Non-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof in which Na is added to the steel components to appropriately precipitate precipitates and adjust the crystal grain size, thereby improving magnetic properties. [Solution] The non-oriented electrical steel sheet of the present invention contains, by weight, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001 to 0.1% Na, with the balance being Fe and unavoidable impurities. The method for producing the non-oriented electrical steel sheet of the present invention includes the steps of hot-rolling a slab containing, by weight, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001 to 0.1% Na, with the balance being Fe and unavoidable impurities, to produce a hot-rolled sheet; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; and annealing the cold-rolled sheet.

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the embodiment of the present invention relates to a non-oriented electrical steel sheet in which Na is added to the steel components to appropriately precipitate precipitates and adjust the crystal grain size to improve magnetic properties, and a manufacturing method thereof. [Background technology]

[0002] In recent years, we have experienced a serious climate crisis due to global warming, and the reduction of carbon emissions, or so-called carbon neutrality, is gaining importance worldwide. The steel industry is developing technologies to reduce the carbon emitted during the manufacturing process by reducing the amount of molten iron used in conventional blast furnace operations, which emit large amounts of carbon, and by replacing any shortfall in molten iron with iron scrap, which does not emit carbon during the manufacturing process. However, iron scrap contains large amounts of Cu, Cr, Ni, etc., which can cause a problem of degrading the quality of electrical steel sheets, for which iron loss is important.

[0003] When the iron loss of electrical steel sheets deteriorates, the energy efficiency of motors and small transformers decreases, requiring more electrical energy. This ultimately leads to the operation of additional coal- and oil-fired power plants, which in turn increases the carbon emissions generated during the power generation process. The addition of calcium has been proposed to solve the problem of non-uniform magnetic properties when copper is mixed into ultra-low aluminum non-oriented electrical steel sheets due to the use of scrap. However, this method does not provide any solution to the calcium oxide that reacts with oxygen in the steel and deteriorates the magnetic properties, and is therefore limited in its magnetic properties improvement.

[0004] In addition, the addition of magnesium has been proposed to solve the problem of non-uniform magnetic properties when copper is mixed into aluminum non-oriented electrical steel sheets due to scrap. However, this method also has limitations in improving magnetic properties, as it does not provide any solution to the magnesium oxides that react with oxygen in the steel and inevitably reduce magnetic properties.

[0005] In addition, when using low-cost iron scrap, a method of controlling Sol-Al and Mn within an appropriate range has been proposed as a way to solve the problem of poor punching workability caused by the contamination of Cu, Ni, Sn, Ni, Cr, etc. However, this method does not provide any method for controlling Cu sulfide and Al nitride, which deteriorate magnetic properties, and there is a limit to the improvement of magnetic properties. Summary of the Invention [Problem to be solved by the invention]

[0006] One embodiment of the present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof in which Na is added to the steel composition to appropriately precipitate precipitates and adjust the grain size, thereby improving magnetic properties. [Means for solving the problem]

[0007] A non-oriented electrical steel sheet according to an embodiment of the present invention contains, by weight, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001% to 0.1% Na, with the remainder being Fe and unavoidable impurities.

[0008] The non-oriented electrical steel sheet according to an 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 %).

[0009] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more 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%).

[0010] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more 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%).

[0011] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more 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%).

[0012] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more 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%).

[0013] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sb: 0.06% by weight or less (excluding 0% by weight), Zn: 0.01% by weight or less (excluding 0% by weight), B: 0.0050% by weight or less (excluding 0% by weight), Ca: 0.0050% by weight or less (excluding 0% by weight), Mg: 0.0050% by weight or less (excluding 0% by weight), and Zr: 0.005% by weight or less (excluding 0% by weight).

[0014] A non-oriented electrical steel sheet according to an embodiment of the present invention may contain one or more of Cu sulfide, Mn sulfide, Al nitride, and composite precipitates thereof, each having a grain size of 5 nm to 1,000 nm.

[0015] Cu sulfide, Mn sulfide, Al nitride, and composite precipitates of these with a particle size of 5 nm to 1,000 nm, with a density of 0.01 particles / μm 2 ~20 pieces / μm 2 It can be said that.

[0016] The average particle size of one or more of Cu sulfide, Mn sulfide, Al nitride and composite precipitates thereof may be 100 to 500 nm.

[0017] The non-oriented electrical steel sheet according to an embodiment of the present invention may have an average grain size of 10 to 50 μm.

[0018] The area fraction of crystal grains having a grain size of 10 to 100 μm may be 80% or more.

[0019] A method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of hot-rolling a slab containing, by weight, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001% to 0.1% Na, with the remainder being Fe and unavoidable impurities, to produce a hot-rolled sheet; cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; and annealing the cold-rolled sheet.

[0020] The slab may further contain Cu: 0.2 wt % or less (excluding 0 wt %) and Sn: 0.1 wt % or less (excluding 0 wt %).

[0021] The slab may further contain one or more of C: 0.005% by weight or less (excluding 0% by weight), N: 0.01% by weight or less (excluding 0% by weight), and S: 0.01% by weight or less (excluding 0% by weight).

[0022] The slab may further contain one or more of Ti: 0.005% by weight or less (excluding 0% by weight), Nb: 0.005% by weight or less (excluding 0% by weight), and V: 0.005% by weight or less (excluding 0% by weight).

[0023] The slab may further contain one or more 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%).

[0024] The slab may further contain one or more 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%).

[0025] The slab may further contain one or more of Sb: 0.06% by weight or less (excluding 0% by weight), Zn: 0.01% by weight or less (excluding 0% by weight), B: 0.0050% by weight or less (excluding 0% by weight), Ca: 0.0050% by weight or less (excluding 0% by weight), Mg: 0.0050% by weight or less (excluding 0% by weight), and Zr: 0.005% by weight or less (excluding 0% by weight).

[0026] Slabs can be produced using up to 80% by weight of blast furnace hot metal and 20% by weight or more of scrap iron.

[0027] The cold-rolled sheet annealing step can involve annealing at a temperature of 900°C to 1100°C for 60 seconds to 180 seconds. [Effects of the Invention]

[0028] In the non-oriented electrical steel sheet according to an embodiment of the present invention, by appropriately adding Na and appropriately forming precipitates, it is possible to form uniform grain size and grain size distribution of crystal grains and improve magnetic properties. In addition, the non-oriented electrical steel sheet according to an embodiment of the present invention has excellent quality even when manufactured using scrap containing a large amount of Cu or Sn, and can reduce carbon generated during the manufacturing process, thereby improving economic efficiency. Ultimately, the non-oriented electrical steel sheet according to an embodiment of the present invention contributes to the production of motors for environmentally friendly automobiles, motors for highly efficient home appliances, and super premium class electric motors. DETAILED DESCRIPTION OF THE INVENTION

[0029] 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. Therefore, 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.

[0030] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present 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 "comprising" refers to the inclusion of particular features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0031] When a part is referred to as being "on" or "above" another part, it is above the other part, and there may be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them. Furthermore, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, the inclusion of an additional element means that the remaining iron (Fe) is replaced by the additional amount of the additional element.

[0032] 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 otherwise defined.

[0033] Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily understand and practice the present invention.

[0034] A non-oriented electrical steel sheet according to an embodiment of the present invention contains, by weight, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001% to 0.1% Na, with the remainder being Fe and unavoidable impurities. The steel composition is the steel composition of the steel sheet substrate, excluding the insulating coating present on the steel sheet surface. The reasons for limiting the components of the non-oriented electrical steel sheet will be explained below.

[0035] Si:0.2~4.0wt% Silicon (Si) is a basic component of electrical steel sheets and plays a role in increasing the material's non-resistivity and reducing core loss. If the Si content is too low, problems with decreased core loss may occur. Conversely, if the Si content is too high, the magnetic flux density may deteriorate rapidly, the material may become brittle, and problems may occur with rollability, cold rolling, and weldability. More specifically, the Si content may be 0.3 to 3.5 wt. %. More specifically, the Si content may be 1.0 to 3.3 wt. %.

[0036] Mn:0.05~1.00wt% Manganese (Mn), like Si and Al, increases resistivity and reduces iron loss. It also reacts with S to form Mn sulfides, and at high temperatures reacts with nitrogen, Al, and Si to form (Al, Si, Mn) nitrides, which hinder grain growth. If the Mn content is too low, the iron loss improvement effect may be insufficient. If the Mn content is too high, the magnetic flux density may decrease, and precipitates may form, resulting in poor iron loss and magnetic flux density. More specifically, Mn can be contained in an amount of 0.10 to 0.90 wt.%.

[0037] Al:0.005~2.000wt% Aluminum (Al) has the same effect as Si, increasing the material's non-resistivity and reducing iron loss. It also reduces magnetic anisotropy and magnetic deviation between the rolling direction and the perpendicular direction. If the Al content is too low, the non-resistivity increase will be small, and the effect of reducing iron loss may be almost nonexistent. If the Al content is too high, the magnetic flux density will be very poor, making it difficult to apply to rotating equipment such as motors and stationary equipment such as small transformers. Furthermore, Al reacts with nitrogen in the steel or heat treatment atmosphere to form Al nitrides, which may interfere with the movement of magnetic domains. More specifically, it can be contained at 0.005 to 1.000 wt.%.

[0038] Na:0.001%~0.100wt% Sodium (Na) coarsens precipitates in steel sheets, reducing their number density and thereby growing the crystal grains more uniformly, improving magnetic properties. If the Na content is too low, the precipitate coarsening effect may not be fully achieved, and magnetic properties may not be fully improved. If the Na content is too high, it may form high-melting-point Na oxides, which may inhibit grain growth or interfere with the movement of magnetic domains, resulting in a deterioration of magnetic properties. More specifically, the Na content may be 0.0015 to 0.0950 wt %. More specifically, the Na content may be 0.005 to 0.05 wt %. To properly add sodium to steel, a method can be applied in which an appropriate amount of sodium oxide or sodium hydroxide is added to the molten iron during the steelmaking process. To increase the sodium yield, a method can also be applied in which the molten iron is wrapped in thin iron or aluminum foil.

[0039] The non-oriented electrical steel sheet according to an 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 %).

[0040] Cu: 0.2% by weight or less Copper (Cu) increases the fraction of cube-oriented and cube-like grains in non-oriented electrical steel sheets. It also forms sulfides to inhibit grain growth, which inhibits grain growth during cold-rolled sheet annealing, increasing hysteresis loss and worsening iron loss. Appropriate Cu addition increases the size of sulfides and precipitates and reduces their density, preventing iron loss degradation. Specifically, Cu can be added in an amount of 0.0001 to 0.2 wt. %. More specifically, Cu can be added in an amount of 0.001 to 0.15 wt. %.

[0041] Sn: 0.1% by weight or less Tin (Sn) can be added to non-oriented electrical steel sheets containing a large amount of Cu to coarsen the size of Cu sulfides, Mn sulfides, and Al nitrides and reduce the density of the precipitates. This is because Sn segregated at grain boundaries reduces the free energy required for the precipitation of precipitates. If too much Sn is added, the grain boundary segregation of Sn exerts a strong inhibitory effect on grain growth, resulting in a deterioration in core loss. Specifically, Sn can be contained in an amount of 0.0001 to 0.1 wt. %. More specifically, Sn can be contained in an amount of 0.001 to 0.08 wt. %.

[0042] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more 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%).

[0043] C: 0.0050% by weight or less Carbon (C) combines with Ti, Nb, V, and other elements inevitably present in steel to form carbides, which impede the movement of magnetic domains and impair magnetic properties. Furthermore, when the final product is used, magnetic aging occurs due to heat generated in the material itself when a current is applied, which deteriorates iron loss and reduces the efficiency of electrical equipment. Specifically, C can be contained in an amount of 0.0001 to 0.005 wt. %. More specifically, C can be contained in an amount of 0.0005 to 0.003 wt. %.

[0044] N: 0.0100% by weight or less Nitrogen (N) reacts with Al, Si, and Cr to form nitrides. These nitrides inhibit grain growth, increasing the grain boundary fraction and reducing hysteresis loss. They also inhibit magnetic domain movement and rotation, reducing eddy current loss. Therefore, the amount of nitrides formed must be minimized. However, the use of iron scrap inevitably increases the N content, making it almost impossible to avoid nitride formation. Therefore, by increasing the size of the nitrides, the number of precipitates can be reduced, reducing their ability to inhibit grain growth and the likelihood of interfering with magnetic domain movement. Specifically, N can be contained in an amount of 0.0001 to 0.01 wt. Specifically, N can be contained in an amount of 0.0005 to 0.005 wt.

[0045] S: 0.0100% by weight or less Sulfur (S) is an element that reacts with Cu, Mn, and other elements in steel to precipitate Cu sulfides and Mn sulfides. The greater the amount of these precipitates remaining in the final steel sheet, the worse the iron loss. On the other hand, excessive S segregates toward the center of the slab during casting, preventing uniform precipitation of Mn sulfides or Cu sulfides during the subsequent hot rolling process, resulting in an undesirably non-uniform microstructure. Furthermore, excessive S may weaken the effects of Na on coarsening sulfides and reducing the amount of precipitation. More specifically, S may be contained in an amount of 0.0001 to 0.01 wt. More specifically, S may be contained in an amount of 0.0005 to 0.005 wt.

[0046] The non-oriented electrical steel sheet according to an embodiment of the present invention may further include one or more 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%).

[0047] Ti: 0.0050% by weight or less Titanium (Ti) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides within the base material, which inhibit grain growth and domain wall motion, thereby deteriorating core loss. Therefore, the Ti content may be 0.0050 wt% or less. The lower limit is not particularly limited, but can be set to 0.0003 wt% from the perspective of steelmaking costs. In other words, Ti can be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, Ti can be contained in an amount of 0.0003 to 0.0030 wt%.

[0048] Nb: 0.0050% by weight or less Niobium (Nb) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides within the base material, which inhibit grain growth and domain wall motion, thereby deteriorating core loss. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not particularly limited, but can be set to 0.0003 wt% from the perspective of steelmaking costs. In other words, Nb can be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, Nb can be contained in an amount of 0.0003 to 0.0030 wt%.

[0049] V: 0.0050% by weight or less Vanadium (V) has a strong tendency to form precipitates in steel, forming fine carbides, nitrides, or sulfides within the base material, which inhibit grain growth and domain wall motion, thereby deteriorating core loss. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not particularly limited, but can be set to 0.0003 wt% from the perspective of steelmaking costs. In other words, V can be contained in an amount of 0.0003 to 0.0050 wt%. More specifically, V can be contained in an amount of 0.0003 to 0.0030 wt%.

[0050] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more 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%).

[0051] Mo: 0.100% by weight or less Excessive addition of molybdenum (Mo) may inhibit the segregation of segregating elements and reduce the texture improving effect. Therefore, Mo can be contained in an amount of 0.1 wt% or less. There is no particular lower limit, but Mo can be contained in an amount of 0.001 wt% or more because it segregates to the surface and grain boundaries to improve the texture. More specifically, Mo can be contained in an amount of 0.001 to 0.100 wt%. Even more specifically, Mo can be contained in an amount of 0.005 to 0.050 wt%.

[0052] Ni: 0.100% by weight or less Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which may have a detrimental effect on magnetic properties. More specifically, Ni may be contained in an amount of 0.001 to 0.100 wt %. Even more specifically, Ni may be contained in an amount of 0.005 to 0.050 wt %.

[0053] Cr: 0.100% by weight or less Chromium (Cr) plays a role in increasing the resistance and improving core loss. If there is too much Cr, the magnetic flux density may decrease. More specifically, when Cr is further contained, it may be contained in an amount of 0.001 to 0.100 wt %. More specifically, it may be contained in an amount of 0.005 to 0.050 wt %.

[0054] P: 0.100% by weight or less Phosphorus (P) deteriorates hot working characteristics and reduces productivity compared to improving magnetic properties. Therefore, P can be contained in an amount of 0.100 wt% or less. The lower limit is not particularly limited, but it can be 0.005 wt% because P segregates at the surface and grain boundaries of the steel sheet to suppress surface oxidation during annealing, hinders the diffusion of elements through grain boundaries, and hinders recrystallization in the {111} / / ND orientation, improving the texture. More specifically, P can be contained in an amount of 0.005 to 0.100 wt%. Even more specifically, P can be contained in an amount of 0.010 to 0.050 wt%.

[0055] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more 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%).

[0056] When elements such as bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are added, they segregate at the grain boundaries, easing the stress concentration at the grain boundaries during cold rolling and reducing the stress concentration at the grain boundaries during the subsequent recrystallization annealing process. <111> / / Improves magnetic flux density by suppressing recrystallization of ND-oriented crystal grains. When these are added appropriately, the aforementioned effects can be obtained. However, if they are added in excess, excessive segregation can occur, suppressing grain growth and potentially resulting in poor magnetic flux density and core loss. Therefore, these elements can be independently added in an amount of 0.2 wt% or less. More specifically, these elements can be independently added in an amount of 0.0001 to 0.2000 wt%. More specifically, these elements can be independently added in an amount of 0.001 to 0.100 wt%. More specifically, these elements can be independently added in an amount of 0.005 to 0.050 wt%.

[0057] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sb: 0.06% by weight or less (excluding 0% by weight), Zn: 0.01% by weight or less (excluding 0% by weight), B: 0.0050% by weight or less (excluding 0% by weight), Ca: 0.0050% by weight or less (excluding 0% by weight), Mg: 0.0050% by weight or less (excluding 0% by weight), and Zr: 0.005% by weight or less (excluding 0% by weight).

[0058] Sb: 0.06% by weight or less Antimony (Sb) can be added to improve magnetic properties by segregating at grain boundaries and surfaces, improving the texture of the material and suppressing surface oxidation. Adding too much Sb can severely segregate at grain boundaries, degrading surface quality, increasing hardness, potentially causing breakage of the cold-rolled sheet and reducing rollability. Therefore, Sb can be added within the aforementioned range. More specifically, Sb can be added in an amount of 0.01 to 0.05 wt.%.

[0059] Zn: 0.01% by weight or less If the zinc (Zn) content is too high, it may act as an impurity and cause magnetic deterioration. Therefore, Zn can be further added within the range mentioned above. Specifically, it can be contained in an amount of 0.0001 to 0.01% by weight. More specifically, it can be contained in an amount of 0.0005 to 0.005% by weight.

[0060] B: 0.0050% by weight or less Excessive addition of boron (B) can cause deterioration of magnetic properties due to the formation of inclusions in the steel. Therefore, B can be contained in an amount of 0.005% by weight or less. The lower limit is not particularly limited, but can be set to 0.0001% by weight from the perspective of steelmaking costs. Specifically, B can be contained in an amount of 0.0001 to 0.0050% by weight. More specifically, B can be contained in an amount of 0.0005 to 0.0030% by weight.

[0061] Ca: 0.0050% by weight or less Calcium (Ca) may react with C, S, N, etc. to form fine carbides, nitrides, or sulfides, which can adversely affect magnetic properties. Therefore, Ca may be contained in an amount of 0.005% by weight or less. The lower limit is not particularly limited, but may be set to 0.0001% by weight from the perspective of steelmaking costs. Specifically, Ca may be contained in an amount of 0.0001 to 0.0050% by weight. More specifically, Ca may be contained in an amount of 0.0005 to 0.0030% by weight.

[0062] Mg: 0.0050% by weight or less Magnesium (Mg) is an element that mainly combines with S to form sulfides, which may affect the surface oxide layer of the base steel. Therefore, Mg can be contained in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but can be set to 0.0001 wt% from the perspective of steelmaking costs. In other words, Mg can be contained in an amount of 0.0001 to 0.0050 wt%. More specifically, Mg can be contained in an amount of 0.0005 to 0.0030 wt%.

[0063] Zr: 0.0050% by weight or less Excessive addition of zirconium (Zr) can cause deterioration of magnetic properties through the formation of inclusions in the steel. Therefore, Zr can be contained in an amount of 0.005% by weight or less. The lower limit is not particularly limited, but can be set to 0.0001% by weight from the perspective of steelmaking costs. In other words, Zr can be contained in an amount of 0.0001 to 0.0050% by weight. More specifically, Zr can be contained in an amount of 0.0005 to 0.0030% by weight.

[0064] The balance includes Fe and unavoidable impurities. The unavoidable impurities are impurities that are mixed in during the steelmaking step and the manufacturing process of the non-oriented electrical steel sheet, and are widely known in the art, so a detailed description will be omitted. In addition to the alloy components described above in one embodiment of the present invention, various additional elements may be included within a range that does not detract from the technical concept of the present invention. When an additional element is further included, it may be included in place of the balance Fe.

[0065] A non-oriented electrical steel sheet according to an embodiment of the present invention may contain one or more of Cu sulfides, Mn sulfides, Al nitrides, and composite precipitates thereof, each having a grain size of 5 nm to 1,000 nm. In an embodiment of the present invention, the addition of Na may coarsen the sulfides and nitrides, thereby reducing the density of the precipitates. The grain size of the precipitates may be measured based on a cross section parallel to the rolled surface (ND surface) of the steel sheet. More specifically, the measurement may be performed over a thickness range of 1 / 4t to 3 / 4t relative to the total thickness t of the steel sheet. The grain size of the precipitates is determined by imagining a virtual circle with the same area as the area occupied by the precipitate, and the diameter of the circle is the grain size of the precipitate. The area occupied by the precipitate refers to the area where S is aggregated in the case of sulfides, or where N is aggregated in the case of nitrides, and where the content is higher than that of the steel sheet matrix (i.e., the area excluding sulfides and nitrides).

[0066] Cu sulfide, Mn sulfide, Al nitride, and their composites and precipitates with a particle size of 5nm to 1,000nm, with a density of 0.01 particles / μm 2 ~20 pieces / μm 2 Precipitates with a grain size of 5 nm or less are excluded from the number density because they do not have a significant effect on the properties of the steel sheet. Precipitates with a grain size of more than 1000 nm are also excluded because they are virtually impossible to form. If the number density of precipitates is too low, it is difficult to adequately obtain the effect of controlling the crystal grain size by the precipitates. If there are too many precipitates, there is a possibility that magnetic deterioration will occur due to the precipitates. More specifically, the number density of precipitates is 0.01 to 17.0 particles / μm 2 The number density of precipitates can be measured in a manner similar to the method for measuring the particle size of precipitates described above, and can be measured over an area of ​​at least 0.01 mm x 0.01 mm or more to reduce measurement deviation.

[0067] The average particle size of one or more of Cu sulfide, Mn sulfide, Al nitride, and composite precipitates thereof may be 100 to 500 nm. If the average particle size is too small, the number of precipitates may increase, which may adversely affect magnetic properties. If the particle size is too large, the adverse effect on magnetic properties per precipitate may increase. More specifically, the average particle size of the precipitates may be 150 to 495 nm. "Average" refers to the average based on the number of precipitates.

[0068] The non-oriented electrical steel sheet according to an embodiment of the present invention may have an average grain size of 10 to 50 μm. In this embodiment of the present invention, by appropriately precipitating precipitates, it is possible to suppress grain growth during annealing of the cold-rolled sheet, and prevent deterioration of iron loss due to grain growth. If the grain size is too small or too large, there is a possibility that the magnetic properties will be inferior. More specifically, the average grain size may be 10 to 50 μm.

[0069] In one embodiment of the present invention, the grain size can be measured in a plane parallel to the steel sheet surface. More specifically, it can be measured in a thickness range of 1 / 4t to 3 / 4t with respect to the total thickness t of the steel sheet. The grain size is measured by imagining a virtual circle having the same area as the grain, and the grain size of that circle is the grain size. The average grain size can be measured by dividing the number of grains present within the area to be measured. More specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 10.0 to 45.0 μm. The grain size and distribution can be measured using an optical microscope and SEM-EBSD.

[0070] The area fraction of crystal grains having a grain size of 10 to 100 μm may be 80% or more. In one embodiment of the present invention, the grain size is controlled by appropriately precipitating precipitates, so that the crystal grain size can be formed uniformly. A low area fraction means that multiple crystal grains with very small or very large grain sizes are formed, which adversely affects magnetic properties. In one embodiment of the present invention, the crystal grain size is formed uniformly, reducing anisotropy and improving iron loss. More specifically, the area fraction may be 80 to 100%. More specifically, it may be 82 to 98%.

[0071] The non-oriented electrical steel sheet according to an embodiment of the present invention is excellent in iron loss. Specifically, the iron loss (W 15 / 50 ) is the iron loss when a magnetic flux density of 1.5T is induced at a frequency of 50Hz. More specifically, non-oriented electrical steel sheets have the iron loss (W 15 / 50 ) may be 7.0 W / kg or less. More specifically, the non-oriented electrical steel sheet may have an iron loss (W 15 / 50 ) may be 4.0 to 7.0 W / kg. More specifically, it may be 4.2 to 6.7 W / kg. The iron loss is an average value in the rolling direction and the direction perpendicular to the rolling direction, and the reference thickness may be 0.5 mm.

[0072] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of hot-rolling a slab to manufacture a hot-rolled sheet, cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet, and annealing the cold-rolled sheet. Each step will be described in detail below.

[0073] First, the slab is hot rolled. The alloy composition of the slab has been explained in the alloy composition of the non-oriented electrical steel sheet, so a duplicate explanation will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab is substantially the same. Specifically, the slab contains, by weight, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001% to 0.1% Na, with the remainder being Fe and unavoidable impurities. Other additional elements have been explained in the alloy components of the non-oriented electrical steel sheet, so duplicate explanations will be omitted.

[0074] The slab can be heated before hot rolling. There are no restrictions on the heating temperature, but it can be heated to 1250°C or lower. If the slab heating temperature is too high, precipitates such as AlN and MnS present in the slab will re-dissolve and then precipitate finely during hot rolling and annealing, which can inhibit grain growth and reduce magnetic properties. Slabs can be produced using 80% by weight or less of blast furnace hot metal and 20% by weight or more of iron scrap. Iron scrap contains a larger amount of S or N than blast furnace hot metal, which can lead to the precipitation of large amounts of precipitates such as nitrides and sulfides. In one embodiment of the present invention, the addition of an appropriate amount of Na reduces the number density of precipitates, reduces the adverse effects on magnetic properties, and uniformly grows the crystal grain size, thereby improving magnetic properties.

[0075] Returning to the explanation of the hot rolling step, the slab is hot rolled to produce a hot rolled sheet. The thickness of the hot rolled sheet can be 1.0 to 3.5 mm. In the step of producing the hot rolled sheet, the finish rolling temperature can be 800°C or higher. Specifically, it can be 800 to 1000°C. The hot rolled sheet can be coiled at a temperature of 700°C or lower.

[0076] After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet. In this case, the annealing temperature may be 850 to 1150°C. If the annealing temperature is less than 850°C, the structure may not grow or may grow finely, resulting in little effect in increasing magnetic flux density. If the annealing temperature exceeds 1150°C, the magnetic properties may deteriorate and the rolling workability may be impaired due to deformation of the sheet. More specifically, the temperature range may be 950 to 1125°C. More specifically, the annealing temperature of the hot-rolled sheet is 900 to 1100°C. Hot-rolled sheet annealing is performed as needed to increase orientation favorable for magnetic properties, and may be omitted.

[0077] The hot-rolled sheet is then pickled and cold-rolled to the desired thickness. Depending on the thickness of the hot-rolled sheet, a reduction of 40-95% can be applied, and cold-rolled to a final thickness of 0.1-0.7 mm. To achieve the desired reduction, cold-rolling can be performed once or twice or more times with intermediate annealing.

[0078] The cold-rolled sheet is subjected to cold-rolled sheet annealing. The cold-rolled sheet annealing step can be carried out in a hydrogen (H2) and nitrogen (N2) gas mixture and atmosphere. The gas mixture may contain up to 40% by volume of hydrogen and 60% by volume of nitrogen. The cold-rolled sheet annealing step may involve annealing at a temperature of 900°C to 1100°C for 60 to 180 seconds. In one embodiment of the present invention, annealing is performed at a relatively high temperature, but proper precipitation of precipitates prevents the crystal grain size from growing too large, thereby preventing magnetic deterioration. Furthermore, annealing at a high temperature after proper precipitation of precipitates allows the crystal grains to grow uniformly. If the annealing temperature is too low or the annealing time is too short, crystal grain growth may be insufficient, resulting in an excessive increase in hysteresis loss and thus poor iron loss. If the annealing temperature is too high or the annealing time is too long, crystal grains may grow too large, resulting in an excessive increase in eddy current loss and thus poor iron loss.

[0079] After annealing the cold-rolled sheet, an insulating film can be formed. The insulating film can be an organic, inorganic, or organic-inorganic composite film, or it can be an insulating film.

[0080] The present invention will be described in more detail with reference to the following examples, but these examples are merely for illustrative purposes and are not intended to limit the scope of the present invention.

[0081] Example 1 Slabs were produced using the components shown in Tables 1 and 2, with the balance being Fe and unavoidable impurities. They were heated to 1200°C and hot-rolled to a thickness of 2.5 mm. The hot-rolled sheets were heated to 1070°C and then water-cooled. The hot-rolled steel was pickled and then rolled once to a thickness of 0.5 mm. The cold-rolled sheets were then annealed at 1000°C for 180 seconds. The W15 / 50 core loss (unit: W / kg), average size and number density of complex precipitates, average grain size, and area fraction of grains between 10 μm and 100 μm for the inventive and comparative materials listed in Table 1 are shown in Table 2. For each test piece, 5 test pieces of 60 mm wide x 60 mm long were cut, and the iron loss was measured in the rolling direction and the direction perpendicular to the rolling direction using a single sheet tester, and the average was expressed. The grain size and distribution were measured using SEM-EBSD.

[0082] [Table 1]

[0083] [Table 2]

[0084] [Table 3]

[0085] As shown in Tables 1 to 3, it can be seen that when the steel components are appropriately adjusted, the average crystal grain size is appropriately adjusted and the iron loss is excellent. It can be seen that comparative material 1 contains an excess of C, which causes a large amount of carbides to form, preventing the crystal grains from growing properly and resulting in poor magnetic properties. Comparative materials 2 and 3 do not contain an appropriate amount of Si, which results in inadequate control of phase transformation, inadequate control of the average crystal grain size, and the crystal grain area fraction of 10 to 100 μm being formed at less than 80%, resulting in inferior magnetic properties. Comparative materials 4 and 5 do not contain an appropriate amount of Mn, which results in inadequate control of phase transformation, inadequate control of the average crystal grain size, and the crystal grain area fraction of 10 to 100 μm being formed at less than 80%, confirming that the magnetic properties are inferior. Comparative materials 6 and 7 did not contain an appropriate amount of Al. In particular, comparative material 6 contained too little Al, resulting in poor magnetic properties, while comparative material 7 contained more Al than the appropriate amount. It is presumed that excessive formation of Al nitrides inhibited grain growth, preventing the grains from growing appropriately and resulting in poor magnetic properties.

[0086] It can be seen that Comparative Materials 8 to 15 do not contain an appropriate amount of Na, and precipitates are not properly precipitated, which causes crystal grains to not grow properly, resulting in inferior magnetic properties.

[0087] The present invention is not limited to the examples, and may 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 may be embodied in other specific forms without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above-described examples are illustrative in all respects and are not limiting.

Claims

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

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

3. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of C: 0.005% by weight or less (excluding 0% by weight), N: 0.01% by weight or less (excluding 0% by weight), and S: 0.01% by weight or less (excluding 0% by weight).

4. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Ti: 0.005% by weight or less (excluding 0% by weight), Nb: 0.005% by weight or less (excluding 0% by weight), and V: 0.005% by weight or less (excluding 0% by weight).

5. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more 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. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more 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. 2. The non-oriented electrical steel sheet according to claim 1, further comprising one or more of Sb: 0.06% by weight or less (excluding 0% by weight), Zn: 0.01% by weight or less (excluding 0% by weight), B: 0.005% by weight or less (excluding 0% by weight), Ca: 0.005% by weight or less (excluding 0% by weight), Mg: 0.005% by weight or less (excluding 0% by weight), and Zr: 0.005% by weight or less (excluding 0% by weight).

8. 2. The non-oriented electrical steel sheet according to claim 1, comprising one or more of Cu sulfide, Mn sulfide, Al nitride, and composite precipitates thereof, each having a particle size of 5 nm to 1,000 nm.

9. Cu sulfide, Mn sulfide, Al nitride, and composite precipitates thereof, each having a particle size of 5 nm to 1,000 nm, and a number density of at least one of these is 0.01 particles / μm ２ ~20 pieces / μm ２ The non-oriented electrical steel sheet according to claim 8, wherein

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

11. 2. The non-oriented electrical steel sheet according to claim 1, wherein the average grain size is 10 to 50 μm.

12. 2. The non-oriented electrical steel sheet according to claim 1, wherein the area fraction of crystal grains having a grain size of 10 to 100 μm is 80% or more.

13. a step of producing a hot-rolled sheet by hot-rolling a slab containing, in weight percent, 0.2% to 4.0% Si, 0.05 to 1% Mn, 0.005 to 2.0% Al, and 0.001 to 0.1% Na, with the balance being Fe and unavoidable impurities; cold rolling the hot-rolled sheet to produce a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

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

15. 14. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more of C: 0.005% by weight or less (excluding 0% by weight), N: 0.01% by weight or less (excluding 0% by weight), and S: 0.01% by weight or less (excluding 0% by weight).

16. 14. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more of Ti: 0.005% by weight or less (excluding 0% by weight), Nb: 0.005% by weight or less (excluding 0% by weight), and V: 0.005% by weight or less (excluding 0% by weight).

17. 14. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more 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. 14. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more 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. 14. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more of Sb: 0.06% by weight or less (excluding 0% by weight), Zn: 0.01% by weight or less (excluding 0% by weight), B: 0.005% by weight or less (excluding 0% by weight), Ca: 0.005% by weight or less (excluding 0% by weight), Mg: 0.005% by weight or less (excluding 0% by weight), and Zr: 0.005% by weight or less (excluding 0% by weight).

20. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the slab is produced using 80% by weight or less of blast furnace hot metal and 20% by weight or more of iron scrap.

21. The method for producing a non-oriented electrical steel sheet according to claim 13, wherein the cold-rolled sheet annealing step comprises annealing at a temperature of 900°C to 1100°C for 60 seconds to 180 seconds.

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