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

Abstract

According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance including Fe and unavoidable impurities, and the amount of precipitates per unit area (P) in the surface portion extending from the surface of the steel sheet inward to 1 / 20 of the total thickness. S The amount of precipitates per unit area (P) in the central portion, which accounts for more than 1 / 20 to 1 / 2 of the total thickness. I The ratio is less than 1.2.

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, wherein the magnetic properties are improved by adjusting the dew point and tension during a pre-rolling annealing process to form appropriate precipitates according to the thickness of the steel sheet. 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 recent years, in particular, with the increasing attention paid to environmentally friendly vehicles that replace internal combustion engines with electric motors, the demand for non-oriented electrical steel sheets used as core materials for drive motors has been continuously increasing. Therefore, non-oriented electrical steel sheets with both excellent magnetic properties and strength are required.

[0003] The magnetic properties of non-oriented electrical steel sheets are mainly evaluated using iron loss and magnetic flux density. Iron loss refers to the energy loss that occurs at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. Lower iron loss allows for the manufacture of more energy-efficient motors under the same conditions, while higher magnetic flux density enables motor miniaturization or reduces copper losses. Therefore, using non-oriented electrical steel sheets with low iron loss and high magnetic flux density allows for the manufacture of drive motors with excellent efficiency and torque, thereby improving the driving range and output of environmentally friendly vehicles.

[0004] Depending on the operating conditions of the motor, the properties of the non-oriented electrical steel sheet to be considered will also change. As a standard for evaluating the properties of non-oriented electrical steel sheets used in motors, the iron loss W15 / 50 under a 1.5T magnetic field at a commercial frequency of 50Hz is widely adopted. However, in non-oriented electrical steel sheets with a thickness of less than 0.35mm used in environmentally friendly automotive drive motors, low magnetic fields of 1.0T or less and magnetic properties at high frequencies above 400Hz are often more important. Therefore, in many cases, W15 / 50 is used instead. 10 / 400 Iron loss is used to evaluate the properties of non-oriented electrical steel sheets.

[0005] To improve the magnetic properties of non-oriented electrical steel sheets, alloying elements such as Si, Al, and Mn are commonly added. By adding these elements, the resistivity of the steel increases, reducing eddy current losses and lowering total iron losses. Furthermore, these alloying elements, acting as substitutes dissolved in the iron, exert a strengthening effect, thereby increasing strength. On the other hand, as the amount of Si, Al, and Mn added increases, the magnetic flux density decreases, leading to increased brittleness. If a certain amount is added, cold rolling becomes impossible, hindering industrial production. In particular, for electrical steel sheets, thinner sheets offer better high-frequency iron losses, but the reduced rollability due to brittleness becomes a fatal problem. The maximum known sum of Si, Al, and Mn content for industrial production is approximately 4.5% by weight. Beyond this, by optimizing the content of trace elements, the highest grade of non-oriented electrical steel sheets with excellent magnetic properties and strength can be produced.

[0006] The method of improving magnetic properties by controlling the texture of non-oriented electrical steel sheets is also widely used. Texture control is a method of promoting the development of crystal orientations that are conducive to magnetism and suppressing crystal orientations that are detrimental to magnetism during the deformation, recovery, and recrystallization of materials using various methods. It is known that crystal orientations with {001} planes are conducive to magnetism, while crystal orientations with {111} planes are detrimental to magnetism. Many methods are known to selectively develop several crystal orientations by changing the manufacturing conditions of non-oriented electrical steel sheets.

[0007] When producing non-oriented electrical steel sheets using a double rolling and double annealing process, the {111} / / ND crystal orientation, which is detrimental to magnetism, can be suppressed, while the {001} / / ND crystal orientation, which is beneficial to magnetism, can be strengthened. This process is known to have excellent effects on texture improvement; however, compared to existing single rolling methods, the increased manufacturing cost due to the addition of cold rolling and intermediate annealing processes, coupled with the unstable formation of the surface oxide layer during annealing and cold rolling, leads to problems such as the formation of additional precipitates on the surface or uneven formation of the surface oxide layer, resulting in deterioration of magnetic properties. Therefore, its application in actual mass production is limited. Summary of the Invention

[0008] (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, wherein the magnetic properties are improved by adjusting the dew point and tension during the pre-annealing process before cold rolling to form appropriate precipitates according to the thickness of the steel sheet.

[0009] (II) Technical Solution According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 1.5 to 4.5% Si, 0.1 to 2.0% Al, and 0.1 to 2.0% Mn, with the balance comprising Fe and unavoidable impurities. The number of precipitates per unit area (P) in the surface portion of the steel plate extending from the surface inwards to 1 / 20 of the total thickness. S The amount of precipitates per unit area (P) in the central portion, which accounts for more than 1 / 20 to 1 / 2 of the total thickness. I The ratio is less than 1.2.

[0010] It may contain an oxide layer that extends from the surface inwards, and the thickness of the oxide layer may be 5 to 300 nm.

[0011] In a cross-section including the rolling direction of the steel plate, the maximum length of the oxide layer interruption with an oxide layer thickness of 5 nm or less can be 500 nm or less in the rolling direction.

[0012] In a cross section including the rolling direction of the steel plate, the length of the oxide layer interruption with a thickness of less than 5 nm can be 0.01 to 1000 nm per 10 μm in the rolling direction.

[0013] 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%; S: 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%.

[0014] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or their total content being 0.005 to 0.200 by weight.

[0015] 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%.

[0016] 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%.

[0017] 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 %, 1.5 to 4.5% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, with the balance being Fe and unavoidable impurities; setting the dew point of the steel sheet at -50°C to -10°C, in an atmosphere containing 3 to 30% by volume hydrogen, and applying 0.2 kgf / mm². 2 Up to 3.0 kgf / mm 2 The process includes a pre-annealing step before cold rolling under tension; a step of cold rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0018] 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%; S: 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%.

[0019] The slab may also contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or their combined content ranging from 0.005 to 0.200 by weight.

[0020] 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%.

[0021] 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%.

[0022] After manufacturing hot-rolled steel sheets, subsequent steps can be performed while the hot-rolled steel sheets still have residual oxide scale.

[0023] Before the pre-annealing step of cold rolling, the hot-rolled plate may also be pickled and pre-cold rolled.

[0024] The reduction rate in the pre-cooling rolling step can be 30% to 80%.

[0025] The homogenization temperature of the pre-rolling annealing step can be 800 to 1100°C, and the annealing time can be 1 to 30 minutes.

[0026] The reduction rate in the manufacturing process of cold-rolled sheet can be 40% to 85%.

[0027] The annealing process for cold-rolled steel sheets can be carried out at a homogenization temperature of 850 to 1100°C in a dew point atmosphere below 0°C.

[0028] (III) Beneficial Effects According to an embodiment of the present invention, the non-oriented electrical steel sheet does not suffer from surface degradation, thus further improving magnetic properties.

[0029] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention can help manufacture environmentally friendly automotive motors, high-efficiency home appliance motors, and ultra-high-end electric motors. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the interrupted portion in the cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention. Detailed Implementation

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In addition, unless otherwise specified, % means weight, 1 ppm is 0.0001 weight.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 1.5 to 4.5% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, with the balance being Fe and unavoidable impurities.

[0040] The reasons for the compositional restrictions on non-oriented electrical steel sheets will be described below.

[0041] Si: 1.5 to 4.5% 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, rolling productivity decreases sharply, and a surface oxide layer and oxides that are detrimental to magnetism may form. Therefore, Si can be contained in quantities of 1.5 to 4.5% by weight. More specifically, it can be contained in quantities of 2.0 to 4.3% by weight. More specifically, it can be contained in quantities of 2.5 to 4.2% by weight.

[0042] Al: 0.1 to 2.0% by weight Aluminum (Al) serves to increase the resistivity of materials, reduce iron loss, and improve strength through solid solution strengthening. If too little Al is added, fine nitrides form, making it difficult to achieve the desired magnetic improvement. If too much Al is added, excessive nitride formation leads to magnetic degradation, causing problems in all processes, including steelmaking and continuous casting, and potentially resulting in a significant decrease in productivity. Therefore, Al can be present in quantities from 0.1 to 2.0% by weight. More specifically, it can be present in quantities from 0.2 to 1.6% by weight. More specifically, it can be present in quantities from 0.3 to 1.5% by weight.

[0043] 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%.

[0044] 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%; S: 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%.

[0045] P: less than 0.1% by weight Phosphorus (P) is a grain boundary segregating element that can increase magnetic flux density, but if too much is added, it increases the brittleness of the steel plate and worsens its weldability. More specifically, P can be present in amounts from 0.0001 to 0.0500% by weight.

[0046] 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.

[0047] S: less than 0.005% by weight Sulfur (S) forms fine precipitates of MnS and CuS, which may lead to deterioration of magnetic properties and hot-rolling processability. More specifically, S may contain 0.0001 to 0.0030% by weight.

[0048] 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 0.003% by weight.

[0049] 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.

[0050] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or their total content being 0.005 to 0.200 by weight.

[0051] Sn and Sb The role of tin (Sn) and antimony (Sb) is to segregate at grain boundaries during the initial stage of final recrystallization annealing, thereby suppressing the development of {111} orientation, which leads to magnetic degradation. If too much Sn and Sb are added, it hinders the recovery and growth of coarse extended bands, potentially leading to surface quality deterioration. Therefore, one or more of Sn and Sb can be further added within the aforementioned range. More specifically, Sn can be present in 0.005 to 0.200% by weight, or Sb can be present in 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 increases 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, thereby inhibiting grain growth and potentially leading to a decrease in magnetic flux density and iron loss.

[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 can adversely affect magnetism. More specifically, Ni may contain 0.001 to 0.03% 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%; 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 0.0050 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] B: Less than 0.0050% by weight If excessive boron (B) is added, it may form inclusions in the steel, causing magnetic degradation. Therefore, B can be contained in amounts up to 0.005% by weight, with no particular limit on the lower limit, but due to steelmaking costs, it can be 0.0001% by weight. More specifically, B can be contained in amounts from 0.0001 to 0.0030% by weight.

[0062] 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 be present from 0.0003 to 0.0050% by weight. More specifically, V can be present from 0.0003 to 0.0030% by weight.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] As described above, in one embodiment of the present invention, the magnetism can be improved by appropriately adjusting the alloy composition of the steel plate and forming precipitates of appropriate thickness.

[0070] Figure 1 The diagram shows a cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0071] like Figure 1 As shown, taking a cross-section including the thickness direction (ND direction) as a reference, the non-oriented electrical steel sheet 100 includes a surface portion 20 extending from the surface of the steel sheet inwards to 1 / 20 of the total thickness and a central portion 10 exceeding 1 / 20 to 1 / 2 of the total thickness. For convenience, Figure 1 The diagram shows that surface portion 20 exists on only one side, but surface portion 20 exists on both sides.

[0072] In one embodiment of the present invention, by appropriately adjusting the ratio of precipitates present in the central portion 10 and the surface portion 20, the magnetic properties can be improved without the surface portion of the non-oriented electrical steel sheet deteriorating.

[0073] Specifically, the number of precipitates per unit area of ​​surface portion 20 (P) S ) and the amount of precipitates per unit area of ​​the central part 10 (P) I The ratio of (P) S / P I The value can be below 1.20. If this ratio is too high, it indicates that there are a large number of precipitates on the surface portion 20 or too few precipitates in the central portion 10. When there are a large number of precipitates on the surface portion 20, the magnetic properties of the surface portion 20 deteriorate due to the large number of precipitates, and ultimately the overall magnetic properties of the non-oriented electrical steel sheet 100 deteriorate. When there are too few precipitates in the central portion 10, the grains grow significantly, and the iron loss also increases. More specifically, the number of precipitates per unit area of ​​the surface portion 20 (P... S ) and the amount of precipitates per unit area of ​​the central part 10 (P) I The ratio of (P) S / P I The value can range from 0.90 to 1.19.

[0074] In one embodiment of the invention, precipitates refer to granular particles formed by the aggregation of elemental components present in the electrical steel sheet. More specifically, particles are formed by the combination of one or more elements selected from Si, Al, Mn, Ti, Nb, Cu, and Zr with one or more elements selected from C, N, S, and O. Precipitates can be measured by observing at least 200 μm of the cross-section including the thickness direction (ND direction), more specifically, the plane perpendicular to the rolling direction of the steel sheet (TD plane), using TEM. 2 Region. Precipitates with a particle size smaller than 0.03 μm have little effect on magnetism and are therefore excluded from the proportional calculation. In this case, the particle size refers to the diameter of a virtual circle with an area equal to the area occupied by the precipitate. As described below, an oxide layer 30 may exist on the surface layer of the surface portion 20, but the oxide layer 30 is excluded from the precipitate density calculation (both the measured area and the number of precipitates are excluded).

[0075] More specifically, the density of precipitates on the surface portion 20 can be 0.5 precipitates / μm. 2 Up to 2.5 cells / μm 2 The density of precipitates in the central part 10 can be 0.3 particles / μm. 2 Up to 2.0 cells / μm 2 .

[0076] Figure 2 The diagram shows a cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0077] like Figure 2 As shown, the non-oriented electrical steel sheet 100 includes an oxide layer 30 that extends from the surface inwards.

[0078] The oxide layer 30 can be formed by oxygen penetrating into the steel plate during the manufacturing process of electrical steel plate.

[0079] The oxide layer 30 is defined as the portion with an oxygen content of 0.01% by weight or more extending from the surface of the steel plate inwards. For the detection and thickness of the oxide layer 30, after processing the TD surface of the specimen with FIB, observation using TEM and EDS reveals that the portion with an oxygen content of 0.01% by weight or more is considered the oxide layer. At this point, the steel plate specimen does not have an insulating coating, or if an insulating coating has formed, a specimen with the insulating coating removed can be used. To reduce measurement errors based on location, the specimen can be measured at least 20 times in the RD direction with a minimum length of 200 μm and at intervals of 1 μm or more in the TD direction, and the average value is taken.

[0080] The thickness of oxide layer 30 can be from 5 to 300 nm. If the thickness of oxide layer 30 is too thin, Al concentration in oxide layer 30 cannot be adequately achieved, and the aforementioned AlN suppression effect may not be fully realized. If the thickness of oxide layer 30 is too thick, a large amount of oxygen will penetrate into the steel plate, which may lead to a deterioration in magnetic properties. More specifically, the thickness of oxide layer 30 can be from 10 to 290 nm. The thickness of oxide layer 30 can be the average thickness of oxide layer 30 in the measured sample.

[0081] like Figure 2 As shown, in a cross-section including the rolling direction of the steel sheet, there exists an oxide layer interruption with a thickness of 5 nm or less. The maximum length of this oxide layer interruption with a thickness of 5 nm or less in the rolling direction can be 500 nm or less. When an interruption exceeding 500 nm exists, during the cold-rolled sheet annealing step, the atmosphere gas can cause further formation of oxides or nitrides, potentially having a significant negative impact on the magnetism. For measurement reference, measurements can be performed at a distance of 200 μm or more in the rolling direction. More specifically, the maximum length of the oxide layer interruption with a thickness of 5 nm or less can be 50 to 490 nm in the rolling direction.

[0082] like Figure 2 As shown, in a cross-section including the steel plate in the rolling direction, there exists an oxide layer interruption with a thickness of less than 5 nm. The length of this interruption (DC) L This can be 0.01 to 1000 nm per 10 μm in the rolling direction. For example... Figure 2 As shown, multiple oxide layer interruptions may exist in the sample. In this case, the sum of the lengths of all oxide layer interruptions falls within the aforementioned range. Although the absence of almost no oxide layer interruptions is ideal in terms of magnetism, at 0.2 kgf / mm... 2 Up to 3.0 kgf / mm 2 The oxide layer is inevitably disrupted during annealing under tension and final cold rolling, leading to the formation of interruptions. Therefore, aside from the ideal case of no oxide layer interruptions, the shorter the interruption length, the more advantageous it is in terms of magnetism. Conversely, if the oxide layer interruption is too long, further oxidation and nitriding occur at the interruption site, similarly increasing iron loss, which can cause problems. More specifically, the length of the interruption (DC) L The length of the interruption (DC) can range from 1 to 900 nm per 10 μm in the rolling direction. More specifically, the length of the interruption (DC) L The length of the interruption (DC) can be 100 to 800 nm per 10 μm in the rolling direction. More specifically, the length of the interruption (DC) L The length of the interruption can be 300 to 750 nm per 10 μm in the rolling direction. The method for measuring and determining the interruption can be the same as that for measuring and determining the oxide layer. When there are multiple interruptions, they can be represented by the sum of the lengths of the multiple interruptions.

[0083] The oxide layer 30 and the oxide layer interruption can be appropriately formed by adjusting the conditions in the pre-annealing process before cold rolling. A more specific method will be described below in connection with the manufacturing method of non-oriented electrical steel sheets.

[0084] Due to the surface concentration of Al, the oxide layer 30 can contain more than 50% by weight of Al. More specifically, Al can contain 50 to 70% by weight. Apart from Al and O, the remaining alloy composition is the same as that of the aforementioned non-oriented electrical steel sheet. Compared to the overall thickness of the non-oriented electrical steel sheet 100, the oxide layer 30 is very thin, and therefore has no substantial impact on the alloy composition of the non-oriented electrical steel sheet 100.

[0085] As described above, in one embodiment of the present invention, by appropriately controlling the steel composition and the thickness and interruption ratio of the surface oxide layer within a certain range, precipitates are appropriately formed in different locations, thereby improving magnetism. Generally, as the steel plate thickness decreases, the iron loss tends to improve, and the iron loss of different steel plate thicknesses described in the present invention is achieved through the following formula.

[0086] Iron loss (W) 10 / 400 ≤9.8×EXP(1.5×t), where t: steel plate thickness (mm) Iron loss (W) 10 / 400 ) is the iron loss when a magnetic flux density of 1.0T is excited at a frequency of 400Hz. EXP represents the natural constant (e).

[0087] Specifically, based on a thickness of 0.25 mm, the iron loss (W) of the non-oriented electrical steel sheet of the present invention is... 10 / 400 The magnetic flux density (B) can be below 14.0 W / kg. 50 The magnetic flux density (B) can be above 1.63T. 50 ) refers to the magnetic flux density induced under a magnetic field of 5000 A / m. More specifically, it refers to the iron loss (W) of non-oriented electrical steel sheets. 10 / 400 The flux density (B50) can be 10.0 to 14.0 W / kg.

[0088] A method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention includes: a step of hot rolling a slab to manufacture a hot-rolled steel sheet; a pre-rolling annealing step of annealing the steel sheet; a step of cold rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0089] The following describes each step in detail.

[0090] First, the slab is hot-rolled.

[0091] 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.

[0092] Specifically, by weight percent, the slab contains Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance including Fe and unavoidable impurities.

[0093] Other additional elements are already described in the alloy composition of non-oriented electrical steel sheets, so a repeating description is omitted.

[0094] 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.

[0095] 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 800 to 1000°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.

[0096] After manufacturing hot-rolled steel sheets, subsequent steps can be performed with residual oxide scale remaining on the hot-rolled steel 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 with the pickling process omitted, 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, leading to 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. Residual oxide scale refers to oxide scale with a thickness of at least 1 μm remaining on the hot-rolled sheet. Here, oxide scale thickness refers to the sum of the oxide scale thicknesses generated 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, resulting in a decrease in steel sheet yield. More specifically, residual oxide scale with a thickness of 0.1 to 1 μm is permissible.

[0097] In one embodiment of the present invention, after manufacturing the hot-rolled steel sheet, a pre-cold rolling annealing step for annealing the hot-rolled steel sheet can be performed directly. Alternatively, after pre-cooling the hot-rolled steel sheet, a pre-cold rolling annealing step for annealing the pre-cooled rolled sheet can be performed.

[0098] Pre-cooling rolling differs from cold rolling as described below because it is the first rolling step in a process where the material is rolled to an intermediate thickness rather than the final product thickness, then intermediate annealing is performed, followed by cold rolling to the final product thickness.

[0099] For pre-cooling rolling, a reduction rate of 30% to 80% can be used to improve the final cold-rolled productivity and grain size in the final product sheet. Alternatively, if rolling productivity is not a concern, the invention can also be performed in a reversible mill. The pre-cooled rolled sheet can have a thickness of 0.3 to 1.5 mm. More specifically, the reduction rate can be 60% to 75% and the thickness can be 0.6% to 1.3 mm.

[0100] The reduction rate in pre-cooling rolling can be calculated as (thickness of steel plate before rolling – thickness of steel plate after rolling) / thickness of steel plate before rolling. If the reduction rate in the pre-cooling rolling step is too low, the rolling load during the final cold rolling will increase, thus reducing productivity. An increase in the final reduction rate may promote finer grains. <111> The issue of / ND orientation recrystallization. On the other hand, if the reduction rate is too high, the cold rolling load increases, and the possibility of sheet breakage also increases.

[0101] The pre-cooling rolling step can be performed at a temperature between 60 and 300°C. At this temperature, the temperature of the steel sheet naturally rises due to friction between the steel sheet and the rolls, or it can be increased by external heating. If the temperature is too low, the rolling load will increase significantly, causing the steel sheet to slide between the rolls instead of being rolled, potentially leading to problems such as twisting. If the temperature is too high, a thick oxide layer will form on the surface of the steel sheet, deteriorating its magnetic properties and potentially causing problems such as rolling oil ignition. More specifically, it is preferable to perform the process at a temperature between 70 and 250°C. The aforementioned temperatures refer to the temperature of the steel sheet.

[0102] As mentioned above, the pre-cooling rolling step can be omitted if necessary.

[0103] Next, in the pre-cold rolling annealing step, the hot-rolled steel sheet or pre-cooled rolled sheet is annealed. In one embodiment of the invention, by adjusting the dew point and tension in the pre-cold rolling annealing step, an oxide layer 30 can be appropriately formed.

[0104] Simultaneously, in the pre-rolling annealing step, the atmosphere is a mixture of hydrogen and nitrogen gas containing at least 3 to 30% by volume of hydrogen. If the hydrogen content is low, an oxide layer will further form during heat treatment, remaining in the final product and potentially contributing to increased iron loss. While higher hydrogen content is better, excessive use increases the process load, thus increasing processing costs. Therefore, annealing can be carried out in an atmosphere with a hydrogen content of 3 to 30% by volume. More specifically, hydrogen can be present in the atmosphere at 5 to 25% by volume, with the remainder being nitrogen.

[0105] The dew point can be between -50°C and -10°C. If the dew point is too low, nitriding caused by nitrogen in the atmosphere occurs, promoting the formation of nitrides in the steel plate, which may increase iron loss. If the dew point is too high, further surface oxidation occurs, accompanied by pickling problems, leaving a residual oxide layer on the surface, which may also lead to increased iron loss. More specifically, the dew point can be between -50°C and -20°C. More specifically, the dew point can be the dew point relative to the atmosphere during the soaking process.

[0106] Additionally, 0.2 kgf / mm can be applied. 2 Up to 3.0 kgf / mm 2 The tension is crucial. If the tension is too low, the steel plate will come into contact with the furnace interior, causing scratches on the surface and potentially leading to surface quality issues. If the tension is too high, the steel plate will deform at high temperatures during annealing, potentially causing problems with magnetic flux density and iron loss. More specifically, the tension can be from 0.3 to 2.5 kgf / mm². 2 More specifically, tension can be measured at the outlet side of the annealing furnace and can be measured using a tension meter.

[0107] In the pre-rolling annealing step, the soaking temperature can be between 800 and 1100°C. If the annealing temperature is too low, recrystallized structures will not form or will grow finely, resulting in a small increase in magnetic flux density. Conversely, if the annealing temperature is too high, the magnetic properties will decrease, and the rolling operability will deteriorate due to plate deformation. More specifically, the temperature range can be between 830 and 1080°C. The soaking time can be between 1 minute and 30 minutes.

[0108] The aforementioned pre-cold rolling annealing can be performed in a vertical or horizontal continuous annealing apparatus. If surface oxide removal is omitted after hot rolling, it can be performed after pre-cold rolling annealing. It is known that excessive surface oxide residue in the final manufactured non-oriented electrical steel sheet can impair magnetism. The inventors investigated the effect of residual surface oxide on magnetic properties and confirmed that there is almost no deterioration in magnetic properties when the residue is below 300 nm in the final product sheet. Furthermore, even if the surface oxide is completely removed before cold rolling, a surface oxide layer of approximately 3 nm will form during final annealing due to the influence of the atmospheric gas.

[0109] On the other hand, when cold rolling is performed with residual oxide scale, the oxide scale is pressed into the surface and exists therein. Furthermore, the oxide scale exists in segments due to rolling, and preferably, the surface length of the oxide scale without such segments is at most 500 nm or less. If the interruption length is 500 nm or more, nitrogen (N2) from the atmosphere gas in the final annealing step will penetrate into the interrupted areas and form nitrides, potentially leading to increased iron loss. Therefore, when the surface oxide layer in the final product sheet is at least 300 nm long, and the interruption length of the surface oxide layer is at most 500 nm or less, excellent magnetic properties can be ensured, as described in this invention.

[0110] In addition, during the pickling process preceding the final cold rolling step, the surface oxide layer is completely removed, or may be less than 300 nm thick. Pickling refers not only to acid immersion but also to all methods of physical and chemical peeling. Pickling methods can include acid immersion, sandblasting, or surface grinding.

[0111] Next, the annealed steel sheet is cold-rolled to produce cold-rolled sheet. At this stage, cold rolling can be performed at a reduction rate of 40% to 85%. If the reduction rate is too low, the deformation energy accumulated in the rolled steel sheet is small, making recrystallization difficult in subsequent annealing processes, resulting in residual rolled microstructure. This may cause problems with improving magnetic flux density and iron loss. On the other hand, if the reduction rate is too high, it will hinder 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. The reduction rate can be 60% to 75%. For the cold rolling step, either a tandem cold rolling mill or a reverse mill can be used. A tandem cold rolling mill utilizes multiple rolling stands for continuous cold rolling of the steel sheet, while a reverse mill uses 12 or more rolls for discontinuous cold rolling. The final rolled thickness can range from 0.1 mm to 0.35 mm.

[0112] Next, the cold-rolled sheet is annealed. The annealing process for cold-rolled sheet can be carried out in a dew point atmosphere below 0°C. More specifically, annealing can be carried out in a dew point temperature atmosphere ranging from -50°C to -10°C.

[0113] For the annealing process of cold-rolled steel sheets, annealing can be carried out at a soaking temperature of 850 to 1100°C. If the soaking temperature is too low, the grains cannot grow sufficiently, hysteresis losses increase, and iron loss deterioration may occur. If the soaking temperature is too high, eddy current losses increase, and magnetic flux density may drop sharply. More specifically, annealing can be carried out at a temperature of 900 to 1050°C. Soaking can be performed for 10 to 300 seconds.

[0114] During the annealing process of cold-rolled sheet, all (i.e., more than 99%) of the processed structures formed in the cold rolling step can recrystallize.

[0115] After annealing, cold-rolled steel sheets can be coated with an insulating film. This 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.

[0116] 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.

[0117] Example A slab was manufactured, containing 3.4% Si, 0.8% Al, 1.2% Mn, and other impurities by weight. The slab was heated to 1150°C and hot-rolled at a finishing temperature of 900°C to produce a hot-rolled sheet with a thickness of 2.3 mm. The hot-rolled sheet was pickled, then pre-rolled to a thickness of 0.8 mm, and subjected to pre-cold rolling annealing under the temperature, dew point, hydrogen fraction, and tension conditions specified in Table 1. After cold rolling to a thickness of 0.25 mm, a final recrystallization annealing was performed for 100 seconds at a dew point of -50°C and a soaking temperature of 1000°C.

[0118] The main characteristic values ​​of each sample after the manufacturing process are shown in Table 2.

[0119] For oxide layer thickness, the thickness of the parts containing more than 5% by weight of Al and more than 3% by weight of O on the surface of the base material after the TD surface of the sample is processed by FIB and observed by TEM is measured more than 20 times at intervals of at least 1 μm, and the average value is recorded.

[0120] The maximum length of the oxide layer interruption was recorded as the maximum value of the following measurement: when the aluminum oxide layer is observed by TEM at a depth of 200 μm or more in the rolling direction, the length of the part where the oxide layer is interrupted and the base material is exposed is measured in the rolling direction.

[0121] In addition, it also indicates the total length of the oxide layer interruption within every 10 μm in the rolling direction.

[0122] For the analysis of precipitates of different thicknesses in steel plates, TEM measurements were used to determine the 200 μm thickness of the surface and central portions. 2 The proportion of precipitates with a diameter of 0.03 μm or more in the region.

[0123] For magnetic properties such as magnetic flux density and iron loss, five 60mm wide × 60mm long samples were cut from each specimen. A single sheet tester was used to measure the values ​​in the rolling direction and perpendicular to the rolling direction, and the average values ​​were recorded. Here, W10 / 400 refers to the iron loss when a magnetic flux density of 1.0T is excited at a frequency of 400Hz, and B50 refers to the magnetic flux density induced in the steel plate under a magnetic field of 5000A / m.

[0124] Table 1 Table 2 As shown in Tables 1 and 2, the invention example that forms precipitates and oxide layers of appropriate thickness by appropriately adjusting the steel composition and process conditions results in excellent iron loss and magnetic flux density.

[0125] On the other hand, if the steel composition and process conditions are not properly adjusted, and precipitates and oxide layers are not formed at the appropriate thickness, the iron loss and magnetic flux density will be poor.

[0126] 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.

[0127] [Explanation of reference numerals in the attached figures] 100: Non-oriented electrical steel sheet; 10: Surface part 20: Central part; 30: Oxide layer

Claims

1. A non-oriented electrical steel sheet, wherein, By weight percent, the non-oriented electrical steel sheet comprises Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance including Fe and unavoidable impurities. The number of precipitates per unit area (P) in the surface portion of the steel plate extending from the surface inwards to 1 / 20 of the total thickness. S The amount of precipitates per unit area (P) in the central portion, which accounts for more than 1 / 20 to 1 / 2 of the total thickness. I The ratio is less than 1.

2.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet includes an oxide layer that extends from the surface inwards. The thickness of the oxide layer is 5 to 300 nm.

3. The non-oriented electrical steel sheet according to claim 1, wherein, In a cross-section including the rolling direction of the steel plate, the maximum length of the oxide layer interruption with an oxide layer thickness of 5 nm or less is 500 nm or less in the rolling direction.

4. The non-oriented electrical steel sheet according to claim 1, wherein, In a cross section including the rolling direction of the steel plate, the total length of the oxide layer interruption with an oxide layer thickness of less than 5 nm is 0.01 to 1000 nm per 10 μm in the rolling direction.

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%; S: 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 Sn, Sb, 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 %: Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance comprising Fe and unavoidable impurities; The steel plate was subjected to a dew point of -50°C to -10°C, an atmosphere containing 3 to 30% hydrogen by volume, and an application of 0.2 kgf / mm. 2 Up to 3.0 kgf / mm 2 The pre-annealing step of cold rolling is performed under tension; The steps of cold rolling annealed steel sheets to manufacture cold-rolled sheets; and The annealing step for the cold-rolled sheet.

10. 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%; S: 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%.

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

12. 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%.

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: 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%.

14. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, After the hot-rolled steel sheet is manufactured, subsequent steps are performed while the hot-rolled steel sheet still has residual oxide scale.

15. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, Prior to the pre-annealing step of cold rolling, a step of pre-cold rolling the hot-rolled plate is also included.

16. The method for manufacturing non-oriented electrical steel sheet according to claim 15, wherein, The reduction rate in the pre-cooling rolling step is 30% to 80%.

17. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The homogenization temperature of the pre-annealing step before cold rolling is 800 to 1100°C.

18. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The reduction rate in the process of manufacturing the cold-rolled sheet is 40% to 85%.

19. The method for manufacturing non-oriented electrical steel sheet according to claim 9, wherein, The annealing step of the cold-rolled sheet is carried out in a dew point atmosphere below 0°C at a homogenization temperature of 850 to 1100°C.

Images