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 contains, in wt%, 1.0-5.5% of Si, 0.05-3.5% of Al, and 0.05-3.5% of Mn, with the remainder comprising Fe and inevitable impurities, wherein an AlN nitride layer having a thickness of 5-100 nm is present inside the steel sheet in the thickness direction from the surface of the steel sheet.

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 with improved magnetism by forming a concentrated nitride layer on the surface through two pickling steps after hot rolling, and a method for manufacturing the same.

[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 by iron loss. In particular, for ultra-thin non-oriented electrical steel sheets of 0.10 mm or less, magnetic properties in a higher frequency range are important, so the characteristics can be evaluated using W5 / 2000 iron loss measured at a low field of 0.5 T and a high frequency of 2000 Hz.

[0005] 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 with improved magnetism by forming a concentrated nitride layer on the surface through two pickling steps after hot rolling, and a method for manufacturing the same.

[0006] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percent, Si: 1.0 to 5.5%, Al: 0.05 to 3.5%, Mn: 0.05 to 3.5%, the remainder being Fe and unavoidable impurities, and there is an AlN nitride layer with a thickness of 5 to 100 nm inside the steel sheet in the thickness direction from the surface of the steel sheet.

[0007] The nitride layer may contain 8 to 30 weight% of Al, 0.05 to 5 weight% of N, and 10 to 65 weight% of O.

[0008] The density of AlN nitride particles with a particle size of 30 nm or larger in the thickness direction from the steel plate surface is 0.04 particles / ㎛ 2 Up to 4 pieces / ㎛ 2 It could be.

[0009] AlN nitride may have more than 50% nitride connected to the AlN nitride layer.

[0010] The AlN nitride may have 50% or more of the nitride connected to the above AlN nitride layer.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015]

[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 comprising, in weight%, Si: 1.0 to 5.5%, Al: 0.05 to 3.5%, Mn: 0.05 to 3.5%, and the remainder being Fe and unavoidable impurities; a pickling step of performing pickling on the hot-rolled steel sheet at least twice; 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 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] After the step of manufacturing hot-rolled steel sheets, a step of annealing the hot-rolled steel sheets may be further included.

[0022] The pickling step may include a first pickling step, a cooling step, and a second pickling step.

[0023] In the first pickling step and the second pickling step, the temperature of the steel plate is 50 to 100°C, respectively, and in the cooling step, the temperature of the steel plate may be 40°C or lower.

[0024] In the first and second pickling steps, pickling can be performed for 50 to 250 seconds at an acid concentration of 2 to 25 weight%, respectively.

[0025] The cold-rolled sheet annealing step is performed in a mixed atmosphere of H2 and N2 containing 5 to 25 volume% of H2, and the dew point of the atmosphere may be -20℃ or lower.

[0026] The cold-rolled sheet annealing step can be performed at a cracking temperature of 900°C or higher and maintained at the cracking temperature for 10 to 120 seconds.

[0027] A non-oriented electrical steel sheet according to one embodiment of the present invention has an AlN nitride layer concentrated in the surface layer appropriately formed therein, which hinders the penetration of nitrogen from the outside, thereby hindering the formation of AlN inside the steel sheet and preventing a decrease in magnetism caused by AlN, and has excellent magnetism.

[0028] Accordingly, a non-oriented electrical steel sheet according to one embodiment of the present invention can be usefully used as an automobile motor.

[0029] FIG. 1 is a schematic diagram showing a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0034] 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.

[0035] 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.

[0036] 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.

[0037]

[0038] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.0 to 5.5%, Al: 0.05 to 3.5%, Mn: 0.05 to 3.5%, and the remainder being Fe and unavoidable impurities.

[0039] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0040]

[0041] Si: 1.0 to 5.5 wt%

[0042] 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 brittleness of the material increases, causing a sharp decrease in rolling productivity and potentially forming a surface oxide layer and oxides that are harmful to magnetism. More specifically, it may contain 1.5 to 5.0 weight% of Si. More specifically, it may contain 2.0 to 4.5 weight%. More specifically, it may contain 2.5 to 4.0 weight%.

[0043]

[0044] Al: 0.05 to 3.5 wt%

[0045] Aluminum (Al) plays a role in increasing the resistivity of the material to lower iron loss and improve rollability, as well as enhancing 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. More specifically, it may contain 0.1 to 3.0 weight% of Al. More specifically, it may contain 0.15 to 2.0 weight%. More specifically, it may contain 0.2 to 1.5 weight%.

[0046]

[0047] Mn: 0.05 to 3.5 wt%

[0048] 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, promoting the formation of a {111} texture that is unfavorable to magnetism, which causes a rapid decrease in magnetic flux density. More specifically, it may contain 0.1 to 3.0 weight% of Mn. More specifically, it may contain 0.15 to 2.0 weight%. More specifically, it may contain 0.2 to 1.5 weight%.

[0049]

[0050] 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%).

[0051] P: 0.1 wt% or less

[0052] 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.

[0053] C: 0.005 wt% or less

[0054] 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 0.0035 weight% of C.

[0055] S: 0.005 wt% or less

[0056] 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 0.0050 weight% of S. More specifically, it may contain 0.0005 to 0.0045 weight% of S.

[0057] Ti: 0.005 wt% or less

[0058] 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 0.0050 weight% of Ti. More specifically, it may contain 0.0005 to 0.0030 weight% of Ti.

[0059] N: 0.005 wt% or less

[0060] 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 0.0030 weight% of N.

[0061]

[0062] 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.

[0063] Sn

[0064] 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.

[0065] Sb

[0066] 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.

[0067] Bi, Pb, Ge, and As

[0068] 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.

[0069]

[0070] 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%).

[0071] Cu: 0.005 to 0.200 wt%

[0072] 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.

[0073] Cr: 0.01 to 0.50 wt%

[0074] 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.

[0075] Ni: 0.05 wt% or less

[0076] 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.

[0077] Zn: 0.01 wt% or less

[0078] 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%.

[0079] Co: 0.05 wt% or less

[0080] 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.

[0081]

[0082] 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%).

[0083] Mo: 0.030 wt% or less

[0084] 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%.

[0085] B: 0.0050 wt% or less

[0086] 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%.

[0087] V: 0.0050 wt% or less

[0088] 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%.

[0089] Ca: 0.0050 wt% or less

[0090] 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.

[0091] Nb: 0.0050 wt% or less

[0092] 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.

[0093] Zr: 0.0050 wt% or less

[0094] 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%.

[0095] Te: 0.0100 wt% or less

[0096] 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.

[0097] Mg: 0.0050 wt% or less

[0098] 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%.

[0099]

[0100] 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.

[0101]

[0102] As described above, in one embodiment of the present invention, a concentrated nitride layer is formed on the surface to hinder the penetration of nitrogen from the outside, thereby hindering the formation of AlN inside the steel plate and preventing a decrease in magnetism caused by AlN, and the magnetism is excellent.

[0103] FIG. 1 schematically shows a cross-section of a non-oriented electrical steel sheet (100) according to one embodiment of the present invention. As shown in FIG. 1, the non-oriented electrical steel sheet (100) according to one embodiment of the present invention has an AlN nitride layer (10) with a thickness of 5 to 100 nm inside the steel sheet in the thickness direction from the surface of the steel sheet. By properly forming the AlN nitride layer (10) to hinder the penetration of nitrogen from the outside, the formation of AlN inside the steel sheet is hindered, and the deterioration of magnetism caused by AlN can be prevented. If the thickness of the AlN nitride layer (10) is too thin, it is difficult to sufficiently perform the role of the aforementioned AlN nitride layer (20). If the thickness of the AlN nitride layer (10) is too thick, the AlN nitride layer (20) itself will deteriorate magnetism. More specifically, the thickness of the AlN nitride layer (10) may be 10 to 50 nm. More specifically, the thickness of the AlN nitride layer (10) can be 15 to 45 nm.

[0104] The nitrided layer can be determined as a portion of the steel plate surface where the N content is 0.005 weight% or more. The N content by thickness can be quantitatively measured by processing the cross-section of the steel plate with FIB and using TEM EDS. If an insulating film is present on the surface of the non-oriented electrical steel plate, the insulating film can be removed and the thickness of the AlN nitrided layer (20) can be measured. The thickness of the nitrided layer can be measured at 20 or more different locations and the average can be obtained.

[0105] The AlN nitride layer (10) may contain 8 to 30 weight% of Al, 0.05 to 5 weight% of N, and 10 to 65 weight% of O. If too little Al is contained in the AlN nitride layer (10), the oxide layer cannot be formed densely, so nitrogen in the surface layer diffuses deeply into the base material, and a large amount of AlN nitride is formed, which may cause a problem of deterioration of magnetic properties. If too much Al is contained in the AlN nitride layer (10), cracks are easily formed in the AlN nitride layer (10) formed in the surface layer, so a problem of deterioration of magnetic properties may occur due to the formation of a large amount of nitride caused by nitrogen diffusion inside the base material.

[0106] If too little N is contained in the AlN nitride layer (10), excessive oxidation relative to nitriding may occur, and magnetic degradation problems may occur due to the formation of oxides inside the base material. If too much N is contained in the AlN nitride layer (10), excessive nitriding relative to oxidation may occur, causing the layer thickness to become excessively thick or magnetic degradation problems may occur due to the excessive formation of nitride inside the base material.

[0107] If too little O is contained in the AlN nitride layer (10), excessive nitriding occurs relative to oxidation, causing the layer thickness to become excessively thick or magnetic degradation problems may occur due to excessive formation of nitride inside the base material. If too much O is contained in the AlN nitride layer (10), excessive oxidation occurs relative to nitriding, causing magnetic degradation problems due to oxide formation inside the base material.

[0108] More specifically, the AlN nitride layer (10) may contain 10 to 27 weight% of Al, 1.00 to 4.50 weight% of N, and 20 to 55 weight% of O. The remaining components may be the same as the components of the steel plate described above.

[0109] In one embodiment of the present invention, the density of AlN nitride (20) having a particle size of 30 nm or more in the thickness direction from the surface of the steel plate is 0.04 particles / ㎛ 2Up to 4.00 pieces / ㎛ 2 It can be distinguished as containing more than 6 weight percent of N, unlike the AlN nitride layer (10). AlN nitride (20) can be measured by observing a cross-section including the thickness direction of the steel plate. More specifically, it can be observed as a cross-section perpendicular to the TD direction. The cross-section can be precisely processed with FIB and observed using the EDS technique through a transmission electron microscope (TEM). Since AlN nitride (20) with a particle size of less than 30 nm does not significantly affect magnetism, the density of AlN nitride (20) with a particle size of 30 nm or more can be calculated. The particle size of AlN nitride (20) can be measured as the diameter of a virtual circle assumed to have the same area as the area occupied by the nitride. If there is too little AlN nitride (20), the oxide may be over-formed or the oxide may be over-formed deep inside the base material, causing the magnetism to deteriorate. If there is too much AlN nitride (20), it may hinder the movement of magnetic domains and degrade magnetism. More specifically, the density of AlN nitride (20) is 0.50 to 3.50 pieces / ㎛ 2 It could be.

[0110] The AlN nitride (20) may have 50% or more of the nitride connected to the AlN nitride layer (10). Being connected means that the location of the AlN nitride layer (10) overlaps with the location of the AlN nitride (20) at least partially. It is also considered connected if the AlN nitride (20) is entirely contained within the AlN nitride layer (10). When the AlN nitride (20) is connected to the AlN nitride layer (10), the effect on magnetism is reduced.

[0111] This ratio refers to the number ratio. The AlN nitride (20) may have 97% or more of the nitride connected to the AlN nitride layer (10). The nitride at this time can also be calculated based on AlN nitride (20) with a particle size of 30 nm or more.

[0112] In one embodiment of the present invention, the iron loss (W) of a non-oriented electrical steel sheet 5 / 2000 ) may be 24.6 W / Kg or less. Iron loss (W 5 / 2000 ) is the iron loss when a magnetic flux density of 0.5T is induced at a frequency of 2000 Hz. More specifically, the iron loss (W of non-oriented electrical steel) 5 / 2000 ) may be 18.0 to 22.0 W / kg. In one embodiment of the present invention, iron loss may be expressed based on a thickness of 0.10 mm.

[0113] The magnetic flux density (B50) of the non-oriented electrical steel sheet may be 1.62T or higher. More specifically, it may be 1.63 to 1.65T.

[0114] Iron loss and magnetic flux density can be measured by cutting five specimens of 60 mm in width × 60 mm in length × number of sheets from the specimen and measuring the rolling direction and the rolling perpendicular direction with a single sheet tester, and then calculating the average.

[0115] 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; a pickling step of performing pickling on the hot-rolled steel sheet at least twice; 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.

[0116]

[0117] Below, each step is explained in detail.

[0118] First, the slab is hot-rolled.

[0119] 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.

[0120] Specifically, the slab contains Si: 1.0 to 5.5%, Al: 0.05 to 3.5%, Mn: 0.05 to 3.5% by weight, and the remainder is Fe and unavoidable impurities.

[0121] As other additional elements have been explained in the alloy composition of non-oriented electrical steel sheets, redundant explanations are omitted.

[0122] 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.

[0123] 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 870 to 950°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 1.4 to 3.0 mm.

[0124] 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 1150°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 1100°C. The cracking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0125] Next, the hot-rolled steel plate is pickled two or more times. By performing pickling two or more times, the AlN nitride layer (10) is concentrated and formed thinly on the surface, thereby improving the magnetic properties.

[0126] The pickling step may include a first pickling step, a cooling step, and a second pickling step.

[0127] In the first pickling step and the second pickling step, the temperature of the steel plate may be 50 to 100°C, respectively, and in the cooling step, the temperature of the steel plate may be 40°C or lower. In the pickling step, the temperature must be within an appropriate range so that sufficient pickling can be achieved. In the cooling step after pickling, areas of the oxide layer that are not dense can be effectively removed through thermal shrinkage of the surface. More specifically, in the first pickling step and the second pickling step, the temperature of the steel plate may be 60 to 90°C, respectively, and in the cooling step, the temperature of the steel plate may be 15 to 35°C.

[0128] In the first and second pickling steps, pickling can be performed for 50 to 250 seconds at an acid concentration of 2 to 25 weight%, respectively. If the pickling concentration is too low or the pickling time is too short, it is difficult to achieve sufficient pickling. If the pickling concentration is too high or the pickling time is too long, surface defects and cold-rolled plate breakage due to intergranular over-corrosion may occur. More specifically, pickling can be performed for 60 to 240 seconds at an acid concentration of 3 to 20 weight%.

[0129] Next, a hot-rolled steel sheet is cold-rolled to produce a cold-rolled sheet. In the step of producing the cold-rolled sheet, the total reduction rate may be 75 to 90%. The total reduction rate can be calculated from the thickness of the steel sheet before cold rolling and the thickness after cold rolling. If the reduction rate is too low, additional rolling is required to obtain an appropriate final thickness, and productivity may be inferior. If the reduction rate is too high, a texture unfavorable to magnetism is formed, and iron loss may be inferior. More specifically, in the step of producing the cold-rolled sheet, the total reduction rate may be 77 to 88%.

[0130] After cold rolling, the thickness may be 0.10 to 0.35 mm. If the thickness is too thin, problems may arise in terms of the strength of the steel sheet, and if the thickness is too thick, it may have an adverse effect on ultra-high frequency iron loss. More specifically, the thickness may be 0.15 to 0.30 mm.

[0131] In one embodiment of the present invention, cold rolling may be performed once without intermediate annealing, or may include two or more cold rollings including intermediate annealing.

[0132] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. The cold-rolled sheet annealing step is performed in a mixed atmosphere of H2 and N2 containing 5 to 25 volume% of H2, and the dew point of the atmosphere may be -20°C or lower. By annealing in a suitable atmosphere, an AlN nitride layer (10) can be properly formed on the surface of the steel sheet.

[0133]

[0134] During the cracking stage, the cracking temperature may be 900°C. If the cracking temperature is too low, the crystal grains may not grow sufficiently, leading to increased hysteresis loss and a problem of deterioration in iron loss. More specifically, annealing may be performed at a temperature of 930 to 1030°C. Cracking may be performed for 10 to 120 seconds.

[0135] 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.

[0136] 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.

[0137]

[0138] 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.

[0139]

[0140] Example 1

[0141] A slab was prepared with the composition of Table 1, including the remainder Fe and unavoidable impurities. It was heated to 1150°C and hot-rolled at a finishing temperature of 950°C to produce a hot-rolled sheet with a thickness of 2.0 mm. The hot-rolled sheet was annealed at 1100°C for 4 minutes and then pickled. Subsequently, it was pickled twice under the conditions summarized in Table 1 below. At this time, the concentration of the pickling solution was 10% HCl, and the pickling time was 100 seconds for each. It was cold-rolled to produce a thickness of 0.10 mm. Then, a non-oriented electrical steel sheet was produced by cracking for 90 seconds under the conditions of the temperature, H210 volume%, N290 volume%, and dew point of -40°C summarized in Table 1 below.

[0142] To analyze the AlN nitride layer of the manufactured non-oriented electrical steel sheet, the cross-section of each specimen in the rolling direction (TD) was processed into FIB and observed with a transmission electron microscope (TEM) at a magnification of 100,000 to determine the thickness as the average value of measurements taken at 20 or more points, and the compositional content was analyzed through EDS analysis at 20 or more points, and the results are shown in Table 2.

[0143] AlN nitride is 300㎛ at x100,000 magnification up to 3㎛ into the surface with respect to the plane perpendicular to the TD direction. 2 The above area was observed using a transmission electron microscope (TEM), and its density was summarized in Table 2 below.

[0144] Magnetic properties such as magnetic flux density and iron loss were determined by cutting five specimens of 60 mm in width × 60 mm in length for each sample, measuring the rolling direction and the rolling perpendicular direction using a single sheet tester, and expressing the result as the average. At this time, W5 / 2000 is the iron loss when a magnetic flux density of 0.5T is induced at a frequency of 2000Hz, and B50 means the magnetic flux density induced in a magnetic field of 5000A / m.

[0145] Classification SiAlMn 1st Pickling Temperature Cooling Temperature 2nd Pickling Temperature Cold Rolled Sheet Annealing Cracking Temperature (°C) Cold Rolled Sheet Annealing Dew Point Temperature (°C) 13.35 1.40 0.50 60 209 0960 -40 23.35 1.40 0.50 70 208 0960 -40 33.35 1.40 0.50 80 207 0960 -40 43.35 1.40 0.50 90 206 0960 -40 53.65 1.00 0.80 60 3060 1010 -30 63.65 1.00 0.80 70 3070 1 010-3073.651.000.808030801010-3083.651.000.809030901010-3093.950.601.107530751010-35103.950.601.107530751010-35111.303.150.907530751010-35125.250.350.20 7530751010-35134.150.050.657530751010-35142.203.350.257530751010-35153.651.400.057530751010-35162.200.253.257530751010-35173.651.000.804030751010-35183 .651.000.8011030751010-35193.651.000.807550751010-35203.651.000.807560751010-35213.651.000.807530401010-35223.651.000.8075301101010-35233.351.400.50751 Sanse1010-35243.651.000.80751 time Sanse1010-35253.651.000.80753075850-35263.651.000.80753075880-35273.651.000.807530751010-10283.651.000.807530751010-15

[0146] Classification AlN Nitride Layer Thickness Al (Wt%) in Nitride Layer N (Wt%) in Nitride Layer O (Wt%) in Nitride Layer AlN Nitride Density W 5 / 2000 (W / kg) B 50 (T) 1 20 1 4 2.00 4 2 2.10 20.11 63 Invention Example 2 20 1 0 3.00 3 8 2.70 20.71 63 Invention Example 3 30 1 6 2.00 5 11.60 20.61 63 Invention Example 4 20 1 3 4.00 4 4 3.20 20.81 63 Invention Example 5 30 2 1 3.00 4 7 2.50 20.31 63 Invention Example 6 20 1 5 3.00 5 4 0.90 20.11 63 Invention Example 7 20 1 7 2.00 3 7 1.60 20.61 63 Invention Example 8 20 2 44.00423.1020.91.63 Invention Example 920214.00532.9021.01.63 Invention Example 1030263.00511.4021.11.63 Invention Example 1130193.00482.4024.11.61 Invention Example 1220134.00472.7023.51.60 Invention Example 13552.00390.0224.31.61 Invention Example 1470352.00445.1023.21.60 Invention Example 152014 4.00482.9023.81.61 Invention Example 16 20152.00422.2023.31.60 Invention Example 17 80182.00454.7023.61.61 Invention Example 18 5157.00415.6024.31.61 Invention Example 19 70252.00426.2024.61.61 Invention Example 20 70276.00476.1023.71.61 Invention Example 21 80252.00524.4023.51.61 Invention Example 22 51 46.00486.2024.11.61 Invention Example 23130152.00718.4024.81.60 Comparative Example 24110232.006610.3025.11.60 Comparative Example 2530260.02566.3024.21.61 Invention Example 2630170.01527.2024.51.61 Invention Example 2780240.01497.1023.91.61 Invention Example 2870250.02526.9024.31.61 Invention Example

[0147] As shown in Tables 1 and 2, when the steel composition is properly controlled and the pickling conditions and cold-rolled sheet cracking conditions are properly controlled, an AlN nitride layer is properly formed on the surface and the formation of internal AlN nitrides is suppressed, and it can be confirmed that the magnetism is excellent.

[0148] On the other hand, if the steel composition is not properly controlled, or if the pickling and cold-rolled sheet annealing conditions are not properly controlled, the AlN nitride layer is not properly formed, and it can be confirmed that the magnetic properties are inferior.

[0149] In addition, among the examples of the invention, when the steel composition is more appropriately controlled and the first pickling temperature, cooling temperature, second pickling temperature, cracking temperature, and dew point temperature are satisfied, it can be confirmed that the nitride layer and nitride properties are more appropriately controlled and the magnetism is even better.

[0150]

[0151] 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.

[0152] [Explanation of the symbol]

[0153] 100: Non-oriented electrical steel sheet 10: AlN nitride layer

[0154] 20: AlN nitride

Claims

1. In weight%, it comprises Si: 1.0 to 5.5%, Al: 0.05 to 3.5%, Mn: 0.05 to 3.5%, and the remainder being Fe and unavoidable impurities, and A non-oriented electrical steel sheet having an AlN nitride layer with a thickness of 5 to 100 nm within the steel sheet in the thickness direction from the surface of the steel sheet.

2. In Paragraph 1, The above AlN nitride layer is a non-oriented electrical steel sheet comprising 8 to 30 weight% Al, 0.05 to 5 weight% N and 10 to 65 weight% O.

3. In Paragraph 1, The density of AlN nitride particles with a particle size of 30 nm or more in the thickness direction from the surface of the steel plate is 0.04 particles / ㎛ 2 Up to 4 pieces / ㎛ 2 Non-oriented electrical steel sheet.

4. In Paragraph 3, The above AlN nitride is a non-oriented electrical steel sheet in which the nitride connected to the above AlN nitride layer is 50% or more.

5. 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.

6. 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.

7. 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.

8. 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.

9. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing, by weight%, Si: 1.0 to 5.5%, Al: 0.05 to 3.5%, Mn: 0.05 to 3.5%, and the remainder being Fe and unavoidable impurities; A pickling step of performing pickling on the hot-rolled steel plate at least twice; A step of manufacturing a cold-rolled plate by cold-rolling the above hot-rolled steel plate and A method for manufacturing a non-oriented electrical steel sheet comprising a cold-rolled sheet annealing step for annealing the above cold-rolled sheet.

10. In Paragraph 9, 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: 0.005 wt% or less, S: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

11. In Paragraph 9, 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.

12. In Paragraph 9, 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.

13. In Paragraph 9, 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.

14. In Paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, comprising, after the step of manufacturing the hot-rolled steel sheet, an additional step of annealing the hot-rolled steel sheet.

15. In Paragraph 9, The above pickling step is a method for manufacturing a non-oriented electrical steel sheet comprising a first pickling step, a cooling step, and a second pickling step.

16. In Paragraph 15, A method for manufacturing a non-oriented electrical steel sheet, wherein the temperature of the steel sheet in the first pickling step and the second pickling step is 50 to 100°C, respectively, and the temperature of the steel sheet in the cooling step is 40°C or lower.

17. In Paragraph 15, A method for manufacturing a non-oriented electrical steel sheet by pickling at an acid concentration of 2 to 25 weight% for 50 to 250 seconds in each of the first and second pickling steps.

18. In Paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above cold-rolled sheet annealing step is performed in an atmosphere of mixed H2 and N2 containing 5 to 25 volume% of H2, and the dew point of the atmosphere is -20℃ or lower.

19. In Paragraph 9, The above cold-rolled sheet annealing step is a method for manufacturing a non-oriented electrical steel sheet in which the cracking temperature is 900°C or higher and maintained at the cracking temperature for 10 to 120 seconds.

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