Non-oriented electrical steel sheet and method for producing same

Abstract

The non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, 0.2% to 4.0% of Si, 0.05% to 1% of Mn, 0.005% to 2.0% of Al, and 0.001% to 0.1% of Na, with the remainder comprising Fe and unavoidable impurities.

Description

Technical Field

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, wherein Na is added to the steel composition to allow precipitates to be properly precipitated and the grain size is adjusted to improve magnetic properties. Background Art

[0002] In recent years, due to global warming, we are experiencing an extreme climate crisis, and carbon neutrality activities to reduce carbon emissions have become increasingly important worldwide. In the steel industry, a technology is being developed to reduce the amount of molten iron used in traditional blast furnace ironmaking, which emits a large amount of carbon, and to reduce the carbon generated in the manufacturing process by replacing the shortage of molten iron with iron scrap that does not generate carbon in the manufacturing process. However, iron scrap contains a large amount of elements such as Cu, Cr, and Ni, and there is a problem of deterioration in the quality of electrical steel sheets, in which iron loss is very important.

[0003] If the iron loss of electrical steel sheets deteriorates, the energy efficiency of equipment such as motors and small transformers will decrease, requiring more electricity. As a result, additional coal and oil-fired power plants will need to be started up, which will increase carbon emissions from the power generation process.

[0004] When Cu from scrap used is mixed into ultra-low aluminum non-oriented electrical steel sheets, a method of adding Ca is proposed to solve the problem of uneven magnetic properties. However, this method does not provide a solution to calcium oxides that react with oxygen in steel to deteriorate magnetic properties, so there is a limit to the improvement of magnetic properties.

[0005] In addition, when Cu derived from scrap used is mixed into aluminum non-oriented electrical steel sheets, a method of adding Mg is proposed to solve the problem of uneven magnetic properties. However, this method also does not provide a solution to magnesium oxide that reacts with oxygen in steel to inevitably reduce magnetic properties, so there is a limit to the improvement of magnetic properties.

[0006] Furthermore, when using low-cost iron scrap, as a method for solving the deterioration of punching workability caused by the mixing of Cu, Ni, Sn, Ni, Cr, etc., a method of controlling Sol-Al and Mn within an appropriate range has been proposed. However, this method does not provide a control method for Cu sulfide or Al nitride that causes deterioration of magnetic properties, so there is a limit to the improvement of magnetic properties. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] In one embodiment of the present invention, a non-oriented electrical steel sheet and a manufacturing method thereof are provided. Specifically, in one embodiment of the present invention, a non-oriented electrical steel sheet and a manufacturing method thereof are provided. By adding Na to the steel composition, precipitates are appropriately precipitated and the grain size is adjusted to improve the magnetic properties.

[0009] (II) Technical Solution

[0010] The non-oriented electrical steel sheet according to one embodiment of the present invention, by weight%, contains 0.2% to 4.0% of Si, 0.05 to 1% of Mn, 0.005 to 2.0% of Al, and 0.001% to 0.1% of Na, and the balance contains Fe and inevitable impurities.

[0011] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain Cu of 0.2% by weight or less and excluding 0% by weight, and Sn of 0.1% by weight or less and excluding 0% by weight.

[0012] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of C of 0.005% by weight or less and excluding 0% by weight, N of 0.01% by weight or less and excluding 0% by weight, and S of 0.01% by weight or less and excluding 0% by weight.

[0013] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of Ti of 0.005% by weight or less and excluding 0% by weight, Nb of 0.005% by weight or less and excluding 0% by weight, and V of 0.005% by weight or less and excluding 0% by weight.

[0014] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of Mo of 0.1% by weight or less and excluding 0% by weight, Ni of 0.1% by weight or less and excluding 0% by weight, Cr of 0.1% by weight or less and excluding 0% by weight, and P of 0.1% by weight or less and excluding 0% by weight.

[0015] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of Bi of 0.2% by weight or less and excluding 0% by weight, Pb of 0.2% by weight or less and excluding 0% by weight, Ge of 0.2% by weight or less and excluding 0% by weight, and As of 0.2% by weight or less and excluding 0% by weight.

[0016] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sb of 0.06% by weight or less, excluding 0% by weight, Zn of 0.01% by weight or less, excluding 0% by weight, B of 0.0050% by weight or less, excluding 0% by weight, Ca of 0.0050% by weight or less, excluding 0% by weight, Mg of 0.0050% by weight or less, excluding 0% by weight, and Zr of 0.005% by weight or less, excluding 0% by weight.

[0017] The 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 their composite precipitates having a particle size of 5 nm to 1000 nm.

[0018] The number density of one or more of Cu sulfide, Mn sulfide, Al nitride, and their composite precipitates having a particle size of 5 nm to 1000 nm may be 0.01 piece / μm 2 to 20 pieces / μm 2 。

[0019] The average particle size of one or more of Cu sulfide, Mn sulfide, Al nitride, and their composite precipitates may be 100 to 500 nm.

[0020] The average grain size of the non-oriented electrical steel sheet according to an embodiment of the present invention may be 10 to 50 μm.

[0021] The area fraction of grains having a particle size of 10 to 100 μm may be 80% or more.

[0022] The manufacturing method of the non-oriented electrical steel sheet according to an embodiment of the present invention includes: a step of hot rolling a slab to manufacture a hot rolled sheet, wherein the slab contains, by weight%, 0.2% to 4.0% of Si, 0.05 to 1% of Mn, 0.005 to 2.0% of Al, and 0.001% to 0.1% of Na, and the balance contains Fe and inevitable impurities; 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.

[0023] The slab may further contain Cu of 0.2% by weight or less, excluding 0% by weight, and Sn of 0.1% by weight or less, excluding 0% by weight.

[0024] The slab may further contain one or more of C of 0.005% by weight or less, excluding 0% by weight, N of 0.01% by weight or less, excluding 0% by weight, and S of 0.01% by weight or less, excluding 0% by weight.

[0025] The slab may further contain one or more of Ti at 0.005 wt% or less, excluding 0 wt%, Nb at 0.005 wt% or less, excluding 0 wt%, and V at 0.005 wt% or less, excluding 0 wt%.

[0026] The slab may further contain one or more of Mo at 0.1 wt% or less, excluding 0 wt%, Ni at 0.1 wt% or less, excluding 0 wt%, Cr at 0.1 wt% or less, excluding 0 wt%, and P at 0.1 wt% or less, excluding 0 wt%.

[0027] The slab may further contain one or more of Bi at 0.2 wt% or less, excluding 0 wt%, Pb at 0.2 wt% or less, excluding 0 wt%, Ge at 0.2 wt% or less, excluding 0 wt%, and As at 0.2 wt% or less, excluding 0 wt%.

[0028] The slab may further contain one or more of Sb at 0.06 wt% or less, excluding 0 wt%, Zn at 0.01 wt% or less, excluding 0 wt%, B at 0.0050 wt% or less, excluding 0 wt%, Ca at 0.0050 wt% or less, excluding 0 wt%, Mg at 0.0050 wt% or less, excluding 0 wt%, and Zr at 0.005 wt% or less, excluding 0 wt%.

[0029] The slab may be manufactured using blast furnace hot metal at 80 wt% or less and iron scrap at 20 wt% or more.

[0030] The cold-rolled sheet annealing step may be annealing at a temperature of 900°C to 1100°C for 60 seconds to 180 seconds.

[0031] (III) Advantageous Effects

[0032] For the non-oriented electrical steel sheet according to an embodiment of the present invention, by appropriately adding Na and appropriately forming precipitates, the grain size and grain size distribution can be uniformly formed, thereby improving the magnetic properties.

[0033] In addition, for the non-oriented electrical steel sheet according to an embodiment of the present invention, even when manufactured using a large amount of scrap containing Cu or Sn, it has excellent quality, can reduce carbon generated during the manufacturing process, and can improve economic efficiency.

[0034] Ultimately, the non-oriented electrical steel sheet according to an embodiment of the present invention contributes to the manufacture of motors for environmentally friendly vehicles, motors for high-efficiency household appliances, and ultra-high-end electric motors. Detailed Embodiments

[0035] The terms first, second, third, etc. are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another part, component, region, layer, or segment. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, or segment described below can also be described as the second part, component, region, layer, or segment.

[0036] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present invention. Unless otherwise clearly indicated to the contrary in the context, the singular forms used herein are also intended to include the plural forms. The use of "comprising" in the specification may specifically refer to a certain characteristic, field, integer, step, action, element, and / or component, but does not exclude the existence or addition of other characteristics, fields, integers, steps, actions, elements, and / or components.

[0037] If a part is described as being above another part, there may be other parts directly above the other part or there may be other parts in between. When a part is described as being directly above another part, there are no other parts in between.

[0038] In addition, unless otherwise specifically stated, % represents weight %, and 1 ppm is 0.0001 weight %.

[0039] In one embodiment of the present invention, further comprising additional elements means that the additional elements replace the remaining iron (Fe), and the replacement amount is equivalent to the added amount of the additional elements.

[0040] Although not otherwise defined, the meanings of all terms used herein (including technical terms and scientific terms) are the same as those commonly understood by those of ordinary skill in the art to which the present invention pertains. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0041] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0042] An non-oriented electrical steel sheet according to an embodiment of the present invention, by weight %, the non-oriented electrical steel sheet comprises 0.2% to 4.0% of Si, 0.05 to 1% of Mn, 0.005 to 2.0% of Al, and 0.001% to 0.1% of Na, and the balance comprises Fe and unavoidable impurities. The steel components are the steel components of the steel sheet substrate, except for the insulating coating film present on the steel sheet surface.

[0043] The reasons for the compositional limitations of non-oriented electrical steel sheets are described below.

[0044] Si: 0.2 to 4.0% by weight

[0045] Silicon (Si) is a basic component of electrical steel sheets and plays a role in increasing the resistivity of the material to reduce core loss. If the Si content is too low, problems such as deterioration of core loss may occur. On the other hand, if the Si content is too high, the magnetic flux density deteriorates severely and the brittleness becomes stronger, and problems may occur in rollability, cold rollability, and weldability. More specifically, it may contain 0.3 to 3.5% by weight. More specifically, it may contain 1.0 to 3.3% by weight.

[0046] Mn: 0.05 to 1.00% by weight

[0047] Manganese (Mn), like Si and Al, plays a role in increasing the resistivity to reduce core loss. On the other hand, Mn reacts with S to form Mn sulfide and reacts with nitrogen, Al, and Si at high temperatures to form (Al, Si, Mn) nitride, thus hindering grain growth. If the Mn content is too low, the effect of improving core loss may be insufficient. If the Mn content is too high, not only the magnetic flux density decreases, but also the core loss and magnetic flux density may deteriorate due to the formation of precipitates. More specifically, it may contain 0.10 to 0.90% by weight.

[0048] Al: 0.005 to 2.000% by weight

[0049] Aluminum (Al) has the same effect as Si, plays a role in increasing the resistivity of the material to reduce core loss, and also plays a role in reducing magnetic anisotropy to reduce the magnetic deviation between the rolling direction and the perpendicular direction. If the Al content is too low, the increase in resistivity is low, and there may be almost no effect of reducing core loss. If the Al content is too high, the magnetic flux density becomes too poor to be applied to rotating equipment such as motors or stationary equipment such as small transformers. In addition, in steel or a heat treatment environment, it reacts with nitrogen to form Al nitride, which may hinder the movement of magnetic domains. More specifically, it may contain 0.005 to 1.000% by weight.

[0050] Na: 0.001% to 0.100% by weight

[0051] Sodium (Na) reduces the number density of precipitates by coarsening the precipitates in the steel sheet, thereby playing a role in improving the magnetic properties by uniformly growing the grain size. If the Na content is too low, the coarsening effect of the precipitates cannot be fully obtained, and the magnetic property improvement may be insufficient. If the Na content is too high, high-melting-point Na oxides are formed, which inhibits grain growth or hinders the movement of magnetic domains, possibly leading to magnetic property deterioration. More specifically, it may contain 0.0015 to 0.0950% by weight. More specifically, it may contain 0.005 to 0.05% by weight.

[0052] In order to appropriately add Na to the steel, it is possible to add an appropriate amount of sodium oxide or sodium hydroxide to the molten steel during the steelmaking process. In order to improve the Na yield, it is also possible to use the method of wrapping with thin iron or aluminum foil and then adding.

[0053] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain Cu of 0.2% by weight or less, excluding 0% by weight, and Sn of 0.1% by weight or less, excluding 0% by weight.

[0054] Cu: 0.2% by weight or less

[0055] Copper (Cu) plays a role in increasing the fraction of grains with cube (Cube) orientation and orientations similar to Cube in the non-oriented electrical steel sheet. In addition, it has the effect of suppressing grain growth by forming sulfides, and suppresses grain growth during annealing of the cold-rolled sheet, increasing the hysteresis loss, thereby causing deterioration of iron loss. If Cu is added appropriately, the sizes of sulfides and precipitates become coarser, and the densities of sulfides and precipitates decrease, so that the iron loss will not deteriorate. Specifically, it may further contain 0.0001 to 0.2% by weight of Cu. More specifically, it may further contain 0.001 to 0.15% by weight of Cu.

[0056] Sn: 0.1% by weight or less

[0057] Tin (Sn) plays a role in coarsening the sizes of Cu sulfides, Mn sulfides, and Al nitrides and reducing the density of precipitated precipitates in the non-oriented electrical steel sheet containing a large amount of Cu, so tin can be further added. This is because Sn segregated at the grain boundaries reduces the free energy for the precipitation of precipitates. If too much Sn is added, the grain growth inhibition force becomes stronger due to Sn grain boundary segregation, and there is a problem of iron loss deterioration. Specifically, Sn may contain 0.0001 to 0.1% by weight. More specifically, it may contain 0.001 to 0.08% by weight.

[0058] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of C of 0.005 wt% or less and excluding 0 wt%, N of 0.01 wt% or less and excluding 0 wt%, and S of 0.01 wt% or less and excluding 0 wt%.

[0059] C: 0.0050 wt% or less

[0060] Carbon (C) combines with elements such as Ti, Nb, and V inevitably contained in the steel to form carbides, which hinder the movement of magnetic domains, resulting in poor magnetic properties. Moreover, when using the final product, due to the applied current, magnetic aging caused by the heat generated by the material itself leads to deterioration of iron loss, thereby reducing the efficiency of electrical equipment. Specifically, C may contain 0.0001 to 0.005 wt%. More specifically, it may contain 0.0005 to 0.003 wt%.

[0061] N: 0.0100 wt% or less

[0062] Nitrogen (N) has the characteristic of reacting with Al, Si, Cr to form nitrides. Such nitrides hinder grain growth, increase the grain boundary fraction, resulting in deterioration of hysteresis loss, and hinder the movement and rotation of magnetic domains, leading to deterioration of eddy current loss. Therefore, it is necessary to minimize the amount formed. However, when using iron scrap, the N content inevitably increases, so it is almost impossible to avoid the formation of nitrides. Therefore, by coarsening the size of the nitrides, reducing the number of precipitates, and reducing the grain growth inhibition force, and it is necessary to reduce the probability of hindering the movement of magnetic domains. Specifically, N may contain 0.0001 to 0.01 wt%. More specifically, N may contain 0.0005 to 0.005 wt%.

[0063] S: 0.0100 wt% or less

[0064] Sulfur (S) is an element that reacts with elements such as Cu and Mn in the steel to precipitate Cu sulfide and Mn sulfide. The more the amount of such precipitates remaining in the final steel sheet, the worse the iron loss. On the other hand, if the S content is too much, segregation occurs in the center of the slab during casting, and precipitates of Mn sulfide or Cu sulfide will not precipitate uniformly during the subsequent hot rolling process, so the microstructure becomes uneven, which is not preferred. In addition, if the S content is too much, the effect of coarsening and reducing the precipitation amount of sulfides caused by Na may be weakened. More specifically, S may contain 0.0001 to 0.01 wt%. More specifically, it may contain 0.0005 to 0.005 wt%.

[0065] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Ti of 0.005% by weight or less, excluding 0% by weight, Nb of 0.005% by weight or less, excluding 0% by weight, and V of 0.005% by weight or less, excluding 0% by weight.

[0066] Ti: 0.0050% by weight or less

[0067] Titanium (Ti) has a very strong tendency to form precipitates in steel, and forms fine carbides, nitrides or sulfides inside the base metal, inhibiting grain growth and magnetic domain wall movement, thus leading to deterioration of iron loss. Therefore, the Ti content may be 0.0050% by weight or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0003% by weight. That is, Ti may contain 0.0003 to 0.0050% by weight. More specifically, it may contain 0.0003 to 0.0030% by weight.

[0068] Nb: 0.0050% by weight or less

[0069] Niobium (Nb) has a very strong tendency to form precipitates in steel, and forms fine carbides, nitrides or sulfides inside the base metal, inhibiting grain growth and magnetic domain wall movement, thus leading to deterioration of iron loss. Therefore, the Nb content may be 0.0050% by weight or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0003% by weight. That is, Nb may contain 0.0003 to 0.0050% by weight. More specifically, Nb may contain 0.0003 to 0.0030% by weight.

[0070] V: 0.0050% by weight or less

[0071] Vanadium (V) has a very strong tendency to form precipitates in steel, and forms fine carbides, nitrides or sulfides inside the base metal, inhibiting grain growth and magnetic domain wall movement, thus leading to deterioration of iron loss. Therefore, the V content may be 0.0050% by weight or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0003% by weight. That is, V may contain 0.0003 to 0.0050% by weight. More specifically, V may contain 0.0003 to 0.0030% by weight.

[0072] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Mo of 0.1% by weight or less, excluding 0% by weight, Ni of 0.1% by weight or less, excluding 0% by weight, Cr of 0.1% by weight or less, excluding 0% by weight, and P of 0.1% by weight or less, excluding 0% by weight.

[0073] Mo: 0.100% by weight or less

[0074] When excessive molybdenum (Mo) is added, the segregation of segregation elements is inhibited, which may reduce the effect of texture improvement. Therefore, Mo may be contained in an amount of 0.1% by weight or less, and its lower limit is not particularly limited. However, since it segregates at the surface and grain boundaries and plays a role in improving the texture, it may be contained in an amount of 0.001% by weight or more. More specifically, Mo may be contained in an amount of 0.001 to 0.100% by weight. More specifically, Mo may be contained in an amount of 0.005 to 0.050% by weight.

[0075] Ni: 0.100% by weight or less

[0076] Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which may have an adverse effect on magnetism. More specifically, Ni may be contained in an amount of 0.001 to 0.100% by weight. More specifically, Ni may be contained in an amount of 0.005 to 0.050% by weight.

[0077] Cr: 0.100% by weight or less

[0078] Chromium (Cr) plays a role in improving iron loss by increasing the resistivity. If the Cr content is too high, the magnetic flux density may decrease. More specifically, when further containing Cr, it may be contained in an amount of 0.001 to 0.100% by weight. More specifically, it may be contained in an amount of 0.005 to 0.050% by weight.

[0079] P: 0.100% by weight or less

[0080] Phosphorus (P) causes deterioration of hot rolling processing characteristics and reduces productivity compared to magnetic improvement. Therefore, P may be contained in an amount of 0.100% by weight or less, and its lower limit is not particularly limited. However, since it segregates at the surface and grain boundaries of the steel sheet, it inhibits surface oxidation during annealing, hinders the diffusion of elements through the grain boundaries, and hinders the recrystallization of the {111} / / ND orientation, thus also playing a role in improving the texture. Therefore, it may be 0.005% by weight. More specifically, P may be contained in an amount of 0.005 to 0.100% by weight. More specifically, P may be contained in an amount of 0.010 to 0.050% by weight.

[0081] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Bi except 0% by weight and 0.2% by weight or less, Pb except 0% by weight and 0.2% by weight or less, Ge except 0% by weight and 0.2% by weight or less, and As except 0% by weight and 0.2% by weight or less.

[0082] When further adding elements such as bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As), due to segregation at grain boundaries, the stress concentration at grain boundaries is relieved during cold rolling, and the recrystallization of <111> / / ND-oriented grains is suppressed during subsequent recrystallization annealing, thereby increasing the magnetic flux density. When these elements are added appropriately, the aforementioned effects can be further obtained. However, if the content is too high, a large amount of segregation occurs, inhibiting grain growth, and thus the magnetic flux density and iron loss will deteriorate instead. Therefore, each of these elements can independently further contain 0.2% by weight or less. More specifically, each of these elements can independently further contain 0.0001 to 0.2000% by weight. More specifically, each of these elements can independently further contain 0.001 to 0.100% by weight. More specifically, each of these elements can independently further contain 0.005 to 0.050% by weight.

[0083] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Sb of 0.06% by weight or less and excluding 0% by weight, Zn of 0.01% by weight or less and excluding 0% by weight, B of 0.0050% by weight or less and excluding 0% by weight, Ca of 0.0050% by weight or less and excluding 0% by weight, Mg of 0.0050% by weight or less and excluding 0% by weight, and Zr of 0.005% by weight or less and excluding 0% by weight.

[0084] Sb: 0.06% by weight or less

[0085] Antimony (Sb) segregates at grain boundaries and the surface, playing a role in improving the texture of the material and suppressing surface oxidation. Therefore, antimony can be added to improve the magnetism. If too much Sb is added, severe grain boundary segregation occurs, the surface quality deteriorates, the hardness increases, and it may cause the cold-rolled sheet to break, thereby reducing the rollability. Therefore, Sb can be further added within the aforementioned range. More specifically, it can further contain 0.01 to 0.05% by weight of Sb.

[0086] Zn: 0.01% by weight or less

[0087] When the zinc (Zn) content is excessive, as an impurity, it may cause the magnetism to deteriorate. Therefore, Zn can be further added within the aforementioned range. Specifically, it can contain 0.0001 to 0.01% by weight. More specifically, it can contain 0.0005 to 0.005% by weight.

[0088] B: 0.0050% by weight or less

[0089] When an excessive amount of boron (B) is added, it may lead to deterioration of magnetism by forming inclusions in the steel. Therefore, B may be contained at 0.005 wt% or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0001 wt%. Specifically, it may be contained at 0.0001 to 0.0050 wt%. More specifically, B may be contained at 0.0005 to 0.0030 wt%.

[0090] Ca: 0.0050 wt% or less

[0091] Calcium (Ca) reacts with elements such as C, S, and N to form fine carbides, nitrides, or sulfides, which may have an adverse effect on magnetism. Therefore, Ca may be contained at 0.005 wt% or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0001 wt%. Specifically, it may be contained at 0.0001 to 0.0050 wt%. More specifically, it may be contained at 0.0005 to 0.0030 wt%.

[0092] Mg: 0.0050 wt% or less

[0093] Magnesium (Mg) is an element that mainly combines with S to form sulfides and may affect the oxide layer on the surface of matrix iron. Therefore, Mg may be contained at 0.005 wt% or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0001 wt%. That is, Mg may be contained at 0.0001 to 0.0050 wt%. More specifically, it may be contained at 0.0005 to 0.0030 wt%.

[0094] Zr: 0.0050 wt% or less

[0095] When an excessive amount of zirconium (Zr) is added, it may lead to deterioration of magnetism by forming inclusions in the steel. Therefore, Zr may be contained at 0.005 wt% or less, and its lower limit is not particularly limited, but due to steelmaking costs, it may be 0.0001 wt%. That is, Zr may be contained at 0.0001 to 0.0050 wt%. More specifically, it may be contained at 0.0005 to 0.0030 wt%.

[0096] The balance contains Fe and inevitable impurities. For the inevitable impurities, they are impurities mixed in during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets, which are well-known in the art, so specific descriptions are omitted. In one embodiment of the present invention, in addition to the aforementioned alloying components, the addition of other elements is not excluded, and the inclusion method may be different within the scope of not impairing the technical idea of the present invention. If additional elements are further included, they replace a part of the Fe in the balance.

[0097] An non-oriented electrical steel sheet according to an embodiment of the present invention may include one or more of Cu sulfide, Mn sulfide, Al nitride, and their composite precipitates having a particle size of 5 nm to 1000 nm. In an embodiment of the present invention, due to the addition of Na, the sulfides and nitrides coarsen, and the density of the precipitates may decrease. For the particle size of the precipitates, measurement can be based on a cross-section parallel to the rolling plane (ND plane) of the steel sheet. More specifically, with respect to the entire thickness t of the steel sheet, measurement can be performed at a thickness in the range of 1 / 4t to 3 / 4t. For the particle size of the precipitates, assuming a virtual circle having the same area as the occupied area of the precipitate, the diameter of this circle is the particle size of the precipitate. The occupied area of the precipitate refers to the part where S aggregates in the case of sulfide and N aggregates in the case of nitride, so that the content is higher than the matrix part of the steel sheet (i.e., the part excluding sulfide and nitride).

[0098] The number density of one or more of Cu sulfide, Mn sulfide, Al nitride, and their composite precipitates having a particle size of 5 nm to 1000 nm may be 0.01 particles / μm 2 to 20 particles / μm 2 . Precipitates having a particle size of less than 5 nm have little effect on the properties of the steel sheet, so they are excluded from the number density. Precipitates having a particle size greater than 1000 nm are also excluded because it is actually difficult to generate them. If the number density of the precipitates is too small, it is difficult to appropriately obtain the grain size control effect caused by the precipitates. If there are too many precipitates, magnetic deterioration may occur due to the precipitates. More specifically, the number density of the precipitates may be 0.01 to 17.0 particles / μm 2 . For the number density of the precipitates, the measurement method is similar to the aforementioned measurement method of the particle size of the precipitates. In order to reduce the measurement deviation, measurement can be performed for an area of at least 0.01 mm × 0.01 mm or more.

[0099] The average particle size of one or more of Cu sulfide, Mn sulfide, Al nitride, and their composite precipitates may be 100 to 500 nm. If the average particle size is too small, the number of precipitates increases, which may have an adverse effect on magnetism. If the particle size is too large, the adverse effect of each precipitate on magnetism may become larger. More specifically, the average particle size of the precipitates may be 150 to 495 nm. The average refers to the average with respect to the number of precipitates.

[0100] An 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 an embodiment of the present invention, by appropriately precipitating the precipitates, the growth of grains during annealing of the cold-rolled sheet can be suppressed, and deterioration of iron loss caused by grain growth can be prevented. If the grain size is too small or too large, the magnetism may deteriorate. More specifically, the average grain size may be 10 to 50 μm.

[0101] In one embodiment of the present invention, the grain size can be measured with respect to a plane parallel to the plate surface of the steel sheet. More specifically, with respect to the entire thickness t of the steel sheet, the measurement can be carried out at a thickness in the range of 1 / 4t to 3 / 4t. For the grain size, assuming a virtual circle having the same area as the grain area, the diameter of the circle is the grain size. The average grain size can be measured by dividing the number of grains present in the area to be measured by the area to be measured. More specifically, for the non-oriented electrical steel sheet according to one embodiment of the present invention, its average grain size can be 10.0 to 45.0 μm. For the grain size and distribution, optical microscopy and SEM-EBSD can be used for measurement.

[0102] The area fraction of grains having a particle size of 10 to 100 μm can be 80% or more. In one embodiment of the present invention, the grain size is adjusted by appropriately precipitating precipitates, so that the grain size can be uniformly formed. A low area fraction means that a large number of grains having too small or too large a particle size are formed, which has an adverse effect on magnetism. In one embodiment of the present invention, since the grain size is uniformly formed, anisotropy can be reduced, thereby improving iron loss. More specifically, the area fraction can be 80 to 100%. More specifically, it can be 82 to 98%.

[0103] The non-oriented electrical steel sheet according to one embodiment of the present invention has excellent iron loss. Specifically, the iron loss (W 15 / 50 ) of the non-oriented electrical steel sheet is the iron loss when excited at a magnetic flux density of 1.5 T at a frequency of 50 Hz. More specifically, the non-oriented electrical steel sheet can be such that the iron loss (W 15 / 50 ) is 7.0 W / kg or less. More specifically, the non-oriented electrical steel sheet can be such that the iron loss (W 15 / 50 ) is 4.0 to 7.0 W / kg. More specifically, it can be 4.2 to 6.7 W / kg. The iron loss is the average value in the rolling direction and the direction perpendicular to rolling, and the reference thickness can be 0.5 mm.

[0104] A method for manufacturing a 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 step of annealing the cold-rolled sheet, which is a cold-rolled sheet annealing step.

[0105] The following describes in detail according to each step.

[0106] First, the slab is hot rolled.

[0107] For the alloy composition of the slab, it has been described in the alloy composition of the aforementioned non-oriented electrical steel sheet, so repeated description is omitted. During the manufacturing process of the non-oriented electrical steel sheet, the alloy composition does not substantially change, so the alloy composition of the non-oriented electrical steel sheet and the slab is substantially the same.

[0108] Specifically, by weight percentage, the slab contains 0.2% to 4.0% of Si, 0.05 to 1% of Mn, 0.005 to 2.0% of Al, and 0.001% to 0.1% of Na, and the balance contains Fe and inevitable impurities.

[0109] For other additional elements, they have been described in the alloy composition of the non-oriented electrical steel sheet, so the repeated description is omitted.

[0110] Before hot rolling the slab, heating can be carried out. The heating temperature of the slab is not restricted, but the slab can be heated to below 1250°C. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab will dissolve again and then precipitate finely during hot rolling and annealing, thus inhibiting grain growth and possibly causing a decrease in magnetism.

[0111] The slab can be manufactured using 80% by weight or less of blast furnace hot metal and 20% by weight or more of iron scrap. Compared with blast furnace hot metal, there is a large amount of S or N in iron scrap, and due to these elements, a large amount of precipitates such as nitrides and sulfides may precipitate. In one embodiment of the present invention, by adding an appropriate amount of Na, the number density of precipitates can be reduced, the adverse effect on magnetism can be reduced, and the grain size can grow uniformly, thereby improving magnetism.

[0112] Returning to the description of the hot rolling step, the slab is hot rolled to manufacture a hot rolled sheet. The thickness of the hot rolled sheet can be 1.0 to 3.5 mm. In the step of manufacturing the hot rolled sheet, the finish rolling temperature can be 800°C or higher. Specifically, it can be 800 to 1000°C. For the hot rolled sheet, coiling can be carried out at a temperature below 700°C.

[0113] After the step of manufacturing the hot rolled sheet, a step of annealing the hot rolled sheet can also be included. At this time, the annealing temperature of the hot rolled sheet can be 850 to 1150°C. If the annealing temperature of the hot rolled sheet is lower than 850°C, the structure will not grow or grow finely, and the effect of increasing the magnetic flux density is small. If the annealing temperature is higher than 1150°C, the magnetic properties will instead decrease, and due to the deformation of the sheet shape, the rolling workability may become poor. More specifically, the temperature range can be 950 to 1125°C. More specifically, the annealing temperature of the hot rolled sheet is 900 to 1100°C. The annealing of the hot rolled sheet is carried out to increase the orientation beneficial to magnetism as needed, and it can also be omitted.

[0114] Next, the hot rolled sheet is pickled and cold rolled to a predetermined sheet thickness. Depending on the thickness of the hot rolled sheet, different reduction ratios can be adopted, but it can be cold rolled with a reduction ratio of 40 to 95% to a final thickness of 0.1 to 0.7 mm. In order to adjust the reduction ratio, one cold rolling or two or more cold rollings including intermediate annealing can be carried out.

[0115] Anneal the cold-rolled sheet after cold rolling.

[0116] The cold-rolled sheet annealing step can be carried out in a mixed gas atmosphere of hydrogen (H2) and nitrogen (N2). The mixed gas can contain 40% by volume or less of hydrogen and 60% by volume or more of nitrogen.

[0117] The cold-rolled sheet annealing step can be annealing at a temperature of 900 °C to 1100 °C for 60 seconds to 180 seconds. In one embodiment of the present invention, annealing is carried out at a higher temperature, but the precipitates precipitate appropriately, thereby preventing excessive growth of the grain size and preventing the resulting magnetic deterioration. In addition, in a state where the precipitates precipitate appropriately, by annealing at a high temperature, the grains can grow uniformly. If the annealing temperature is too low or the time is too short, the grain growth is not sufficient, and the iron loss may deteriorate due to an excessive increase in the hysteresis loss. If the annealing temperature is too high or the time is too long, the grain growth is too large, and the iron loss may deteriorate due to an excessive increase in the eddy current loss.

[0118] After annealing the cold-rolled sheet, an insulating coating film can be formed. The insulating coating film can be processed into an organic film, an inorganic film, and an organic-inorganic composite film, or can be treated with other insulating film-forming agents.

[0119] Hereinafter, the present invention will be described in further detail by way of examples. However, the following examples are only for illustrating the present invention, and the present invention is not limited to the following examples.

[0120] Example 1

[0121] Manufacture a slab containing the components shown in Tables 1 and 2 and the balance of Fe and inevitable impurities. The slab is heated to 1200 °C and hot-rolled to a thickness of 2.5 mm. After the hot-rolled sheet is heated to a temperature of 1070 °C, water cooling is then carried out. After pickling the steel material subjected to the hot-rolled sheet annealing treatment in this way, it is cold-rolled at one time to a thickness of 0.5 mm. The cold-rolled steel sheet is held at a temperature of 1000 °C for 180 seconds for cold-rolled sheet annealing. The W15 / 50 iron loss (unit: W / kg), the average size of the composite precipitates, the number density, the average grain size, and the area fraction of grains of 10 μm to 100 μm of the inventive materials and comparative materials shown in Table 1 are shown in Table 2.

[0122] For the iron loss, specimens with a width of 60 mm × a length of 60 mm × 5 sheets are cut, and the iron loss of each specimen is measured in the rolling direction and the direction perpendicular to the rolling by a single-sheet tester, and the average value is represented.

[0123] For the grain size and distribution, measurement is carried out using SEM-EBSD.

[0124]

Table 1

[0125]

[0126]

Table 2

[0127]

[0128]

Table 3

[0129]

[0130] As shown in Tables 1 to 3, when the steel composition is appropriately adjusted, it can be confirmed that the average grain diameter is appropriately adjusted and excellent iron loss is achieved.

[0131] Comparative Material 1 contains an excessive amount of C, so a large amount of carbides are generated, and thus the grains do not grow properly, and it can be confirmed that the magnetism is poor.

[0132] Comparative Material 2 and Comparative Material 3 do not contain an appropriate amount of Si, so the phase transformation is not appropriately controlled, the average grain diameter is not appropriately controlled, and the grain area fraction of 10 to 100 μm is also less than 80%, and it can be confirmed that the magnetism is poor.

[0133] Comparative Material 4 and Comparative Material 5 do not contain an appropriate amount of Mn, so the phase transformation is not appropriately controlled, the average grain diameter is not appropriately controlled, and the grain area fraction of 10 to 100 μm is also less than 80%, and it can be confirmed that the magnetism is poor.

[0134] Comparative Material 6 and Comparative Material 7 do not contain an appropriate amount of Al. In particular, Comparative Material 6 has poor magnetism due to too little Al, while Comparative Material 7 contains an excessive amount of Al exceeding the appropriate amount, and it is estimated that excessive Al nitrides will be formed, inhibiting grain growth, and thus the grains will not form properly, and it can be confirmed that the magnetism is poor.

[0135] Comparative Materials 8 to 15 do not contain an appropriate amount of Na, and the precipitates do not precipitate properly, so the grains do not grow properly, and it can be confirmed that the magnetism is poor.

[0136] The present invention can be implemented in various different ways and is not limited to the above embodiments. Those of ordinary skill in the technical field to which the present invention pertains can understand that the present invention can be implemented in other specific ways without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above embodiments are exemplary in all aspects and not restrictive.

Claims

1. An non-oriented electrical steel sheet, wherein, by weight%, the non-oriented electrical steel sheet contains 0.2% to 4.0% of Si, 0.05 to 1% of Mn, 0.005 to 2.0% of Al and 0.001 to 0.1% of Na, and the balance contains Fe and inevitable impurities.

2. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains Cu of 0.2% by weight or less and excluding 0% by weight, and Sn of 0.1% by weight or less and excluding 0% by weight.

3. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains one or more of C of 0.005% by weight or less and excluding 0% by weight, N of 0.01% by weight or less and excluding 0% by weight, and S of 0.01% by weight or less and excluding 0% by weight.

4. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains one or more of Ti of 0.005% by weight or less and excluding 0% by weight, Nb of 0.005% by weight or less and excluding 0% by weight, and V of 0.005% by weight or less and excluding 0% by weight.

5. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains one or more of Mo of 0.1% by weight or less and excluding 0% by weight, Ni of 0.1% by weight or less and excluding 0% by weight, Cr of 0.1% by weight or less and excluding 0% by weight, and P of 0.1% by weight or less and excluding 0% by weight.

6. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains one or more of Bi of 0.2% by weight or less and excluding 0% by weight, Pb of 0.2% by weight or less and excluding 0% by weight, Ge of 0.2% by weight or less and excluding 0% by weight, and As of 0.2% by weight or less and excluding 0% by weight.

7. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet further contains one or more of Sb of 0.06% by weight or less and excluding 0% by weight, Zn of 0.01% by weight or less and excluding 0% by weight, B of 0.005% by weight or less and excluding 0% by weight, Ca of 0.005% by weight or less and excluding 0% by weight, Mg of 0.005% by weight or less and excluding 0% by weight, and Zr of 0.005% by weight or less and excluding 0% by weight.

8. The non-oriented electrical steel sheet according to claim 1, wherein, the non-oriented electrical steel sheet contains one or more of Cu sulfide, Mn sulfide, Al nitride and their composite precipitates with a particle size of 5 nm to 1000 nm.

9. The non-oriented electrical steel sheet according to claim 8, wherein, The number density of one or more of Cu sulfide, Mn sulfide, Al nitride, and their composite precipitates with a particle size of 5 nm to 1000 nm is 0.01 particles / μm 2 to 20 particles / μm 2 .

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

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

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

13. A method for manufacturing a non-oriented electrical steel sheet, comprising: a step of hot rolling a slab to produce a hot-rolled sheet, wherein, by weight %, the slab contains 0.2% to 4.0% of Si, 0.05 to 1% of Mn, 0.005 to 2.0% of Al, and 0.001 to 0.1% of Na, and the balance contains Fe and inevitable impurities; a step of 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 manufacturing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains Cu of 0.2% by weight or less and excluding 0% by weight, and Sn of 0.1% by weight or less and excluding 0% by weight.

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

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

17. The method for manufacturing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more of Mo of 0.1% by weight or less and excluding 0% by weight, Ni of 0.1% by weight or less and excluding 0% by weight, Cr of 0.1% by weight or less and excluding 0% by weight, and P of 0.1% by weight or less and excluding 0% by weight.

18. The method for manufacturing a non-oriented electrical steel sheet according to claim 13, wherein the slab further contains one or more of Bi of 0.2% by weight or less and excluding 0% by weight, Pb of 0.2% by weight or less and excluding 0% by weight, Ge of 0.2% by weight or less and excluding 0% by weight, and As of 0.2% by weight or less and excluding 0% by weight.

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

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

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

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