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

Abstract

The non-oriented electrical steel sheet according to one embodiment of the present application contains, in weight %, Si: 1.5 to 5.0 %, Al: 0.1 to 2.0 %, Mn: 0.1 to 2.0 %, the balance containing Fe and inevitable impurities, the maximum value of an orientation distribution function (ODF) occurring in a 2=45° section of Euler space is 3.0 or less, the non-oriented electrical steel sheet contains a surface portion and a center portion to a depth of 50 µm in a direction from the surface of the steel sheet toward the inside, and the ratio of the average grain size in the surface portion to the average grain size in the center portion is 0.4 to 0.6.

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 texture is uniformly developed in different orientations by adjusting the diameter of the work rolls and the coefficient of friction between the work rolls and the steel sheet during cold rolling, thereby minimizing anisotropy. 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 enhance 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. Especially for electrical steel sheets, thinner sheets offer better high-frequency iron losses, while the reduced rollability due to brittleness becomes a fatal problem.

[0006] Methods to improve magnetic properties by controlling the texture of non-oriented electrical steel sheets are also known. Texture control involves promoting the development of crystal orientations favorable to magnetism and suppressing crystal orientations unfavorable to magnetism during the deformation, recovery, and recrystallization of materials using various methods. It is known that crystal orientations with {001} planes are favorable to magnetism, while crystal orientations with {111} planes are unfavorable 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 and {110} / / ND crystal orientations, which are beneficial to magnetism, can be strengthened. This process is known to have excellent effects on texture improvement; however, the added intermediate annealing during cold rolling increases manufacturing costs. Furthermore, although the magnetic properties in the rolling direction are improved due to the developed texture, the magnetic properties deteriorate in the direction rotating 45 to 60° from the rolling direction. In many cases, when used in rotating machinery, the magnetic properties are hardly improved, limiting practical applications. 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 texture is uniformly developed in different orientations by adjusting the diameter of the work rolls and the coefficient of friction between the work rolls and the steel sheet during cold rolling, thereby minimizing anisotropy.

[0009] (II) Technical Solution According to one embodiment of the present invention, 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%, with the balance comprising Fe and unavoidable impurities, in Euler space. The maximum value of the orientation distribution function (ODF) appearing in the 2=45° section is below 3.0.

[0010] According to one embodiment of the present invention, a non-oriented electrical steel sheet includes a surface portion and a central portion extending from the surface of the steel sheet to a depth of 50 μm, wherein the ratio of the average grain size in the surface portion to the average grain size in the central portion is 0.4 to 0.6.

[0011] 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%.

[0012] 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.

[0013] 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%.

[0014] 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%.

[0015] According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 1.

[0016] [Formula 1] B 50L -B 50(55°) ≤0.05T In Equation 1, B 50L The magnetic flux density B measured in the rolling direction 50 B 50(55°) The magnetic flux density B is measured in a direction at a 55-degree angle to the rolling direction. 50 .

[0017] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: a step of hot rolling a slab to manufacture 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, with the balance being Fe and unavoidable impurities; a step of pre-cooling the hot-rolled steel sheet; a first annealing step of annealing the pre-cooled steel sheet; a step of cold rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a second annealing step of annealing the cold-rolled sheet.

[0018] In the process of manufacturing cold-rolled steel sheets, the product of the diameter (mm) of the working roll and the coefficient of friction (μ) between the working roll and the steel sheet in at least one pass can be between 10 and 30.

[0019] 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%.

[0020] 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.

[0021] 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%.

[0022] 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%.

[0023] After manufacturing hot-rolled steel sheets, subsequent steps can be performed while the hot-rolled steel sheets still have residual oxide scale.

[0024] After the first annealing step, the average grain size of the steel plate can be 50 to 120 μm.

[0025] The reduction rate in the manufacturing process of cold-rolled sheet can be 20% to 55%.

[0026] The soaking temperature in the second annealing step can be between 750 and 1150°C.

[0027] (III) Beneficial Effects According to one embodiment of the present invention, the non-oriented electrical steel sheet has excellent magnetic properties due to its uniform and well-developed texture.

[0028] Furthermore, according to one embodiment of the present invention, non-oriented electrical steel sheet helps to improve the performance of environmentally friendly automotive drive motors.

[0029] With its high magnetic anisotropy, it can achieve high torque when used in the manufacture of automobile motors. Attached Figure Description

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

[0031] Figure 2 This is a graph showing the orientation distribution function (ODF) results of the non-oriented electrical steel sheet manufactured in Example B6. 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. The word "comprising" as used in the specification can specifically refer to a feature, domain, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, and / or components.

[0034] If one part is described as being on top of another part, then other parts may exist directly on top of or in between the other part. If one part is described as being directly on top of another part, then no other parts exist 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 5.0% 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: 1.50 to 5.00% 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 drops sharply, and surface oxide layers and oxides that are detrimental to magnetism may form. Therefore, Si can be present in quantities of 1.50 to 5.00% by weight. More specifically, it can be present in quantities of 2.00 to 4.50% by weight. More specifically, it can be present in quantities of 2.50 to 4.30% by weight.

[0042] 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 from 0.1 to 2.0% by weight. More specifically, it can be contained in quantities from 0.15 to 1.7% by weight. More specifically, it can be contained in quantities from 0.2 to 1.6% 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 0.15 to 1.7 wt%. More specifically, it can be present in quantities from 0.2 to 1.6 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) 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.

[0046] C: less than 0.0050% 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 0.0035% by weight. More specifically, C may contain 0.0010 to 0.0030% by weight.

[0047] S: less than 0.0050% by weight Sulfur (S) forms fine precipitates of MnS and CuS, which may lead to deterioration of magnetic properties and hot workability. More specifically, S may contain 0.0001 to 0.0050% by weight. More specifically, S may contain 0.0005 to 0.0045% by weight.

[0048] Ti: less than 0.0050% by weight Titanium (Ti) exhibits a strong tendency to form precipitates in steel, and it can form fine carbides, nitrides, or sulfides within the base metal, thereby inhibiting grain growth and domain wall movement, potentially leading to iron loss degradation. More specifically, Ti may comprise 0.0001 to 0.0050% by weight. More specifically, Ti may comprise 0.0005 to 0.0030% by weight.

[0049] N: less than 0.0050% 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 0.0050% by weight. More specifically, N may contain 0.0005 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 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. However, 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 reduced rollability. Specifically, Sn may further comprise 0.005 to 0.200% by weight. More specifically, it may further comprise 0.010 to 0.080% by weight.

[0052] Sb 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 further added to enhance magnetism. However, 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 reduced rollability. Specifically, Sb may further comprise 0.005 to 0.200% by weight. More specifically, it may further comprise 0.010 to 0.080% by weight.

[0053] 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.

[0054] 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%.

[0055] 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.

[0056] 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.

[0057] 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 0.03% by weight.

[0058] 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.

[0059] 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.

[0060] 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%.

[0061] Mo: less than 0.030% by weight If excessive molybdenum (Mo) is added, it can suppress the segregation of segregating elements, potentially reducing the texturing improvement effect. Therefore, Mo can be contained in amounts up to 0.03 wt%, with no particular lower limit, but since it improves texture through surface and grain boundary segregation, it can be contained in amounts of 0.001 wt% or more. More specifically, Mo can be contained from 0.001 to 0.010 wt%. More specifically, Mo can be contained from 0.005 to 0.010 wt%.

[0062] B: Less than 0.0050% by weight If excessive boron (B) is added, inclusions and other impurities will form in the steel, potentially leading to deterioration of its magnetic properties. Therefore, B can be contained in amounts up to 0.005% by weight, with no particular lower limit, but due to steelmaking costs, it can be as low as 0.0001% by weight. More specifically, B can be contained from 0.0001 to 0.0030% by weight.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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 below 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] As mentioned above, in one embodiment of the present invention, the alloy composition of the steel plate can be appropriately adjusted. In the process of performing pre-cold rolling and cold rolling, by adjusting the diameter of the work roll and the friction coefficient between the work roll and the steel plate during cold rolling, the texture can be made to develop uniformly in different orientations, so as to minimize magnetic anisotropy.

[0071] Specifically, according to an embodiment of the present invention, the non-oriented electrical steel sheet has an Euler space of The maximum value of the orientation distribution function (ODF) appearing in the 2=45° section can be below 3.0.

[0072] The orientation distribution function (ODF) is a method for quantitatively analyzing the texture distribution in steel sheets. It can quantify the degree of distribution of a specific crystal orientation in the steel sheet. Orientation intensity refers to the relative strength of a specific crystal orientation compared to random texture.

[0073] Euler space is the space used to describe crystal orientation. 1, Φ, 2. A three-dimensional space formed by three corners, in which The 2=45° section is the key area to observe because it is easy to grasp the well-developed texture in steel with symmetrical deformation.

[0074] In one embodiment of the invention, the orientation distribution function (ODF) is measured on the rolling vertical plane (TD plane), and the measurement area is at least 5 mm × 5 mm. To reduce errors caused by the measurement position, data needs to be measured over a sufficiently wide area, and more than 20 samples need to be measured. The data can be combined for a single calculation.

[0075] As a measurement method, an EBSD mounted on the SEM can be used, and analysis can be performed using OIM analysis software. The tolerance angle relative to the orientation can be set to 15°.

[0076] A maximum value of 3.0 or less for the Orientation Distribution Function (ODF) indicates that textures with different orientations are evenly developed, rather than textures with only a specific orientation being developed. More specifically, the maximum value of the Orientation Distribution Function (ODF) can be between 1.5 and 2.5.

[0077] Figure 1 The image schematically illustrates a cross-section of a non-oriented electrical steel sheet 100 according to an embodiment of the present invention. Figure 1 As shown, a non-oriented electrical steel sheet 100 according to an embodiment of the present invention includes a surface portion 20 and a central portion 10 extending from the surface of the steel sheet to a depth of 50 μm. For example... Figure 1 As shown, the surface portion 20 exists on both surfaces of the steel plate, and the center portion 10 may be located between the two surface portions 20.

[0078] In one embodiment of the present invention, the ratio of the average grain size in the surface portion 20 to the average grain size in the central portion 10 (surface portion / central portion) can be 0.40 to 0.60. When the grains in the surface portion 20 are smaller than those in the central portion 10, the hysteresis loss in the surface portion increases, the permeability decreases, and the magnetic properties may deteriorate. When the grains in the surface portion 20 are larger than those in the central portion 10, the eddy current loss in the surface portion increases, and textures that are unfavorable to magnetization may develop. More specifically, the ratio of the average grain size in the surface portion 20 to the average grain size in the central portion 10 (surface portion / central portion) can be 0.45 to 0.57. For the grain size, assuming there is a virtual circle with the same area as the grain, the grain size can be calculated from the diameter of the circle. Measurements are performed with the rolling vertical plane (TD plane) as a reference, and the average area of ​​each grain is calculated by counting the number of grains in the areas of the surface portion 20 and the central portion 10. The grain size can then be calculated from a circle having that area. When the inner surface portion 20 of the steel plate exists on two surfaces, the average grain size of the upper surface portion and the lower surface portion can be taken.

[0079] As mentioned above, in one embodiment of the present invention, magnetic anisotropy can be minimized by making the textures of different orientations uniformly developed. Specifically, the non-oriented electrical steel sheet according to an embodiment of the present invention can satisfy the following formula 1.

[0080] [Formula 1] B 50L -B 50(55°) ≤0.05T In Equation 1, B 50L The magnetic flux density B measured in the rolling direction 50 B 50(55°) The magnetic flux density B is measured in a direction at a 55-degree angle to the rolling direction. 50 .

[0081] Equation 1 represents the difference in magnetic flux density along the rolling direction (RD direction) and in a direction at a 55-degree angle to the rolling direction. The smaller this difference, the smaller the magnetic anisotropy. Specifically, the value on the left side of Equation 1 can be from 0.01 to 0.03 T.

[0082] In one embodiment of the present invention, the iron loss (W) of non-oriented electrical steel sheet is... 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 The value can be 10.0 to 12.0 W / kg. In one embodiment of the invention, the iron loss can be expressed based on a thickness of 0.25 mm.

[0083] 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; pre-cooling the hot-rolled steel sheet; a first annealing step of annealing the pre-cooled steel sheet; cold rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a second annealing step of annealing the cold-rolled sheet.

[0084] The following describes each step in detail.

[0085] First, the slab is hot-rolled.

[0086] 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.

[0087] 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%, with the balance including Fe and unavoidable impurities.

[0088] Other additional elements are already described in the alloy composition of non-oriented electrical steel sheets, so a repeating description is omitted.

[0089] 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.

[0090] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 1.50 to 2.50 mm. If the hot-rolled sheet is too thick, the coarse elongated microstructure at the center 10 of the final non-oriented electrical steel sheet will be strongly developed, potentially leading to a well-developed texture with a specific orientation. Furthermore, if the hot-rolled sheet is too thin, insufficiently grown fine grains will remain on the surface 20 of the final non-oriented electrical steel sheet, potentially worsening iron loss. More specifically, the thickness of the hot-rolled sheet can be 1.60 to 2.30 mm.

[0091] In the manufacturing process of hot-rolled sheets, the final rolling temperature can be above 800°C. Specifically, it can be between 870 and 950°C. Hot-rolled sheets can be coiled at temperatures above 600°C.

[0092] 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 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, 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. Furthermore, pre-cooling rolling can be performed directly after hot rolling without external heating of the steel sheet. In other words, the annealing of hot-rolled steel plates can be omitted.

[0093] Next, the hot-rolled steel sheet undergoes pre-cooling rolling. Pre-cooling rolling differs from the cold rolling described below because it is the first rolling step in the following process: rolling to an intermediate thickness rather than the final product thickness, followed by intermediate annealing, and then cold rolling to the final product thickness.

[0094] For pre-cooling rolling, a reduction rate of 40% 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, pre-cooling rolling can also be performed in a reversible mill. The pre-cooled rolled sheet can have a thickness of 0.30 to 1.50 mm. More specifically, the reduction rate can be 50% to 78% and the thickness can be 0.40 to 1.00 mm.

[0095] 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> There is the issue of 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.

[0096] Next, in the first annealing step, the pre-cooled rolled steel sheet is annealed.

[0097] In one embodiment of the invention, after the first annealing step, by appropriately adjusting the average grain size within the steel sheet, the texture with different orientations can be made uniformly developed. Specifically, after the first annealing step, the average grain size of the steel sheet can be 50 to 120 μm. If the average grain size is too small, due to the excessively high grain boundary fraction, grains with the {111} / / ND orientation will develop during the second annealing process after the second cold rolling, potentially leading to a deterioration in magnetic properties. If the average grain size is too large, the development of the {111} / / ND orientation will be suppressed, but the cubic orientation will develop, which may result in a deterioration in magnetism at 55°. More specifically, after the first annealing step, the average grain size of the steel sheet can be 60 to 110 μm.

[0098] The first annealing step can be performed by homogenizing at a temperature of 750 to 1150°C for 5 to 20 seconds. If the homogenization temperature is too low, the coarse microstructure in the center will not be fully restored, resulting in a poor final product. <100> Orientation will not be fully developed, and magnetism may deteriorate. If the homogenization temperature is too high, fine precipitates will form on the surface, resulting in a final product with {011}. <100> The orientation will not be fully developed, and the magnetism may deteriorate. More specifically, the first annealing step can be carried out at a temperature of 850 to 1050°C for homogenization.

[0099] If the soaking time is too short, the fine microstructure on the surface will not recrystallize sufficiently, and the surface grains of the final product may be too small relative to the central grains. If the soaking time is too long, the surface grains may overgrow. More specifically, soaking time can be 7 to 17 seconds.

[0100] Returning to the description of the manufacturing method of non-oriented electrical steel sheet, after the first annealing step, the annealed steel sheet is cold rolled to manufacture cold-rolled sheet.

[0101] In one embodiment of the present invention, the product of the diameter (mm) of the working roll in at least one pass and the coefficient of friction (μ) between the working roll and the steel plate can be from 10.0 to 30.0.

[0102] In one embodiment of the invention, the diameter of the work roll and the coefficient of friction during cold rolling are key factors in optimizing the diameter difference between the central grain 10 and the surface grain 20 of the final manufactured non-oriented electrical steel sheet and in developing a random texture to obtain excellent magnetic properties in all directions.

[0103] If the work roll diameter is large, the contact area between the work roll and the material increases at a given reduction rate, allowing for greater shear deformation. Conversely, a smaller work roll diameter reduces the amount of shear deformation. The coefficient of friction depends on the roughness of the work roll and the steel plate, the type of rolling oil, etc. Under given conditions, a higher coefficient of friction allows for greater shear deformation. If the product of the work roll diameter and the coefficient of friction is large, the amount of shear deformation applied to the material increases, which can be controlled so that the grain size on the surface is smaller than that in the center. However, if the product of the work roll diameter and the coefficient of friction is too large, excessive fine grains will form on the surface. If the product of the work roll diameter and the coefficient of friction is too small, the surface grains will grow to a similar size to those in the center, potentially deteriorating the magnetic properties at high frequencies above 400 Hz. More specifically, the product of the work roll diameter and the coefficient of friction can be between 11.0 and 29.5.

[0104] In one embodiment of the invention, cold rolling can be performed in multiple passes, and the aforementioned work roll diameter and friction coefficient characteristics can be satisfied in more than one of the multiple passes. More specifically, they can be satisfied in the final pass.

[0105] The diameter of the work roll can be 300 to 600 mm. More specifically, it can be 350 to 500 mm.

[0106] The coefficient of friction between the work roll and the steel plate can be from 0.02 to 0.10 μ. The coefficient of friction can be measured using the method disclosed in Korean Patent KR1996-0021206. More specifically, the coefficient of friction can be from 0.03 to 0.08 μ.

[0107] In the manufacturing process of cold-rolled sheet, the reduction rate can be between 20% and 55%. If the reduction rate is too low, the rotatable cubic orientation develops, and the magnetism at 55° may deteriorate. If the reduction rate is too high, the {111} / / ND orientation develops, and the overall magnetism may deteriorate. More specifically, the reduction rate can be between 25% and 50%. The final rolled thickness can be between 0.1 mm and 0.35 mm.

[0108] Next, the cold-rolled sheet is annealed in a second annealing step. This second annealing step can be performed at 750 to 1150°C. If the soaking temperature is too low, the grains cannot grow sufficiently, hysteresis losses increase, and iron loss deterioration may occur. More specifically, annealing can be performed at a temperature of 900 to 1050°C. The second annealing step can be soaked for 50 to 120 seconds. The dew point can be below -10°C.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] Example 1 A slab is manufactured containing the composition shown in Table 1, 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 the thicknesses shown in Table 2 below.

[0113] Then, omitting the hot-rolled annealing, the steel sheet was pre-cold-rolled to the thicknesses shown in Table 2, followed by a first annealing at 750 to 1050°C for 15 seconds. The average grain size of the steel sheet after the first annealing was measured and is shown in Table 2. The steel sheet after the first annealing was then cold-rolled under the conditions shown in Table 3 to achieve a final thickness of 0.25 mm. The cold-rolled steel sheet was then subjected to a second annealing at a dew point of -20°C and a soaking temperature of 950°C for 70 seconds.

[0114] To analyze the texture of the manufactured non-oriented electrical steel sheet, 30 10mm × 20mm samples were cut from each specimen. Three groups of 10 samples were fixed together, ensuring the observation surface was a TD surface. The observation surface was then mirror-polished until scratch-free. EBSD measurements were performed with a height of 5000μm, a width of approximately 2500μm (including all 10 0.25mm samples), and a step size of 1μm. The three sets of measurement data were merged using the merging function of OIM software, and the ODF was calculated in one go. The results are shown in Table 4.

[0115] For magnetic properties such as magnetic flux density and iron loss, five 60mm wide × 60mm long sheets were cut from each sample. Magnetic flux density was measured in the rolling direction and at 55° using a single sheet tester, and the results are shown. For iron loss, measurements were taken in the rolling direction and perpendicular to the rolling direction, and the average value is expressed. At this point, W... 10 / 400 B50 refers to the iron loss when a magnetic flux density of 1.0T is excited at a frequency of 400Hz. B50 refers to the magnetic flux density induced under a magnetic field of 5000A / m.

[0116] Table 1 Table 2 Table 3 Table 4 Table 5 As shown in Tables 1 to 5, the invention example of achieving uniform texture by appropriately adjusting the steel composition and process conditions results in excellent iron loss and magnetic flux density, while minimizing magnetic anisotropy.

[0117] On the other hand, if the steel composition and process conditions are not properly adjusted, resulting in an inappropriate texture, iron loss and magnetic flux density will be poor or magnetic anisotropy will be high.

[0118] 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.

[0119] [Explanation of reference numerals in the attached figures] 100: Non-oriented electrical steel sheet; 10: Center section 20: Surface part

Claims

1. A non-oriented electrical steel sheet, wherein, By weight percent, the non-oriented electrical steel sheet comprises Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance including Fe and unavoidable impurities. Euler space The maximum value of the orientation distribution function (ODF) appearing in the 2=45° section is below 3.

0. The non-oriented electrical steel sheet includes a surface portion and a central portion extending from the surface of the steel sheet to a depth of 50 μm. The ratio of the average grain size in the surface portion to the average grain size in the central portion is 0.4 to 0.

6.

2. 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%.

3. 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.

4. 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%.

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: 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%.

6. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following formula 1. [Formula 1] B 50L -B 50(55°) ≤0.05T In Equation 1, B 50L The magnetic flux density B measured in the rolling direction 50 B 50(55°) The magnetic flux density B is measured in a direction at a 55-degree angle to the rolling direction. 50 .

7. 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 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance comprising Fe and unavoidable impurities; The step of pre-cooling the hot-rolled steel sheet; The first annealing step involves annealing the pre-cooled rolled steel sheet; The steps of cold rolling annealed steel sheets to manufacture cold-rolled sheets; and The second annealing step involves annealing the cold-rolled sheet. In the process of manufacturing cold-rolled sheet, the product of the diameter (mm) of the work roll and the coefficient of friction (μ) between the work roll and the steel sheet in at least one pass is 10 to 30.

8. The method for manufacturing non-oriented electrical steel sheet according to claim 7, 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%.

9. The method for manufacturing non-oriented electrical steel sheet according to claim 7, 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.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 7, 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%.

11. The method for manufacturing non-oriented electrical steel sheet according to claim 7, 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%.

12. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, After the hot-rolled steel sheet is manufactured, subsequent steps are performed while the hot-rolled steel sheet still has residual oxide scale.

13. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, After the first annealing step, the average grain size of the steel plate is 50 to 120 μm.

14. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The reduction rate in the process of manufacturing the cold-rolled sheet is 20% to 55%.

15. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The soaking temperature in the second annealing step is 750 to 1150°C.

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