Non-oriented electrical steel sheet and method for manufacturing same

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention comprises, based on wt%, 1.5-5.0% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, and the remainder of Fe and inevitable impurities, in which a maximum value of an orientation distribution function (ODF) shown in a φ2=45˚ cross-section of an Euler space is 3.0 or less, and comprises a central portion and a surface portion that is at a depth of up to 50 ㎛ in the inward direction from the surface of the steel sheet, wherein a ratio of an average grain size within the surface portion to an average grain size within the central portion is 0.4-0.6.

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, wherein anisotropy is minimized by uniformly developing a grain structure in each direction by controlling the diameter of a work roll and the coefficient of friction between the work roll and the steel sheet 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 The properties of non-oriented electrical steel sheets are often evaluated by iron loss.

[0005] A common method for improving the magnetic properties of non-oriented electrical steel is to add alloying elements such as Si, Al, and Mn. These alloying elements increase the resistivity of the steel, reducing eddy current losses and lowering overall core loss. Furthermore, these alloying elements can act as substitutional elements in the steel, strengthening it and increasing its strength. However, increasing the amount of alloying elements like Si, Al, and Mn leads to lower magnetic flux density and increased brittleness. Adding more than a certain amount makes cold rolling impossible, making commercial production impossible. In particular, thinner electrical steel sheets exhibit superior high-frequency core loss, but the resulting brittleness can be a critical issue.

[0006] Methods for improving magnetic properties by controlling the texture of non-oriented electrical steel sheets are also known. Texture control is a method for promoting the development of crystal orientations favorable to magnetism and suppressing crystal orientations unfavorable to magnetism during the process of deforming, recovering, and recrystallizing a material through various methods. It is known that crystal orientations with {001} planes are favorable to magnetism, and crystal orientations with {111} planes are unfavorable to magnetism. Many methods are known for selectively developing several crystal orientations by varying the manufacturing conditions of non-oriented electrical steel sheets.

[0007] When non-oriented electrical steel sheets are produced through a double-rolling and double-annealing process, the {111} / ND crystal orientation, which is unfavorable to magnetism, can be suppressed, and crystal orientations such as {001} / ND and {110} / ND, which are favorable to magnetism, can be strengthened. Although the above process is well known to be excellent in improving texture, it has the disadvantage of increasing manufacturing cost due to the addition of a cold-rolling intermediate annealing process. In addition, although the magnetic properties in the rolling direction are improved depending on the developed texture, the magnetic properties in the direction rotated 45 to 60° from the rolling direction deteriorate, so when used in rotating equipment, there are many cases where there is almost no improvement in magnetic properties, which limits its practical application.

[0008] 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, wherein anisotropy is minimized by uniformly developing a grain structure in each direction by controlling the diameter of a work roll and the coefficient of friction between the work roll and the steel sheet during cold rolling.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, 1.5 to 5.0% of Si, 0.1 to 2.0% of Al, and 0.1 to 2.0% of Mn, with the remainder being Fe and unavoidable impurities, and the maximum value of the orientation distribution function (ODF) shown in a φ2=45˚ cross-section of Euler space is 3.0 or less.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention includes a surface portion and a center portion from the surface of the steel sheet to a depth of 50 ㎛ in the inward direction, and the ratio of the average grain size in the surface portion to the average grain size in the center portion is 0.4 to 0.6.

[0011] 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%).

[0012] 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.

[0013] 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%).

[0014] 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%).

[0015] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0016] [Formula 1]

[0017] B 50L - B 50(55°) ≤ 0.05 T

[0018] (B in Equation 1 50LMagnetic flux density B measured in the rolling direction 50 , B 50(55°) is the magnetic flux density B measured in a direction at an angle of 55° to the rolling direction. 50 )

[0019]

[0020] 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 %, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, and Mn: 0.1 to 2.0%, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; a step of preliminarily cold-rolling the hot-rolled steel sheet; a first annealing step of annealing the preliminarily cold-rolled steel sheet; a step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a second annealing step of annealing the cold-rolled sheet.

[0021] In at least one pass during the manufacturing process of the cold rolled sheet, the product of the diameter (mm) of the work roll and the coefficient of friction (μ) between the work roll and the steel sheet may be 10 to 30.

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

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

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

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

[0026] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains.

[0027] After the first annealing step, the average grain size of the steel sheet may be 50 to 120 μm.

[0028] In the process of manufacturing cold rolled sheets, the reduction ratio can be 20 to 55%.

[0029] The cracking temperature in the second annealing step may be 750 to 1150°C.

[0030] A non-oriented electrical steel sheet according to one embodiment of the present invention has an evenly developed aggregate structure and thus has excellent magnetic properties.

[0031] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to improving the performance of an eco-friendly vehicle drive motor.

[0032] Because it has high magnetic anisotropy, high torque can be obtained when manufactured into automobile motors.

[0033] Figure 1 is a schematic diagram showing a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0034] Figure 2 is a graph showing the orientation distribution function (ODF) results of the non-oriented electrical steel sheet manufactured in Example B6.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0039] 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.

[0040] 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.

[0041] 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.

[0042]

[0043] 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 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities.

[0044] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0045]

[0046] Si: 1.50 to 5.00 wt%

[0047] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and increases strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects may be insufficient. If too much Si is added, the material becomes brittle, which drastically reduces rolling productivity and may form a surface oxide layer and oxides that are harmful to magnetism. Therefore, Si may be included in an amount of 1.50 to 5.00 wt%. More specifically, it may be included in an amount of 2.00 to 4.50 wt%. More specifically, it may be included in an amount of 2.50 to 4.30 wt%.

[0048]

[0049] Al: 0.1 to 2.0 wt%

[0050] Aluminum (Al) increases the resistivity of the material, thereby reducing iron loss and improving rollability, and plays a role in improving workability during cold rolling. If too little Al is added, it may be difficult to achieve the effect of reducing high-frequency iron loss, and the precipitation temperature of AlN may be lowered, which may cause fine nitride formation, which may reduce magnetism. If too much Al is added, excessive nitride formation may deteriorate magnetism, and problems may occur in all processes such as steelmaking and continuous casting, which may significantly reduce productivity. Therefore, Al may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.15 to 1.7 wt%. Even more specifically, it may be included in an amount of 0.2 to 1.6 wt%.

[0051]

[0052] Mn: 0.1 to 2.0 wt%

[0053] Manganese (Mn) improves iron loss by increasing the resistivity of the material and plays a role in forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration, and if too much Mn is added, fine MnS is excessively precipitated and promotes the formation of {111} texture, which is unfavorable for magnetism, resulting in a rapid decrease in magnetic flux density. Therefore, Mn may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.15 to 1.7 wt%. More specifically, it may be included in an amount of 0.2 to 1.6 wt%.

[0054]

[0055] 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%).

[0056] P: 0.1 wt% or less

[0057] Phosphorus (P) not only plays a role in increasing the resistivity of a material, but also can improve magnetic flux density as a grain boundary segregation element. However, if too much P is added, it increases the brittleness of the steel plate, resulting in poor weldability. More specifically, P may be included in an amount of 0.0001 to 0.0500 wt%. More specifically, P may be included in an amount of 0.0010 to 0.0200 wt%.

[0058] C: 0.0050 wt% or less

[0059] 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 may be included in an amount of 0.0001 to 0.0035 wt%. More specifically, C may be included in an amount of 0.0010 to 0.0030 wt%.

[0060] S: 0.0050 wt% or less

[0061] Sulfur (S) can form fine precipitates, MnS and CuS, which can deteriorate magnetic properties and hot workability. More specifically, S may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, S may be included in an amount of 0.0005 to 0.0045 wt%.

[0062] Ti: 0.0050 wt% or less

[0063] 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 base metal, thereby inhibiting grain growth and domain wall migration. More specifically, Ti may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, Ti may be included in an amount of 0.0005 to 0.0030 wt%.

[0064] N: 0.0050 wt% or less

[0065] Nitrogen (N) not only forms fine AlN precipitates within the base material, but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall migration, thereby worsening iron loss. More specifically, N may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, N may be included in an amount of 0.0005 to 0.0030 wt%.

[0066]

[0067] 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.

[0068] Sn

[0069] 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 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 0.080 wt%.

[0070] Sb

[0071] Antimony (Sb) can be additionally added to improve magnetism because it improves the material's texture 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%.

[0072] Bi, Pb, Ge, and As

[0073] 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.

[0074]

[0075] 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%).

[0076] Cu: 0.005 to 0.200 wt%

[0077] 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%.

[0078] Cr: 0.01 to 0.50 wt%

[0079] 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%.

[0080] Ni: 0.05 wt% or less

[0081] 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.

[0082] Zn: 0.01 wt% or less

[0083] 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%.

[0084] Co: 0.05 wt% or less

[0085] 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.

[0086]

[0087] 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%).

[0088] Mo: 0.030 wt% or less

[0089] 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%.

[0090] B: 0.0050 wt% or less

[0091] 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%.

[0092] V: 0.0050 wt% or less

[0093] 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%.

[0094] Ca: 0.0050 wt% or less

[0095] 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.

[0096] Nb: 0.0050 wt% or less

[0097] 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%.

[0098] Zr: 0.0050 wt% or less

[0099] 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%.

[0100] Te: 0.0100 wt% or less

[0101] 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%.

[0102] Mg: 0.0050 wt% or less

[0103] 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%.

[0104]

[0105] 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).

[0106]

[0107] As described above, in one embodiment of the present invention, by appropriately controlling the alloy composition of the steel plate and performing preliminary cold rolling and cold rolling, by controlling the diameter of the work roll and the coefficient of friction between the work roll and the steel plate during cold rolling, the aggregate structure can be developed evenly in each direction, thereby minimizing magnetic anisotropy.

[0108] Specifically, in a non-oriented electrical steel sheet according to one embodiment of the present invention, the maximum value of the orientation distribution function (ODF) appearing in a φ2=45˚ cross-section of Euler space may be 3.0 or less.

[0109] The orientation distribution function (ODF) is a quantitative method for analyzing the grain distribution within a steel sheet. It quantifies the extent to which a specific crystal orientation is distributed within the steel sheet. Orientation strength refers to how strongly a specific crystal orientation is developed compared to a random grain structure.

[0110] Euler space is a three-dimensional space composed of three angles, φ1, Φ, and φ2, used to express crystal orientations. Among them, the φ2=45˚ cross-section is a region to be observed in detail because it is easy to understand the aggregate structure that develops in steel materials with symmetric deformation.

[0111] In one embodiment of the present invention, the measurement plane of the orientation distribution function (ODF) targets the rolling vertical direction plane (TD plane), and the measurement area is at least 5 mm × 5 mm. In order to reduce errors depending on the measurement position, data for a sufficiently large area must be measured, and the data can be measured for 20 or more specimens and combined for calculation at once.

[0112] The measurement method uses EBSD mounted on an SEM, and can be analyzed using OIM analysis software, and the error angle for orientation can be set to 15°.

[0113] A maximum value of the orientation distribution function (ODF) of 3.0 or less indicates that not only aggregations in a specific orientation develop, but rather that aggregations develop evenly across orientations. More specifically, the maximum value of the orientation distribution function (ODF) may be between 1.5 and 2.5.

[0114] FIG. 1 schematically illustrates a cross-section of a non-oriented electrical steel sheet (100) according to an embodiment of the present invention. As shown in FIG. 1, the non-oriented electrical steel sheet (100) according to an embodiment of the present invention includes a surface portion (20) extending from the surface of the steel sheet to a depth of 50 μm inward and a center portion (10). As shown in FIG. 1, the surface portion (20) may be present on both surfaces of the steel sheet, and the center portion (10) may be located between the two surface portions (20).

[0115] In one embodiment of the present invention, the ratio of the average grain size in the surface portion (20) to the average grain size in the center portion (10) (surface portion / center portion) may be 0.40 to 0.60. When the grains in the surface portion (20) are smaller than those in the center portion (10), hysteresis loss may increase and magnetic permeability may decrease in the surface portion, which may deteriorate the magnetic properties. When the grains in the surface portion (20) are larger than those in the center portion (10), eddy current loss may increase and a texture that is unfavorable for magnetization may develop. More specifically, the ratio of the average grain size in the surface portion (20) to the average grain size in the center portion (10) (surface portion / center portion) may be 0.45 to 0.57. The grain size may be obtained by assuming a virtual circle having the same area as the corresponding grain and using the diameter of the circle. It is measured based on the rolling vertical direction plane (TD plane), and the number of crystal grains within the surface (20) and center (10) area is counted to obtain the average area of ​​each crystal grain, and it can be obtained by calculating with a circle having this area. When the surface (20) within the steel plate exists on both surfaces, the crystal grain diameters of the upper surface and lower surface can be obtained by averaging them.

[0116] As described above, in one embodiment of the present invention, the aggregate structure can be developed uniformly in each direction, thereby minimizing magnetic anisotropy. Specifically, a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0117] [Formula 1]

[0118] B 50L - B 50(55°) ≤ 0.05 T

[0119] (B in Equation 1 50L Magnetic flux density B measured in the rolling direction 50 , B 50(55°) is the magnetic flux density B measured in a direction at an angle of 55° to the rolling direction. 50 )

[0120] Equation 1 represents the difference in magnetic flux density in the rolling direction (RD direction) and in a direction at an angle of 55° to the rolling direction, and a smaller difference indicates a smaller magnetic anisotropy. Specifically, the value of the left side of Equation 1 can be 0.01 to 0.03 T.

[0121] In one embodiment of the present invention, the iron loss (W) of the non-oriented electrical steel sheet 10 / 400 ) may be less than 12.5 W / Kg. Iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. More specifically, the iron loss (W) of non-oriented electrical steel sheet 10 / 400 ) may be 10.0 to 12.0 W / kg. In one embodiment of the present invention, the iron loss may be expressed based on a thickness of 0.25 mm.

[0122]

[0123] 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 to manufacture a hot-rolled steel sheet; preliminarily cold-rolling the hot-rolled steel sheet; a first annealing step of annealing the preliminarily cold-rolled steel sheet; a step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a second annealing step of annealing the cold-rolled 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%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, with the remainder being Fe and unavoidable 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 it 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 manufacture a hot-rolled sheet. The hot-rolled sheet may have a thickness of 1.50 to 2.50 mm. If the hot-rolled sheet is too thick, a coarse ductile structure may be strongly developed in the center (10) of the final non-oriented electrical steel sheet to be manufactured, and a texture of a specific orientation may develop. In addition, if the hot-rolled sheet is too thin, insufficiently grown fine crystal grains may remain in the surface (20) of the final non-oriented electrical steel sheet to be manufactured, resulting in poor core loss. More specifically, the hot-rolled sheet may have a thickness of 1.60 to 2.30 mm.

[0132] In the process of manufacturing hot-rolled sheets, the finishing rolling temperature may be 800°C or higher. Specifically, it may be 870 to 950°C. The hot-rolled sheets may be coiled at a temperature of 600°C or higher.

[0133] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains. That is, after hot rolling, scale removal processes such as pickling, shot blasting, or surface grinding can be omitted, and subsequent steps can be performed. By performing cold rolling without the pickling process, friction between the rolling work rolls and the steel sheet increases, so that shear deformation is simultaneously applied in addition to plane deformation during rolling, and a specific orientation develops during recrystallization annealing. In one embodiment of the present invention, scale refers to a portion on the surface of the steel sheet where elements such as Fe, Al, and Si combine with oxygen to form a phase different from that of the base metal. Remaining scale means that at least 1 μm of scale remains on the hot-rolled sheet. In this case, the scale thickness refers to the sum of the scale thicknesses formed on both surfaces of the steel sheet. If the remaining scale thickness is too thin, the effect due to the scale residue may not be fully exerted. Even if the scale thickness is thicker, the effect is not improved, and there is a problem of a reduced yield of the steel sheet. More specifically, scales with a thickness of 0.1 to 1 μm may remain. Furthermore, pre-cold rolling can be performed without applying heat from the outside of the steel sheet after hot rolling. In other words, hot-rolled sheet annealing can be omitted.

[0134] Next, the hot-rolled steel sheet undergoes preliminary cold rolling. Preliminary cold rolling is distinguished from cold rolling, described later, in that it is the first rolling step in a process that involves rolling to an intermediate thickness, rather than the final product thickness, followed by intermediate annealing and then cold rolling to the final product thickness.

[0135] Preliminary cold rolling can be performed at a reduction ratio of 40 to 80% to improve final cold rolling productivity and grain size in the final product sheet. Furthermore, if rolling productivity is not a consideration, the present invention also allows preliminary cold rolling to be performed in a reverse mill. The preliminarily cold rolled sheet can have a thickness of 0.30 to 1.50 mm. More specifically, the reduction ratio can be 50 to 78% and the thickness can be 0.40 to 1.00 mm.

[0136] The preliminary cold rolling reduction can be calculated as (steel thickness before rolling - steel thickness after rolling) / steel thickness before rolling. If the reduction ratio is too low in the preliminary cold rolling stage, the rolling load increases during the final cold rolling, which reduces productivity and increases the final reduction ratio, which causes fine grains. <111> Problems that promote azimuth re-determination may arise. Conversely, if the reduction ratio is too high, the cold rolling load increases and the possibility of plate fracture increases.

[0137] Next, in the first annealing step, the pre-cold rolled steel sheet is annealed.

[0138] In one embodiment of the present invention, after the first annealing step, by appropriately adjusting the average grain size of the grains in the steel sheet, the orientation-specific aggregate structure can be developed evenly. Specifically, after the first annealing step, the average grain size of the steel sheet may be 50 to 120 μm. If the average grain size is too small, the grain boundary fraction may be excessively high, so that grains having a {111} / ND orientation may develop during the second annealing process after the second cold rolling, resulting in inferior magnetic properties. If the average grain size is too large, the development of the {111} / ND orientation is suppressed, but the Cube orientation may develop, resulting in inferior magnetism at 55°. More specifically, after the first annealing step, the average grain size of the steel sheet may be 60 to 110 μm.

[0139] The first annealing step can be performed at a temperature of 750 to 1150°C for 5 to 20 seconds. If the annealing temperature is too low, the coarse microstructure in the center will not recover sufficiently, resulting in {001} of the final product. <100> If the fracture temperature is too high, fine precipitates may form on the surface, resulting in {011} defects in the final product. <100> The magnetic properties may be poor due to insufficient development of the magnetic field. More specifically, the first annealing step may cause cracking at temperatures between 850 and 1050°C.

[0140] If the soaking time is too short, the surface microstructure may not be sufficiently recrystallized, resulting in surface grains in the final product being excessively smaller than those in the core. If the soaking time is too long, surface grains may grow excessively. More specifically, soaking can last between 7 and 17 seconds.

[0141] Again, returning to the description of the method for manufacturing non-oriented electrical steel sheets, after the first annealing step, the annealed steel sheet is cold rolled to manufacture a cold-rolled sheet.

[0142] In one embodiment of the present invention, the product of the diameter (mm) of the work roll and the coefficient of friction (μ) between the work roll and the steel plate in at least one pass may be 10.0 to 30.0.

[0143] In one embodiment of the present invention, the work roll diameter and friction coefficient in cold rolling are major factors that optimize the difference in diameter between the central (10) grains and the surface (20) grains of the finally manufactured non-oriented electrical steel sheet, and develop a random aggregate structure to bring out excellent magnetic properties in all directions.

[0144] When the work roll diameter is large, the area where the work roll comes into contact with the material increases at a given reduction ratio, so that a larger shear strain can be applied, and when the work roll diameter is small, the amount of shear strain decreases. The coefficient of friction is determined by the roughness of the work roll and the steel sheet, the type of rolling oil, etc., and under given conditions, a larger coefficient of friction allows a larger shear strain to be applied. When the product of the work roll diameter and the friction coefficient is large, the amount of shear strain applied to the material increases, so that the surface grain size can be controlled to be smaller than that of the center. However, if the product of the work roll diameter and the friction coefficient is too large, an excessive number of fine grains may be formed on the surface (20). If the product of the work roll diameter and the friction coefficient is too small, the surface grains may grow to a similar size to that of the center, which may result in poor magnetic properties at high frequencies of 400 Hz or higher. More specifically, the product of the work roll diameter and the friction coefficient may be 11.0 to 29.5.

[0145] In one embodiment of the present invention, cold rolling may be performed through multiple passes, and the aforementioned work roll diameter and friction coefficient characteristics may be satisfied in at least one of the multiple passes. More specifically, they may be satisfied in the last pass.

[0146] The work roll diameter may be 300 to 600 mm, more specifically 350 to 500 mm.

[0147] The coefficient of friction between the work roll and the steel plate may be 0.02 to 0.10 μ. The coefficient of friction can be measured using the method of Patent Publication No. KR1996-0021206. More specifically, the coefficient of friction may be 0.03 to 0.08 μ.

[0148] In the cold rolled sheet manufacturing step, the reduction ratio may be 20 to 55%. If the reduction ratio is too low, the Rotated Cube orientation may develop, resulting in poor magnetism at 55°. If the reduction ratio is too high, the {111} / ND orientation may develop, resulting in poor overall magnetism. More specifically, the reduction ratio may be 25 to 50%. The final rolled thickness may be 0.1 mm to 0.35 mm.

[0149] Next, in the second annealing step, the cold-rolled sheet is annealed. The second annealing step can be performed at 750 to 1150°C. If the soaking temperature is too low, the grains may not grow sufficiently, which may lead to increased hysteresis loss and deterioration of iron loss. More specifically, the annealing can be performed at a temperature of 900 to 1050°C. The second annealing step can be performed for 50 to 120 seconds. The dew point may be -10°C or lower.

[0150] 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.

[0151] 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.

[0152]

[0153] 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.

[0154]

[0155] Example 1

[0156] A slab was manufactured using the components shown in Table 1 and containing the remainder Fe and unavoidable impurities. This was heated to 1150°C and hot-rolled at a finishing temperature of 950°C to manufacture a hot-rolled sheet having the thickness shown in Table 2 below.

[0157] Afterwards, the hot-rolled sheet was preliminarily cold-rolled to the thickness shown in Table 2 below without annealing, and was first annealed by soaking at 750 to 1050°C for 15 seconds. The average grain size of the first-annealed steel sheet was measured and summarized in Table 2 below. The first-annealed steel sheet was cold-rolled under the conditions summarized in Table 3 below to obtain a final thickness of 0.25 mm. The cold-rolled steel sheet was second-annealed at a dew point of -20°C and a soaking temperature of 950°C for 70 seconds.

[0158] In order to analyze the texture of the manufactured non-oriented electrical steel sheet, 30 specimens measuring 10 mm × 20 mm were cut for each specimen, mounted in three sets of 10 specimens each so that the observation surface was the TD plane, and the observation surface was polished to a mirror-like surface without scratches. The EBSD measurement applied the conditions of 5000 μm in height, approximately 2500 μm in width (including all 10 0.25 mm specimens), and 1 μm in step size. The three sets of measurement data were merged using the merging function of the OIM software to calculate the ODF at once, and the results are shown in Table 4.

[0159] Magnetic properties such as magnetic flux density and iron loss were measured by cutting 60 mm wide × 60 mm long × 5 sheets of each specimen into single sheet tester and measuring the magnetic flux density in the rolling direction and 55° direction and displaying the results. Iron loss was measured in the rolling direction and the direction perpendicular to the rolling and displayed as the average. At this time, W 10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, and B50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0160] 시편번호Si[%]Al[%]Mn[%]C[ppm]S[ppm]N[ppm]Ti[ppm]Nb[ppm]V[ppm]A12.701.60.7281416111915A22.701.60.7281313231721A32.701.60.720181824819A42.701.60.7131817171810A52.701.60.7171614141616A62.701.60.7244317171714A72.701.60.7261313111313A82.701.60.7141416141418B13.300.61.6137314121123B23.300.61.635131565139B33.300.61.616329241910B43.300.61.6172012142021B53.300.61.6131313171318B63.300.61.6281716141715B73.300.61.6294214131817B83.300.61.6311318181313C13.750.21.668199241920C23.750.21.6211611212316C33.750.21.6291712231412C43.750.21.62188171818C53.750.21.631451391411C63.750.21.6281516131512C73.750.21.625171671715C83.750.21.6274217141418D14.200.50.22298118923D24.200.50.2171611121611D34.200.50.2143510122113D44.200.50.291614141614D54.200.50.2161716161717D64.200.50.2213320151821D74.200.50.2161720101724D84.200.50.2311312131313

[0161] Specimen numberHot rolled plate thickness [mm]1stThickness after cold rolling [mm]1stCold rolling reduction rate [%]1st Annealed grain size [μm]A12.180.507736A22.180.507778A32.180.507781A42.610 .607782A52.180.507776A62.180.507780A72.180.507784A82.180.50 7782B11.760.407758B21.760.407776B31.270.2977102B41.760.4077 141B51.760.407763B61.760.407781B71.760.407797B81.760.407710 8C11.760.407758C21.260.4068103C32.690.408561C41.760.4077107 C51.760.407772C61.760.4077101C71.760.407763C81.760.4077104D 11.510.3577103D21.510.3577107D31.510.3577110D41.510.3577102 D51.510.3577105D61.510.3577104D71.510.3577101D81.510.3577107

[0162] Specimen number 2nd cold rolling reduction rate 2nd cold rolling WR diameter 2nd cold rolling friction coefficient Diameter X friction coefficient [%] [mm] (μ) A 1 5 0 3 8 0 0.03 1 1.4 A 2 5 0 3 8 0 0.14 5 3.2 A 3 5 0 2 2 0 0.03 6.6 A 4 5 8 3 8 0 0.03 1 1.4 A 5 5 0 4 2 0 0.07 2 9 4 A 6 5 0 4 2 0 0.07 2 9 4 A 7 5 0 4 2 0 0.07 2 9 .4A8504200.0729.4B1384200.0521.0B2383800.0519.0B3144200.0521.0 B4383800.0519.0B5384200.0625.2B6383800.0622.8B7384200.0625.2B83 83800.0622.8C1384200.0312.6C2383800.0311.4C3384200.0312.6C4383 800.0311.4C5384200.0729.4C6383800.0726.6C7384200.0729.4C8383800 .0726.6D1284000.0520.0D2286500.0532.5D3284000.014.0D4284000.052 0.0D5284000.0624.0D6284000.0624.0D7284000.0624.0D8284000.0624.0

[0163] Specimen number φ2=45˚Maximum azimuth strengthSurface grain size [㎛]Center grain size [㎛]Surface / center A14.745810.56A22.431840.37A32.157760.75A45.128810.35A52.247840.56A62.438760.50A72.142820.51A81.943770.56B12.446550.84B22.242510.82B32.351760.67B45.338810.47B52.141830.49B62.435810.43B72. 346790.58B82.444820.54C12.138520.73C22.260840.71C34.543760.57C42.341840.49C52.443840.51C62.337810.46C72.143780.55C8 2.639770.51D12.539500.78D22.130820.37D32.355820.67D42.443810.53D52.438760.50D62.337780.47D72.144780.56D82.239810.48

[0164] Specimen number W10 / 400 B50L[T] B50(55˚)[T] Δ B50[T] A1 12.01.66 1.620.04 A2 12.51.68 1.630.05 A3 12.81.68 1.630.05 A4 12.61.66 1.620.04 A5 11.31.68 1.660.02 A6 11.31.68 1.660.02 A7 11.51.6 81.660.02A811.21.681.660.02B112.61.681.630.05B212.61.681.630.05B312.41.681.6 30.05B411.91.661.620.04B511.21.681.660.02B611.51.681.660.02B711.11.681.660.02 B811.31.681.660.02C112.61.681.630.05C212.41.681.630.05C311.91.661.620.04C411 .51.681.660.02C511.31.681.660.02C611.51.681.660.02C711.31.681.660.02C811.31.6 81.660.02D112.51.681.630.05D212.31.681.630.05D312.61.681.630.05D411.41.681.6 60.02D511.21.681.660.02D611.31.681.660.02D711.41.681.660.02D811.41.681.660.02

[0165] As shown in Tables 1 to 5, it can be confirmed that the invention example, in which the steel component is appropriately controlled and the process conditions are appropriately controlled so that the aggregate structure is uniformly formed, has excellent iron loss and magnetic flux density, and at the same time, minimizes magnetic anisotropy.

[0166] On the other hand, if the steel component is not properly controlled or the process conditions are not properly controlled, and the aggregate structure is not properly formed, it can be confirmed that the iron loss and magnetic flux density are inferior or the magnetic anisotropy is high.

[0167]

[0168] 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.

[0169] [Explanation of symbols]

[0170] 100: Non-oriented electrical steel sheet 10: Center

[0171] 20: Surface area

Claims

1. Contains Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities. The maximum value of the orientation distribution function (ODF) appearing in the φ2=45˚ section of the Euler space is 3.0 or less, Including the surface and center from the surface of the steel plate to a depth of 50㎛ in the inward direction, A non-oriented electrical steel sheet having a ratio of the average grain size within the surface portion to the average grain size within the center portion of 0.4 to 0.

6.

2. 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%).

3. 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.

4. 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%).

5. 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%).

6. In paragraph 1, A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] B 50L - B 50(55°) ≤ 0.05 T (B in Equation 1 50L B is the magnetic flux density measured in the rolling direction 50 , B 50(55°) is the magnetic flux density B measured in a direction at an angle of 55° to the rolling direction. 50 ) 7. 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 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities; A step of preliminarily cold rolling the above hot-rolled steel plate; A first annealing step for annealing a cold-rolled steel sheet; A step for manufacturing cold rolled steel sheets by cold rolling an annealed steel sheet, and A second annealing step for annealing the above cold rolled sheet; Including, A method for manufacturing a non-oriented electrical steel sheet, wherein the product of the diameter (mm) of the work roll and the coefficient of friction (μ) between the work roll and the steel sheet in at least one pass during the steps of manufacturing the cold rolled sheet is 10 to 30.

8. In paragraph 7, 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%).

9. In paragraph 7, 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.

10. In paragraph 7, 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%).

11. In paragraph 7, 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%).

12. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the subsequent steps are performed while the scale remaining on the hot-rolled steel sheet remains after manufacturing the hot-rolled steel sheet.

13. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet having an average grain size of 50 to 120 ㎛ after the first annealing step.

14. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet having a reduction ratio of 20 to 55% in the step of manufacturing the above cold rolled sheet.

15. In paragraph 7, A method for manufacturing a non-oriented electrical steel sheet having a cracking temperature of 750 to 1,150°C in the second annealing step.

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