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, in weight %, 1.5-5.0% Si, 0.1-3.0% Al, and 0.1-3.0% Mn, the remainder being Fe and inevitable impurities. The KAM value measured at a spot of 10% overall thickness in the thickness direction from the surface of the steel sheet is 1.5° or less, and at a spot of 50% overall thickness is 0.7° or less.

Description

Non-oriented electrical steel sheet and method of manufacturing the same

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, which simultaneously improves strength and high-frequency iron loss by controlling the reduction ratio during rough rolling and controlling the KAM value according to the thickness of the steel sheet.

[0002] Non-oriented electrical steel is primarily used in motors that convert electrical energy into mechanical energy, and excellent magnetic properties are required to achieve high efficiency in this process. In particular, with the recent rise in interest in eco-friendly vehicles driven by motors instead of internal combustion engines, the demand for non-oriented electrical steel used as core materials for drive motors is increasing, and to meet this demand, non-oriented electrical steel with excellent magnetic properties and strength is required.

[0003] The magnetic properties of non-oriented electrical steel are primarily evaluated based on iron loss and magnetic flux density. Iron loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. Lower iron loss allows for the manufacture of motors with higher energy efficiency under the same conditions, whereas higher magnetic flux density enables motor miniaturization or reduced copper loss. Therefore, by utilizing non-oriented electrical steel with low iron loss and high magnetic flux density, drive motors with excellent efficiency and torque can be produced, 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 motor's operating conditions. A widely used general standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors is W15 / 50, which represents the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, for non-oriented electrical steel sheets with a thickness of 0.35mm or less used in drive motors for eco-friendly vehicles, magnetic properties are often critical at low fields of 1.0T or less and high frequencies above 400Hz; therefore, W 10 / 400 Iron loss is frequently used to evaluate the characteristics of non-oriented electrical steel sheets. Additionally, due to the increase in rotational speed, strength characteristics, which were previously not considered significant, are now being evaluated as important properties.

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

[0006] Among the important magnetic properties of non-oriented electrical steel, the most basic and efficient methods to reduce iron loss include increasing the addition of elements with high resistivity, such as Si, Al, and Mn, or reducing the thickness of the steel sheet. Increasing the addition of Si, Al, and Mn increases the resistivity of the steel, thereby reducing eddy current losses within the iron loss of non-oriented electrical steel and effectively lowering iron loss. Since eddy current losses account for a larger proportion of iron loss in the case of high-frequency iron loss, this method can be very effective for reducing high-frequency iron loss. However, the effect varies depending on the addition ratio, and since magnetic flux density deteriorates as the amount of alloying elements increases, it is necessary to properly control the addition ratio between the appropriate amount of Si, Al, and Mn to secure excellent iron loss and magnetic flux density. Reducing the thickness is also a very effective method for reducing iron loss by significantly decreasing eddy current losses, but thin steel sheets have the disadvantage of lower productivity and processability.

[0007] Various techniques have been reported to improve magnetic properties by improving the texture using special additive elements such as REM, or by introducing additional manufacturing processes such as hot rolling, double rolling, and double annealing, in order to reduce iron loss while increasing magnetic flux density in non-oriented electrical steel sheets. However, since all of these techniques cause an increase in manufacturing costs or entail difficulties in mass production, it can be said that there is a need to develop a technology that is commercially viable while possessing excellent magnetic properties. Furthermore, technologies are being developed to suppress and control the formation of inclusions by strictly limiting the amount of impurities added and adding elements such as Ca; however, this also causes an increase in manufacturing costs, and it is difficult to clearly secure its effectiveness.

[0008] The strength of steel sheets tends to increase as the alloy content increases. However, since elements such as Si and Al are highly brittle and have varying effects on strength, their content and ratio must be optimized to ensure high strength characteristics. Meanwhile, although strength improves with finer grain size, there exists an optimal grain size that minimizes iron loss; therefore, technology to appropriately control grain size is also required to simultaneously achieve high strength and low iron loss.

[0009] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, which simultaneously improves strength and high-frequency iron loss by controlling the reduction ratio during rough rolling and adjusting the KAM value according to the steel sheet thickness.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, the remainder being Fe and unavoidable impurities, and has a KAM value of 1.5° or less measured at a position 10% of the total thickness in the thickness direction from the surface of the steel sheet, and a KAM value of 0.7° or less measured at a position 50% of the total thickness in the thickness direction from the surface of the steel sheet.

[0011] The difference between the KAM value measured at 10% of the total thickness in the thickness direction from the steel plate surface and the KAM value measured at 50% of the total thickness in the thickness direction from the steel plate surface may be -1.2 to 0.3°.

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less, C: 0.01 wt% or less, S: 0.015 wt% or less, Ti: 0.005 wt% or less, and N: 0.01 wt% or less.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, respectively or in their combined amount.

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

[0015] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0016] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises: a step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities; a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0017] The steps for manufacturing hot-rolled steel sheets include a rough rolling step and a finishing rolling step, and the rough rolling step includes a plurality of passes, and the reduction rate in the pass before the last pass is 30 to 47%.

[0018] The slab may further include one or more of P: 0.1 wt% or less, C: 0.01 wt% or less, S: 0.015 wt% or less, Ti: 0.005 wt% or less, and N: 0.01 wt% or less.

[0019] The slab may further contain 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, either individually or in their combined amount.

[0020] The slab may further include one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

[0021] The slab may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0022] The reduction rate of the last pass in the rough rolling stage can be 25 to 47%.

[0023] In the rough rolling stage, the sum of the reduction rates before the last pass and the last pass may be 55 to 94%.

[0024] A non-oriented electrical steel sheet according to one embodiment of the present invention can secure low iron loss and high strength characteristics by increasing the residual stress of the recovery structure directly below the surface layer and reducing hysteresis loss.

[0025] 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 electric motors.

[0026] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0027] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0028] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0029] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0030] In one embodiment of the present invention, the meaning of including additional elements is that the remainder of iron (Fe) is replaced by an amount of the additional element.

[0031] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0032] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0033]

[0034] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percent, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities.

[0035] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0036]

[0037] Si: 1.5 to 5.0 wt%

[0038] Silicon (Si) plays a role in increasing the resistivity of the material to lower iron loss and increasing strength through solid solution strengthening. If too little Si is added, the effect of improving iron loss and strength may be insufficient. If too much Si is added, the magnetic flux density decreases significantly, and rolling performance may deteriorate due to increased brittleness. Therefore, Si may be included in an amount of 1.5 to 5.0 weight%. More specifically, it may be included in an amount of 1.6 to 4.5 weight%. Even more specifically, it may be included in an amount of 1.6 to 4.3 weight%.

[0039]

[0040] Al: 0.1 to 3.0 wt%

[0041] Aluminum (Al) increases the resistivity of the material to lower iron loss and improve rollability, and reduces magnetic anisotropy to reduce magnetic deviation in the rolling direction and the direction perpendicular to rolling. 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, nitrides may be excessively formed, which can degrade magnetism. Therefore, Al may be included in an amount of 0.1 to 3.0 weight%. More specifically, it may be included in an amount of 0.2 to 2.9 weight%. Even more specifically, it may be included in an amount of 0.5 to 2.5 weight%.

[0042]

[0043] Mn: 0.10 to 3.0 wt%

[0044] Manganese (Mn) plays a role in improving iron loss and texture by increasing the resistivity of the material. If too little Mn is added, fine sulfides are formed, causing magnetic degradation, and if too much Mn is added, it can adversely affect magnetic flux density. Therefore, Mn may be included in an amount of 0.1 to 3.0 weight%. More specifically, it may be included in an amount of 0.2 to 2.9 weight%. Even more specifically, it may be included in an amount of 0.5 to 2.5 weight%.

[0045]

[0046] In one embodiment of the present invention, the non-oriented electrical steel sheet may have a resistivity of 63.0 μΩ·cm or higher at 25°C. The iron loss of the non-oriented electrical steel sheet is divided into hysteresis loss and eddy current loss; however, if the resistivity of the steel is increased by adding elements such as Si, Al, and Mn, the eddy current loss can be significantly reduced. In particular, as the frequency increases, the proportion of eddy current loss in the total iron loss increases; therefore, to achieve excellent high-frequency iron loss, it is necessary to control the resistivity of the steel above a certain level, and through the present invention, excellent characteristics can be secured when the resistivity (ρ) of the steel is 63 μΩ·cm or higher. More specifically, the resistivity (ρ) may be 64.0 to 90.0 μΩ·cm.

[0047] In one embodiment of the present invention, resistivity can be measured using the 4-terminal method, Van Der Pawu method, Four-Point Probe method, Eddy Current method, etc.

[0048]

[0049] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less, C: 0.01 wt% or less, S: 0.015 wt% or less, Ti: 0.005 wt% or less, and N: 0.01 wt% or less.

[0050] P: 0.1 wt% or less

[0051] Phosphorus (P) has the effect of improving the texture of steel as a grain boundary and surface segregation element. However, if too much P is added, it may inhibit grain growth, thereby reducing iron loss, and reduce rolling performance due to grain boundary segregation, which may also reduce productivity. More specifically, it may contain 0.0001 to 0.0500 weight% of P. More specifically, it may contain 0.0020 to 0.0200 weight% of P.

[0052] C: 0.010 wt% or less

[0053] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, which can impede grain boundary or domain wall movement and degrade magnetic properties. More specifically, it may contain 0.0001 to 0.0050 weight% of C. More specifically, it may contain 0.0005 to 0.0035 weight% of C.

[0054] S: 0.015 wt% or less

[0055] Sulfur (S) can form fine precipitates, such as MnS and CuS, which can degrade magnetic properties and hot workability. More specifically, it may contain 0.0001 to 0.0100 weight% of S. More specifically, it may contain 0.0005 to 0.0040 weight% of S.

[0056] Ti: 0.0050 wt% or less

[0057] Titanium (Ti) has a very strong tendency to form precipitates in steel and can degrade iron loss by forming fine carbides, nitrides, or sulfides within the base material, thereby inhibiting grain growth and domain wall movement. More specifically, it may contain 0.0005 to 0.0035 weight% of Ti.

[0058] N: 0.01 wt% or less

[0059] Nitrogen (N) not only forms fine AlN precipitates inside the base material but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall movement, which can worsen iron loss. More specifically, it may contain 0.0001 to 0.0050 weight% of N. More specifically, it may contain 0.0005 to 0.0035 weight% of N.

[0060] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, respectively or in their combined amount.

[0061] Sn

[0062] Tin (Sn) can be added to improve magnetism because it plays a role in improving the texture of the material and suppressing surface oxidation by segregating at grain boundaries and surfaces. If too much Sn is added, grain boundary segregation becomes severe, leading to deterioration of surface quality and an increase in hardness, which may cause fracture of the cold-rolled sheet and a decrease in rollability. Specifically, 0.005 to 0.200 weight% of Sn may be further included. More specifically, 0.010 to 0.080 weight% may be further included.

[0063] Sb

[0064] Antimony (Sb) can be additionally added to improve magnetism because it plays a role in improving the texture of the material and suppressing surface oxidation by segregating at grain boundaries and surfaces. If too much Sb is added, grain boundary segregation becomes severe, leading to deterioration of surface quality and increased hardness, which may cause cold-rolled sheet fracture and reduce rollability. Specifically, 0.005 to 0.200 weight% of Sb may be additionally included. More specifically, 0.010 to 0.080 weight% may be additionally included.

[0065] Bi, Pb, Ge, and As

[0066] When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are added, they segregate at grain boundaries, alleviating stress concentration at grain boundaries during cold rolling, which in the subsequent recrystallization annealing process <111> By suppressing the recrystallization of / ND orientation grains, magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained; however, if included in excessive amounts, a large amount of segregation occurs, which inhibits grain growth and may actually result in inferior magnetic flux density and iron loss.

[0067]

[0068] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more 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%).

[0069] Cu: 0.005 to 0.200 wt%

[0070] Copper (Cu) plays a role in forming sulfides together with Mn. If more Cu is added, or if too little is added, (Cu · Mn)S may precipitate finely, which can degrade magnetism. If too much Cu is added, high-temperature brittleness occurs, which can form cracks during continuous casting or hot rolling. More specifically, it may contain 0.01 to 0.10 weight% of Cu.

[0071] Cr: 0.01 to 0.50 wt%

[0072] Chromium (Cr) plays a role in improving iron loss by increasing resistivity. If too little Cr is added, the effect of increasing resistivity may not be sufficient. If too much Cr is included, magnetic flux density may decrease. More specifically, 0.050 to 0.20 weight% of Cr may be included.

[0073] Ni: 0.05 wt% or less

[0074] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a harmful effect on magnetism. More specifically, it may contain 0.001 to 0.03 weight percent of Ni.

[0075] Zn: 0.01 wt% or less

[0076] If the content of zinc (Zn) is excessive, it acts as an impurity and can impair magnetism. Therefore, Zn may be added within the aforementioned range. More specifically, Zr may be included in an amount of 0.001 to 0.005 weight%.

[0077] Co: 0.05 wt% or less

[0078] Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it increases high-temperature strength, which can cause the coil shape to be defective after hot rolling.

[0079]

[0080] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0081] Mo: 0.030 wt% or less

[0082] If molybdenum (Mo) is added in excess, it may suppress the segregation of segregated elements, thereby reducing the texture improvement effect. Therefore, Mo may be included in an amount of 0.03 weight% or less. The lower limit is not specifically limited, but since it plays a role in improving the texture by segregating at the surface and grain boundaries, it may be included in an amount of 0.001 weight% or more. More specifically, Mo may be included in an amount of 0.001 to 0.010 weight%. Even more specifically, Mo may be included in an amount of 0.005 to 0.010 weight%.

[0083] B: 0.0050 wt% or less

[0084] If an excessive amount of boron (B) is added, it may cause deterioration of magnetic properties through the formation of inclusions within the steel. Therefore, B may be included in an amount of 0.005 weight% or less. The lower limit is not specifically limited, but it may be 0.0001 weight% due to steelmaking costs. More specifically, B may be included in an amount of 0.0001 to 0.0030 weight%.

[0085] V: 0.0050 wt% or less

[0086] Vanadium (V) has a very strong tendency to form precipitates in steel and degrades iron loss by forming fine carbides or nitrides inside the base material, thereby inhibiting grain growth and domain wall movement. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not specifically limited, but it may be 0.0003 wt% due to steelmaking costs. That is, V may be included in 0.0003 to 0.0050 wt%. More specifically, V may be included in 0.0003 to 0.0030 wt%.

[0087] Ca: 0.0050 wt% or less

[0088] Calcium (Ca) has a very strong tendency to form precipitates within the steel and degrades iron loss by forming fine sulfides inside the base material, thereby inhibiting grain growth and domain wall movement.

[0089] Nb: 0.0050 wt% or less

[0090] Niobium (Nb) has a very strong tendency to form precipitates in steel and degrades iron loss by forming fine carbides or nitrides within the base material, thereby inhibiting grain growth and domain wall movement. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not specifically limited, but it may be 0.0003 wt% due to steelmaking costs. That is, it may contain 0.0003 to 0.0050 wt% of Nb. More specifically, it may contain 0.0003 to 0.0030 wt% of Nb.

[0091] Zr: 0.0050 wt% or less

[0092] If an excessive amount of zirconium (Zr) is added, it may cause deterioration of magnetic properties through the formation of inclusions within the steel. Therefore, Zr may be included in an amount of 0.005 weight% or less. The lower limit is not specifically limited, but it may be set to 0.0001 weight% due to steelmaking costs. That is, Zr may be included in an amount of 0.0001 to 0.0050 weight%. More specifically, it may be included in an amount of 0.0005 to 0.0030 weight%.

[0093] Te: 0.0100 wt% or less

[0094] Tellurium (Te) can be added to prevent the oxide layer, which is fractured during rolling, from being pressed into the base material and to detach it, as it diffuses into the oxide layer on the surface of the hot-rolled coil, increases the coefficient of friction between the oxide layer and the rolling work roll, and increases hardness by concentrating beneath the oxide layer. If the amount of Te added is too small, the effect may be negligible. If too much Te is added, the oxide layer detaches easily, causing the base material to come into direct contact with the work roll, which reduces the above effect, and excessive deformation bands may be generated within the steel sheet during cold rolling, leading to the development of a {111} / ND texture that is unfavorable to magnetism. More specifically, it may contain 0.0001 to 0.007 weight% of tellurium.

[0095] Mg: 0.0050 wt% or less

[0096] Magnesium (Mg) is an element that primarily combines with S to form sulfides and can affect the surface oxide layer of the base iron. Therefore, Mg may be included in an amount of 0.0050 wt% or less. The lower limit is not specifically limited, but it may be 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%.

[0097]

[0098] The remainder comprises Fe and unavoidable impurities. The unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets; as this is widely known in the field, a detailed description is 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. If additional elements are included, they replace the remainder, Fe.

[0099]

[0100] As described above, in one embodiment of the present invention, strength and magnetism can be simultaneously improved by adjusting the KAM value according to the thickness of the non-oriented electrical steel sheet.

[0101] Specifically, the KAM value measured at 10% of the total thickness in the thickness direction from the surface of the steel plate is 1.5° or less, and the KAM value measured at 50% of the total thickness in the thickness direction from the surface of the steel plate is 0.7° or less.

[0102] Kernel Average Misorientation (KAM) refers to the difference in orientation between a pixel and the kernel surrounding it, regardless of grains or grain boundaries.

[0103] In one embodiment of the present invention, the KAM value (hereinafter also referred to as “10% KAM”) measured at a position 10% of the total thickness in the thickness direction from the surface of the steel plate is 1.5° or less. If the KAM value at the surface of the steel plate is too small, productivity may be significantly reduced. If the KAM value at the surface of the steel plate is too large, residual stress may hinder magnetization and degrade magnetism, and accelerate aging during motor operation, which may further degrade magnetism. More specifically, the KAM value measured at a position 10% of the total thickness in the thickness direction from the surface of the steel plate may be 0.4 to 1.5°. More specifically, the KAM value measured at a position 10% of the total thickness in the thickness direction from the surface of the steel plate may be 0.5 to 1.4°.

[0104] In one embodiment of the present invention, the KAM value (hereinafter also referred to as “50% KAM”) measured at a position 50% of the total thickness in the thickness direction from the surface of the steel plate is 0.7° or less. If the KAM value at the center of the steel plate is too small, productivity may be significantly reduced. If the KAM value at the surface of the steel plate is too large, residual stress may hinder magnetization and degrade magnetism, and accelerate aging during motor operation, which may further degrade magnetism. More specifically, the KAM value measured at a position 50% of the total thickness in the thickness direction from the surface of the steel plate may be 0.3 to 0.7°. More specifically, the KAM value measured at a position 50% of the total thickness in the thickness direction from the surface of the steel plate may be 0.4 to 0.6°.

[0105] The KAM value at each thickness can be measured on a plane parallel to the steel plate rolling plane (plane perpendicular to the ND direction). If an insulating film is formed on the surface of the steel plate, the insulating film is excluded from the thickness to calculate the position for each thickness. The KAM value for each thickness can be measured by removing the steel plate through processing to the corresponding thickness on a plane parallel to the steel plate rolling plane (plane perpendicular to the ND direction). The KAM value can be analyzed using the commercial program OIM Analysis by measuring the Electron Backscatter Diffraction (EBSD) pattern of the steel plate cross-section using a Scanning Electron Microscope (SEM). To reduce errors due to measurement location, measurements can be taken using three or more non-overlapping samples with an area of ​​3 mm × 3 mm, and the average value can be calculated.

[0106] The difference (50% KAM - 10% KAM) between the KAM value measured at 10% of the total thickness in the thickness direction from the steel plate surface and the KAM value measured at 50% of the total thickness in the thickness direction from the steel plate surface may be -1.2 to 0.3°. If this difference is too small, it means that the 10% KAM value is too large compared to the 50% KAM value, and the magnetization interference effect in the surface layer is strong, which may lead to deterioration of magnetic quality. Conversely, if this difference is too large, it means that the 50% KAM value is too large compared to the 10% KAM value, and the magnetization interference effect in the center is strong, which may lead to deterioration of magnetic quality. More specifically, the difference between the KAM value measured at 10% of the total thickness in the thickness direction from the steel plate surface and the KAM value measured at 50% of the total thickness in the thickness direction from the steel plate surface may be -1.0 to -0.1°.

[0107] As described above, in one embodiment of the present invention, strength and magnetism can be simultaneously improved by adjusting the KAM value according to thickness. Specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have a yield strength of 250 MPa or more. More specifically, it may be 270 to 600 MPa. Even more specifically, it may be 400 to 550 MPa. The yield strength can be measured by performing a room temperature tensile test on a JIS-13B tensile test specimen using a room temperature tensile testing machine.

[0108] A non-oriented electrical steel sheet according to one embodiment of the present invention may have a tensile strength of 400 MPa or more. More specifically, it may be 410 to 800 MPa. More specifically, it may be 550 to 750 MPa. The tensile strength can be measured by performing a room temperature tensile test on a JIS-13B tensile test specimen using a room temperature tensile testing machine.

[0109] The iron loss (W10 / 400) may be 13.5 W / Kg or less, and the iron loss (W10 / 800) may be 40.0 W / Kg or less. The thickness standard may be 0.20 mm. More specifically, the iron loss (W10 / 400) may be 10.0 to 13.0 W / kg. Also, the iron loss (W10 / 800) may be 25.0 to 37.0 W / kg. The iron loss (W10 / 400) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. The iron loss (W10 / 800) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 800 Hz. Iron loss (W10 / 400) and iron loss (W10 / 800) can be measured using a single sheet tester for the rolling direction and the rolling vertical direction, and the average value can be determined.

[0110]

[0111] 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 weight percent, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities to produce a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet to produce a cold-rolled sheet; and an annealing step for the cold-rolled sheet.

[0112] Below, each step is explained in detail.

[0113] First, the slab is hot-rolled.

[0114] As the alloy composition of the slab has been explained in the aforementioned section on the alloy composition of non-oriented electrical steel sheets, a redundant explanation is omitted. Since the alloy composition does not substantially change during the manufacturing process of non-oriented electrical steel sheets, the alloy composition of the non-oriented electrical steel sheets and the slab is substantially the same.

[0115] Specifically, the slab contains Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0% by weight, and the remainder is Fe and unavoidable impurities.

[0116] As other additional elements have been explained in the alloy composition of non-oriented electrical steel sheets, redundant explanations are omitted.

[0117] The slab can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1200°C or lower. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, which can inhibit grain growth and reduce magnetism.

[0118] Next, the slab is hot-rolled to produce a hot-rolled plate.

[0119] In one embodiment of the present invention, low iron loss characteristics can be secured by controlling the reduction rate during rough rolling to reduce residual stress in the extreme surface layer of the hot-rolled plate and increasing residual stress in the recovery structure immediately below the surface layer to reduce hysteresis loss.

[0120] Specifically, the steps for manufacturing hot-rolled steel sheets include a rough rolling step and a finishing rolling step, and the rough rolling step includes a plurality of passes, and the reduction rate in the pass before the last pass may be 30 to 47%.

[0121] The rough rolling stage is a process in which a slab transferred from a casting machine is first rolled into the form of a steel plate to produce a bar, and is composed of about 1 to 5 rolling mills, and the finishing rolling stage is a process in which the rough-rolled steel plate (bar) is rolled to the final hot-rolling target thickness to make a hot-rolled coil, and is composed of a continuous multi-stage rolling mill.

[0122] The rough rolling stage can consist of 3 to 4 passes. A pass refers to the number of times a material passes through a rolling roll. For example, if the rough rolling stage consists of 4 passes, the last pass is the 4th pass, and the pass before the last pass is the 3rd pass. The reduction ratio can be calculated as (thickness of steel plate before pass - thickness of steel plate after pass) / thickness of steel plate before pass × 100 (%).

[0123] If the reduction ratio in the pass before the last pass is too low, shear deformation may not be properly applied, and the effect may not be fully manifested. If the reduction ratio in the pass before the last pass is too high, the leading edge of the coil may be lifted upward or sag downward, preventing proper rolling. More specifically, the reduction ratio in the pass before the last pass may be 35 to 45%.

[0124] In the rough rolling stage, the reduction ratio of the last pass may be 25 to 47%. If the reduction ratio in the pass is too low, shear deformation may not be properly applied. If the reduction ratio in the last pass is too high, the leading edge of the coil may be lifted upward or sag downward, preventing proper rolling. More specifically, the reduction ratio in the last pass may be 30 to 40%.

[0125] In the rough rolling stage, the sum of the reduction ratios before the last pass and the last pass may be 55 to 94%. If the sum of the reduction ratios before the last pass and the last pass in the rough rolling stage is too low, shear deformation may not be properly applied, and the effect may not be fully manifested. If the sum of the reduction ratios before the last pass and the last pass is too high, the leading edge of the coil may be lifted upward or sagged downward, preventing proper rolling. More specifically, the sum of the reduction ratios before the last pass and the last pass may be 70 to 90%.

[0126] In one embodiment of the present invention, the finishing rolling may consist of 3 to 7 passes (i.e., n is 3 to 7). If the number of passes is too low, the rolling load may become too high, making the operation difficult. If the number of passes is too high, productivity may decrease.

[0127] The thickness of the hot-rolled plate may be 1.0 to 4.5 mm. In the step of manufacturing the hot-rolled plate, the finish rolling temperature may be 800°C or higher. Specifically, it may be 800 to 1000°C. The hot-rolled plate may be wound at a temperature of 700°C or lower. More specifically, the thickness of the hot-rolled plate may be 1.5 to 4.3 mm.

[0128] After manufacturing the hot-rolled steel sheet, an additional step of annealing the hot-rolled sheet may be included. At this time, the cracking temperature may be 850 to 1100°C. If the annealing temperature is too low, a recrystallization structure is not formed or grows finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, magnetic properties may actually deteriorate, and rolling workability may worsen due to deformation of the sheet shape. More specifically, the temperature range may be 830 to 1080°C. The cracking time may be 10 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0129] Next, a cold-rolled sheet is manufactured by cold-rolling a hot-rolled steel sheet. At this time, cold rolling can be performed with a reduction rate of 40 to 85%. If the reduction rate is too low, the deformation energy accumulated in the rolled steel sheet is small, making it difficult to recrystallize during the subsequent annealing process. As a result, the rolled structure remains, which may cause problems in improving magnetic flux density and iron loss. Conversely, if the reduction rate is too high, during the subsequent annealing process <111> / ND orientation. Recrystallization of the grains is promoted and the grains become finer, which may result in problems such as reduced magnetic flux density and increased iron loss. More specifically, the reduction ratio may be 60 to 75%. For the cold rolling step, 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 using 12 or more rolling rolls may be used. The final rolled thickness may be 0.1 mm to 0.35 mm.

[0130] The step of manufacturing cold-rolled sheets can be performed once or two or more times with intermediate annealing in between.

[0131] Next, the cold-rolled sheet is annealed during the annealing stage. In the process of annealing the cold-rolled sheet, there are generally no significant restrictions on the annealing temperature as long as it is a temperature typically applied to non-oriented electrical steel. The iron loss of non-oriented electrical steel is closely related to grain size. The iron loss of non-oriented electrical steel can be classified into hysteresis loss and eddy current loss; hysteresis loss decreases as the grain size increases, while conversely, eddy current loss increases as the grain size increases. Consequently, there exists an optimal grain size at which the sum of hysteresis and eddy current losses is minimized. Therefore, it is important to determine and apply an annealing temperature that can secure the optimal grain size, and an annealing temperature of 850 to 1100°C is suitable. If the annealing temperature is too low, the grains become too fine, increasing hysteresis loss; if it is too high, the grains become too coarse, increasing eddy current loss and resulting in inferior iron loss. In addition, the annealing time is also suitable if it is between 10 and 300 seconds, and to prevent magnetic deterioration caused by the formation of an oxide layer, annealing can be performed in a hydrogen or mixed atmosphere of argon and nitrogen.

[0132] During the annealing process of the cold-rolled sheet, all (i.e., more than 99%) of the processed structure formed during the cold rolling stage can be recrystallized.

[0133] After annealing the cold-rolled sheet, an insulating film can be formed. The insulating film can be treated with organic, inorganic, or organic-inorganic composite films, and it is also possible to treat it with other insulating coating materials.

[0134] The non-oriented electrical steel sheet manufactured in this way has the aforementioned KAM values ​​according to steel composition and thickness.

[0135]

[0136] The present invention will be explained in more detail below through examples. However, these examples are merely for illustrating the invention and the invention is not limited thereto.

[0137]

[0138] Examples

[0139] A slab was prepared with a composition including the remainder Fe and unavoidable impurities as shown in Table 1. It was heated to 1170°C, hot-rolled to a thickness of 2.2 mm, and coiled at 680°C. During this process, rough rolling was performed in a total of 4 passes, and the reduction rates for the 3rd and 4th passes were set as shown in Table 1 below. The hot-rolled steel sheet was annealed at 1000°C for 50 seconds. After annealing, the pickled specimen was cold-rolled to a thickness of 0.2 mm, and finally, cold-rolled annealing was performed. During this process, cold-rolled annealing was carried out at 1000°C for 50 seconds.

[0140] The KAM value was measured by processing steel plates from 0.1 mm (50% of the thickness) to 0.18 mm (10% of the thickness) and observing the cross-section parallel to the rolling plane using EBSD.

[0141] Yield strength was measured using the 0.2% offset method during tensile testing.

[0142] Tensile strength was measured using a room temperature tensile testing machine after processing plate-shaped JISB-13B tensile specimens.

[0143] Iron loss (W10 / 400) and iron loss (W10 / 800) were measured using a single sheet tester.

[0144] Category SiAlMn 3rd Pass Downward Rate (%) 4th Pass Downward Rate (%) 3rd + 4th Pass Downward Rate (%) 14.20.20.24 34 790 23.50.70.34 625 71 32.30.60.23 535 70 41.83.02.93 536 71 51.81.70.34 626 726 3.50.60.43 74 68 37 4.10.82.93 738 758 4.32.22.84 139 80 93.52.92.84 529 74 105.02.91.43 94 180 111.50.12. 0323769123.40.11.2392968133.53.01.5364379142.81.00.1363066154.92.73.0473380162.61.80.9294271173.50.42.6482876184.21.80.8474289195.01.21.9322557204.50.40.4302555214.80.61.4474794

[0145] Classification 10% KAM(°) 50% KAM(°) 50% KAM - 10% KAM(°) YP(MPa) TS(MPa) W10 / 400 W10 / 800(W / kg)(W / kg) 10.6 0.6 0.0 40 95 48 11.6 29.5 Invention Example 2 1.10.4 - 0.7 38 75 28 12.2 32.8 Invention Example 3 0.40.40.0 318 45 6 12.6 36.0 Invention Example 4 0.40.7 0.3 38 65 42 11.2 29.5 Invention Example 5 1.30 .4-0.932546810.927.3 Invention Example 61.10.5-0.638452512.133.9 Invention Example 70.60.3-0.344559212.133.1 Invention Example 81.20.6-0.649765212.131.2 Invention Example 90.60.60.047463213.035.5 Invention Example 101.30.5-0.854370111.026.8 Invention Example 1 10.6 0.7 0.1 276413 12.9 35.6 Invention Example 1 2 1.1 0.4 -0.7 3715 10 12.9 34.3 Invention Example 1 3 1.4 0.4 -1.0 4666 22 11.8 30.9 Invention Example 1 4 0.6 0.3 -0.3 356497 12.9 35.4 Invention Example 1 5 1.1 0.4 -0.7 546705 12.3 32.6 Invention Example 1 6 1.7 0.8 -0.93 7652314.844.3 Comparative Example 171.60.9-0.739854214.241.7 Comparative Example 180.90.6-0.346261111.229.5 Inventive Example 190.80.6-0.249764611.529.9 Inventive Example 201.30.5-0.843257411.631.1 Inventive Example 211.20.6-0.646360810.927.2 Inventive Example

[0146] As shown in Tables 1 and 2, when the steel composition and reduction ratio during rough rolling are appropriately controlled, the KAM value for each thickness is appropriately controlled, and it can be confirmed that both strength and iron loss are excellent.

[0147] On the other hand, for steel grades 16 and 17, the reduction ratio before the last pass of rough rolling is too small or too large, so the KAM values ​​of the surface and center of the steel plate are not properly controlled, and it can be confirmed that the iron loss is inferior.

[0148]

[0149] The present invention is not limited to the embodiments described above but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without altering the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. In weight%, it comprises Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities, and The KAM value measured at a position 10% of the total thickness in the thickness direction from the surface of the steel plate is 1.5° or less, and Non-oriented electrical steel sheet having a KAM value of 0.7° or less measured at 50% of the total thickness in the thickness direction from the surface of the steel sheet.

2. In Paragraph 1, A non-oriented electrical steel sheet in which the difference between the KAM value measured at 10% of the total thickness in the thickness direction from the steel sheet surface and the KAM value measured at 50% of the total thickness in the thickness direction from the steel sheet surface is -1.2 to 0.3°.

3. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of P: 0.1 wt% or less, C: 0.01 wt% or less, S: 0.015 wt% or less, Ti: 0.005 wt% or less, and N: 0.01 wt% or less.

4. In Paragraph 1, A non-oriented electrical steel sheet further comprising 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, either individually or in their combined amount.

5. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

6. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

7. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing, in weight percent, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities; A step of manufacturing a cold-rolled plate by cold-rolling the above hot-rolled steel plate and Cold-rolled plate annealing step for annealing the above-mentioned cold-rolled plate; Includes, The step of manufacturing the above hot-rolled steel sheet includes a rough rolling step and a finish rolling step, and A method for manufacturing a non-oriented electrical steel sheet, wherein the above rough rolling step includes a plurality of passes, and the reduction rate in the pass prior to the last pass is 30 to 47%.

8. In Paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises one or more of P: 0.1 wt% or less, C: 0.01 wt% or less, S: 0.015 wt% or less, Ti: 0.005 wt% or less, and N: 0.01 wt% or less.

9. In Paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, respectively or in their combined amount.

10. In Paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

11. In Paragraph 7, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

12. In Paragraph 7, The above rough rolling step is a method for manufacturing non-oriented electrical steel sheets in which the reduction rate of the last pass is 25 to 47%.

13. In Paragraph 7, The above rough rolling step is a method for manufacturing non-oriented electrical steel sheets in which the sum of the reduction rates before the last pass and the last pass is 55 to 94%.