Non-oriented electrical steel sheet, motor core, and method for manufacturing the same

Abstract

The non-oriented electrical steel sheet according to one embodiment of the present application contains, in weight %, Si: 3.2 to 4.5 %, Al: 1.2 to 2.5 %, and Mn: 0.1 to 2.5 %, with the balance containing Fe and inevitable impurities, and satisfies the following Formula 1. [Formula 1] (Length of protruding oxide layer site / Length of entire oxide layer) ≤ 0.1

Description

Technical Field

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same, wherein appropriate conditions are adjusted during cold rolling to form a suitable oxide layer, thereby simultaneously improving magnetic properties. Background Technology

[0002] Non-oriented electrical steel sheets are mainly used in motors that convert electrical energy into mechanical energy. To achieve high efficiency in the conversion process, non-oriented electrical steel sheets need to have excellent magnetic properties. In 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. Furthermore, due to the increase in rotational speed, strength properties, which were not previously considered very important, are now being evaluated as crucial.

[0005] Therefore, when considering recent energy efficiency improvement policies and the application direction of non-oriented electrical steel sheets, it can be said that developing non-oriented electrical steel sheets with low high-frequency iron loss, high magnetic flux density, and excellent strength is an essential technology.

[0006] The most basic and effective methods for reducing iron loss, a crucial magnetic property of non-oriented electrical steel sheets, are increasing the addition of high-resistivity elements Si, Al, and Mn, or reducing the thickness of the steel sheet. Increasing the addition of Si, Al, and Mn increases the resistivity of the steel, thereby reducing eddy current losses in the iron loss of non-oriented electrical steel sheets and ultimately reducing iron loss. For high-frequency iron loss, where eddy current losses account for a larger proportion, this method can be very effective in reducing high-frequency iron loss. However, the effect varies depending on the addition ratio, and the magnetic flux density deteriorates with increasing alloying element addition. Therefore, appropriate addition amounts and proper control of the Si, Al, and Mn addition ratio are required to ensure excellent iron loss and magnetic flux density. Reducing the thickness is also a method that significantly reduces eddy current losses and is very effective in reducing iron loss; however, thinner steel sheets have disadvantages such as reduced productivity and machinability.

[0007] As methods to reduce iron loss and increase magnetic flux density in non-oriented electrical steel sheets, some reports have proposed using special additives such as REM to improve texture and thus enhance magnetic properties, or introducing additional manufacturing processes such as warm rolling, double rolling, and double annealing. However, these techniques all lead to increased manufacturing costs or difficulties in large-scale production. Therefore, it can be said that there is a need to develop a technology with excellent magnetic properties that is easy to commercially produce. In addition, some techniques are being developed to suppress and control inclusion formation by minimizing the amount of impurities added and by adding elements such as Ca. However, these techniques also increase manufacturing costs, and it is difficult to definitively guarantee their effectiveness. Summary of the Invention

[0008] (a) Technical problems to be solved One embodiment of the present invention provides a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet, a motor core, and a method for manufacturing the same, wherein appropriate conditions are adjusted during cold rolling to form a suitable oxide layer, thereby improving magnetic properties.

[0009] (II) Technical Solution According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities, and satisfies the following formula 1.

[0010] [Formula 1] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.1 According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 2.

[0011] [Equation 2] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.05 In Equation 2, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

[0012] According to one embodiment of the present invention, the non-oriented electrical steel sheet may contain Mn: 0.7 to 2.5 by weight.

[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: 0.005 to 0.1 wt%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0016] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of the following: Mo: 0.001 to 0.1 wt%, 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] According to one embodiment of the present invention, the average grain size of the non-oriented electrical steel sheet can be 50 to 150 μm, and the yield strength can be 480 MPa or more.

[0018] According to one embodiment of the present invention, the non-oriented electrical steel sheet has an iron loss (W10 / 400) of less than 12.0 W / Kg and a magnetic flux density (B50) of more than 1.60 T.

[0019] According to one embodiment of the present invention, the motor core is composed of a plurality of non-oriented electrical steel sheets stacked together, wherein the non-oriented electrical steel sheets contain, by weight %, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance containing Fe and unavoidable impurities, and satisfy the following formula 1.

[0020] [Formula 1] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.1 A method for manufacturing a 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, wherein the slab comprises, by weight %, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities; a step of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet, wherein the step of manufacturing the cold-rolled sheet includes two or more passes, wherein the deformation rate (έ1) of the first pass may be 200 / s or less, and the sum of the deformation rates of the first pass and the second pass (έ1+έ2) may be 1100 / s or less.

[0021] In the process of manufacturing cold-rolled sheet, the ratio of the deformation rate of the highest-speed pass (έmax) to the total deformation rate of the entire process (έtotal) can be 0.3 or less.

[0022] 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%.

[0023] 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.

[0024] 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: 0.005 to 0.1 wt%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0025] The slab may also contain one or more of the following: Mo: 0.001 to 0.1 wt%, 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%.

[0026] A method for manufacturing a motor core according to an embodiment of the present invention includes a step of stress-relief annealing of the aforementioned non-oriented electrical steel sheet, wherein the stress-relief annealing step satisfies the following formula 3 or formula 4.

[0027] [Formula 3] 6≤[O]×[Al]≤240 [Formula 4] 480≤[O]×[Al]≤2400 In Equations 3 and 4, [O] represents the O content (ppm) in the atmosphere during stress-relief annealing, and [Al] represents the Al content (wt%) in the non-oriented electrical steel sheet.

[0028] The stress-relief annealing step can be performed by homogenizing at a temperature of 700 to 850°C for 1 hour.

[0029] According to one embodiment of the present invention, the motor core comprises, by weight %, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities. The surface of the single sheet constituting the motor core satisfies Formula 1 below, and the side surface of the single sheet satisfies Formula 5 below.

[0030] [Formula 1] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.1 [Formula 5] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.093 The surface of a single sheet constituting the motor core can satisfy Equation 2 below, and the side surface of the single sheet can satisfy Equation 6 below.

[0031] [Equation 2] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.05 [Formula 6] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.047 In Equations 2 and 6, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

[0032] (III) Beneficial Effects According to one embodiment of the present invention, the non-oriented electrical steel sheet has excellent magnetic flux density, iron loss and yield strength due to the appropriate grain size of the formed grains.

[0033] 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

[0034] Figure 1 and Figure 2 This is a schematic diagram of a cross-section of a non-oriented electrical steel sheet including the thickness direction according to an embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of a cross-section of a motor core according to an embodiment of the present invention.

[0036] Figure 4 and Figure 5 This is a schematic diagram of a cross-section of a non-oriented electrical steel sheet including the thickness direction according to an embodiment of the present invention. Detailed Implementation

[0037] 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.

[0038] 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.

[0039] 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.

[0040] In addition, unless otherwise specified, % means weight, 1 ppm is 0.0001 wt%.

[0041] In one embodiment of the present invention, the additional element refers to the additional element replacing the balance of iron (Fe), and the replacement amount is equivalent to the amount of additional element added.

[0042] 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.

[0043] 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.

[0044] According to one embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance comprising Fe and unavoidable impurities.

[0045] The reasons for the compositional restrictions on non-oriented electrical steel sheets will be described below.

[0046] Si: 3.20 to 4.50% 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 magnetic flux density decreases significantly, and the increased brittleness may worsen rollability. Therefore, Si can be present in quantities of 3.20 to 4.5% by weight. More specifically, it can be present in quantities of 3.30 to 4.30% by weight. More specifically, it can be present in quantities of 3.50 to 4.20% by weight.

[0047] Al: 1.20 to 2.50% by weight The role of aluminum (Al) is to increase the resistivity of the material, reduce iron loss, improve rollability, and reduce magnetic anisotropy, thereby minimizing magnetic deviations in the rolling direction and perpendicular to the rolling direction. If too little Al is added, it may be difficult to achieve the desired reduction in high-frequency iron loss. If too much Al is added, excessive nitride formation may occur, potentially leading to magnetic degradation. Therefore, Al can be present in quantities of 1.20 to 2.50% by weight. More specifically, it can be present in quantities of 1.30 to 2.40% by weight. More specifically, it can be present in quantities of 1.40 to 2.30% by weight.

[0048] Mn: 0.10 to 2.50% by weight Manganese (Mn) is used to increase the resistivity of materials, improve iron loss, and enhance texture. If too little Mn is added, fine sulfide formation occurs, leading to magnetic degradation; conversely, excessive Mn can negatively impact magnetic flux density. Therefore, Mn can be present in quantities from 0.10 to 2.50 wt%. More specifically, it can be present in quantities from 0.30 to 2.50 wt%. More specifically, it can be present in quantities from 0.70 to 2.50 wt%. More specifically, it can be present in quantities from 0.70 to 2.30 wt%. More specifically, it can be present in quantities from 0.70 to 2.20 wt%.

[0049] In one embodiment of the present invention, the non-oriented electrical steel sheet may have a resistivity of 63.0 μΩ·cm or higher at 25°C. The iron loss of non-oriented electrical steel sheets is divided into hysteresis loss and eddy current loss. Increasing the resistivity of the steel by adding elements such as Si, Al, and Mn can significantly reduce eddy current loss. In particular, the proportion of eddy current loss in the total iron loss increases with frequency. Therefore, for excellent high-frequency iron loss, the resistivity of the steel needs to be controlled above a certain level. Through the present invention, when the resistivity (ρ) of the steel reaches 63 μΩ·cm or higher, excellent characteristics can be ensured. More specifically, the resistivity (ρ) can be from 70.0 to 90.0 μΩ·cm.

[0050] In one embodiment of the present invention, resistivity can be measured using a conventional resistivity meter such as the four-point method.

[0051] 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%.

[0052] P: less than 0.100% by weight Phosphorus (P) is a grain boundary and surface segregation element that improves the texture of steel. However, if too much P is added, it inhibits grain growth, leading to poorer iron loss, decreased rollability due to grain boundary segregation, and reduced productivity. More specifically, P can be contained in amounts from 0.0001 to 0.0500% by weight. More specifically, P can be contained in amounts from 0.0010 to 0.0200% by weight.

[0053] 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 0.0005 to 0.0045% by weight.

[0054] 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-rolling processability. More specifically, S may contain 0.0005 to 0.0045% by weight.

[0055] Ti: less than 0.0050% 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 0.0005 to 0.0035% by weight.

[0056] 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 0.0005 to 0.0045% by weight.

[0057] 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.

[0058] Sn Tin (Sn) is added to improve the texture of the material by segregating at grain boundaries and surfaces, and to inhibit surface oxidation. Therefore, tin can be added to enhance magnetism. However, if too much Sn is added, severe grain boundary segregation occurs, leading to deteriorated surface quality, increased hardness, and consequently, breakage of the cold-rolled sheet, potentially resulting in decreased rollability. Specifically, Sn may further comprise 0.005 to 0.200% by weight. More specifically, it may further comprise 0.010 to 0.150% by weight.

[0059] Sb Antimony (Sb) acts as a segregant at grain boundaries and surfaces to improve the texture of the material and inhibit surface oxidation. Therefore, antimony can be further added to enhance magnetic properties. However, excessive Sb addition leads to severe grain boundary segregation, deterioration of surface quality, and increased hardness, resulting in 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 0.150% by weight.

[0060] 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.

[0061] 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: 0.005 to 0.1 wt%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0062] 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.

[0063] 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.

[0064] Ni: 0.005 to 0.100% 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 0.050% by weight.

[0065] 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 further added within the aforementioned range. More specifically, Zr can contain 0.001 to 0.005% by weight.

[0066] 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.

[0067] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of the following: Mo: 0.001 to 0.1 wt%, 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%.

[0068] Mo: 0.001 to 0.100 wt% 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 below 0.1 wt%, with no particular lower limit, but due to its role in improving texture through surface and grain boundary segregation, it can be contained in amounts above 0.001 wt%. More specifically, Mo can be contained in amounts from 0.001 to 0.050 wt%. More specifically, Mo can be contained in amounts from 0.005 to 0.030 wt%.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] Figure 1 The image schematically shows a cross-section of a non-oriented electrical steel sheet 100 according to an embodiment of the present invention.

[0078] like Figure 1 As shown, a non-oriented electrical steel sheet 100 according to an embodiment of the present invention includes an oxide layer 20 extending from the surface to the interior and a steel sheet base material 10. In one embodiment of the present invention, the oxide layer 20 refers to a layer formed on the surface of the base material composed of oxides such as Al and Si combined with oxygen. When a cross-section including the thickness direction (ND direction) of the steel sheet is observed using TEM, it forms an interface with the base material and can be distinguished from the steel sheet base material 10 by compositional analysis. Figure 1 The diagram shows an oxide layer 20 on the upper surface of the steel sheet, but oxide layers 20 may also be present on both the upper and lower surfaces. In this case, the steel sheet base material 10 is present between the upper and lower surface oxide layers 20. The oxide layer 20 is very thin relative to the overall thickness of the non-oriented electrical steel sheet 100, and therefore does not affect the overall alloy composition of the non-oriented electrical steel sheet 100.

[0079] Although Figure 1 The term "insulating coating" is omitted, but an insulating coating will also be present on the surface of the non-oriented electrical steel sheet 100. In this case, the insulating coating and the oxide layer 20 can be distinguished by SEM and TEM, and by confirming the composition of the insulating coating during compositional analysis.

[0080] like Figure 1 As shown, the oxide layer 20 is formed to have a certain roughness with the steel plate base material 10, and sometimes there may be protrusions 21 of the oxide layer 20 penetrating into the steel plate base material 10. In one embodiment of the present invention, the protrusion 21 refers to the oxide layer 20 protruding into the steel plate in the direction of thickness T relative to the virtual boundary line 22 between the oxide layer 20 and the steel plate base material 10 in the direction of interior of the steel plate (ND direction). O The above section. For virtual boundary line 22, the average thickness of the oxide layer can be defined as the interface when the oxide layer forms a completely uniform thickness. The thickness T of oxide layer 20. O The average thickness of the oxide layer can be used to determine this.

[0081] In one embodiment of the present invention, the protrusion 21 may be formed to satisfy Formula 1.

[0082] [Formula 1] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.100 The length P of the protruding oxide layer 20 portion L This refers to the length occupied by the protrusion 21 on the translation line 23, which is a parallel movement of the oxide layer 20 thickness T from the virtual boundary line 22 toward the interior of the steel plate (ND direction). O The translation line. When there are multiple protrusions 21, it can be the length P of the protruding oxide layer 20 portion of all protrusions 21. L sum.

[0083] The overall length of the oxide layer refers to the length of the oxide layer 20 in the direction perpendicular to the thickness direction within the cross-section of the steel plate, including the thickness direction. That is, the overall transverse length of the cross-section of the object being measured.

[0084] When Equation 1 is greater than 0.100, it represents the length P of the protruding oxide layer. L The magnetization process is relatively long. In this case, the movement of magnetic domains is hindered during magnetization, resulting in a deterioration in magnetism. More specifically, the value of Equation 1 can be between 0.030 and 0.095.

[0085] like Figure 2 As shown, in one embodiment of the present invention, oxide 30 may be present in the steel plate base material 10. Oxide 30 exists separately from oxide layer 20, and is distinct from protrusion 21 connected to oxide layer 20. Oxide layer 20, protrusion 21, and oxide 30 refer to portions formed by the combination of Si, Al, etc., with oxygen. The cross-section including the thickness direction (ND direction) of the steel plate is observed using TEM, SEM, etc., and the O composition is distinguished from the steel plate base material 10 during compositional analysis. The area of ​​oxide 30 can be determined using commercial image analysis tools with SEM and TEM images. If image analysis tools are not used, the average length of the longest and shortest lengths of the internal oxides can be taken as the average length, and the area can be manually calculated as a sphere or rectangle depending on its shape. However, since there may be differences from the accurate calculated value, image analysis tools can be used.

[0086] During measurement, the area is not calculated based on a single image, but rather by observing at least multiple images to ensure that the oxide layer extends at least 10 μm along its length before measuring the area. Magnification and resolution are sufficient as long as the internal oxide layer can be observed. Specifically, a magnification of 20,000x or higher can be used for measurement.

[0087] According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 2.

[0088] [Equation 2] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.050 In Equation 2, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

[0089] In one embodiment of the present invention, when the oxide 30 is generated in large quantities relative to the oxide layer 20 or when the oxide layer 20 is thick, the movement of magnetic domains is hindered during magnetization, thereby deteriorating the magnetism. More specifically, the value of Equation 2 can be from 0.015 to 0.049.

[0090] Oxide 30 is mainly generated on the surface of the non-oriented electrical steel sheet 100. In one embodiment of the present invention, for ease of measurement, only oxide 30 from the surface of the steel sheet to 2% of the overall thickness is included in the calculation of Equation 2.

[0091] According to one embodiment of the present invention, the average grain size of the non-oriented electrical steel sheet can be from 50 to 150 μm. If the grains are too small, hysteresis loss may increase. If the grains are too large, eddy current loss may increase, and iron loss may worsen. For the grains, the number of grains is measured in a cross-section including the thickness direction, and the average grain area is obtained by dividing the number of grains by the total area. The grain size can then be determined. The grain size can be determined by using a virtual circle of the same area. More specifically, the average grain size can be from 60 to 130 μm.

[0092] As previously stated, in one embodiment of the present invention, strength and magnetism can be simultaneously improved by adjusting the steel composition and forming a suitable oxide layer 20. Specifically, according to one embodiment of the present invention, the non-oriented electrical steel sheet has an iron loss (W10 / 400) of less than 12.0 W / kg and a magnetic flux density (B50) of more than 1.60 T. The thickness standard can be 0.20 mm. More specifically, the iron loss (W10 / 400) can be 8.50 to 10.50 W / kg. The magnetic flux density (B50) can be 1.61 to 1.70 T. The iron loss (W10 / 400) is the iron loss when excited with a magnetic flux density of 1.0 T at a frequency of 400 Hz. The magnetic flux density (B50) is the magnetic flux density induced under a magnetic field of 5000 A / m. For iron loss (10 / 400) and magnetic flux density (B50), a single sheet tester can be used to measure them in the rolling direction and the direction perpendicular to the rolling, and the average value can be taken.

[0093] Furthermore, one embodiment of the invention also exhibits excellent mechanical strength. More specifically, the yield strength can be 480 MPa or higher. More specifically, the yield strength can be 500 to 650 MPa. The yield strength can be measured under 0.2% offset conditions in a tensile test.

[0094] Figure 3The image schematically illustrates a cross-section of a motor core 200 according to an embodiment of the present invention. Figure 3 As shown, the motor core 200 according to one embodiment of the present invention can be formed by stacking multiple of the aforementioned non-oriented electrical steel sheets 100. Although Figure 3 Not shown, but an insulating coating may exist between the non-oriented electrical steel sheets 100.

[0095] According to an embodiment of the present invention, the motor core 200 contains, by weight %, Si: 3.2 to 4.5%, Al: 1.2 to 2.5% and Mn: 0.1 to 2.5%, with the balance being Fe and unavoidable impurities. The surface 101 of the single sheet constituting the motor core 200 satisfies the following formula 1, and the side surface 102 of the single sheet satisfies the following formula 5.

[0096] [Formula 1] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.1 [Formula 5] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.093 The steel composition of the non-oriented electrical steel sheet 100 inside the motor core 200 is the same as that of the aforementioned non-oriented electrical steel sheet 100, therefore, a repetitive description is omitted. During the manufacturing process of the motor core 200, the steel composition remains substantially unchanged.

[0097] Furthermore, the oxide layer 20, protrusions 21, and oxide 30 characteristics of the surface 101 of the single non-oriented electrical steel sheet 100 in the motor core 200, as represented by Formulas 1 and 2, are also the same as those of the aforementioned non-oriented electrical steel sheet 100.

[0098] On the other hand, such as Figure 4 As shown, according to an embodiment of the present invention, the motor core 200 has features related to oxide layer 20, protrusions 21 and oxide 30 on the side 102 of a single non-oriented electrical steel sheet 100.

[0099] like Figure 4 As shown, in a motor core 200 according to an embodiment of the present invention, a single non-oriented electrical steel sheet 100 includes an oxide layer 20 and a steel sheet base material 10 present in the internal direction (ND perpendicular direction) on the side 102. In one embodiment of the present invention, the oxide layer 20 refers to a layer formed by the combination of Si, Al and oxygen. When observing the cross-section including the thickness direction (ND direction) of the steel sheet by SEM, TEM, etc., and performing composition analysis, it is distinguished from the steel sheet base material 10 by the oxygen composition. Figure 4The diagram shows an oxide layer 20 on one side of the steel sheet, but an oxide layer 20 may also be present on both sides. In this case, the steel sheet base material 10 is present between the oxide layer 20 on one side and the oxide layer 20 on the other side. The oxide layer 20 is very thin relative to the overall thickness of the non-oriented electrical steel sheet 100, and therefore does not affect the overall alloy composition of the non-oriented electrical steel sheet 100.

[0100] like Figure 4 As shown, the oxide layer 20 is formed to have a certain roughness with the steel plate base material 10, and sometimes there may be protrusions 21 of the oxide layer 20 penetrating into the steel plate base material 10. In one embodiment of the present invention, the protrusion 21 refers to the thickness T of the oxide layer 20 protruding into the steel plate in the direction (perpendicular to ND) relative to the virtual boundary line 24 between the oxide layer 20 and the steel plate base material 10. O The portion. For virtual boundary line 24, the average thickness of the oxide layer can be used, defining the interface where the oxide layer forms a completely uniform thickness as the boundary line. The thickness T of oxide layer 20. O The average thickness of the oxide layer can be used to determine this.

[0101] In one embodiment of the present invention, the protrusion 21 may be formed to satisfy formula 5.

[0102] [Formula 5] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.093 The length P of the protruding oxide layer 20 portion L This refers to the length occupied by the protrusion 21 on the translation line 25, which is the thickness T of the oxide layer 20 that is moved parallel to the virtual boundary line 24 in the direction (ND direction) towards the interior of the steel plate. O The translation line. When there are multiple protrusions 21, it can be the length P of the protruding oxide layer 20 portion of all protrusions 21. L sum.

[0103] The overall length of the oxide layer refers to the length of the oxide layer 20 in the thickness direction (ND direction) of the steel plate cross-section, including the thickness direction. That is, the overall longitudinal length of the cross-section of the object being measured.

[0104] When Equation 5 is greater than 0.093, it indicates the length P of the protruding oxide layer. L The time is relatively long. In this case, the magnetism will deteriorate due to the impeded magnetization process. More specifically, the value of Equation 5 can be between 0.050 and 0.093.

[0105] Although Figure 4 and Figure 5 The middle part is omitted, but as... Figure 1An oxide layer 20 may exist on the surface 101 of the steel plate shown. The length calculation of the protrusion 21 excludes the oxide layer 20 existing on the surface 101 of the steel plate.

[0106] like Figure 5 As shown, in one embodiment of the present invention, oxide 30 may be present in the steel plate base material 10. The oxide 30 exists separately from the oxide layer 20, and is distinct from the protrusion 21 connected to the oxide layer 20. The protrusion 21 and oxide 30 refer to the portions formed by the combination of Si, Al and oxygen. When observing the cross-section including the thickness direction (ND direction) of the steel plate by SEM, TEM, etc., and performing composition analysis, they are distinguished from the steel plate base material 10 by the oxygen composition.

[0107] According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 6.

[0108] [Formula 6] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.047 In Equations 2 and 6, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

[0109] In one embodiment of the invention, when the oxide 30 is generated in large quantities relative to the oxide layer 20 or when the oxide layer 20 is thick, the magnetization process is hindered, thereby deteriorating the magnetism. More specifically, the value of Equation 6 can be from 0.025 to 0.047.

[0110] Oxide 30 is mainly formed on the side of the non-oriented electrical steel sheet 100. In one embodiment of the present invention, for ease of measurement, only oxide 30 from the side of the steel sheet to 2% of the overall thickness is included in the calculation of Equation 6.

[0111] As previously described, for the non-oriented electrical steel sheet 100 present inside the motor core 200 of one embodiment of the present invention, strength and magnetism can be simultaneously improved by the steel composition and the formation of a suitable oxide layer 20. Specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention has an iron loss (W10 / 400) of less than 12.0 W / kg and a magnetic flux density (B50) of more than 1.60 T. The thickness standard can be 0.20 mm. More specifically, the iron loss (W10 / 400) can be 8.50 to 10.50 W / kg. The magnetic flux density (B50) can be 1.61 to 1.70 T. The iron loss (W10 / 400) is the iron loss when excited with a magnetic flux density of 1.0 T at a frequency of 400 Hz. The magnetic flux density (B50) is the magnetic flux density induced under a magnetic field of 5000 A / m. For iron loss (10 / 400) and magnetic flux density (B50), the non-oriented electrical steel sheet inside the motor core 200 can be separated into individual sheets, and measured using a single sheet tester in the rolling direction and the rolling perpendicular direction, and the average value is taken.

[0112] Furthermore, the non-oriented electrical steel sheet 100 present inside the motor core 200 of one embodiment of the present invention also possesses excellent mechanical strength. More specifically, the yield strength can be 480 MPa or higher. More specifically, the yield strength can be 500 to 650 MPa. The yield strength can be measured under 0.2% offset conditions in a tensile test.

[0113] A method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention includes: hot rolling a slab to manufacture a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0114] The following describes each step in detail.

[0115] First, the slab is hot-rolled.

[0116] 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.

[0117] Specifically, by weight percent, the slab contains 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance including Fe and unavoidable impurities.

[0118] Other additional elements are already described in the alloy composition of non-oriented electrical steel sheets, so a repeating description is omitted.

[0119] 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.

[0120] Next, the slab is hot-rolled to produce hot-rolled plates.

[0121] The thickness of hot-rolled sheet can be from 1.0 to 4.5 mm. In the manufacturing process of hot-rolled sheet, the final rolling temperature can be above 800°C. Specifically, it can be from 800 to 1000°C. For hot-rolled sheet, coiling can be performed at temperatures below 700°C. More specifically, the thickness of hot-rolled sheet can be from 1.5 to 4.3 mm.

[0122] After manufacturing the hot-rolled steel sheet, an annealing step can be included. In this case, the soaking temperature can be between 850 and 1100°C. If the annealing temperature is too low, recrystallization will not form or will result in fine growth, leading to a low increase in magnetic flux density. Conversely, if the annealing temperature is too high, the magnetic properties will decrease, potentially causing poor rolling operability due to sheet deformation. More specifically, the temperature range can be between 830 and 1080°C. The soaking time can be between 10 and 300 seconds. The hot-rolled sheet annealing step can also be omitted.

[0123] Next, the hot-rolled steel sheet is cold-rolled to produce a cold-rolled sheet. In one embodiment of the invention, by adjusting the deformation speed of each pass during the production of the cold-rolled sheet, the oxide layer generated on the surface of the non-oriented electrical steel sheet and the oxide layer inside the steel sheet base material can be appropriately formed.

[0124] The process of manufacturing cold-rolled sheet involves two or more passes, with the deformation speed (έ1) of the first pass being 200 / s or less, and the sum of the deformation speeds of the first and second passes (έ1+έ2) being 1100 / s or less.

[0125] The first pass is the first pass in the cold rolling process. In one embodiment of the invention, the number of passes is determined by the number of times the rolls pass through the work rolls. In one embodiment of the invention, the deformation rate can be calculated using the reduction amount, rolling speed, and roll diameter for each pass.

[0126] If the deformation rate (έ1) of the first pass is too high, the surface deformation of the base material will be uneven, and the formation behavior of oxides during the annealing of cold-rolled steel will be locally uneven, resulting in a large number of protrusions, which will have an adverse effect on the magnetic properties of the steel sheet. More specifically, the deformation rate (έ1) of the first pass can be 100 to 198 / s.

[0127] The second pass is the second pass in the cold rolling process. If the sum of the deformation rates of the first and second passes (έ1+έ2) is too large, the surface deformation of the base material will be uneven, and the formation behavior of oxides during the annealing of the cold-rolled sheet will be locally uneven. Relative to the oxide layer area, a large amount of internal oxides may be generated, which will have an adverse effect on the magnetic properties of the steel sheet. More specifically, the sum of the deformation rates of the first and second passes (έ1+έ2) can be 850 to 1070 / s.

[0128] Furthermore, in one embodiment of the invention, the ratio of the deformation rate of the pass with the highest deformation rate (έhighest) to the deformation rate of the entire process (έtotal) may be 0.3 or less. The overall deformation rate of the process (έtotal) can be determined by adding the deformation rates of each pass in the process of manufacturing the cold-rolled sheet. If this ratio is too large, a large amount of oxide may form.

[0129] The total number of cold rolling passes can be 5 to 8.

[0130] For the total reduction rate in cold rolling, it can be between 40% and 95%. 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. Therefore, problems may arise in terms of 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 results in finer grains, which may lead to decreased magnetic flux density and increased iron loss. The reduction rate can be 60% to 85%. For the cold rolling step, either a tandem cold rolling mill or a reverse mill can be used. A tandem cold rolling mill uses multiple rolling stands for continuous cold rolling of the steel sheet, while a reverse mill uses 12 or more rolls for discontinuous cold rolling. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0131] The manufacturing process of cold-rolled sheets can involve one cold rolling operation or two or more cold rolling operations with intermediate annealing. Even if two cold rolling operations are performed, the number of passes and deformation rate can be calculated for the overall cold rolling process.

[0132] Next, in the annealing step of the cold-rolled sheet, the cold-rolled sheet is annealed. In the annealing process of the cold-rolled sheet, the annealing temperature is not significantly restricted, as long as it is generally applicable to non-oriented electrical steel sheets. The iron loss of non-oriented electrical steel sheets is closely related to the grain size. The iron loss of non-oriented electrical steel sheets can be divided into hysteresis loss and eddy current loss. Hysteresis loss decreases with larger grain size, while eddy current loss increases with larger grain size. Therefore, there exists an appropriate grain size that minimizes the sum of hysteresis loss and eddy current loss. Therefore, it is important to derive and apply an annealing temperature that ensures the optimal grain size; a suitable annealing temperature is 850 to 1100°C. If the annealing temperature is too low, the grains are too fine, leading to increased hysteresis loss; conversely, if the annealing temperature is too high, the grains are too coarse, leading to increased eddy current loss and worsened iron loss. In addition, the annealing time is suitable to be between 10 and 300 seconds. In order to prevent magnetic degradation caused by the formation of an oxide layer, annealing can be carried out in a mixed atmosphere of hydrogen or argon and nitrogen.

[0133] 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.

[0134] 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.

[0135] A method for manufacturing a motor core according to an embodiment of the present invention includes a step of stress-relief annealing of a non-oriented electrical steel sheet, wherein the stress-relief annealing step satisfies the following formula 3 or formula 4.

[0136] [Formula 3] 6≤[O]×[Al]≤240 [Formula 4] 480≤[O]×[Al]≤2400 In Equations 3 and 4, [O] represents the O content (ppm) in the atmosphere during stress-relief annealing, and [Al] represents the Al content (wt%) in the non-oriented electrical steel sheet.

[0137] The non-oriented electrical steel sheet and its manufacturing method have been described previously, so a repeat description is omitted. When manufacturing motor cores, processes such as punching and lamination are involved, including a stress-relief annealing step to remove stress generated during the punching process.

[0138] During stress-relief annealing, depending on the annealing atmosphere, iron loss may actually worsen, especially when Al and O in the base material react strongly, forming an oxide layer on the surface. Therefore, it is necessary to appropriately control the O concentration in the atmosphere according to the Al content. In one embodiment of the present invention, the O content in the atmosphere is adjusted to satisfy formula 3 or formula 4.

[0139] If Equations 3 and 4 are not satisfied, i.e., the [O]×[Al] value is less than 6 or greater than 240 and less than 480, the oxide layer formation is insufficient or excessive, and the adhesion between the base material and the coating will deteriorate. Furthermore, if it is greater than 2400, rust may occur after annealing due to excessive oxidation. Therefore, by adjusting the annealing atmosphere during stress-relief annealing, the sides of a single sheet can satisfy Equation 5 or 6.

[0140] [Formula 5] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.093 [Formula 6] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.047 In Equation 6, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

[0141] For a single sheet surface, since the steel plates are stacked together, they are not actually affected by the stress-relief annealing atmosphere and directly satisfy Equation 1 or Equation 2.

[0142] Besides oxygen, the other atmosphere can be nitrogen, or conventional atmosphere gases such as LNG and air.

[0143] The stress-relief annealing step can be performed by homogenizing at a temperature of 700 to 850°C for 1 hour. This can further improve the magnetic properties. More specifically, homogenization can be performed at a temperature of 720 to 800°C for 1.5 to 4 hours.

[0144] 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.

[0145] Example 1 A slab was manufactured, containing, by weight percent, the composition shown in Tables 1 and 2, with the balance being Fe and unavoidable impurities. The slab was heated to 1160°C and hot-rolled to a thickness of 2.2 mm, then coiled at 700°C. The hot-rolled steel sheet was then annealed at 1000°C for 50 seconds. After annealing, a pickled sample was cold-rolled to a thickness of 0.2 mm, with the deformation speed adjusted for each pass as shown in Table 3. Then, cold-rolled annealing was performed. This cold-rolled annealing was carried out at 1000°C for 50 seconds.

[0146] For resistivity at 25℃, the four-point method is used for measurement.

[0147] For yield strength, the tensile test is performed under 0.2% offset conditions.

[0148] For iron loss (W10 / 400) and magnetic flux density (B50), five 60mm wide × 60mm long samples were cut from each specimen. The rolling direction and the rolling perpendicular direction were measured using a single sheet tester, and the average value was shown.

[0149] For oxide layers and oxides, oxygen components were measured using automated SEM and GDS.

[0150] Table 1 Table 2 Table 3 As shown in Tables 1 to 3, steel grades A1 to A8, which have excellent iron loss, magnetic flux density, and yield strength, are produced by properly adjusting the cold rolling conditions to achieve appropriate oxide layer and oxide formation.

[0151] On the other hand, A9 to A16 are due to improper cold rolling conditions, resulting in inadequate formation of oxide and oxidizing layers, thus leading to poor magnetic properties or strength.

[0152] Example 2 A slab was manufactured, containing, by weight percent, the composition shown in Tables 4 and 5, with the balance being Fe and unavoidable impurities. The slab was heated to 1140°C and hot-rolled to a thickness of 2.1 mm, then coiled at 710°C. The hot-rolled steel sheet was then annealed at 1000°C for 60 seconds. After annealing, a pickled sample was cold-rolled to a thickness of 0.2 mm, with the deformation speed adjusted for each pass as shown in Table 3. Then, cold-rolled annealing was performed. This cold-rolled annealing was carried out at 1000°C for 60 seconds.

[0153] Stress-relief annealing was simulated on cold-rolled steel sheets after annealing, and annealed for 2 hours at 740°C in an atmosphere with the oxygen content shown in Table 5 (the remainder being nitrogen). Table 6 shows the magnetic properties and strength of individual steel sheets after stress-relief annealing, as well as the characteristics of the oxide layer and oxides on the sides of each sheet. At this point, the shape and distribution of the oxide layer and oxides were observed using SEM on the surface areas excluding the top and bottom 5% thickness.

[0154] Table 4 Table 5 Table 6 As shown in Tables 4 to 6, steel grades B1 to B7, which have excellent iron loss, magnetic flux density, and yield strength, are formed by appropriately adjusting the cold rolling conditions and the atmosphere conditions during SRA to properly form oxide layers and oxides on the surface and sides.

[0155] On the other hand, B8 to B14 are due to improper cold rolling conditions or improper atmosphere conditions during SRA, resulting in inadequate formation of oxide layers and oxides on the surface and sides, thus leading to poor magnetic properties or strength.

[0156] 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.

[0157] [Explanation of reference numerals in the attached figures] 100: Non-oriented electrical steel sheet; 10: Steel sheet base material 20: Oxide layer; 21: Protrusion 22: Virtual boundary line; 23: Translation line 24: Virtual side boundary line; 25: Side translation line 30: Oxides; 101: Steel plate surface 102: Side of steel plate; 200: Motor core

Claims

1. A non-oriented electrical steel sheet, wherein, The non-oriented electrical steel sheet, by weight percent, comprises 3.2 to 4.5% Si, 1.2 to 2.5% Al, and 0.1 to 2.5% Mn, with the balance including Fe and unavoidable impurities, and satisfies the following formula 1. [Formula 1] (Length of protruding oxide layer / Length of overall oxide layer) ≤ 0.

1.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following formula 2. [Equation 2] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.05 In Equation 2, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

3. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet contains Mn: 0.7 to 2.5 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: 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%.

5. 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.

6. 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: 0.005 to 0.1 wt%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

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: Mo: 0.001 to 0.1 wt%, 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%.

8. The non-oriented electrical steel sheet according to claim 1, wherein, The average grain size of the non-oriented electrical steel sheet is 50 to 150 μm, and the yield strength is above 480 MPa.

9. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet has an iron loss (W10 / 400) of less than 12.0 W / Kg and a magnetic flux density (B50) of more than 1.60 T.

10. A motor core, wherein, The motor core is composed of multiple non-oriented electrical steel sheets stacked together. By weight percent, the non-oriented electrical steel sheets contain 3.2 to 4.5% Si, 1.2 to 2.5% Al, and 0.1 to 2.5% Mn, with the balance including Fe and unavoidable impurities, and satisfy the following formula 1. [Formula 1] (Length of protruding oxide layer / Length of overall oxide layer) ≤ 0.

1.

11. 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 %, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance comprising Fe and unavoidable impurities; The steps of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and The cold-rolled sheet annealing step involves annealing the cold-rolled sheet. The process of manufacturing cold-rolled steel sheets involves two or more passes. The deformation speed (έ1) of the first pass is less than 200 / s, and the sum of the deformation speeds of the first and second passes (έ1+έ2) is less than 1100 / s.

12. The method for manufacturing non-oriented electrical steel sheet according to claim 11, wherein, In the step of manufacturing the cold-rolled sheet, The ratio of the deformation speed of the highest-speed pass (έhighest) to the total deformation speed of the entire process (έtotal) is 0.3 or less.

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

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

15. The method for manufacturing non-oriented electrical steel sheet according to claim 11, 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: 0.005 to 0.1 wt%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

16. The method for manufacturing non-oriented electrical steel sheet according to claim 11, wherein, The slab further comprises one or more of the following: Mo: 0.001 to 0.1 wt%, 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%.

17. A method for manufacturing a motor core, comprising: The step of stress-relief annealing the non-oriented electrical steel sheet according to claim 1 The stress-relief annealing step satisfies either Equation 3 or Equation 4 below. [Formula 3] 6≤[O]×[Al]≤240 [Formula 4] 480≤[O]×[Al]≤2400 In Equations 3 and 4, [O] represents the O content (ppm) in the atmosphere during stress-relief annealing, and [Al] represents the Al content (wt%) in the non-oriented electrical steel sheet.

18. The method for manufacturing a motor core according to claim 17, wherein, The stress-relief annealing step involves homogenization at a temperature of 700 to 850°C for 1 hour.

19. A motor core, wherein, It contains, by weight percent, 3.2 to 4.5% Si, 1.2 to 2.5% Al and 0.1 to 2.5% Mn, with the balance being Fe and unavoidable impurities. The surface of a single sheet constituting the motor core satisfies Equation 1 below, and the side surface of the single sheet satisfies Equation 5 below. [Formula 1] (Length of protruding oxide layer / Length of total oxide layer) ≤ 0.1 [Formula 5] (Length of protruding oxide layer / Length of overall oxide layer) ≤ 0.

093.

20. The method for manufacturing a motor core according to claim 19, wherein, The surface of a single sheet constituting the motor core satisfies the following formula 2, and the side surface of the single sheet satisfies the following formula 6. [Equation 2] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.05 [Formula 6] (Area of ​​internal oxides / Area of ​​total oxide layer) ≤ 0.047 In Equations 2 and 6, the area of ​​internal oxides refers to the sum of the areas of oxides present in the steel plate base material.

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