Non-oriented electrical steel sheet and its manufacturing method

Abstract

Provided is a non-oriented electrical steel sheet and its manufacturing method, which increases the amount of shot balls projected during scale removal, increases the number of nucleation sites in the electrical steel sheet, ensures fine crystal grains after annealing of the cold-rolled sheet, and increases the omnidirectional yield strength of the electrical steel sheet. [Solution] The non-oriented electrical steel sheet of the present invention is characterized in that it contains, by weight, 2.0-6.5% Si, 0.1-1.3% Al, 0.3-2.0% Mn, with the remainder being Fe and unavoidable impurities, the area fraction of crystal grains having a grain size of 10% or less of the sheet thickness is 10.0%-35.0%, and the number fraction is 15%-55%, and further contains one or more of 0.2% by weight or less Cr (excluding 0%), 0.06% by weight or less Sn (excluding 0%), and 0.06% by weight or less Sb (excluding 0%), and further contains 0.005% by weight or less of one or more of C, N, S, Ti, Nb, and V.

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 in which the amount of shot balls injected during descaling is increased to increase the accumulated energy on the surface, thereby improving strength in both the rolling direction and the direction perpendicular to the rolling direction, and a manufacturing method thereof. [Background technology]

[0002] Non-oriented electrical steel sheets are mainly used in motors that convert electrical energy into mechanical energy, and in order to achieve high efficiency in this process, the excellent magnetic properties of non-oriented electrical steel sheets are required. In particular, as environmentally friendly technologies have been attracting attention in recent years, it has become increasingly important to increase the efficiency of motors, which account for more than half of the total electrical energy consumption, and as a result, the demand for non-oriented electrical steel sheets with excellent magnetic properties is also increasing. The magnetic properties of non-oriented electrical steel sheets are mainly 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. The lower the iron loss, the more energy-efficient a motor can be manufactured under the same conditions, and the higher the magnetic flux density, the more compact the motor can be and the less copper loss it can be. Therefore, it is important to create non-oriented electrical steel sheets with low iron loss and high magnetic flux density.

[0003] The characteristics of non-oriented electrical steel sheets that must be considered vary 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 place emphasis on W15 / 50, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, not only do motors for various applications place emphasis on W15 / 50 iron loss, but they may also evaluate iron loss at other frequencies or applied magnetic fields depending on the main operating conditions. In particular, for non-oriented electrical steel sheets used in recent electric vehicle drive motors, magnetic properties at low magnetic fields of 1.0T or less and high frequencies of 400Hz or more are often important, so the characteristics of non-oriented electrical steel sheets are evaluated at iron loss such as W10 / 400. Motor cores are divided into stator cores and rotor cores, and in order to satisfy the recent demand for compact, high-output motors for HEVs and the like, there is a strong demand for non-oriented electrical steel sheets used in stator cores to have excellent magnetic properties, such as high magnetic flux density and low core loss.

[0004] Furthermore, as a means of achieving smaller size and higher output in HEV drive motors and the like, there is a trend toward higher motor rotation speeds. However, because HEV drive motors have a large outer diameter, large centrifugal forces act on the rotor core, and depending on the structure, there may be a very narrow section (1 to 2 mm) called the rotor core bridge, so the non-oriented electrical steel sheet used in the rotor core is now required to have higher strength than before. Therefore, the ideal properties of non-oriented electrical steel sheet used in motor cores are not only excellent magnetic properties, but also high strength for rotor cores and higher magnetic flux density and lower iron loss for stator cores. Thus, even if the same non-oriented electrical steel sheet is used for motor cores, the properties required for rotor cores and stator cores are significantly different. However, from the viewpoint of increasing material yield, it is preferable to simultaneously extract the rotor core material and the stator core material from the same steel sheet and then stack the respective core materials to assemble them into the rotor core or stator core. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a non-oriented electrical steel sheet and a manufacturing method thereof, specifically, a non-oriented electrical steel sheet in which the amount of shot balls injected during descaling is increased, the number of nucleation sites in the electrical steel sheet is increased, fine crystal grains are secured after annealing of the cold-rolled sheet, and the omnidirectional yield strength of the electrical steel sheet is increased, and a manufacturing method thereof is also aimed at. [Means for solving the problem]

[0006] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.0-6.5% Si, 0.1-1.3% Al, 0.3-2.0% Mn, and the remainder being Fe and unavoidable impurities, and has an area fraction of crystal grains having a grain size of 10% or less of the sheet thickness of 10.0%-35.0% and a number fraction of 15%-55%. The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of Cr: 0.2 wt % or less (except 0%), Sn: 0.06 wt % or less (except 0%), and Sb: 0.06 wt % or less (except 0%). The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more of C, N, S, Ti, Nb, and V in an amount of 0.005 wt % or less. The non-oriented electrical steel sheet of the present invention may further contain one or more of Cu: 0.01 to 0.2 wt %, P: 0.100 wt % or less, B: 0.002 wt % or less, Mo: 0.01 wt % or less, Mg: 0.005 wt % or less, and Zr: 0.005 wt % or less. The non-oriented electrical steel sheet of the present invention may have an average crystal grain size of 5 to 50 μm.

[0007] In the non-oriented electrical steel sheet of the present invention, the yield strength measured in the rolling direction and the yield strength measured in the direction perpendicular to the rolling direction can satisfy the following formulas 1 and 2. [Formula 1] (Y.P. 0.2R +YP0.2C ) / 2≧480 [Formula 2] │YP 0.2R -YP 0.2C │ / {(YP 0.2R +YP 0.2C ) / 2}≦0.025 (In formula 1 and formula 2, YP 0.2R indicates the yield strength (MPa) measured in the rolling direction, and YP 0.2C indicates the yield strength (MPa) measured in the direction perpendicular to the rolling direction.) Iron loss (W 10 / 1000 ) can satisfy the following formula 3. [Formula 3] W 10 / 1000 ≦40+t×240 (W in Eq. 3) 10 / 1000 is 1000H Z (The iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1.0 T, and t is the thickness of the steel plate (mm).) The non-oriented electrical steel sheet according to an embodiment of the present invention may have a thickness of 0.10 to 0.30 mm.

[0008] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab containing, by weight, 2.0-6.5% Si, 0.1-1.3% Al, 0.3-2.0% Mn, and the balance being Fe and unavoidable impurities to produce a hot rolled sheet, removing scale present on the surface of the hot rolled sheet, cold rolling the hot rolled sheet from which the scale has been removed to produce a cold rolled sheet, and annealing the cold rolled sheet, in which the scale removing step is performed by using shot balls at a rate of 15 kg / (min m 2 )~35kg / (min m 2 ) onto the steel plate to remove scale. The shot balls may be made of an Fe-based alloy. The step of annealing the cold-rolled sheet may be performed at a temperature of 700 to 850°C. The method may further include a step of hot-rolled strip annealing prior to the step of removing the scale. Effect of the Invention

[0009] According to the present invention, the amount of shot balls projected during descaling can be increased to form a large amount of fine recrystallization, thereby improving the yield strength in all directions including the rolling direction (RD) and the direction perpendicular to the rolling direction (TD). This will also enable additional improvements in the performance of motors for environmentally friendly automobiles, motors for highly efficient home appliances, and super-premium electric motors. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] 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, 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. The terminology used herein is merely for the purpose of referring to specific 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 "comprises" is intended 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.

[0011] When an element is described as being "on" or "above" another element, it may be exactly on or above the other element, or it may have other elements between them. In contrast, when an element is described as being "directly on" another element, there are no other elements between them. Moreover, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In the present invention, the term "additionally containing an additional element" means that the additional amount of the additional element is substituted for the balance iron (Fe). 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 as having 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail so as to enable those skilled in the art to easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0012] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.0 to 6.5% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities. The reasons for limiting the alloy components of the steel plate will be explained below. Si:2.0~6.5wt% Silicon (Si) plays a role in increasing the resistivity of the material and reducing iron loss, and if the amount added is too small, the effect of improving high-frequency iron loss may be insufficient. Conversely, if the amount added is too large, the hardness of the material increases, the cold rolling property is extremely deteriorated, and the productivity and punching property may be deteriorated. Therefore, Si can be added within the above-mentioned range. More specifically, it can be contained in 2.5 to 5.0 wt %. More specifically, it can be contained in 3.0 to 4.0 wt %.

[0013] Al: 0.1~1.3% by weight Aluminum (Al) plays a role in increasing the resistivity of the material and reducing iron loss. If the amount added is too small, it will not be effective in reducing high-frequency iron loss, and fine nitrates may be formed, which may deteriorate the magnetic property. Conversely, if the amount added is too large, it may cause problems in all processes such as steelmaking and continuous casting, and may significantly reduce productivity. Therefore, Al can be added within the above-mentioned range. More specifically, it can be contained at 0.5 to 1.2 wt %. More specifically, it can be contained at 0.7 to 1.0 wt %.

[0014] Mn:0.3~2.0wt% Manganese (Mn) is an element that plays a role in increasing the resistivity of the material, improving iron loss, and forming sulfides. If the amount of Mn added is too small, sulfides may precipitate finely, reducing magnetic properties. Conversely, if the amount of Mn added is too large, it may promote the formation of {111} texture, which is unfavorable to magnetic properties, and reduce magnetic flux density, so Mn can be added within the above-mentioned range. More specifically, Mn can be contained in an amount of 0.5 to 1.5 wt %.

[0015] In the present invention, the resistivity may be 55 to 80 μΩ·cm. The non-oriented electrical steel sheet of the present invention may further contain one or more of Cr: 0.2% or less (excluding 0%), Sn: 0.06% or less (excluding 0%), and Sb: 0.06% or less (excluding 0%). Cr: 0.20% by weight or less Chromium (Cr) plays a role in increasing the resistivity of the material and reducing iron loss. Therefore, Cr can be added in the above-mentioned range. More specifically, 0.010 to 0.10 wt % can be contained. More specifically, 0.050 to 0.040 wt % can be contained. As mentioned above, when an additional element is further contained, it is contained in place of the remaining Fe.

[0016] Sn: 0.06% by weight or less and Sb: 0.06% by weight or less Tin (Sn) and antimony (Sb) are elements that segregate at grain boundaries, and are added to suppress the diffusion of nitrogen through grain boundaries, suppress the {111} texture that is harmful to magnetism, and increase the advantageous {100} texture to improve magnetic properties. If the amount of each of Sn and Sb added is too large, it hinders grain growth, reduces magnetism, and deteriorates rollability. Therefore, Sn and Sb can be added within the above-mentioned ranges. More specifically, Sn: 0.005 to 0.050 wt % and Sb: 0.005 to 0.050 wt % can be included. More specifically, it may contain 0.01 to 0.02 wt % of Sn and 0.01 to 0.02 wt % of Sb.

[0017] The steel plate base material may further contain one or more of Cu: 0.01 to 0.2 wt %, P: 0.100 wt % or less, B: 0.002 wt % or less, Mo: 0.01 wt % or less, Mg: 0.005 wt % or less, and Zr: 0.005 wt % or less. Cu:0.01~0.20wt% Copper (Cu) plays a role in forming sulfides together with Mn. When Cu is further added, if the amount added is too small, CuMnS may precipitate finely, which may deteriorate the magnetic property. If the amount added of Cu is too large, high-temperature brittleness may occur, which may cause cracks to form during continuous casting or hot rolling. More specifically, Cu may be contained in an amount of 0.05 to 0.10 wt%.

[0018] P: 0.100% by weight or less Phosphorus (P) not only plays a role in increasing the resistivity of the material, but also plays a role in improving the texture by segregating to the grain boundaries, increasing the resistivity, and reducing iron loss, so it can be added additionally. However, if too much P is added, it will result in the formation of a texture unfavorable to magnetism, and will not have the effect of improving the texture, and will segregate excessively to the grain boundaries, reducing rollability and workability, which may make production difficult. Therefore, P can be added within the above-mentioned range. More specifically, P can be contained in 0.001 to 0.090 wt %. More specifically, P can be contained in 0.005 to 0.085 wt %.

[0019] B: 0.002% by weight or less, Mo: 0.01% by weight or less, Mg: 0.005% by weight or less, and Zr: 0.005% by weight or less In the case of boron (B), molybdenum (Mo), magnesium (Mg), and zirconium (Zr), they react with impurity elements to form fine sulfides, carbides, and nitrates, which have a detrimental effect on magnetic properties, so their contents can be limited as described above.

[0020] The steel plate base material may further contain one or more of C, N, S, Ti, Nb, and V in an amount of 0.005% by weight or less. C: 0.005% by weight or less When a large amount of carbon (C) is added, it expands the austenite region, increases the phase transformation range, inhibits the grain growth of ferrite during annealing, and increases iron loss. It also combines with Ti and other elements to form carbides, degrades magnetism, and increases iron loss due to magnetic aging during use after processing the final product into an electrical product. Therefore, C can be added within the above range. More specifically, C can be contained in an amount of 0.003 wt% or less.

[0021] S: 0.005% by weight or less Sulfur (S) forms fine sulfides inside the base material, inhibits grain growth, and weakens iron loss, so it is preferable to add it in as small an amount as possible. If a large amount of S is included, it may combine with Mn and the like to form precipitates or cause high-temperature brittleness during hot rolling. Therefore, S may be further included in an amount of 0.005% by weight or less. Specifically, S may be further included in an amount of 0.0030% by weight or less. More specifically, S may be further included in an amount of 0.0001 to 0.0030% by weight.

[0022] N: 0.005% by weight or less Nitrogen (N) strongly bonds with Al, Ti, etc. to form nitrates, which inhibit grain growth and, when precipitated, impede magnetic domain movement, so it is preferable to add a small amount of N. Therefore, N can be added within the above-mentioned range. More specifically, N can be added in an amount of 0.003 wt % or less.

[0023] Ti, Nb, V: 0.005% by weight or less Titanium (Ti), niobium (Nb), vanadium (V), and the like are also strong carbonaceous cargo-forming elements, so it is preferable to avoid adding them as much as possible, and each should be contained at 0.01 wt% or less.

[0024] The balance is composed of Fe and inevitable impurities. The inevitable impurities are impurities that are mixed in during the steelmaking step and the manufacturing process of the grain-oriented electrical steel sheet, and are widely known in the art, so a detailed description will be omitted. In the present invention, the addition of elements other than the above-mentioned alloy components is not excluded, and various elements may be included within a range that does not impair the technical concept of the present invention. When an additional element is further included, it is included in place of the balance Fe.

[0025] The steel sheet of the present invention secures fine grain crystals in the steel sheet to improve mechanical strength and at the same time ensures appropriate magnetism. Specifically, the area fraction of crystal grains having a grain size of 10% or less of the sheet thickness can be 10.0% to 35.0%, and the number fraction can be 15% to 55%. Crystal grains having a grain size of 10% or less of the sheet thickness are useful for improving mechanical strength. On the other hand, when only the area fraction of fine crystal grains is secured, or only the number fraction is secured, problems may occur in terms of workability. More specifically, the area fraction of crystal grains having a grain size of 10% or less of the sheet thickness can be 15% to 35%, and the number fraction can be 15% to 55%.

[0026] In the present invention, the grain size and area / number ratio of the crystal grains can be measured based on a plane parallel to the rolled surface (ND surface) of the steel sheet. The grain size and area / number ratio of the crystal grains do not vary depending on the measurement thickness position, but a specific measurement thickness position may be 1 / 2 the thickness of the steel sheet. The grain size of the crystal grains can be determined by assuming a virtual circle having the same area as the crystal grain, and the diameter of the circle can be regarded as the grain size of the crystal grain. The lower limit of the fine recrystallized grain size is not particularly limited, but can be set to 0.1 μm, which is the measurement limit. The non-oriented electrical steel sheet of the present invention may have an average crystal grain size of 5 to 50 μm. If the average crystal grain size is too small, the magnetic properties and workability are poor. If the average crystal grain size is too large, the mechanical strength may be poor. More specifically, the average crystal grain size may be 10 to 40 μm. By adjusting the crystal grain size, the shot ball projection amount during descaling of the hot-rolled sheet is adjusted upward to increase the number of nucleation sites during recrystallization, thereby ensuring the fraction of fine recrystallization. This will be described in detail in the manufacturing method of a non-oriented electrical steel sheet described later, so a duplicated description will be omitted.

[0027] In the non-oriented electrical steel sheet of the present invention, the yield strength measured in the rolling direction and the yield strength measured in the direction perpendicular to the rolling direction can satisfy the following formulas 1 and 2. [Formula 1] (Y.P. 0.2R +YP 0.2C ) / 2≧480 [Formula 2] │YP 0.2R -YP 0.2C │ / {(YP 0.2R +YP 0.2C ) / 2}≦0.025 (In formula 1 and formula 2, YP 0.2R indicates the yield strength (MPa) measured in the rolling direction, and YP 0.2C indicates the yield strength (MPa) measured in the direction perpendicular to the rolling direction.) Satisfying formula 1 and formula 2 means that the yield strength measured in both the rolling direction and the direction perpendicular to the rolling direction is excellent, which is useful in ensuring the strength of the rotor when the non-oriented electrical steel sheet is used to manufacture the core of a motor, particularly the rotor.

[0028] The non-oriented electrical steel sheet of the present invention has a low core loss (W 10 / 1000 ) can satisfy the following formula 3. [Formula 3] W 10 / 1000 ≦40+t×240 (W in Eq. 3) 10 / 1000 indicates the iron loss (W / kg) when a magnetic flux density of 1.0T is induced at a frequency of 1000Hz, and t indicates the thickness of the steel plate (mm). More specifically, the following formula can be satisfied. W 10 / 1000 ≦30+t×150 In this case, the iron loss may be the average value of the iron loss measured in the rolling direction (RD direction) and the direction perpendicular to the rolling direction (TD direction). More specifically, the iron loss (W 10 / 1000 ) can be 55 to 70 W / kg.

[0029] The non-oriented electrical steel sheet of the present invention may have a thickness of 0.10 to 0.30 mm. The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab to produce a hot-rolled sheet, removing scale present on the surface of the hot-rolled sheet, cold rolling the hot-rolled sheet from which the scale has been removed to produce a cold-rolled sheet, and cold-rolling the cold-rolled sheet.

[0030] First, the slab is hot rolled. The alloy composition of the slab has been described above in relation to the alloy composition of the non-oriented electrical steel sheet, so a duplicated description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab is substantially the same. Specifically, the slab contains, by weight, 2.0 to 6.5% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the remainder being Fe and unavoidable impurities. For other additional elements, The alloy components of non-oriented electrical steel sheets have been explained above, so a duplicate explanation will be omitted.

[0031] The slab can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1100-1250°C. If the slab heating temperature is too high, the precipitates that impair the magnetic property will re-melt and precipitate finely after hot rolling. The slab is then hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 2 to 3.0 mm. The method may further include a step of annealing the hot-rolled sheet after the step of producing the hot-rolled sheet. The hot-rolled sheet annealing is preferably performed when producing a high-grade electrical steel sheet without phase transformation, and is effective in improving the texture of the final annealed sheet and increasing the magnetic flux density. At this time, the step of annealing the hot-rolled sheet can be annealed at a temperature of 850 to 1200 ° C. If the temperature of the hot-rolled sheet annealing is too low, the structure does not grow or grows finely, and the effect of increasing the magnetic flux density cannot be expected. If the temperature of the hot-rolled sheet annealing is too high, the magnetic properties may deteriorate and the rolling workability may deteriorate due to deformation of the sheet. The hot-rolled sheet annealing is performed to increase the orientation favorable to magnetism as necessary, and can be omitted. The annealed hot-rolled sheet can be pickled.

[0032] Next, scale present on the surface of the hot-rolled steel sheet is removed. In the present invention, the scale is removed by shot ball blasting, and the amount of shot balls projected is increased to increase the number of nucleation sites during recrystallization, thereby ensuring the fraction of fine recrystallization. The scale removal step involves using shot balls at 15 to 35 kg / (min m 2 ) onto the steel plate to remove scale. If the amount of shot balls is too small, nucleation sites are not sufficiently secured, making it difficult to ensure sufficient fine recrystallization. Conversely, if the amount of shot balls is too large, the steel plate surface is significantly damaged, so the upper limit can be appropriately adjusted. More specifically, the amount of shot balls is 17 to 30 kg / (min m 2 Even if the same amount is projected per area, the amount of fine crystal grains obtained varies depending on the length of time for which the projection is performed. Therefore, in one embodiment of the present invention, the amount of projection is defined according to the time and area.

[0033] The average particle size of the shot balls is 0.1-1 mm, and the shot balls can be projected for 1-60 seconds. More specifically, the average particle size of the shot balls is 0.3-0.8 mm, and the shot balls can be projected for 5-30 seconds. The average particle size of the shot balls and the shot ball projection time can also affect the surface nucleation sites. The material of the shot balls is not particularly limited, but an Fe-based alloy can be used. After shot ball projection, the steel sheet with the increased projection amount can be smoothed by immersing in a pickling solution. The pickling solution is not particularly limited, and hydrochloric acid can be used. If the concentration of the pickling solution and the immersion time are too low or too short, the roughness of the steel sheet with the increased projection amount increases, and surface problems may occur. Conversely, if the concentration of the pickling solution and the immersion time are too high or too long, problems such as extensive damage to the steel sheet surface may occur. More specifically, the steel sheet can be pickled by immersing in the pickling solution for 10 to 60 seconds.

[0034] Next, the hot rolled sheet is cold rolled to produce a cold rolled sheet. The cold rolling is final rolled to a thickness of 0.15 mm to 0.65 mm. If necessary, a second cold rolling can be performed after the first cold rolling and intermediate annealing, and the final reduction ratio can be in the range of 50 to 95%. Next, the cold-rolled sheet is annealed. The cold-rolled sheet is annealed at a temperature in the range of 700 to 850°C for 10 to 1000 seconds so that the grain size in the cross section of the steel sheet is 5 to 50 μm. If the cold-rolled sheet annealing temperature is too low, the grains may become small, and the core loss may deteriorate. If the temperature is too high, the grains may become coarse, and the mechanical strength may decrease. More specifically, the annealing can be performed in the range of 740 to 820°C. In cold-rolled annealed thick steel plate, 80% or more of the structure processed by cold rolling can be recrystallized. Next, after annealing the cold-rolled sheet, an insulating film can be formed. The insulating film can be an organic, inorganic, or organic-inorganic composite film, and can also be a film agent capable of providing insulation. For example, the insulating film can be formed by applying an insulating film-forming composition containing 40 to 70% by weight of metal phosphate and 0.5 to 10% by weight of silica.

[0035] The present invention will be described in more detail with reference to the following examples, which are merely for illustrative purposes and are not intended to limit the scope of the present invention. Working Example The slabs shown in Tables 1 and 2 below were manufactured. The slabs were heated to 1150°C and hot-rolled at 850°C to produce hot-rolled sheets with a thickness of 2.3 mm. The hot-rolled sheets were annealed at 1100°C for 4 minutes. Next, steel shot balls with an average diameter of 0.5 μm were blasted at the amount and time shown in Table 3 below to remove scale, and the sheets were pickled. After that, the sheets were cold-rolled to a thickness of 0.27 mm, and then cold-rolled sheets were annealed at 800°C for 5 minutes. The content of each component was measured by ICP wet analysis. The average diameter of crystal grains, the area fraction and the number fraction of fine grains were measured by polishing the TD cross section of the specimen and measuring the area fraction by 100 mm. 2 After measuring with EBSD to obtain the above area, the samples were merged using the Merge function of the OIM software, and the Average, Area fraction, and Number fraction values ​​calculated using the Grain Size (diameter) function were used. The yield strength was tested based on the ISO 6892-1, 2 standard. Magnetic properties such as iron loss were measured by cutting five test pieces of 60 mm width x 60 mm length for each test piece and measuring them in the rolling direction and perpendicular to the rolling direction using a single sheet tester.

[0036] [Table 1]

[0037] [Table 2]

[0038] [Table 3]

[0039] [Table 4]

[0040] As shown in Tables 1 to 4, the examples in which the alloy components and the shot ball projection amount were appropriately adjusted had excellent strength due to sufficient fine recrystallization, and it was confirmed that the deviation in yield strength between the rolling direction and the direction perpendicular to the rolling direction was small. On the other hand, in the case where the alloying components are not properly adjusted, fine recrystallization is not properly formed, and the yield strength value is deteriorated. Also, in the case where the amount of shot balls thrown was small, fine recrystallization was not properly formed, and the yield strength value was deteriorated. In addition, in the case where the amount of shot balls projected is excessive, it can be confirmed that a plurality of fine recrystallizations are formed, and the yield strength anisotropy is deteriorated. Also, it can be seen that in the cases where the shot ball projection time was too short or too long, the yield strength and magnetic properties were relatively deteriorated compared to the steel types 1 to 8. It can be seen that the yield strength and magnetic properties are relatively poor.

[0041] The present invention is not limited to the examples, and can be manufactured in various different forms, and a person having ordinary skill 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 characteristics of the present invention. Therefore, it should be understood that the above-described examples are illustrative in all respects and not limiting.

Claims

1. The alloy comprises, by weight percent, 2.0 to 6.5% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities; A non-oriented electrical steel sheet, characterized in that the area fraction of crystal grains having a grain size of 10% or less of the sheet thickness is 10.0% to 35.0%, and the number fraction is 15% to 55%.

2. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cr: 0.2 wt % or less (excluding 0%), Sn: 0.06 wt % or less (excluding 0%), and Sb: 0.06 wt % or less (excluding 0%).

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising at least one of C, N, S, Ti, Nb and V in an amount of 0.005% by weight or less.

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cu: 0.01 to 0.2 wt %, P: 0.100 wt % or less, B: 0.002 wt % or less, Mo: 0.01 wt % or less, Mg: 0.005 wt % or less, and Zr: 0.005 wt % or less.

5. 2. The non-oriented electrical steel sheet according to claim 1, characterized in that the average grain size is 5 to 50 μm.

6. 2. The non-oriented electrical steel sheet according to claim 1, wherein the yield strength measured in the rolling direction and the yield strength measured in the direction perpendicular to the rolling direction satisfy the following formulas 1 and 2: [Formula 1] (YP ０．２Ｒ +YP ０．２Ｃ ) / 2≧480 [Formula 2] │YP ０．２Ｒ -YP ０．２Ｃ │ / {(YP ０．２Ｒ +YP ０．２Ｃ ) / 2}≦0.025 (In Formula 1 and Formula 2, YP ０．２Ｒ indicates the yield strength (MPa) measured in the rolling direction, and YP ０．２Ｃ indicates the yield strength (MPa) measured in the direction perpendicular to the rolling direction.)

7. Iron loss (W １０／１０００ 2. The non-oriented electrical steel sheet according to claim 1, wherein: [Formula 3] W １０／１０００ ≦40+t×240 (In formula 3, W １０／１０００ indicates the iron loss (W / kg) when a magnetic flux density of 1.0 T is induced at a frequency of 1000 Hz, and t indicates the thickness of the steel plate (mm).

8. A step of producing a hot-rolled sheet by hot rolling a slab containing, in weight percent, 2.0 to 6.5% Si, 0.1 to 1.3% Al, 0.3 to 2.0% Mn, and the balance being Fe and unavoidable impurities; removing scale present on the surface of the hot-rolled sheet; cold rolling the descaled hot-rolled sheet to produce a cold-rolled sheet; and The cold-rolled sheet is annealed, The step of removing the scales involves subjecting the shot balls to a pressure of 15 to 35 kg / (min.m ２ ) onto the steel sheet to remove scale.

9. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the average particle size of the shot balls is 0.1 to 1 mm, and the shot balls are projected for 1 to 60 seconds.

10. The method for producing a non-oriented electrical steel sheet according to claim 8, characterized in that the material of the shot balls is an Fe-based alloy.

11. The method for producing a non-oriented electrical steel sheet according to claim 8, wherein the cold-rolled sheet annealing step comprises annealing at a temperature of 700 to 850°C.

12. The method for producing a non-oriented electrical steel sheet according to claim 8, further comprising a step of annealing the hot-rolled sheet prior to the step of removing the scale.

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