Non-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a non-oriented electrical steel sheet that has crystal grains with a specific orientation and has excellent uniformity in magnetism in all directions, and a method for manufacturing the same. The alloy contains, by weight, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the remainder being Fe and unavoidable impurities. <111> / / The area fraction of ND grains is 20% or less, <110> / / Area fraction of ND grains <100> / / The ratio of the area fraction of ND grains is 1.01 or more, <100> / / The surface fraction of ND crystal grains is 10% or more, and further contains one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%), and further contains one or more of P: 0.1 wt% or less (excluding 0%), C: 0.003 wt% or less (excluding 0%), S: 0.004 wt% or less (excluding 0%), Ti: 0.003 wt% or less (excluding 0%), and N: 0.003 wt% or less (excluding 0%).

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a non-oriented electrical steel sheet in which crystal grains having a specific orientation are formed by annealing between pre-rolling and cold rolling in the process of pre-rolling and cold rolling a hot-rolled sheet, and by rapidly raising the temperature during the annealing, thereby achieving excellent uniformity in magnetic properties in the entire direction, and a manufacturing method thereof. [Background technology]

[0002] Recently, amid increasing disasters caused by climate change, countries around the world have announced roadmaps for achieving carbon neutrality by 2050. Total carbon emissions are expected to reach 39 billion tons in 2020, of which internal combustion engines account for 24%, or 9.4 billion tons. Therefore, there is a strong demand for achieving carbon neutrality in this sector through the electrification of internal combustion engines. As a result, electrification is rapidly progressing in the mobility sector, with electric vehicles at the forefront. The driving motors required for new mobility vehicles must be able to increase mileage and top speed. This is directly linked to the low iron loss characteristics of electrical steel sheets. Low iron loss in electrical steel sheets can further improve efficiency and increase mileage. Therefore, low iron loss at high frequencies is essential for electrical steel sheets. To this end, electrical steel sheets typically contain large amounts of silicon and other elements, such as aluminum, manganese, and chromium, to ensure low iron loss at high frequencies.

[0003] However, adding large amounts of high-resistivity alloying elements such as Si, Al, Mn, and Cr can result in a problem of low magnetic flux density. In particular, materials with high magnetic flux density are essential for materials that require continuous weight reduction, such as environmentally friendly electric vehicle drive motors. For this reason, methods have been proposed to improve the properties by thinning the hot-rolled sheet, such as adding high Al and improving the magnetic properties through double annealing and double rolling.In addition, a method has been proposed to thin the hot-rolled sheet through a thin slab manufacturing method.

[0004] However, the method of reducing the thickness of hot-rolled sheets is difficult to mass-produce due to the increased rolling load in the general hot-rolling process. Although the addition of high Al and the double annealing and double rolling processes have been confirmed to partially improve the magnetic properties, the {110} <001> The Goss texture also develops, which deteriorates the circumferential properties of the motor, and the surface defects caused by the high Al addition also increase significantly. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the object of the present invention is to provide a non-oriented electrical steel sheet having excellent uniformity in magnetic properties in the entire direction, which is obtained by annealing the hot-rolled sheet between pre-rolling and cold rolling and rapidly raising the temperature during the annealing step, thereby forming crystal grains with a specific orientation. [Means for solving the problem]

[0006] The non-oriented electrical steel sheet of the present invention contains, by weight %, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the remainder being Fe and unavoidable impurities, <111> / / The area fraction of ND grains is 20% or less, <110> / / Area fraction of ND grains <100> / / The area fraction ratio of ND crystal grains is 1.01 or more.

[0007] <100> / / ND grains are grains <100> The grains have an axis within 15 degrees of the normal (ND) axis of the steel plate surface. <111> / / ND grains are grains <111> This indicates grains whose axes lie within 15 degrees of the normal (ND) axis of the steel plate surface. <110> / / ND grains are grains <110> This refers to grains whose axes lie within 15 degrees of the normal (ND) axis of the steel sheet surface. Area fraction refers to the ratio of the area occupied by grains of a specific orientation to the total area of ​​the steel sheet, as measured by electron backscatter diffraction (EBSD).

[0008] The non-oriented electrical steel sheet of the present invention is <100> / / The area fraction of ND grains can be 10% or more. The non-oriented electrical steel sheet of the present invention may further contain one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0009] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.1% or less (excluding 0%), C: 0.003% or less (excluding 0%), S: 0.004% or less (excluding 0%), Ti: 0.003% or less (excluding 0%), and N: 0.003% or less (excluding 0%).

[0010] The non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), V: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Nb: 0.0050% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%).

[0011] The non-oriented electrical steel sheet of the present invention may further contain one or more of Sn, Sb, Bi, Pb, Ge, and As in an amount of 0.005 to 0.200 wt % each or in total.

[0012] The non-oriented electrical steel sheet of the present invention can satisfy one or more of the following formulas 1 to 3.

[0013] [Formula 1] (B50 L +B50 C ) / 2≧1.63

[0014] [Formula 2] {(B50 L +B50 C +B50 60 ) / 3} / {(B50 L +B50 C ) / 2}≧0.95

[0015] [Formula 3] B50 60 / {(B50 L +B50 C ) / 2}≧0.90 (However, in formulas 1 to 3, B50 L is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 C is the magnetic flux density (B50, Tesla) measured in the direction perpendicular to the rolling direction, and B50 60 indicates the magnetic flux density (B50, Tesla) measured in a direction at an angle of 60° to the rolling direction.

[0016] The non-oriented electrical steel sheet of the present invention can satisfy the following formula 4.

[0017] [Formula 4] (W10 / 400 L +W10 / 400 C ) / 2≦6.885×e (2.99×t) (However, in formula 4, W10 / 400 L is the iron loss measured in the rolling direction (W10 / 400, W / kg), and W10 / 400 C is the iron loss (W10 / 400, W / kg) measured in the direction perpendicular to the rolling direction, e is the Napier number, and t is the thickness of the electrical steel sheet (mm).

[0018] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab containing, by weight, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the balance being Fe and unavoidable impurities, to produce a hot-rolled sheet; pre-cold rolling the hot-rolled sheet at a reduction ratio of 20 to 80% to produce a pre-cold-rolled sheet; a heating step of heating the pre-cold-rolled sheet at a temperature increase rate of 20°C / s or more; an intermediate annealing step of annealing the pre-cold-rolled sheet; a step of cold-rolling the annealed pre-cold-rolled sheet at a reduction ratio of 30 to 80% to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0019] The step of producing a hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher. The step of producing a hot-rolled sheet may include a step of water-cooling after a time of 0.1 seconds or more has elapsed after finish rolling. The step of producing the hot rolled sheet may include a step of coiling at a temperature of 600 to 800°C.

[0020] The slab may further contain one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0021] The slab may further contain one or more of the following: P: 0.1% or less (excluding 0%), C: 0.003% or less (excluding 0%), S: 0.004% or less (excluding 0%), Ti: 0.003% or less (excluding 0%), N: 0.003% or less (excluding 0%).

[0022] The slab may further contain one or more of Sn, Sb, Bi, Pb, Ge, and As in an amount of 0.005 to 0.200 wt % each or in total.

[0023] The slab may further contain one or more of Mo: 0.03% by weight or less (excluding 0%), B: 0.0050% by weight or less (excluding 0%), V: 0.0050% by weight or less (excluding 0%), Ca: 0.0050% by weight or less (excluding 0%), Nb: 0.0050% by weight or less (excluding 0%), and Mg: 0.0050% by weight or less (excluding 0%). [Effects of the Invention]

[0024] The non-oriented electrical steel sheet of the present invention has excellent magnetic flux density and iron loss in all directions. Ultimately, the non-oriented electrical steel sheet of the present invention contributes to the production of environmentally friendly motors for automobiles, highly efficient motors for home appliances, and super premium motor cores. DETAILED DESCRIPTION OF THE INVENTION

[0025] Terms such as "first," "second," and "third" are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0026] The terminology used herein is for the purpose of referring to particular embodiments and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used herein, the term "comprises" refers to the inclusion of certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components. When a part is described as being "on" or "above" another part, it may be exactly on or above the other part, or it may have other parts between them. In contrast, when a part is referred to as being "on" another part, there are no other parts between them.

[0027] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined. Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In the present invention, the term "additionally containing an additional element" means that the remaining iron (Fe) is substituted by the additional amount of the additional element.

[0028] The present invention will now be described in detail so that those skilled in the art can easily practice the present invention, but the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0029] The non-oriented electrical steel sheet of the present invention contains, by weight, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the remainder being Fe and unavoidable impurities. First, the reasons for limiting the components of non-oriented electrical steel sheets will be explained.

[0030] Si::2.5~4.0wt% Silicon (Si) plays a role in increasing the resistivity of the material and reducing iron loss, so it is necessary to add a relatively large amount. If the amount of Si added is too small, the effect of improving high-frequency iron loss is negligible. If the amount of Si added is too large, the hardness of the material increases, reducing productivity and punchability, which is not preferable. More specifically, the Si content can be 2.9 to 3.7 wt %.

[0031] Al:0.03~2.0wt% Aluminum (Al) increases the material's resistivity and reduces iron loss, so it must be added in large amounts. If the amount of Al added is too small, it will not be effective in reducing high-frequency iron loss, and fine nitrates may form, potentially degrading magnetic properties. If the amount of Al added is too large, it may cause problems with the mold flux's physical properties during the continuous casting process, significantly reducing productivity. More specifically, the Al content may be 0.1 to 1.8 wt %, and even more specifically, the Al content may be 0.5 to 1.5 wt %.

[0032] Mn:0.03~2.0wt% Manganese (Mn) increases the material's resistance, improves iron loss, and plays a role in forming sulfides. If too little Mn is added, fine MnS precipitates, which may deteriorate the magnetic properties. If too much Mn is added, it may have adverse effects on the magnetic properties. <111> / / It may promote the formation of an ND texture, resulting in a rapid decrease in magnetic flux density. More specifically, Mn may be contained in an amount of 0.05 to 1.9 wt %.

[0033] The non-oriented electrical steel sheet of the present invention may further contain one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

[0034] Cu:0.005~0.200wt% Copper (Cu) plays a role in forming sulfides with Mn. If Cu is added, too little may cause the precipitation of fine (Cu Mn)S, which may deteriorate the magnetic properties. If too much Cu is added, high-temperature brittleness may occur, which may cause cracks during continuous casting or hot rolling. More specifically, Cu may be contained in an amount of 0.01 to 0.10 wt%.

[0035] Cr:0.01~0.50wt% Chromium (Cr) plays a role in increasing the resistance and improving the iron loss. If the amount of Cr added is too small, the effect of increasing the resistance may be insufficient. If the amount of Cr added is too large, the magnetic flux density may decrease. More specifically, the Cr content may be 0.050 to 0.20 wt %.

[0036] Ni: 0.05% by weight or less Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrates, which may have a detrimental effect on magnetic properties. More specifically, Ni may be contained in an amount of 0.001 to 0.03 wt %.

[0037] Zn: 0.01% by weight or less If the zinc (Zn) content is excessive, it may act as an impurity and cause inferior magnetic properties. Therefore, Zn can be further added within the above-mentioned range. More specifically, Zn can be contained in an amount of 0.001 to 0.005 wt %.

[0038] The non-oriented electrical steel sheet of the present invention may further contain one or more of P: 0.1% or less (excluding 0%), C: 0.003% or less (excluding 0%), S: 0.004% or less (excluding 0%), Ti: 0.003% or less (excluding 0%), and N: 0.003% or less (excluding 0%).

[0039] P: 0.1% by weight or less Phosphorus (P) is a grain boundary segregation element that can improve magnetic flux density, but if added in an excessive amount, it increases the brittleness of the steel sheet and deteriorates weldability. More specifically, P can be contained in an amount of 0.0001 to 0.0500 wt %.

[0040] C: 0.003% by weight or less Carbon (C) reacts with N, Ti, Nb, V, etc. to form fine carbides, which can impede grain growth and magnetic domain movement, potentially resulting in a deterioration in magnetic properties. More specifically, C can be contained in an amount of 0.0001 to 0.0025 wt %.

[0041] S: 0.004% by weight or less Sulfur (S) is an element that forms sulfides such as MnS, and can inhibit grain growth and impair magnetic properties. More specifically, S can be contained in an amount of 0.0001 to 0.0030 wt %.

[0042] Ti: 0.003% by weight or less Titanium (Ti) can be limited because it forms carbonaceous cargo and plays a role in hindering magnetic domain movement. More specifically, Ti can be contained in an amount of 0.0001 to 0.0025 wt %.

[0043] N: 0.003% by weight or less Nitrogen (N) may combine with Ti, Nb, and V to form nitrates, which may reduce grain growth. More specifically, N may be contained in an amount of 0.0001 to 0.0025 wt %.

[0044] The non-oriented electrical steel sheet of the present invention may further contain one or more of Sn, Sb, Bi, Pb, Ge, and As in an amount of 0.005 to 0.200 wt % each or in total. When the aforementioned elements are added, they segregate at the grain boundaries, alleviating stress concentration at the grain boundaries during cold rolling, and the resulting stress is then released during the subsequent recrystallization annealing process. <111> / / Suppresses recrystallization of ND-oriented crystal grains and improves magnetic flux density. When these elements are added appropriately, the aforementioned effects can be further enhanced. However, if added in excess, significant segregation occurs, suppressing grain growth and resulting in poor magnetic flux density and core loss. More specifically, the alloy may contain one or more of Sn, Sb, Bi, Pb, Ge, and As, each or in a total amount of more than 0.010 to 0.100 wt.%.

[0045] The non-oriented electrical steel sheet of the present invention may further contain one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, and Mg: 0.0050 wt% or less. These react with the inevitably contained C, S, N, etc. to form fine carbides, nitrates, or sulfides, which may adversely affect the magnetic properties, so the upper limit can be set as described above.

[0046] Other impurities In addition to the above-mentioned elements, inevitable impurities may be included. The inevitable impurities are impurities that are mixed in during the steelmaking step and the manufacturing process of the non-oriented electrical steel sheet, and since they are widely known in the art, detailed explanations will be omitted. The present invention does not exclude the addition of elements other than the above-mentioned alloy components, and various elements may be included within a range that does not impair the technical concept of the present invention. When an additional element is further included, it is included by replacing the remaining Fe.

[0047] The non-oriented electrical steel sheet of the present invention is <111> / / The area fraction of ND grains is 20% or less, <110> / / Area fraction of ND grains <100> / / The area fraction ratio of ND crystal grains is 1.01 or more. where: <100> / / ND grains are grains <100> The grains have an axis within 15 degrees of the normal (ND) axis of the steel plate surface. <111> / / ND grains are grains <111> This indicates grains whose axes lie within 15 degrees of the normal (ND) axis of the steel plate surface. <110> / / ND grains are grains <110> This refers to grains whose axes lie within 15 degrees of the normal (ND) axis of the steel sheet surface. Area fraction refers to the ratio of the area occupied by grains of a specific orientation to the total area of ​​the steel sheet, as measured by electron backscatter diffraction (EBSD).

[0048] EBSD is generally performed using a scanning electron microscope, such as a JEOL JSM-7200F equipped with a TSL EBSD measuring device. The range of 15 degrees or less means that the angle between the normal axis of the steel sheet surface and any plane containing the orientation is within 15 degrees, and measurement is possible using the TSL EBSD Crystal Orientation Analysis Program (OIM). In this way, when the orientation of the crystal grains is appropriately adjusted, the magnetic properties can be improved more uniformly in the entire direction of the steel sheet.

[0049] The grain orientation and its area fraction of the present invention are determined by cutting a steel sheet parallel to the sheet thickness direction, and analyzing the crystal orientation of the grains in the center region of the cut surface through electron backscatter diffraction (EBSD) measurement, with a measurement interval of 2 μm and a total measurement area of ​​3000 μm × 3000 μm.

[0050] Non-oriented electrical steel sheets have a body-centered cubic crystal structure, and there are crystal orientations that are more likely to be magnetized by an externally applied magnetic field. <001> It is easiest to magnetize when it is in a azimuth direction. <111> The orientation of the crystal grain is the most difficult to magnetize. <111> / / From ND <100> / / ND means that it can exhibit a higher magnetic flux density with the same applied magnetic field.

[0051] Therefore, in the steel plate <111> / / If there are many ND crystal grains, magnetization by an externally applied magnetic field does not occur easily, the magnetic flux density is inferior, and iron loss increases, making it impossible to achieve the desired motor efficiency, so it is desirable to minimize this. <111> / / The area fraction of ND crystal grains is 20% or less. More specifically, <111> / / The area fraction of ND crystal grains can be 15% or less, and the smaller the fraction, the better the magnetic properties, but there is no lower limit (excluding 0%). More specifically, <111> The area fraction of / / ND crystal grains may be 5 to 19%, and more specifically, the area fraction of 111> / / ND crystal grains may be 10 to 15%. <110> / / Area fraction of ND grains <100> / / Ratio of area fraction of ND grains ( <100> / <110> ) may be 1.01 or greater.

[0052] <110> / / ND grains are <111> / / Although this orientation is not as difficult to magnetize as ND crystal grains, it increases the magnetic deviation in the rolling direction and in the direction perpendicular to the rolling direction, which is disadvantageous in ensuring uniform magnetism in the entire steel sheet. However, <110> / / ND grains are <111> / / Since it is more advantageous than ND crystal grains in ensuring magnetic flux density and low iron loss characteristics, it is necessary to control the proportion appropriately. Therefore, to ensure uniform magnetism across the entire steel sheet, <100> / / Increase the ratio of ND grains, <110> / / By reducing the ratio of ND crystal grains, the magnetic properties can be further improved. <110> / / Area fraction of ND grains <100> / / Ratio of area fraction of ND grains ( <100> / <110> ) is preferably 1.01 or more. More specifically, it can be 1.04 or more, and the higher this ratio, the more advantageous it is for magnetic properties, and there is no upper limit. More specifically, it may be 1.10 to 1.9.

[0053] Inside the steel plate <100> / / When there are many ND crystal grains, the motor exhibits high magnetic flux density and low iron loss characteristics when an external magnetic field is applied, which can significantly improve motor efficiency. <100> / / The area fraction of ND grains can be 10% or more. More specifically, <100> / / The area fraction of ND crystal grains can be 20% or more, and the higher the area fraction, the more advantageous the magnetic properties are, and there is no particular upper limit. More specifically, <100> / / The area fraction of ND crystal grains may be 20% to 50%.

[0054] In the present invention, crystal grains having a specific orientation are formed, and the magnetism is uniform and excellent in all directions. Specifically, the non-oriented electrical steel sheet of the present invention can satisfy one or more of the following formulas 1 to 3.

[0055] [Formula 1] (B50 L +B50 C ) / 2≧1.63

[0056] [Formula 2] {(B50 L +B50 C +B50 60 ) / 3} / {(B50 L +B50 C ) / 2}≧0.95

[0057] [Formula 3] B50 60 / {(B50 L +B50 C) / 2}≧0.90

[0058] (However, in formulas 1 to 3, B50 L is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 C is the magnetic flux density (B50, Tesla) measured in the direction perpendicular to the rolling direction, and B50 60 indicates the magnetic flux density (B50, Tesla) measured in a direction at an angle of 60° to the rolling direction. B50 means the magnetic flux density induced in a magnetic field of 5000 A / m.

[0059] Equation 1 is a general method for evaluating the magnetic flux density of non-oriented electrical steel sheets, and represents the average value of the magnetic flux density (B50) in the rolling direction (L) and the direction perpendicular to the rolling direction (C). Equation 2 is obtained by dividing the average value of the magnetic flux density (B50) measured in the rolling direction (L), the perpendicular direction (C) and the direction at an angle of 60° to the rolling direction of the steel sheet by the average value of Equation 1. This means that the magnetic flux density is excellent not only in the conventional rolling direction (L) and the perpendicular direction (C), but also in the direction at an angle of 60°. In other words, since the present invention has excellent magnetism in the entire direction of the steel sheet, the magnetic flux density (B50) is maintained even in the 60° direction, which has been known to have the poorest magnetic flux density in the past. 60 Therefore, according to the present invention, the magnetic flux density (B50 60 ) higher than the average ratio.

[0060] Equation 3 is the magnetic flux density (B50) of the steel plate measured in a direction at an angle of 60°. 60 ) divided by the average magnetic flux density in the rolling direction (L) and the perpendicular direction (C) of the steel sheet. Because the magnetic flux density is high in the entire steel sheet, the magnetic flux density in the direction at an angle of 60° (B50 60) and the ratio of formula 1. In the conventional double annealing and double rolling method, the {100} <001> Exact Cube texture and {110} <001> By developing the Goss texture, the magnetic flux density increases only in the rolling direction and in the direction perpendicular to the rolling direction of the steel sheet, but the magnetic flux density in the direction at an angle of 60° to the rolling direction is very poor, and the magnetic properties of the steel sheet cannot be evaluated as being excellent in the entire direction. <100> / / By applying optimal non-resistance improving alloying elements to increase the surface fraction of ND crystal grains, high-temperature hot rolling and coiling, and rapid heating technology with stepwise cold reduction and intermediate annealing, it is possible to manufacture non-oriented electrical steel sheets for drive motors that have excellent magnetic flux density not only in the rolling direction and perpendicular directions of the steel sheet, but also in the direction at an angle of 60° to the rolling direction.

[0061] Furthermore, the non-oriented electrical steel sheet of the present invention can satisfy the following formula 4.

[0062] [Formula 4] (W10 / 400 L +W10 / 400 C ) / 2≦6.885×e (2.99×t) (However, in formula 4, W10 / 400 L is the iron loss measured in the rolling direction (W10 / 400, W / kg), and W10 / 400 C is the iron loss (W10 / 400, W / kg) measured in the direction perpendicular to the rolling direction, e is the Napier number, and t is the thickness of the electrical steel sheet (mm).

[0063] W10 / 400 is the iron loss when a magnetic flux density of 1.0 T is applied at a frequency of 400 Hz. Equation 4 shows that by ensuring excellent magnetic flux density in the entire direction of the steel sheet according to equations 1 to 3, iron loss is significantly reduced and motor efficiency can be improved. Such iron loss characteristics are affected not only by magnetic flux density characteristics but also by the thickness of the steel sheet, so this means the iron loss that can be achieved by a steel sheet that exhibits excellent magnetic flux density in the entire direction of the steel sheet, as in the present invention, depending on the thickness of the steel sheet.

[0064] The method for producing a non-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab containing, by weight, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the balance being Fe and unavoidable impurities, to produce a hot-rolled sheet; pre-cold rolling the hot-rolled sheet at a reduction of 20 to 80% to produce a pre-cold-rolled sheet; an intermediate annealing step of annealing the pre-cold-rolled sheet by heating at a heating rate of 20°C / s or more; cold rolling the pre-annealed pre-cold-rolled sheet at a reduction of 30 to 80% to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0065] Each step will be explained in detail below. First, a slab is manufactured. The reasons for limiting the addition ratio of each component in the slab are the same as those for limiting the composition of the non-oriented electrical steel sheet described above, and therefore a repeated explanation will be omitted. The composition of the slab does not substantially change during the manufacturing process, such as hot rolling, hot-rolled sheet annealing, preliminary cold rolling, first annealing, cold rolling, and second annealing, which will be described later, so the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially the same. Before the step of producing the hot-rolled sheet, the slab can be heated to 1100°C or higher. Specifically, the slab is charged into a heating furnace and heated to 1100 to 1250°C. When heated to a temperature above 1250°C, the precipitates remelt and can be finely precipitated after hot rolling.

[0066] The heated slab is hot-rolled to a thickness of 1.5 to 4.0 mm to produce a hot-rolled sheet. In one embodiment of the present invention, a step of pre-cold rolling is also included before cold rolling, so that even if the thickness of the hot-rolled sheet is relatively thick, a non-oriented electrical steel sheet of an appropriate thickness can be produced. More specifically, the thickness of the hot-rolled sheet can be 1.5 to 3.5 mm. The step of producing a hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher. If the hot rolling finish rolling temperature is too low, the rolling load increases and the hot rolling workability decreases. In addition, a large amount of deformed structure remains in the hot-rolled steel sheet, which causes an increase in the rolling load during the subsequent preliminary cold rolling process. In addition, the deformed structure is removed during intermediate annealing. <111> / / Recrystallization of ND-oriented crystal grains is promoted, resulting in inferior magnetic flux density. Therefore, the higher the finish rolling temperature in hot rolling, the better. More specifically, finish rolling at a temperature of 860 to 1000°C is desirable.

[0067] The step of producing a hot-rolled sheet may include a step of water-cooling after a time of 0.1 seconds or more has elapsed after finish rolling. After finish rolling, cooling is performed for coiling. However, if water cooling is performed immediately after finish rolling (i.e., for less than 0.1 seconds), the steel sheet is rapidly cooled, which can cause deformation and residual stress in the steel sheet, making coiling difficult. In addition, in terms of the microstructure, the deformation stress after finish rolling remains without being released, which can increase the rolling load in the subsequent cold rolling step and cause microstructure deformation. <111> / / It may cause recrystallization in the ND orientation. Therefore, immediately after hot finishing rolling, maintaining the hot rolling deformation structure for 0.1 seconds or more to allow recovery and recrystallization to occur reduces the rolling load during the subsequent preliminary cold rolling. <111> / / This will suppress the generation of ND-oriented recrystallized grains. More specifically, water cooling can be performed after 0.3 to 5.0 seconds, and even more specifically, water cooling can be performed after 0.5 to 3.0 seconds.

[0068] The steps for producing a hot-rolled sheet may include a coiling step at a temperature of 600 to 800°C. A rough rolling step may also be included before the finish rolling step. If the temperature during the coiling step is controlled too low, the recovery and recrystallization of the hot-rolled deformation structure may not be achieved properly. Rapid cooling of the steel sheet at a low temperature increases the cooling load, making it difficult to coil an overcooled coil. Conversely, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during coiling, resulting in thicker scale formation and intergranular oxidation problems. Intergranular oxidation of the hot-rolled sheet may promote intergranular corrosion during the subsequent pickling process, potentially resulting in surface streak defects and severe wear of the rolling rolls. Therefore, the coiling temperature is preferably 600 to 800°C, and more specifically, coiling can be performed at a temperature of 600 to 750°C.

[0069] It is most desirable to carry out pickling and preliminary cold rolling immediately after producing the hot-rolled sheet, but the method may further include annealing the hot-rolled sheet at a temperature in the range of 600 to 1100°C after the step of producing the hot-rolled sheet. If the annealing temperature of the hot-rolled sheet is too low, the recrystallized structure will not form or will grow fine, resulting in little effect in increasing the magnetic flux density. If the annealing temperature is too high, the magnetic properties will deteriorate and the rolling workability may be impaired due to deformation of the sheet. More specifically, the temperature range may be 700 to 1050°C. The hot-rolled sheet annealing is performed to increase the orientation advantageous for magnetic properties as needed, and can be omitted. The annealing method is not particularly limited, and the annealing can be performed in a batch or continuous manner. The hot-rolled sheet may be pickled as necessary.

[0070] Next, the hot-rolled sheet is preliminarily cold-rolled at 20 to 80% to produce a preliminarily cold-rolled sheet. Preliminary cold rolling can be performed in a PCM (Pickling & Cold Rolling Mill) that includes a pickling process to improve rolling productivity, or in a TCM (Tandem Cold Rolling Mill) that only performs cold rolling. <100> / / To improve the ND crystal grain fraction, rolling is performed within a reduction range of 20 to 80%. At the same time, if rolling productivity is not a consideration, preliminary cold rolling using a reverse mill is also possible in the present invention. Preliminary cold rolling is different from cold rolling, which will be described later, in that it is the first rolling step in the process of rolling to an intermediate thickness rather than the final product thickness, followed by intermediate annealing, and then cold rolling to the final product thickness.

[0071] The preliminary cold rolling reduction can be calculated by (steel sheet thickness before rolling - steel sheet thickness after rolling) / steel sheet thickness before rolling. If the reduction in the preliminary cold rolling step is too low, the rolling load during the final cold rolling increases, productivity decreases, the final reduction increases, and fine grains are formed. <111> / / This may cause problems with promoting ND recrystallization. Conversely, if the reduction is too high, the cold rolling load increases, increasing the possibility of sheet fracture. Therefore, the reduction in the preliminary cold rolling step is preferably within a range of 20 to 80%, and more specifically, the lower limit of the reduction can be 20%, 30%, 40%, 50%, 60%, 70%, or 80%, and the upper limit of the reduction can be 80%, 70%, 60%, 50%, 40%, 30%, or 20%.

[0072] The step of producing a pre-cold-rolled sheet can be carried out at a temperature of 60 to 300°C. This temperature can be raised either by the natural temperature rise of the steel sheet due to friction between the steel sheet and the rolling rolls, or by applying heat from an external source. If the temperature is too low, the rolling load increases significantly, and the steel sheet may not be rolled between the rolling rolls, resulting in problems such as slippage and twisting. If the temperature is too high, oxidation of Si and Al may occur on the surface of the steel sheet, deteriorating its magnetic properties and causing problems such as ignition of the rolling oil. More specifically, the step is preferably carried out at a temperature of 70 to 250°C.

[0073] Next, the pre-cold rolled sheet is heated at a temperature rising rate of 20°C / s or more and subjected to intermediate annealing. <100> / / Promotes recrystallization in the ND orientation, ultimately improving magnetic properties. If the heating rate is too low, <111> / / Recrystallization of the ND orientation is promoted, making it difficult to fully achieve the aforementioned effects. A heating rate of 500°C / s or higher is difficult to control, resulting in a temperature rise higher than the target annealing temperature, making it difficult to ensure a uniform microstructure. More specifically, heating can be performed at a rate between 30°C / s and 500°C / s. The aforementioned heating rate can be measured in the temperature range from a starting temperature of 100°C to a finishing temperature of 600°C. The above-mentioned temperature rise rate can be measured in the temperature range from a starting temperature of 100°C to a finishing temperature of 600°C.

[0074] The intermediate annealing temperature can be in the range of 600 to 1100°C. If the annealing temperature is too low, the size of the crystal grains becomes fine, the number of crystal grain boundaries increases, and the grain boundaries are easily broken down during the final cold rolling. <111> / / ND orientation recrystallization nuclei increase, ultimately reducing magnetic flux density. Conversely, if the annealing temperature is too high, the crystal grains increase significantly, which can lead to problems such as increased sheet breakage due to cracks occurring at the crystal grain boundaries during final cold rolling. Preferably, annealing can be performed at a temperature of 750 to 1050°C. After the intermediate annealing, the annealed sheet can be pickled as needed. Since the pickling method is widely known, detailed description thereof will be omitted.

[0075] Next, in the step of cold rolling, the intermediately annealed pre-cold rolled sheet is cold rolled at a reduction ratio of 30 to 80%. If the reduction is too low, the deformation energy stored in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which may cause problems in improving magnetic flux density and iron loss. <111> / / This may cause problems such as accelerated recrystallization of ND-oriented crystal grains, resulting in finer crystal grains, poorer magnetic flux density, and increased core loss. More specifically, the lower limit of the rolling reduction may be 30%, 40%, 50%, 60%, 70%, or 80%. The upper limit of the rolling reduction may be 80%, 70%, 60%, 50%, 40%, or 30%.

[0076] Next, the step of annealing the cold-rolled sheet can be performed at a temperature in the range of 600 to 1200°C. If the annealing temperature is too low, <111> / / The recrystallization of ND-oriented crystal grains is accelerated, resulting in finer crystal grains and making it impossible to ensure excellent magnetic flux density. Annealing at temperatures that are too high can cause the crystal grains to grow coarse, increasing iron loss, and potentially creating oxide or nitride layers on the steel sheet surface from the annealing atmosphere, which increases iron loss. More specifically, annealing can be performed at temperatures between 750 and 1100°C. After the cold-rolled sheet annealing step, a step of forming an insulating coating on the steel sheet to ensure insulation and corrosion resistance may be further included. Since the insulating coating is widely known, detailed description thereof will be omitted.

[0077] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to the following examples. [Example]

[0078] Slabs were manufactured as shown in Table 1 below. In addition to the components listed in Table 1, P: 0.01%, C: 0.0020%, S: 0.0025%, N: 0.0020%, Ti: 0.0025%, Cu: 0.02%, Cr: 0.04%, Ni: 0.02% were added by weight, and Zn, Mo, B, Ca, Mg, Nb, V, etc. were all added in an amount of 0.002% or less each, with the remainder being Fe. The slab was heated to 1150°C, hot-finish rolled at 920°C, water-cooled after 1 second, and coiled at 650°C to produce a hot-rolled sheet. The hot-rolled sheet was then pickled and pre-cold rolled. Pre-cold rolling was performed at 85°C with the reduction shown in Table 1, followed by heating at the heating rate shown in Table 1 below and intermediate annealing at 1000°C for 30 seconds. The intermediate-annealed steel sheet was then final cold-rolled with the secondary reduction shown in Table 1 below to produce a cold-rolled sheet with the thickness shown in Table 1. Final annealing was performed at 950°C for 60 seconds in a dry hydrogen and nitrogen gas atmosphere. The crystal grain orientation of the steel sheet after cold rolling and annealing was measured by electron backscatter diffraction (EBSD), and the fraction of each orientation is summarized in Table 2 below. The magnetic properties were measured using Epstein testers prepared at different angles using an Epstein tester. The results are summarized in Tables 2 and 3 below.

[0079] [Table 1]

[0080] [Table 2]

[0081] [Table 3]

[0082] As shown in Tables 1 to 3, examples in which the preliminary cold rolling reduction, the temperature rise rate, and the final cold rolling reduction conditions were appropriately adjusted are as follows: <100> / / High ND fraction, <111> / / ND and <110> / / The ND fraction is controlled, and it can be confirmed that the magnetism is uniform and excellent in all directions. [Example]

[0083] Hot rolling was performed on a slab with the same composition as No. 6 in Table 1 of Example 1. The slab was heated to 1200°C, and a 3.0 mm hot-rolled sheet was produced by varying the hot-finishing temperature, the time required for water cooling after finish rolling, and the coiling temperature. The hot-rolled sheet was pre-cold rolled at 100°C to a thickness of 0.7 mm with a reduction of 76.7%. The sheet was then heated to 950°C at a heating rate of 50°C / s and then intermediate annealed for 10 seconds. The intermediate-annealed steel sheet was then final cold-rolled to a thickness of 0.25 mm with a secondary reduction of 64%. Final annealing was performed by heating at a heating rate of 100°C / s and at 1050°C for 20 seconds. The magnetic properties and grain orientation fraction of the final product were analyzed using the same method as in Example 1 and are shown in Tables 4 and 5.

[0084] [Table 4]

[0085] [Table 5]

[0086] As can be seen in Tables 4 and 5, the finish hot rolling temperature is completed at 850°C or higher, and is maintained for at least 0.1 seconds immediately after rolling to promote recovery and recrystallization of the hot rolled structure. As a result, the final steel sheet after cold rolling <111> / / The ND structure fraction was reduced, ensuring excellent magnetic flux density characteristics in the entire direction of the steel sheet. It was confirmed that in order to ensure such recovery and recrystallized hot-rolled structure, it is necessary to coil the coil at a temperature in the range of 600 to 800°C.

[0087] The present invention is not limited to the above-described embodiment, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, the embodiment described above should be understood to be illustrative in all respects and not limiting.

Claims

1. The alloy contains, by weight, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the balance being Fe and unavoidable impurities; The area fraction of <111> / / ND crystal grains is 20% or less, A non-oriented electrical steel sheet characterized in that the ratio of the area fraction of <100> / / ND crystal grains to the area fraction of <110> / / ND crystal grains is 1.01 or more. (However, <100> / / ND crystal grains are crystal grains whose <100> axis is within a range of 15 degrees from the axis normal to the surface of the steel sheet (ND), <111> / / ND crystal grains are crystal grains whose <111> axis is within a range of 15 degrees from the axis normal to the surface of the steel sheet (ND), and <110> / / ND crystal grains are crystal grains whose <110> axis is within a range of 15 degrees from the axis normal to the surface of the steel sheet (ND).)

2. 2. The non-oriented electrical steel sheet according to claim 1, wherein the area fraction of <100> / / ND crystal grains is 10% or more.

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Cu: 0.005 to 0.2 wt %, Cr: 0.01 to 0.5 wt %, Ni: 0.05 wt % or less (excluding 0%), and Zn: 0.01 wt % or less (excluding 0%).

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of P: 0.1% by weight or less (excluding 0%), C: 0.003% by weight or less (excluding 0%), S: 0.004% by weight or less (excluding 0%), Ti: 0.003% by weight or less (excluding 0%), and N: 0.003% by weight or less (excluding 0%).

5. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Sn, Sb, Bi, Pb, Ge, and As in an amount of 0.005 to 0.200 wt %, respectively, or in total.

6. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Mo: 0.03% by weight or less (except 0%), B: 0.0050% by weight or less (except 0%), V: 0.0050% by weight or less (except 0%), Ca: 0.0050% by weight or less (except 0%), Nb: 0.0050% by weight or less (except 0%), and Mg: 0.0050% by weight or less (except 0%).

7. 2. The non-oriented electrical steel sheet according to claim 1, wherein the following formula 1 is satisfied: [Formula 1] (B50 Ｌ +B50 Ｃ ) / 2≧1.63 (However, in formula 1, B50 Ｌ is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 Ｃ indicates the magnetic flux density (B50, Tesla) measured in the direction perpendicular to the rolling direction.

8. 2. The non-oriented electrical steel sheet according to claim 1, wherein the following formula 2 is satisfied: [Formula 2] {(B50 Ｌ +B50 Ｃ +B50 ６０ ) / 3} / {(B50 Ｌ +B50 Ｃ ) / 2}≧0.95 (However, in formula 2, B50 Ｌ is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 Ｃ is the magnetic flux density (B50, Tesla) measured in the direction perpendicular to the rolling direction, and B50 ６０ indicates the magnetic flux density (B50, Tesla) measured in a direction forming an angle of 60° with the rolling direction.

9. 2. The non-oriented electrical steel sheet according to claim 1, wherein the following formula 3 is satisfied: [Formula 3] B50 ６０ / {(B50 Ｌ +B50 Ｃ ) / 2}≧0.90 (However, in formula 3, B50 Ｌ is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 Ｃ is the magnetic flux density (B50, Tesla) measured in the direction perpendicular to the rolling direction, and B50 ６０ indicates the magnetic flux density (B50, Tesla) measured in a direction forming an angle of 60° with the rolling direction.

10. 2. The non-oriented electrical steel sheet according to claim 1, wherein the following formula 4 is satisfied: [Formula 4] (W10 / 400) Ｌ +W10 / 400 Ｃ ) / 2≦6.885×% （２．９９×ｔ） (However, in formula 4, W10 / 400 Ｌ is the iron loss measured in the rolling direction (W10 / 400, W / kg), and W10 / 400 Ｃ is the iron loss (W10 / 400, W / kg) measured in the direction perpendicular to the rolling direction, e is the Napier number, and t is the thickness of the electrical steel sheet (mm).

11. A step of producing a hot-rolled sheet by hot-rolling a slab containing, in weight percent, 2.5 to 4.0% Si, 0.03 to 2.0% Al, and 0.03 to 2.0% Mn, with the balance being Fe and unavoidable impurities; pre-cold rolling the hot-rolled sheet by 20 to 80% to produce a pre-cold-rolled sheet; an intermediate annealing step of heating and annealing the pre-cold-rolled sheet at a temperature rising rate of 20 ° C. / s or more; Cold rolling the intermediately annealed pre-cold rolled sheet at a reduction rate of 30 to 80% to produce a cold rolled sheet; a cold-rolled sheet annealing step of annealing the cold-rolled sheet; A method for producing a non-oriented electrical steel sheet, comprising:

12. The method for producing a non-oriented electrical steel sheet according to claim 11, wherein the step of producing the hot-rolled sheet includes a step of finish rolling at a temperature of 850°C or higher.

13. The method for producing a non-oriented electrical steel sheet according to claim 11, wherein the step of producing the hot-rolled sheet includes a step of water-cooling after a time of 0.1 seconds or more has elapsed since the finish rolling.

14. The method for manufacturing a non-oriented electrical steel sheet according to claim 11, wherein the step of manufacturing the hot-rolled sheet includes a step of coiling at a temperature of 600 to 800°C.

15. 12. The method for producing a non-oriented electrical steel sheet according to claim 11, wherein the slab further contains one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

16. 12. The method for producing a non-oriented electrical steel sheet according to claim 11, wherein the slab further contains one or more of P: 0.1% by weight or less (excluding 0%), C: 0.003% by weight or less (excluding 0%), S: 0.004% by weight or less (excluding 0%), Ti: 0.003% by weight or less (excluding 0%), and N: 0.003% by weight or less (excluding 0%).

17. The method for producing a non-oriented electrical steel sheet according to claim 11, wherein the slab further contains one or more of Sn, Sb, Bi, Pb, Ge, and As in an amount of 0.005 to 0.200 wt %, respectively or in total.

18. 12. The method for producing a non-oriented electrical steel sheet according to claim 11, wherein the slab further contains one or more of Mo: 0.03% by weight or less (except 0%), B: 0.0050% by weight or less (except 0%), V: 0.0050% by weight or less (except 0%), Ca: 0.0050% by weight or less (except 0%), Nb: 0.0050% by weight or less (except 0%), and Mg: 0.0050% by weight or less (except 0%).

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