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, 0.1-3.5% of Al, and 0.01-3.5% of Mn, with the remainder comprising Fe and inevitable impurities, and contains 1.0-8.5 % of Si, 0.05-6.5% of Al, 0.05-4.5% of Mn, and 0.5-10.0% of O in a surface layer within 2 µm of the surface of the steel sheet in the thickness direction.

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 appropriately controlling the steel composition of the steel sheet surface through direct heating during the cold-rolled sheet annealing process, 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 based on iron loss.

[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 appropriately controlling the steel composition of the steel sheet surface through direct heating during the cold-rolled sheet annealing process, 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%, Si: 1.0 to 5.5%, Al: 0.1 to 3.5%, Mn: 0.01 to 3.5%, and the remainder being Fe and unavoidable impurities, and in weight%, in a surface layer within 2 μm in the thickness direction from the surface of the steel sheet, Si: 1.0 to 8.5%, Al: 0.05 to 6.5%, Mn: 0.05 to 4.5%, and O: 0.5 to 10.0%.

[0007] The difference between the Si content on the surface of the steel plate and the Si content within 2㎛ in the thickness direction from the surface of the steel plate may be 20% or less.

[0008] The density of AlN is 0.001 to 0.1 particles / ㎛ in the thickness direction from the surface of the steel plate in the range of 2㎛ to 3㎛. 2 It could be.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] 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.

[0013]

[0014] 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: 0.1 to 3.5%, Mn: 0.01 to 3.5%, 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.

[0015] The cold-rolled sheet annealing stage includes a heating stage and a cracking stage.

[0016] In the heating step, the fraction of carbon monoxide (CO) in the atmosphere may be 100 to 1000 ppm.

[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] In the heating step, the heating rate can be 20 to 60°C / second.

[0022] In the heating step, the dew point temperature can be 30 to 70°C.

[0023] During the cracking stage, the dew point temperature can be -30℃ or lower.

[0024] In the cracking stage, the cracking temperature can be 750 to 1050℃.

[0025] A non-oriented electrical steel sheet according to one embodiment of the present invention has an alloy composition in the surface layer appropriately controlled to prevent 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.

[0026] Accordingly, a non-oriented electrical steel sheet according to one embodiment of the present invention can be usefully used as an automobile motor.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0032] 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.

[0033] 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.

[0034] 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.

[0035]

[0036] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.0 to 5.5%, Al: 0.1 to 3.5%, Mn: 0.01 to 3.5%, and the remainder being Fe and unavoidable impurities.

[0037] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0038]

[0039] Si: 1.0 to 5.5 wt%

[0040] 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%.

[0041]

[0042] Al: 0.1 to 3.5 wt%

[0043] 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 0.2 to 3.2 weight% of Al. More specifically, it may contain 0.3 to 2.0 weight%. More specifically, it may contain 0.5 to 1.5 weight%.

[0044]

[0045] Mn: 0.01 to 3.50 wt%

[0046] 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 0.10 to 3.0 weight% of Mn. More specifically, it may contain 0.20 to 2.00 weight%. More specifically, it may contain 0.30 to 1.50 weight%.

[0047]

[0048] 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%).

[0049] P: 0.1 wt% or less

[0050] 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.

[0051] C: 0.005 wt% or less

[0052] 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.

[0053] S: 0.005 wt% or less

[0054] 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.

[0055] Ti: 0.005 wt% or less

[0056] 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.

[0057] N: 0.005 wt% or less

[0058] 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.

[0059]

[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 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%.

[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 (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%).

[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, the alloy composition of the surface layer is appropriately controlled to prevent 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.

[0101] 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 includes a surface layer (20) with a thickness of 2 μm from the steel sheet surface in the thickness direction and a center layer (10) with a thickness of more than 2 μm from the steel sheet surface in the thickness direction.

[0102] In one embodiment of the present invention, the alloy composition of the surface layer (20) is controlled to suppress the formation of AlN in the central layer (10) and prevent magnetic degradation through AlN.

[0103] Specifically, the surface layer (20) contains, in weight percent, Si: 1.0 to 8.5%, Al: 0.05 to 6.5%, Mn: 0.05 to 4.5%, and O: 0.5 to 10.0%. If the amount of Si in the surface layer (20) is too small, the oxide layer is not dense, and nitrogen diffuses into the base material during annealing, forming a large amount of precipitates such as AlN, which may cause magnetic deterioration problems. If the amount of Si in the surface layer (20) is too large, a large amount of oxide is formed inside the base material, which may cause magnetic deterioration or increase surface brittleness, which may cause surface quality problems due to cracking or breakage. More specifically, the surface layer (20) may contain 4.0 to 6.0 weight percent of Si.

[0104] If the amount of Al in the surface layer (20) is too small, the oxide layer is not dense, and nitrogen diffuses into the base material during annealing, forming a large amount of precipitates such as AlN, which may cause magnetic deterioration problems. If the amount of Al in the surface layer (20) is too large, a large amount of oxide is formed inside the base material, which may cause magnetic deterioration problems. More specifically, the surface layer (20) may contain 1.50 to 3.50 weight% of Al.

[0105] If the amount of Mn in the surface layer (20) is too low, nitrogen diffusion into the base material during annealing becomes easier, or the base material becomes susceptible to corrosion after annealing, which may cause magnetic deterioration problems. If the amount of Mn in the surface layer (20) is too high, a large amount of oxide may be formed inside the base material, which may cause magnetic deterioration problems. More specifically, the surface layer (20) may contain 0.50 to 3.50 weight% of Mn.

[0106] If the amount of O in the surface layer (20) is too small, the oxide layer may not be sufficiently formed, and a problem of magnetic degradation may occur due to the formation of fine precipitates such as AlN by nitrogen diffusion. If the amount of O in the surface layer (20) is too large, additional oxide may be formed under the dense oxide layer, and a problem of magnetic degradation may occur. More specifically, the surface layer (20) may contain 4.0 to 9.0 weight percent of O.

[0107] The content of alloy components within the surface layer (20) may vary depending on the thickness direction. In this case, the content of alloy components can be obtained as an average over the thickness direction. In one embodiment of the present invention, the alloy components within the surface layer (20) can be measured using GDS, etc. To reduce deviations depending on the measurement location, the content can be measured at at least five locations and obtained as an average. In the case where an insulating film is additionally present on a non-oriented electrical steel sheet, the change in the measured value of Al from the coating layer in the thickness center direction can be observed to determine the location where the Al content has a maximum value as the surface layer of the base material, and the alloy components within the surface layer (20) can be measured.

[0108] The difference between the Si content on the surface of the steel plate and the Si content within 2㎛ in the thickness direction from the surface of the steel plate may be 20% or less.

[0109] In one embodiment of the present invention, the surface layer (20) has a concentration gradient in which the Si concentration increases from the surface in the inward direction. The difference in Si content can be calculated as [(Si content inside 2㎛) - (Si content at the surface)] / (Si content inside 2㎛) × 100. At this time, the Si content is based on weight%. If the difference in Si content is too large, a localized Si depletion region is formed in the surface layer, which lowers the resistivity and increases eddy current loss, making it disadvantageous for magnetism. More specifically, the difference between the Si content on the surface of the steel plate and the Si content inside 2㎛ in the thickness direction from the surface of the steel plate may be 10 to 18%.

[0110] As previously described, by appropriately adjusting the alloy composition in the surface layer (20), the density of AlN can be reduced in the range of 2㎛ to 3㎛ in the thickness direction from the surface of the steel plate, thereby improving magnetism. Specifically, the density of AlN in the range of 2㎛ to 3㎛ in the thickness direction from the surface of the steel plate is 0.001 to 0.100 pieces / ㎛ 2 It is possible. At the given thickness, it is generally common for some AlN to be inevitably formed during the conventional process; however, excessively reducing AlN is undesirable because it inevitably incurs additional processes and costs, thereby worsening product productivity or manufacturing costs. If there is too much AlN, it can hinder domain wall movement during the magnetization process, potentially degrading magnetic properties. More specifically, within the range of 2㎛ to 3㎛ in the thickness direction from the steel sheet surface, the AlN density is 0.010 to 0.060 particles / ㎛ 2 It could be.

[0111] AlN can be measured using an electron microscope or the like for a cross-section including the thickness direction of the steel plate, specifically at a magnification of 10,000x or higher based on a plane perpendicular to the rolling direction (TD direction). Due to measurement limitations, AlN with a particle size of 10 nm or more may be included in the density calculation. In this case, the particle size is determined by assuming a circle with an area equal to the area occupied by AlN and calculating the diameter of that circle.

[0112] In one embodiment of the present invention, the iron loss (W) of a non-oriented electrical steel sheet 5 / 2000 ) may be 24.0W / 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 20.0 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] In one embodiment of the present invention, the magnetic flux density (B50) of the non-oriented electrical steel sheet may be 1.61T or higher. The magnetic flux density (B50) is the magnetic flux density induced when induced at 5,000 A / m. More specifically, the magnetic flux density (B50) may be 1.62 to 1.65T.

[0114]

[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 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: 1.5 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.

[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, 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%.

[0126] 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.

[0127] 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.

[0128] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. In one embodiment of the present invention, the cold-rolled sheet annealing step includes a heating step and a cracking step.

[0129] In the heating stage, the fraction of carbon monoxide (CO) in the atmosphere may be 100 to 1000 ppm. In one embodiment of the present invention, the steel composition of the steel plate surface layer (20) can be appropriately controlled by heating the steel plate with a direct flame during the heating stage. Through direct flame heating, carbon monoxide is present in the atmosphere. If too little carbon monoxide is present, it means that electric or radiant heating was used instead of direct flame heating, or that even if direct flame heating was used, combustion was not achieved with an appropriate air-fuel ratio, making it difficult to obtain an appropriate steel composition in the surface layer (20), and ultimately, the magnetic properties deteriorate. If too much carbon monoxide is present, it becomes problematic because it can form a non-density oxide layer on the steel surface layer, which deteriorates the magnetic properties or reduces the adhesion of the insulating film. More specifically, in the heating stage, the fraction of carbon monoxide in the atmosphere may be 200 to 750 ppm. The heating stage refers to the range from room temperature to 600°C.

[0130] In the heating step, the heating rate may be 20 to 60°C / second. Since heating is performed via direct flame in the heating step, the aforementioned heating rate can be achieved. If the heating rate is too low, it is difficult to obtain a suitable steel composition in the surface layer (20), and ultimately, the magnetism deteriorates. If the heating rate is too fast, a large difference in quality may occur depending on the area due to an uneven temperature gradient. More specifically, the heating rate may be 25 to 55°C / second.

[0131] In the heating step, the dew point temperature may be 30 to 70°C. If the dew point is too low in the heating step, it is difficult to obtain a suitable steel composition in the surface layer (20), and ultimately, the magnetism deteriorates. Conversely, if the dew point is too high, the O content in the surface layer (20) increases, which reduces the adhesion of the insulating film on the surface layer and may cause surface defects. More specifically, in the heating step, the dew point temperature may be 40 to 65°C.

[0132] The cracking stage is a heat treatment stage in which the steel plate is maintained at a constant temperature. In the cracking stage, the dew point temperature may be -30°C or lower. If the dew point temperature is too high in the cracking stage, an excessively loose oxide layer may form on the surface, leading to magnetic deterioration due to nitrogen diffusion and nitride formation within the base material. More specifically, the dew point temperature in the cracking stage may be -40 to -70°C.

[0133] During the cracking stage, the cracking temperature may be 750 to 1050°C. If the cracking temperature is too low, the grains may not grow sufficiently, leading to increased hysteresis loss and deterioration of iron loss. Conversely, if the cracking temperature is too high, the grains may overgrow or shape deformation of the steel sheet may occur, resulting in deterioration of magnetic properties. More specifically, annealing may be performed at a temperature of 950 to 1020°C. The cracking stage may be performed for 50 to 120 seconds.

[0134] 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.

[0135] 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.

[0136]

[0137] 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.

[0138]

[0139] Example 1

[0140] 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. Afterward, it was cold-rolled to produce a thickness of 0.10 mm. Subsequently, a non-oriented electrical steel sheet was produced by cracking for 90 seconds under the heating and cracking conditions summarized in Table 1 below.

[0141] The surface layer alloy composition of the manufactured non-oriented electrical steel sheet was analyzed by GDS, and the average result of the analysis of the same specimen five times is shown in Table 2.

[0142] AlN specimens were prepared using FIB on a vertical plane of TD, and then observed using a transmission electron microscope (TEM) at a magnification of 100,000x to determine their density, which is summarized in Table 2 below.

[0143] For magnetic properties such as magnetic flux density and iron loss, five specimens measuring 60 mm in width × 60 mm in length were cut for each sample, and the iron loss and magnetic flux density were measured using a single sheet tester; the average values ​​measured in the rolling direction and the direction perpendicular to rolling were indicated. 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.

[0144] Classification SiAlMn Heating Stage CO Concentration (ppm) Heating Stage Heating Rate (°C / sec) Heating Stage Dew Point Temperature (°C) Cracking Temperature (°C) Cracking Stage Dew Point Temperature (°C) 13.35 1.40.50 216 38 429 40-40 23.35 1.40.50 425 515 39 60-40 33.35 1.40.50 336 44 449 80-40 43.35 1.40.50 68 237 58 1000-40 53.6 51.00.80 42 34 247 9 40-70 63.6 51.00.80 71 44 94 1960-70 73.6 51.00.80 7 235159980-7083.651.00.8036526361000-7093.950.61.102983239980-50103.950.61.1043527621000-50111.303.20.906215254800-50125.250.40.2037844531000-50134.150.10.651575347900-401 42.203.40.2586228611000-40153.651.40.053523657950-40162.200.33.255174247950-40173.651.00.80444755950-45183.651.00.8013273438950-45193.651.00.801311362950-45203.651.00.80 4696949950-45213.651.00.808815224950-45223.651.00.803954277950-45233.651.00.806273937700-45243.651.00.8044335411100-45253.651.00.808624253950-15263.651.00.802374848950-10

[0145] Classification Surface Layer Alloy Composition (Wt%) SiAlMnO Surface -2㎛ Si Content Difference (%) 2-3㎛ AlN Density W 5 / 2000(W / kg) B 50(T) 14.1 2.9 0 0.7 0 6.8 1 30.0 25 20.6 1.63 Example 2 4.3 3.1 0 0.6 0 7.1 1 60.0 48 20.4 1.63 Example 3 4.0 3.2 0 0.8 5.4 1 20.0 1 1 21.3 1.63 Example 4 4.1 2.8 0 0.7 0 6.2 1 50.0 59 20.7 1.63 Example 5 4.5 2.3 0 1.3 0 8.7 1 40.0 18 20.6 1.63 Example 6 4.7 2.1 0 1.4 0 6.4 1 60.0 27 21.3 1.63 Example 7 4.3 2.101.307.3130.05220.41.63 Example 8 4.52.401.406.6160.03521.41.63 Example 9 5.01.702.004.2110.01820.61.63 Example 105.71.803.308.3130.04220.71.63 Example 111.35.702.106.2210.03922.91.61 Example 128.11.200.307.7230.06223.11.61 Example 136.90.071.004.3140.12322.7 1.61 Example 14 3.16.3 00.5 06.71 50.14 7 22.81.61 Example 15 4.3 3.1 00.0 67.3 1 50.0 3 6 23.41.61 Example 16 2.8 0.5 04.1 08.61 10.0 27 22.81.61 Example 17 3.71.1 00.8 00.3 37 0.2 35 24.21.60 Comparative Example 18 6.2 4.8 02.8 01 3.4 4 60.3 1 22 5.11.59 Comparative Example 19 4.72.2 01.1 02.3 210.1 24 23.11.61 Example 20 5.12.1 01.3 01.8230.11922.81.61 Example 214.72.301.402.2240.13223.21.61 Example 224.62.301.303.1240.14222.71.61 Example 235.22.101.205.7140.03122.91.61 Example 245.42.401.307.2160.02122.91.61 Example 254.72.301.501.5230.10923.21.61 Example 264.52.301.203.2220.133231.61 Example

[0146]

[0147] As shown in Tables 1 and 2, when the steel composition is properly controlled and the carbon monoxide concentration is properly controlled during the heating stage of cold-rolled sheet annealing, the surface layer alloy composition is properly controlled and internal AlN formation is suppressed, and it can be confirmed that the magnetism is excellent.

[0148] On the other hand, in the comparative example where the steel composition is not properly controlled or the carbon monoxide concentration is not properly controlled during the heating stage of cold-rolled sheet annealing, and the surface layer alloy composition is not properly controlled, it can be confirmed that a large amount of internal AlN is generated and the magnetic properties are inferior.

[0149] Among the examples, it can be confirmed that the magnetism is even better when all conditions regarding the dew point, heating rate, and cracking temperature in the heating and cracking stages are satisfied.

[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: Core layer

[0154] 20: Surface layer

Claims

1. In weight%, it comprises Si: 1.0 to 5.5%, Al: 0.1 to 3.5%, Mn: 0.01 to 3.5%, and the remainder being Fe and unavoidable impurities, and A non-oriented electrical steel sheet comprising, in weight percent, Si: 1.0 to 8.5%, Al: 0.05 to 6.5%, Mn: 0.05 to 4.5%, and O: 0.5 to 10.0% in a surface layer within 2 μm in the thickness direction from the surface of the steel sheet.

2. In Paragraph 1, Non-oriented electrical steel sheet in which the difference between the Si content on the steel sheet surface and the Si content within 2㎛ in the thickness direction from the steel sheet surface is 20% or less.

3. In Paragraph 1, The density of AlN is 0.001 to 0.1 particles / ㎛ in the thickness direction from the surface of the steel plate in the range of 2㎛ to 3㎛. 2 Non-oriented electrical steel sheet.

4. 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.

5. 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.

6. 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.

7. 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.

8. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab comprising, by weight, Si: 1.0 to 5.5%, Al: 0.1 to 3.5%, Mn: 0.01 to 3.5%, 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 above cold-rolled plate annealing step includes a heating step and a cracking step, and A method for manufacturing a non-oriented electrical steel sheet in which the fraction of carbon monoxide (CO) in the atmosphere during the heating step is 100 to 1000 ppm.

9. In Paragraph 8, 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.

10. In Paragraph 8, 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.

11. In Paragraph 8, 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.

12. In Paragraph 8, 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.

13. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the heating rate in the above heating step is 20 to 60℃ / sec.

14. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet in which the dew point temperature in the heating step is 30 to 70°C.

15. In Paragraph 8, A method for manufacturing non-oriented electrical steel sheets in which the dew point temperature at the cracking stage is -30℃ or lower.

16. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet in which the cracking temperature in the cracking step is 750 to 1050℃.

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