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 1.5-5.0 wt% of Si, 0.1-2.0 wt% of Al, and 0.1-2.0 wt% of Mn, with the balance being Fe and inevitable impurities, wherein the area fraction of crystal grains having orientations within 15° from {411}<148> is 25% or more.

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, wherein a magnetic field is applied during stress relief annealing to simultaneously obtain excellent magnetic flux density and iron loss.

[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 The characteristics of non-oriented electrical steel sheets are often evaluated based on iron loss.

[0005] Meanwhile, to manufacture motors from non-oriented electrical steel sheets, the sheets are punched into a motor shape and subjected to stress-relief annealing to remove stress generated during the punching process. At this stage, while iron loss is improved through grain growth, magnetic flux density may deteriorate to some extent. Therefore, a method is required to suppress the deterioration of magnetic flux density while improving iron loss by growing grains during stress-relief annealing.

[0006] 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 a magnetic field is applied during stress relief annealing to simultaneously obtain excellent magnetic flux density and iron loss.

[0007] 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 2.0%, Mn: 0.1 to 2.0%, and the remainder being Fe and unavoidable impurities.

[0008] {411} <148> The area fraction of crystal grains having an angle of 15° or less from is 25% or more.

[0009] {411} <148> The average grain size of crystal grains having an angle of 15° or less from is 80 to 100 μm.

[0010] 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: 0.005 wt% or less, S: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0011] 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.

[0012] According to one embodiment of the present invention, one or more of non-oriented 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 may be further included.

[0013] 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.

[0014] 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 comprising, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, 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; a cold-rolled sheet annealing step for annealing the cold-rolled sheet; and a stress-relieving annealing step for the annealed cold-rolled sheet.

[0015] Stress relief annealing can be performed by applying a magnetic field of 0.5 to 2.0 T.

[0016] The slab may further include one or more of P: 0.1 wt% or less, C: 0.005 wt% or less, S: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] The annealing stage of the cold-rolled sheet may have a cracking temperature of 600 to 830°C.

[0021] When a magnetic field is applied during the stress relief annealing step, the temperature is 500 to 810°C, and the magnetic field application time may be 20 minutes or more.

[0022] When a magnetic field is applied during the stress relief annealing step, the product of the temperature (°C) and the magnetic field application time (min) can be 25 × 1000 to 70 × 1000.

[0023] A non-oriented electrical steel sheet according to one embodiment of the present invention exhibits excellent iron loss and magnetic flux density simultaneously after stress relief annealing.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0028] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0029] 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.

[0030] 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.

[0031] 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.

[0032]

[0033] 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 2.0%, Mn: 0.1 to 2.0%, and the remainder being Fe and unavoidable impurities.

[0034] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0035]

[0036] Si: 1.5 to 5.0 wt%

[0037] 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 hardness of the material increases, which may result in inferior productivity and stamping performance. 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 2.0 to 4.5 weight%. Even more specifically, it may be included in an amount of 3.2 to 3.75 weight%.

[0038]

[0039] Al: 0.1 to 2.0 wt%

[0040] Aluminum (Al) plays a role in increasing the resistivity of the material to lower iron loss, improve rollingability, and enhance workability during cold rolling. If too little Al is added, it may be difficult to obtain the effect of reducing high-frequency iron loss, and the precipitation temperature of AlN may be lowered, leading to the formation of fine nitrides that may degrade magnetism. If too much Al is added, excessive nitrides may be formed, degrading magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. Therefore, Al may be included in an amount of 0.1 to 2.0 weight%. More specifically, it may be included in an amount of 0.5 to 1.8 weight%. Even more specifically, it may be included in an amount of 0.7 to 1.5 weight%.

[0041]

[0042] Mn: 0.1 to 2.0 wt%

[0043] Manganese (Mn) plays a role in improving iron loss by increasing the resistivity of the material and forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic degradation; if too much Mn is added, fine MnS is excessively precipitated and the magnetic domain structure changes, which can adversely affect iron loss. Therefore, Mn may be included in an amount of 0.1 to 2.0 weight%. More specifically, it may be included in an amount of 0.2 to 1.8 weight%. Even more specifically, it may be included in an amount of 0.4 to 1.5 weight%.

[0044]

[0045] In one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet may be 55 μΩ·cm or higher. While a higher resistivity is preferable for reducing eddy current losses in high-frequency rotating machinery, if it becomes too large, the magnetic flux density may be inferior. In one embodiment of the present invention, the resistivity can be estimated from the formula 13.25+11.3×([Si]+[Al]+[Mn] / 2+[Cu] / 2+[Cr] / 2). In this case, if Cu and Cr are not included, it can be calculated as 0. More specifically, the resistivity may be 58 to 80 μΩ·cm.

[0046]

[0047] 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 (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%).

[0048] P: 0.1 wt% or less

[0049] Phosphorus (P) not only plays a role in increasing the resistivity of the material but can also improve magnetic flux density as a grain boundary segregation element. However, if too much P is added, it increases the brittleness of the steel sheet, resulting in poor weldability. More specifically, it may contain 0.0001 to 0.0500 weight% of P. More specifically, it may contain 0.0010 to 0.0200 weight% of P.

[0050] C: 0.005 wt% or less

[0051] 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 0.003 weight% of C.

[0052] S: 0.005 wt% or less

[0053] Sulfur (S) can form fine precipitates, such as MnS and CuS, which can worsen magnetic properties and hot workability. More specifically, it may contain 0.0001 to 0.0030 weight% of S.

[0054] Ti: 0.005 wt% or less

[0055] 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 0.0001 to 0.0030 weight% of Ti.

[0056] N: 0.005 wt% or less

[0057] 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 0.0030 weight% of N.

[0058]

[0059] 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.

[0060] Sn

[0061] 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.

[0062] Sb

[0063] 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.

[0064] Bi, Pb, Ge, and As

[0065] 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.

[0066]

[0067] 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%).

[0068] Cu: 0.005 to 0.200 wt%

[0069] 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.

[0070] Cr: 0.01 to 0.50 wt%

[0071] 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.

[0072] Ni: 0.05 wt% or less

[0073] 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.

[0074] Zn: 0.01 wt% or less

[0075] If the content of zinc (Zn) is excessive, it can act as an impurity and impair magnetism. Therefore, Zn may be added within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 weight%.

[0076] Co: 0.05 wt% or less

[0077] 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.

[0078]

[0079] 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 (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%).

[0080] Mo: 0.030 wt% or less

[0081] 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%.

[0082] B: 0.0050 wt% or less

[0083] 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%.

[0084] V: 0.0050 wt% or less

[0085] 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%.

[0086] Ca: 0.0050 wt% or less

[0087] 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.

[0088] Nb: 0.0050 wt% or less

[0089] 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.

[0090] Zr: 0.0050 wt% or less

[0091] 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%.

[0092] Te: 0.0100 wt% or less

[0093] 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.

[0094] Mg: 0.0050 wt% or less

[0095] 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%.

[0096]

[0097] 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.

[0098]

[0099] A non-oriented electrical steel sheet according to one embodiment of the present invention is {411} <148> The area fraction of grains having an angle of 15° or less from may be 25% or more. {411} <148> Crystal grains having an angle of 15° or less from <111> / ND <100> Approaching / ND helps improve iron loss, and even if the crystal grain size grows significantly, the deterioration of magnetic flux density can be minimized. {411} <148> When the area fraction of crystal grains having an angle of 15° or less from is too low, it is difficult to obtain the aforementioned effect sufficiently. More specifically, the area fraction may be 25 to 40%.

[0100] {411} <148> Orientation refers to the orientation represented by Miller indices, indicating the relationship between the grains and the rolling plane (ND plane) and the rolling direction (RD direction) of the steel sheet. The area fraction of the grains can be measured through electron backscatter diffraction pattern (EBSD) analysis for a cross-section including the thickness direction of the steel sheet, more specifically the TD plane. In this case, the area ratio can be obtained by performing image analysis with the error angle set to 15° or less.

[0101] A non-oriented electrical steel sheet according to one embodiment of the present invention is {411} <148> The average grain size of crystal grains having an angle of 15° or less from may be 80 to 100 μm. {411} <148> If the crystal grains having an angle of 15° or less from are too small, <111> Due to the high strength of / ND, the magnetic enhancement effect cannot be fully obtained. If the crystal grains are too large, a problem may arise where high-frequency iron loss is degraded. More specifically, {411} <148> The average grain size of crystal grains having an angle of 15° or less from may be 85 to 95 μm.

[0102] The grain size can be determined by assuming a circle with an area equal to the area occupied by the grain and using the diameter of that circle. More specifically, through electron backscatter diffraction pattern (EBSD) analysis {411} <148> It can be obtained by finding crystal grains having an angle of 15° or less from and analyzing them via image analysis.

[0103] {411} <148> The average grain size of grains other than those having an angle of 15° or less from may be 60 to 80 μm. In one embodiment of the present invention, {411} <148> By selectively growing only grains having an angle of 15° or less from and reducing the grain size of the remaining grains, iron loss and magnetic flux density can be simultaneously improved. More specifically, {411} <148> The average grain size of crystal grains other than those having an angle of 15° or less from may be 65 to 75 μm.

[0104] More specifically {411} <148> The difference in grain size between crystal grains having an angle of 15° or less from and other crystal grains may be 10 to 30 μm.

[0105]

[0106] As previously mentioned, in one embodiment of the present invention, magnetic flux density and iron loss can be improved simultaneously.

[0107] Specifically, in one embodiment of the present invention, the iron loss (W) of a non-oriented electrical steel sheet based on a thickness of 0.25 mm 10 / 400 ) may be 12.0W / Kg or less. Iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0T is induced at a frequency of 400 Hz. More specifically, the iron loss (W of non-oriented electrical steel) 10 / 400 ) can be 10.5 to 11.6 W / kg.

[0108] In addition, in one embodiment of the present invention, the magnetic flux density (B) of a non-oriented electrical steel sheet based on a thickness of 0.25 mm 50 ) can be 1.65T or more. Magnetic flux density (B 50 ) is the magnetic flux density measured at 5000 A / m. More specifically, the magnetic flux density of non-oriented electrical steel (B 50 ) can be 1.66 to 1.70T.

[0109]

[0110] 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 comprising, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, 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; a cold-rolled sheet annealing step for annealing the cold-rolled sheet; and a stress-relieving annealing step for the annealed cold-rolled sheet.

[0111]

[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 2.0%, Mn: 0.1 to 2.0% 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, a hot-rolled plate is manufactured by hot-rolling a slab. 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 coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled plate may be 1.5 to 4.3 mm.

[0119] 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 800 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 30 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0120] 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 90%. 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 85%. 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.

[0121] The step of manufacturing cold-rolled sheets can be performed once or two or more times with intermediate annealing in between.

[0122] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. In one embodiment of the present invention, the cracking temperature during cold-rolled sheet annealing is set low to form a large number of unrecrystallized cells, and the unrecrystallized cells are grown during the stress relief annealing process to improve iron loss. Specifically, the cracking temperature may be 600 to 830°C. More specifically, it may be 630 to 820°C.

[0123] After annealing a cold-rolled sheet, the area occupied by unrecrystallization within the steel sheet may be 5% or more. Unrecrystallization can be measured based on a cross-section including the thickness direction (ND direction) of the steel sheet. More specifically, it can be measured based on a cross-section (TD plane) cut in the direction perpendicular to rolling (TD direction). Unrecrystallization can be identified as grains that are elongated in the rolling direction. If the area occupied by unrecrystallization is too small, the effect of improving iron loss during the stress relief annealing process may not be sufficient. More specifically, the area occupied by unrecrystallization within the steel sheet may be 4% or more. More specifically, it may be 5% to 85%.

[0124] 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.

[0125] In addition, after annealing the cold-rolled sheet, the annealed cold-rolled sheet can be punched and laminated. Subsequently, stress relief annealing is performed to remove the stress imparted to the sheet due to punching.

[0126] The stress relief annealing step can be performed at a temperature of 700°C to 850°C for a time of 10 minutes to 300 minutes. If the temperature is too low or the time is too short during stress relief annealing, grain growth is insufficient and an appropriate improvement in iron loss cannot be obtained. If the temperature is too high or the time is too long during stress relief annealing, grain growth may be excessive and magnetic flux density may be inferior.

[0127] In one embodiment of the present invention, stress relief annealing can be performed by applying a magnetic field of 0.5 to 2.0 T. When stress relief annealing is performed by applying such a magnetic field, due to the crystal magnetic anisotropy energy, {411} <148> It becomes possible to selectively grow grains having an angle of 15° or less from. As a result, {411} <148> The area fraction of crystal grains having an angle of 15° or less from increases, iron loss is improved, and magnetic flux density degradation can be suppressed.

[0128] When a magnetic field is applied, the temperature is 500 to 810°C, and the magnetic field application time may be 20 minutes or more. If these conditions are properly controlled, {411} <148> It can assist in the growth of crystal grains having an angle of 15° or less from. More specifically, the temperature when the magnetic field is applied is 650 to 810°, and the magnetic field application time may be 25 minutes to 90 minutes.

[0129] The product of the temperature (°C) and the magnetic field application time (minutes) when a magnetic field is applied during the stress relief annealing step may be 25 × 1000 to 70 × 1000. Specifically, the product of the temperature (°C) and the magnetic field application time (minutes) when a magnetic field is applied during the stress relief annealing step may be 26 × 1000 to 65 × 1000.

[0130]

[0131] 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.

[0132]

[0133] Example 1

[0134] A slab was prepared with a composition including the remainder of Fe and unavoidable impurities as shown in Table 1. The C, S, N, and Ti content of the slab were all controlled to 0.0025 wt%. This was heated to 1150°C and hot-rolled at a finishing temperature of 850°C to produce a hot-rolled plate with a thickness of 2.0 mm.

[0135] Subsequently, the hot-rolled sheet was annealed at 1,100°C for 4 minutes and then pickled. Afterward, it was cold-rolled to a thickness of 0.25 mm. Subsequently, the cold-rolled sheet was annealed for 90 seconds. The temperature during cold-rolled sheet annealing and the fraction of unrecrystallized sheets after annealing are summarized in Table 1 below.

[0136] After that, stress relief annealing was performed by applying a magnetic field for the temperatures and times listed in Table 1 below, and then maintaining the temperature at 825℃ for 1 hour.

[0137] The area fraction and average grain size of the steel sheets after stress-relief annealing were measured using SEM-EBSD. Iron loss and magnetic flux density were measured using a single sheet tester as the average of the rolling direction and the rolling perpendicular direction.

[0138] Classification SiMnAl Cold Rolled Sheet Annealing Temperature (°C) Unrecrystallized Area Fraction (%) SRA Total Recrystallized Grain Average Grain Size (㎛) Magnetic Field Strength (T) Magnetic Field Application Time (min) Magnetic Field Application Average Temperature (°C) Time × Temperature / 1000 13.5 1.2 0.7 780 618 1.13 5750 262 4.2 0.3 0.38 00 719 1.53 5750 263 4.5 0.5 0.48 106 22 1.46 720 43 43.8 1.1 1.17 30 819 1.23 78 003053.20.71.26508351.2607504562.81.71.57106680.7758006073.90.40.475032121.5358002882.51.51.48207191.8458103693.70.70.776022111 .54075030104.80.20.580010170.76572047113.30.91.39102320.53876029123.11.41.28503270.74570032133.80.70.36208830.25572040143.10.80 .97906231.42077015153.70.50.476034131.65045023162.91.71.57708161.33582029172.51.31.77907171.72575019182.71.91.57807151.83568024

[0139] Category{411} <148> (Area %){411} <148> Average particle size (㎛){411} <148> Excluded average particle size (㎛) Magnetic flux density before SRA (B50, T) Magnetic flux density after SRA (B50, T) Iron loss before SRA W10 / 400 (W / kg) Iron loss after SRA W10 / 400 (W / kg) Remarks 1 278565 1.66 1.672 2.11 0.7 Invention Example 2 269172 1.65 1.662 3.59.7 Invention Example 3 259565 1.65 1.662 5.49.4 Invention Example 4 3 28972 1.67 1.672 8.91 0.3 Invention Example 5 3 18864 1.67 1.68 42.51 1.6 Invention Example 6 299569 1.66 1.663 2.41 0.8 Invention Example 7 299175 1.66 1.673 5.21 1.4 Invention Example 8 288774 1.67 1.672 3.71 1.2 Invention Example 9 26867 1.66 1.663 2.59.7 Invention Example 10 3288691.651.6634.210.4 Invention Example 111883691.671.6816.612.4 Comparative Example 121795671.681.6918.012.1 Comparative Example 132265671.641.6146.712.8 Comparative Example 142175751.631.5921.312.5 Comparative Example 151877791.641.6138.912.6 Comparative Example 161671761.631.5925.712.1 Comparative Example 172076771.641.6029.411.8 Comparative Example 182171721.641.5927.412.3 Comparative Example

[0140] As shown in Tables 1 and 2, the inventive example in which the magnetic field strength is appropriately controlled during stress relief annealing is {411} <148> It can be confirmed that the texture grows selectively and the magnetic flux density does not significantly deteriorate after stress relief annealing. On the other hand, in the comparative example where the magnetic field strength was not properly controlled during stress relief annealing, it can be confirmed that the magnetic flux density significantly deteriorates after stress relief annealing.

[0141] In addition, among the invention examples, if the annealing temperature of the cold-rolled plate is not properly controlled, it can be confirmed that the iron loss after stress relief annealing is somewhat inferior.

[0142] In addition, among the examples of the invention, if the magnetic field application time, pulse width, frequency, etc. are not properly adjusted, it can be confirmed that the magnetic flux density is partially lowered after stress relief annealing.

[0143]

[0144] 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 2.0%, Mn: 0.1 to 2.0%, and the remainder being Fe and unavoidable impurities, and {411} <148> Non-oriented electrical steel sheet having an area fraction of grains having an angle of 15° or less from 25% or more.

2. In Paragraph 1, {411} <148> Non-oriented electrical steel sheet having an average grain size of 80 to 100 μm with an angle of 15° or less from.

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