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

Abstract

By optimally controlling the steel composition and optimizing the manufacturing method, we can provide non-oriented electrical steel sheets with excellent magnetic properties through uniform control of the microstructure. [Solution] The alloy contains, by weight, 2.5-4% Si, 0.1-1.0% Mn, 0.001-0.005% S, 0.002-0.01% Cu, with the remainder being Fe and unavoidable impurities, and is characterized by having an FGS (average grain size of crystal grains that are the bottom 10% or less of all crystal grains based on grain size) of ≧15 μm, and further containing, by weight, one or more of C: 0.005% or less, Al: 0.5-1.5%, N: 0.005% or less, P: 0.2% or less, Sn: 0.2% or less, and Ti: 0.005% or less, and further containing, by weight, one or more of Sb: 0.2% or less, Ni: 0.05% or less, Cr: 0.05% or less, Zr: 0.01% or less, Mo: 0.01% or less, and V: 0.01% or less.

Description

[Technical Field]

[0001] The present invention relates to non-oriented electrical steel sheets and methods for manufacturing the same, and more particularly to non-oriented electrical steel sheets with uniform microstructure and excellent iron loss properties and methods for manufacturing the same. [Background technology]

[0002] Recently, with the strengthening of regulations on environmental protection and energy conservation, there has been an increasing demand for improved efficiency in energy conversion devices such as motors and generators, which convert electrical energy into mechanical energy or vice versa. Since non-oriented electrical steel sheets are used as core materials in such rotating equipment as motors and generators, and stationary equipment such as small transformers, the demand for improved efficiency in motors and generators has led to a demand for improved properties in non-oriented electrical steel sheets. The typical magnetic properties of non-oriented electrical steel sheets are iron loss and magnetic flux density. The lower the iron loss of a non-oriented electrical steel sheet, the less iron loss is lost during the magnetization process of the iron core, improving efficiency. The higher the magnetic flux density, the greater the magnetic field that can be induced with the same energy, and the less current can be applied to obtain the same magnetic flux density, thus improving energy efficiency. Therefore, it can be said that the development technology for non-oriented electrical steel sheets with excellent magnetism, possessing both low iron loss and high magnetic flux density, is essential for improving energy efficiency.

[0003] To explain the properties of non-oriented electrical steel sheets in more detail, efficient methods for reducing iron loss in non-oriented electrical steel sheets include increasing the amount of Si, Al, and Mn added, which are elements with high resistivity, or reducing the thickness of the steel sheet. However, thinner steel sheets have the disadvantage of lower productivity and workability, leading to increased processing costs. Increasing the amount of Si, Al, and Mn added increases the resistivity of the steel and reduces eddy current loss, which is part of the iron loss in non-oriented electrical steel sheets. However, the iron loss does not decrease unconditionally in proportion to the amount added as the amount increases. Conversely, increasing the amount of alloying elements adds degrades the magnetic flux density. Therefore, in order to ensure excellent iron loss and magnetic flux density, the appropriate amount of additives and the addition ratio between Si, Al, and Mn must be appropriately controlled. Impurities other than Si, Al, and Mn that are inevitably present must be controlled more strictly. Most impurities degrade magnetism by forming precipitates with C, N, S, etc., which suppress the growth of crystal grains or hinder the movement of magnetic domain walls, so controlling their content is extremely important.

[0004] While non-oriented electrical steel sheets have relatively low iron loss, attempts have been made to improve their magnetic flux density by utilizing special additive elements such as REM to improve the texture and thus enhance their magnetic properties, or by introducing additional manufacturing processes such as warm rolling, double rolling, and double annealing. However, all of these technologies either increase manufacturing costs or make mass production difficult, so it can be said that there is a need to develop technologies that offer excellent magnetic properties while being commercially viable. Furthermore, technologies have been developed to suppress and control the formation of inclusions by minimizing the amount of impurities added and adding elements such as Ca, but these also increase manufacturing costs, and it is not easy to clearly ensure their effectiveness.

[0005] Many technologies have been developed through sustained efforts to solve these problems. Among the conventional technologies relating to non-oriented electrical steel sheets, Patent Document 1 presents a method for improving the texture and ensuring excellent magnetism by controlling the heating rate during the final annealing of non-oriented electrical steel sheets to 50°C / s or higher. However, it does not take into account areas where the magnetism may be inferior due to non-uniform microstructure, separate from the result of improved texture due to rapid heating. Existing technologies propose ways to improve magnetism by controlling inclusions and improving texture through controlling impurities such as S, As, Nb, and Ti in the composition and controlling the hot-rolled sheet annealing conditions. However, these technologies are considered difficult to apply commercially due to the increased manufacturing costs required to minimize impurities and the long hot-rolled sheet annealing times.

[0006] Furthermore, conventional technology has presented a method to obtain high-strength steel sheets before stress relief annealing and low iron loss steel sheets during annealing due to the ease of grain growth, by reducing specific impurity elements in the steel to very low levels and adding a skin pass process. However, this method has the disadvantage of causing increased costs due to the extremely low control of impurities. Furthermore, a technique has been proposed in which the precipitation of MnS is suppressed by adding rare earth elements such as Ca, Mg, and REM, resulting in small crystal grains before stress relief, but with improved iron loss due to grain growth during stress relief annealing. However, this also involves increased manufacturing costs due to the addition and control of additional elements, and it is difficult to ensure its effectiveness if stress relief annealing is not performed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-199787 [Overview of the project] [Problems that the invention aims to solve]

[0008] An object of the present invention is to provide a non-oriented electrical steel sheet excellent in magnetism through uniform control of a microstructure by optimally controlling the components of steel and optimizing the manufacturing method.

Means for Solving the Problems

[0009] The non-oriented electrical steel sheet of the present invention contains, in weight %, Si: 2.5 to 4%, Mn: 0.1 to 1.0%, S: 0.001 to 0.005%, Cu: 0.002 to 0.01%, and the balance consists of Fe and unavoidable impurities. The non-oriented electrical steel sheet has FGS (average grain size of grains that are 10% or less in terms of grain size among all the grains) ≧ 15 μm. The non-oriented electrical steel sheet further contains one or more of C: 0.005% or less, Al: 0.5 to 1.5%, N: 0.005% or less, P: 0.2% or less, Sn: 0.2% or less, and Ti: 0.005% or less in weight %. The non-oriented electrical steel sheet further contains one or more of Sb: 0.2% or less, Ni: 0.05% or less, Cr: 0.05% or less, Zr: 0.01% or less, Mo: 0.01% or less, and V: 0.01% or less in weight %.

[0010] The non-oriented electrical steel sheet has FGS (average grain size of grains that are 10% or less in terms of grain size among all the grains) / GS (average grain size of all the grains) ≧ 0.15. The non-oriented electrical steel sheet has FGA (average area of grains that are 10% or less in terms of grain size among all the grains) / TGA (average area of all the grains) ≧ 0.005. The composition of the non-oriented electrical steel sheet satisfies the following formula 1. [[ID=二十]] [Formula 1] 0.4 ≦ ([Mn] + 10 × [Cu]) × 1000 × [S] ≦ 1.5 (Here, [Mn], [Cu], and [S] are the addition amounts (weight %) of Mn, Cu, and S, respectively)

[0011] The present invention relates to a method for manufacturing non-oriented electrical steel sheets, comprising the steps of: hot rolling a slab containing, by weight %, Si: 2.5~4%, Mn: 0.1~1.0%, S: 0.001~0.005%, Cu: 0.002~0.01%, with the remainder being Fe and unavoidable impurities, to produce a hot-rolled sheet; cold rolling the hot-rolled sheet to produce a cold-rolled sheet; and cold-annealing the cold-rolled sheet, wherein in the cold-annealing step, the average heating rate from 600°C to the soaking temperature is 15~50°C / s, and the average cooling rate from the soaking temperature to 600°C is 10~40°C / s. The heating rate and cooling rate satisfy the following [Equation 2]. [Formula 2] 200≦([Heating rate]×[Cooling rate])≦500 (Here, [heating rate] and [cooling rate] are the average heating rate and average cooling rate between 600°C and the soaking temperature during cold-rolled sheet annealing, respectively, and the unit is °C / s.)

[0012] The slab further contains one or more of the following in weight percent: C: 0.005% or less, Al: 0.5-1.5%, N: 0.005% or less, P: 0.1% or less, Sn: 0.1% or less, and Ti: 0.005% or less. The composition of the slab satisfies the following equation 1. [Formula 1] 0.4≦([Mn]+10×[Cu])×1000×[S]≦1.5 (Here, [Mn], [Cu], and [S] are the amounts (by weight) of Mn, Cu, and S added to the slab, respectively.) The soaking temperature during the cold-rolled sheet annealing stage is 900-1100°C. The method for manufacturing the non-oriented electrical steel sheet further includes the step of coating the cold-rolled sheet, which has been annealed, with an insulating film. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a non-oriented electrical steel sheet in which the composition system is optimally controlled. Furthermore, according to the present invention, the manufacturing conditions for non-oriented electrical steel sheets can be optimized. Furthermore, according to the present invention, it is possible to provide a non-oriented electrical steel sheet in which the microstructure after annealing of the cold-rolled sheet is more uniformly controlled. Furthermore, according to the present invention, it is possible to provide non-oriented electrical steel sheets with excellent iron loss properties. [Modes for carrying out the invention]

[0014] The terms first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the invention. The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular form used herein also includes plural forms unless the phrase explicitly indicates otherwise. The meaning of “includes” as used in this specification is to embody specific characteristics, regions, integers, stages, operations, elements, and / or components, and does not exclude the presence or addition of other characteristics, regions, integers, stages, operations, elements, and / or components. When one part is described as being "on top of" or "on" another part, it may be directly on top of or on the other part, or the other part may be present between them. In contrast, when one part is described as being "directly on top of" another part, the other part is not present between them. Also, unless otherwise specified, % means weight percent, and 1 ppm is 0.0001 weight percent. In this invention, the inclusion of additional elements means that the additional amount of the additional elements replaces the remaining iron (Fe). Although not defined differently, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have the meaning corresponding to the relevant technical literature and the content disclosed herein, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0015] The embodiments of the present invention will be described below in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein. The most efficient way to reduce iron loss in non-oriented electrical steel sheets is to increase the resistivity of the steel by adding silicon (Si), aluminum (Al), and manganese (Mn). However, while adding Si, Al, and Mn to Fe reduces iron loss, it is unavoidable that the saturation magnetic flux density decreases. In high-alloy systems with large amounts of Si, Al, and Mn, the cold-rolling performance deteriorates due to increased brittleness of the material, making it difficult to ensure productivity. Therefore, in order to achieve low iron loss while maintaining high magnetic flux density and ensuring productivity, an appropriate combination of Si, Al, and Mn addition amounts and ratios is necessary.

[0016] Copper (Cu) and sulfur (S) are elements that must be added in trace amounts or kept at extremely low levels depending on the purpose. In non-oriented electrical steel sheets, precipitates and inclusions suppress grain growth and hinder the movement of magnetic domain walls, thereby reducing magnetism. Therefore, in the case of Cu and S, they not only form sulfides together with Mn, making the grain distribution uneven, but the fine sulfides themselves can also reduce magnetism, so their addition amounts must be appropriately controlled. The non-oriented electrical steel sheet of the present invention contains, by weight percent, Si: 2.5-4%, Mn: 0.1-1.0%, S: 0.001-0.005%, Cu: 0.002-0.01%, with the remainder being Fe and other unavoidable impurities. The non-oriented electrical steel sheet of one embodiment of the present invention may further contain one or more of the following in weight percent: C: 0.005% or less, Al: 0.5 to 1.5%, N: 0.005% or less, P: 0.2% or less, Sn: 0.2% or less, and Ti: 0.005% or less. The non-oriented electrical steel sheet of the present invention may further contain one or more of the following in weight percent: Sb: 0.2% or less, Ni: 0.05% or less, Cr: 0.05% or less, Zr: 0.01% or less, Mo: 0.01% or less, and V: 0.01% or less.

[0017] First, let me explain the reason for limiting the composition of non-oriented electrical steel sheets. Si:2.5~4.0wt% Silicon (Si) plays a role in increasing the resistivity of the material and reducing iron loss. If it is added in excessively small amounts, the effect of improving iron loss may be insufficient. Therefore, adding Si at a content of 2.5% by weight or more is advantageous for the development of low-iron-loss non-oriented electrical steel sheets. Conversely, if silicon is added in excessive amounts, the brittleness of the material increases, which can lead to sheet fracture during coiling and cold rolling, causing a sharp decrease in rolling productivity. Therefore, Si can be added within the aforementioned range. More specifically, Si may be included in an amount of 2.6 to 3.7% by weight.

[0018] Mn:0.10~1.00wt% Manganese (Mn) plays a role in increasing the resistivity of the material, improving iron loss, and promoting sulfide formation. However, if added in excessive amounts, fine sulfide precipitates may form, reducing magnetism. Conversely, if added in excessive amounts, it may promote the formation of a {111} texture unfavorable to magnetism, leading to a decrease in magnetic flux density. Therefore, Mn can be added within the aforementioned range. More specifically, the material can contain 0.20 to 0.60% by weight of Mn.

[0019] Al: 0.5~1.5% by weight Aluminum (Al) plays a role in increasing the resistivity of the material and reducing iron loss, improving rollability or workability during cold rolling, and reducing magnetic anisotropy, thereby reducing magnetic deviation in the rolling direction and perpendicular to the rolling direction. However, if added in excessive amounts, it will not be effective in reducing high-frequency iron loss, and the deposition temperature of AlN will be lowered, leading to the formation of fine nitrides and a decrease in magnetism. Conversely, if added in excessive amounts, too many nitrides will be formed, degrading magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. Therefore, Al can be added within the aforementioned range. More specifically, it can contain 0.7 to 1.0% by weight of Al.

[0020] C: 0.0050% by weight or less, Carbon (C) may suppress ferrite grain growth during annealing, leading to a greater degree of magnetic degradation during processing. It can also combine with Ti, Nb, etc., to form carbides, further reducing magnetism. In the final product, when processed into electrical products, magnetic aging increases iron loss, reducing the efficiency of electrical equipment. Therefore, the carbon content may be 0.0040% by weight or less.

[0021] S:0.0010~0.0050wt% Sulfur (S) is preferable to be added in small amounts because it forms fine sulfides such as MnS, CuS, and (Cu,Mn)S within the matrix material, which are detrimental to magnetic properties, thereby suppressing grain growth and weakening iron loss. However, if added at less than 0.0010% by weight, it is detrimental to texture formation and promotes the formation of fine sulfides, reducing magnetism, so it is preferable to contain 0.001% or more. Furthermore, if the content exceeds 0.0050% by weight, it can suppress grain growth due to increased sulfide formation or significantly worsen the degree of magnetism after processing, so S can be added within the aforementioned range. More specifically, S can be included in a quantity of 0.0013 to 0.0040% by weight.

[0022] N: 0.0040% by weight or less Nitrogen (N) strongly binds with Al, Ti, Nb, etc., forming nitrides within the base material and suppressing grain growth, thus worsening iron loss. Therefore, it is preferable to have a low nitrogen content, and in this invention, it is limited to 0.0040% by weight or less. More specifically, it contains 0.0005 to 0.0035% by weight.

[0023] Ti: 0.0050% by weight or less Titanium (Ti) is an element with a very strong tendency to form precipitates within steel. It combines with C and N to form fine carbides or nitrides within the base material, suppressing grain growth. Therefore, the more titanium is added, the more carbides and nitrides are formed, resulting in a poorer texture, worsening iron loss, and thus degrading magnetism. For this reason, its content is limited to 0.0050% by weight or less. More specifically, it contains 0.0010 to 0.0040% by weight.

[0024] Cu: 0.0020~0.0100% Copper (Cu) can combine with manganese (Mn) and sulfur (S) to form fine sulfides. However, if added at a concentration of less than 0.002%, it actually promotes the formation of fine sulfides and reduces magnetism; therefore, it should be present at a concentration of 0.002% or more. Furthermore, if added at a concentration exceeding 0.01%, the amount of sulfides increases, so the Cu content may be between 0.0020% and 0.0100% by weight. More specifically, it should be present at 0.0050% to 0.0080% by weight.

[0025] In addition to the elements mentioned above, P, Sn, and Sb, which are generally known to improve texture, may be added for additional magnetic improvement. However, if the amount added is excessive, it can suppress grain growth and reduce productivity, so the amount added should be 0.2% or less for each element. In the case of Ni and Cr, which are elements that are inevitably added in the steelmaking process, they react with impurity elements to form fine sulfides, carbides, and nitrides, which have a detrimental effect on magnetism, so their content should be limited to 0.05% by weight or less for each element. Also, since Zr, Mo, and V are strong carbonitride-forming elements, it is preferable that they not be added if possible, and their content should be limited to 0.01% by weight or less for each element.

[0026] The remainder of the elements other than those mentioned above may include Fe and other unavoidable impurities. Additional elements may be added insofar as they do not impair the technical concept of the present invention. In this case, the remaining Fe is added as a substitute. It is also possible to limit the addition of additional elements. As an example of additional elements, one or more of the following may be further included: Sb: 0.2% or less, Ni: 0.05% or less, Cr: 0.05% or less, Zr: 0.01% or less, Mo: 0.01% or less, and V: 0.01% or less. In other words, the non-oriented electrical steel sheet of the present invention contains Si: 2.5-4%, Mn: 0.1-1.0%, S: 0.001-0.005%, Cu: 0.002-0.01%, with the remainder being Fe and unavoidable impurities. Furthermore, the non-oriented electrical steel sheet of the present invention satisfies the following formula 1 for Mn, Cu, and S. [Formula 1] 0.40≦([Mn]+10×[Cu])×1000×[S]≦1.5 (Here, [Mn], [Cu], and [S] are the amounts (by weight) of Mn, Cu, and S added, respectively.)

[0027] The reason why Mn, Cu, and S are controlled in this invention to satisfy [Equation 1] is as follows. Generally, in non-oriented electrical steel sheets, Mn is an element added along with Si and Al to increase resistivity, and sulfides are mainly known as MnS. However, Cu is also an element that forms sulfides, and CuS alone or in combination with MnS can form sulfides. Such sulfides precipitate finely, suppressing grain growth and making the microstructure more uniform, and hindering the movement of magnetic domain walls during magnetization, thereby reducing magnetism. Fine sulfides have a greater effect on reducing magnetism than coarser sulfides. In addition, generally, the amount of Cu added is less than that of Mn, but the lower the amount added, the lower the deposition temperature and the finer the deposition. Therefore, along with the existing control of Mn and S addition amounts, the amount of Cu added must also be strictly controlled. Thus, non-oriented electrical steel sheets in which the content of Mn, Cu, and S is controlled to satisfy [Equation 1] can have a uniform microstructure. More specifically, the value of Equation 1 may be between 0.70 and 1.50.

[0028] Non-oriented electrical steel sheets may have a FGS (Fine Grain Size) of ≥ 15 μm, which is the average grain size of grains in the bottom 10% or less of the total grain size. More specifically, the FGS may be 15 to 30 μm, or more specifically, 20 to 25 μm. More specifically, FGS refers to the average grain size of grains that make up 10% or less of the total grains in the steel sheet area being measured, based on grain size. For example, assuming there are 100 grains being measured, FGS refers to the average grain size of the grain group consisting of the smallest grain and the 10th smallest grain (i.e., the 1st to 10th grain group). Here, average grain size refers to the number-average grain size. The larger the FGS, the lower the hysteresis loss among the generated iron loss, resulting in improved iron loss. The grains being measured may have a grain size of 5 μm or larger. The reference surface for measuring grain size is not particularly limited and may be a surface parallel to the rolling surface (ND surface). While there is virtually no deviation in the thickness direction of the plate, grain size can be measured at thicknesses between 1 / 5t and 1 / 2t. The grain size is measured by assuming a hypothetical surface with the same area as the grain and measuring the diameter of that circle.

[0029] Since large deviations can occur when measuring small areas, FGS should be measured from specimens with an area of ​​at least 5 mm x 5 mm. More specifically, FGS can directly image microtissue and utilize image analyzers, and measurements can also be taken using EBSD programs. The aforementioned non-oriented electrical steel sheet may have FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15. Specifically, FGS / GS may be 0.15 to 0.25, or more specifically, 0.15 to 0.2. The aforementioned non-oriented electrical steel sheet may have FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005. Specifically, FGA / TGA may be 0.005 to 0.02, and more specifically, 0.005 to 0.0015. Furthermore, when a magnetic flux density of 1.5T is induced at a frequency of 50Hz, the non-oriented electrical steel sheet exhibits iron loss W, which is the average loss in the rolling direction and the direction perpendicular to the rolling direction. 15 / 50 It may be 2.0 W / kg or less. Specifically, W 15 / 50 This may be 1.5 to 2.0 W / kg, or more specifically, 1.8 to 2.0 W / kg.

[0030] When a magnetic flux density of 1.0T is induced at a frequency of 400Hz, the aforementioned non-oriented electrical steel sheet exhibits iron loss W, which is the average loss in the rolling direction and the direction perpendicular to the rolling direction. 10 / 400 It may be 16.5 W / kg or less. Specifically, W 10 / 400 This can be 10.0 to 16.5 W / kg, or more specifically, 15.0 to 16.5 W / kg. The present invention relates to a method for manufacturing non-oriented electrical steel sheets, comprising the steps of hot-rolling a slab; cold-rolling a hot-rolled sheet; and annealing a cold-rolled sheet. Hot-rolled sheet annealing may be added if necessary, and may also include multiple cold-rolling steps, including intermediate annealing, for additional magnetic enhancement. The following examples of manufacturing methods are merely illustrative and do not necessarily have to be followed.

[0031] As an example, the method for manufacturing non-oriented electrical steel sheets of the present invention includes the steps of: heating a slab containing, by weight percent, C: 0.005% or less, Si: 2.0~4.0%, Mn: 0.1~1.0%, S: 0.001~0.005%, Al: 0.5~1.5%, N: 0.005% or less, Ti: 0.005% or less, Cu: 0.002~0.01%, with the remainder being Fe and other unavoidable impurities; hot rolling the slab to form a hot-rolled sheet; cold rolling the hot-rolled sheet to form a cold-rolled sheet; and cold annealing the cold-rolled sheet. In the composition of the slab, Mn, Cu, and S satisfy the following equation [Equation 1]. [Formula 1] 0.4≦([Mn]+10×[Cu])×1000×[S]≦1.5 (Here, [Mn], [Cu], and [S] are the amounts (by weight) of Mn, Cu, and S added, respectively.) Subsequently, since there is no substantial change in the steel composition during the manufacturing process of the non-oriented electrical steel sheet, the composition of the slab and the composition of the aforementioned non-oriented electrical steel sheet are substantially identical. A redundant explanation of the slab composition will be omitted.

[0032] The process may further include a step of heating the slab before the stage of manufacturing the hot-rolled sheet. The step of heating the slab may be a step of heating at 1200°C or lower. Specifically, it may be a step of heating at 950 to 1200°C, or more specifically, at 1000 to 1200°C. If the reheating temperature of the slab exceeds 1200°C, precipitates such as nitrides, carbides, and sulfides present in the slab may be redissolved, and then finely precipitated during hot rolling and annealing, which may suppress grain growth and reduce magnetism. Therefore, the slab heating temperature should be controlled to 1200°C or lower. In the step of hot-rolling the slab to form a hot-rolled sheet, the thickness of the formed hot-rolled sheet may be 2.0 to 3.0 mm. Specifically, the thickness of the hot-rolled sheet may be 2.3 to 2.5 mm.

[0033] The formed hot-rolled sheet is rolled up at a temperature of 700°C or lower and cooled in air. The wound hot-rolled sheet may undergo a hot-rolled sheet annealing step, or the hot-rolled sheet annealing step may be omitted. The hot-rolled sheet annealing step is performed at 950 to 1150°C. Specifically, the hot-rolled sheet annealing step is performed at 975 to 1025°C. If the temperature during the hot-rolled sheet annealing step is below 950°C, grain growth will be insufficient, making it difficult to obtain a texture favorable for magnetism during cold-rolled post-annealing. If the temperature exceeds 1150°C, the grains may grow excessively, resulting in an excessive number of surface defects in the sheet. The method for manufacturing the non-oriented electrical steel sheet further includes a step of pickling the annealed hot-rolled sheet after the hot-rolled sheet annealing step. The step of pickling the annealed hot-rolled sheet may be a conventional pickling method. The step of cold rolling the hot-rolled sheet may be a single cold-rolling step or a step of two or more cold-rolling steps including intermediate annealing. The thickness of the formed cold-rolled sheet may be 0.10 to 0.50 mm, specifically 0.30 to 0.40 mm. During the cold rolling stage, the reduction ratio may be 50-95%.

[0034] In the cold-rolled sheet annealing stage, there are no major restrictions on the annealing temperature, as long as it is within the range of temperatures typically used for cold-rolled non-oriented electrical steel sheets. However, since the cold-rolled sheet annealing process is a crucial element that greatly affects the microstructure and texture of the non-oriented electrical steel sheet and thus influences its magnetism, its conditions must be controlled more precisely. Iron loss in non-oriented electrical steel sheets is closely related to grain size. Iron loss in non-oriented electrical steel sheets can be divided into hysteresis loss and eddy current loss. Hysteresis loss decreases as grain size increases, while eddy current loss increases as grain size increases. Therefore, there is an optimal grain size that minimizes the sum of hysteresis loss and eddy current loss. Thus, from a macroscopic perspective, it is important to derive and apply the cold-rolled sheet annealing temperature that ensures the optimal grain size, and a soaking temperature of 900 to 1100°C is appropriate during cold-rolled sheet annealing. If the soaking temperature during cold-rolled sheet annealing is below 900°C, the grains become excessively fine and hysteresis loss increases, and if it exceeds 1100°C, the grains become excessively coarse and eddy current loss increases, resulting in inferior iron loss. Therefore, it should be controlled to 900 to 1100°C.

[0035] However, from a microscopic perspective, even with the same grain size, the greater the uniformity of the microstructure, the greater the reduction in iron loss. Even with similar average grain sizes, the more extremely fine and extremely coarse grains there are compared to the average grain size, the worse the iron loss will be. Therefore, ensuring uniformity of the microstructure improves magnetism. In the cold-rolled sheet annealing stage, the average heating rate from 600°C to the soaking annealing temperature during cold-rolled sheet annealing may be 15 to 50°C / s, and the average cooling rate from the soaking temperature to 600°C during cold-rolled sheet annealing may be 10 to 40°C / s. Specifically, the heating rate may be 20 to 40°C / s, and the cooling rate may be 10 to 30°C / s. If the heating rate is less than 15°C / s, there may be a problem where the fraction of texture unfavorable to magnetism increases, resulting in inferior magnetism, and if it exceeds 50°C / s, there may be a problem where the crystal grains become non-uniform, resulting in inferior magnetism. Similarly, if the cooling rate is less than 10°C / s, there may be a problem where the fraction of texture unfavorable to magnetism increases, and if it exceeds 40°C / s, there may be a problem where the residual stress present in the sheet after annealing increases, resulting in inferior magnetism.

[0036] Furthermore, during the cold-rolled sheet annealing stage, the heating rate and cooling rate satisfy the following equation 2. [Formula 2] 200≦([Heating rate]×[Cooling rate])≦500 (Here, [heating rate] and [cooling rate] are the average heating rate and average cooling rate between 600°C and the soaking temperature during cold-rolled sheet annealing, respectively, and the unit is °C / s.) The method for manufacturing the non-oriented electrical steel sheet further includes the step of coating the cold-rolled sheet, which has been annealed, with an insulating film. The insulating coating may be organic, inorganic, or an organic-inorganic composite coating, or it may be any other insulating coating agent.

[0037] The non-oriented electrical steel sheet manufactured by the above method for manufacturing non-oriented electrical steel sheets may have FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of the total grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​the total grains) ≥ 0.005. Furthermore, the non-oriented electrical steel sheet manufactured by the above method for manufacturing non-oriented electrical steel sheets has iron loss W 15 / 50 It is also acceptable if the iron loss is 2.0 W / kg or less. 10 / 400 It may be 16.5 W / kg or less.

[0038] The present invention will be described in more detail below through examples. However, these examples are merely illustrative and the present invention is not limited thereto. [Examples] Example 1 - Comparison based on Mn, Cu, and S content We attempted to manufacture steel ingots with the composition shown in Table 1 below through vacuum melting and to investigate the effects of varying the amounts of Mn, S, and Cu added, as well as the following [Equation 1], on the uniformity of the microstructure (size and fraction, area of ​​fine crystal grains) and magnetism. [Formula 1] 0.4≦([Mn]+10×[Cu])×1000×[S]≦1.5 (Here, [Mn], [Cu], and [S] are the amounts (by weight) of Mn, Cu, and S added, respectively.) Each steel ingot was heated to 1160°C, hot-rolled to a thickness of 2.4 mm, and then wound up. The hot-rolled steel sheets, cooled in air, were hot-rolled and pickled at 1000°C, then cold-rolled to a thickness of 0.35 mm, and finally cold-rolled annealing was performed. During this process, the soaking temperature for cold-rolled sheet annealing was controlled between 950°C and 1100°C, with a heating rate of 23°C / s and a cooling rate of 13°C / s to satisfy the following equation [Equation 2]. [Formula 2] 200≦([Heating rate]×[Cooling rate])≦500 (Here, [heating rate] and [cooling rate] are the average heating rate and cooling rate between 600°C during cold-rolled sheet annealing and the soaking temperature of the cold-rolled sheet, respectively, and the unit is °C / s.)

[0039] The microstructure of each specimen was observed to analyze the grain size, and the iron loss W, which is the average loss in the rolling direction and perpendicular to the rolling direction, was determined when a magnetic flux density of 1.5T was induced at a frequency of 50Hz through Epstein sample processing. 15 / 50and W, which is the average loss in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz 10 / 400 was measured, and the results are shown in Table 2 below.

[0040] [Table 1]

[0041] [Table 2]

[0042] In Table 2 above, FGS is the average grain size of grains that are 10% or less in size among all the grains, GS is the average grain size of all the grains, FGA is the average area of grains that are 10% or less in size among all the grains, and TGA is the average area of all the grains. As shown in Table 2, A2, A5, A7, A8, and A9, in which Si, Al, Mn, S, and Cu of the present invention satisfy their respective component addition amounts and [Equation 1], satisfy the relational expressions of FGS (average grain size of grains that are 10% or less in size among all the grains) ≥ 15 μm, FGS (average grain size of grains that are 10% or less in size among all the grains) / GS (average grain size of all the grains) ≥ 0.15, and FGA (average area of grains that are 10% or less in size among all the grains) / TGA (average area of all the grains) ≥ 0.005. As a result, the iron losses W 15 / 50 and W 10 / 400 are shown to be very excellent. On the contrary, A1 does not satisfy the controlled content ranges of S and Cu respectively, and does not satisfy [Equation 1] either. Therefore, it does not satisfy the relational expressions of FGS (average grain size of grains that are 10% or less in size among all the grains) ≥ 15 μm, FGS (average grain size of grains that are 10% or less in size among all the grains) / GS (average grain size of all the grains) ≥ 0.15, and FGA (average area of grains that are 10% or less in size among all the grains) / TGA (average area of all the grains) ≥ 0.005. As a result, the iron losses W 15 / 50 and W 10 / 400This indicates that it is at a disadvantage.

[0043] A3 and A10 do not satisfy the controlled content range for Mn, nor do they satisfy [Equation 1], and therefore the following relationships are not satisfied: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005. As a result, iron loss W 15 / 50 and W 10 / 400 This indicates that it is inferior. Although A4 satisfies [Equation 1], it does not satisfy the controlled content range for S and Cu, and therefore does not satisfy the relationships FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005. As a result, iron loss W 15 / 50 and W 10 / 400 This indicates that it is inferior.

[0044] On the other hand, A6 and A11 satisfied the controlled content ranges for Mn, S, and Cu, but did not satisfy [Equation 1], nor did they satisfy the relationships FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005. As a result, iron loss W 15 / 50 and W 10 / 400 This indicates that it is inferior.

[0045] Example 2 - Control of annealing and cooling rates of cold-rolled sheet We manufactured steel ingots with the composition shown in Table 3 below through vacuum melting and varied the amounts of Mn, S, and Cu to investigate the effects of the amount of Mn, S, and Cu added, as well as the heating and cooling rates during cold-rolled sheet annealing, on the uniformity of the microstructure (size, fraction, and area of ​​fine crystal grains) and magnetism. [Formula 1] 0.4≦([Mn]+10×[Cu])×1000×[S]≦1.5 (Here, [Mn], [Cu], and [S] are the amounts (by weight) of Mn, Cu, and S added, respectively.) Each steel ingot was heated to 1190°C, hot-rolled to a thickness of 2.3 mm, and then coiled. The hot-rolled steel sheets, cooled in air, were hot-rolled and pickled at 1050°C, then cold-rolled to a thickness of 0.35 mm, and finally cold-rolled annealing was performed. At this time, the target temperature for cold-rolled annealing was between 950 and 1100°C, and the effects of varying the heating rate and cooling rate during annealing were confirmed using the following [Equation 2]. [Formula 2] 200≦([Heating rate]×[Cooling rate])≦500 (Here, [heating rate] and [cooling rate] are the average heating rate and cooling rate between 600°C and the maximum temperature during cold-rolled sheet annealing, respectively, and the unit is °C / s.) The microstructure of each specimen was observed and the grain size was analyzed, and iron loss W was determined through Epstein sample processing. 15 / 50 and W 10 / 400 The measurements were taken and the results are shown in Table 4 below.

[0046] [Table 3]

[0047] [Table 4]

[0048] The aforementioned heating rate and cooling rate are the average heating rate and cooling rate between 600°C and the maximum temperature during cold-rolled sheet annealing, respectively. The aforementioned FGS, GS, FGA, TGA and iron loss W 15 / 50 , W10 / 400 The explanation is the same as in Example 1 above. As shown in Table 4 above, B2, B3, B6, B7, B9, and B12 of the present invention, which satisfy all of the following relationships with Si, Al, Mn, S, and Cu in their respective component addition ranges and the relationship between [Equation 1] and the heating rate, cooling rate, and [Equation 2] during cold-rolled sheet annealing, satisfy all of the following relationships: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of the total grains) ≥ 0.15, and FGA (average grain size of grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​the total grains) ≥ 0.005. As a result, iron loss W 15 / 50 and W 10 / 400 It demonstrates that it is excellent.

[0049] On the other hand, B1 satisfies all of the following conditions regarding the amount of Si, Al, Mn, S, and Cu added: [Equation 1], and also satisfies the heating rate and cooling rate ranges during cold-rolled sheet annealing, but does not satisfy [Equation 2]. As a result, the following relationships are not satisfied: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005, resulting in iron loss W 15 / 50 and W 10 / 400 This indicates that it is at a disadvantage.

[0050] Although B4 satisfied the respective component addition ranges and [Equation 1] for Si, Al, Mn, S, and Cu, the heating rate during cold-rolled sheet annealing did not meet the control range and did not satisfy [Equation 2]. As a result, the following relationships were not satisfied: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005, resulting in iron loss W 15 / 50 and W 10 / 400 It was shown to be inferior. B5 did not satisfy the component addition amount range and [Equation 1], nor did it satisfy [Equation 2] during cold-rolled sheet annealing, and as a result it did not satisfy the relationships FGS (average grain size of grains in the bottom 10% or less of the total grains based on grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grains based on grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grains based on grain size) / TGA (average area of ​​all grains) ≥ 0.005, resulting in iron loss W 15 / 50 and W 10 / 400 This indicates that it is at a disadvantage.

[0051] Although B8 satisfied the respective component addition ranges and [Equation 1] for Si, Al, Mn, S, and Cu, it did not satisfy [Equation 2] with respect to the cooling rate during cold-rolled sheet annealing. As a result, the following relationships were not satisfied: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005, resulting in iron loss W 15 / 50 and W 10 / 400 This indicates that it is at a disadvantage. In B10, the Si, Al, Mn, S, and Cu all satisfied their respective component addition ranges and [Equation 1], and also satisfied [Equation 2] during cold-rolled sheet annealing. However, the heating rate and cooling rate did not satisfy their respective control ranges, resulting in iron loss W not satisfying the following relationships: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005. 15 / 50 and W 10 / 400 This indicates that it is at a disadvantage.

[0052] B11 does not satisfy the control range for Cu and [Equation 1], nor the heating rate during cold-rolled sheet annealing and [Equation 2], and as a result the following relationships are not satisfied: FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005, resulting in iron loss W 15 / 50 and W 10 / 400 This indicates that it is inferior. B13 does not satisfy the control range of S and [Equation 1], nor does it satisfy the heating rate and cooling rate during cold-rolled sheet annealing and [Equation 2], and as a result the relationships FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, and FGA (average area of ​​grains in the bottom 10% or less of the total grain size) / TGA (average area of ​​all grains) ≥ 0.005 are not satisfied, resulting in iron loss W 15 / 50 and W 10 / 400 This indicates that it is inferior.

Claims

1. A non-oriented electrical steel sheet, In weight percent, it contains Si: 2.5-4%, Mn: 0.1-1.0%, S: 0.001-0.005%, Cu: 0.002-0.01%, with the remainder being Fe and unavoidable impurities. FGS (average grain size of grains in the bottom 10% or less of the total grain size) ≥ 15 μm, The aforementioned non-oriented electrical steel sheet has FGS (average grain size of grains in the bottom 10% or less of the total grain size) / GS (average grain size of all grains) ≥ 0.15, A non-oriented electrical steel sheet characterized in that the composition of the non-oriented electrical steel sheet satisfies the following formula 1. [Formula 1] 0.4≦([Mn]+10×[Cu])×1000×[S]≦1.5 (Here, [Mn], [Cu], and [S] are the amounts (by weight) of Mn, Cu, and S added, respectively.)

2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of the following in weight percent: C: 0.005% or less, Al: 0.5 to 1.5%, N: 0.005% or less, P: 0.2% or less, Sn: 0.2% or less, and Ti: 0.005% or less.

3. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of the following in weight percent: Sb: 0.2% or less, Ni: 0.05% or less, Cr: 0.05% or less, Zr: 0.01% or less, Mo: 0.01% or less, and V: 0.01% or less.

4. The non-oriented electrical steel sheet according to claim 1, characterized in that FGA (average area of ​​crystal grains in the bottom 10% or less based on grain size) / TGA (average area of ​​all crystal grains) ≥ 0.

005.

5. A method for manufacturing a non-oriented electrical steel sheet according to any one of claims 1 to 4, A step of producing a hot-rolled sheet by hot-rolling a slab containing, by weight percent, Si: 2.5-4%, Mn: 0.1-1.0%, S: 0.001-0.005%, Cu: 0.002-0.01%, with the remainder being Fe and unavoidable impurities. The steps of cold rolling the hot-rolled sheet to produce a cold-rolled sheet and The step includes annealing the cold-rolled sheet, During the cold-rolled sheet annealing stage, the average heating rate between 600°C and the soaking temperature is 15 to 50°C / s, and the average cooling rate between the soaking temperature and 600°C is 10 to 40°C / s. A method for manufacturing non-oriented electrical steel sheets, characterized by satisfying the following formula 2. [Formula 2] 200≦([heating rate]×[cooling rate])≦500 (Here, [heating rate] and [cooling rate] are the average heating rate and average cooling rate between 600°C and the soaking temperature during cold-rolled sheet annealing, respectively, and the unit is °C / s.)

6. The method for manufacturing a non-oriented electrical steel sheet according to claim 5, characterized in that the slab further comprises one or more of the following in weight percent: C: 0.005% or less, Al: 0.5 to 1.5%, N: 0.005% or less, P: 0.1% or less, Sn: 0.1% or less, and Ti: 0.005% or less.

7. In the stage of annealing the cold-rolled sheet The method for manufacturing a non-oriented electrical steel sheet according to claim 5, characterized in that the soaking temperature is 900 to 1100°C.

8. The method for manufacturing a non-oriented electrical steel sheet according to claim 5, further comprising the step of coating the annealed cold-rolled sheet with an insulating film after annealing the cold-rolled sheet.

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