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

Abstract

According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, 0.001 to 0.08% Sn, 0.001 to 0.08% Sb and 0.0002 to 0.0007% B, with the balance being Fe and unavoidable impurities. When the elemental content is measured along the thickness direction of the steel sheet in a surface portion ranging from the surface to the interior in a range of 0.3 to 1 μm, the weight ratio of the maximum Si content to the maximum Al content is 25 or less.

Description

Technical Field

[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 the segregation of B, Sn, and Sb, and by adjusting the conditions during the cold-rolled sheet annealing process, densely enriches Al and Si on the surface to simultaneously improve mechanical strength and magnetic properties. Background Technology

[0002] Non-oriented electrical steel sheets are mainly used in motors that convert electrical energy into mechanical energy. To achieve high efficiency in the conversion process, non-oriented electrical steel sheets need to have excellent magnetic properties. In particular, with the increasing attention paid to environmentally friendly vehicles that replace internal combustion engines with electric motors in recent years, the demand for non-oriented electrical steel sheets used as core materials for drive motors is constantly increasing. Therefore, non-oriented electrical steel sheets with both excellent magnetic properties and strength are required.

[0003] Motor cores can be divided into stator cores and rotor cores. In order to meet the miniaturization and high output requirements of HEV drive motors, there is a strong demand for non-oriented electrical steel sheets used for stator cores to have excellent magnetic properties such as high magnetic flux density and low iron loss.

[0004] Furthermore, as a means to achieve miniaturization and high output of the HEV drive motor, the motor speed tends to increase. However, since the outer diameter of the HEV drive motor is large, a large centrifugal force acts on the rotor core. Depending on the structure, there will be a very narrow part called the rotor core bridging part. Therefore, the non-oriented electrical steel sheet used for the rotor core also requires mechanical strength.

[0005] Therefore, the characteristics of non-oriented electrical steel sheets used for motor cores are as follows: for rotor cores, in addition to magnetic properties, high strength is required; for stator cores, high magnetic flux density and low iron loss are required. As mentioned above, even for non-oriented electrical steel sheets used in the same motor core, the required characteristics for rotor and stator cores are quite different. However, from the viewpoint of improving material yield, it is preferable to select rotor core materials and stator core materials from steel sheets of the same material simultaneously during motor core manufacturing, and then stack the core materials to assemble them into a rotor core or stator core. Summary of the Invention

[0006] (a) Technical problems to be solved 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 utilizes the segregation of B, Sn, and Sb, and by adjusting the conditions during the cold-rolled sheet annealing process, densely enriches Al and Si on the surface to simultaneously improve mechanical strength and magnetic properties.

[0007] (II) Technical Solution According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, 0.001 to 0.08% Sn, 0.001 to 0.08% Sb and 0.0002 to 0.0007% B, with the balance being Fe and unavoidable impurities. When the elemental content is measured along the thickness direction of the steel sheet in a surface portion ranging from the surface to the interior in a range of 0.3 to 1 μm, the weight ratio of Al content to Si at the site with the highest Al content is 25 or less.

[0008] When the elemental content is measured along the thickness direction of the steel plate on the surface, the maximum Al content can be 1.8% by weight or more.

[0009] When the elemental content is measured along the thickness direction of the steel plate on the surface, the Si content at the site with the highest Al content can be more than 0.5% by weight.

[0010] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further contain S: less than 0.005% by weight and excluding 0%, and satisfies the following formula 1.

[0011] [Formula 1] 0.7≤([Sn]+[Sb]+[S]×10) / ([B]×100)≤5.2 In Equation 1, [Sn], [Sb], [S] and [B] represent the contents (by weight%) of Sn, Sb, S and B, respectively.

[0012] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

[0013] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Bi, Pb, Ge and As, with each or their total content being 0.005 to 0.200 by weight.

[0014] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0015] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: Mo: less than 0.03 wt% and excluding 0%; B: less than 0.0050 wt% and excluding 0%; V: less than 0.0050 wt% and excluding 0%; Ca: less than 0.0050 wt% and excluding 0%; Nb: less than 0.0050 wt% and excluding 0%; Zr: less than 0.005 wt% and excluding 0%; Te: less than 0.01 wt% and excluding 0%; and Mg: less than 0.0050 wt% and excluding 0%.

[0016] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: hot rolling a slab to manufacture a hot-rolled steel sheet, wherein the slab comprises, by weight %, 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 balance comprising Fe and unavoidable impurities; cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0017] The annealing process for cold-rolled steel sheets involves a homogenization temperature of 900 to 1050°C, a hydrogen content of 10 to 35% by volume in the atmosphere, and a dew point of -55 to -15°C.

[0018] The slab may also contain S: less than 0.005% by weight and excluding 0%, and satisfy the following formula 1.

[0019] [Formula 1] 0.7≤([Sn]+[Sb]+[S]×10) / ([B]×100)≤5.2 In Equation 1, [Sn], [Sb], [S] and [B] represent the contents (by weight%) of Sn, Sb, S and B, respectively.

[0020] The slab may also contain one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

[0021] The slab may also contain one or more of Bi, Pb, Ge and As, with each or their combined content ranging from 0.005 to 0.200 by weight.

[0022] The slab may also contain one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, and Zn: less than 0.01 wt% and excluding 0%.

[0023] The slab may also contain one or more of the following: Mo: less than 0.03 wt% and excluding 0%; B: less than 0.0050 wt% and excluding 0%; V: less than 0.0050 wt% and excluding 0%; Ca: less than 0.0050 wt% and excluding 0%; Nb: less than 0.0050 wt% and excluding 0%; Zr: less than 0.005 wt% and excluding 0%; Te: less than 0.01 wt% and excluding 0%; Co: less than 0.05 wt% and excluding 0%; and Mg: less than 0.0050 wt% and excluding 0%.

[0024] (III) Beneficial Effects According to an embodiment of the present invention, the non-oriented electrical steel sheet exhibits excellent mechanical strength after cold rolling annealing and excellent high-frequency iron loss characteristics after stress-relief annealing. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating a cross-section of a steel plate according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic diagram illustrating the analysis of Al and Si concentrations of a steel plate according to a thickness according to an embodiment of the present invention. Detailed Implementation

[0027] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below can also be described as a second part, component, region, layer, or segment.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. As used in the specification, "comprising" can specifically refer to a feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, and / or components.

[0029] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, there are no other parts in between.

[0030] In addition, unless otherwise specified, % means weight, 1 ppm is 0.0001 weight.

[0031] In one embodiment of the present invention, the additional element refers to the additional element replacing the balance of iron (Fe), and the amount of replacement is equivalent to the amount of additional element added.

[0032] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0033] The embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0034] According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, 0.001 to 0.08% Sn, 0.001 to 0.08% Sb and 0.0002 to 0.0007% B, with the balance comprising Fe and unavoidable impurities.

[0035] The reasons for the compositional restrictions on non-oriented electrical steel sheets will be described below.

[0036] Si: 1.5 to 5.0% by weight Silicon (Si) serves to increase the resistivity of materials, reduce iron loss, and improve strength through solid solution strengthening. If too little Si is added, the improvement in iron loss and strength may be insufficient. If too much Si is added, the material becomes more brittle, leading to cracking during coiling and cold rolling, which can drastically reduce rolling productivity. Therefore, Si can be contained in quantities of 1.5 to 5.0 wt%. More specifically, it can contain 2.0 to 4.5 wt%. More specifically, it can contain 3.0 to 4.0 wt%. More specifically, it can contain 3.0 to 3.8 wt%.

[0037] Al: 0.1 to 2.0% by weight The role of aluminum (Al) is to increase the resistivity of materials, reduce iron loss, improve rollability, and enhance workability during cold rolling. If too little Al is added, it may be difficult to achieve the desired reduction in high-frequency iron loss, the precipitation temperature of AlN will decrease, leading to fine nitride formation and potentially decreased magnetic properties. If too much Al is added, excessive nitride formation will result in magnetic degradation, causing problems in all processes, including steelmaking and continuous casting, and potentially leading to a significant decrease in productivity. Therefore, Al can be contained in quantities of 0.1 to 2.0% by weight. More specifically, it can be contained in quantities of 0.3 to 1.9% by weight. More specifically, it can be contained in quantities of 0.5 to 1.5% by weight.

[0038] Mn: 0.1 to 2.0% by weight Manganese (Mn) serves to increase the resistivity of materials, improve iron loss, and form sulfides. If too little Mn is added, fine sulfide particles form, leading to magnetic degradation. If too much Mn is added, excessive fine MnS precipitation promotes the formation of a {111} texture, which is detrimental to magnetism, resulting in a sharp decrease in magnetic flux density. Therefore, Mn can be present in quantities from 0.1 to 2.0 wt%. More specifically, it can be present in quantities from 0.2 to 1.6 wt%. More specifically, it can be present in quantities from 0.3 to 1.5 wt%.

[0039] Sn: 0.001 to 0.080% by weight Tin (Sn) acts as a segregant at grain boundaries and surfaces, thereby improving the texture of the material and inhibiting surface oxidation. Therefore, tin can be added to improve magnetism. If too little Sn is added, the effect may be insufficient. If too much Sn is added, grain boundary segregation becomes severe, leading to deterioration of surface quality, increased hardness causing cold-rolled sheet fracture, and potentially decreased rollability. Therefore, Sn can be added within the aforementioned range. More specifically, it can contain 0.01 to 0.08% by weight. More specifically, it can contain 0.03 to 0.05% by weight.

[0040] Sb: 0.001 to 0.080% by weight Antimony (Sb) acts as a segregant at grain boundaries and surfaces, thereby improving the texture of the material and inhibiting surface oxidation. Therefore, antimony can be added to improve magnetism. If too little Sb is added, the effect may be weak. If too much Sb is added, grain boundary segregation becomes severe, leading to deterioration of surface quality, increased hardness causing cold-rolled sheet fracture, and potentially decreased rollability. Therefore, Sb can be added within the aforementioned range. More specifically, it can contain 0.01 to 0.08% by weight. More specifically, it can contain 0.03 to 0.05% by weight.

[0041] B: 0.0002 to 0.0007% by weight Boron (B) is a highly segregating element in steel; even trace amounts can cause segregation, potentially significantly impacting the formation of the surface oxide layer. In particular, B may compete with segregating elements such as S, Sn, and Sb for surface segregation, thereby altering the degree of surface oxide formation and potentially leading to the formation of nitrides directly beneath the surface. Therefore, B can be present in quantities of 0.0002 to 0.0007% by weight. More specifically, it can be present in quantities of 0.0003 to 0.0006% by weight.

[0042] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further contain S: less than 0.005% by weight and excluding 0%, and satisfies the following formula 1.

[0043] [Formula 1] 0.7≤([Sn]+[Sb]+[S]×10) / ([B]×100)≤5.2 In Equation 1, [Sn], [Sb], [S] and [B] represent the contents (by weight%) of Sn, Sb, S and B, respectively.

[0044] S: less than 0.0050% by weight Sulfur (S) forms fine sulfides within the matrix, inhibiting grain growth and thus reducing iron loss. Therefore, a lower content is better. If the content is too high, it will combine with Mn and other elements, inhibiting grain growth or potentially significantly exacerbating magnetic degradation after processing. More specifically, S may contain 0.0001 to 0.0050% by weight. More specifically, it may contain 0.0010 to 0.0035% by weight.

[0045] On the other hand, in the composition of non-oriented electrical steel sheets, Sn, Sb, S, and B are components that can segregate on the surface and alter the behavior of the oxide layer. They have a competitive tendency to segregate on the surface. S or Sn / Sb exist in different ways within the steel lattice and are therefore unrelated to each other, but B competes with S or Sn / Sb. Therefore, to reduce surface nitrides, it is necessary to satisfy Equation 1, which represents the relationship between the contents of S, Sn, Sb, and B elements that can segregate on the surface and suppress oxidation. More specifically, the value of Equation 1 can be from 1.0 to 5.0.

[0046] According to an embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

[0047] P: less than 0.1% by weight Phosphorus (P) not only increases the resistivity of materials but also, as a grain boundary segregation element, can increase magnetic flux density. However, if too much P is added, it increases the brittleness of the steel sheet and worsens its weldability. More specifically, P can be present in quantities of 0.0001 to 0.0500% by weight. More specifically, P can be present in quantities of 0.0010 to 0.0200% by weight.

[0048] C: less than 0.005% by weight Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, thereby hindering the movement of grain boundaries or magnetic domain walls and potentially leading to deterioration of magnetic properties. More specifically, C may contain 0.0001 to 0.003% by weight.

[0049] Ti: less than 0.005% by weight Titanium (Ti) has a very strong tendency to form precipitates in steel, and it forms fine carbides, nitrides, or sulfides within the base material, thereby inhibiting grain growth and domain wall movement, which may lead to iron loss degradation. More specifically, Ti may contain 0.0001 to 0.0030% by weight.

[0050] N: less than 0.005% by weight Nitrogen (N) not only forms fine AlN precipitates within the matrix, but also combines with other impurities to form fine precipitates, inhibiting grain growth and domain wall movement, potentially leading to deterioration of iron losses. More specifically, N may contain 0.0001 to 0.0030% by weight.

[0051] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Bi, Pb, Ge and As, with each or their total content being 0.005 to 0.200 by weight.

[0052] Bi, Pb, Ge and As When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are further added, segregation occurs at grain boundaries. During cold rolling, this alleviates stress concentration at the grain boundaries and suppresses stress during subsequent recrystallization annealing processes. <111> / / Recrystallization of ND-oriented grains, thereby increasing magnetic flux density. When these elements are added appropriately, the aforementioned effects can be further achieved; however, if the content is too high, excessive segregation will occur, inhibiting grain growth and potentially leading to a decrease in magnetic flux density and iron loss. More specifically, it may also contain one or more of Bi, Pb, Ge, and As, in amounts of 0.010 to 0.150% by weight, individually or in combination.

[0053] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0054] Cu: 0.005 to 0.200% by weight The role of copper (Cu) is to form sulfides with Mn. If too little Cu is added, fine (Cu·Mn)S precipitates, potentially leading to magnetic degradation. If too much Cu is added, it can cause high-temperature brittleness, leading to cracking during continuous casting or hot rolling. More specifically, Cu can be present in amounts from 0.01 to 0.10% by weight.

[0055] Cr: 0.01 to 0.50% by weight Chromium (Cr) is added to increase resistivity and improve iron loss. If too little Cr is added, the resistivity increase may be insufficient. If too much Cr is added, it may lead to a decrease in magnetic flux density. More specifically, Cr can be present in amounts ranging from 0.050 to 0.20% by weight.

[0056] Ni: less than 0.05% by weight Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which may adversely affect magnetism. More specifically, Ni may contain 0.001 to 0.030% by weight.

[0057] Zn: less than 0.01% by weight If the zinc (Zn) content is too high, it may act as an impurity and cause a decrease in magnetic properties. Therefore, Zn can be added further within the aforementioned range. More specifically, Zn can be present in amounts from 0.001 to 0.005% by weight.

[0058] Co: less than 0.05% by weight Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it increases high-temperature strength and may lead to poor shape of hot-rolled coils.

[0059] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of the following: Mo: less than 0.03 wt% and excluding 0%; V: less than 0.0050 wt% and excluding 0%; Ca: less than 0.0050 wt% and excluding 0%; Nb: less than 0.0050 wt% and excluding 0%; Zr: less than 0.0050 wt% and excluding 0%; Te: less than 0.0100 wt% and excluding 0%; and Mg: less than 0.0050 wt% and excluding 0%.

[0060] Mo: less than 0.030% by weight If excessive molybdenum (Mo) is added, it may suppress the segregation of segregating elements and reduce the texture improvement effect. Therefore, Mo can be contained in amounts of 0.03 wt% or less, with no particular lower limit, but it can be contained in amounts of 0.001 wt% or more because it improves texture through segregation at the surface and grain boundaries. More specifically, Mo can be contained in amounts of 0.001 to 0.010 wt%. More specifically, Mo can be contained in amounts of 0.005 to 0.010 wt%.

[0061] V: less than 0.0050% by weight Vanadium (V) exhibits a strong tendency to precipitate in steel, forming fine carbides or nitrides within the base metal. This inhibits grain growth and domain wall movement, leading to deterioration of iron losses. Therefore, the V content can be below 0.0050% by weight, with no particular lower limit, but due to steelmaking costs, it can be as low as 0.0003% by weight. That is, V can contain 0.0003 to 0.0050% by weight. More specifically, V can contain 0.0003 to 0.0030% by weight.

[0062] Ca: less than 0.0050% by weight Calcium (Ca) has a very strong tendency to form precipitates in steel and forms fine sulfides inside the base metal, which inhibits grain growth and magnetic domain wall movement, thus leading to iron loss deterioration.

[0063] Nb: less than 0.0050% by weight Niobium (Nb) has a very strong tendency to form precipitates in steel, and it forms fine carbides or nitrides within the base metal, inhibiting grain growth and domain wall movement, thus leading to deterioration of iron loss. Therefore, the Nb content can be below 0.0050% by weight, with no particular lower limit, but due to steelmaking costs, it can be 0.0003% by weight. That is, Nb can be present from 0.0003 to 0.0050% by weight. More specifically, Nb can be present from 0.0003 to 0.0030% by weight.

[0064] Zr: less than 0.0050% by weight Adding excessive amounts of zirconium (Zr) can lead to inclusions and other defects in the steel, causing magnetic degradation. Therefore, Zr can be present in quantities of less than 0.005% by weight, with no particular lower limit, but due to steelmaking costs, it can be as low as 0.0001% by weight. That is, Zr can be present in quantities from 0.0001 to 0.0050% by weight. More specifically, it can be present in quantities from 0.0005 to 0.0030% by weight.

[0065] Te: less than 0.0100% by weight Tellurium (Te) diffuses into the oxide layer on the surface of hot-rolled coils, increasing the coefficient of friction between the oxide layer and the rolling mill rolls, while also accumulating in the lower part of the oxide layer, thereby increasing hardness. Therefore, tellurium can be added to allow the oxide layer, which breaks off during rolling, to detach without being pressed into the base material. If too little Te is added, the effect may be insignificant. If too much Te is added, the oxide layer is easily detached, and the base material directly contacts the rolling mill rolls, thus reducing the effect and generating excessive deformation bands within the steel sheet during cold rolling, potentially leading to the development of a detrimental {111} / / ND texture. More specifically, tellurium can be contained in amounts from 0.0001 to 0.007% by weight.

[0066] Mg: less than 0.0050% by weight Magnesium (Mg) is an element that primarily combines with sulfur to form sulfides, which may affect the oxide layer on the surface of the base iron. Therefore, Mg can be contained in amounts up to 0.0050% by weight, with no particular lower limit, but due to steelmaking costs, it can be as low as 0.0001% by weight. That is, Mg can be contained from 0.0001 to 0.0050% by weight. More specifically, it can be contained from 0.0005 to 0.0030% by weight.

[0067] The balance includes Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking process and the manufacturing process of the non-oriented electrical steel sheet; these impurities are well-known in the art and therefore omitted in detail. In one embodiment of the invention, in addition to the aforementioned alloy composition, the addition of elements is not excluded, and various elements may be included without prejudice to the technical concept of the invention. When additional elements are further included, they replace a portion of the Fe in the balance.

[0068] As mentioned above, in one embodiment of the present invention, the alloy composition of the steel plate can be appropriately adjusted, and in the cold-rolled plate annealing process, Al and Si are densely enriched on the surface by adjusting the conditions, so as to simultaneously improve mechanical strength and magnetism.

[0069] Figure 1 The image schematically illustrates a cross-section of a steel plate according to an embodiment of the present invention. Figure 1 As shown, a surface portion 10 may exist within a range of 0.3 to 1 μm from the surface 11 of the steel plate inward. Figure 1 The image shows an example where the surface portion 10 exists on both sides of the steel plate, but the surface portion 10 may also exist only on one side of the steel plate.

[0070] In one embodiment of the present invention, when the elemental content of the surface portion 10 is measured along the thickness direction, the weight ratio of the maximum Si content to the maximum Al content may be 25 or less.

[0071] For the surface portion 10, when an insulating film is present on the surface of the electrical steel plate described below, the area in the internal direction, excluding the insulating film, can be in the range of 0.3 to 1 μm, based on the surface 11 of the steel plate substrate.

[0072] The elemental content in the thickness direction can be measured using a glow discharge spectrometer (GDS). To reduce errors caused by the measurement position, measurements should be taken at least 2 cm intervals and calculated as the average value with three surrounding points. Figure 2 The figure shows an example of Al and Si content in the thickness direction.

[0073] Due to the enrichment of Al and Si, the surface portion 10 contains a greater amount of Al and Si compared to the interior of the steel plate. At this point, by adjusting the diffusion rates of Al and Si, the weight ratio of Al content to Si at the location with the highest Al content can be adjusted (Al / Si weight ratio). 最大(max) / Si 最大Al Adjust to below 25. When the Al content at the site with the highest Al content is at a weight ratio of Al to Si (Al... 最大 / Si 最大Al When the Al content is too high, the Al enrichment layer becomes overly developed, potentially leading to delamination between the base material and the coating. More specifically, within the surface portion 10, the weight ratio of Al content to Si at the site with the highest Al content (Al / Si) is... 最大 / Si 最大Al The value can range from 1.0 to 15.0.

[0074] When the elemental content is measured along the thickness direction of the steel plate on the surface portion 10, the maximum Al content can be 1.8% by weight or more. 最大 When the content of Al is too low, it means that Al enrichment in the surface portion 10 will not occur densely. This will lead to the formation of a large number of fine inclusions inside the steel plate due to the infiltration of N2, O2, etc. from the external air, which may have an adverse effect on the magnetism. More specifically, when the elemental content is measured along the thickness direction of the steel plate in the surface portion 10, the maximum Al content (Al... 最大 It can be 1.8 to 15% by weight.

[0075] Furthermore, when the elemental content is measured along the thickness direction of the steel plate on the surface portion 10, the Si content at the location with the highest Al content (Si) is... 最大Al The Si content can be above 0.5% by weight. 最大AlWhen the Si content is too low, it means that Si enrichment within the surface portion 10 will not occur densely. This can lead to the formation of numerous fine inclusions or precipitates inside the steel plate due to the infiltration of N2, O2, etc. from the external air, which may adversely affect the magnetism. More specifically, when the elemental content is measured along the thickness direction of the steel plate in the surface portion 10, Si (Si... 最大Al The content can be 0.5 to 4% by weight.

[0076] As previously stated, in one embodiment of the present invention, magnetism can be improved by appropriately enriching Si and Al in the surface portion 10. Specifically, in a non-oriented electrical steel sheet according to an embodiment of the present invention, the B50 can be 1.64 or higher. More specifically, in a non-oriented electrical steel sheet according to an embodiment of the present invention, the B50 can be from 1.64 to 1.70T.

[0077] Furthermore, in one embodiment of the present invention, the iron loss (W) of the non-oriented electrical steel sheet is calculated based on a thickness of 0.25 mm. 10 / 400 Iron loss (W) can be below 12.5 W / kg. 10 / 400 The iron loss is the iron loss when a magnetic flux density of 1.0T is excited at a frequency of 400Hz. More specifically, the iron loss (W) of non-oriented electrical steel sheet. 10 / 400 Iron loss (W) can range from 10.0 to 12.3 W / kg. 10 / 800 The iron loss (W) can be below 34.5 W / kg. More specifically, the iron loss (W) 10 / 800 Iron loss (W) can range from 30.0 to 34.5 W / kg. 10 / 800 The iron loss is the result of exciting a magnetic flux density of 1.0T at a frequency of 800Hz.

[0078] A method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention includes: hot rolling a slab to manufacture a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0079] The following is a detailed description of each step.

[0080] First, the slab is hot-rolled.

[0081] The alloy composition of the slab has already been described in the previous section on the alloy composition of non-oriented electrical steel sheets, so it will not be repeated here. The alloy composition does not substantially change during the manufacturing process of non-oriented electrical steel sheets; therefore, the alloy composition of non-oriented electrical steel sheets and slabs is essentially the same.

[0082] Specifically, by weight percent, the slab contains 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 balance including Fe and unavoidable impurities.

[0083] Other additional elements are already described in the alloy composition of non-oriented electrical steel sheets, so a repeating description is omitted.

[0084] Before hot rolling, the slab can be heated. The heating temperature of the slab is not limited, but it can be heated to below 1200℃. If the slab is heated to too high a temperature, precipitates such as AlN and MnS present in the slab will precipitate finely again during hot rolling and annealing after solution treatment, thus inhibiting grain growth and potentially leading to a decrease in magnetic properties.

[0085] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be from 1.0 to 4.5 mm. In the process of manufacturing the hot-rolled sheet, the final rolling temperature can be above 800°C. Specifically, it can be from 850 to 950°C. For hot-rolled sheets, coiling can be performed at a temperature above 600°C. More specifically, the thickness of the hot-rolled sheet can be from 1.5 to 4.3 mm.

[0086] After manufacturing hot-rolled steel sheets, subsequent steps can be performed with residual oxide scale on the sheets. That is, after hot rolling, oxide scale removal processes such as pickling, sandblasting, or surface grinding can be omitted, and subsequent steps can proceed directly. Because cold rolling is performed without pickling, the friction between the rolling mill rolls and the steel sheet increases. Therefore, during rolling, in addition to planar deformation, shear deformation is also applied simultaneously, resulting in the development of specific orientations during recrystallization annealing. In one embodiment of the invention, oxide scale refers to the portion of the steel sheet surface formed by the combination of elements such as Fe, Al, and Si with oxygen, resulting in a phase different from the base material. The presence of oxide scale indicates that at least 1 μm of oxide scale remains on the hot-rolled sheet. Here, oxide scale thickness refers to the sum of the oxide scale thicknesses formed on both surfaces of the steel sheet. If the residual oxide scale thickness is too thin, the effect of the residual oxide scale may not be fully realized. Even if the oxide scale thickness is thicker, the effect will not improve, leading to a decrease in steel sheet yield. More specifically, an oxide scale thickness of 0.1 to 1 μm can remain.

[0087] After manufacturing the hot-rolled sheet, a hot-rolled sheet annealing step may be included. The annealing temperature can be from 950 to 1150°C. The time can be from 10 to 300 seconds. If necessary, the hot-rolled sheet annealing step can be omitted.

[0088] Next, the hot-rolled steel sheet is cold-rolled to produce cold-rolled sheet. At this stage, cold rolling can be performed at a reduction rate of 70% to 90%. If the reduction rate is too low, the deformation energy accumulated within the rolled steel sheet is small, making recrystallization difficult in subsequent annealing processes, resulting in residual rolled microstructure and problems with magnetic flux density and iron loss improvement. On the other hand, if the reduction rate is too high, it hinders the subsequent annealing process from promoting... <111> / / Recrystallization of ND-oriented grains can lead to finer grains, potentially resulting in decreased magnetic flux density and increased iron loss. More specifically, the reduction rate can be 58% to 67%. For the cold rolling step, either a tandem cold rolling mill or a reverse mill can be used. A tandem cold rolling mill uses multiple rolling stands for continuous cold rolling of the steel sheet, while a reverse mill uses 12 or more rolls for discontinuous cold rolling. Furthermore, single-pass cold rolling or two or more passes with intermediate annealing can be performed. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0089] Next, the cold-rolled sheet is annealed.

[0090] The annealing process for cold-rolled steel sheets involves a homogenization temperature of 900 to 1050°C, a hydrogen content of 10 to 35% by volume in the atmosphere, and a dew point of -55 to -15°C.

[0091] If the soaking temperature is too low, the grain size will not grow sufficiently, potentially leading to a deterioration in magnetic properties. If the soaking temperature is too high, the grain size will grow excessively, also potentially leading to a deterioration in magnetic properties. More specifically, the soaking temperature can be between 930 and 1020°C.

[0092] If the hydrogen fraction in the atmosphere is too low, the atmosphere inside the annealing furnace will turn into an oxidizing atmosphere, potentially leading to oxidation problems. If the hydrogen fraction is too high, there is a risk of explosion within the annealing furnace. More specifically, the hydrogen fraction in the atmosphere can be 15 to 30% by volume. Besides hydrogen, the remainder can be oxygen and nitrogen. More specifically, nitrogen can comprise 65 to 90% by volume.

[0093] If the dew point of the atmosphere is too low, a suitable Si / Al enrichment layer will not form, and nitrogen permeation may occur, leading to the formation of fine nitrides. If the dew point of the atmosphere is too high, severe surface oxidation may occur. More specifically, the dew point of the atmosphere can be between -50 and -30°C.

[0094] Annealing time can be 40 to 100 seconds. More specifically, annealing time can be 50 to 90 seconds.

[0095] After annealing, cold-rolled steel sheets can be coated with an insulating film. The insulating film can be processed into organic films, inorganic films, and organic-inorganic composite films, or it can be treated with other insulating film-forming agents.

[0096] In addition, after the cold-rolled sheet annealing step, a stress-relief annealing step can be included, in which the cold-rolled sheet is annealed at 700 to 800°C. The annealing time can be 40 to 120 minutes.

[0097] The present invention will be further described in detail below by way of examples. However, the following examples are merely illustrative and the present invention is not limited to the following examples.

[0098] Example 1 A slab is manufactured containing the components shown in Tables 1 and 2, with the balance being Fe and unavoidable impurities. The slab is heated to 1150°C and hot-rolled at a finishing temperature of 950°C to produce a hot-rolled plate with a thickness of 1.8 mm.

[0099] Then, 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 then annealed for 60 seconds under the conditions shown in Table 2 below.

[0100] GDS analysis was performed on the surface of the manufactured non-oriented electrical steel sheet, and the results are shown in Table 3.

[0101] For magnetic flux density and iron loss, for each specimen, five 60mm wide × 60mm long specimens were cut out, measured using a single sheet tester, and the values ​​were displayed.

[0102] At this time, W 10 / 400 The iron loss W is the result of exciting a magnetic flux density of 1.0T at a frequency of 400Hz. 10 / 800 The iron loss is calculated when a magnetic flux density of 1.0T is excited at a frequency of 800Hz. (B) 50 It is the magnetic flux density induced under a magnetic field of 5000 A / m.

[0103] Table 1 Table 2 Table 3 As shown in Tables 1 to 3, when the steel composition and the annealing conditions of the cold-rolled sheet are properly adjusted, Si and Al are densely enriched in the surface layer, which confirms excellent iron loss and magnetic flux density.

[0104] On the other hand, when the steel composition is not properly adjusted or the annealing conditions of the cold-rolled sheet are not properly adjusted, and a proper surface layer is not formed, it can be confirmed that the iron loss and magnetic flux density are poor.

[0105] This invention can be implemented in various ways and is not limited to the embodiments described herein. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

[0106] [Explanation of reference numerals in the attached figures] 100: Non-oriented electrical steel sheet; 10: Surface part 11: Steel plate surface

Claims

1. A non-oriented electrical steel sheet, wherein, The non-oriented electrical steel sheet, by weight percent, comprises 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 balance including Fe and unavoidable impurities. When the elemental content is measured along the thickness direction of the steel plate in the surface portion ranging from 0.3 to 1 μm from the surface inward, the weight ratio of the maximum Si content to the maximum Al content is less than 25.

2. The non-oriented electrical steel sheet according to claim 1, wherein, When the elemental content is measured along the thickness direction of the steel plate on the surface, the maximum Al content is 1.8% by weight or more.

3. The non-oriented electrical steel sheet according to claim 1, wherein, When the elemental content is measured along the thickness direction of the steel plate on the surface, the Si content at the site with the highest Al content is 0.5% by weight or more.

4. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises S: less than 0.005% by weight and excluding 0%, and satisfies 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 (by weight%) of Sn, Sb, S and B, respectively.

5. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

6. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Bi, Pb, Ge and As, with each or their combined content ranging from 0.005 to 0.200 by weight.

7. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

8. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

9. A method for manufacturing a non-oriented electrical steel sheet, comprising: The step of hot rolling a slab to produce a hot-rolled steel sheet, wherein the slab comprises, by weight %, 1.5 to 5.0% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, 0.001 to 0.08% Sn, 0.001 to 0.08% Sb and 0.0002 to 0.0007% B, with the balance comprising Fe and unavoidable impurities; The steps of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and The cold-rolled sheet annealing step involves annealing the cold-rolled sheet. The annealing step of the cold-rolled sheet is a homogenization temperature of 900 to 1050°C, a hydrogen fraction of 10 to 35% by volume in the atmosphere, and a dew point of -55 to -15°C.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The slab further comprises S: less than 0.005% by weight and excluding 0%, and satisfies 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 (by weight%) of Sn, Sb, S and B, respectively.

11. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The slab further comprises one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; Ti: less than 0.005% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

12. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The slab also contains one or more of Bi, Pb, Ge and As, with each or their combined content ranging from 0.005 to 0.200 by weight.

13. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The slab further comprises one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

14. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The slab further comprises one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

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