Non-oriented electrical steel sheet and its manufacturing method

Abstract

A non-oriented electrical steel sheet and a manufacturing method thereof are provided. [Solution] The non-oriented electrical steel sheet of the present invention contains, by weight, 3.1-3.8% Si, 0.5-1.5% Al, 0.3-1.5% Mn, 0.01-0.15% Cr, 0.003-0.08% Sn, 0.003-0.06% Sb, with the remainder being Fe and unavoidable impurities, satisfies the following formula 1, and includes a surface portion and a central portion that exist from the surface of the steel sheet toward the inside of the steel sheet to 1 / 10 of the thickness of the steel sheet, and when the non-oriented electrical steel sheet is punched out, the length of the plastically deformed portion is 100 μm or less, and the plastically deformed portion is the length from the punched end where the hardness of the surface portion exceeds 1.10 times the hardness of the central portion. [Formula 1] 0.03≦([Cr]+[Sn]+[Sb])≦0.2 (In formula 1, [Cr], [Sn], and [Sb] represent the contents (wt%) of Cr, Sn, and Sb, respectively.)

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 and a manufacturing method thereof that can ensure magnetism and extend the life of a die in a high alloy system by adjusting the dew point in the initial heating stage during annealing of a cold-rolled sheet in accordance with the alloy composition in the steel sheet and the surface roughness of the cold-rolled sheet, thereby forming an appropriate surface portion in the steel sheet, and that can thereby extend the life of a die in a high alloy system. [Background technology]

[0002] Efficient use of electrical energy has become a major issue in order to improve the global environment, including saving energy, reducing fine dust generation, and reducing greenhouse gas emissions. Currently, more than 50% of all electrical energy is consumed by electric motors, so in order to use electricity efficiently, it is essential that electric motors become more efficient. Recently, interest in highly efficient drive motors has grown rapidly with the rapid development of the environmentally friendly automobile sector (hybrids, plug-in hybrids, electric vehicles, fuel cell vehicles, etc.). At the same time, the demand for efficient use of electrical energy has become higher than ever before due to the recognition of high efficiency in high-efficiency motors for home appliances and super premium motors for heavy electrical equipment, as well as continued government regulations.

[0003] On the other hand, in order to increase the efficiency of electric motors, optimization in all areas, from material selection to design, assembly, and control, is extremely important. In terms of materials, there is a strong demand for low iron loss and high strength electromagnetic steel sheets. Automobile drive motors and air conditioner compressor motors must operate not only in the commercial frequency range but also in the high frequency range, so low iron loss characteristics at high frequencies are extremely important. High strength characteristics are also important to ensure stability during high-speed rotation. For this reason, a method is known in which large amounts of elements such as Si, Al, and Mn are added to simultaneously ensure low iron loss at high frequencies and high strength.

[0004] However, when large amounts of elements such as Si, Al, and Mn are added, it shortens the life of the die used in the punching process of the motor manufacturing process, so it is necessary to improve the material properties in order to extend the life of the die in such high alloy systems. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a non-oriented electrical steel sheet and a manufacturing method thereof, which is capable of adjusting the dew point in the initial heating stage of annealing the cold-rolled sheet according to the alloy composition in the steel sheet and the surface roughness of the cold-rolled sheet, thereby forming an appropriate surface part in the steel sheet, thereby ensuring magnetism and at the same time extending the life of the die in a high alloy system, and a manufacturing method thereof. [Means for solving the problem]

[0006] The non-oriented electrical steel sheet of the present invention contains, by weight%, 3.1 to 3.8% Si, 0.5 to 1.5% Al, 0.3 to 1.5% Mn, 0.01 to 0.15% Cr, 0.003 to 0.08% Sn, 0.003 to 0.06% Sb, with the remainder being Fe and unavoidable impurities, and satisfies the following formula 1: The non-oriented electrical steel sheet includes a surface portion and a central portion that are present from the surface of the steel sheet toward the inside of the steel sheet up to 1 / 10 of the thickness of the steel sheet, and is characterized in that when the non-oriented electrical steel sheet is punched, the length of the plastically deformed portion is 100 μm or less, and the plastically deformed portion is the length from the punched end to the portion where the hardness of the surface portion exceeds 1.10 times the hardness of the central portion. [Formula 1] 0.03≦([Cr]+[Sn]+[Sb])≦0.2 (In formula 1, [Cr], [Sn], and [Sb] represent the contents (wt%) of Cr, Sn, and Sb, respectively.)

[0007] The steel sheet of the present invention may further contain Cu: 0.01 to 0.2 wt %. The steel plate may further contain one or more of P: 0.08% by weight or less, Mo: 0.03% by weight or less, B: 0.0050% by weight or less, Ca: 0.0050% by weight or less, and Mg: 0.0050% by weight or less.

[0008] The steel plate may further contain one or more of C, N, S, Ti, Nb, and V in an amount of 0.005% by weight or less. The surface roughness of the steel sheet is preferably 0.15 to 0.35 μm. The hardness of the surface portion is preferably 1.05 to 1.10 times that of the central portion.

[0009] A method for producing a non-oriented electrical steel sheet of the present invention includes the steps of: hot rolling a slab containing, by weight, 3.1-3.8% Si, 0.5-1.5% Al, 0.3-1.5% Mn, 0.01-0.15% Cr, 0.003-0.08% Sn, 0.003-0.06% Sb, 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 cold-rolling the cold-rolled sheet. The step of annealing the cold-rolled sheet includes a first heating step of heating the cold-rolled sheet from 200°C to 500°C, a second heating step of heating the cold-rolled sheet from a temperature above 500°C to less than the soaking temperature, and a soaking step, and is characterized in that the following formula 2 is satisfied.

[0010] [Formula 1] 0.030≦([Cr]+[Sn]+[Sb])≦0.200 [Formula 2] {([Cr]+[Sn]+[Sb])×[Sheet thickness]} / {([Si]+[Al])×[Sheet roughness]}≦[DP] (In the formulas 1 and 2, [Si], [Al], [Cr], [Sn] and [Sb] respectively represent the contents (weight%) of Si, Al, Cr, Sn and Sb, [sheet thickness] represents the sheet thickness (μm) of the cold-rolled sheet after the step of producing the cold-rolled sheet, [sheet roughness] represents the surface roughness (μm) of the cold-rolled sheet after the step of producing the cold-rolled sheet, and [DP] represents the dew point (°C) in the first heating stage.)

[0011] After the step of producing the cold-rolled sheet, the surface roughness of the cold-rolled sheet may be 0.15 to 0.35 μm. The dew point in the first temperature increase stage can be from 0 to 50°C. The dew point in the second heating stage and the heat soaking stage is preferably -30 to 10°C. Effect of the Invention

[0012] According to the present invention, the non-oriented electrical steel sheet of the present invention can ensure magnetic properties and at the same time extend the life of dies in high alloy systems. When the non-oriented electrical steel sheet of the present invention is used to manufacture a motor, the motor can be driven with a small current even at high speed rotation, resulting in excellent motor efficiency. Ultimately, the non-oriented electrical steel sheet of the present invention can contribute to the manufacture of environmentally friendly motors for automobiles, highly efficient motors for home appliances, and super-premium class electric motors. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram of a side cross section of a non-oriented electrical steel sheet according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining a plastically deformed portion during punching of a non-oriented electrical steel sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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. Thus, the first part, component, region, layer or section described below may be read as the second part, component, region, layer or section without departing from the scope of the present invention. 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 form includes the plural form unless the text clearly indicates otherwise. As used herein, the meaning of "comprising" embodies certain features, regions, integers, steps, operations, elements and / or components and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements and / or components.

[0015] When an element is referred to as being "on" another element, it means that it is directly on top of the other element, or there may be other elements between them. In contrast, when an element is referred to as being "directly on" another element, there are no other elements between them. 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 the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined. Moreover, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0016] In an embodiment of the present invention, the term "additionally containing an additional element" means that the additional amount of the additional element is substituted for the remaining iron (Fe). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0017] In one embodiment of the present invention, the dew point is adjusted in the initial heating stage during annealing of the cold-rolled sheet according to the alloy composition in the steel sheet and the surface roughness of the cold-rolled sheet to form an appropriate surface area in the steel sheet, thereby ensuring magnetism and at the same time extending the life of the mold in high alloy systems. A non-oriented electrical steel sheet according to an embodiment of the present invention contains, by weight, 3.1-3.8% Si, 0.5-1.5% Al, 0.3-1.5% Mn, 0.01-0.15% Cr, 0.003-0.08% Sn, 0.003-0.06% Sb, and the remainder being Fe and unavoidable impurities. First, the reasons for limiting the components of non-oriented electrical steel sheets will be explained.

[0018] Si:3.10~3.80wt% Silicon (Si) plays a role in increasing the resistivity of the material, reducing iron loss, and increasing strength. If too little Si is added, the effect of improving high-frequency iron loss and strength is insufficient, while if too much is added, the hardness of the material increases, decreasing productivity and punchability, which is not preferable. Specifically, it is preferable for Si to be contained in an amount of 3.20 to 3.60% by weight.

[0019] Al: 0.50~1.50% by weight Aluminum (Al) plays a role in increasing the resistivity of the material, reducing iron loss, and improving strength. If too little Al is added, the effect of reducing high-frequency iron loss and improving strength is insufficient, and there is a risk that nitrides will be formed finely, reducing magnetic properties. Conversely, if too much is added, there is a risk that problems will arise in all processes, such as steelmaking and continuous casting, and productivity will be greatly reduced. Therefore, it is preferable to add Al within the above-mentioned range. Specifically, it is preferable to include 0.50 to 1.30 weight % of Al.

[0020] Mn:0.3~1.5wt% Manganese (Mn) plays a role in increasing the resistivity of the material, improving core loss, and forming sulfides. If too little Mn is added, there is a risk that MnS will precipitate finely and reduce magnetic properties. Conversely, if too much Mn is added, there is a risk that the formation of {111} texture, which is unfavorable to magnetic properties, will be promoted, resulting in a decrease in magnetic flux density. Therefore, it is preferable to add Mn within the above-mentioned range. Specifically, it is preferable to include 0.5 to 1.4 wt% Mn. More specifically, it is preferable to include 1.0 to 1.3 wt% Mn.

[0021] Specific resistance 45 μΩ cm or more The resistivity is a value calculated from 13.25 + 11.3 × ([Si] + [Al] + [Mn] / 2), where [Si], [Al], and [Mn] indicate the content (weight %) of Si, Al, and Mn, respectively. The higher the resistivity, the lower the iron loss. If the resistivity is too low, the iron loss will increase, making it difficult to use as a high-efficiency motor. Specifically, the resistivity should be 50 to 80 μΩ·cm. More specifically, the resistivity should be 60 to 75 μΩ·cm.

[0022] Cr:0.010~0.150wt%, Sn:0.003~0.080wt%, Sb:0.003~0.060wt% Chromium (Cr), tin (Sn), and antimony (Sb) segregate to the surface when the annealing conditions are appropriately adjusted. When Cr, Sn, and Sb are contained within the above-mentioned ranges, segregation occurs appropriately. If the amount is less than the above-mentioned range, there is no surface segregation effect, and if it is too much, the brittleness of the material may be strengthened, which may cause problems. Specifically, it is preferable to contain Cr: 0.010 to 0.100 weight%, Sn: 0.005 to 0.050 weight%, and Sb: 0.005 to 0.030 weight%, respectively.

[0023] In one embodiment of the present invention, the non-oriented electrical steel sheet preferably satisfies Formula 1. [Formula 1] 0.030≦([Cr]+[Sn]+[Sb])≦0.200 (In formula 1, [Cr], [Sn], and [Sb] represent the contents (wt%) of Cr, Sn, and Sb, respectively.) Formula 1 is the range in which surface segregation is most efficient. If the value is smaller than the lower limit of formula 1, there is a problem that the dew point must be lowered to efficiently segregate, and there is a risk of reduced productivity. On the other hand, if the value is larger than the upper limit of formula 1, there is a risk that rolling becomes impossible. Specifically, the value of formula 1 is preferably 0.030 to 0.100. The non-oriented electrical steel sheet according to an embodiment of the present invention may further include Cu: 0.01 to 0.2 wt %.

[0024] Cu:0.01~0.20wt% Copper (Cu) plays a role in forming sulfides together with Mn. When Cu is further added, if too little Cu is added, there is a risk that CuMnS will precipitate finely and reduce the magnetic property. On the other hand, if too much Cu is added, there is a risk that high-temperature brittleness will occur and cracks will form during continuous casting or hot rolling. Specifically, it is preferable that Cu is contained in an amount of 0.01 to 0.10 wt%.

[0025] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of P: 0.08 wt.% or less, Mo: 0.03 wt.% or less, B: 0.0050 wt.% or less, V: 0.0050 wt.% or less, Ca: 0.0050 wt.% or less, Nb: 0.0050 wt.% or less, and Mg: 0.0050 wt.% or less.

[0026] P: 0.08% by weight or less Phosphorus (P) accumulates on the surface and plays a role in controlling the fraction of the internal oxide layer. If the amount of P added is too small, it may be difficult to form a uniform internal oxide layer. On the other hand, if the amount of P added is too large, the melting point of the Si-based oxide may fluctuate, and the internal oxide layer may be formed suddenly. Therefore, it is preferable to control the P content within the above-mentioned range. Specifically, it is preferable to include 0.005 to 0.07 wt % of P.

[0027] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of Mo: 0.03 wt % or less, B: 0.0050 wt % or less, Ca: 0.0050 wt % or less, and Mg: 0.0050 wt % or less. These may react with the inevitably contained C, S, N, etc. to form fine carbides, nitrides, or sulfides, which may adversely affect magnetic properties, so it is preferable to limit the upper limit as described above.

[0028] Other impurities In addition to the above-mentioned elements, unavoidable impurities such as carbon (C), sulfur (S), nitrogen (N), titanium (Ti), niobium (Nb), and vanadium (V) may be included. It is preferable to limit the amount of C, N, and Ti, since they form carbonitrides and play a role in preventing magnetic domain movement, and it is preferable to limit the amount of S, since it forms sulfides and may deteriorate grain growth. Each of these elements should be contained in an amount of 0.0040% by weight or less.

[0029] N combines with Ti, Nb, and V to form nitrides, and plays a role in reducing grain growth. C reacts with N, Ti, Nb, V, etc. to form fine carbides, which play a role in impeding grain growth and magnetic domain movement. S forms sulfides and deteriorates grain growth. When impurity elements are further contained in this way, one or more of C, S, N, Ti, Nb and V may be contained in an amount of 0.005 wt % or less each.

[0030] FIG. 1 shows a schematic diagram of a side cross section of a non-oriented electrical steel sheet according to one embodiment of the present invention. The non-oriented electrical steel sheet in Fig. 1 is merely for illustrating the present invention, and the present invention is not limited thereto. Therefore, the structure of the non-oriented electrical steel sheet can be modified in various ways. As shown in FIG. 1, a non-oriented electrical steel sheet 100 according to an embodiment of the present invention includes a surface portion 20 and a center portion 10 that extend from the surface of the steel sheet toward the inside of the steel sheet up to 1 / 10 of the thickness of the steel sheet. The surface roughness of the steel sheet is preferably 0.15 to 0.35 μm. If the sheet roughness is too high, the amount of residual oxygen on the sheet surface increases, making it difficult to control the dew point, and if the sheet roughness is reduced too much, there is a risk of a decrease in rolling productivity.

[0031] The hardness of the surface portion 20 is preferably 1.05 to 1.10 times that of the central portion 10. In one embodiment of the present invention, a large amount of alloying components such as Si, Al, and Mn are added, and the alloying components are concentrated in the surface portion 20 during the manufacturing process, so that the hardness of the surface portion 20 is increased compared to that of the central portion 10. In one embodiment of the present invention, the precipitation characteristics and oxidation characteristics of the surface portion 20 are adjusted to appropriately adjust the hardness, so that the life of the mold can be extended despite the high alloy system. At this time, the hardness is Vickers hardness, and can be measured with a micro Vickers hardness tester under a load of 10 g. More specifically, the hardness of the surface portion 20 is preferably 1.06 to 1.09 times that of the central portion 10. The hardness of the surface portion 20 is preferably 230-285, and the hardness of the central portion 10 is preferably 200-265. Specifically, the hardness of the surface portion 20 is preferably 245-275, and the hardness of the central portion 10 is preferably 220-255.

[0032] In the non-oriented electrical steel sheet 100, the hardness may be uniform over the entire surface of the steel sheet. However, the hardness of the punched end increases during punching. In particular, the hardness of the surface portion 20 increases significantly compared to the center portion 10, which shortens the life of the die. In one embodiment of the present invention, the precipitation and oxidation characteristics of the surface portion 20 are controlled to suppress the area where the hardness of the surface portion 20 increases during punching, thereby minimizing the deterioration of iron loss due to punching. Specifically, when punching the non-oriented electrical steel sheet, it is preferable that the length of the plastic deformation portion is 100 μm or less. In this case, the plastic deformation portion is the length of the portion from the punched end where the hardness of the surface portion 20 exceeds 1.10 times the hardness of the center portion 10.

[0033] FIG. 2 shows a method for measuring the length of the plastically deformed portion. When a steel plate is punched, a punched end is generated as shown at the right end of FIG. 2. The punched end has a slope, a shear surface, a fracture surface, and a burr. While measuring the hardness from the punched end toward the opposite end, the length of the portion where the hardness of the surface portion 20 exceeds 1.10 times the hardness of the central portion 10 is measured. This is called the length of the plastically deformed portion. More specifically, the length of the plastically deformed portion is preferably 90 μm or less. The lower limit is not particularly limited, but may be 50 μm or more. During punching, the clearance is set to 8% of the thickness, and the length of the plastically deformed portion can be measured.

[0034] The non-oriented electrical steel sheet according to an embodiment of the present invention is also excellent in magnetic properties. Specifically, after punching, the core loss (W 10 / 400 ) should be 13.5W / kg or less. 10 / 400 ) is the iron loss when a magnetic flux density of 1.0T is induced at a frequency of 400Hz. More specifically, the iron loss of non-oriented electrical steel sheet (W 10 / 400 ) should be 10.0 to 12.5 W / kg.

[0035] A method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of hot rolling a slab containing, by weight, 3.1-3.8% Si, 0.5-1.5% Al, 0.3-1.5% Mn, 0.01-0.15% Cr, 0.003-0.08% Sn, 0.003-0.06% Sb, 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 cold-rolling the cold-rolled sheet. [Formula 1] 0.030≦([Cr]+[Sn]+[Sb])≦0.200 Each step will be explained in detail below.

[0036] First, a slab is manufactured. The reason for limiting the addition ratio of each component in the slab is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated explanation will be omitted. Since the composition of the slab does not substantially change during the manufacturing process such as hot rolling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing described below, the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially the same. Before the step of producing a hot-rolled sheet, the slab can be heated. Specifically, the slab is charged into a heating furnace and heated to 1100 to 1250°C. When heated to a temperature exceeding 1250°C, precipitates may re-melt and precipitate finely after hot rolling. The heated slab is hot-rolled to 2 to 2.3 mm to produce a hot-rolled sheet. In the stage of producing the hot-rolled sheet, the finish rolling temperature is preferably 800 to 1000°C.

[0037] After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet. At this time, the annealing temperature of the hot-rolled sheet is preferably 850 to 1150°C. If the annealing temperature of the hot-rolled sheet is less than 850°C, the structure does not grow or grows finely, so that the effect of increasing the magnetic flux density is reduced, while if the annealing temperature exceeds 1150°C, the magnetic properties are rather deteriorated, and there is a risk that the workability during rolling is deteriorated due to deformation of the sheet shape. Specifically, the temperature range is preferably 950 to 1125°C. More specifically, the annealing temperature of the hot-rolled sheet is preferably 900 to 1100°C. The hot-rolled sheet annealing is performed to increase the orientation favorable to magnetism as necessary, and may be omitted.

[0038] Next, the hot-rolled sheet is pickled and cold-rolled to a predetermined sheet thickness. Although different application is possible depending on the thickness of the hot-rolled sheet, cold rolling can be applied to a rolling reduction of 70 to 95% so that the final thickness is 0.2 to 0.65 mm. In order to match the rolling reduction, it is preferable to perform one cold rolling or two or more cold rollings with intermediate annealing in between. After the step of producing the cold-rolled sheet, the surface roughness of the cold-rolled sheet is preferably 0.15 to 0.35 μm. If the sheet roughness is too high, the amount of residual oxygen on the sheet surface increases, making it difficult to control the dew point, and if the sheet roughness is reduced too much, there is a risk of reducing rolling productivity.

[0039] The cold-rolled sheet is subjected to cold-rolled sheet annealing. The step of annealing the cold-rolled sheet includes a first heating stage in which the cold-rolled sheet is heated from 200°C to 500°C, a second heating stage in which the cold-rolled sheet is heated from above 500°C to below the soaking temperature, and a soaking stage, and satisfies the following formula 2. [Formula 2] {([Cr]+[Sn]+[Sb])×[Sheet thickness]} / {([Si]+[Al])×[Sheet roughness]}≦[DP] (In formula 2, [Si], [Al], [Cr], [Sn] and [Sb] respectively represent the contents (weight%) of Si, Al, Cr, Sn and Sb, [sheet thickness] represents the sheet thickness (μm) of the cold-rolled sheet after the step of producing the cold-rolled sheet, [sheet roughness] represents the surface roughness (μm) of the cold-rolled sheet after the step of producing the cold-rolled sheet, and [DP] represents the dew point (°C) in the first heating stage.)

[0040] If the dew point in the first temperature rise stage does not satisfy formula 2, that is, if the dew point is not sufficiently high, the amount of oxidation of the surface portion 10 will be greater than the amount of segregation, making it difficult to appropriately adjust the hardness of the surface portion 10. Specifically, the dew point in the first temperature rise stage is preferably 0 to 30°C. In the second heating stage, the cold-rolled sheet is heated from a temperature exceeding 500°C to a temperature lower than the soaking temperature. The dew point in the second heating stage is preferably -30 to 10°C. In the second heating stage, the dew point can be adjusted to be lower than that in the first heating stage to prevent oxidation. Specifically, the dew point in the second heating stage is preferably -30 to 0°C. Specifically, the dew point in the second heating stage is preferably -30 to -10°C. More specifically, the dew point in the second heating stage is preferably 10 to 60°C lower than that in the first heating stage.

[0041] The soaking step is a step in which the temperature is maintained uniformly without any fluctuation after the soaking temperature is reached. The soaking temperature can be 800 to 1070°C. If the soaking temperature is too low, recrystallization is not sufficiently performed, while if the soaking temperature is too high, the grain size becomes too large, which may deteriorate the high-frequency core loss. The soaking step can be adjusted to the same dew point as the second heating step. The soaking time can be 10 seconds to 5 minutes. The method further includes forming an insulating layer, which is a method well known in the field of non-oriented electrical steel sheets, and therefore will not be described in detail.

[0042] Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples. Example 1 A slab with the composition shown in Table 1 below was manufactured. All of the components other than those listed in Table 1, such as C, S, N, Ti, Nb, and V, were controlled to 0.003% by weight or less, with the remainder being Fe. The slab was heated to 1150°C and hot-finish rolled at 850°C to produce a hot-rolled sheet with a thickness of 2.0 mm. The hot-rolled sheet was annealed at 1100°C for 4 minutes and then pickled. It was then cold-rolled to produce a sheet with a thickness and surface roughness as shown in Table 2, and then cold-rolled sheet annealing was performed.

[0043] The dew point in the first heating stage was adjusted as shown in Table 2 below, and the dew point in the second heating stage and the soaking stage was adjusted to about -10° C. The soaking temperature in the soaking stage was 970° C. and maintained for 3 minutes. The hardness of the surface was measured by grinding the surface of the steel plate to 1 / 20 of the total thickness with smooth sandpaper of #1000 or more, and then fine polishing and electrolytic polishing were performed to prevent stress from being induced on the surface by polishing. The hardness of the center was measured by polishing the surface of the steel plate to 1 / 2 of the total thickness with smooth sandpaper of #1000 or more, and then fine polishing and electrolytic polishing were performed to prevent stress from being induced on the surface by polishing.

[0044] For each test piece, 5 test pieces measuring 60 mm wide x 60 mm long were cut, and the iron loss was measured in the rolling direction and the direction perpendicular to the rolling direction using a single sheet tester, and the average value was shown. The plastically deformed portion was cut as described above with a tolerance of 8% of the thickness. The length where the ratio of the hardness of the surface portion to the hardness of the center portion exceeded 1.10 was measured by moving 5 μm from the punched end. Hardness, iron loss (W 10 / 400 ) and the length of the plastically deformed part are summarized in Table 3.

[0045] [Table 1]

[0046] [Table 2]

[0047] [Table 3]

[0048] As shown in Tables 1 to 3, in the examples that satisfy the alloy components and manufacturing process conditions, it can be confirmed that the precipitation and oxidation characteristics of the surface portion are appropriately adjusted, the iron loss is improved, and the length of the plastically deformed portion is short. It can be confirmed that test pieces 2 and 9 do not satisfy formula 2, and the length of the plastically deformed portion is long, resulting in inferior iron loss. It can be confirmed that test pieces 3 and 4 have low amounts of alloying elements such as Si, Al, and Mn added, and therefore have inferior iron loss. It can be confirmed that test pieces Nos. 7, 10, 11, and 12, which contain small amounts of Cr, Sn, and Sb, have a long length of the plastically deformed portion and are inferior in iron loss. It can be seen that in test piece No. 8, Cr, Sn, and Sb were added in excessive amounts, which resulted in a long length of the plastically deformed portion and inferior core loss.

[0049] The present invention is not limited to the above-mentioned embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will 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-mentioned embodiments are illustrative in all respects and are not limiting. [Explanation of symbols]

[0050] 100: Non-oriented electrical steel sheet, 10: Center part, 20: Surface part

Claims

1. The alloy contains, by weight, 3.1 to 3.8% Si, 0.5 to 1.5% Al, 0.3 to 1.5% Mn, 0.01 to 0.15% Cr, 0.003 to 0.08% Sn, 0.003 to 0.06% Sb, with the balance being Fe and unavoidable impurities, and satisfies the following formula 1: The surface portion and the center portion are located from the surface of the steel plate to 1 / 10 of the thickness of the steel plate in the direction toward the inside of the steel plate, A non-oriented electrical steel sheet, characterized in that when the non-oriented electrical steel sheet is punched, the length of the plastically deformed portion is 100 μm or less, and the plastically deformed portion is the length of a portion from the punched end where the hardness of the surface portion exceeds 1.10 times the hardness of the central portion. [Formula 1] 0.03≦([Cr]+[Sn]+[Sb])≦0.2 (In formula 1, [Cr], [Sn] and [Sb] represent the contents (wt%) of Cr, Sn and Sb, respectively.)

2. The non-oriented electrical steel sheet according to claim 1, further comprising Cu: 0.01 to 0.2 wt %.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.08 wt % or less, Mo: 0.03 wt % or less, B: 0.0050 wt % or less, Ca: 0.0050 wt % or less, and Mg: 0.0050 wt % or less.

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising 0.005% by weight or less of one or more of C, N, S, Ti, Nb, and V.

5. 2. The non-oriented electrical steel sheet according to claim 1, characterized in that the surface roughness of the steel sheet is 0.15 to 0.35 μm.

6. The non-oriented electrical steel sheet according to claim 1, characterized in that the hardness of the surface portion is 1.05 to 1.10 times the hardness of the central portion.

7. A step of producing a hot-rolled sheet by hot-rolling a slab containing, by weight, 3.1 to 3.8% Si, 0.5 to 1.5% Al, 0.3 to 1.5% Mn, 0.01 to 0.15% Cr, 0.003 to 0.08% Sn, 0.003 to 0.06% Sb, 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 annealing the cold-rolled sheet. The step of annealing the cold-rolled sheet includes a first heating step of heating the cold-rolled sheet from 200 ° C. to 500 ° C., a second heating step of heating the cold-rolled sheet from above 500 ° C. to less than a soaking temperature, and a soaking step; A method for producing a non-oriented electrical steel sheet, characterized in that the following formula 2 is satisfied: [Formula 1] 0.030≦([Cr]+[Sn]+[Sb])≦0.200 [Formula 2] {([Cr] + [Sn] + [Sb]) × [sheet thickness]} / {([Si] + [Al]) × [sheet roughness]} ≦ [DP] (In Formula 1 and Formula 2, [Si], [Al], [Cr], [Sn] and [Sb] respectively represent the contents (wt%) of Si, Al, Cr, Sn and Sb, [Sheet Thickness] represents the sheet thickness (μm) of the cold-rolled sheet after the step of producing the cold-rolled sheet, [Sheet Roughness] represents the surface roughness (μm) of the cold-rolled sheet after the step of producing the cold-rolled sheet, and [DP] represents the dew point (° C.) at the first heating stage.)

8. 8. The method of claim 7, wherein the surface roughness of the cold-rolled sheet after the step of producing the cold-rolled sheet is 0.15 to 0.35 μm.

9. The method for producing a non-oriented electrical steel sheet according to claim 7, wherein the dew point in the first heating step is 0 to 50°C.

10. The method for producing a non-oriented electrical steel sheet according to claim 7, wherein a dew point in the second heating step and the soaking step is -30 to 10°C.

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