Non-oriented electrical steel sheet and method of manufacturing the same

Abstract

According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight%,: Si: 0.1 to 4.5%, Al: 0.001 to 2.0%, Mn: 0.01 to 2.0%, S: less than 0.0100% and excluding 0%, Cu: 0.01 to 0.08%, P: 0.08 to 0.10%, Ca: less than 0.005% and excluding 0%, and Ti: less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities, and the total content of Ca and Ti being more than 0.0010% by weight.

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 excellent magnetic properties are obtained even when the steel composition contains a large amount of sulfur, by using scrap iron to manufacture the slab. Background Technology

[0002] Non-oriented electrical steel sheets are mainly used in motors that convert electrical energy into mechanical energy. To achieve high efficiency in the energy conversion process, non-oriented electrical steel sheets need to have excellent magnetic properties. In particular, with the increasing attention paid to environmentally friendly vehicles powered by electric motors rather than internal combustion engines, the demand for non-oriented electrical steel sheets as materials for drive motor cores is increasing. Therefore, non-oriented electrical steel sheets with excellent magnetic properties and strength are required.

[0003] The magnetic properties of non-oriented electrical steel sheets are primarily evaluated using iron loss and magnetic flux density. Iron loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization achieved under a specific magnetic field. Lower iron loss allows for the manufacture of more energy-efficient motors under the same conditions; higher magnetic flux density enables motor miniaturization or reduces copper losses. Therefore, by using non-oriented electrical steel sheets with low iron loss and high magnetic flux density, drive motors with excellent efficiency and torque can be manufactured, thereby improving the driving range and output power of environmentally friendly vehicles.

[0004] Depending on the operating conditions of the motor, the characteristics of the non-oriented electrical steel sheet to be considered will also change. To evaluate the characteristics of non-oriented electrical steel sheets used in motors, a widely adopted standard is the iron loss (W15 / 50) under a 1.5T magnetic field at a commercial frequency of 50Hz. However, in non-oriented electrical steel sheets with a thickness of less than 0.35mm used in environmentally friendly automotive drive motors, since low magnetic fields of 1.0T or lower and magnetic characteristics at high frequencies above 400Hz are often very important, the iron loss W is typically used instead. 10 / 400 To evaluate the properties of non-oriented electrical steel sheets.

[0005] On the other hand, due to the recent impact of global warming, we are currently facing a severe climate crisis, and "carbon neutrality" actions aimed at reducing carbon emissions are receiving high attention worldwide. In the steel industry, technologies are being developed to reduce the use of molten iron from traditional blast furnaces, which emit high levels of carbon, by replacing it with scrap iron, which emits no carbon during the manufacturing process. However, scrap iron contains a large amount of impurities such as sulfur (S), which degrades magnetic properties, thus posing a problem of deteriorating the magnetic properties of electrical steel sheets.

[0006] When the magnetism of electrical steel plates deteriorates, the energy efficiency of motors or small transformers decreases, requiring more electrical energy. This ultimately leads to the additional operation of coal-fired power plants that use fossil fuels, resulting in an increase in carbon emissions during the power generation process.

[0007] When non-oriented electrical steel sheets undergo reheating heat treatment, the temperature difference between the contact and non-contact areas of the skid leads to uneven formation of precipitates, which in turn causes deviations in magnetic properties. As a method to solve this problem, the prior art provides a method of adding rare earth metals to form oxysulfides, thereby neutralizing the magnetic degradation caused by sulfur and causing Ti precipitates to recrystallize on the oxysulfides to solve the magnetic degradation problem. However, it does not provide a solution to solve the magnetic degradation problem caused by a large amount of sulfur.

[0008] Furthermore, although a method has been proposed to control the composition of Ti, C, N, Mn, and S to form spherical (Mn,Cu, Ti)S sulfides with Ti and Mn, thereby suppressing the formation of fine Ti inclusions and increasing coarse inclusions, thus solving the magnetic degradation problem, no solution has been provided that can solve the magnetic degradation problem caused by a large amount of S.

[0009] Furthermore, although a method has been proposed to improve the magnetic properties in the rolling direction by adjusting the Ca and S content in the steel composition to induce CaS precipitation to improve grain growth, and then performing leveling rolling after final annealing, no solution has been provided to address the problems caused by the large amount of S that adversely affects the magnetism.

[0010] As mentioned above, research on magnetic enhancement methods is urgently needed for steel components containing a large amount of sulfur. Summary of the Invention

[0011] (a) Technical problems to be solved One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, which obtains excellent magnetic properties even when the steel composition contains a large amount of sulfur by using scrap iron to manufacture the slab.

[0012] (II) Technical Solution According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight%, 0.1 to 4.5% Si, 0.001 to 2.0% Al, 0.01 to 2.0% Mn, 0.01 to 2.0% S, less than 0.0100% and excluding 0%, Cu, 0.01 to 0.08% P, 0.08 to 0.10% Ca, less than 0.005% and excluding 0%, and Ti, less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities, and the total content of Ca and Ti being more than 0.0010% by weight.

[0013] According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 1.

[0014] [Formula 1] 0.28 ≤ [P] 1 / 2 × ([Cu] × [P] 1 / 2 + 1) ≤ 0.32 In Equation 1, [P] and [Cu] represent the contents (by weight%) of P and Cu, respectively.

[0015] According to one embodiment of the non-oriented electrical steel sheet of the present invention, the number density of sulfides with a particle size of 0.1 to 0.5 μm or less can be 5 to 33 particles / mm. 2 .

[0016] According to an embodiment of the present invention, the amount of sulfides containing one or more of Ca and Ti in all sulfides can be from 5% to 90%.

[0017] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of C: less than 0.005% by weight and excluding 0% and N: less than 0.0100% by weight and excluding 0%.

[0018] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

[0019] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of the following: Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05% and excluding 0%.

[0020] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of the following: Mo: less than 0.05% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

[0021] According to one embodiment of the present invention, the average grain size of the grains in the steel sheet can be from 15.0 to 80.0 μm.

[0022] A method for manufacturing a 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 steel sheet, wherein the slab comprises, by weight %, Si: 0.1 to 4.5%, Al: 0.001 to 2.0%, Mn: 0.01 to 2.0%, S: less than 0.0100% and excluding 0%, Cu: 0.01 to 0.08%, P: 0.08 to 0.10%, Ca: less than 0.005% and excluding 0%, and Ti: less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities; a step of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0023] In the hot-rolled steel sheet manufacturing process, the coiling temperature can satisfy Equation 2.

[0024] [Equation 2] [CT] ≥ 705+(63546 × [Cu] × [P]) 1 / 2 In Equation 2, [CT] is the winding temperature (°C), and [Cu] and [P] are the contents of Cu and P in the slab (by weight %), respectively.

[0025] The slab may further include one or more of C: less than 0.005% by weight and excluding 0% and N: less than 0.0100% by weight and excluding 0%.

[0026] The slab may further contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

[0027] The slab may further comprise one or more of the following: Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05% and excluding 0%.

[0028] The slab may further contain one or more of the following: Mo: less than 0.05% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

[0029] The slab can be manufactured using less than 80% by weight of blast furnace iron and more than 20% by weight of scrap iron.

[0030] (III) Beneficial Effects According to one embodiment of the present invention, the amount of carbon generated during the manufacturing process can be reduced by using scrap iron.

[0031] According to one embodiment of the present invention, the non-oriented electrical steel sheet has both excellent magnetic flux density and high-frequency iron loss.

[0032] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention can help manufacture environmentally friendly automotive motors, high-efficiency home appliance motors, and ultra-high-end motor cores. Attached Figure Description

[0033] Figure 1 The results are from SEM analysis of the sulfides in the invention material 18.

[0034] Figure 2 The results are from SEM analysis of sulfides in comparative material 49. Detailed Implementation

[0035] The terms “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. Therefore, without departing from the scope of the invention, a “first” part, component, region, layer, or section as described below may be referred to as a “second” part, component, region, layer, or section.

[0036] The technical terms used herein are for describing specific embodiments only and are not intended to limit the invention. Unless otherwise expressly stated herein, the singular forms used also include the plural forms. The word "comprising" as used in the specification is intended to describe the presence of a particular feature, region, integer, step, operation, element, and / or component, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0037] When referring to a part as "above" or "on top of" another part, it can be directly above or on top of the other part, or there can be other parts in between. Conversely, when referring to a part as "directly above" another part, there are no other parts in between.

[0038] In addition, unless otherwise specified, % refers to weight, 1 ppm is 0.0001 weight.

[0039] In one embodiment of the invention, further including an additional element means replacing the iron (Fe) in the balance with an equal amount of the corresponding additional element.

[0040] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries shall be interpreted as having meanings consistent with relevant technical literature and current disclosure, and shall not be interpreted as having ideal or overly formal meanings unless otherwise defined.

[0041] The embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in many different ways and is not limited to the embodiments described.

[0042] According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight%, Si: 0.1 to 4.5%, Al: 0.001 to 2.0%, Mn: 0.01 to 2.0%, S: less than 0.0100% and excluding 0%, Cu: 0.01 to 0.08%, P: 0.08 to 0.10%, Ca: less than 0.005% and excluding 0%, and Ti: less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities.

[0043] First, the reasons for the compositional restrictions on non-oriented electrical steel sheets will be explained.

[0044] Si: 0.100 to 4.500% by weight Silicon (Si) increases the resistivity of the material, thereby reducing iron loss. If too little Si is added, the effect on improving iron loss may be insufficient. If too much Si is added, the material becomes more brittle, leading to a sharp decline in rolling productivity and potentially exacerbating the deterioration of magnetic flux density. Therefore, Si can be present in quantities from 0.100 to 4.500 wt%. More specifically, it can be present in quantities from 0.100 to 2.500 wt%. More specifically, it can be present in quantities from 0.100 to 1.000 wt%. More specifically, it can be present in quantities from 0.100 to 0.500 wt%.

[0045] Al: 0.0010 to 2.000% by weight The role of aluminum (Al) is to increase the resistivity of the material to reduce iron loss and to reduce magnetic anisotropy to decrease magnetic deviation in the rolling direction and perpendicular to the rolling direction. If too little Al is added, it is difficult to ensure sufficient resistivity and may be difficult to achieve adequate improvement in iron loss. If too much Al is added, the magnetic flux density will deteriorate and may cause problems in all processes such as steelmaking and continuous casting, resulting in a significant decrease in productivity. Therefore, Al can be contained from 0.0010 to 2.000% by weight. More specifically, Al can be contained from 0.0050 to 1.000% by weight. More specifically, Al can be contained from 0.0050 to 0.300% by weight.

[0046] Mn: 0.010 to 2.000% by weight Manganese (Mn) increases the resistivity of materials, thereby improving iron loss. Furthermore, Mn reacts with sulfur (S) to form Mn sulfides, and at high temperatures reacts with nitrogen, Al, and Si to form (Al, Si, Mn) nitrides, which also inhibit grain growth. If the Mn content is too low, sufficient iron loss improvement is difficult to achieve; if too much Mn is added, the magnetic flux density decreases, and fine MnS particles precipitate excessively, hindering domain movement and potentially worsening both magnetic flux density and iron loss. Therefore, Mn can be present from 0.010 to 2.000% by weight. More specifically, Mn can be present from 0.010 to 1.000% by weight. More specifically, Mn can be present from 0.010 to 0.100% by weight.

[0047] S: less than 0.0100% by weight Sulfur (S) is an element that reacts with Cu, Mn, and other elements in steel to precipitate sulfides. The finer and more abundant the sulfide precipitates, the stronger the effect of hindering magnetic domain movement, thus resulting in a decrease in magnetic properties. If the S content is too high, sulfides will precipitate excessively, and the effect of reducing the resistance to magnetic domain movement caused by the coarsening of sulfides may be weakened. Therefore, S can be contained in amounts of 0.0100% by weight or less. More specifically, it can be contained in amounts of 0.0005% to 0.0100% by weight. More specifically, it can be contained in amounts of 0.0010% to 0.0100% by weight.

[0048] Cu: 0.010 to 0.080% by weight Like Mn, copper (Cu) reacts with sulfur (S) to precipitate sulfides. If the Cu content is too low, Mn sulfides will increase, potentially worsening iron loss. If the Cu content is moderate, Mn sulfides will decrease, and Cu sulfides will form larger sulfides than Mn sulfides, thus improving iron loss. If the Cu content is too high, Cu sulfides will increase excessively, potentially further worsening iron loss. Therefore, Cu can be present in quantities from 0.010 to 0.080% by weight. More specifically, Cu can be present in quantities from 0.010 to 0.080% by weight.

[0049] P: 0.080 to 0.100% by weight Phosphorus (P) is a known alloying element that improves the texture of electrical steel sheets and also enhances strength through grain boundary segregation and solid solution strengthening. When added in appropriate amounts, it can improve magnetic and mechanical properties. On the other hand, excessive P content increases the brittleness of the material, leading to poor rolling operability. Therefore, P content is typically between 0.0800 and 0.1000% by weight.

[0050] According to an embodiment of the present invention, the non-oriented electrical steel sheet can satisfy the following formula 1.

[0051] [Formula 1] 0.28 ≤ [P] 1 / 2 × ([Cu] × [P] 1 / 2 + 1) ≤ 0.32 In Equation 1, [P] and [Cu] represent the contents (by weight%) of P and Cu, respectively.

[0052] When Cu and P are included to satisfy Equation 1, the magnetic and mechanical properties can be improved simultaneously.

[0053] Ca: less than 0.0050% by weight If calcium (Ca) is present in appropriate amounts, the fine sulfides in sulfur-containing steel components will become slightly coarser, which helps grain growth and thus improves magnetic quality. However, if too much Ca is added, the magnetic properties may deteriorate. More specifically, Ca can be present in amounts from 0.0003 to 0.0050% by weight.

[0054] Ti: less than 0.0050% by weight If a small amount of titanium (Ti) is present, the sulfides in the sulfur-containing steel composition will become more uniform, resulting in improved magnetic properties. This is due to the earlier precipitation of Ti sulfides compared to Cu or Ca sulfides. However, if the Ti content is too high, the magnetic properties may deteriorate. More specifically, Ti can be present in amounts from 0.0003 to 0.0050% by weight.

[0055] In one embodiment of the invention, by including Ti and Ca, the sulfides become more uniform in the S-containing steel composition, thereby improving the magnetic properties. However, to achieve this effect, it is necessary to include Ti and Ca in a total content of 0.0010% by weight or more. More specifically, the total content of Ti and Ca can be from 0.0010 to 0.0100% by weight.

[0056] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of C: less than 0.005% by weight and excluding 0% and N: less than 0.0100% by weight and excluding 0%.

[0057] C: less than 0.0050% by weight Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, hindering grain boundary or magnetic wall movement and potentially leading to deterioration of magnetic properties. More specifically, C may contain 0.0001 to 0.0030% by weight.

[0058] N: less than 0.0100% by weight Nitrogen (N) is characterized by reacting with Al, Si, and Cr to form nitrides. These nitrides hinder grain growth, increase the grain boundary fraction, thereby deteriorating hysteresis losses, and may also impede the movement and rotation of magnetic domains, thus deteriorating eddy current losses. More specifically, N may contain 0.0001 to 0.0085% by weight.

[0059] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

[0060] Sn and Sb Tin (Sn) and antimony (Sb) segregate at grain boundaries during the initial stage of final recrystallization annealing, thereby inhibiting the development of {111} orientation that leads to magnetic degradation. Excessive addition of Sn and Sb hinders the recovery and growth of coarse, extended banded structures, potentially causing surface quality deterioration. Therefore, one or more of Sn and Sb can be further added within the aforementioned range. More specifically, it may contain 0.005 to 0.200 wt% Sn or 0.005 to 0.200 wt% Sb.

[0061] Bi, Pb, Ge and As When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are added, they segregate at grain boundaries, alleviating stress concentration at grain boundaries during cold rolling and suppressing stress during recrystallization annealing, a subsequent process. <111> / / Recrystallization of ND-oriented grains increases magnetic flux density. Adding appropriate amounts of these elements can achieve the aforementioned effects, but excessive amounts can lead to excessive segregation, inhibiting grain growth and potentially worsening magnetic flux density and iron loss.

[0062] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of the following: Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

[0063] Cr: 0.01 to 0.50% by weight Chromium (Cr) plays a role in increasing resistivity to improve iron loss. If too little Cr is added, the resistivity increase may be insufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr can be contained in amounts from 0.050 to 0.20% by weight.

[0064] Ni: less than 0.05% by weight Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, Ni may contain 0.001 to 0.03% by weight.

[0065] Zn: less than 0.01% by weight If the zinc (Zn) content is too high, it will act as an impurity and may lead to a decrease in magnetic properties. Therefore, Zn can be added further within the range mentioned above. More specifically, Zr can be contained in amounts from 0.001 to 0.005% by weight.

[0066] Co: less than 0.05% by weight Cobalt (Co) does not form fine-sized precipitates that reduce the magnetism of steel sheets, but it increases high-temperature strength and may lead to poor shape of hot-rolled steel coils.

[0067] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further comprise one or more of the following: Mo: less than 0.05% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.0050% by weight and excluding 0%; Te: less than 0.0100% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

[0068] Mo: less than 0.050% by weight If excessive molybdenum (Mo) is added, it inhibits the segregation of segregating elements, which may reduce the texture improvement effect. Therefore, Mo can be contained in amounts of 0.03 wt% or less, with no particular lower limit, but due to its function of improving texture by segregating at the surface and grain boundaries, Mo can be contained in amounts of 0.001 wt% or more. More specifically, Mo can be contained in amounts of 0.001 to 0.010 wt%. More specifically, Mo can be contained in amounts of 0.005 to 0.010 wt%.

[0069] B: Less than 0.0050% by weight If excessive boron (B) is added, it may lead to deterioration of the magnetic properties of the steel by forming inclusions. Therefore, B can be contained in amounts up to 0.005% by weight, with no particular lower limit, but considering the cost of steelmaking, it can be set to 0.0001% by weight. More specifically, B can be contained in amounts from 0.0001 to 0.0030% by weight.

[0070] V: less than 0.0050% by weight Vanadium (V) has a strong tendency to form precipitates in steel, creating fine carbides or nitrides within the base metal. This inhibits grain growth and magnetic wall movement, leading to deterioration of iron losses. Therefore, the V content can be below 0.0050% by weight, with no particular lower limit, but considering steelmaking costs, it can be as low as 0.0003% by weight. In other words, V can be present from 0.0003 to 0.0050% by weight. More specifically, V can be present from 0.0003 to 0.0030% by weight.

[0071] Nb: less than 0.0050% by weight Niobium (Nb) has a strong tendency to form precipitates in steel, creating fine carbides or nitrides within the base metal. This inhibits grain growth and magnetic wall movement, leading to deterioration of iron losses. Therefore, the Nb content can be below 0.0050% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0003% by weight. That is, Nb can be present from 0.0003 to 0.0050% by weight. More specifically, Nb can be present from 0.0003 to 0.0030% by weight.

[0072] Zr: less than 0.0050% by weight Excessive addition of zirconium (Zr) can degrade magnetic properties in steel by forming inclusions. Therefore, Zr content can be below 0.005% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0001% by weight. That is, Zr content can range from 0.0001 to 0.0050% by weight. More specifically, it can range from 0.0005 to 0.0030% by weight.

[0073] Te: less than 0.0100% by weight Tellurium (Te) diffuses into the oxide layer on the surface of hot-rolled steel coils, thereby increasing the coefficient of friction between the oxide layer and the rolling mill rolls. It also accumulates in the lower part of the oxide layer, increasing hardness. Therefore, tellurium (Te) can be added to allow the oxide layer, which breaks off during rolling, to detach rather than be pressed into the base material. If the amount of Te added is too small, its effect may be negligible. If too much Te is added, the oxide layer is easily detached, and the base material will directly contact the rolling mill rolls, thus weakening the aforementioned effect. Furthermore, during cold rolling, excessive deformation bands may form inside the steel sheet, potentially leading to the development of a texture that is detrimental to magnetism. More specifically, tellurium can be present in amounts from 0.0001 to 0.007% by weight.

[0074] Mg: less than 0.0050% by weight Magnesium (Mg) is an element that primarily combines with sulfur to form sulfides, which can affect the oxide layer on the surface of the base iron. Therefore, Mg can be contained in amounts up to 0.0050% by weight, with no particular lower limit, but considering steelmaking costs, it can be set at 0.0001% by weight. That is, Mg can be contained from 0.0001 to 0.0050% by weight. More specifically, Mg can be contained from 0.0005 to 0.0030% by weight.

[0075] The balance includes Fe and unavoidable impurities. Regarding unavoidable impurities, these are impurities introduced during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets, which are well known in the art and therefore omitted in detail. In one embodiment of the invention, the addition of other elements besides the above-described alloy components is not excluded, and multiple elements may be included without impairing the technical concept of the invention. In cases where additional elements are further included, the corresponding amount replaces the iron (Fe) in the balance.

[0076] In one embodiment of the invention, even if the steel contains a large amount of sulfur (S), the magnetic degradation caused by S can be minimized by appropriately precipitating sulfides. Specifically, the number density of sulfides with a particle size of 0.1 to 0.5 μm can be 5.0 to 33.0 particles / mm². 2 Sulfides with a particle size of 0.1 to 0.5 μm have a significant detrimental effect on magnetism. This can be mitigated by controlling the number density to 5.0 to 33.0 particles / mm. 2 This minimizes the adverse effects on magnetism. More specifically, the number density of sulfides with a particle size of 0.1 to 0.5 μm can be 5.0 to 30.0 particles / mm. 2 .

[0077] Sulfides refer to substances formed by the agglomeration of sulfur (S) in particle form, meaning the portion with a sulfur content significantly higher than that of the steel plate matrix. In one embodiment of this invention, when measured using TEM or SEM, substances with an agglomerated particle size of at least 1 nm and a sulfur content significantly higher than that of the steel plate matrix are defined as sulfides. There are no particular limitations on the reference cross section for sulfide measurement, but it can be the normal plane (TD plane) of the rolling direction perpendicular to the steel plate (TD direction). The particle size of the sulfide refers to the diameter of a virtual circle with an area equal to the area occupied by the sulfide. The average particle size of the sulfide can be calculated by analyzing images obtained through TEM, SEM, and EDS using an image analysis program. To reduce bias caused by different measurement locations, for samples with an area of ​​5 mm × 5 mm or more, non-overlapping locations can be measured at 10 μm × 10 μm intervals, and the average value relative to the total amount of sulfides can be calculated.

[0078] Besides sulfur (S), sulfides can also contain one or more of the elements Ca, Mn, Al, and Cu. In addition to the elements mentioned above, they can also form complex precipitates with C, N, and O. That is, sulfides can contain precipitates represented by (Ca, Mn, Al, Cu) and (S, C, N, O). In this case, (A, B) refers to individual or combined precipitates of A and B. More specifically, sulfides can contain one or more of CaS, MnS, and CuS.

[0079] According to one embodiment of the present invention, the amount of sulfides containing one or more of Ca and Ti in the total sulfides can be from 5% to 90%. The inclusion of Ca and Ti means that the Ca or Ti content is much higher than that of the matrix phase of the steel sheet. More specifically, it can contain more than 0.1% by weight of Ca and more than 0.1% by weight of Ti.

[0080] According to one embodiment of the present invention, the average grain size of the non-oriented electrical steel sheet can be from 15.0 to 80.0 μm. If the average grain size is too small, the iron loss may deteriorate due to excessive increase in hysteresis loss. If the average grain size is too large, the iron loss may deteriorate due to excessive increase in eddy current loss. More specifically, the average grain size of the steel sheet can be from 20.0 to 77.0 μm. The grain size can be measured at a thickness ranging from 1 / 4t to 3 / 4t relative to the total thickness t of the steel sheet. For the grain size, a virtual circle with the same area as the grain area is assumed, and the diameter of this circle is taken as the grain size. The average grain size can be measured by dividing the area of ​​the object being measured by the number of grains present within that area.

[0081] According to one embodiment of the present invention, the non-oriented electrical steel sheet exhibits excellent magnetic flux density and excellent iron loss. Specifically, according to one embodiment of the present invention, the non-oriented electrical steel sheet has excellent iron loss (W15 / 50 The magnetic flux density (B) can be below 6.00 W / kg, and the magnetic flux density (B) can be below 6.00 W / kg. 50 It can be 1.75T or more.

[0082] B 50 It refers to the magnetic flux density induced under a magnetic field of 5000 A / m.

[0083] W 15 / 50 The iron loss is calculated when the magnetic flux density is 1.5T under 50Hz excitation.

[0084] In one embodiment of the present invention, B 50 and W 15 / 50 This represents the average value obtained by averaging the values ​​measured in the rolling direction (RD direction) and the rolling perpendicular direction (TD direction). More specifically, for a non-oriented electrical steel sheet according to an embodiment of the present invention, its iron loss (W) 15 / 50 The flux density (B) can be 3.50 to 5.50 W / kg. 50 The thickness can range from 1.76T to 1.85T. The standard thickness can be 0.5mm.

[0085] A method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention includes: hot rolling a slab to manufacture a hot-rolled steel sheet; cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0086] Each step is explained in detail below.

[0087] First, the slab is hot-rolled.

[0088] The alloy composition of the slab has already been described in the section on the alloy composition of non-oriented electrical steel sheets, so a repeating explanation is omitted. During the manufacturing process of non-oriented electrical steel sheets, the alloy composition remains substantially unchanged; therefore, the alloy composition of non-oriented electrical steel sheets and slabs is essentially the same.

[0089] Specifically, by weight percent, the slab comprises Si: 0.1 to 4.5%, Al: 0.001 to 2.0%, Mn: 0.01 to 2.0%, S: less than 0.0100% and excluding 0%, Cu: 0.01 to 0.08%, P: 0.08 to 0.10%, Ca: less than 0.005% and excluding 0%, and Ti: less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities.

[0090] Other additional elements have already been described in the alloy composition of non-oriented electrical steel sheets, so repeated descriptions are omitted.

[0091] For slabs, they can be manufactured using less than 80% by weight of blast furnace iron and more than 20% by weight of scrap iron. The sulfur content in scrap iron is much higher than that in blast furnace iron, and due to this sulfur, sulfides and other precipitates may precipitate in large quantities. In one embodiment of the invention, by adding an appropriate amount of Ca and properly adjusting the particle size of the precipitates, the adverse effects on magnetism can be reduced, and uniform grain growth can be achieved, thereby improving magnetism.

[0092] Before hot rolling, the slab can be heated. The heating temperature of the slab is not limited, but it can be heated to below 1200°C. If the slab is heated to too high a temperature, precipitates such as AlN and MnS present in the slab will re-dissolve and may precipitate finely during subsequent hot rolling and annealing, thereby inhibiting grain growth and reducing magnetism.

[0093] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be from 1.0 to 4.5 mm. In one embodiment of the invention, a pre-cold rolling step may be additionally included before cold rolling, so that even if the thickness of the hot-rolled sheet is relatively thick, a non-oriented electrical steel sheet of appropriate thickness can be produced. More specifically, the thickness of the hot-rolled sheet can be from 1.5 to 3.5 mm.

[0094] The hot-rolled sheet manufacturing process may include a finishing rolling step at a temperature above 850°C.

[0095] If the hot-rolled finishing temperature is too low, the rolling load will increase, leading to a decrease in hot-rolling operability. Additionally, hot-rolled steel sheets retain a significant amount of deformed microstructure, which also contributes to the increased rolling load during subsequent pre-cooling rolling processes. Furthermore, intermediate annealing promotes the formation of microstructures from the deformed microstructure. <111> The recrystallization of ND-oriented grains leads to a decrease in magnetic flux density. Therefore, the higher the hot-rolling finishing temperature, the better; more specifically, finishing rolling is preferably performed at a temperature of 860 to 1000°C.

[0096] In the hot-rolled sheet manufacturing process, the coiling temperature can satisfy Equation 2.

[0097] [Equation 2] [CT] ≥ 705+(63546 × [Cu] × [P]) 1 / 2 In Equation 2, [CT] is the winding temperature (°C), and [Cu] and [P] are the contents of Cu and P in the slab (by weight %), respectively.

[0098] When the winding temperature is adjusted as in Equation 2, the amount of sulfides that cause iron loss deterioration due to the impediment of magnetic domain movement will decrease.

[0099] After manufacturing hot-rolled steel sheets and before cold rolling, hot-rolled sheets can be annealed. The soaking temperature during annealing can be between 800 and 1200°C. If the annealing temperature is too low, recrystallization will not occur or the recrystallized structure will grow finely, resulting in a weak increase in magnetic flux density; if the annealing temperature is too high, the magnetic properties will decrease, and the sheet shape may deform, potentially worsening rolling operability. More specifically, the temperature range can be between 830 and 1170°C. The soaking time can be between 15 and 180 seconds. Annealing can also be omitted for hot-rolled sheets if necessary.

[0100] Returning to the description of the manufacturing method for non-oriented electrical steel sheets, hot-rolled steel sheets are cold-rolled to produce cold-rolled sheets. At this stage, cold rolling can be performed with a reduction rate of 40% to 95%. If the reduction rate is too low, the accumulated deformation energy in the rolled steel sheet is small, making recrystallization difficult in subsequent annealing processes. This results in residual rolled microstructure, potentially causing problems in improving magnetic flux density and iron loss. On the other hand, if the reduction rate is too high, it hinders the subsequent annealing process from promoting... <111> / / Recrystallization of ND-oriented grains, resulting in finer grains, may lead to decreased magnetic flux density and increased iron loss. More specifically, the reduction rate can be 40% to 70%. The thickness can be 0.1 mm to 0.7 mm. More specifically, it can be 0.15 mm to 0.50 mm. For the cold rolling step, a tandem cold rolling mill that uses multiple mill stands for continuous cold rolling of the steel sheet can be used, or a reversible rolling mill that uses 12 or more rolls for discontinuous cold rolling can be used.

[0101] Next, the cold-rolled sheet is annealed.

[0102] The annealing step of the cold-rolled sheet can be performed at a temperature of 800°C to 1100°C for 60 to 300 seconds. In one embodiment of the invention, although annealing is performed at a higher temperature, excessive grain growth is prevented due to appropriate sulfide precipitation, and the resulting deterioration of magnetic properties can be prevented. Furthermore, by performing annealing at a high temperature with appropriate sulfide precipitation, uniform grain growth can be achieved. If the annealing temperature is too low or the time is too short, grain growth cannot proceed sufficiently, and iron loss may deteriorate due to excessive increase in hysteresis loss. If the annealing temperature is too high or the time is too long, the grains grow too large, and iron loss may deteriorate due to excessive increase in eddy current loss. More specifically, the annealing step of the cold-rolled sheet can be performed at a temperature of 950°C to 1050°C for 120 to 240 seconds.

[0103] Following the annealing step of cold-rolled steel sheet, a further step of forming an insulating coating may be included to ensure the insulation and corrosion resistance of the steel sheet. Since the insulating coating is already well-known, specific details are omitted.

[0104] The present invention will be further described in detail below by way of examples. However, these examples are only for illustration and the present invention is not limited to the following examples.

[0105] Example 1 A slab containing the alloy composition specified in Tables 1 and 2, the balance of Fe, and unavoidable impurities is prepared, heated to 1200°C, and hot-rolled to a thickness of 2.5 mm. The hot-rolled steel sheet is then coiled at the coiling temperature specified in Table 3. The coiled steel is pickled and then cold-rolled to a thickness of 0.5 mm. Subsequently, the cold-rolled sheet is annealed at 1000°C for 180 seconds.

[0106] After processing the magnetic measurement sample, the iron loss W was measured. 15 / 50 and magnetic flux density B 50 The results are shown in Table 3 below.

[0107] For magnetic properties, Epstein specimens were prepared for various angles and measured using an Epstein tester. The average results in the rolling direction and the rolling perpendicular direction are summarized in Table 3 below.

[0108] The number density of sulfides with a particle size of 0.1 to 0.5 μm and the ratio of Ti to Ca sulfides were measured using a scanning electron microscope (SEM) in a 5 mm x 5 mm area at 10 μm x 10 μm intervals, and the results are summarized in Table 3.

[0109] The average grain size was measured using the intercept procedure based on ASTM standard E112-96, and the results are summarized in Table 3.

[0110] Table 1 Table 2 Table 3 As shown in Tables 1 to 3, for the embodiments in which the sulfide and grain size are appropriately formed by adjusting the steel composition, it can be confirmed that the iron loss and magnetic flux density are excellent.

[0111] On the other hand, steel grades 21 to 49 did not adequately contain P, Ca, and Ti, resulting in excessively fine or excessive sulfide formation, which in turn led to inadequate grain growth and reduced iron loss W. 10 / 400 and magnetic flux density B 50 The performance was poor.

[0112] Figure 1The results are from SEM analysis of the sulfides in the invention material 18. Figure 2 The results are from SEM analysis of sulfides in comparative material 49. Figure 1 It can be confirmed that coarse sulfides are appropriately formed; from Figure 2 It can be confirmed that multiple fine sulfides were formed.

[0113] This invention is not limited to the embodiments described above, and can be manufactured in various different ways. Those skilled in the art should understand that other specific methods can be used without altering the technical concept or essential features of the invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims

1. A non-oriented electrical steel sheet, wherein, By weight percent, the non-oriented electrical steel sheet comprises Si: 0.1 to 4.5%, Al: 0.001 to 2.0%, Mn: 0.01 to 2.0%, S: less than 0.0100% and excluding 0%, Cu: 0.01 to 0.08%, P: 0.08 to 0.10%, Ca: less than 0.005% and excluding 0%, and Ti: less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities. The combined content of Ca and Ti is 0.0010% by weight or more.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet satisfies the following formula 1. [Formula 1] 0.28 ≤ [P] 1 / 2 × ([Cu] × [P] 1 / 2 + 1) ≤ 0.32 In Equation 1, [P] and [Cu] represent the contents (by weight%) of P and Cu, respectively.

3. The non-oriented electrical steel sheet according to claim 1, wherein, The number density of sulfides with a particle size of 0.1 to 0.5 μm is 5 particles / mm. 2 Up to 33 / mm 2 the following.

4. The non-oriented electrical steel sheet according to claim 3, wherein, The total amount of sulfides containing one or more of Ca and Ti ranges from 5% to 90%.

5. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of C: less than 0.005% by weight and excluding 0% and N: less than 0.010% by weight and excluding 0%.

6. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

7. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05% and excluding 0%.

8. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Mo: less than 0.05% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

9. The non-oriented electrical steel sheet according to claim 1, wherein, The average grain size of the grains in the steel plate is 15 to 80 μm.

10. A method for manufacturing a non-oriented electrical steel sheet, comprising: The step of hot rolling a slab to produce a hot-rolled steel sheet, wherein the slab comprises, by weight %, Si: 0.1 to 4.5%, Al: 0.001 to 2.0%, Mn: 0.01 to 2.0%, S: less than 0.0100% and excluding 0%, Cu: 0.01 to 0.08%, P: 0.08 to 0.10%, Ca: less than 0.005% and excluding 0%, and Ti: less than 0.005% and excluding 0%, with the balance including Fe and unavoidable impurities; The steps of cold rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and The annealing step for the cold-rolled sheet.

11. The method for manufacturing non-oriented electrical steel sheet according to claim 10, wherein, In the hot-rolled steel sheet manufacturing step, the coiling temperature satisfies Equation 2. [Equation 2] [CT] ≥ 705 + (63546 x [Cu] x [P]) 1 / 2 In Equation 2, [CT] is the winding temperature (°C), and [Cu] and [P] are the contents of Cu and P in the slab (by weight %), respectively.

12. The method for manufacturing non-oriented electrical steel sheet according to claim 10, wherein, The slab further comprises one or more of C: less than 0.005% by weight and excluding 0% and N: less than 0.010% by weight and excluding 0%.

13. The method for manufacturing non-oriented electrical steel sheet according to claim 10, wherein, The slab further comprises one or more of Sn, Sb, Bi, Pb, Ge and As, with each or the total content being 0.005 to 0.200 by weight.

14. The method for manufacturing non-oriented electrical steel sheet according to claim 10, wherein, The slab further comprises one or more of the following: Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

15. The method for manufacturing non-oriented electrical steel sheet according to claim 10, wherein, The slab further comprises one or more of the following: Mo: less than 0.05% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

16. The method for manufacturing non-oriented electrical steel sheet according to claim 10, wherein, The slab is manufactured using less than 80% by weight of blast furnace iron and more than 20% by weight of scrap iron.

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