Non-oriented electrical steel sheet and its manufacturing method

Abstract

The objective of this invention is to provide a non-oriented electrical steel sheet with excellent high-frequency iron loss characteristics by strictly controlling the composition of the non-oriented electrical steel sheet and appropriately controlling the distribution of the reduction rate during hot rolling and the MFS during finish rolling to form a predetermined texture. [Solution] The electrical steel sheet of the present invention is characterized in that it contains, by weight%, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and unavoidable impurities, wherein Al, Si, and Mn satisfy a predetermined relational expression 1, and the texture of the steel sheet is formed to satisfy a predetermined relational expression 3. [Relationship 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 [Relationship 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma.15≧0.40

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 manufacturing method for a non-oriented electrical steel sheet that is used mainly as a material for the iron cores of rotating machines such as motors and generators, and stationary machines such as small transformers. The present invention relates to a non-oriented electrical steel sheet that has excellent high-frequency iron loss and can be manufactured by optimally controlling the steel composition, optimizing the manufacturing conditions, and improving the texture, and to a manufacturing method for the same. [Background technology]

[0002] Recently, with the strengthening of environmentally friendly policies worldwide, there has been an increasing demand for improved efficiency in motors and generators, which are energy conversion devices that convert electrical energy into mechanical energy and mechanical energy into electrical energy. In rotating devices such as motors and generators and stationary devices such as small transformers, non-oriented electrical steel sheets are used as iron core materials and have an important influence on efficiency. Therefore, the demand for improved efficiency in motors and generators is leading to a demand for improved properties of non-oriented electrical steel sheets.

[0003] The key magnetic properties of non-oriented electrical steel are iron loss and magnetic flux density. Lower iron loss reduces the iron loss lost during the magnetization process, improving efficiency. Higher magnetic flux density allows for a stronger magnetic field to be induced with the same energy, and less current can be applied to achieve the same magnetic flux density, improving energy efficiency. Recently, high-frequency iron loss has emerged as a more important iron loss characteristic than commercial frequency (50 Hz) iron loss. This is because, as motor rotation speeds increase, high-frequency iron loss has a greater impact on efficiency than commercial frequency iron loss. For example, in the case of non-oriented electrical steel used in drive motors for eco-friendly automobiles, high-frequency iron loss at 400 Hz is considered a more important characteristic. Therefore, taking into account recent policies to improve energy efficiency and the trend toward the use of non-oriented electrical steel, it is essential to develop technology for non-oriented electrical steel that offers low high-frequency iron loss, high magnetic flux density, and excellent magnetic properties.

[0004] Among the important properties of non-oriented electrical steel sheets, the most basic and efficient ways to reduce iron loss are to increase the amount of Si, Al, and Mn, which are elements with high resistivity, or to reduce the thickness of the steel sheet. Increasing the amount of Si, Al, and Mn increases the steel's resistivity, thereby reducing eddy-current loss in the iron loss of non-oriented electrical steel sheets, thereby reducing iron loss. In the case of high-frequency iron loss, eddy-current loss accounts for a larger proportion of iron loss, making this a highly effective method for reducing high-frequency iron loss. However, the effectiveness varies depending on the addition ratio, and the magnetic flux density decreases as the amount of alloying elements increases. Therefore, to ensure excellent iron loss and magnetic flux density, it is necessary to properly control the appropriate addition amounts and the addition ratio between Si, Al, and Mn. Reducing the thickness is also very effective in reducing iron loss by significantly reducing eddy-current loss, but thin steel sheets have the disadvantage of poor productivity and formability. However, with the recent increase in demand for thinner products due to energy efficiency, product development is expected to continue toward ever thinner thicknesses.

[0005] As a method for improving magnetic flux density while reducing iron loss in non-oriented electrical steel sheets, various techniques have been reported, including the use of special additive elements such as REM to improve texture and magnetic properties, as well as the introduction of additional manufacturing processes such as warm rolling, double rolling, and double annealing. However, all of these techniques increase manufacturing costs and make mass production difficult, so it is necessary to develop technologies that provide excellent magnetic properties while also being commercially easy to produce. Furthermore, technologies have been developed to minimize the amount of added impurities and suppress and control the formation of inclusions by adding elements such as Ca, but these also increase manufacturing costs and make it difficult to clearly demonstrate their effectiveness.

[0006] There have been continuous efforts to solve these problems, and many technologies have been developed. Patent Document 1, one of the prior art technologies for non-oriented electrical steel sheets, proposes a method of improving magnetic properties by improving the texture by setting the composition weight ratio (MnO / SiO2) of MnO to SiO2 in oxide-based inclusions in the steel to 0.43 or less, and performing finish rolling during hot rolling in the ferrite single-phase region at a finish rolling temperature of 700°C or more while maintaining a friction coefficient between the steel and the roll of 0.2 or less, followed by hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing. However, this method has limitations, such as poor productivity and difficulty in commercial production, because the thickness of the hot-rolled sheet must be controlled to 1.0 mm or less.

[0007] Patent Document 2 proposes a method of controlling the heating rate during final annealing to 50°C / s or more in order to improve the texture of non-oriented electrical steel sheets and ensure excellent magnetic properties. However, this method does not take into consideration the fact that although rapid heating can improve the texture, magnetic properties may deteriorate as the microstructure becomes non-uniform.

[0008] In addition, in Patent Document 3, in order to manufacture a non-oriented electrical steel sheet having excellent magnetic properties in the rolling direction, a process of skin pass rolling at a rolling reduction rate of 3 to 10% and re-annealing is further carried out in addition to the processes of hot rolling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing. However, this also has the problem of increased costs due to the additional processes.

[0009] Patent Document 4 proposes a method for obtaining a steel sheet with low iron loss by reducing specific impurity elements contained in steel to a very low level and ensuring ease of grain growth by adding a skin pass process. However, this method has the drawback of causing an increase in cost due to the extremely low level of impurities.

[0010] Patent Document 5 proposes a technology in which the addition of rare earth elements such as Ca, Mg, and REM suppresses the precipitation of MnS, resulting in small crystal grains before stress relief, but the crystal grains grow during stress relief annealing, resulting in excellent iron loss. However, this also has the drawback of increasing manufacturing costs due to the addition and control of additional elements, and of making it difficult to ensure the effect if stress relief annealing is not performed. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-102739 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-199787 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-265720 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-050686 [Patent Document 5] Korean Patent Publication No. 2001-0100866 Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a non-oriented electrical steel sheet that has excellent high-frequency iron loss characteristics by strictly controlling the chemical composition of the non-oriented electrical steel sheet and appropriately controlling the distribution of the reduction rate during hot rolling and the MFS during finish rolling to form a predetermined texture.

[0013] Furthermore, the technical problems to be solved by the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those having ordinary skill in the technical field to which the present invention pertains from the following description. [Means for solving the problem]

[0014] Therefore, the non-oriented electrical steel sheet of the present invention has the following features: In weight percent, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities, wherein Al, Si, and Mn satisfy the following relational formula 1: The texture of the steel sheet is formed so as to satisfy the following relational expression 3. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Equation 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma.15≧0.40 where Vcube.15, Vrated-cube.15, and Vgamma.15 are the volume fractions of the (001)[0-10], (001)[-1-10], and (111)[-1-12] textures, respectively, when the tolerance angle is 15°.

[0015] The texture of the steel sheet can further satisfy the following relational expression 4: [Equation 4] (Vcube.15-Vcube.10) / Vcube.15≦0.90 Here, Vcube.15 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 15°, and Vcube.10 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 10°.

[0016] The texture of the steel sheet can further satisfy the following relational expression 5: [Equation 5] (Vgamma.15-Vgamma.10) / Vgamma.15≧0.50 Here, Vgamma.15 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 15°, and Vgamma.10 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 10°.

[0017] In the present invention, the non-oriented electrical steel sheet may have a resistivity (ρ) of 63 μΩcm or more at room temperature.

[0018] The non-oriented electrical steel sheet may have an iron loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more.

[0019] Here, iron loss W10 / 40 is the average loss (W / Kg) in the rolling direction and perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and magnetic flux density B50 is the magnitude of the magnetic flux density (Tesla) induced when a magnetic field of 5000 A / m is applied.

[0020] The non-oriented electrical steel sheet may further contain at least one of Sn and Sb in an amount of 0.2% or less.

[0021] The non-oriented electrical steel sheet may further contain Cu and Ni, either singly or in combination, in an amount of 0.05% or less.

[0022] The non-oriented electrical steel sheet may further contain Cr in the range of 0.1% or less.

[0023] The non-oriented electrical steel sheet may further contain Zr, Mo and V, either singly or in combination, in an amount of 0.01% or less.

[0024] Further, the method for producing a non-oriented electrical steel sheet of the present invention comprises the steps of: A method for producing a non-oriented electrical steel sheet, comprising the steps of: reheating a slab containing, by weight, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, with the balance being Fe and inevitable impurities; hot-rolling the reheated slab to produce a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet and then annealing it with or without cold rolling; pickling the hot-rolled annealed steel sheet and then air-cooling it; cold-rolling the air-cooled hot-rolled steel sheet; and final annealing the cold-rolled cold-rolled steel sheet, The Al, Si, and Mn satisfy the following relational formula 1: During the hot rolling, hot rolling is carried out at a temperature of 950°C or higher with a total reduction of 80% or higher, and the tension of the hot-rolled sheet is controlled in the final stage of finish rolling so as to satisfy the requirements of the following relational expression 2. [Equation 1] 0.6≦([Al]+[Mn]) / [Si]≦1 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Equation 2] 20.0≦MFS(kgf / mm2) at the final stage of finish hot rolling≦40.0

[0025] In the present invention, the texture of the final-annealed electrical steel sheet is formed to satisfy the following relational expression 3-5, and the resistivity (ρ) at room temperature may be 63 μΩcm or more, while the iron loss (W10 / 400) after final annealing may be 12.0 W / Kg or less, and the magnetic flux density (B50) may be 1.60 T or more. [Equation 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma.15≧0.4 [Equation 4] (Vcube.15-Vcube.10) / Vcube.15≦0.9 [Equation 5] (Vgamma.15-Vgamma.10) / Vgamma.15≧0.5 where Vcube.15, Vrated-cube.15, and Vgamma.15 are the volume fractions of the (001)[0-10], (001)[-1-10], and (111)[-1-12] textures, respectively, when the tolerance angle is 15°. Vcube.10 and Vgamma.10 are the volume fractions of the (001)[0-10] and (111)[-1-12] textures, respectively, when the tolerance angle is 10°. [Effects of the Invention]

[0026] According to the present invention, by controlling the steel composition and appropriately controlling the distribution of reduction ratios during hot rolling and the MFS of finish rolling to improve the texture, it is possible to effectively provide a non-oriented electrical steel sheet with excellent magnetic properties, which has a resistivity (ρ) of 63 μΩcm or more at room temperature, an iron loss (W10 / 400) of 12.0 W / Kg or less after final annealing, and a magnetic flux density (B50) of 1.60 T or more. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be described below.

[0028] The present invention proposes a method for producing a non-oriented electrical steel sheet in which the essential elements Si, Mn, and Al are added in amounts of 2.5 to 4.5%, 0.1 to 2.5%, and 0.5 to 2.5% to the chemical composition of a conventional non-oriented electrical steel sheet, respectively, and the Al, Mn, and Si satisfy the following relational expression 1. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00

[0029] In addition, in the present invention, when manufacturing a non-oriented electrical steel sheet from a slab of the above-mentioned chemical composition, the slab undergoes the usual hot rolling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing. In this case, in the hot rolling after reheating the slab, the slab is rolled at a temperature of 950°C or higher so that the total reduction in the hot rolling is 80% or more. In the final stage of finish rolling, the MFS (kgf / mm) of the following relational expression 2 is obtained. 2 The method is characterized in that the tension applied to the steel sheet is controlled so that the tensile strength (ρ) of the final annealed product is 20.0 to 40.0. As a result, the texture of the final annealed product is formed to satisfy the following relational expression 3, making it possible to provide an electrical steel sheet having excellent high-frequency core loss and magnetic flux density, i.e., a resistivity (ρ) of 63 μΩcm or more at room temperature, an iron loss (W10 / 400) of 12.0 W / Kg or less, and a magnetic flux density (B50) of 1.60 T or more. [Equation 2] 20.0≦MFS (kgf / mm2) at the final rolling stage of finish hot rolling≦40.0 [Equation 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma.15≧0.40 where Vcube.15, Vrated-cube.15, and Vgamma.15 are the volume fractions of the (001)[0-10], (001)[-1-10], and (111)[-1-12] textures, respectively, when the tolerance angle is 15°.

[0030] Specifically, the key elements whose amounts and contents must be controlled in this invention are Si, Al, Mn, N, and S. The most efficient way to reduce iron loss is to increase the resistivity of steel by adding Si, Al, and Mn. In particular, at high frequencies, the relative importance of eddy current loss in iron loss increases, further enhancing the effect of increasing resistivity. However, while increasing the amount of Si, Al, Mn, and other elements reduces iron loss, it also reduces saturation magnetic flux density, degrading magnetic flux density, and increases material brittleness, degrading cold rolling ability, and reducing productivity. Therefore, in order to achieve low iron loss and high magnetic flux density while also ensuring productivity, it is necessary not only to control the amounts of Si, Al, and Mn added, but also to appropriately combine the addition ratios of each element. This is why we propose the above Relational Formula 1.

[0031] Meanwhile, improving the texture of non-oriented electrical steel sheets to facilitate magnetization can simultaneously improve core loss and magnetic flux density. Since a decrease in magnetic flux density is inevitable as the amount of alloy added increases, improving the texture is necessary to minimize the decrease in magnetic flux density and achieve high magnetic flux density characteristics. Elements such as Al and Mn are known to improve texture when added, but this effect can only be achieved by appropriately controlling the process conditions so that the texture can be improved along with the addition of the elements. In light of this, the present invention proposes the above-mentioned Relational Formula 2.

[0032] The non-oriented electrical steel sheet of the present invention, obtained from this viewpoint, contains, by weight, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities, with Al, Si, and Mn satisfying the above relational formula 1, and the texture of the steel sheet being formed to satisfy the above relational formula 3. The electrical steel sheet of the present invention having such a texture can exhibit excellent high-frequency iron loss and magnetic flux density, with a resistivity (ρ) of 63 μΩcm or more at room temperature, an iron loss (W10 / 400) of 12.0 W / Kg or less, and a magnetic flux density (B50) of 1.60 T or more.

[0033] The reasons for limiting the compositional elements and contents of the electrical steel sheet of the present invention will be explained below, where "%" means % by weight.

[0034] Si: 2.50 to 4.50% The Si element is a major element added to increase the resistivity of steel and reduce eddy current loss in iron loss. To ensure low iron loss, especially in the high frequency range, 2.50% or more of Si must be added. However, as the amount of Si added increases, the magnetic flux density decreases significantly and the rollability deteriorates due to increased brittleness. Therefore, the amount of Si added is preferably limited to 4.50% or less. More preferably, it is limited to the range of 3.00 to 4.20%.

[0035] Mn: 0.10 to 2.50% The Mn element, along with Si and Al, increases resistivity and reduces iron loss, while also improving texture. However, if the amount added is too small, fine sulfides are formed, and if the amount added is excessive, the magnetic flux density decreases significantly. Therefore, the amount added is limited to 0.10 to 2.50%, and more preferably, to the range of 0.50 to 2.00%.

[0036] Al: 0.50 to 2.50% The Al element plays an important role in increasing resistivity and reducing iron loss, along with Si, and is added to reduce magnetic anisotropy and magnetic deviation between the rolling direction and the direction perpendicular to the rolling direction. However, if the amount added is small, the iron loss reduction effect is not significant, and if the amount added is too large, the magnetic flux density significantly deteriorates. Therefore, the amount added is limited to 0.50 to 2.50%, and more preferably, to the range of 0.60 to 2.30%.

[0037] C: 0.0050% or less C combines with Ti, Nb, etc. to form carbides, which deteriorates magnetic properties, and when processed into electrical appliances after use, increases iron loss due to magnetic aging, reducing the efficiency of electrical appliances. Therefore, it is preferable to limit C to 0.0050% or less.

[0038] S: 0.0010~0.0050% S is an element that forms sulfides such as MnS, CuS, and (Cu, Mn)S, which are harmful to magnetic properties, so it is preferable to add as little as possible. However, if added at 0.0010% or less, it is actually detrimental to the formation of texture and promotes the formation of fine sulfides, resulting in a decrease in magnetic properties. Therefore, the content should be 0.0010% or more, and if added at more than 0.0050%, the increase in sulfides results in a decrease in magnetic properties, so the content should be 0.0010 to 0.0050%.

[0039] N: 0.0050% or less N is an element that is harmful to magnetism by forming nitrides through strong bonding with Al, Ti, Nb, etc., and inhibiting grain growth, so it is preferable to contain it in small amounts, and in the present invention it is limited to 0.0050% or less.

[0040] Ti: 0.0050% or less Ti combines with C and N to form fine carbides and nitrides, which inhibit grain growth and reduce magnetic flux density. The more Ti is added, the more the texture deteriorates due to the increased amount of carbides and nitrides, resulting in poor magnetic properties. Therefore, in the present invention, the content is limited to 0.0050% or less.

[0041] P: 0.002 to 0.020% P has the effect of improving the texture of steel as a grain boundary and surface segregation element, but if its addition amount is less than 0.002%, the effect is slight, and if added in excess of 0.020%, it inhibits grain growth, thereby deteriorating iron loss, and grain segregation deteriorates rollability, resulting in reduced productivity. Therefore, its addition amount must be controlled to 0.002 to 0.020%.

[0042] In addition to the above elements, Sn and Sb, which are generally known to improve texture, may be added to further improve magnetic properties. However, if added in excessive amounts, they inhibit grain growth and deteriorate magnetic properties. Therefore, in the present invention, one or more of Sn and Sb may be further added in a range of 0.2% or less.

[0043] Furthermore, Cu and Ni may be added for the purpose of improving magnetic properties, but may react with impurity elements to form fine sulfides, carbides, and nitrides, which may have a detrimental effect on magnetic properties. Therefore, in the present invention, Cu and Ni may be further added alone or in combination within a range of 0.05% or less.

[0044] Cr is similar to Cu and Ni, but has the effect of increasing resistivity and improving magnetic properties, so it can be added in the range of 0.1% or less.

[0045] Furthermore, since Zr, Mo, V, etc. are strong carbonitride-forming elements, it is preferable to avoid adding them as much as possible. In the present invention, Zr, Mo, and V may be contained alone or in combination of two or more kinds in an amount of 0.01% or less.

[0046] The non-oriented electrical steel sheet of the present invention may further contain one or more of Bi, Pb, Ge, and As in an amount of 0.200 wt% or less, each or in total. More specifically, it may contain one or more of Bi, Pb, Ge, and As in an amount of 0.0001 to 0.200 wt% or less, each or in total. Even more specifically, it may contain one or more of Bi, Pb, Ge, and As in an amount of 0.001 to 0.100 wt% or less, each or in total.

[0047] In addition to the above composition, the remainder is composed of Fe and other unavoidable impurities.

[0048] On the other hand, in the present invention, Si, Al, and Mn are added in an amount of Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, and Al: 0.50 to 2.05%, and it is necessary that the above Al, Mn, and Si satisfy the following relational expression 1, and the specific reasons for this are as follows. [Equation 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively.

[0049] Iron loss in non-oriented electrical steel sheets can be divided into hysteresis loss and eddy-current loss. Adding elements such as Si, Al, and Mn increases the resistivity of the steel, significantly reducing eddy-current loss. In particular, as the frequency increases, the proportion of eddy-current loss in total iron loss increases. Therefore, to achieve excellent high-frequency iron loss, it is necessary to control the resistivity of the steel above a certain level. Through the present invention, we have confirmed that excellent properties can be achieved when the resistivity (ρ) of the steel is 63 μΩcm or higher. Among Si, Al, and Mn, Si is the element that most significantly increases the resistivity of steel. However, increasing the amount of Si increases the brittleness of the steel and reduces productivity. Therefore, to maintain a resistivity of 63 μΩcm or higher while also ensuring productivity, appropriate amounts of Al and Mn must be added along with Si. After investigating the appropriate addition ratio, we derived the above-mentioned Relational Formula 1. It is known that Al has a greater effect on increasing the resistivity of steel than Mn, but Al should not be added in particularly larger amounts than Mn.

[0050] The electrical steel sheet of the present invention may also have a texture that satisfies the following relational expression 3. If the value defined by the following relational expression 3 is less than 0.4, magnetization is not easy, and there may be a problem of deterioration in magnetic properties. [Equation 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma.15≧0.40 where Vcube.15, Vrated-cube.15, and Vgamma.15 are the volume fractions of the (001)[0-10], (001)[-1-10], and (111)[-1-12] textures, respectively, when the tolerance angle is 15°.

[0051] Furthermore, the electrical steel sheet of the present invention may have a texture that further satisfies the following relational expression 4. If the value defined by the following relational expression 4 exceeds 0.90, the concentration of texture that facilitates magnetization decreases, which may result in a problem of deterioration in magnetic properties. [Equation 4] (Vcube.15-Vcube.10) / Vcube.15≦0.90 Here, Vcube.15 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 15°, and Vcube.10 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 10°.

[0052] Furthermore, the electrical steel sheet of the present invention may have a texture that further satisfies the following relational expression 5. If the value defined by the following relational expression 5 is less than 0.50, the texture that is difficult to magnetize may be strengthened, which may cause a problem of deterioration in magnetic properties. [Equation 5] (Vgamma.15-Vgamma.10) / Vgamma.15≧0.50 Here, Vgamma.15 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 15°, and Vgamma.10 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 10°.

[0053] Generally, the texture fraction is determined based on a tolerance angle of 15°. However, in reality, the smaller the tolerance angle, the closer the texture is to the original texture, and the smaller the tolerance angle, the greater the effect on magnetic properties. Therefore, it does not appear that the texture has been improved simply by adjusting the fraction at 15°. The (001)[0-10] and (001)[-1-10] textures, which are favorable for magnetic properties, improve their texture as the fraction with a lower tolerance angle increases, thereby improving magnetic properties. Conversely, the (111)[-1-12] Goss texture, which is unfavorable for magnetic properties, improves magnetic properties by reducing the fraction with a low tolerance angle.

[0054] In the present invention, the (001)[0-10] and (001)[-1-10] textures, which are advantageous for magnetic properties, and the (111)[-1-12] texture, which is unfavorable for magnetic properties, satisfy the condition of the above-mentioned relational expression 3. In addition, preferably, the fractional change of each texture due to the tolerance angle satisfies the conditions of the above-mentioned relational expressions 4 and 5, thereby improving the concentration of the textures and enabling the material to exhibit superior magnetic properties.

[0055] The non-oriented electrical steel sheet of the present invention having the above-described texture may have an iron loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more. Here, the iron loss W10 / 40 is the average loss (W / Kg) in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and the magnetic flux density B50 is the magnitude of the magnetic flux density (Tesla) induced when a magnetic field of 5000 A / m is applied.

[0056] The non-oriented electrical steel sheet of the present invention may have a resistivity (ρ) of 63 μΩcm or more at room temperature.

[0057] Next, the method for producing the non-oriented electrical steel sheet of the present invention will be described in detail.

[0058] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of: reheating a slab containing, by weight, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities; hot-rolling the reheated slab to produce a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet, and then hot-rolling and annealing the hot-rolled steel sheet. In a method for producing a non-oriented electrical steel sheet, the method includes a step of annealing a hot-rolled sheet without annealing or cold rolling, a step of pickling the hot-rolled annealed steel sheet and then air-cooling it, a step of cold-rolling the air-cooled hot-rolled steel sheet, and a step of final annealing the cold-rolled cold-rolled steel sheet, the Al, Si, and Mn satisfy the above-mentioned relational expression 1, and during the hot rolling, the hot rolling is performed at a temperature of 950°C or higher with a total reduction of 80% or more, and the tension of the hot-rolled sheet is controlled so as to satisfy the requirement of the above-mentioned relational expression 2 in the final rolling stage of finish rolling.

[0059] That is, the non-oriented electrical steel sheet of the present invention can be produced by subjecting a steel slab having the above-described composition to the usual reheating, hot rolling, hot-rolled sheet annealing, pickling, followed by cold rolling and cold-rolled sheet annealing, and in this case, cold rolling may be carried out once or two or more times with intermediate annealing in between. The following description of the production conditions is a typical example and does not necessarily apply only to the following conditions.

[0060] First, the steel slab is reheated to 1200°C or lower and then hot rolled. If the reheating temperature is 1200°C or higher, precipitates such as nitrides, carbides, and sulfides present in the slab are redissolved and then finely precipitate during hot rolling and annealing, suppressing grain growth and reducing magnetism.

[0061] Next, in the present invention, the reheated slab is hot-rolled to produce a hot-rolled sheet. The texture of non-oriented electrical steel sheet is affected by the texture in the previous step rather than being formed independently during final annealing. Therefore, to improve the texture, precise control of conditions is required from the hot-rolling stage onward. When large stress is applied at low temperatures during hot rolling, the α-fiber content increases excessively, and the magnetization coefficient after final annealing strengthens the γ-fiber texture, which is the texture of the α-fiber. This leads to deterioration of magnetic properties. Therefore, the rolling reduction rate must be appropriately adjusted depending on the temperature. That is, when hot-rolling after slab reheating is performed at a temperature of 950°C or higher and the total hot-rolling reduction rate is 80% or more, the α-fiber and the γ-fiber texture, which is a texture that is difficult to magnetize in the final product, are weakened, improving magnetic properties. Furthermore, when the reduction rate during finish rolling is too large, the magnetization coefficient after final annealing strengthens the γ-fiber texture. Therefore, the MFS (kgf / mm) of the following relational expression 2 can be obtained. 2 ) to be between 20.0 and 40.0, the fraction and concentration of the (001)[0-10] and (001)[-1-10] textures, which are favorable for magnetization, are strengthened in the final product, and the fraction and concentration of the (111)[-1-12] gamma texture, which is unfavorable for magnetization, are reduced, thereby improving magnetic properties. [Equation 2] 20.0≦MFS(kgf / mm2) at the final stage of finish hot rolling≦40.0

[0062] At the final stage of finish rolling, MFS (kgf / mm 2 ) exceeds 40.0, γ-fiber is very strengthened, and conversely, MFS(kgf / mm 2 When MFS (kgf / mm) is less than 20.0, the effect of improving the (001)[0-10] and (001)[-1-10] textures, which are the easy directions of magnetization, is not observed. This is thought to be because the applied deformation amount is too small to show any effect of improving the texture. Therefore, in the final stage of finish rolling, 2 ) is controlled to satisfy the range of 20.0 to 40.0, a texture that satisfies the above-mentioned relational expressions 3-5 is formed, and magnetic properties can be improved.

[0063] Next, in the present invention, after the hot rolling, the hot-rolled sheet is coiled at 700°C or less and cooled in air. The coiled and cooled hot-rolled sheet is then annealed to ensure a recrystallized structure before cold rolling. The conditions for hot-rolled sheet annealing are very important for improving the texture of non-oriented electrical steel sheets, but it is also very important for controlling the distribution of precipitates. The soaking temperature in the hot-rolled sheet annealing process is preferably in the range of 850 to 1100°C. If the hot-rolled sheet annealing temperature is 850°C or less, grain growth is insufficient, the texture deteriorates, and the precipitate distribution is not controlled. If the hot-rolled sheet annealing temperature exceeds 1100°C, grain growth becomes coarse, degrading cold-rollability and causing fine precipitates to precipitate, which can result in a deterioration of magnetic properties.

[0064] In the present invention, the annealed hot-rolled sheet is pickled in a conventional manner and then cold-rolled.

[0065] Cold rolling is performed to a final thickness of 0.10 to 0.30 mm. The thickness of the final product has a significant effect on iron loss, especially high-frequency iron loss. To ensure excellent high-frequency iron loss, the thickness must be 0.3 mm or less. This cold rolling can be performed in a single pass, or in two passes with intermediate annealing, if necessary. In either case, excellent magnetic properties can be achieved through proper texture control only when the final reduction is in the range of 50 to 95%.

[0066] Subsequently, in the present invention, the cold-rolled steel sheet is finally subjected to cold-rolled sheet annealing. In the process of annealing the cold-rolled sheet, the annealing temperature is not particularly limited as long as it is a temperature that is generally applied to non-oriented electrical steel sheets.

[0067] The iron loss of non-oriented electrical steel sheet is closely related to the grain size. Iron loss in non-oriented electrical steel sheet can be divided into hysteresis loss and eddy-current loss. Hysteresis loss decreases as the grain size increases, while eddy-current loss increases as the grain size increases. Therefore, there is an optimum grain size at which the sum of hysteresis loss and eddy-current loss is minimized. Therefore, it is important to determine and apply an annealing temperature that ensures the optimal grain size. The annealing temperature is preferably 850 to 1100°C. If the annealing temperature is lower than 850°C, the grains will be too fine, resulting in increased hysteresis loss. If the annealing temperature exceeds 1100°C, the grains will be too coarse, resulting in increased eddy-current loss and a deterioration in iron loss.

[0068] The final annealed steel sheet is then shipped to the customer after being treated with an insulating coating. The insulating coating can be an organic, inorganic, or organic-inorganic composite coating, or it can be treated with other insulating coating agents. The customer can use the steel sheet as is after processing.

[0069] The non-oriented electrical steel sheet of the present invention manufactured using the above-described composition and manufacturing process can have a texture formed to satisfy the above-described Relational Expressions 3-5, thereby imparting excellent high-frequency iron loss characteristics, such as an iron loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more, and also exhibiting a resistivity (ρ) of 63 μΩcm or more at room temperature. [Example]

[0070] The method for manufacturing a non-oriented electrical steel sheet according to the present invention will be described in detail below with reference to examples. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples.

[0071] (Example) Steel ingots having the chemical compositions shown in Table 1 below were produced by vacuum melting. Each of the produced steel ingots was heated to 1180°C, hot-rolled to a thickness of 2.1 mm, coiled, and cooled in air. The cooled hot-rolled sheet was then hot-annealed at 900 to 1050°C. The hot-annealed hot-rolled sheet was then pickled and cold-rolled to a thickness of 0.2 mm, and then finally cold-rolled at a temperature in the range of 900 to 1050°C.

[0072] The room-temperature resistivity of each test specimen manufactured as described above was measured, and the results are shown in the following Table 2. In addition, EBSD test specimens were prepared, and the texture fraction was measured by EBSD measurement, and the results are also shown in the following Table 2. Then, the measured texture fraction was calculated using Relation 3-5, and the results are also shown in the following Table 2.

[0073] After processing the magnetic test specimens, the iron loss W10 / 400 and magnetic flux density B50 were measured, and the results are also shown in Table 2 below. Meanwhile, in this experiment, the iron loss W10 / 400 indicates the average loss (W / Kg) in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and the magnetic flux density B50 indicates the magnitude of the magnetic flux density (Tesla) induced when a magnetic field of 5000 A / m is applied.

[0074] [Table 1] *The remaining components in Table 1 are Fe and unavoidable impurities, and the relationship 1 is ([Al] + [Mn]) / [Si].

[0075] [Table 2] *MFS in Table 2 refers to the MFS at the final stage of finish hot rolling in relational expression 2, relational expression 3 represents (2*Vcube.15+Vrotated-cube.15) / Vgamma.15, relational expression 4 represents (Vcube.15-Vcube.10) / Vcube.15, and relational expression 5 represents (Vgamma.15-Vgamma.10) / Vgamma.15.

[0076] As shown in Table 1-2 above, No. 1-15 steel (invention example) that met the conditions of the electrical steel sheet composition and manufacturing process of the present invention had a texture that satisfied all of the requirements of Relational Formula 3-5, and therefore exhibited excellent magnetic properties, with an iron loss (W10 / 400) of 12.0 W / Kg or less and a magnetic flux density (B50) of 1.60 T or more after final annealing. In addition, the resistivity at room temperature was 63 μΩcm or more.

[0077] In contrast, Steel No. 16 was a case in which the amount of Si added and Relational Expression 1 were outside the ranges of the present invention, did not satisfy the requirements of Relational Expression 4, and exhibited deteriorated W10 / 400 and magnetic flux density B50.

[0078] Furthermore, in Steel No. 17, Mn and Relational Formula 1 did not satisfy the ranges of the present invention, and as a result, none of the requirements of Relational Formulas 3-5 were satisfied, resulting in deterioration in iron loss W10 / 400 and magnetic flux density B50.

[0079] Furthermore, in the case of Steel No. 18, the amount of Al added and Relational Expression 1 were outside the ranges of the present invention, and all of the requirements of Relational Expressions 4 and 5 were not satisfied, resulting in deterioration in iron loss W10 / 400 and magnetic flux density B50.

[0080] Furthermore, in the case of No. 19 steel, not only the amounts of Mn and Al added but also the relational expression 1 were outside the range of the present invention, and all of the requirements of the relational expressions 3-5 were not satisfied, resulting in deterioration of the iron loss W10 / 400 and the magnetic flux density B50.

[0081] Furthermore, No. 20 steel was a case in which Relational Formula 1 did not satisfy the range of the present invention, and did not satisfy the requirements of Relational Formula 3, resulting in deterioration in iron loss W10 / 400 and magnetic flux density B50. In addition, the resistivity at room temperature was also less than 63 μΩcm.

[0082] Although the composition and Relational Formula 1 of Steel No. 21 were within the scope of the present invention, the total reduction rate at 950°C or higher during hot rolling was less than 80%, which did not satisfy the requirements of Relational Formulas 3-4, and the iron loss W10 / 400 and magnetic flux density B50 were deteriorated.

[0083] The composition and relational formula 1 of the No. 22 steel are within the scope of the present invention, but the MFS (kgf / mm 2 ) was outside the range of the present invention, failed to satisfy the relational expression 4-5, and the iron loss W10 / 400 and magnetic flux density B50 deteriorated.

[0084] In the case of No. 23 steel, the composition and Relational Formula 1 were within the range of the present invention, but the total reduction rate at 950°C or higher during hot rolling and the MFS of Relational Formula 2 were outside the range of the present invention, and Relational Formulas 3 and 5 were not satisfied, resulting in deterioration in iron loss W10 / 400 and magnetic flux density B50. In addition, the resistivity at room temperature was also less than 63 μΩcm.

[0085] Steel No. 24 had an Al content and a total reduction rate during hot rolling outside the range of the present invention, did not satisfy the requirements of Relational Formula 3-4, and exhibited poor iron loss W10 / 400 and magnetic flux density B50.

[0086] Steel No. 25 not only failed to satisfy the Mn content and Relational Formula 1, but also failed to satisfy all of the requirements of Relational Formulas 3-5, as the MFS of Relational Formula 2 was outside the range of the present invention, resulting in deterioration of iron loss W10 / 400 and magnetic flux density B50.

[0087] The composition and Relational Formula 1 of Steel No. 26 were within the ranges of the present invention, but the total reduction rate during hot rolling and the MFS of Relational Formula 2 were outside the ranges of the present invention, and the requirements of Relational Formulas 3 and 5 were not met, resulting in deterioration of iron loss W10 / 400 and magnetic flux density B50.

[0088] Steel No. 27 not only had Mn and Al contents outside the ranges of the present invention, but also had total reduction ratio during hot rolling and MFS in relational expression 2 outside the ranges of the present invention, and did not satisfy the requirements of relational expressions 3-4, resulting in deterioration of iron loss W10 / 400 and magnetic flux density B50.

[0089] Steel No. 28 was a case in which not only the Mn and Al contents and Relational Formula 1 were outside the ranges of the present invention, but also the MFS of Relational Formula 2 during hot rolling was outside the ranges of the present invention, and did not satisfy all of the requirements of Relational Formulas 3-5, resulting in deterioration in iron loss W10 / 400 and magnetic flux density B50.

[0090] Steel No. 29 was a case in which not only the Mn and Al contents and Relational Formula 1 were outside the ranges of the present invention, but also the total reduction rate during hot rolling and MFS of Relational Formula 2 were outside the ranges of the present invention, and did not satisfy all of the requirements of Relational Formulas 3-5, resulting in deterioration in iron loss W10 / 400 and magnetic flux density B50.

[0091] On the other hand, in the case of No. 30 steel, not only the composition relational formula 1 was out of the range of the present invention, but also the total reduction rate during hot rolling and the MFS of relational formula 2 were out of the range of the present invention, and all of the requirements of relational formulas 4 and 5 were not satisfied, and the iron loss W10 / 400 and magnetic flux density B50 were deteriorated.

[0092] Although the present invention has been described above with reference to the embodiments, those skilled in the art may modify and change the present invention in various ways within the scope of the basic idea of ​​the present invention, and the scope of the rights of the present invention may be interpreted based on the claims.

Claims

1. In weight percent, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, and the balance being Fe and inevitable impurities, wherein Al, Si, and Mn satisfy the following relational formula 1: A non-oriented electrical steel sheet characterized in that the texture of the steel sheet is formed so as to satisfy the following relational expression 3: [Relationship 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Relationship 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma. 15≧0.40 where Vcube.15, Vrated-cube.15, and Vgamma.15 are the volume fractions of the (001)[0-10], (001)[-1-10], and (111)[-1-12] textures, respectively, when the tolerance angle is 15°.

2. 2. The non-oriented electrical steel sheet according to claim 1, wherein the texture of the steel sheet further satisfies the following relational expression 4: [Relationship 4] (Vcube.15-Vcube.10) / Vcube. 15≦0.90 Here, Vcube.15 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 15°, and Vcube.10 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 10°.

3. 3. The non-oriented electrical steel sheet according to claim 1, wherein the texture of the steel sheet further satisfies the following relational expression 5: [Relationship 5] (Vgamma.15-Vgamma.10) / Vgamma. 15≧0.50 Here, Vgamma.15 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 15°, and Vgamma.10 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 10°.

4. 2. The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet has a resistivity (ρ) of 63 μΩcm or more at room temperature.

5. 2. The non-oriented electrical steel sheet according to claim 1, wherein the core loss (W10 / 400) of the non-oriented electrical steel sheet is 12.0 W / Kg or less and the magnetic flux density (B50) is 1.60 T or more. Here, iron loss W10 / 40 is the average loss (W / kg) in the rolling direction and the direction perpendicular to the rolling direction when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz, and magnetic flux density B50 is the magnitude (Tesla) of the magnetic flux density induced when a magnetic field of 5000 A / m is applied.

6. The non-oriented electrical steel sheet according to claim 1, further comprising at least one of Sn and Sb in an amount of 0.2% or less.

7. The non-oriented electrical steel sheet according to claim 1, further containing Cu and Ni, either singly or in combination, in an amount of 0.05% or less.

8. The non-oriented electrical steel sheet according to claim 1, further comprising Cr in a range of 0.1% or less.

9. The non-oriented electrical steel sheet according to claim 1, further containing Zr, Mo and V alone or in combination of two or more thereof in an amount of 0.01% or less.

10. A method for producing a non-oriented electrical steel sheet, comprising the steps of: reheating a slab containing, by weight, C: 0.0050% or less, Si: 2.50 to 4.50%, Mn: 0.10 to 2.50%, P: 0.002 to 0.020%, S: 0.0010 to 0.0050%, Al: 0.50 to 2.50%, N: 0.0050% or less, Ti: 0.0050% or less, with the balance being Fe and inevitable impurities; hot-rolling the reheated slab to produce a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet and then annealing it with or without cold rolling; pickling the hot-rolled annealed steel sheet and then air-cooling it; cold-rolling the air-cooled hot-rolled steel sheet; and final annealing the cold-rolled cold-rolled steel sheet, The Al, Si, and Mn satisfy the following relational formula 1: a method for producing a non-oriented electrical steel sheet, characterized in that during the hot rolling, hot rolling is carried out at a temperature of 950°C or higher and a total reduction of 80% or higher, and the tension of the hot-rolled sheet is controlled in the final stage of finish rolling so as to satisfy the requirement of the following relational expression 2: [Relationship 1] 0.60≦([Al]+[Mn]) / [Si]≦1.00 Here, [Al], [Mn], and [Si] are the amounts (wt %) of Al, Mn, and Si added, respectively. [Relationship 2] 20.0≦MFS (kgf / mm2) at the final stage of finish hot rolling≦40.0

11. 11. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the texture of the final-annealed electrical steel sheet is formed to satisfy the following relational expression 3, and the resistivity (ρ) at room temperature is 63 μΩcm or more, the iron loss (W10 / 400) after final annealing is 12.0 W / Kg or less, and the magnetic flux density (B50) is 1.60 T or more. [Relationship 3] (2*Vcube.15+Vrotated-cube.15) / Vgamma. 15≧0.40 where Vcube.15, Vrated-cube.15, and Vgamma.15 are the volume fractions of the (001)[0-10], (001)[-1-10], and (111)[-1-12] textures, respectively, when the tolerance angle is 15°.

12. The method for producing a non-oriented electrical steel sheet according to claim 10, wherein the texture of the final-annealed electrical steel sheet further satisfies the following relational expression 4: [Relationship 4] (Vcube.15-Vcube.10) / Vcube. 15≦0.90 Here, Vcube.15 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 15°, and Vcube.10 is the volume fraction of the (001)[0-10] texture when the tolerance angle is 10°.

13. The method for producing a non-oriented electrical steel sheet according to claim 11 or 12, wherein the texture of the final-annealed electrical steel sheet further satisfies the following relational expression 5: [Relationship 5] (Vgamma.15-Vgamma.10) / Vgamma. 15≧0.50 Here, Vgamma.15 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 15°, and Vgamma.10 is the volume fraction of the (111)[-1-12] texture when the tolerance angle is 10°.

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