Non-oriented electrical steel sheet and method for manufacturing same

Abstract

A non-oriented electrical steel sheet according to an embodiment includes, by weight %, Si: 0.2 to 4.0%, Mn: 0.05 to 1%, Al: 0.005 to 2.0%, and Na: 0.001 to 0.1%, with a remainder being Fe and unavoidable impurities

Description

BACKGROUND OF THE INVENTION (a) Field of the Invention

[0001] An embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, an embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, in which a magnetism is improved by adding Na to a steel component to appropriately precipitate precipitates and controlling a grain diameter.(b) Description of the Related Art

[0002] Recently, an extreme climate crisis due to global warming is experienced, and so-called carbon neutral activities to reduce carbon emissions are becoming important worldwide. A steel industry field is developing a technology to reduce carbon emissions during the manufacturing process by reducing the amount of a molten iron used in conventional blast furnace operations, which emits large amounts of carbon, and replacing the insufficient amount of the molten iron with an iron scrap, which does not generate carbon during the manufacturing process. However, since the iron scrap includes large amounts of Cu, Cr, and Ni, there is a problem that the quality of the electrical steel, which requires an core loss, deteriorates. If the core loss of the electrical steel sheet deteriorates, the energy efficiency of motors and small transformers decreases, requiring more electric energy, as a result, additional coal-fired and oil-fired power plants are operated, which increases carbon emissions generated during the power generation process. To solve the problem of non-uniform magnetic properties when Cu due to using the scrap is mixed in an ultra-low-aluminum non-oriented electrical steel sheet, a method of adding Ca is proposed. However, this method does not provide any solution for a Ca oxide, which reacts with oxygen in the steel sheet and deteriorates the magnetic properties, so there is a limit to improving the magnetism. In addition, a method of adding Mg is proposed to solve the problem of non-uniform magnetic properties when Cu is mixed due to using the scrap in the Al non-oriented electrical steel. However, this method also does not provide any solution for Mg oxide, which reacts with oxygen in the steel sheet and inevitably reduces the magnetic properties, so there is a limit to improving the magnetism. In addition, a method of controlling Sol-Al and Mn within an appropriate range is proposed as a method to solve the deterioration of a punching processability caused by the inclusion of Cu, Ni, Sn, Ni, Cr, etc. when using low-priced iron scrap. However, there is no method provided for controlling Cu sulfide or Al nitride, which deteriorate the magnetic properties, so there is a limit to improving the magnetism.SUMMARY OF THE INVENTION [Technical Problem]

[0003] In one embodiment of the present invention, a non-oriented electrical steel sheet and a method for manufacturing the same are provided. Specifically, in one embodiment of the present invention, a non-oriented electrical steel sheet and a method for manufacturing the same are provided, in which magnetism is improved by adding Na to a steel component, thereby appropriately precipitating precipitates and controlling the grain diameter.[Technical Solution]

[0004] A non-oriented electrical steel sheet according to an embodiment includes, by weight %, Si: 0.2 to 4.0%, Mn: 0.05 to 1%, Al: 0.005 to 2.0%, and Na: 0.001 to 0.1%, with a remainder being Fe and unavoidable impurities

[0005] The non-oriented electrical steel sheet according to an embodiment may further include Cu: 0.2 wt% or less (excluding 0 wt%) and Sn: 0.1 wt% or less (excluding 0 wt%).

[0006] The non-oriented electrical steel sheet according to an embodiment may further include at least one of C: 0.005 wt% or less (excluding 0 wt%), N: 0.01 wt% or less (excluding 0 wt%), and S: 0.01 wt% or less (excluding 0 wt%).

[0007] The non-oriented electrical steel sheet according to an embodiment may further include at least one of Ti: 0.005 wt% or less (excluding 0 wt%), Nb: 0.005 wt% or less (excluding 0 wt%), and V: 0.005 wt% or less (excluding 0 wt%).

[0008] The non-oriented electrical steel sheet according to an embodiment may further include at least one of Mo: 0.1 wt% or less (excluding 0 wt%), Ni: 0.1 wt% or less (excluding 0 wt%), Cr: 0.1 wt% or less (excluding 0 wt%), and P: 0.1 wt% or less (excluding 0 wt%).

[0009] The non-oriented electrical steel sheet according to an embodiment may further include bat least one of Bi: 0.2 wt% or less (excluding 0 wt%), Pb: 0.2 wt% or less (excluding 0 wt%), Ge: 0.2 wt% or less (excluding 0 wt%), and As: 0.2 wt% or less (excluding 0 wt%).

[0010] The non-oriented electrical steel sheet according to an embodiment may further include at least one of Sb: 0.06 wt% or less (excluding 0 wt%), Zn: 0.01 wt% or less (excluding 0 wt%), B: 0.005 wt% or less (excluding 0 wt%), Ca: 0.005 wt% or less (excluding 0 wt%), Mg: 0.005 wt% or less (excluding 0 wt%), and Zr: 0.005 wt% or less (excluding 0 wt%).

[0011] The non-oriented electrical steel sheet according to an embodiment may further include at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof having a particle diameter of 5 nm to 1,000 nm.

[0012] A particle density of at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof having the particle diameter of 5 nm to 1,000 nm may be 0.01 particles Iµm 2< to 20 particles Iµm 2< .

[0013] An average particle dimeter of at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof may be 100 to 500 nm.

[0014] An average grain diameter of the non-oriented electrical steel sheet according to an embodiment may be10 to 50 µ m.

[0015] The area fraction of the grain with the particle diameter of 10 to 100 µm may be 80% or more.

[0016] A manufacturing method of a non-oriented electrical steel sheet according to an embodiment includes manufacturing a hot-rolled sheet by hot-rolling a slab including Si: 0.2% to 4.0%, Mn: 0.05 to 1%, Al: 0.005 to 2.0%, and Na: 0.001 to 0.1% in weight%, with a remainder being Fe and unavoidable impurities; manufacturing a cold rolled sheet by cold rolling the hot rolled sheet; and annealing the cold rolled sheet.

[0017] The slab may further include Cu: 0.2 wt% or less (excluding 0 wt%) and Sn: 0.1 wt% or less (excluding 0 wt%).

[0018] The slab may further include at least one of C: 0.005 wt% or less (excluding 0 wt%), N: 0.01 wt% or less (excluding 0 wt%), and S: 0.01 wt% or less (excluding 0 wt%).

[0019] The slab may further include at least one of Ti: 0.005 wt% or less (excluding 0 wt%), Nb: 0.005 wt% or less (excluding 0 wt%), and V: 0.005 wt% or less (excluding 0 wt%).

[0020] The slab may further include at least one of Mo: 0.1 wt% or less (excluding 0 wt%), Ni: 0.1 wt% or less (excluding 0 wt%), Cr: 0.1 wt% or less (excluding 0 wt%), and P: 0.1 wt% or less (excluding 0 wt%).

[0021] The slab may further include at least one of Bi: 0.2 wt% or less (excluding 0 wt%), Pb: 0.2 wt% or less (excluding 0 wt%), Ge: 0.2 wt% or less (excluding 0 wt%), and As: 0.2 wt% or less (excluding 0 wt%).

[0022] The slab may further include at least one of Sb: 0.06 wt% or less (excluding 0 wt%), Zn: 0.01 wt% or less (excluding 0 wt%), B: 0.005 wt% or less (excluding 0 wt%), Ca: 0.005 wt% or less (excluding 0 wt%), Mg: 0.005 wt% or less (excluding 0 wt%), and Zr: 0.005 wt% or less (excluding 0 wt%).

[0023] The slab may be manufactured using 80 wt% or less of a molten iron and 20 wt% or more of an iron scrap.

[0024] The annealing of the cold rolled sheet may be performed at a temperature of 900°C to 1100°C for 60 to 180 seconds.[Advantageous Effects]

[0025] A non-oriented electrical steel sheet according to one embodiment of the present invention may improve the magnetism by uniformly forming a grain diameter and a grain diameter distribution by appropriately adding Na and appropriately forming precipitates.

[0026] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention has the excellent quality even when manufactured using scrap including a large amount of Cu or Sn, so that carbon generated during the manufacturing process may be reduced and a cost efficiency may be improved.

[0027] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the manufacture of eco-friendly automobile motors, high-efficiency home appliance motors, and super premium-grade electric motors.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, a first element, component, region, layer, or section described below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups.

[0030] It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when a part is said to be "directly on" another part, no other part intervenes.

[0031] Also, unless otherwise specified, % means weight%, and 1 ppm is 0.0001 weight%.

[0032] In one embodiment of the present invention, the inclusion of an additional element means including a remainder of iron (Fe) in an amount equivalent to the additional amount of the additional element.

[0033] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0034] Hereinafter, embodiments of the present invention will be described in detail so that a person having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

[0035] A non-oriented electrical steel sheet according to one embodiment of the present invention includes, in wt%, Si: 0.2% to 4.0%, Mn: 0.05% to 1%, Al: 0.005% to 2.0%, and Na: 0.001% to 0.1%, with a remainder being Fe and unavoidable impurities. The steel composition is a steel composition of the steel sheet material, excluding an insulating film present on the surface of the steel sheet.

[0036] Below, the reasons for the limitation of the components of the non-oriented electrical steel sheet are explained.Si: 0.2 to 4.0 wt%

[0037] Silicon (Si) is a basic component of the electrical steel sheet and plays a role in increasing a resistivity of the material and reducing a core loss. If the Si content is too low, the problem of the core loss deterioration may occur. Conversely, if too much Si is included, the magnetic flux density deteriorates significantly and a brittleness increases, which may cause problems with a rollability, a cold rolling property, and a weldability. More specifically, it may include 0.3 to 3.5 wt%. More specifically, it may include 1.0 to 3.3 wt%.Mn: 0.05 to 1.00 wt%

[0038] Manganese (Mn), like Si and Al, increases resistivity and lowers the core loss. On the other hand, it reacts with S to form Mn sulfide and reacts with nitrogen, Al, and Si at high temperatures to form (Al, Si, Mn) nitride, which also has the effect of inhibiting a grain growth. If the Mn content is too low, the core loss improvement effect may be insufficient. If the Mn content is too high, both the core loss and the magnetic flux density may be deteriorated due to the formation of precipitates along with the decrease in the magnetic flux density. More specifically, it may include 0.10 to 0.90 wt%.Al: 0.005 to 2.000 wt%

[0039] Aluminum (Al) has the same effect as Si in that it increases the resistivity of the material, thereby lowering the core loss, and also reduces a magnetic anisotropy, thereby reducing the magnetic deviation between the rolling direction and the vertical direction. If the Al content is too low, the resistivity increase value may be low and the effect of reducing core loss may be minimal. If too much Al is contained, the magnetic flux density becomes too poor, making it difficult to apply to rotating machines such as motors or stationary machines such as small transformers. In addition, it may hinder the movement of the magnetic domain by forming Al nitride by reacting with nitrogen in the atmosphere in the steel or the heat treatment. More specifically, it may include 0.005 to 1.000 wt%.Na: 0.001% to 0.100 wt%

[0040] Sodium (Na) coarsens the precipitates in the steel sheet, reducing the number density of the precipitates, and thereby uniformly growing the crystal grain diameter to improve the magnetism. If the Na content is too low, the precipitate coarsening effect cannot be sufficiently obtained, and the magnetic improvement may not be sufficiently achieved. If too much Na is included, it may form a Na oxide of a high-melting point, which may suppress the grain growth or inhibit the movement of the magnetic domain, thereby deteriorating the magnetism. More specifically, it may include 0.0015 to 0.0950 wt%. More specifically, it may include 0.005 to 0.05 wt%.

[0041] In order to appropriately add Na to the steel, a method of adding an appropriate amount of sodium oxide or sodium hydroxide to the molten steel during the steelmaking stage may be applied. To increase the sodium, a method of wrapping it in a thin iron or an aluminum foil may be applied.

[0042] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include Cu: 0.2 wt% or less (excluding 0 wt%) and Sn: 0.1 wt% or less (excluding 0 wt%).Cu : 0.2 wt% or less

[0043] Copper (Cu) plays a role in increasing the fraction of the grain with a Cube orientation and a Cube-like orientation in the non-oriented electrical steel sheet. In addition, it has the effect of inhibiting the growth of the grain by forming sulfides, and also has the effect of inhibiting the grain growth during the annealing of the cold rolled sheet, thereby increasing a hysteresis loss and worsening the core loss. By adding Cu appropriately, the size of sulfides and precipitates becomes coarse, and the density of sulfides and precipitates decreases, so that the core loss does not deteriorate. Specifically, it may further include 0.0001 to 0.2 wt% of Cu. More specifically, it may further include 0.001 to 0.15 wt%.Sn: 0.1 wt% or less

[0044] Tin (Sn) may be added more to coarsen Cu sulfide, Mn sulfide, and Al nitride in the non-oriented electrical steel sheet including the large amount of Cu, and to reduce the density of precipitates. This is because the free energy for the precipitation of the precipitates is reduced by Sn segregated at the grain boundary. If too much Sn is added, there is a problem that the core loss deteriorates due to the strong inhibition of the grain growth caused by Sn grain boundary segregation. Specifically, Sn may be included in an amount of 0.0001 to 0.1 wt%. More specifically, it may include 0.001 to 0.08 wt%.

[0045] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of C: 0.005 wt% or less (excluding 0 wt%), N: 0.01 wt% or less (excluding 0 wt%), and S: 0.01 wt% or less (excluding 0 wt%).C: 0.0050 wt% or less

[0046] Carbon (C) combines with Ti, Nb, V, etc., which are inevitably included in the steel, to form carbides, which hinder the movement of the magnetic domains and deteriorate magnetic properties, in addition, when the final product is used, a magnetic aging occurs due to heat generated in the material itself when a current is applied, which deteriorates the core loss and reduces the efficiency of electrical devices. Specifically, it may include 0.0001 to 0.005 wt% of C. More specifically, it may include 0.0005 to 0.003 wt%.N: 0.0100 wt% or less

[0047] Nitrogen (N) has the characteristic of reacting with Al, Si, and Cr to form nitrides. These nitrides hinder the grain growth, increase the grain boundary fraction, and deteriorate the hysteresis loss, and also hinder the movement and rotation of the magnetic domain, thereby deteriorating an eddy current loss. Therefore, it is necessary to minimize the amount formed. However, since the use of the iron scrap inevitably increases the N content, it is almost impossible to avoid the formation of nitrides. Therefore, it is necessary to reduce the number of the precipitates by coarsening the size of the nitride, thereby reducing the inhibition of the grain growth and reducing the probability of interfering with the movement of the magnetic domains. Specifically, it may include 0.0001 to 0.01 wt% of N. More specifically, it may include 0.0005 to 0.005 wt% of N.S: 0.0100 wt% or less

[0048] Sulfur (S) is an element that reacts with Cu, Mn, etc. in the steel to precipitate Cu sulfide and Mn sulfide. The more of these precipitates remain in the final steel sheet, the worse the core loss becomes. On the other hand, if too much S is contained, it is undesirable because it segregates in the center of the slab during the casting, and the precipitates of Mn sulfide or Cu sulfide are not uniformly precipitated during the subsequent hot rolling process, which makes the microstructure uneven. In addition, if too much S is included, the effect of Na on coarsening and reducing the precipitation of sulfides may be weakened. More specifically, S may be included in an amount of 0.0001 to 0.01 wt%. More specifically, it may include 0.0005 to 0.005 wt%.

[0049] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Ti: 0.005 wt% or less (excluding 0 wt%), Nb: 0.005 wt% or less (excluding 0 wt%), and V: 0.005 wt% or less (excluding 0 wt%).Ti: 0.0050 wt% or less

[0050] Titanium (Ti) has a very strong tendency to form the precipitates inside the steel, and forms fine carbides, nitrides, or sulfides inside the parent metal, which inhibits the grain growth and a domain wall movement, thereby deteriorating the core loss. Therefore, the Ti content may be less than 0.0050 wt%. The lower limit is not specifically limited, but may be set at 0.0003 wt% due to steelmaking costs. That is, each may include 0.0003 to 0.0050 wt% of Ti. More specifically, it may include 0.0003 to 0.0030 wt%.Nb: 0.0050 wt% or less

[0051] Niobium (Nb) has a strong tendency to form precipitates within steel, and forms fine carbides, nitrides, or sulfides within the parent metal, which inhibits grain growth and domain wall movement, thereby deteriorating core loss. Therefore, the Nb content may be less than 0.0050 wt%. The lower limit is not specifically limited, but may be set to 0.0003 wt% due to steelmaking costs. That is, it may include 0.0003 to 0.0050 wt% of Nb. More specifically, it may include 0.0003 to 0.0030 wt% of Nb.V: 0.0050 wt% or less

[0052] Vanadium (V) has a very strong tendency to form precipitates within the steel, and forms fine carbides, nitrides, or sulfides within the parent metal, thereby inhibiting the grain growth and the domain wall movement, thereby deteriorating core loss. Therefore, the V content may be 0.0050 wt% or less, respectively. The lower limit is not specifically limited, but may be set to 0.0003 wt% due to steelmaking costs. That is, it may include 0.0003 to 0.0050 wt% of V. More specifically, it may include 0.0003 to 0.0030 wt% of V.

[0053] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.1 wt% or less (excluding 0 wt%), Ni: 0.1 wt% or less (excluding 0 wt%), Cr: 0.1 wt% or less (excluding 0 wt%), and P: 0.1 wt% or less (excluding 0 wt%).Mo: 0.100 wt% or less

[0054] If molybdenum (Mo) is added in excessive amounts, the effect of improving the texture may be reduced by suppressing the segregation of segregating elements. Therefore, it may include Mo in the amount of 0.1 wt% or less. The lower limit is not particularly limited, but it may be included in the amount of 0.001 wt% or more because it plays a role in improving the aggregate structure by segregating on the surface and grain boundaries. More specifically, it may include 0.001 to 0.100 wt% of Mo. More specifically, it may include 0.005 to 0.050 wt% of Mo.Ni: 0.100 wt% or less

[0055] Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which may have a detrimental effect on the magnetism. More specifically, it may include 0.001 to 0.100 wt% of Ni. More specifically, it may include 0.005 to 0.050 wt% of Ni.Cr: 0.100 wt% or less

[0056] Chromium (Cr) plays a role in improving the core loss by increasing the resistivity. If too much Cr is included, the magnetic flux density may decrease. More specifically, when Cr is included, it may be included in an amount of 0.001 to 0.100 wt%. More specifically, it may 0.005 to 0.050 wt%.P: 0.100 wt% or less

[0057] Phosphorus (P) deteriorates hot working characteristics, which reduces the productivity compared to improving the magnetism. Therefore, it may contain P in an amount of 0.100 wt% or less. The lower limit is not particularly limited, but it may be 0.005 wt% because it segregates on the surface and grain boundaries of the steel sheet to suppress the surface oxidation during the annealing, hinders the diffusion of elements through the grain boundaries, and improves the texture by hindering recrystallization in the {111} / IND orientation. More specifically, it may include 0.005 to 0.100 wt% of P. More specifically, it may include 0.010 to 0.050 wt% of P.

[0058] The non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Bi: 0.2 wt% or less (excluding 0 wt%), Pb: 0.2 wt% or less (excluding 0 wt%), Ge: 0.2 wt% or less (excluding 0 wt%), and As: 0.2 wt% or less (excluding 0 wt%).

[0059] Elements such as bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As), when being additionally added, are segregated at the grain boundaries, thereby alleviating the stress concentration at the grain boundaries during the cold rolling, and thereby inhibiting the recrystallization of <111> / / ND orientation grains in the subsequent recrystallization annealing process, thereby improving the magnetic flux density. If these are added appropriately, the aforementioned effects may be additionally obtained, but if they are included in too much, a large amount of the segregation may occur, inhibiting the grain growth and resulting in the lower magnetic flux density and core loss. In addition, each of these may be independently included in an amount of 0.2 wt% or less. More specifically, each of these may be independently included in 0.0001 to 0.2000 wt% more. More specifically, each of these may be independently included 0.001 to 0.100 wt% more. More specifically, each of these may be independently included 0.005 to 0.050 wt% more.

[0060] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further include at least one of Sb: 0.06 wt% or less (excluding 0 wt%), Zn: 0.01 wt% or less (excluding 0 wt%), B: 0.0050 wt% or less (excluding 0 wt%), Ca: 0.0050 wt% or less (excluding 0 wt%), Mg: 0.0050 wt% or less (excluding 0 wt%), and Zr: 0.005 wt% or less (excluding 0 wt%).Sb: 0.06 wt% or less

[0061] Antimony (Sb) may be added to improve the magnetism because it improves the aggregate structure of the material by being segregated at the grain boundaries and surfaces and suppresses the surface oxidation. If too much Sb is added, the grain boundary segregation becomes severe, the surface quality deteriorates, the hardness increases, and the cold-rolled sheets may fracture, thereby reducing the rollability. Therefore, Sb may be further added within the above-mentioned range. More specifically, it may further include 0.01 to 0.05 wt% of Sb.Zn: 0.01 wt% or less

[0062] Zinc (Zn) may act as an impurity and reduce the magnetism when the content is excessive. Therefore, Zn may be further added within the above-mentioned range. Specifically, it may be included in 0.0001 to 0.01 wt%. More specifically, it may include 0.0005 to 0.005 wt%.B: 0.0050 wt% or less

[0063] If boron (B) is added in excessive amounts, it may cause the deterioration of the magnetism through the formation of inclusions in the steel sheet. Therefore, B may be included in an amount of 0.005 wt% or less. The lower limit is not specifically limited, but may be set to 0.0001 wt% due to a steelmaking cost. Specifically, it may include 0.0001 to 0.0050 wt%. More specifically, it may include 0.0005 to 0.0030 wt% of B.Ca: 0.0050 wt% or less

[0064] Calcium (Ca) may react with C, S, N, etc. to form fine carbides, nitrides, or sulfides, which may adversely affect the magnetism. Therefore, it may include Ca in an amount of 0.005 wt% or less. The lower limit is not specifically limited, but may be set to 0.0001 wt% due to a steelmaking cost. Specifically, it may include 0.0001 to 0.0050 wt%. More specifically, it may include 0.0005 to 0.0030 wt%.Mg: 0.0050 wt% or less

[0065] Magnesium (Mg) is an element that mainly combines with sulfur to form sulfides, and may affect the surface oxide layer of iron. Therefore, it may include Mg in an amount of 0.005 wt% or less. The lower limit is not specifically limited, but may be set to 0.0001 wt% due to a steelmaking cost. That is, it may include 0.0001 to 0.0050 wt% of Mg. More specifically, it may include 0.0005 to 0.0030 wt%.Zr: 0.0050 wt% or less

[0066] If zirconium (Zr) is added in excessive amounts, it may cause the deterioration of the magnetism through the formation of inclusions in the steel sheet. Therefore, it may include Zr in an amount of 0.005 wt% or less. The lower limit is not specifically limited, but may be set to 0.0001 wt% due to a steelmaking cost. That is, it may include 0.0001 to 0.0050 wt% of Zr. More specifically, it may include 0.0005 to 0.0030 wt%.

[0067] The remainder includes iron and unavoidable impurities. As for unavoidable impurities, they are impurities mixed in during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets, and since this is widely known in the field, a detailed description is omitted. In one embodiment of the present invention, addition of elements other than the alloy components described above is not excluded, and various elements may be included within a range that does not harm the technical idea of the present invention. If additional elements are included, they are included to replace the remainder, Fe.

[0068] The non-oriented electrical steel sheet according to one embodiment of the present invention may include at least one of Cu sulfide, Mn sulfide, Al nitride, and composite precipitates thereof having a grain diameter of 5 nm to 1,000 nm. In one embodiment of the present invention, due to the addition of Na, sulfides and nitrides may be coarsened and the density of the precipitates may be reduced. The particle diameter of the precipitate may be measured based on the cross-section parallel to the rolling surface (an ND surface) of the steel sheet. More specifically, it may be measured at a thickness ranging from 1 / 4t to 3 / 4t with respect to the total thickness t of the steel sheet. The particle size of the precipitate is assumed to be the diameter of an imaginary circle with the same area as the area occupied by the precipitate, and the diameter of that circle is used as the particle size of the precipitate. The occupied area of the precipitate means the area where S is aggregated in the case of sulfide and N is aggregated in the case of nitride, and the area with a higher content compared to the base portion of the steel sheet (i.e., the area excluding sulfide and nitride).

[0069] The number density of at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof having the particle diameter of 5 nm to 1,000 nm may be 0.01 / µm 2< to 20 / µm 2< . The precipitates with the particle diameter of 5 nm or less do not have a significant effect on the properties of the steel sheet, so they are excluded from the number density. The precipitates with the particle diameter exceeding 1000 nm are practically difficult to form and are therefore excluded. If the number density of the precipitates is too small, it is difficult to properly obtain the effect of the grain diameter control due to the precipitates. If there is too much precipitate, the magnetic deterioration due to the precipitate may occur. More specifically, the number density of the precipitates may be 0.01 to 17.0 / µm 2< . The number density of the precipitates may be measured similarly to the measurement method for the particle diameter of the precipitates described above, and may be measured over the area of at least 0.01 mm × 0.01 mm to reduce a measurement error.

[0070] At least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof may have an average particle diameter of 100 to 500 nm. If the average particle diameter is too small, the number of the precipitates increases, which may have a negative effect on the magnetism. If the particle diameter is too large, the adverse effect on the magnetism per each precipitate may be significant. More specifically, the average particle diameter of the precipitate may be 150 to 495 nm. The average refers to the average number of the precipitates.

[0071] The non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain diameter of 10 to 50 µm. In one embodiment of the present invention, by appropriately precipitating the precipitates, the grain growth may be suppressed during the annealing of the cold rolled sheets, and the deterioration of the core loss due to the grain growth may be prevented. If the crystal grain diameter is too small or too large, the magnetism may be degraded. More specifically, the average crystal grain diameter may be 10 to 50 µm.

[0072] In one embodiment of the present invention, the grain diameter may be measured with respect to a plane parallel to the surface of the steel sheet. More specifically, it may be measured at a thickness ranging from 1 / 4t to 3 / 4t with respect to the total thickness t of the steel sheet. The grain diameter is determined by assuming a virtual circle with the same area as the grain diameter of the grain, and the grain diameter of that circle is used as the grain diameter. The average grain diameter may be measured by dividing the number of the grains within the area being measured by the area of the interest. More specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have the average grain diameter of 10.0 to 45.0 µm. The grain diameter and distribution may be measured using an optical microscope and SEM-EBSD.

[0073] The area fraction of the crystal grains having the diameter of 10 to 100 µm may be 80% or more. In one embodiment of the present invention, the grain diameter of the crystal grains is controlled by appropriately precipitating the precipitate, so that the grain diameter of the crystal grains may be formed uniformly. The low area fraction means that grains are too small or too large, which has a negative effect on the magnetism. In one embodiment of the present invention, the crystal grain diameter is formed uniformly, thereby reducing an anisotropy and improving the core loss. More specifically, the area fraction may be between 80 and 100%. More specifically, it may be between 82 and 98%.

[0074] The non-oriented electrical steel sheet according to one embodiment of the present invention has the excellent core loss. Specifically, the core loss (W15 / 50) of the non-oriented electrical steel is the core loss when the magnetic flux density of 1.5 T is induced at a frequency of 50 Hz. More specifically, the non-oriented electrical steel sheet may have the core loss (W15 / 50) of 7.0 W / kg or less. More specifically, the non-oriented electrical steel sheet may have the core loss (W15 / 50) of 4.0 to 7.0 W / kg. More specifically, it may be 4.2 to 6.7 W / kg. The core loss is the average value in the rolling direction and the direction perpendicular to the rolling, and the standard thickness may be 0.5 mm.

[0075] A method for manufacturing the non-oriented electrical steel sheet according to one embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled sheet; a step of cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet. Below, each step is explained in detail.

[0076] First, the slab is hot rolled.

[0077] The alloy composition of the slab is explained in the alloy composition of the non-oriented electrical steel sheet mentioned above. Therefore, the duplicate explanations are omitted. Since the alloy composition does not substantially change during the manufacturing process of non-oriented electrical steel sheets, the alloy compositions of non-oriented electrical steel sheets and slabs are substantially the same.

[0078] Specifically, the slab includes, in wt%, Si: 0.2% to 4.0%, Mn: 0.05% to 1%, Al: 0.005% to 2.0%, and Na: 0.001% to 0.1%, with the remainder being Fe and inevitable impurities.

[0079] As for other additional elements, they have been described in the alloy composition of the non-oriented electrical steel sheets, so any duplicate description will be omitted.

[0080] The slab may be heated before the hot rolling. The heating temperature of the slab is not limited, but the slab may be heated to below 1250°C. If the slab heating temperature is too high, precipitates such as AIN and MnS present in the slab may be re-dissolved and then finely precipitated during the hot rolling and the annealing, which may inhibit the grain growth and reduce the magnetism.

[0081] The slab may be manufactured using 80 wt% or less of the molten iron and 20 wt% or more of the iron scrap. Compared to the molten iron, the iron scrap includes a large amount of S or N, which may cause a large amount of precipitates such as nitrides and sulfides to be precipitated. In one embodiment of the present invention, by adding an appropriate amount of Na, the number density of the precipitates may be reduced, thereby reducing the adverse effects on the magnetism, and the crystal grain diameter may be uniformly grown to improve the magnetism.

[0082] Returning to the description of the hot rolling stage, the slab is hot rolled to produce the hot rolled sheet. The hot rolled sheet thickness may be 1.0 to 3.5 mm. In the stage of manufacturing the hot rolled sheet, the finishing rolling temperature may be 800°C or higher. Specifically, it may be between 800 and 1000°C. The hot rolled steel sheet may be coiled at a temperatures below 700°C.

[0083] After the step of manufacturing the hot-rolled sheet, a step of annealing the hot-rolled sheet may be further included. At this time, the hot-rolled sheet annealing temperature may be 850 to 1150°C. If the annealing temperature of the hot-rolled sheet is lower than 850°C, the structure does not grow or grows finely, so the effect of increasing the magnetic flux density is small. If the annealing temperature exceeds 1150°C, the magnetic properties may deteriorate, and the rolling workability may deteriorate due to the deformation of the sheet shape. More specifically, the temperature range may be 950 to 1125°C. More specifically, the annealing temperature of hot rolled steel is 900 to 1100°C. Annealing of the hot-rolled sheet is performed to increase the orientation favorable to the magnetism as needed, and may also be omitted.

[0084] Next, the hot-rolled sheet is acid-pickled and cold-rolled to the desired thickness. This may be applied differently depending on the thickness of the hot-rolled sheet, but it may be cold rolled to the final thickness of 0.1 to 0.7 mm by applying the rolling reduction ratio of 40 to 95%. To match the rolling reduction ratio, one cold rolling or two or more cold rollings with an intermediate annealing may be performed.

[0085] The cold rolled sheet that is cold-rolled undergo a cold rolled sheet annealing.

[0086] The cold rolled sheet annealing may be performed in a mixed gas and an atmosphere of hydrogen (H 2 ) and nitrogen (N 2 ). The mixed gas may include 40% hydrogen or less by volume and 60% nitrogen or more by volume.

[0087] In the cold rolled sheet annealing, the annealing be performed at a temperature of 900°C to 1100°C for 60 to 180 seconds. In one embodiment of the present invention, the annealing is performed at a relatively high temperature, but the precipitates are appropriately precipitated, thereby preventing the grain diameter from growing significantly, thereby preventing the magnetic deterioration caused by this. In addition, by annealing at high temperature in the state where the precipitate is properly precipitated, the crystal grains may be grown uniformly. If the annealing temperature is too low or the annealing time is too short, the grain growth may not occur sufficiently, and the core loss may be deteriorated due to the excessive increase in a hysteresis loss. If the annealing temperature is too high or the annealing time is too long, the grains may grow too large, which may result in the excessive increase in an eddy current loss and the deterioration of the core loss.

[0088] After the cold rolled sheet annealing, an insulating film may be formed. The insulating film may be treated with an organic, inorganic, or organic-inorganic composite film, and it may also be treated with other insulating film agents.

[0089] Hereinafter, the present invention is described in more detail through examples. However, these examples are only intended to illustrate the present invention, and the present invention is not limited thereto.Example 1

[0090] A slab was manufactured with components listed in Table 1, Table 2 and the remainder including Fe and unavoidable impurities. It was heated to 1200°C and hot rolled to a thickness of 2.5 mm. The hot-rolled sheet was heated to a temperature of 1070°C and then water-cooled. The steel material annealed in this way was acid-pickled and rolled once to a thickness of 0.5 mm. The cold-rolled sheet was annealed in a cold-rolled sheet by maintaining it at a temperature of 1000°C for 180 seconds. The W15 / 50 core loss (unit: W / kg) of the inventive and comparative materials listed in Table 1, the average size and the number density of the composite precipitates, the average grain diameter, and the area fraction of the grains having the size of 10 µm to 100 µm are summarized in Table 2.

[0091] For each specimen, the core loss was measured by cutting the specimen of 60 mm width × 60 mm length ×5 number of sheets using a single sheet tester in the rolling direction and the direction perpendicular to the rolling direction, and expressed as an average.

[0092] The grain diameter and distribution were measured using SEM-EBSD. (Table 1)RemarkCSiMnAlNaSNInventive material10.00454.00.171.6460.00160.0030.002Inventive material20.00420.80.331.6850.04600.0020.010Inventive material30.00111.20.470.2890.00340.0060.005Inventive material40.00101.30.470.1880.02730.0050.002Inventive material50.00471.40.420.5180.00870.0060.006Inventive material60.00243.10.961.9480.08220.0020.003Inventive material70.00342.60.231.8660.00520.0070.009Inventive material80.00471.40.660.7410.09810.0030.004Comparative material10.00611.90.921.3580.00220.0040.001Comparative material20.00120.120.611.5100.03510.0060.006Comparative material30.00314.30.850.6380.01590.0020.005Comparative material40.00213.00.040.8790.01430.0100.010Comparative material50.00303.41.081.6970.05270.0010.005Comparative material60.00402.90.990.0030.08790.0080.001Comparative material70.00293.50.392.0560.04530.0060.003Comparative material80.00233.40.811.7370.00070.0130.009Comparative material90.00180.30.881.4180.10130.0040.012Comparative material100.00400.60.511.4860.10080.0080.007Comparative material110.00384.00.491.0950.00060.0010.004Comparative material120.00121.90.631.3030.00080.0100.001Comparative material130.00171.20.930.1860.10240.0070.003Comparative material140.0030.30.81.10.00040.0030.003Comparative material150.0033.40.71.20.10080.0030.003 (Table 2) RemarkCuSnNiMoCrPInventive material10.050.070.08---Inventive material20.170.06-0.01--Inventive material30.180.05--0.07-Inventive material40.090.02---0.01Inventive material50.020.090.05---Inventive material60.020.06-0.04--Inventive material70.170.01----Inventive material80.130.10---0.01Comparative material10.050.10----Comparative material20.070.03----Comparative material30.040.05----Comparative material40.110.09----Comparative material50.040.05----Comparative material60.110.05----Comparative material70.110.06----Comparative material80.100.07----Comparative material90.130.03----Comparative material100.250.05----Comparative material110.570.01----Comparative material120.110.12----Comparative material130.150.18----Comparative material140.110.050.030.030.050.03Comparative material150.120.050.070.030.040.03 (Table 3) W1 5 / 50 Core loss (W / kg)Precipitate average particle diameter (nm)Numbe r density (number / µm 2< )avera ge grain partic le diam eter ( µm)0-100 µ m grain area fractio n (%)Inventiv e material 14.91662.028.885Inventiv e material 24.328112.212.190Inventiv e material 36.549010.313.593Inventiv e material 44.52059.711.697Inventiv e material 55.71770.0115.486Inventiv e material 64.83900.0710.084Inventiv e material 74.721610.422.392Inventiv e material 85.037916.640.083Compar ative material 17.42865.48.513Compar ative material 27.43095.375.042Compar ative material 38.82005.554.068Compar ative material 48.743013.877.065Compar ative material 58.33616.68.238Compar ative material 67.617613.160.065Compar ative material 77.74864.68.828Compar ative material 87.55149.18.222Compar ative material 97.257715.09.043Compar ative material 109.252224.88.842Compar ative material 119.760032.39.218Compar ative material 1210.135894.39.123Compar ative material 1311.3365150.29.248Compar ative material 148.461214.198.394Compar ative material 1512.910587.57.627

[0093] As shown in Tables 1 to 3, when the steel component is appropriately controlled, it may be confirmed that the average crystal grain diameter is appropriately controlled and the core loss is excellent.

[0094] Comparative material 1 includes an excessive amount of C, which causes a large amount of carbide to be generated, it may be confirmed that the grain does not grow properly, and the magnetism is poor.

[0095] Comparative materials 2 and 3 do not include Si properly, and as a result, the phase transformation is not properly controlled, the average grain diameter is not properly controlled, and the grain area fraction of 10 to 100 µm is formed to be less than 80%, confirming that the magnetism is inferior.

[0096] Comparative materials 4 and 5 do not include Mn properly, and as a result, the phase transformation is not properly controlled, the average grain diameter is not properly controlled, and the grain area fraction of 10 to 100 µm is formed to be less than 80%, confirming that the magnetism is inferior.

[0097] Comparative material 6 and comparative material 7 do not include Al properly, and in particular, comparative material 6 includes too little Al, resulting in poor magnetism, while comparative material 7 includes more Al than the appropriate amount, presumably resulting in the excessive formation of Al nitride, which inhibits the grain growth and prevents the grain from growing properly, confirming that the magnetism is poor.

[0098] Comparative Materials 8 to 15 do not include Na properly, so that the precipitates are not properly precipitated, and as a result, the grains do not grow properly, confirming that the magnetism is poor.

[0099] Although exemplary embodiments of the present invention were described above, those skilled in the art would understand that the present invention may be implemented in various ways without changing the spirit or necessary features. Therefore, the embodiments described above are only examples and should not be construed as being limitative in any respects.

Claims

1. A non-oriented electrical steel sheet, comprising: by weight %, Si: 0.2 to 4.0%, Mn: 0.05 to 1%, Al: 0.005 to 2.0%, and Na: 0.001 to 0.1%, with a remainder being Fe and unavoidable impurities.

2. The non-oriented electrical steel sheet of claim 1, further comprising: Cu: 0.2 wt% or less (excluding 0 wt%) and Sn: 0.1 wt% or less (excluding 0 wt%).

3. The non-oriented electrical steel sheet of claim 1, further comprising: at least one of C: 0.005 wt% or less (excluding 0 wt%), N: 0.01 wt% or less (excluding 0 wt%), and S: 0.01 wt% or less (excluding 0 wt%).

4. The non-oriented electrical steel sheet of claim 1, further comprising: at least one of Ti: 0.005 wt% or less (excluding 0 wt%), Nb: 0.005 wt% or less (excluding 0 wt%), and V: 0.005 wt% or less (excluding 0 wt%).

5. The non-oriented electrical steel sheet of claim 1, further comprising: at least one of Mo: 0.1 wt% or less (excluding 0 wt%), Ni: 0.1 wt% or less (excluding 0 wt%), Cr: 0.1 wt% or less (excluding 0 wt%), and P: 0.1 wt% or less (excluding 0 wt%).

6. The non-oriented electrical steel sheet of claim 1, further comprising: at least one of Bi: 0.2 wt% or less (excluding 0 wt%), Pb: 0.2 wt% or less (excluding 0 wt%), Ge: 0.2 wt% or less (excluding 0 wt%), and As: 0.2 wt% or less (excluding 0 wt%).

7. The non-oriented electrical steel sheet of claim 1, further comprising: at least one of Sb: 0.06 wt% or less (excluding 0 wt%), Zn: 0.01 wt% or less (excluding 0 wt%), B: 0.005 wt% or less (excluding 0 wt%), Ca: 0.005 wt% or less (excluding 0 wt%), Mg: 0.005 wt% or less (excluding 0 wt%), and Zr: 0.005 wt% or less (excluding 0 wt%).

8. The non-oriented electrical steel sheet of claim 1, further comprising: at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof having a particle diameter of 5 nm to 1,000 nm.

9. The non-oriented electrical steel sheet of claim 8, wherein: a particle density of at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof having the particle diameter of 5 nm to 1,000 nm is 0.01 particles Iµm2 to 20 particles / µm2.

10. The non-oriented electrical steel sheet of claim 8, wherein: an average particle dimeter of at least one of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof is 100 to 500 nm.

11. The non-oriented electrical steel sheet of claim 1, wherein: an average grain diameter is 10 to 50 µm.

12. The non-oriented electrical steel sheet of claim 1, wherein: an area fraction of the grain with the particle diameter of 10 to 100 µm is 80% or more.

13. A method for manufacturing a non-oriented electrical steel sheet, comprising: manufacturing a hot-rolled sheet by hot-rolling a slab including Si: 0.2% to 4.0%, Mn: 0.05 to 1%, Al: 0.005 to 2.0%, and Na: 0.001 to 0.1% in weight%, with a remainder being Fe and unavoidable impurities; manufacturing a cold rolled sheet by cold rolling the hot rolled sheet; and annealing the cold rolled sheet.

14. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab further includes Cu: 0.2 wt% or less (excluding 0 wt%) and Sn: 0.1 wt% or less (excluding 0 wt%).

15. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab further includes at least one of C: 0.005 wt% or less (excluding 0 wt%), N: 0.01 wt% or less (excluding 0 wt%), and S: 0.01 wt% or less (excluding 0 wt%).

16. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab further includes at least one of Ti: 0.005 wt% or less (excluding 0 wt%), Nb: 0.005 wt% or less (excluding 0 wt%), and V: 0.005 wt% or less (excluding 0 wt%).

17. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab further includes at least one of Mo: 0.1 wt% or less (excluding 0 wt%), Ni: 0.1 wt% or less (excluding 0 wt%), Cr: 0.1 wt% or less (excluding 0 wt%), and P: 0.1 wt% or less (excluding 0 wt%).

18. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab further includes at least one of Bi: 0.2 wt% or less (excluding 0 wt%), Pb: 0.2 wt% or less (excluding 0 wt%), Ge: 0.2 wt% or less (excluding 0 wt%), and As: 0.2 wt% or less (excluding 0 wt%).

19. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab further includes at least one of Sb: 0.06 wt% or less (excluding 0 wt%), Zn: 0.01 wt% or less (excluding 0 wt%), B: 0.005 wt% or less (excluding 0 wt%), Ca: 0.005 wt% or less (excluding 0 wt%), Mg: 0.005 wt% or less (excluding 0 wt%), and Zr: 0.005 wt% or less (excluding 0 wt%).

20. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the slab is manufactured using 80 wt% or less of a molten iron and 20 wt% or more of an iron scrap.

21. The method for manufacturing the non-oriented electrical steel sheet of claim 13, wherein: the annealing of the cold rolled sheet is performed at a temperature of 900°C to 1100°C for 60 to 180 seconds.

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