Non-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof, specifically a non-oriented electrical steel sheet having improved magnetic properties by appropriately adjusting the contents of Sb, Sn, Cu, Cr, and Mg, and a manufacturing method thereof. [Solution] The non-oriented electrical steel sheet of the present invention contains, by weight, Si: 3.0-4.0%, Al: 0.3-1.5%, Mn: 0.1-0.6%, one or more of Sn and Sb: 0.006-0.1%, C: 0.0015-0.0040%, Cr: 0.01-0.03%, Cu: 0.003-0.008%, and Mg: 0.0005-0.0025%, with the remainder being Fe and unavoidable impurities.

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet having improved magnetic properties by appropriately adjusting the contents of Sb, Sn, Cu, Cr, and Mg, and a manufacturing method thereof. [Background technology]

[0002] Non-oriented electrical steel sheets are primarily used in motors that convert electrical energy into mechanical energy, and their excellent magnetic properties are required to ensure high efficiency during this process. In recent years, environmentally friendly technologies have been gaining attention, making it extremely important to increase the efficiency of motors, which account for more than half of total electrical energy consumption. As a result, demand for non-oriented electrical steel sheets with excellent magnetic properties is also increasing.

[0003] The magnetic properties of non-oriented electrical steel sheets are primarily evaluated by 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 production of motors with higher energy efficiency under the same conditions, while higher magnetic flux density allows for the miniaturization of motors or reduction of copper loss. Therefore, it is important to create non-oriented electrical steel sheets with low iron loss and high magnetic flux density.

[0004] The characteristics of non-oriented electrical steel sheets that should be considered also change depending on the operating conditions of the motor. As a standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors, most motors use the iron loss W when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. 15 / 50 However, motors for a wide range of applications all have W 15 / 50 Iron loss is not the most important factor, and iron loss at other frequencies or applied magnetic fields may be evaluated depending on the main operating conditions. In particular, for the non-oriented electrical steel sheets used in the drive motors of recent electric vehicles, magnetic properties at low magnetic fields of 1.0 T or less and high frequencies of 400 Hz or more are often important. 10 / 400The characteristics of non-oriented electrical steel sheets are evaluated using iron loss such as

[0005] The most common method for improving the magnetic properties of non-oriented electrical steel sheets is to add alloying elements such as silicon. Adding these alloying elements increases the steel's resistivity, and the higher the resistivity, the lower the eddy current loss and the lower the overall iron loss. However, the more silicon added, the lower the magnetic flux density and the greater the brittleness. Adding more than a certain amount of silicon makes cold rolling impossible, making commercial production impossible. While thinner electrical steel sheets tend to have lower iron loss, the reduced rollability due to brittleness can be a fatal problem. Adding elements such as aluminum and manganese to further increase the steel's resistivity allows the production of the highest quality non-oriented electrical steel sheets with excellent magnetic properties.

[0006] For non-oriented electrical steel sheets used in electric vehicle drive motors, high-frequency iron loss (over 400 Hz) is important. As the frequency increases, the proportion of eddy current loss in iron loss increases. Therefore, increasing resistivity and reducing thickness are advantageous. However, as steel sheet thickness decreases, the cold reduction ratio increases, leading to the development of {111} / / ND texture and poor magnetic properties. If the thickness of the hot-rolled sheet is reduced to reduce the cold reduction ratio in an attempt to address this issue, the steel sheet shape cannot be adequately controlled during the cold rolling process, resulting in increased thickness deviation in the width direction and resulting in dimensional defects in motor cores. Furthermore, as steel sheet becomes thinner, the coil length increases, increasing the operating time for the continuous annealing process and reducing annealing productivity.

[0007] To solve these problems, attempts have been made to thoroughly remove impurities during the steelmaking process to produce ultra-clean steel, or to add specific elements to reduce inclusions and precipitates in the steel to improve magnetic properties, but these methods are limited in their practical application due to limitations in commercial production conditions. Furthermore, methods have been proposed for improving texture by controlling the annealing temperature and atmosphere and the deformation rate of the steel sheet during rolling, but these techniques are very limited in their practical use due to factors such as increased manufacturing costs, reduced productivity, and insufficient results. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a non-oriented electrical steel sheet and a manufacturing method thereof, specifically a non-oriented electrical steel sheet having improved magnetic properties by appropriately adjusting the contents of Sb, Sn, Cu, Cr, and Mg, and a manufacturing method thereof. [Means for solving the problem]

[0009] The non-oriented electrical steel sheet of the present invention is characterized by containing, by weight%, Si: 3.0-4.0%, Al: 0.3-1.5%, Mn: 0.1-0.6%, one or more of Sn and Sb: 0.006-0.1%, C: 0.0015-0.0040%, Cr: 0.01-0.03%, Cu: 0.003-0.008%, and Mg: 0.0005-0.0025%, with the remainder being Fe and unavoidable impurities.

[0010] The non-oriented electrical steel sheet of the present invention can satisfy the following formula 1. [Formula 1] 0.66≦([Sn]+[Sb]) / ([Cr]+[Cu]+[Mg])≦2 (In formula 1, [Sn], [Sb], [Cr], [Cu], and [Mg] represent the contents (wt%) of Sn, Sb, Cr, Cu, and Mg, respectively.)

[0011] The non-oriented electrical steel sheet of the present invention may further contain one or more of N, S, Ti, Nb and V in an amount of 0.0003 to 0.0030 wt % each.

[0012] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.005 to 0.05% by weight, Mo: 0.001 to 0.01% by weight, and Ni: 0.005 to 0.04% by weight.

[0013] The non-oriented electrical steel sheet of the present invention may have an average crystal grain size of 55 to 75 μm.

[0014] In the non-oriented electrical steel sheet of the present invention, an oxide layer exists from the surface toward the inside of the steel sheet, and the thickness of the oxide layer can be 10 to 50 nm.

[0015] The oxide layer may contain 1.0 to 30 wt % Al and 0.5 to 10.0 wt % Si.

[0016] The weight ratio of the Al content to the Si content in the oxide layer may be 5-20.

[0017] The distribution density of AlN precipitates with a diameter of 10 to 500 nm at a depth of 2 μm from the surface to the interior of the steel sheet is 3 particles / mm 2 It can be the following:

[0018] The thickness of the steel plate can be 0.10 to 0.35 mm.

[0019] The method for producing a non-oriented electrical steel sheet of the present invention is characterized by comprising the steps of: hot rolling a slab containing, by weight, 3.0-4.0% Si, 0.3-1.5% Al, 0.1-0.6% Mn, 0.006-0.1% at least one of Sn and Sb, 0.0015-0.0040% C, 0.01-0.03% Cr, 0.003-0.008% Cu, and 0.0005-0.0025% Mg, with the remainder being Fe and unavoidable impurities, and satisfying the following formula 1 to produce a hot-rolled sheet; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; and final annealing the cold-rolled sheet:

[0020] [Formula 1] 0.66≦([Sn]+[Sb]) / ([Cr]+[Cu]+[Mg])≦2 (In formula 1, [Sn], [Sb], [Cr], [Cu], and [Mg] represent the contents (wt%) of Sn, Sb, Cr, Cu, and Mg, respectively.)

[0021] The method may further include a step of heating the slab to 1200°C or less before the step of producing the hot rolled sheet.

[0022] The finish rolling temperature in the stage of producing the hot rolled sheet can be 800°C or higher.

[0023] After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet at 850 to 1150°C.

[0024] The final annealing step may involve annealing the cold-rolled sheet at a soaking temperature of 900° C. or higher for 15 seconds or more.

[0025] In the final annealing step, the cold-rolled sheet may be annealed in an atmosphere containing 40% by volume or less of hydrogen (H2) and 60% by volume or more of nitrogen, with a dew point of 0 to -40°C. [Effects of the Invention]

[0026] According to one embodiment of the present invention, a non-oriented electrical steel sheet having excellent high-frequency iron loss can be provided, which can contribute to improving the performance of drive motors for environmentally friendly automobiles that use the highest quality non-oriented electrical steel sheet. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic diagram of a cross section of a non-oriented electrical steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0029] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" means to embody certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0030] When a part is referred to as being "on" or "above" another part, it can be directly on or above the other part, with other parts intervening. In contrast, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0031] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0032] In one embodiment of the present invention, the inclusion of an additional element means that an additional amount of the additional element is included in place of the remaining iron (Fe).

[0033] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further analyzed to have a meaning that fits the relevant technical literature and the presently disclosed content, and are not interpreted as having an ideal or overly formal meaning unless otherwise defined.

[0034] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0035] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, by weight, 3.0-4.0% Si, 0.3-1.5% Al, 0.1-0.6% Mn, 0.006-0.1% of one or more of Sn and Sb, 0.0015-0.0040% C, 0.01-0.03% Cr, 0.003-0.008% Cu, 0.0005-0.0025% Mg, and the remainder being Fe and unavoidable impurities.

[0036] The reasons for limiting the components of the non-oriented electrical steel sheet will be explained below.

[0037] Si:3.0~4.0wt% Silicon (Si) increases the resistivity of the material and reduces iron loss. If too little Si is added, the iron loss improvement effect may be insufficient. If too much Si is added, the brittleness of the material increases, rolling productivity drops sharply, and an oxide layer and oxides that are harmful to magnetism may form in the surface layer. Therefore, Si may be contained in an amount of 3.0 to 4.0 wt. %. More specifically, it may be contained in an amount of 3.1 to 3.8 wt. %.

[0038] Al: 0.3~1.5% by weight Aluminum (Al) increases the resistivity of the material and reduces iron loss. If too little Al is added, fine nitrides are formed or the oxide layer on the surface is not dense enough, making it difficult to achieve magnetic improvement. If too much Al is added, excessive nitrides are formed, degrading magnetic properties and causing problems in all processes, including steelmaking and continuous casting, significantly reducing productivity. Therefore, the Al content can be 0.30 to 1.50 wt. %. More specifically, the Al content can be 0.40 to 1.30 wt. %.

[0039] Mn:0.1~0.6wt% Manganese (Mn) increases the resistivity of the material, improving core loss, and plays a role in forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration. If too much Mn is added, fine MnS is excessively precipitated, promoting the formation of a {111} texture that is unfavorable to magnetism and resulting in a rapid decrease in magnetic flux density. Therefore, Mn can be contained in an amount of 0.1 to 0.6 wt. %. More specifically, Mn can be contained in an amount of 0.2 to 0.5 wt. %.

[0040] One or more of Sn and Sb: 0.006 to 0.100% by weight Tin (Sn) and antimony (Sb) segregate at the surface and grain boundaries of steel sheets to suppress surface oxidation during annealing, prevent element diffusion through grain boundaries, and prevent recrystallization in the {111} / / ND orientation, improving texture. If too little Sn or Sb is added, the above-mentioned effects are insufficient. If too much Sn or Sb is added, the amount of grain boundary segregation increases, reducing toughness and productivity, which may be lower than the improvement in magnetic properties. Therefore, one or more of Sn and Sb may be contained in an amount of 0.006 to 0.100 wt. More specifically, one or more of Sn and Sb may be contained in an amount of 0.010 to 0.070 wt. When Sn or Sb is contained alone, this refers to the content of each element. When both Sn and Sb are contained, this refers to the combined amount of Sn and Sb.

[0041] C:0.0015~0.0040wt% Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, which reduces magnetic properties, so the lower the content, the better. However, in one embodiment of the present invention, Cr, Cu, and Mg are contained in appropriate amounts, C Even if it is contained in a certain amount or more, it does not affect the magnetic property, so it can be contained in an amount of 0.0015% by weight or more. in particular, The content of C may be 0.0015 to 0.0040% by weight, more specifically, 0.0020 to 0.0035% by weight.

[0042] Cr:0.0100~0.0300wt% Chromium (Cr) does not tend to form fine precipitates, but it can prevent the formation of an Al-based oxide layer on the surface and form Cr-based carbides, which can deteriorate magnetic properties. If too little Cr is added, the Al-based oxide layer may become too thick, or round-shaped oxides or nitrides may form on the surface, which can deteriorate magnetic properties. If too much Cr is added, it may be difficult to form a dense oxide layer, which can deteriorate magnetic properties. Therefore, the Cr content may be 0.0100 to 0.0300 wt.%. More specifically, the Cr content may be 0.0120 to 0.0275 wt.%.

[0043] Cu:0.0030~0.0080wt% Copper (Cu) is an element that can form sulfides at high temperatures, and when added in large amounts, it also affects the composition of the surface oxide layer. Adding an appropriate amount has the effect of coarsening fine CuS or MnCuS precipitates, improving magnetic properties. Therefore, Cu can be contained in an amount of 0.0030 to 0.0080 wt. %. More specifically, Cu can be contained in an amount of 0.0040 to 0.0077 wt. %.

[0044] Mg:0.0005~0.0025wt% Magnesium (Mg) is an element that mainly combines with S to form sulfides, which can affect the surface oxide layer of the base iron. Therefore, Mg can be contained in an amount of 0.0005 to 0.0025 wt %. More specifically, Mg can be contained in an amount of 0.0008 to 0.0020 wt %.

[0045] The non-oriented electrical steel sheet according to one embodiment of the present invention satisfies the following formula 1. [Formula 1] 0.66≦([Sn]+[Sb]) / ([Cr]+[Cu]+[Mg])≦2.00

[0046] More specifically, the value of Equation 1 can be 0.68 to 1.95.

[0047] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain at least one of N, S, Ti, Nb, and V in an amount of 0.0003 to 0.0030 wt % each.

[0048] N:0.0003~0.0030wt% Nitrogen (N) not only forms fine AlN precipitates inside the base material, but also combines with other impurities to form fine precipitates that inhibit grain growth and worsen iron loss, so the lower the N content, the better, and it can be contained at 0.0003 to 0.0030 wt %, and more preferably, it is controlled at 0.0005 to 0.0025 wt %.

[0049] S:0.0003~0.0030% by weight Sulfur (S) forms fine precipitates such as MnS, CuS, and (Mn, Cu)S, which deteriorate magnetic properties and hot workability, so it is best to keep the content low. Therefore, if S is further included, it can be contained in an amount of 0.0003 to 0.0030 wt. %. More specifically, it can be contained in an amount of 0.0005 to 0.0025 wt. %.

[0050] Ti:0.0003~0.0030wt% Titanium (Ti) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides inside the base material, which inhibit grain growth and deteriorate core loss. Therefore, the Ti content is 0 It must be controlled to below 0.004%, more preferably below 0.002%.

[0051] Nb:0.0003~0.0030wt% Niobium (Nb) forms fine carbides or nitrides inside the matrix, which inhibits grain growth and domain wall movement, thereby deteriorating core loss. Therefore, the Nb content is 0 It must be controlled to below 0.004%, more preferably below 0.002%.

[0052] V:0.0003~0.0030wt% Vanadium (V) forms fine carbides or nitrides inside the matrix, which inhibits grain growth and domain wall movement, thereby deteriorating core loss. Therefore, the V content is 0It must be controlled to below 0.004%, more preferably below 0.002%.

[0053] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of P: 0.005 to 0.05 wt %, Mo: 0.001 to 0.01 wt %, and Ni: 0.005 to 0.04 wt %.

[0054] P:0.005~0.050wt% Phosphorus (P) segregates at the surface and grain boundaries of the steel sheet to suppress surface oxidation during annealing, prevent element diffusion through grain boundaries, and prevent recrystallization in the {111} / / ND orientation, improving the texture. If too little P is added, these effects are insufficient. If too much P is added, hot working properties deteriorate, which can reduce productivity compared to magnetic improvement. Therefore, if P is further included, it can be contained in an amount of 0.005 to 0.050 wt. More specifically, P can be further included in an amount of 0.007 to 0.045 wt.

[0055] Mo:0.001~0.01wt% Molybdenum (Mo) segregates to the surface and grain boundaries to improve texture. If too little Mo is added, the {111} texture develops, which can lead to poor magnetic properties. If too much Mo is added, it can suppress the segregation of Sn and P, reducing the texture improvement effect. Therefore, if Mo is added, it can be included in an amount of 0.001 to 0.01 wt%.

[0056] Ni: 0.005~0.04% by weight Nickel (Ni) increases the ductility of steel and promotes the segregation of Sn and P. If too much Ni is added, the magnetic flux density may drop sharply. Therefore, if Ni is added, it can be included in an amount of 0.005 to 0.04 wt%.

[0057] The balance is composed of Fe and unavoidable impurities. Unavoidable impurities are impurities that are mixed in during the steelmaking stage and the manufacturing process of grain-oriented electrical steel sheets, and as they are widely known in the relevant field, detailed description thereof will be omitted. This does not exclude the addition of elements other than the alloy components described above in one embodiment of the present invention, and various elements may be included within a range that does not impair the technical concept of the present invention. When additional elements are included, they are included in place of the balance of Fe.

[0058] The unavoidable impurities include, for example, B and Zr, and the B content must be controlled to 0.002% by weight or less, and the Zr content must be controlled to 0.005% by weight or less.

[0059] Fig. 1 shows a cross section of a non-oriented electrical steel sheet according to one embodiment of the present invention. As shown in Fig. 1, an oxide layer 20 exists from the surface toward the interior of the electrical steel sheet 100. The electrical steel sheet 100 excluding the oxide layer 20 is classified as the base material 10 of the electrical steel sheet.

[0060] The electrical steel sheet 100 is exposed to oxygen during the manufacturing process, and oxygen in the atmosphere penetrates into the steel sheet, so that an oxygen concentration gradient may exist from the surface toward the interior.

[0061] The oxide layer 20 and the base material 10 are divided into an oxide layer 20 having an oxygen content of 40% by weight or more and a base material 10 having an oxygen content of less than 40% by weight. The thickness of the oxide layer 20 thus divided may be 10 to 50 nm. By forming an oxide layer 20 of such an appropriate thickness, diffusion of nitrogen in the atmosphere during annealing into the base material is suppressed, thereby suppressing the formation of fine nitrides, thereby improving magnetic properties. The thickness of the oxide layer 20 over the entire surface of the steel sheet may vary, and in one embodiment of the present invention, the thickness of the oxide layer 20 refers to the average thickness within the steel sheet.

[0062] In addition to oxygen present due to oxygen penetration during the manufacturing process, the oxide layer 20 contains a large amount of Al that has diffused and concentrated in the base material 10. On the other hand, the increase in Al and O can relatively decrease the Si content.

[0063] Specifically, the oxide layer 20 may contain 1.0 to 30 wt% Al and 0.5 to 10.0 wt% Si. More specifically, the oxide layer 20 may contain 40 to 70 wt% O, 1 to 30 wt% Al, and 0.5 to 10.0 wt% Si, with the remainder being Fe and unavoidable impurities. The formation of an oxide layer enriched in Al suppresses the formation of rounded oxides and fine nitrides within the base material, improving magnetic properties. As with O, a concentration gradient of Al may exist, with the Al content increasing from the base material toward the surface, and the aforementioned range refers to the average content in the oxide layer 20.

[0064] The weight ratio of the Al content to the Si content in the oxide layer 20 may be 5 to 20. When the amount of Al in the oxide layer 20 is increased in this manner, a dense oxide layer is formed, which suppresses the formation of fine precipitates under the surface layer that may occur during the final annealing process, thereby obtaining excellent magnetic properties. More specifically, the weight ratio of the Al content to the Si content in the oxide layer 20 may be 7.0 to 17.0.

[0065] The non-oriented electrical steel sheet according to an embodiment of the present invention may have an average grain size of 55 to 75 μm. The magnetic properties of the non-oriented electrical steel sheet are superior within the above range. The grain size is calculated by dividing the measured area by the number of grains. 0.5 The grain size can be measured based on a plane parallel to the rolled surface (ND plane), and can be measured within the base material 10. Specifically, the average grain size can be 60 to 70 μm.

[0066] In one embodiment of the present invention, the density of AlN precipitates in the surface area can be reduced by appropriately controlling the alloying components. Specifically, the distribution density of AlN precipitates with a diameter of 10 to 500 nm at a depth of 2 μm or less from the surface of the steel sheet toward the inside is reduced to 3 precipitates / mm. 2 By lowering the distribution density of AlN inclusions in this way, it is possible to suppress fine precipitates that hinder domain wall motion, thereby contributing to improved magnetic properties. More specifically, the distribution density of AlN precipitates can be set to 0.5 to 2.5 precipitates / mm 2In this case, the diameter of AlN can be measured based on a plane parallel to the rolling surface (ND plane). The diameter of AlN can be calculated by assuming a circle with the same area as AlN.

[0067] The thickness of the steel plate can be 0.10 to 0.35 mm.

[0068] As described above, one embodiment of the present invention provides an optimal alloy composition, which improves the precipitate characteristics and enhances magnetic properties. Specifically, the iron loss (W) of non-oriented electrical steel sheets can be reduced. 10 / 400 ) is 12.5W / kg or less, magnetic flux density (B 50 ) becomes 1.650T or more. Iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. 50 ) is the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, the iron loss (W 10 / 400 ) is 11.6W / kg or less, magnetic flux density (B 50 ) can be 1.660T or more.

[0069] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of hot rolling a slab to manufacture a hot-rolled sheet, cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet, and final annealing the cold-rolled sheet.

[0070] First, the slab is hot rolled.

[0071] The alloying elements of the slab have been explained in the section on the alloying elements of the non-oriented electrical steel sheet, so a duplicate explanation will be omitted. Since the alloying elements do not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloying elements of the non-oriented electrical steel sheet and the slab are substantially the same.

[0072] Specifically, slabs Is heavyThe alloy contains, in terms of content, 3.0 to 4.0% Si, 0.3 to 1.5% Al, 0.1 to 0.6% Mn, 0.006 to 0.1% one or more of Sn and Sb, 0.0015 to 0.0040% C, 0.01 to 0.03% Cr, 0.003 to 0.008% Cu, and 0.0005 to 0.0025% Mg, with the remainder being Fe and unavoidable impurities, and satisfies the above formula 1.

[0073] Other additional elements have been explained in the alloying elements of non-oriented electrical steel sheets, so duplicate explanations will be omitted.

[0074] The slab is heated before hot rolling. There are no restrictions on the heating temperature of the slab, but it should be heated to 1200°C or less. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab will be redissolved and then finely precipitate during hot rolling and annealing, which can inhibit grain growth and reduce magnetic properties.

[0075] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet is 2 to 2.3 mm. The finish rolling temperature in the hot-rolled sheet production step can be 800°C or higher, specifically 800 to 1000°C. The hot-rolled sheet can be coiled at a temperature of 700°C or lower.

[0076] After the step of producing a hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet. The annealing temperature for the hot-rolled sheet may be 850 to 1150°C. If the annealing temperature for the hot-rolled sheet is too low, the texture may not develop or may develop too finely, making it difficult to obtain a texture favorable for magnetic properties during annealing after cold rolling. If the annealing temperature is too high, the magnetic crystal grains may grow excessively, resulting in excessive surface defects in the sheet. Annealing of the hot-rolled sheet may be performed to increase the orientation favorable for magnetic properties, if necessary, or may be omitted. The annealed hot-rolled sheet may be pickled.

[0077] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. The cold rolling is performed to a final thickness of 0.1 mm to 0.35 mm. The reduction ratio during the cold rolling step can be adjusted to 85% or more. More specifically, the reduction ratio can be 85 to 95%. If the reduction ratio is too low, thickness variations across the width of the steel sheet can occur.

[0078] Next, the cold-rolled sheet undergoes final annealing. The cold-rolled sheet is annealed at a soaking temperature of 900°C or higher for at least 15 seconds. Since the iron loss of non-oriented electrical steel sheet is closely related to the size of the crystal grains, annealing is performed at an appropriate temperature and time. More specifically, the sheet is annealed at a soaking temperature of 950 to 1100°C for 30 to 150 seconds.

[0079] In the final annealing step, the cold-rolled sheet is annealed in an atmosphere containing 40% or less by volume of hydrogen (H2) and 60% or more by volume of nitrogen, with a dew point of 0 to -40°C. Specifically, the annealing is performed in an atmosphere containing 5 to 40% by volume of hydrogen and 60 to 95% by volume of nitrogen. During the final annealing process, the average grain size becomes 55 to 75 μm, and all (i.e., 99% or more) of the worked structure formed in the previous cold rolling step is recrystallized.

[0080] After final annealing, an insulating coating is formed, which can be an organic, inorganic, or organic / inorganic composite coating, or can be any other insulating coating material.

[0081] The present invention will be described in more detail below with reference to examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. [Example]

[0082] Slabs were produced from the components shown in Tables 1 and 2, with the balance consisting of Fe and unavoidable impurities. They were heated to 1150°C and hot rolled at a finishing temperature of 830°C to produce hot-rolled sheets with a thickness of 2.3 mm. The hot-rolled sheets were annealed at 1030°C for 100 seconds, then cold-rolled to a thickness of 0.27 mm and recrystallized at 950°C for 88 seconds.

[0083] The thickness of the oxide layer for each test piece, the Al and Si content in the oxide layer, and the distribution density W of AlN in the surface layer 10 / 400 Iron loss, B 50 The magnetic flux density is shown in Table 3.

[0084] The thickness of the oxide layer was measured by processing the test piece with FIB to produce a smooth cross section, photographing this with a TEM at high magnification, and measuring the thickness of the oxide layer at 10 or more points on the surface of the base material. The average value was shown.

[0085] acid The thickness of the oxide layer was measured at 10 or more points on the surface of the base material by processing the test piece with FIB to produce a smooth cross section, photographing this with a high magnification TEM, and the average value was calculated.

[0086] For each test piece, magnetic properties such as magnetic flux density and iron loss were measured by cutting five test pieces of 60 mm wide x 60 mm long x 5 pieces, measuring the rolling direction and the direction perpendicular to the rolling direction with a single sheet tester, and the average values ​​were shown. 10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, and B 50 means the magnetic flux density induced in a magnetic field of 5000 A / m.

[0087] [Table 1] [Table 2]

[0088] [Table 3]

[0089] As shown in Tables 1 to 3, in the cases of A4, B4, C3, C4, D3, and D4, in which the alloy components are appropriately controlled, an oxide layer is appropriately formed, and less AlN is formed, resulting in excellent magnetic properties.

[0090] On the other hand, it can be seen that Al contains too little Cr, so that the oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0091] It can be seen that A2 contains too little Mg, so the oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0092] It can be seen that in A3, the value of Equation 1 is too large, so the oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0093] Since B1 contains a large amount of Sn and Sb and the value of Equation 1 is too large, an oxide layer cannot be formed properly, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0094] It can be seen that B2 contains a large amount of Mg, so that an oxide layer cannot be formed properly, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0095] It can be seen that in B3, the value of Equation 1 is too small, so the oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0096] It can be seen that C1 contains a large amount of Cu, so that an oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0097] It can be seen that C2 contains small amounts of Sn and Sb, and the value of Equation 1 is too small, so the oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0098] It can be seen that D1 contains too little Cu, so the oxide layer cannot be properly formed, and a large amount of AlN is formed, resulting in poor magnetic properties.

[0099] It can be seen that D2 contains too much Cr, which prevents the oxide layer from forming properly, resulting in the formation of a large amount of AlN, resulting in poor magnetic properties.

[0100] It can be seen that D5 contains too little Al, which prevents the oxide layer from forming properly, resulting in poor magnetic properties.

[0101] The present invention is not limited to the examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above example is illustrative in all respects and not limiting. [Explanation of symbols]

[0102] 100 Non-oriented electrical steel sheet 10 Base material 20 Oxide layer

Claims

1. The alloy contains, by weight, 3.0 to 4.0% Si, 0.3 to 1.5% Al, 0.1 to 0.6% Mn, 0.006 to 0.1% total of one or more of Sn and Sb, 0.0015 to 0.0040% C, 0.01 to 0.03% Cr, 0.003 to 0.008% Cu, and 0.0005 to 0.0025% Mg, with the balance being Fe and unavoidable impurities, and satisfies the following formula 1: A non-oriented electrical steel sheet characterized in that the distribution density of AlN precipitates having a diameter of 10 to 500 nm at a depth of 2 μm or less from the surface toward the interior of the steel sheet is 3 precipitates / mm 2 or less. [Formula 1] 0.66≦([Sn]+[Sb]) / ([Cr]+[Cu]+[Mg])≦2.00 (In formula 1, [Sn], [Sb], [Cr], [Cu], and [Mg] represent the contents (wt%) of Sn, Sb, Cr, Cu, and Mg, respectively.)

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising at least one of N, S, Ti, Nb and V in an amount of 0.0003 to 0.0030 wt % each.

3. 3. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.005 to 0.05 wt %, Mo: 0.001 to 0.01 wt %, and Ni: 0.005 to 0.04 wt %.

4. 4. The non-oriented electrical steel sheet according to claim 1, wherein the average grain size is 55 to 75 μm.

5. 5. The non-oriented electrical steel sheet according to claim 1, wherein an oxide layer is present from the surface of the steel sheet toward the interior, and the thickness of the oxide layer is 10 to 50 nm.

6. 6. The non-oriented electrical steel sheet according to claim 5, wherein the oxide layer contains 1.0 to 30% by weight of Al and 0.5 to 10.0% by weight of Si.

7. 7. The non-oriented electrical steel sheet according to claim 5, wherein the weight ratio of the Al content to the Si content in the oxide layer is 5 to 20.

8. The non-oriented electrical steel sheet according to any one of claims 1 to 7, characterized in that the thickness is 0.10 to 0.35 mm.

9. a step of manufacturing a hot-rolled sheet by hot-rolling a slab containing, by weight %, 3.0 to 4.0% Si, 0.3 to 1.5% Al, 0.1 to 0.6% Mn, 0.006 to 0.1% total of one or more of Sn and Sb, 0.0015 to 0.0040% C, 0.01 to 0.03% Cr, 0.003 to 0.008% Cu, and 0.0005 to 0.0025% Mg, with the balance being Fe and unavoidable impurities, and satisfying the following formula 1: cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; and final annealing of the cold-rolled sheet; A method for producing a non-oriented electrical steel sheet, characterized in that the distribution density of AlN precipitates having a diameter of 10 to 500 nm at a depth of 2 μm or less from the surface toward the interior of the steel sheet is 3 precipitates / mm 2 or less. [Formula 1] 0.66≦([Sn]+[Sb]) / ([Cr]+[Cu]+[Mg])≦2.00 (In formula 1, [Sn], [Sb], [Cr], [Cu] and [Mg] represent the contents (wt%) of Sn, Sb, Cr, Cu and Mg in the slab, respectively.)

10. The method for manufacturing a non-oriented electrical steel sheet according to claim 9, further comprising the step of heating the slab to 1200°C or less before the step of manufacturing the hot-rolled steel sheet.

11. The method for producing a non-oriented electrical steel sheet according to claim 9 or 10, wherein the finish rolling temperature in the step of producing the hot-rolled sheet is 800°C or higher.

12. The method for manufacturing a non-oriented electrical steel sheet according to any one of claims 9 to 11, further comprising the step of annealing the hot-rolled sheet at 850 to 1150°C after the step of manufacturing the hot-rolled sheet.

13. The method for manufacturing a non-oriented electrical steel sheet according to any one of claims 9 to 12, wherein the final annealing step comprises annealing at a soaking temperature of 900°C or more for 15 seconds or more.

14. The final annealing step is carried out in a hydrogen (H ２ 14. The method for producing a non-oriented electrical steel sheet according to claim 9, wherein the non-oriented electrical steel sheet is annealed in an atmosphere containing 40% by volume or less of Cr, 0.5% by volume or less of Ni, and 60% by volume or more of Ni, and having a dew point of 0 to −40° C.

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