 300 seconds. The hot-rolled sheet annealing step may be omitted.

[0146] 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 95%. 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 can be promoted, and the grains can 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 85%. 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.

[0147] The process of manufacturing cold rolled sheets can be performed once or twice or more with intermediate annealing in between.

[0148] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. The annealing temperature in the cold-rolled sheet annealing process is not particularly limited as long as it is the temperature typically applied to non-oriented electrical steel sheets. The iron loss of non-oriented electrical steel sheets is closely related to grain size. Iron loss in non-oriented electrical steel sheets can be divided into hysteresis loss and eddy current loss. Hysteresis loss decreases as grain size increases, while eddy current loss increases as grain size increases. Therefore, there is an optimal grain size at which the sum of hysteresis loss and eddy current loss is minimized. Therefore, it is important to derive and apply an annealing temperature that can secure the optimal grain size, and an annealing temperature of 850 to 1100°C is appropriate. If the annealing temperature is too low, the grains become too fine, increasing hysteresis loss. If the annealing temperature is too high, the grains become too coarse, increasing eddy current loss and resulting in poor iron loss. Additionally, the annealing time is also appropriate if it is 10 to 300 seconds, and annealing can be performed in a mixed atmosphere of hydrogen or argon and nitrogen to prevent magnetic deterioration due to the formation of an oxide layer.

[0149] During the cold-rolled sheet annealing process, all (i.e., more than 99%) of the processed structure formed during the cold rolling stage can be recrystallized.

[0150] 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.

[0151]

[0152] 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.

[0153]

[0154] Example 1

[0155] Slabs were manufactured using the components listed in Table 1 and the remainder including Fe and unavoidable impurities. These were heated to 1180°C and hot-rolled under the conditions listed in Table 2 below, hot-rolled to a thickness of 2.1 mm, and then coiled at 700°C. The hot-rolled steel sheets were annealed at 1000°C for 60 seconds. After hot-rolled sheet annealing, the pickled specimens were cold-rolled to a thickness of 0.2 mm, and finally cold-rolled. Cold-rolled sheet annealing was performed at 1000°C for 50 seconds.

[0156] The grain size was determined by cutting the steel plate along the TD plane to obtain a specimen, and then analyzing it using an optical microscope and image analyzer.

[0157] The resistivity at 25℃ was measured using the 4-point method.

[0158] Yield strength was measured using the 0.2% offset method during tensile testing.

[0159] Iron loss (W10 / 400) and magnetic flux density (B50) were measured using a single sheet tester.

[0160] Steel grade SiMnAlPCSTiN Resistivity (μΩcm) 12.95 0.16 1.80 0.01 40.00 140.00 150.00 50.00 276 7.82 3.08 1.80 2.18 0.00 80.00 210.00 260.00 150.00 278 2.93 3.78 1.410 .850.0090.00110.00420.00200.001873.544.000.381.870.0110.00420.00450.00080.002081.753.350.561.540.0070.00400.00170.00060.00137 1.763.600.210.990.0030.00230.00170.00350.002266.373.671.730.820.0060.00290.00230.00130.000673.883.370.460.920.0040.00240.0014 0.00330.003564.392.981.621.190.0090.00260.00290.00200.004369.5103.661.590.770.0040.00140.00200.00260.001272.3112.980.701.340. 0050.00260.00240.00290.001666.0124.001.571.390.0110.00170.00290.00330.002183.0133.651.121.340.0080.00170.00300.00080.001376.0 144.141.120.750.0060.00340.00450.00160.003574.8153.810.501.780.0040.00160.00210.00350.002079.2162.480.261.140.0090.00260.0028 0.00080.001155.6173.991.680.480.0050.00160.00100.00200.001873.3182.421.340.460.0040.00180.00340.00220.001253.4193.050.560.820 .0080.00070.00090.00370.003660.1203.750.191.850.0040.00370.00410.00370.001877.6213.451.371.130.0030.00280.00220.00360.004272.7223.091.680.950.0040.00380.00330.00220.002768.4232.920.702.080.0140.00330.00050.00080.004273.7243.121.531.220.0150.00260.00080.00340.001470.9253.270.531.590.0110.00320.00170.00290.003671.2262.931.241.270.0050.00090.00260.00130.001667.7272.921.141.330.0090.00130.00140.00270.002467.7283.051.630.510.0130.00310.00090.00220.001562.7293.480.341.030.0040.00330.00440.00060.001666.1302.881.430.760.0140.00440.00240.00140.004562.5.

[0161] 강종FET-FDT(℃)Max|(R AVE -R j )| (%)GS AVE (㎛)GS STD (㎛)GS STD / GS AVE GS AVEFraction of crystal grains within ±30㎛ (area%) Fraction of crystal grains less than 20㎛ (area%) 18329.9108670.6219.50.5528835.6107380.3618.90.31311731.8145460.3212.20.44413129.0142600.4213.10.41512737.6150620.4116.50.5269824.0110540.4914.30.2175926.0149910.6119.30.67814737.8873 70.4312.40.56911221.6133520.3913.40.231010124.6102330.3212.90.281114232.699450.4515.80.45129239.592560.6112.60.401313429.664420.6615.10.60145624.2133480.3613.20.711514722.2138580.4214.00.56 1612822.1137870.6414.90.421717025.764500.7811.00.791813024.399660.6713.90.34198436.2104530.5115.50.532016537.8118850.7211.50.752115622.776460.6111.40.94225943.268480.7112.60.832310844.71108 30.7511.90.44245848.8130930.7211.10.852517546.5100760.7611.01.012615136.958420.7212.50.892716143.352380.7311.90.672816735.173540.7410.10.90299841.4134570.439.50.943017248.81441070.749.91.07

[0162] Steel grade Yield strength (MPa) W10 / 400 (W / Kg) B50 (T) Classification 15119.96 1.63 Invention example 25318.96 1.62 Invention example 35358.92 1.62 Invention example 46059.19 1.64 Invention example 55199.84 1.64 Invention example 65099.63 1.63 Invention example 75229.4 31.64 Invention example 85079.181.63 Invention example 948710.051.64 Invention example 105169.681.63 Invention example 114889.911.64 Invention example 125638.841.62 Invention example 135808.911.62 Invention example 145529.161.62 Invention example 155559.041. 62 Invention Example 1640512.321.59 Comparative Example 1752912.691.59 Comparative Example 1836012.051.59 Comparative Example 1946813.191.58 Comparative Example 2054912.631.57 Comparative Example 2154112.021.57 Comparative Example 2248512.151.59 Comparative Example 235221 2.581.58Comparative Example 2450612.181.59Comparative Example 2552312.391.57Comparative Example 2648212.381.58Comparative Example 2748412.031.58Comparative Example 2844913.011.58Comparative Example 2946712.861.59Comparative Example 3044212.761.59Comparative Example

[0163] As shown in Tables 1 to 3, No. 1 to 15, in which the steel composition and rolling conditions are appropriately controlled and the crystal grain size is appropriately formed, can be confirmed to have excellent iron loss, magnetic flux density, and yield strength at the same time.

[0164] On the other hand, it can be confirmed that No. 16 to 30, in which the steel composition or rolling conditions were not properly controlled and many fine or coarse grains were formed, have inferior iron loss, magnetic flux density, or yield strength.

[0165]

[0166] 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. Contains Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.5%, and Mn: 0.1 to 2.5%, with the remainder being Fe and inevitable impurities. The area ratio of grains that are 30㎛ smaller than the average grain size or 30㎛ larger than the average grain size is 12% or more, The area ratio of crystal grains with a diameter of 20㎛ or less is 0.8% or less, A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] GS STD / GS AVE ≤ 0.7 (GS in Equation 1 STD stands for the standard deviation of the grain size, and GS AVE ) refers to the average grain size.

2. In paragraph 1, GS above STD Non-oriented electrical steel sheet with a thickness of 30 to 100㎛.

3. In paragraph 1, GS above AVE Non-oriented electrical steel sheet with a thickness of 50 to 160㎛.

4. In paragraph 1, Non-oriented electrical steel sheet 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%).

5. In paragraph 1, A non-oriented electrical steel sheet further comprising 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As.

6. In paragraph 1, A non-oriented electrical steel sheet 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%).

7. In paragraph 1, Non-oriented electrical steel sheet 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%).

8. In paragraph 1, Non-oriented electrical steel sheet having a resistivity (ρ) of 63 μΩ·cm or more at 25℃.

9. In paragraph 1, Non-oriented electrical steel sheet with iron loss (W10 / 400) of 12.0 W / Kg or less and magnetic flux density (B50) of 1.60 T or more. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.5%, and Mn: 0.1 to 2.5% by weight, with 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 Including a cold rolled sheet annealing step for annealing the cold rolled sheet; The step of manufacturing the above hot rolled steel plate includes a rough rolling step and a finish rolling step, The thought rolling step is performed through n passes, where n is 3 or more. Pressure ratio (R) of intermediate passes, not the first or last pass j ) about, The average of the pressure drop of all passes of the rolling process (R AVE ) and a method for manufacturing a non-oriented electrical steel sheet, wherein the largest absolute value of the difference in the reduction ratio of the intermediate pass is 40% or less.

11. In paragraph 10, The above rolling step is a method for manufacturing a non-oriented electrical steel sheet in which the difference between the rolling entry temperature (FET) and the rolling exit temperature (FDT) is 150°C or less.

12. In paragraph 10, A method for manufacturing a non-oriented electrical steel sheet, 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 10, A method for manufacturing a non-oriented electrical steel sheet, 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 10, A method for manufacturing a non-oriented electrical steel sheet, 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 10, A method for manufacturing a non-oriented electrical steel sheet, 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%).

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