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%, 1.5-5.0% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, 0.001-0.08% of Sn, 0.001-0.08% of Sb, and 0.0002-0.0007% of B, with the remainder comprising Fe and inevitable impurities, wherein, when the content of elements is measured in a surface region, extending 0.3-1 µm from the surface toward the inside of the steel sheet, along the thickness direction of the steel sheet, the weight ratio of the maximum Si content to the maximum Al content is 25 or less.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, which utilizes segregation of B, Sn, and Sb and controls conditions in a cold-rolled sheet annealing process to densely concentrate Al and Si on the surface, thereby simultaneously improving mechanical strength and magnetism.

[0002] Non-oriented electrical steel is primarily used in motors that convert electrical energy into mechanical energy. This process requires excellent magnetic properties to achieve high efficiency. In particular, with the recent rise in eco-friendly vehicles powered by motors instead of internal combustion engines, demand for non-oriented electrical steel, used as a drive motor core material, is increasing. This demand is driven by the need for non-oriented electrical steel with both superior magnetic properties and strength.

[0003] Motor cores can be divided into stator cores and rotor cores. In order to meet the demands for miniaturization and high output for HEV drive motors, etc., non-oriented electrical steel sheets used for stator cores are strongly required to have excellent magnetic properties such as high magnetic flux density and low iron loss.

[0004] In addition, as a means of achieving miniaturization and high output of the HEV drive motor, etc., there is a tendency for the rotation speed of the motor to increase, but since the HEV drive motor has a large outer diameter, a large centrifugal force is applied to the rotor core, and depending on the structure, there is a very narrow part called a rotor core bridge part, so mechanical strength is also required for the non-oriented electrical steel sheet used for the rotor core.

[0005] Therefore, the characteristics of non-oriented electrical steel sheets used in motor cores include high strength along with magnetic properties for rotor cores, and high magnetic flux density and low core loss for stator cores. In this way, even if the same non-oriented electrical steel sheet is used for the same motor core, the required characteristics for the rotor core and the stator core are greatly different. However, in manufacturing motor cores, from the viewpoint of increasing material yield, etc., it is preferable to simultaneously produce rotor core material and stator core material from the same material steel sheet, and then laminate the respective core materials to assemble them into a rotor core or a stator core.

[0006] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, which simultaneously improves mechanical strength and magnetism by utilizing segregation of B, Sn, and Sb and controlling conditions in a cold-rolled sheet annealing process to densely concentrate Al and Si on the surface.

[0007] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Sn: 0.001 to 0.08%, Sb: 0.001 to 0.08%, and B: 0.0002 to 0.0007%, with the remainder being Fe and unavoidable impurities, and when the element content is measured in the thickness direction of the steel sheet in a surface portion in a range of 0.3 to 1 ㎛ from the surface of the steel sheet toward the inside, the weight ratio of the Al content to the Si content at the point where the Al content is maximum is 25 or less.

[0008] When measuring the element content in the direction of the steel plate thickness from the surface, the maximum Al content may be 1.8 wt% or more.

[0009] When measuring the element content in the direction of the steel plate thickness from the surface, the Si content at the point where the Al content is maximum may be 0.5 wt% or more.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention further includes S: 0.005 wt% or less (excluding 0%) and can satisfy the following equation 1.

[0011] [Formula 1]

[0012] 0.7 ≤ ([Sn] + [Sb] + [S] × 10) / ([B] × 100) ≤ 5.2

[0013] (In Equation 1, [Sn], [Sb], [S], and [B] represent the contents (weight %) of Sn, Sb, S, and B, respectively.)

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0015] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Bi, Pb, Ge, and As.

[0016] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0017] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0018]

[0019] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Sn: 0.001 to 0.08%, Sb: 0.001 to 0.08%, and B: 0.0002 to 0.0007%, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0020] The cold rolled sheet annealing step has a soaking temperature of 900 to 1050°C, a hydrogen fraction in the atmosphere of 10 to 35 volume%, and a dew point of the atmosphere of -55 to -15°C.

[0021] The slab further contains S: 0.005 wt% or less (excluding 0%) and can satisfy the following equation 1.

[0022] [Formula 1]

[0023] 0.7 ≤ ([Sn] + [Sb] + [S] × 10) / ([B] × 100) ≤ 5.2

[0024] (In Equation 1, [Sn], [Sb], [S], and [B] represent the contents (weight %) of Sn, Sb, S, and B, respectively.)

[0025] The slab may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0026] The slab may further contain 0.005 to 0.200 wt% of each or a combination of Bi, Pb, Ge and As.

[0027] The slab may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0028] The slab may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), Co: 0.05 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent mechanical strength after cold-rolled sheet annealing and excellent high-frequency iron loss characteristics after stress relief annealing.

[0030] Figure 1 is a schematic diagram showing a cross-section of a steel plate according to one embodiment of the present invention.

[0031] Figure 2 is a schematic diagram schematically showing a graph of analysis of Al concentration and Si concentration by thickness of a steel plate according to one embodiment of the present invention.

[0032] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0034] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0035] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0036] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0037] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0038] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0039]

[0040] A non-oriented electrical steel sheet according to one embodiment of the present invention includes, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Sn: 0.001 to 0.08%, Sb: 0.001 to 0.08%, and B: 0.0002 to 0.0007%, with the remainder being Fe and unavoidable impurities.

[0041] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0042]

[0043] Si: 1.5 to 5.0 wt%

[0044] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and increases strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects may be insufficient. If too much Si is added, the material becomes brittle, which may cause sheet fracture during coiling and cold rolling, resulting in a sharp decrease in rolling productivity. Therefore, Si may be included in an amount of 1.5 to 5.0 wt%. More specifically, it may be included in an amount of 2.0 to 4.5 wt%. More specifically, it may be included in an amount of 3.0 to 4.0 wt%. More specifically, it may be included in an amount of 3.0 to 3.8 wt%.

[0045]

[0046] Al: 0.1 to 2.0 wt%

[0047] Aluminum (Al) increases the resistivity of the material, thereby reducing iron loss and improving rollability, and plays a role in improving workability during cold rolling. If too little Al is added, it may be difficult to achieve the effect of reducing high-frequency iron loss, and the precipitation temperature of AlN may be lowered, which may cause fine nitride formation, which may reduce magnetism. If too much Al is added, excessive nitride formation may deteriorate magnetism, and problems may occur in all processes such as steelmaking and continuous casting, which may significantly reduce productivity. Therefore, Al may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.3 to 1.9 wt%. Even more specifically, it may be included in an amount of 0.5 to 1.5 wt%.

[0048]

[0049] Mn: 0.1 to 2.0 wt%

[0050] Manganese (Mn) improves iron loss by increasing the resistivity of the material and plays a role in forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration, and if too much Mn is added, fine MnS is excessively precipitated and promotes the formation of {111} texture, which is unfavorable for magnetism, resulting in a rapid decrease in magnetic flux density. Therefore, Mn may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.2 to 1.6 wt%. More specifically, it may be included in an amount of 0.3 to 1.5 wt%.

[0051] Sn: 0.001 to 0.080 wt%

[0052] Tin (Sn) can be added to improve magnetism because it improves the material's texture and suppresses surface oxidation by segregating at grain boundaries and surfaces. If the amount of Sn added is too small, the effect may not be sufficient. If too much Sn is added, grain boundary segregation becomes severe, which deteriorates the surface quality and increases the hardness, which may cause fracture of the cold-rolled sheet and reduce the rollability. Therefore, Sn can be added within the above-mentioned range. More specifically, it can be included in an amount of 0.01 to 0.08 wt%. More specifically, it can be included in an amount of 0.03 to 0.05 wt%.

[0053] Sb: 0.001 to 0.080 wt%

[0054] Antimony (Sb) can be added to improve magnetism because it improves the material's texture and suppresses surface oxidation by segregating at grain boundaries and surfaces. If the amount of Sb added is too small, the effect may be minimal. If too much Sb is added, grain boundary segregation may become severe, deteriorating the surface quality and increasing the hardness, which may cause fracture of the cold-rolled sheet and reducing the rollability. Therefore, Sb can be added within the above-mentioned range. More specifically, it can be included in an amount of 0.01 to 0.08 wt%. More specifically, it can be included in an amount of 0.03 to 0.05 wt%.

[0055] B: 0.0002 to 0.0007 wt%

[0056] Boron (B) is an element with a very strong tendency to segregate within the steel, and even a trace amount can segregate and significantly affect the formation of an oxide layer on the surface. In particular, B can segregate on the surface while competing with segregating elements such as S, Sn, and Sb, and accordingly, the degree of formation of an oxide layer on the surface can vary, and nitrides can be formed directly beneath the surface. Therefore, the B content can be included in an amount of 0.0002 to 0.0007 wt%. More specifically, it can be included in an amount of 0.0003 to 0.0006 wt%.

[0057]

[0058] A non-oriented electrical steel sheet according to one embodiment of the present invention further includes S: 0.005 wt% or less (excluding 0%) and can satisfy the following equation 1.

[0059] [Formula 1]

[0060] 0.7 ≤ ([Sn] + [Sb] + [S] × 10) / ([B] × 100) ≤ 5.2

[0061] (In Equation 1, [Sn], [Sb], [S], and [B] represent the contents (weight %) of Sn, Sb, S, and B, respectively.)

[0062] S: 0.0050 wt% or less

[0063] Sulfur (S) forms fine sulfides inside the base material, inhibiting grain growth and weakening iron loss, so the lower the content, the better. If the content is too high, it can combine with manganese, etc. to inhibit grain growth or greatly increase the degree of deterioration of magnetism after processing. More specifically, S may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it may be included in an amount of 0.0010 to 0.0035 wt%.

[0064] Meanwhile, among the components of non-oriented electrical steel sheets, Sn, Sb, S, and B, which are components that can segregate on the surface and change the behavior of the oxide layer, tend to segregate competitively on the surface with each other, and S or Sn / Sb have no relationship with each other because they exist differently in the steel lattice, but B has a competitive relationship with S or Sn / Sb. Therefore, in order to reduce surface nitride, it is necessary to satisfy Equation 1, which is the relationship for the element contents of S, Sn, Sn, and B that can segregate on the surface and control oxidation. More specifically, the value of Equation 1 may be 1.0 to 5.0.

[0065]

[0066] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0067] P: 0.1 wt% or less

[0068] Phosphorus (P) not only plays a role in increasing the resistivity of a material, but also can improve magnetic flux density as a grain boundary segregation element. However, if too much P is added, it increases the brittleness of the steel plate, resulting in poor weldability. More specifically, P may be included in an amount of 0.0001 to 0.0500 wt%. More specifically, P may be included in an amount of 0.0010 to 0.0200 wt%.

[0069] C: 0.005 wt% or less

[0070] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, thereby hindering grain boundary or domain wall movement and deteriorating magnetic properties. More specifically, C can be included in an amount of 0.0001 to 0.003 wt%.

[0071] Ti: 0.005 wt% or less

[0072] Titanium (Ti) has a strong tendency to form precipitates within the steel, and can deteriorate iron loss by forming fine carbides, nitrides, or sulfides within the parent material, thereby inhibiting grain growth and domain wall migration. More specifically, Ti may be included in an amount of 0.0001 to 0.0030 wt%.

[0073] N: 0.005 wt% or less

[0074] Nitrogen (N) not only forms fine AlN precipitates within the base material, but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall migration, thereby worsening iron loss. More specifically, N may be included in an amount of 0.0001 to 0.0030 wt%.

[0075]

[0076] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Bi, Pb, Ge, and As.

[0077] Bi, Pb, Ge, and As

[0078] When added, bismuth (Bi), lead (Pb), germanium (Ge) and arsenic (As) segregate at grain boundaries, thereby relieving stress concentration at grain boundaries during cold rolling, and thus reducing stress concentration in the subsequent recrystallization annealing process. <111> / ND By suppressing the recrystallization of the grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained, but if they are included in too much, a large amount of segregation may occur, which may suppress grain growth and result in inferior magnetic flux density and iron loss. More specifically, one or more types of Bi, Pb, Ge, and As may be further included, individually or in combination, in an amount of 0.010 to 0.150 wt%.

[0079]

[0080] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0081] Cu: 0.005 to 0.200 wt%

[0082] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu · Mn)S may occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement may occur, leading to cracks during rolling or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.10 wt%.

[0083] Cr: 0.01 to 0.50 wt%

[0084] Chromium (Cr) increases resistivity and improves iron loss. If too little Cr is added, the resistivity-enhancing effect may not be sufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr may be included in an amount of 0.050 to 0.20 wt%.

[0085] Ni: 0.05 wt% or less

[0086] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, it can contain 0.001 to 0.030 wt% of Ni.

[0087] Zn: 0.01 wt% or less

[0088] Zinc (Zn) can act as an impurity and degrade magnetism if the content is excessive. Therefore, Zn may be added further within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 wt%.

[0089] Co: 0.05 wt% or less

[0090] Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it can increase high-temperature strength and cause poor coil shape after hot rolling.

[0091]

[0092] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less (excluding 0%), 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%).

[0093] Mo: 0.030 wt% or less

[0094] When molybdenum (Mo) is added in excessive amounts, it may suppress segregation of segregating elements, thereby reducing the effect of improving the texture. Therefore, Mo may be included in an amount of 0.03 wt% or less. The lower limit is not particularly limited, but since it plays a role in improving the texture by segregating on the surface and grain boundaries, it may be included in an amount of 0.001 wt% or more. More specifically, Mo may be included in an amount of 0.001 to 0.010 wt%. More specifically, Mo may be included in an amount of 0.005 to 0.010 wt%.

[0095] V: 0.0050 wt% or less

[0096] Vanadium (V) has a very strong tendency to form precipitates within the steel, and forms fine carbides or nitrides within the base metal, thereby inhibiting grain growth and domain wall migration, thereby deteriorating iron loss. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not particularly limited, but may be 0.0003 wt% due to steelmaking costs. That is, V may be included in an amount of 0.0003 to 0.0050 wt%. More specifically, V may be included in an amount of 0.0003 to 0.0030 wt%.

[0097] Ca: 0.0050 wt% or less

[0098] Calcium (Ca) has a strong tendency to form precipitates within the steel, and forms fine sulfides within the parent material, which inhibits grain growth and domain wall movement, thereby deteriorating iron loss.

[0099] Nb: 0.0050 wt% or less

[0100] Niobium (Nb) has a very strong tendency to form precipitates in steel, and forms fine carbides or nitrides inside the base metal, which inhibits grain growth and domain wall migration, thereby deteriorating iron loss. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not particularly limited, but may be 0.0003 wt% due to steelmaking costs. That is, Nb may be included in an amount of 0.0003 to 0.0050 wt%. More specifically, Nb may be included in an amount of 0.0003 to 0.0030 wt%.

[0101] Zr: 0.0050 wt% or less

[0102] Excessive addition of zirconium (Zr) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, Zr can be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. That is, Zr can be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it can be included in an amount of 0.0005 to 0.0030 wt%.

[0103] Te: 0.0100 wt% or less

[0104] Tellurium (Te) diffuses into the oxide layer on the surface of a hot-rolled coil, increases the coefficient of friction between the oxide layer and the rolling work rolls, and concentrates under the oxide layer to improve hardness. Therefore, it can be added to prevent the fractured oxide layer during rolling from being pressed into the base metal and to be removed. If the amount of Te added is too small, the effect may be minimal. If too much Te is added, the oxide layer is easily removed, and the base metal comes into direct contact with the work rolls, reducing the effect. In addition, deformation bands may be excessively generated in the steel sheet during cold rolling, which may lead to the development of a {111} / ND texture that is unfavorable for magnetism. More specifically, tellurium may be included in an amount of 0.0001 to 0.007 wt%.

[0105] Mg: 0.0050 wt% or less

[0106] Magnesium (Mg) is an element that mainly combines with sulfur to form sulfides, and can affect the surface oxide layer of the steel base. Therefore, Mg may be included in an amount of 0.0050 wt% or less. The lower limit is not particularly limited, but may be set to 0.0001 wt% due to steelmaking costs. That is, Mg may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 to 0.0030 wt%.

[0107]

[0108] The remainder comprises iron (Fe) and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. When additional elements are included, they are included in place of the remainder, iron (Fe).

[0109]

[0110] As described above, in one embodiment of the present invention, by appropriately controlling the alloy composition of the steel plate and controlling the conditions in the cold-rolled plate annealing process, Al and Si can be densely concentrated on the surface, thereby simultaneously improving mechanical strength and magnetism.

[0111] Fig. 1 schematically illustrates a cross-section of a steel plate according to one embodiment of the present invention. As shown in Fig. 1, a surface portion (10) may exist within a range of 0.3 to 1 μm from the surface (11) of the steel plate toward the inside. Although Fig. 1 illustrates an example in which the surface portion (10) exists on both sides of the steel plate, it is also possible for the surface portion (10) to exist on only one side of the steel plate.

[0112] In one embodiment of the present invention, when measuring the element content in the thickness direction for the surface portion (10), the weight ratio of the maximum Si content to the maximum Al content may be 25 or less.

[0113] The surface portion (10) may be in the range of 0.3 to 1 ㎛ in the inward direction based on the surface (11) of the steel plate substrate, excluding the insulating film when an insulating film exists on the surface of the electrical steel plate described later.

[0114] The element content in the thickness direction can be measured using a glow discharge spectrometer (GDS). To reduce errors depending on the measurement location, measurements are taken at intervals of at least 2 cm and the average of three surrounding points is obtained. Figure 2 shows an example of the Al and Si contents in the thickness direction.

[0115] The surface portion (10) contains a large amount of Al and Si compared to the inside of the steel plate due to the concentration of Al and Si. At this time, by controlling the amount of diffusion of Al and Si, the weight ratio of the Al content to Si at the point where the Al content is maximum (Al max / Si maxAl ) can be adjusted to 25 or less. The weight ratio of Al content to Si at the point where Al content is maximum (Al max / Si maxAl ) is too large, the Al concentration layer may develop too strongly, causing peeling between the base material and the coating layer. More specifically, the weight ratio of the Al content to Si at the point where the Al content is maximum within the surface portion (10) (Al max / Si maxAl ) can be between 1.0 and 15.0.

[0116] When measuring the element content in the direction of the steel plate thickness at the surface (10), the maximum Al content may be 1.8 wt% or more. The maximum Al content (Al max) is too small, it means that Al enrichment does not occur densely in the surface portion (10), and as a result, a large number of fine inclusions may be formed inside the steel plate by N2, O2, etc. introduced from the outside air, which may have a negative effect on magnetism. More specifically, when measuring the element content in the direction of the steel plate thickness in the surface portion (10), the maximum Al content (Al max ) may be 1.8 to 15 wt%.

[0117] In addition, when measuring the element content in the direction of the steel plate thickness at the surface portion (10), when measuring the element content in the direction of the steel plate thickness at the surface portion (10), the Si content (Si) at the point where the Al content is maximum maxAl ) may be 0.5 wt% or more. Si content (Si maxAl ) is too small, it means that Si concentration in the surface portion (10) does not occur densely, and as a result, a large number of fine inclusions or precipitates may be formed inside the steel plate by N2, O2, etc. introduced from the outside air, which may have a negative effect on magnetism. More specifically, when measuring the element content in the direction of the steel plate thickness in the surface portion (10), Si (Si maxAl ) content may be 0.5 to 4 wt%.

[0118]

[0119] As described above, in one embodiment of the present invention, by appropriately concentrating Si and Al on the surface portion (10), magnetism can be improved. Specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have a B50 of 1.64 or more. More specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have a B50 of 1.64 to 1.70T.

[0120] In addition, in one embodiment of the present invention, the core loss (W) of the non-oriented electrical steel sheet based on a thickness of 0.25 mm 10 / 400 ) may be less than 12.5 W / Kg. Iron loss (W 10 / 400) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. More specifically, the iron loss (W) of non-oriented electrical steel sheet 10 / 400 ) can be 10.0 to 12.3 W / kg. Iron loss (W 10 / 800 ) may be less than 34.5 W / Kg. More specifically, the iron loss (W 10 / 800 ) can be 30.0 to 34.5 W / Kg. Iron loss (W 10 / 800 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 800 Hz.

[0121]

[0122] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet.

[0123]

[0124] Below, each step is explained in detail.

[0125] First, the slab is hot rolled.

[0126] The alloy composition of the slab has been described in the alloy composition of the previously mentioned non-oriented electrical steel sheet, so a duplicate description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab are substantially identical.

[0127] Specifically, the slab contains, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Sn: 0.001 to 0.08%, Sb: 0.001 to 0.08%, and B: 0.0002 to 0.0007%, with the remainder being Fe and unavoidable impurities.

[0128] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0129] Slabs can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1200℃ or lower. If the slab heating temperature is too high, precipitates such as AlN and MnS present within the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, inhibiting grain growth and reducing magnetism.

[0130] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 1.0 to 4.5 mm. In the step of producing the hot-rolled sheet, the finishing rolling temperature can be 800°C or higher. Specifically, it can be 850 to 950°C. The hot-rolled sheet can be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled sheet can be 1.5 to 4.3 mm.

[0131] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains. That is, after hot rolling, scale removal processes such as pickling, shot blasting, or surface grinding can be omitted, and subsequent steps can be performed. By performing cold rolling without the pickling process, friction between the rolling work rolls and the steel sheet increases, so that shear deformation is simultaneously applied in addition to plane deformation during rolling, and a specific orientation develops during recrystallization annealing. In one embodiment of the present invention, scale refers to a portion on the surface of the steel sheet where elements such as Fe, Al, and Si combine with oxygen to form a phase different from that of the base metal. Remaining scale means that at least 1 μm of scale remains on the hot-rolled sheet. In this case, the scale thickness refers to the sum of the scale thicknesses formed on both surfaces of the steel sheet. If the remaining scale thickness is too thin, the effect due to the scale residue may not be fully exerted. Even if the scale thickness is thicker, the effect is not improved, and there is a problem of a reduced yield of the steel sheet. More specifically, scales with a thickness of 0.1 to 1 μm may remain.

[0132] After manufacturing the hot-rolled sheet, an additional step of annealing the hot-rolled sheet may be included. The annealing temperature for the hot-rolled sheet may be 950 to 1150°C. The annealing time may be 10 to 300 seconds. The annealing of the hot-rolled sheet may be omitted if necessary.

[0133] Next, the hot rolled steel sheet is cold rolled to produce a cold rolled sheet. At this time, cold rolling can be performed at a reduction ratio of 70 to 90%. If the reduction ratio is too low, the accumulated strain energy in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which can cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it can cause problems in the subsequent annealing process. <111> / ND The recrystallization of the grains in the direction of the direction is promoted, and the grains become finer, which may cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 58 to 67%. The cold rolling step can be performed using a tandem cold rolling mill that continuously cold rolls the steel sheet using multiple rolling stands, or a reverse rolling mill that discontinuously cold rolls using 12 or more rolling rolls. In addition, one cold rolling or two or more cold rollings with intermediate annealing in between can be performed. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0134] Next, the cold rolled sheet is annealed.

[0135] The cold rolled sheet annealing step has a soaking temperature of 900 to 1050°C, a hydrogen fraction in the atmosphere of 10 to 35 volume%, and a dew point of the atmosphere of -55 to -15°C.

[0136] If the soaking temperature is too low, the grain size may not grow sufficiently, resulting in poor magnetic properties. If the soaking temperature is too high, the grain size may grow excessively, resulting in poor magnetic properties. More specifically, the soaking temperature may be between 930 and 1020°C.

[0137] If the hydrogen fraction in the atmosphere is too low, the atmosphere within the annealing furnace may change to an oxidizing atmosphere, which can cause oxidation problems. If the hydrogen fraction is too high, there is a risk of explosion in the annealing furnace. More specifically, the hydrogen fraction in the atmosphere may be 15 to 30% by volume. The remainder, other than hydrogen, may be oxygen and nitrogen. More specifically, the atmosphere may contain 65 to 90% by volume of nitrogen.

[0138] If the dew point of the atmosphere is too low, an appropriate Si / Al concentration layer cannot be formed, which can lead to nitrogen penetration and the formation of fine nitrides. If the dew point of the atmosphere is too high, severe surface oxidation can occur. More specifically, the dew point of the atmosphere can be between -50°C and -30°C.

[0139] The annealing time may be 40 to 100 seconds. More specifically, the annealing time may be 50 to 90 seconds.

[0140] After cold-rolled sheet annealing, an insulating film can be formed. The insulating film can be treated with organic, inorganic, or organic-inorganic composite films, and can also be treated with other insulating film agents.

[0141] Additionally, after the cold-rolled sheet annealing step, a stress relief annealing step of annealing the cold-rolled sheet at 700 to 800°C may be further included. The annealing time may be 40 to 120 minutes.

[0142]

[0143] The present invention will be described in more detail below through examples. However, these examples are intended only to illustrate the present invention and are not intended to limit the present invention.

[0144]

[0145] Example 1

[0146] A slab was manufactured using the components shown in Table 1, Table 2, and the remainder including Fe and unavoidable impurities. This was heated to 1150°C and hot-rolled at a finishing temperature of 950°C to manufacture a hot-rolled sheet having a thickness of 1.8 mm.

[0147] Afterwards, the hot-rolled sheet was annealed at 1030°C for 100 seconds and cold-rolled to a final thickness of 0.25 mm. The cold-rolled steel sheet was annealed for 60 seconds under the conditions listed in Table 2 below.

[0148] The surface of the manufactured non-oriented electrical steel sheet was analyzed by GDS, and the results are shown in Table 3.

[0149] The magnetic flux density and iron loss were measured using a single sheet tester by cutting 5 sheets of 60 mm width × 60 mm length for each specimen, and the values ​​were presented.

[0150] At this time, W 10 / 400 When a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, W 10 / 800 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 800 Hz. B 50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0151] Classification (weight%) SiMnAlSnSbBS Formula 113.50.691.260.00140.00030.00030.00451.623.61.020.680.00570.00650.00050.00361.033.30.920.980.00190.00310.00030.00301.243.0 1.161.500.00350.00280.00020.00402.353.31.200.790.00500.00050.00030.00271.162.91.480.910.00370.00270.00030.00341.373.60.680.530.00550.00100.00050.00360.983.11.230.790.00320.00410.00060.00340.793.21.391.500.00310.00470.00050.00370.9103.50.441.140 .00590.00750.00060.00370.8113.40.761.010.00230.00620.00060.00350.7123.11.101.440.00620.00330.00030.00211.0133.50.341.170.00 210.00680.00040.00441.3143.41.040.950.00470.00710.00060.00491.0153.71.030.580.00770.00390.00060.00400.9163.60.521.180.0013 0.00670.00030.00391.6173.51.410.780.00710.00330.00030.00471.9183.70.910.890.00150.00380.00060.00500.9191.30.690.750.00230.0 0350.00030.00471.8205.31.450.980.00570.00630.00060.00260.6213.60.050.660.00360.00450.00020.00402.4223.22.201.370.00140.006 40.00070.00360.6233.21.370.050.00430.00210.00050.00491.1243.41.232.200.00160.00720.00050.00461.1253.31.210.720.00050.00500.00030.00170.8263.30.451.200.07900.00580.00030.00163.4273.70.660.620.00790.00050.00020.00452.7283.20.701.040.00040.08500.00060.00332.0293.51.351 .470.00680.00580.00010.00203.3303.10.761.270.07400.07400.00100.00141.6313.20.301.290.00280.00120.00040.00752.0323.00.641.270.00710.00550.00070.0 0230.5333.41.240.670.07500.07500.00030.00225.7343.21.030.670.00620.00100.00060.00340.7353.41.111.320.00450.00680.00050.00320.9364.00.471.290.00 470.00660.00030.00181.0373.80.640.800.00160.00650.00030.00351.4383.20.540.500.00190.00030.00060.00470.8393.70.991.370.00430.00140.00050.00280.7.

[0152] Cracking temperature (℃) Hydrogen fraction (vol%) Dew point (℃) Al max (wt%)Si maxAl (wt%)Al max / Si maxAl194023-372.80.55.6295018-404.20.67.03102020-402.60.83.3495018-374.11.13.7598014-306.22.82.26102017-536.60.611.0796024-454.11.62.6895015-282.41.71.4995020-472.20.63.71095025-414.40.67. 31197030-316.31.44.512103020-209.22.04.61394011-394.91.14.514100034-501.81.31.415103035-485.11.24.316102010-325.01.24.21794032-338.80.614.71894010-417.20.89.019101026-466.30.79.020Cold rolled not possibleCold rolled not possibleCold rolled not possibleCold rolled not possibleCold rolled not possibleCold rolled Unavailable 2198022-3316.20.627.02298022-4220.30.825.42393011-4714.50.436.32496014-3822.10.731.62596014-524.40.58.82692010-174.30.143.02794035-2413.20.433.02896027-3624.50.640.82994017-4622.93.86.03010102 6-498.42.92.931101030-388.80.329.33296022-517.40.237.03394016-448.40.328.03488019-321.60.72.335107016-4327.50.930.6369805-3433.81.228.23794040-491.20.43.038102031-651.70.35.739102014825.20.463.0

[0153] Classification B50 (Tesla) Iron loss W10 / 400 (W / kg) W10 / 800 (W / kg) Remarks 11.65 12.134.2 Invention example 21.65 11.833.1 Invention example 31.65 11.632.9 Invention example 41.65 11.231.8 Invention example 51.66 12.133.5 Invention example 61.66 11.533.0 Invention example 71.67 11.832.7 Invention example 81.66 11.733.2 Invention example 91.66 11.032.0 Invention example 101.68 11.932 .1 Invention Example 111.65 12.2 34.5 Invention Example 121.64 12.133.0 Invention Example 131.65 11.63 1.8 Invention Example 141.65 12.134.1 Invention Example 151.65 11.8 33.8 Invention Example 161.65 11.8 33.2 Invention Example 171.66 11.132.9 Invention Example 181.65 11.0 32.3 Invention Example 191.69 19.5 62.7 Comparative Example 20 Cold rolling not possible Cold rolling not possible Cold rolling Non-comparable example 211.6213.635.1 Comparative example 221.6013.536.4 Comparative example 231.6113.935.2 Comparative example 241.6112.734.8 Comparative example 251.6212.936.2 Comparative example 261.6316.137.0 Comparative example 271.6412.835.5 Comparative example 281.6416.538.1 Comparative example 291.6312.534.7 Comparative example 301.60 14.336.2Comparative Example 311.6512.334.2Invention Example 321.6313.237.8Comparative Example 331.6214.737.2Comparative Example 341.6313.836.5Comparative Example 351.6312.734.6Comparative Example 361.6014.537.2Comparative Example 371.6112.735.0Comparative Example 381.6214.135.7Comparative Example 391.6015.035.8Comparative Example

[0154] As shown in Tables 1 to 3, when the steel composition is appropriately controlled and the conditions for cold-rolled sheet annealing are appropriately controlled, it can be confirmed that Si and Al are densely concentrated in the surface layer, resulting in excellent iron loss and magnetic flux density.

[0155] On the other hand, if the steel component is not properly controlled or the conditions for cold-rolled sheet annealing are not properly controlled, and the surface layer is not properly formed, it can be confirmed that the iron loss and magnetic flux density are inferior.

[0156]

[0157] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0158] [Explanation of symbols]

[0159] 100: Non-oriented electrical steel sheet 10: Surface part,

[0160] 11: Steel plate surface

Claims

1. Contains Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Sn: 0.001 to 0.08%, Sb: 0.001 to 0.08%, and B: 0.0002 to 0.0007%, and the remainder includes Fe and inevitable impurities. A non-oriented electrical steel sheet having a weight ratio of the maximum Si content to the maximum Al content of 25 or less when measuring the element content in the direction of the steel sheet thickness at a surface portion within a range of 0.3 to 1 ㎛ from the surface toward the inside.

2. In paragraph 1, A non-oriented electrical steel sheet having a maximum Al content of 1.8 wt% or more when measuring the element content in the thickness direction of the steel sheet on the surface.

3. In paragraph 1, A non-oriented electrical steel sheet having an Si content of 0.5 wt% or more at the point where the Al content is maximum when measuring the element content in the thickness direction of the steel sheet on the surface.

4. In paragraph 1, S: Non-oriented electrical steel sheet further containing 0.005 wt% or less (excluding 0%) and satisfying the following formula 1. [Formula 1] 0.7 ≤ ([Sn] + [Sb] + [S] × 10) / ([B] × 100) ≤ 5.2 (In Equation 1, [Sn], [Sb], [S], and [B] represent the contents (weight %) of Sn, Sb, S, and B, respectively.) 5. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

6. In paragraph 1, A non-oriented electrical steel sheet further containing 0.005 to 0.200 wt% of each or a combined amount of one or more of Bi, Pb, Ge and As.

7. In paragraph 1, A non-oriented electrical steel sheet further comprising at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

8. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

9. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Sn: 0.001 to 0.08%, Sb: 0.001 to 0.08%, and B: 0.0002 to 0.0007%, with the remainder being Fe and unavoidable impurities; A step of manufacturing a cold rolled sheet by cold rolling the hot rolled steel sheet above, and A cold rolled sheet annealing step for annealing the above cold rolled sheet; Including, A method for manufacturing a non-oriented electrical steel sheet, wherein the cold rolled sheet annealing step has a soaking temperature of 900 to 1050°C, a hydrogen fraction in the atmosphere of 10 to 35 volume%, and a dew point of the atmosphere of -55 to -15°C.

10. In paragraph 9, The above slab further contains S: 0.005 wt% or less (excluding 0%) and a method for manufacturing a non-oriented electrical steel sheet satisfying the following formula 1. [Formula 1] 0.7 ≤ ([Sn] + [Sb] + [S] × 10) / ([B] × 100) ≤ 5.2 (In Equation 1, [Sn], [Sb], [S], and [B] represent the contents (weight %) of Sn, Sb, S, and B, respectively.) 11. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

12. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further contains 0.005 to 0.200 wt% of each or a combined amount of one or more of Bi, Pb, Ge and As.

13. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

14. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

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