Non-oriented electrical steel sheet, motor core, and method for manufacturing same

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention comprises, in weight%, 3.2 to 4.5% of Si, 1.2 to 2.5% of Al, 0.1 to 2.5% of Mn, and the balance being Fe and inevitable impurities, and satisfies equation 1. [Equation 1] (length of protruding oxide layer portion / length of entire oxide layer) ≤ 0.1

Description

Non-oriented electrical steel sheet, motor core and manufacturing method thereof

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same, wherein magnetism is simultaneously improved by forming an appropriate oxide layer by appropriately controlling conditions during cold rolling.

[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 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] One embodiment of the present invention provides a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same, wherein the magnetism is enhanced by appropriately controlling conditions during cold rolling to form an appropriate oxide layer.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention contains Si: 3.2 to 4.5% by weight, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5%, with the remainder being Fe and unavoidable impurities, and satisfies the following equation 1.

[0010] [Formula 1]

[0011] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.1

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 2.

[0013] [Formula 2]

[0014] (Area of ​​internal oxide / Area of ​​total oxide layer) ≤ 0.05

[0015] (In Equation 2, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.)

[0016] A non-oriented electrical steel sheet according to one embodiment of the present invention may contain Mn: 0.7 to 2.5 wt%.

[0017] 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%).

[0018] 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.

[0019] 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: 0.005 to 0.1 wt%, Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0020] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.001 to 0.1 wt%, 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%).

[0021] A non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 150 ㎛ and a yield strength of 480 MPa or more.

[0022] 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.

[0023] A motor core according to one embodiment of the present invention may be a non-oriented electrical steel sheet comprising 3.2 to 4.5% by weight of Si, 1.2 to 2.5% by weight of Al, and 0.1 to 2.5% by weight of Mn, with the remainder being Fe and unavoidable impurities, and satisfying the following formula 1, in which a plurality of non-oriented electrical steel sheets are laminated.

[0024] [Formula 1]

[0025] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.1

[0026] 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, in wt%, Si: 3.2 to 4.5%, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5%, with the remainder being 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 a cold-rolled sheet annealing step of annealing the cold-rolled sheet; wherein the step of manufacturing the cold-rolled sheet includes two or more passes, and the strain rate (1) in the first pass may be 200 / s or less, and the sum (1+2) of the strain rates of the first pass and the second pass may be 1100 / s or less.

[0027] In the step of manufacturing a cold-rolled sheet, the ratio of the strain rate (max) of the pass with the highest strain rate to the strain rate (total) of the entire step may be 0.3 or less.

[0028] 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%).

[0029] 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.

[0030] The slab may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.005 to 0.1 wt%, Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0031] The slab may further include at least one of Mo: 0.001 to 0.1 wt%, 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%).

[0032] A method for manufacturing a motor core according to one embodiment of the present invention includes a step of stress-relief annealing the aforementioned non-oriented electrical steel sheet, and the step of stress-relief annealing satisfies the following equation 3 or equation 4.

[0033] [Equation 3] 6 ≤ [O] × [Al] ≤ 240

[0034] [Equation 4] 480 ≤ [O] × [Al] ≤ 2400

[0035] (In Equations 3 and 4, [O] represents the content of O (ppm) in the atmosphere during stress relief annealing, and [Al] represents the content of Al (wt%) in the non-oriented electrical steel sheet.)

[0036] The stress relief annealing step can be performed at a temperature of 700 to 850°C for more than one hour.

[0037] A motor core according to one embodiment of the present invention comprises Si: 3.2 to 4.5% by weight, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5%, with the remainder being Fe and unavoidable impurities, and a surface of a sheet forming the motor core satisfies the following formula 1, and a side surface of the sheet satisfies the following formula 5.

[0038] [Formula 1]

[0039] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.1

[0040] [Formula 5]

[0041] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.093

[0042] The surface of a sheet forming a motor core can satisfy the following equation 2, and the side surface of the sheet can satisfy the following equation 6.

[0043] [Formula 2]

[0044] (Area of ​​internal oxide / Area of ​​total oxide layer) ≤ 0.05

[0045] [Formula 6]

[0046] (Area of ​​inner oxide / Area of ​​total oxide layer) ≤ 0.047

[0047] (In Equations 2 and 6, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.)

[0048] 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.

[0049] 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.

[0050] FIG. 1 and FIG. 2 are schematic diagrams of a cross-section including the thickness direction of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0051] Figure 3 is a schematic diagram of a cross-section of a motor core according to one embodiment of the present invention.

[0052] Figures 3 and 4 are schematic diagrams of a cross-section including the thickness direction of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0053]

[0054] 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 solely 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.

[0055] 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.

[0056] 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.

[0057] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0058] 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.

[0059] 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.

[0060] 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.

[0061]

[0062] A non-oriented electrical steel sheet according to one embodiment of the present invention includes Si: 3.2 to 4.5% by weight, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5%, with the remainder being Fe and unavoidable impurities.

[0063] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0064]

[0065] Si: 3.20 to 4.50 wt%

[0066] 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 3.20 to 4.5 wt%. More specifically, it may be included in an amount of 3.30 to 4.30 wt%. Even more specifically, it may be included in an amount of 3.50 to 4.20 wt%.

[0067]

[0068] Al: 1.20 to 2.50 wt%

[0069] 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 1.20 to 2.50 wt%. More specifically, it may be included in an amount of 1.30 to 2.40 wt%. More specifically, it may be included in an amount of 1.40 to 2.30 wt%.

[0070]

[0071] Mn: 0.10 to 2.50 wt%

[0072] Manganese (Mn) improves the iron loss by increasing the resistivity of the material and plays a role in improving the aggregate structure. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration, and if too much Mn is added, it can have a negative effect on the magnetic flux density. Therefore, Mn may be included in an amount of 0.10 to 2.50 wt%. More specifically, it may be included in an amount of 0.30 to 2.50 wt%. More specifically, it may be included in an amount of 0.70 to 2.50 wt%. More specifically, it may be included in an amount of 0.70 to 2.30 wt%. More specifically, it may be included in an amount of 0.70 to 2.20 wt%.

[0073]

[0074] 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 it is necessary to control the resistivity of the steel to a certain level or more in order to obtain excellent high-frequency iron loss. 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 70.0 to 90.0 μΩ·cm.

[0075] In one embodiment of the present invention, resistivity can be measured using a conventional resistivity measuring device such as the 4-point method.

[0076]

[0077] 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%).

[0078] P: 0.100 wt% or less

[0079] 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 productivity by lowering rollability due to grain boundary segregation. 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%.

[0080] C: 0.0050 wt% or less

[0081] 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%.

[0082] S: 0.0050 wt% or less

[0083] 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%.

[0084] Ti: 0.0050 wt% or less

[0085] 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.

[0086] N: 0.0050 wt% or less

[0087] 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%.

[0088]

[0089] 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.

[0090] Sn

[0091] Tin (Sn) can be added to improve magnetism because it improves the material's aggregate structure and suppresses surface oxidation by segregating at grain boundaries and surfaces. If too much Sn is added, grain boundary segregation becomes severe, which deteriorates the surface quality and increases hardness, which can cause cold-rolled sheet fracture 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 0.150 wt%.

[0092] Sb

[0093] 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 0.150 wt%.

[0094] Bi, Pb, Ge, and As

[0095] 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.

[0096]

[0097] 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: 0.005 to 0.1 wt%, Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0098] Cu: 0.005 to 0.200 wt%

[0099] 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%.

[0100] Cr: 0.01 to 0.50 wt%

[0101] 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%.

[0102] Ni: 0.005 to 0.100 wt%

[0103] 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 0.050 wt% of Ni.

[0104] Zn: 0.01 wt% or less

[0105] Zinc (Zn) can act as an impurity and degrade magnetism when contained in excessive amounts. Therefore, Zn may be added further within the aforementioned range. More specifically, Zr may be included in an amount of 0.001 to 0.005 wt%.

[0106] Co: 0.05 wt% or less

[0107] 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.

[0108]

[0109] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.001 to 0.1 wt%, 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%).

[0110] Mo: 0.001 to 0.100 wt%

[0111] 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 0.1 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 0.050 wt%. More specifically, Mo may be included in an amount of 0.005 to 0.030 wt%.

[0112] B: 0.0050 wt% or less

[0113] 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%.

[0114] V: 0.0050 wt% or less

[0115] 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%.

[0116] Ca: 0.0050 wt% or less

[0117] 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.

[0118] Nb: 0.0050 wt% or less

[0119] 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%.

[0120] Zr: 0.0050 wt% or less

[0121] 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%.

[0122] Te: 0.0100 wt% or less

[0123] 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%.

[0124] Mg: 0.0050 wt% or less

[0125] 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%.

[0126]

[0127] 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).

[0128]

[0129] FIG. 1 schematically illustrates a cross-section of a non-oriented electrical steel sheet (100) according to one embodiment of the present invention.

[0130] As shown in Fig. 1, a non-oriented electrical steel sheet (100) according to one embodiment of the present invention includes an oxide layer (20) existing from the surface to the inside and a steel sheet base material (10). In one embodiment of the present invention, the oxide layer (20) refers to a layer formed on the surface of the base material composed of oxides in which Al, Si, etc. are combined with oxygen. When a cross-section including the thickness direction (ND direction) of the steel sheet is observed by TEM, it forms an interface with the base material and is distinguished from the steel sheet base material (10) through component analysis. Although Fig. 1 shows that the oxide layer (20) exists on the upper surface of the steel sheet, the oxide layer (20) may exist on both the upper and lower surfaces. In this case, the steel sheet base material (10) exists between the upper surface oxide layer (20) and the lower surface oxide layer (20). Since the oxide layer (20) exists very thinly compared to the overall thickness of the non-oriented electrical steel sheet (100), it does not affect the overall alloy composition of the entire non-oriented electrical steel sheet (100).

[0131] Although omitted in Fig. 1, there are cases where an insulating film exists on the surface of a non-oriented electrical steel sheet (100). In this case, the insulating film and the oxide layer (20) can be distinguished through SEM and TEM, and are distinguished by confirming the components of the insulating film during component analysis.

[0132] As shown in Fig. 1, the oxide layer (20) is formed with a certain roughness with the steel plate base material (10), and occasionally, a protrusion (21) where the oxide layer (20) invades the steel plate base material (10) may exist. In one embodiment of the present invention, the protrusion (21) is formed in a thickness (T) of the oxide layer (20) in the inner direction (ND direction) of the steel plate greater than the imaginary boundary line (22) between the oxide layer (20) and the steel plate base material (10). O ) means the protruding portion. The virtual boundary line (22) can be determined as the interface when the oxide layer is formed with a completely uniform thickness using the average thickness of the oxide layer. The thickness (T) of the oxide layer (20) O ) can be obtained as the average thickness of the oxide layer.

[0133] In one embodiment of the present invention, a protrusion (21) can be formed to satisfy Equation 1.

[0134] [Formula 1]

[0135] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.100

[0136] Length (P) of the protruding oxide layer (20) L ) is the thickness (T) of the oxide layer (20) from the virtual boundary line (22) in the inner direction (ND direction) of the steel plate. O ) means the length occupied by the protrusion (21) of the parallel movement line (23) that has moved parallel to the protrusion (21). In case there are multiple protrusions (21), the length (P) of the protruding oxide layer (20) of all protrusions (21) L ) can be the sum of.

[0137] The length of the entire oxide layer refers to the length of the oxide layer (20) in the direction perpendicular to the thickness direction in the cross-section of the steel plate including the thickness direction. In other words, it refers to the entire horizontal length in the cross-section that is the subject of measurement.

[0138] If Equation 1 exceeds 0.100, the length of the protruding oxide layer portion (P L) means that it is relatively long, and in this case, the movement of the magnetic domains is hindered during the magnetization process, resulting in inferior magnetism. More specifically, the value of Equation 1 can be 0.030 to 0.095.

[0139] As shown in Fig. 2, in one embodiment of the present invention, an oxide (30) may be present in the steel plate base material (10). The oxide (30) exists separately from the oxide layer (20) and is distinct from the protrusion (21) connected to the oxide layer (20). The oxide layer (20), the protrusion (21), and the oxide (30) refer to portions formed by combining Si, Al, etc. with oxygen, and when analyzing the components by observing a cross-section including the thickness direction (ND direction) of the steel plate using a TEM, SEM, etc., they are distinguished from the steel plate base material (10) through the O component. The area of ​​the oxide (30) can be obtained by utilizing a commercial image analysis tool using SEM and TEM images. If the image analysis tool is not used, the average of the longest and shortest lengths of the internal oxide can be used as the average length, and the area can be manually calculated as a sphere or square depending on the shape. However, since there may be a difference from the exact calculated value, an image analysis tool can be utilized.

[0140] When measuring, rather than calculating the area from a single image, observe at least multiple images to ensure that the length of the oxide layer extends at least 10 μm, and then measure the area. Magnification and resolution are appropriate as long as internal oxides can be observed. Specifically, measurements can be made at magnifications of 20,000 or higher.

[0141]

[0142] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 2.

[0143] [Formula 2]

[0144] (Area of ​​internal oxide / Area of ​​total oxide layer) ≤ 0.050

[0145] (In Equation 2, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.)

[0146] In one embodiment of the present invention, if the oxide (30) is produced in a larger amount than the oxide layer (20) or the oxide layer (20) is formed thickly, the magnetism may be deteriorated by hindering the movement of magnetic domains during the magnetization process. More specifically, the value of Equation 2 may be 0.015 to 0.049.

[0147] Oxide (30) is mainly generated on the surface of a non-oriented electrical steel sheet (100), and in one embodiment of the present invention, for the convenience of measurement, only oxide (30) up to 2% of the total thickness on the surface of the steel sheet is included in the calculation of Equation 2.

[0148] The non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 150 μm. If the grain size is too small, hysteresis loss may increase. If the grain size is too large, eddy current loss may increase, which may lead to a decrease in core loss. The number of grains is measured in a cross-section including the thickness direction, and the average grain area is obtained by dividing the number of grains by the total area, and the grain size of the grains can be obtained through this. The grain size can be obtained from the diameter of an imaginary circle having the same area. More specifically, the average grain size may be 60 to 130 μm.

[0149] As described above, in one embodiment of the present invention, by forming a steel composition and an appropriate oxide layer (20), 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 8.50 to 10.50 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.

[0150] Additionally, one embodiment of the present invention also exhibits excellent mechanical strength. More specifically, the yield strength may be 480 MPa or greater. More specifically, the yield strength may be 500 to 650 MPa. The yield strength can be measured under a 0.2% offset condition during a tensile test.

[0151] FIG. 3 schematically illustrates a cross-section of a motor core (200) according to one embodiment of the present invention. As shown in FIG. 3, the motor core (200) according to one embodiment of the present invention may be formed by stacking a plurality of non-oriented electrical steel sheets (100) described above. Although not represented in FIG. 3, an insulating film may be interposed between the non-oriented electrical steel sheets (100).

[0152] A motor core (200) according to one embodiment of the present invention includes Si: 3.2 to 4.5%, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5% by weight, and the remainder includes Fe and unavoidable impurities, and a surface (101) of a sheet forming the motor core (200) satisfies the following equation 1, and a side surface (102) of the sheet satisfies the following equation 5.

[0153] [Formula 1]

[0154] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.1

[0155] [Formula 5]

[0156] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.093

[0157] Since the steel composition of the non-oriented electrical steel sheet (100) in the motor core (200) is the same as that of the non-oriented electrical steel sheet (100) described above, a duplicate description will be omitted. The steel composition does not substantially change during the manufacturing process of the motor core (200).

[0158] In addition, the characteristics of the oxide layer (20), protrusion (21), and oxide (30) expressed by Equations 1 and 2 on the surface (101) of a single sheet of non-oriented electrical steel plate (100) in the motor core (200) are also the same as those of the non-oriented electrical steel plate (100) described above.

[0159] Meanwhile, as shown in FIG. 4, a motor core (200) according to one embodiment of the present invention has characteristics of an oxide layer (20), a protrusion (21), and an oxide (30) on the side surface (102) of a single sheet of non-oriented electrical steel plate (100).

[0160] As shown in Fig. 4, a single sheet of non-oriented electrical steel sheet (100) in a motor core (200) according to one embodiment of the present invention includes an oxide layer (20) and a steel sheet base material (10) existing inwardly (ND vertical direction) from a side surface (102). In one embodiment of the present invention, the oxide layer (20) refers to a layer portion formed by combining Si and Al with oxygen, and when a cross-section including the thickness direction (ND direction) of the steel sheet is observed using SEM, TEM, etc. and a component analysis is performed, it is distinguished from the steel sheet base material (10) by the oxygen component. Although Fig. 4 shows that an oxide layer (20) exists on one side of the steel sheet, an oxide layer (20) may exist on both one side and the other side. In this case, the steel sheet base material (10) exists between the one-side oxide layer (20) and the other-side oxide layer (20). Since the oxide layer (20) exists very thinly compared to the entire thickness of the non-oriented electrical steel sheet (100), it does not affect the overall alloy composition of the entire non-oriented electrical steel sheet (100).

[0161] As shown in Fig. 4, the oxide layer (20) is formed with a certain roughness with the steel plate base material (10), and occasionally, a protrusion (21) where the oxide layer (20) invades the steel plate base material (10) may exist. In one embodiment of the present invention, the protrusion (21) is formed in a thickness (T) of the oxide layer (20) in the inner direction of the steel plate (ND vertical direction) greater than the imaginary boundary line (24) between the oxide layer (20) and the steel plate base material (10). O ) means the protruding portion. The virtual boundary line (24) can be determined as the boundary line when the oxide layer is formed with a completely uniform thickness using the average thickness of the oxide layer. The thickness (T) of the oxide layer (20) O ) can be obtained as the average thickness of the oxide layer.

[0162] In one embodiment of the present invention, a protrusion (21) can be formed to satisfy Equation 5.

[0163] [Formula 5]

[0164] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.093

[0165] Length (P) of the protruding oxide layer (20) L ) is the thickness (T) of the oxide layer (20) from the virtual boundary line (24) in the inner direction (ND direction) of the steel plate. O ) means the length occupied by the protrusion (21) of the parallel movement line (25) that has moved parallel to the protrusion (21). In case there are multiple protrusions (21), the length (P) of the protruding oxide layer (20) of all protrusions (21) L ) can be the sum of.

[0166] The length of the entire oxide layer refers to the length of the oxide layer (20) in the thickness direction (ND direction) in the cross-section of the steel plate including the thickness direction. In other words, it refers to the entire vertical length in the cross-section that is the measurement target.

[0167] If Equation 5 exceeds 0.093, the length of the protruding oxide layer portion (P L ) means that it is relatively long, and in this case, the magnetism is inferior by interfering with the magnetization process. More specifically, the value of Equation 5 can be 0.050 to 0.093.

[0168] Although omitted in FIGS. 4 and 5, an oxide layer (20) may exist on the steel plate surface (101) as in FIG. 1, and the oxide layer (20) existing on the steel plate surface (101) is excluded from the calculation of the length of the protrusion (21).

[0169] As shown in Fig. 5, in one embodiment of the present invention, an oxide (30) may be present in the steel plate base material (10). The oxide (30) exists separately from the oxide layer (20) and is distinct from the protrusion (21) connected to the oxide layer (20). The protrusion (21) and the oxide (30) refer to portions formed by combining Si and Al with oxygen, and when a cross-section including the thickness direction (ND direction) of the steel plate is observed using SEM, TEM, etc. and a component analysis is performed, they are distinguished from the steel plate base material (10) by the component of oxygen.

[0170] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 6.

[0171] [Formula 6]

[0172] (Area of ​​inner oxide / Area of ​​total oxide layer) ≤ 0.047

[0173] (In Equations 2 and 6, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.)

[0174] In one embodiment of the present invention, if the oxide (30) is produced in a larger amount than the oxide layer (20) or the oxide layer (20) is formed thickly, the magnetization process may be hindered, resulting in inferior magnetism. More specifically, the value of Equation 6 may be 0.025 to 0.047.

[0175] Oxide (30) is mainly generated on the side of the non-oriented electrical steel sheet (100), and in one embodiment of the present invention, for the convenience of measurement, only oxide (30) up to 2% of the total thickness on the side of the steel sheet is included in the calculation of Equation 6.

[0176] As described above, the non-oriented electrical steel sheet (100) present inside the motor core (200) of one embodiment of the present invention can simultaneously improve strength and magnetism by forming a steel composition and an appropriate oxide layer (20). Specifically, the 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 8.50 to 10.50 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. Magnetic flux density (B50) refers to the magnetic flux density induced in a magnetic field of 5000 A / m. The iron loss (10 / 400) and magnetic flux density (B50) can be measured by separating the non-oriented electrical steel sheet inside the motor core (200) into individual sheets and measuring them with a single sheet tester in the rolling direction and the direction perpendicular to the rolling, and then measuring the average value.

[0177] In addition, the mechanical strength of the non-oriented electrical steel sheet (100) present within the motor core (200) of one embodiment of the present invention is also excellent. More specifically, the yield strength may be 480 MPa or more. More specifically, the yield strength may be 500 to 650 MPa. The yield strength can be measured under a 0.2% offset condition during a tensile test.

[0178]

[0179] 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.

[0180]

[0181] Below, each step is explained in detail.

[0182] First, the slab is hot rolled.

[0183] 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.

[0184] Specifically, the slab contains Si: 3.2 to 4.5%, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5% by weight, with the remainder being Fe and unavoidable impurities.

[0185] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0186] 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.

[0187] Next, the slab is hot rolled to produce a hot-rolled plate.

[0188] 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.

[0189] 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.

[0190] Next, the hot-rolled steel sheet is cold-rolled to produce a cold-rolled sheet. In one embodiment of the present invention, by controlling the deformation rate of each pass during the cold-rolled sheet production, an oxide layer formed on the surface of the non-oriented electrical steel sheet and an oxide layer formed within the steel sheet base material can be appropriately formed.

[0191] The step of manufacturing a cold rolled sheet includes two or more passes, the strain rate (1) in the first pass is 200 / s or less, and the sum of the strain rates of the first and second passes (1+2) is 1100 / s or less.

[0192] The first pass is the first pass of the cold rolling stage, and in one embodiment of the present invention, the number of passes is based on the number of passes through the work rolls. In one embodiment of the present invention, the strain rate can be calculated based on the rolling reduction per pass, the rolling speed, and the rolling roll diameter.

[0193] If the strain rate (1) in the first pass is too large, the strain is applied unevenly to the surface of the base material, and the formation behavior of oxides becomes locally uneven during the annealing of the cold-rolled sheet, which may cause a large number of protrusions to be formed, which may adversely affect the magnetism of the steel sheet. More specifically, the strain rate (1) in the first pass may be 100 to 198 / s.

[0194] The second pass is the second pass of the cold rolling stage. If the sum (1+2) of the strain rates of the first and second passes is too large, the strain is applied unevenly to the surface of the base material, and the formation behavior of oxides during the annealing of the cold-rolled sheet becomes locally uneven, which may result in the formation of a large number of internal oxides relative to the oxide layer area, which may adversely affect the magnetism of the steel sheet. More specifically, the sum (1+2) of the strain rates of the first and second passes may be 850 to 1070 / s.

[0195] Additionally, in one embodiment of the present invention, the ratio of the strain rate (max) of the pass with the highest strain rate to the strain rate (total) of the entire step may be 0.3 or less. The strain rate (total) of the entire step can be obtained by adding up the strain rates of each pass within the step of manufacturing the cold-rolled sheet. If this ratio is too large, a large number of oxides may be formed.

[0196] The total number of passes in cold rolling can be 5 to 8.

[0197] The total reduction ratio of cold rolling can be 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 may cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it may 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.

[0198] The cold-rolled sheet manufacturing process can be performed once or twice or more times with intermediate annealing between them. Even if two passes are performed, the number of passes and strain rate can be calculated for the entire cold rolling process.

[0199] 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 with increasing grain size, while eddy current loss increases with increasing grain size. Therefore, there is an optimal grain size that minimizes the sum of hysteresis loss and eddy current loss. 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.

[0200] 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.

[0201] 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.

[0202]

[0203] A method for manufacturing a motor core according to one embodiment of the present invention includes a step of stress-relief annealing a non-oriented electrical steel sheet, and the step of stress-relief annealing satisfies the following equation 3 or equation 4.

[0204] [Equation 3] 6 ≤ [O] × [Al] ≤ 240

[0205] [Equation 4] 480 ≤ [O] × [Al] ≤ 2400

[0206] (In Equations 3 and 4, [O] represents the content of O (ppm) in the atmosphere during stress relief annealing, and [Al] represents the content of Al (wt%) in the non-oriented electrical steel sheet.)

[0207] Since the non-oriented electrical steel sheet and its manufacturing method have been described above, a redundant description will be omitted. When manufacturing a motor core, processes such as punching and lamination are performed, and a stress relief annealing step is included to remove the stress generated during the punching process.

[0208] During stress relief annealing, there may be cases where the iron loss actually deteriorates depending on the annealing atmosphere. In particular, since Al of the base metal reacts strongly with O to form an oxide layer on the surface, it is necessary to appropriately control the O concentration of the atmosphere depending on the amount of Al. In one embodiment of the present invention, the content of O in the atmosphere is adjusted to satisfy Equation 3 or Equation 4.

[0209] If Equations 3 and 4 are not satisfied, that is, if the [O] × [Al] value is less than 6 or more than 240 and less than 480, the formation of an oxide layer may be insufficient or excessive, which may result in poor adhesion between the base material and the coating. In addition, if it exceeds 2400, rust may occur after annealing due to excessive oxidation. In this way, by controlling the annealing atmosphere during stress relief annealing, the side surface of the single sheet can satisfy Equation 5 or Equation 6.

[0210] [Formula 5]

[0211] (Length of the protruding oxide layer area / length of the entire oxide layer) ≤ 0.093

[0212] [Formula 6]

[0213] (Area of ​​inner oxide / Area of ​​total oxide layer) ≤ 0.047

[0214] (In Equation 6, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.)

[0215] The surface of the single sheet is laminated with steel plates, so it is virtually unaffected by the stress relief annealing atmosphere and satisfies Equation 1 or Equation 2 as is.

[0216] The remaining atmosphere other than oxygen can be nitrogen, or common atmosphere gases such as LNG and air.

[0217] The stress-relief annealing step can be performed at a temperature of 700 to 850°C for more than one hour. This can further enhance magnetism. More specifically, the annealing can be performed at a temperature of 720 to 800°C for 1.5 to 4 hours.

[0218]

[0219] 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.

[0220]

[0221] Example 1

[0222] Slabs were manufactured with the components listed in Tables 1 and 2, with the remainder including Fe and unavoidable impurities in wt%. They were heated to 1160°C, hot-rolled to a thickness of 2.2 mm, and then coiled at 700°C. The hot-rolled steel sheets were annealed at 1000°C for 50 seconds. After hot-rolled sheet annealing, the pickled specimens were cold-rolled to a thickness of 0.2 mm, and the strain rate of each pass during cold rolling was controlled as shown in Table 3. Afterwards, cold-rolled sheet annealing was performed. At this time, cold-rolled sheet annealing was performed at 1000°C for 50 seconds.

[0223] The resistivity at 25℃ was measured using the 4-point method.

[0224] The yield strength was measured under 0.2% offset conditions during tensile testing.

[0225] Iron loss (W10 / 400) and magnetic flux density (B50) were measured in the rolling direction and the rolling vertical direction using a single sheet tester by cutting 5 sheets of 60 mm width × 60 mm length for each specimen, and the average values ​​were presented.

[0226] The oxide layer and oxide were measured for oxygen components using Auto-SEM and GDS.

[0227] Steel CSiMnPSAlTiA10.00303.211.800.0150.00142.290.0027A20.00143.360.710.0080.00352.220.0042A30.00303.350.980.0040.00181.230.0042A40.00203.700.960.0140.00272. 120.0020A50.00223.221.250.0020.00251.550.0045A60.00113.350.920.0120.00331.44 0.0011A70.00453.740.760.0090.00411.280.0023A80.00314.120.590.0120.00331.500.0 043A90.00192.840.590.0050.00381.220.0019A100.00133.260.850.0070.00421.380.00 29A110.00373.470.650.0090.00182.270.0011A120.00343.101.170.0090.00262.270.002 1A130.00382.911.720.0050.00111.250.0017A140.00234.021.470.0080.00212.240.003 5A150.00443.110.310.0080.00261.490.0040A160.00102.790.210.0120.00341.870.0015

[0228] Steel gradeNOtherResistivity(μΩcm)1(1 / s)1+ 2(1 / s)max / totalA10.0016Sn: 0.1585.61739100.23A20.0020Sb: 0.1280.31308920.22A30.0034Ni: 0.0370.51679950.29A40.0024-84.41278270.22A50.0016Cr: 0.0274.51369480.27A60.0023-72.615510630.22A70.0034Mo: 0.0374.31397450.22A80.0022-80.11688820.22A90.0015Cu 0.0462.52339400.21A100.0027-70.52669370.24A110.0041-81.818111330.29A120.0017-80.513610610.40A130 .0012-70.022711930.27A140.0045-92.315913940.43A150.0016-67.028010360.35A160.0010-67.121011510.37

[0229] Steel Type 1 Type 2 Yield Strength (Mpa) W10 / 400 (W / Kg) B50 (T) Classification A10.0530.0465218.921.62 Invention Example A20.0570.0255298.811.63 Invention Example A30.0520.0225319.671.62 Invention Example A40.0930.0245569.281.62 Invention Example A50.0350.0425299.551.63 Invention Example A60.0520.0445139.301.64 Invention Example A70.0850.0255059.521.62 Invention Example A80.0430.0465379.801 .63 Invention Example A90.1120.04946111.231.57 Comparative Example A100.1570.07652910.591.58 Comparative Example A110.0850.06561711.261.56 Comparative Example A120.1620.03557411.761.58 Comparative Example A130.0940.08548312.131.57 Comparative Example A140.1350.07069411.231.59 Comparative Example A150.1480.06151210.331.59 Comparative Example A160.1470.07449611.681.58 Comparative Example

[0230] As shown in Tables 1 to 3, it can be confirmed that steel grades A1 to A8, in which cold rolling conditions are appropriately controlled and an oxide layer and oxides are appropriately formed, simultaneously exhibit excellent iron loss, magnetic flux density, and yield strength.

[0231] On the other hand, it can be confirmed that A9 to A16 have poor magnetism or strength because the cold rolling conditions were not properly controlled and the oxide layer and oxide were not properly formed.

[0232]

[0233] Example 2

[0234] Slabs were manufactured with the components listed in Tables 4 and 5, with the remainder containing Fe and unavoidable impurities in wt%. They were heated to 1140°C, hot-rolled to a thickness of 2.1 mm, and then coiled at 710°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 the strain rate of each pass during cold rolling was controlled as shown in Table 3. Afterwards, cold-rolled sheet annealing was performed. At this time, cold-rolled sheet annealing was performed at 1000°C for 60 seconds.

[0235] Steel sheets that had undergone cold-rolled sheet annealing were annealed for 2 hours at 740°C in an atmosphere with the oxygen content (remaining nitrogen) listed in Table 5, simulating stress-relief annealing. Table 6 summarizes the magnetic properties and strength of individual sheets of steel sheets after stress-relief annealing, along with the characteristics of the oxide layer and oxides on the side surfaces of the individual sheets. At this time, the shape and distribution of the oxide layer and oxides were observed using a scanning electron microscope (SEM) on the surface area excluding the upper and lower 5% of the thickness.

[0236] 강종CSiMnPSAlTiB10.00283.301.170.0120.00271.350.0020B20.00454.132.130.0150.00161.460.0011B30.00323.721.910.0140.00181.830.0045B40.00403.730.620.0130.00442.240.0032B50.00143.361.590.0070.00361.520.0016B60.00103.801.140.0020.00192.260.0042B70.00263.221.330.0050.00412.290.0044B80.00314.101.910.0100.00131.280.0019B90.00453.130.500.0040.00181.300.0011B100.00402.842.130.0060.00231.910.0035B110.00453.730.970.0050.00122.160.0010B120.00393.832.160.0080.00221.350.0015B130.00143.622.110.0090.00262.050.0036B140.00323.171.880.0120.00351.410.0020

[0237] 강종N기타비저항(μΩcm)1(1 / s)1+ 2(1 / s)max / totalO(ppm) X Al(wt.%)B10.0038Sn 0.11 / Sb 0.0372.415510710.280.3520B. 0.1288.51299410.2380.3B30.0033Cr 0.0386.817410380.20173.9B40.0019Mo 0.0484.21757780.261032.6B50.003Ni / 021Cr 0.0377.41989880.26860.3B60.0044Cu 0.0188.21428550.281787.7B70.0041Ni 0.01 / Cu 0.0383.013110830.292152.6B80.0014-84.81239510.23371.0B90.0013-66.11928980.295.0B100.0016-79.01777777 .0036-85.328510450.29372.0B120.0027-84.015911820.25350.0B130.0035-89.232912470.272569.0B140.0028-7

[0238] Steel Type 1 Type 2 Type 5 Type 6 Yield Strength (Mpa) W10 / 400 (W / Kg) B50 (T) Classification B10.0750.0390.0760.0425459.031.64 Invention Example B20.0880.0300.0620.0455648.831.63 Invention Example B30.0580.0190.0810.0376318.861.63 Invention Example B 40.0840.0310.0870.0275488.841.64 Invention Example B50.0680.0280.0750.0385599.131.64 Invention Example B60.0910.0420.0930.0475648.891.63 Invention Example B70.0450.0470.0720.0415799.09 1.63 Invention Example B80.1080.0760.1230.04364210.711.58 Comparative Example B90.0750.0600.0820.05752411.591.59 Comparative Example B100.1130.0870.0770.07852410.651.58 Comparative Example B110.1750.0740.1 120.04364612.001.56Comparative Example B120.1500.0400.1240.06661412.481.56Comparative Example B130.1690.0840.1560.06563512.831.57Comparative Example B140.1840.1400.1760.14153012.951.56Comparative Example

[0239] As shown in Tables 4 to 6, it can be confirmed that steel grades B1 to B7, in which cold rolling conditions are appropriately controlled and atmospheric conditions are appropriately controlled during SRA, so that oxide layers and oxides are appropriately formed on the surface and side surfaces, have excellent iron loss, magnetic flux density, and yield strength at the same time.

[0240] On the other hand, it can be confirmed that B8 to B14 have poor magnetism or strength because the cold rolling conditions were not properly controlled, the atmospheric conditions during SRA were not properly controlled, and the oxide layer and oxide on the surface and side were not properly formed.

[0241]

[0242] 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.

[0243] [Explanation of symbols]

[0244] 100: Non-oriented electrical steel sheet, 10: Steel sheet base material,

[0245] 20: Oxide layer, 21: Protrusion,

[0246] 22: Virtual boundary line, 23: Parallel movement line,

[0247] 24: Side virtual boundary line, 25: Side parallel movement line

[0248] 30: oxide, 101: steel plate surface,

[0249] 102: Steel plate side, 200: Motor core

Claims

1. A non-oriented electrical steel sheet containing Si: 3.2 to 4.5% by weight, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5% by weight, the remainder being Fe and unavoidable impurities, and satisfying the following formula 1. [Formula 1] (Length of the protruding oxide layer area / length of the total oxide layer) ≤ 0.1 2. In paragraph 1, A non-oriented electrical steel sheet satisfying the following equation 2. [Formula 2] (Area of ​​inner oxide / Area of ​​total oxide layer) ≤ 0.05 (In Equation 2, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.) 3. In paragraph 1, Mn: Non-oriented electrical steel sheet containing 0.7 to 2.5 wt%.

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: 0.005 to 0.1 wt%, Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

7. In paragraph 1, A non-oriented electrical steel sheet further comprising at least one of Mo: 0.001 to 0.1 wt%, 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 an average grain size of 50 to 150 ㎛ and a yield strength of 480 MPa or more.

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 motor core comprising a plurality of non-oriented electrical steel sheets, each of which contains 3.2 to 4.5% Si, 1.2 to 2.5% Al, and 0.1 to 2.5% Mn, with the remainder being Fe and unavoidable impurities, and satisfying the following formula 1. [Formula 1] (Length of the protruding oxide layer area / length of the total oxide layer) ≤ 0.1 A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 3.2 to 4.5% by weight, Al: 1.2 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 A cold rolled sheet annealing step for annealing the above cold rolled sheet; Including, The step of manufacturing the above cold rolled sheet includes two or more passes, A method for manufacturing a non-oriented electrical steel sheet, wherein the strain rate (1) in the first pass is 200 / s or less, and the sum (1+2) of the strain rates of the first and second passes is 1100 / s or less.

12. In paragraph 11, In the step of manufacturing the above cold rolled plate A method for manufacturing a non-oriented electrical steel sheet, wherein the ratio of the strain rate (max) of the pass with the highest strain rate to the strain rate of the entire step (total) is 0.3 or less.

13. In paragraph 11, 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%).

14. In paragraph 11, 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.

15. In paragraph 11, 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: 0.005 to 0.1 wt%, Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

16. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Mo: 0.001 to 0.1 wt%, 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%).

17. A step of stress-relieving annealing the non-oriented electrical steel sheet described in Article 1 is included. A method for manufacturing a motor core satisfying the following formula 3 or formula 4 in the stress relief annealing step. [Equation 3] 6 ≤ [O] × [Al] ≤ 240 [Equation 4] 480 ≤ [O] × [Al] ≤ 2400 (In Equations 3 and 4, [O] represents the content of O (ppm) in the atmosphere during stress relief annealing, and [Al] represents the content of Al (weight%) in the non-oriented electrical steel sheet.) 18. In paragraph 17, A method for manufacturing a motor core in which the stress relief annealing step is performed at a temperature of 700 to 850°C for 1 hour or longer.

19. Contains Si: 3.2 to 4.5%, Al: 1.2 to 2.5%, and Mn: 0.1 to 2.5% by weight, and the remainder includes Fe and inevitable impurities. A motor core wherein the surface of a sheet forming the motor core satisfies the following equation 1, and the side surface of the sheet satisfies the following equation 5. [Formula 1] (Length of the protruding oxide layer area / length of the total oxide layer) ≤ 0.1 [Formula 5] (Length of the protruding oxide layer area / Length of the total oxide layer) ≤ 0.093 20. In paragraph 19, A motor core wherein the surface of a sheet forming a motor core satisfies the following equation 2, and the side surface of the sheet satisfies the following equation 6. [Formula 2] (Area of ​​inner oxide / Area of ​​total oxide layer) ≤ 0.05 [Formula 6] (Area of ​​inner oxide / Area of ​​total oxide layer) ≤ 0.047 (In Equations 2 and 6, the area of ​​the internal oxide means the sum of the areas of the oxides existing in the steel plate base material.)

Images