Non-oriented electrical steel sheet and method for manufacturing same

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention contains, in wt%, 2.6-4.5% of Si, 0.0005-2.5% of Al, 0.05-2.5% of Mn, 0.0051-0.0100% of S, and 0.0002-0.0100% of Ca, with the remainder comprising Fe and inevitable impurities.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[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, which exhibits excellent magnetic properties even when the steel composition contains a large amount of sulfur, by manufacturing a slab using iron scrap.

[0002] Non-oriented electrical steel is primarily used in motors that convert electrical energy into mechanical energy. This process requires excellent magnetic properties to achieve high efficiency. In particular, with the recent rise in eco-friendly vehicles powered by motors instead of internal combustion engines, demand for non-oriented electrical steel, used as a drive motor core material, is increasing. This demand is driven by the need for non-oriented electrical steel with both superior magnetic properties and strength.

[0003] The magnetic properties of non-oriented electrical steel are primarily assessed by core loss and magnetic flux density. Core loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density represents the degree of magnetization achieved under a specific magnetic field. Lower core loss allows for more energy-efficient motors under similar conditions, while higher flux density allows for smaller motors and reduced copper loss. Therefore, non-oriented electrical steel with low core loss and high flux density can be used to create drive motors with superior efficiency and torque, thereby improving the driving range and power output of eco-friendly vehicles.

[0004] The characteristics of non-oriented electrical steel sheets that must be considered also vary depending on the operating conditions of the motor. The general standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors is widely used as W15 / 50, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, in the case of non-oriented electrical steel sheets with a thickness of 0.35mm or less used in eco-friendly vehicle drive motors, magnetic characteristics are often important at low fields of 1.0T or less and high frequencies of 400Hz or higher, so W 10 / 400 The properties of non-oriented electrical steel sheets are often evaluated by iron loss.

[0005] Meanwhile, global warming has recently led to a severe climate crisis, and so-called carbon neutrality initiatives aimed at reducing carbon emissions are gaining traction worldwide. The steel industry is developing technologies to reduce carbon emissions during the manufacturing process by reducing the use of molten iron from conventional blast furnace operations, which emits large amounts of carbon, and replacing it with carbon-free steel scrap. However, steel scrap contains significant amounts of impurities such as sulfur, which degrades magnetism, leading to a deterioration in the magnetic properties of electrical steel sheets.

[0006] When the magnetism of electrical steel deteriorates, the energy efficiency of motors and small transformers decreases, requiring more electrical energy. Consequently, additional thermal power plants using fossil fuels are operated, which increases carbon emissions generated during the power generation process.

[0007] In order to solve the problem of magnetic property deviation by controlling the non-uniform formation of precipitates caused by the temperature difference between the area in contact with the skid and the area not in contact with the skid when performing slab reheating heat treatment of non-oriented electrical steel sheets, a method is provided to form oxysulfides by adding rare earth metals to neutralize the magnetic deterioration caused by S and to complexly precipitate Ti precipitates with oxysulfides to solve the magnetic deterioration problem. However, no method is provided to solve the problem of magnetic deterioration caused by containing a large amount of S.

[0008] In addition, a method was proposed to control the components of Ti, C, N, Mn, and S to form Ti together with Mn as a spherical (Mn, Cu, Ti)S sulfide, thereby suppressing the formation of fine Ti inclusions and increasing coarse inclusions to solve the problem of magnetic deterioration. However, no solution has been provided to solve the problem of magnetic deterioration caused by the inclusion of a large amount of S.

[0009] In addition, a method was proposed to improve grain growth by precipitating CaS by controlling the content of Ca and S in the steel composition and to improve magnetic properties in the rolling direction by performing skin pass rolling after final annealing. However, no solution was provided to solve the problem caused by a large amount of S that has a negative effect on magnetism.

[0010] In this way, research is needed on how to improve magnetism in steel compositions containing a large amount of S.

[0011] 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 exhibits excellent magnetic properties even when the steel composition contains a large amount of sulfur, by manufacturing a slab using iron scrap.

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 2.6 to 4.5%, Al: 0.0005 to 2.5%, Mn: 0.05 to 2.5%, S: 0.0051 to 0.0100%, and Ca: 0.0002 to 0.0100%, with the remainder being Fe and unavoidable impurities.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0014] [Formula 1]

[0015] 0.09 ≤ [Ca] / [S] ≤ 0.50

[0016] (However, in Equation 1, [Ca] and [S] represent the contents (weight%) of Ca and S, respectively.)

[0017] The average particle size of sulfides in the steel plate may be 1 to 10 μm.

[0018] Sulfides may contain one or more of Ca, Mn, Al, and Cu.

[0019] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.002 to 0.02 wt%, C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0020] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0021] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05% or less (excluding 0%).

[0022] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.05 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0023] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have an average grain size of 50 to 80 ㎛ within the steel sheet.

[0024] According to one embodiment of the present invention, a non-oriented electrical steel sheet has a core loss (W 10 / 400 ) is 10.5 W / Kg or less, and the magnetic flux density (B 50 ) may be 1.59T or more.

[0025]

[0026] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, Si: 2.6 to 4.5%, Al: 0.0005 to 2.5%, Mn: 0.05 to 2.5%, S: 0.0051 to 0.0100%, and Ca: 0.0002 to 0.0100%, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; 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.

[0027] Slavs can satisfy the following equation 1.

[0028] [Formula 1]

[0029] 0.09 ≤ [Ca] / [S] ≤ 0.50

[0030] (However, in Equation 1, [Ca] and [S] represent the contents (weight%) of Ca and S, respectively.)

[0031] The slab may further include at least one of P: 0.002 to 0.02 wt%, C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0032] The slab may further contain 0.005 to 0.200 wt% of each or a combination of one or more of Sn, Sb, Bi, Pb, Ge and As.

[0033] The slab may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05% or less (excluding 0%).

[0034] The slab may further include at least one of Mo: 0.05 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0035] The slab can be manufactured using 80 wt% or less of molten iron and 20 wt% or more of iron scrap.

[0036] The cracking temperature in the cold rolled sheet annealing step can be 900 to 1100°C.

[0037]

[0038] One embodiment of the present invention can reduce carbon generated during the manufacturing process by manufacturing using iron scrap.

[0039] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and high-frequency iron loss at the same time.

[0040] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the manufacture of eco-friendly automobile motors, high-efficiency home appliance motors, and super-premium motor cores.

[0041] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0043] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0044] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0045] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0046] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0047] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0048]

[0049] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 2.6 to 4.5%, Al: 0.0005 to 2.5%, Mn: 0.05 to 2.5%, S: 0.0051 to 0.0100%, and Ca: 0.0002 to 0.0100%, with the remainder being Fe and unavoidable impurities.

[0050] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0051]

[0052] Si: 2.6 to 4.5 wt%

[0053] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss. If too little Si is added, the iron loss improvement effect may be insufficient. If too much Si is added, the material becomes brittle, leading to a sharp decline in rolling productivity and a significant deterioration in magnetic flux density. Therefore, the Si content may be 2.6 to 4.5 wt%. More specifically, it may be 2.8 to 4.3 wt%. Even more specifically, it may be 3.0 to 4.0 wt%.

[0054]

[0055] Al: 0.0005 to 2.5 wt%

[0056] Aluminum (Al) acts as an element that increases the resistivity of the material, thereby lowering iron loss and reducing magnetic anisotropy, thereby reducing magnetic deviation in the rolling direction and the direction perpendicular to the rolling direction. If too little Al is added, it may be difficult to secure sufficient resistivity and obtain the full iron loss improvement effect. If too much Al is added, the magnetic flux density deteriorates and problems may occur in all processes such as steelmaking and continuous casting, which may significantly reduce productivity. Therefore, Al may be included in an amount of 0.0005 to 2.5 wt%. More specifically, it may be included in an amount of 0.5 to 2.3 wt%. More specifically, it may be included in an amount of 0.7 to 2.1 wt%.

[0057]

[0058] Mn: 0.05 to 2.5 wt%

[0059] Manganese (Mn) improves iron loss by increasing the resistivity of the material. In addition, it reacts with sulfur to form manganese sulfide and reacts with nitrogen, aluminum, and silicon at high temperatures to form (Al, Si, manganese) nitride, which also has the effect of inhibiting grain growth. It is difficult for manganese to sufficiently improve iron loss, and if too much manganese is added, the magnetic flux density may decrease, and fine manganese sulfide may be excessively precipitated, which may hinder magnetic domain movement, thereby worsening the magnetic flux density and iron loss. Therefore, manganese may be included in an amount of 0.05 to 2.5 wt%. More specifically, it may be included in an amount of 0.5 to 2.0 wt%. More specifically, it may be included in an amount of 0.8 to 1.8 wt%.

[0060] S: 0.0051 to 0.0100 wt%

[0061] Sulfur (S) is an element that reacts with Cu, Mn, etc. in steel to precipitate sulfides. The more finely and extensively it is precipitated, the stronger the effect of hindering magnetic domain movement becomes, resulting in a worsening of magnetism. It is generally known that the effect of hindering magnetism becomes stronger when it is contained at 0.005 wt% or more. In one embodiment of the present invention, a non-oriented electrical steel sheet is manufactured using iron scrap, and iron scrap inevitably contains a large amount of S. Therefore, the lower limit is set to 0.0051 wt%, and even if a large amount of S is contained, a non-oriented electrical steel sheet is manufactured without deterioration of iron loss and magnetic flux density. On the other hand, if the content of S is too high, sulfides are excessively precipitated, which may weaken the effect of reducing the hindrance of magnetic domain movement due to coarsening of sulfides. Therefore, the content of S may be 0.0051 to 0.0100 wt%. More specifically, it may be 0.0060 to 0.0100 wt%.

[0062] Ca: 0.0002 to 0.0100 wt%

[0063] In one embodiment of the present invention, when Ca is appropriately included in a non-oriented electrical steel sheet containing a large amount of S, the size of sulfides becomes coarse, thereby promoting grain growth and improving magnetic quality. However, if too much Ca is added, the sulfides become coarse, increasing residual stress in the matrix structure, which may hinder magnetic domain movement and deteriorate magnetism. More specifically, it may be included in an amount of 0.0005 to 0.0075 wt%. More specifically, it may be included in an amount of 0.0010 to 0.0050 wt%.

[0064] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0065] [Formula 1]

[0066] 0.09 ≤ [Ca] / [S] ≤ 0.50

[0067] (However, in Equation 1, [Ca] and [S] represent the contents (weight%) of Ca and S, respectively.)

[0068] In one embodiment of the present invention, Ca is intended to improve magnetism by coarsenting the size of sulfides in a steel composition containing a large amount of S. Accordingly, it is necessary to include Ca in proportion to the S in the steel. If the value of Equation 1 is included too small, it means that the Ca content is low compared to S, and the coarseness of sulfides is insufficient, which may result in poor magnetism. If the value of Equation 1 is included too large, it means that Ca is included in excess compared to S, and the coarseness of sulfides increases, which may hinder magnetic domain movement and deteriorate magnetism. More specifically, the value of Equation 1 may be 0.10 to 0.47.

[0069]

[0070] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.002 to 0.02 wt%, C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0071] P: 0.002 to 0.02 wt%

[0072] Phosphorus (P) is a grain boundary segregation element that can improve magnetic flux density. If the amount added is too small, the effect is insufficient. If added in excess, it can inhibit grain growth, resulting in poor iron loss. Furthermore, grain boundary segregation can impair rollability, thereby reducing productivity. More specifically, P may be included in an amount of 0.003 to 0.015 wt%.

[0073] C: 0.005 wt% or less

[0074] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, thereby hindering grain boundary or domain wall movement and deteriorating magnetic properties. More specifically, C can be included in an amount of 0.0001 to 0.003 wt%.

[0075] Ti: 0.005 wt% or less

[0076] Titanium (Ti) can be limited because it forms carbonitrides and thus hinders domain movement. More specifically, Ti can be included in an amount of 0.0001 to 0.005 wt%. More specifically, Ti can be included in an amount of 0.0001 to 0.003 wt%.

[0077] N: 0.005 wt% or less

[0078] Nitrogen (N) has the characteristic of reacting with Al, Si, and Cr to form nitrides. These nitrides hinder grain growth, increasing the grain boundary fraction and deteriorating hysteresis loss. They can also hinder the movement and rotation of magnetic domains and deteriorate eddy current loss. More specifically, N may be included in an amount of 0.0001 to 0.0030 wt%.

[0079]

[0080] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0081] Sn and Sb

[0082] Tin (Sn) and antimony (Sb) play a role in suppressing the development of {111} orientation, which segregates at the grain boundary in the early stage of final recrystallization annealing and worsens magnetism. If too much Sn and Sb are added, the recovery and growth of coarse stretched band structure may be hindered and the surface quality may be deteriorated. Therefore, at least one of Sn and Sb may be further added within the above-mentioned range. More specifically, Sn may be included in an amount of 0.005 to 0.200 wt% or Sb may be included in an amount of 0.005 to 0.200 wt%.

[0083] Bi, Pb, Ge, and As

[0084] When added, bismuth (Bi), lead (Pb), germanium (Ge) and arsenic (As) segregate at grain boundaries, thereby relieving stress concentration at grain boundaries during cold rolling, and thus reducing stress concentration in the subsequent recrystallization annealing process. <111> / ND By suppressing the recrystallization of the grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained. However, if they are included in excessive amounts, segregation may occur in large quantities, inhibiting grain growth and lowering the magnetic flux density and iron loss.

[0085]

[0086] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0087] Cu: 0.005 to 0.200 wt%

[0088] Copper (Cu) plays a role in forming sulfides together with manganese (Mn). If too much Cu is added, the grains may not grow beyond an appropriate size, resulting in poor magnetism. More specifically, Cu may be included in an amount of 0.007 to 0.050 wt%. More specifically, it may be included in an amount of 0.008 to 0.030 wt%.

[0089] Cr: 0.01 to 0.50 wt%

[0090] Chromium (Cr) increases resistivity and improves iron loss. If too little Cr is added, the resistivity-enhancing effect may not be sufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr may be included in an amount of 0.050 to 0.20 wt%.

[0091] Ni: 0.05 wt% or less

[0092] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, it can contain 0.001 to 0.03 wt% of Ni.

[0093] Zn: 0.01 wt% or less

[0094] Zinc (Zn) can act as an impurity and degrade magnetism if the content is excessive. Therefore, Zn may be added further within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 wt%.

[0095] Co: 0.05 wt% or less

[0096] Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it can increase high-temperature strength and cause poor coil shape after hot rolling.

[0097]

[0098] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.05 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.0050 wt% or less (excluding 0%), Te: 0.0100 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0099] Mo: 0.050 wt% or less

[0100] When molybdenum (Mo) is added in excessive amounts, it may suppress segregation of segregating elements, thereby reducing the effect of improving the texture. Therefore, Mo may be included in an amount of 0.03 wt% or less. The lower limit is not particularly limited, but since it plays a role in improving the texture by segregating on the surface and grain boundaries, it may be included in an amount of 0.001 wt% or more. More specifically, Mo may be included in an amount of 0.001 to 0.010 wt%. More specifically, Mo may be included in an amount of 0.005 to 0.010 wt%.

[0101] B: 0.0050 wt% or less

[0102] Excessive addition of boron (B) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, B may be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. More specifically, B may be included in an amount of 0.0001 to 0.0030 wt%.

[0103] V: 0.0050 wt% or less

[0104] Vanadium (V) has a very strong tendency to form precipitates within the steel, and forms fine carbides or nitrides within the base metal, thereby inhibiting grain growth and domain wall migration, thereby deteriorating iron loss. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not particularly limited, but may be 0.0003 wt% due to steelmaking costs. That is, V may be included in an amount of 0.0003 to 0.0050 wt%. More specifically, V may be included in an amount of 0.0003 to 0.0030 wt%.

[0105] Nb: 0.0050 wt% or less

[0106] Niobium (Nb) has a very strong tendency to form precipitates in steel, and forms fine carbides or nitrides inside the base metal, which inhibits grain growth and domain wall migration, thereby deteriorating iron loss. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not particularly limited, but may be 0.0003 wt% due to steelmaking costs. That is, Nb may be included in an amount of 0.0003 to 0.0050 wt%. More specifically, Nb may be included in an amount of 0.0003 to 0.0030 wt%.

[0107] Zr: 0.0050 wt% or less

[0108] Excessive addition of zirconium (Zr) can cause deterioration of magnetism through the formation of inclusions in the steel. Therefore, Zr can be included in an amount of 0.005 wt% or less. The lower limit is not particularly limited, but may be 0.0001 wt% due to steelmaking costs. That is, Zr can be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it can be included in an amount of 0.0005 to 0.0030 wt%.

[0109] Te: 0.0100 wt% or less

[0110] Tellurium (Te) diffuses into the oxide layer on the surface of a hot-rolled coil, increases the coefficient of friction between the oxide layer and the rolling work rolls, and concentrates under the oxide layer to improve hardness. Therefore, it can be added to prevent the fractured oxide layer during rolling from being pressed into the base metal and to be removed. If the amount of Te added is too small, the effect may be minimal. If too much Te is added, the oxide layer is easily removed, and the base metal comes into direct contact with the work rolls, reducing the effect. In addition, deformation bands may be excessively generated in the steel sheet during cold rolling, which may lead to the development of a {111} / ND texture that is unfavorable for magnetism. More specifically, tellurium may be included in an amount of 0.0001 to 0.007 wt%.

[0111] Mg: 0.0050 wt% or less

[0112] Magnesium (Mg) is an element that mainly combines with sulfur to form sulfides, and can affect the surface oxide layer of the steel base. Therefore, Mg may be included in an amount of 0.0050 wt% or less. The lower limit is not particularly limited, but may be set to 0.0001 wt% due to steelmaking costs. That is, Mg may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 to 0.0030 wt%.

[0113]

[0114] The remainder comprises iron (Fe) and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these impurities are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. When additional elements are included, they are included in place of the remainder, iron (Fe).

[0115]

[0116] In one embodiment of the present invention, while including a large amount of S in the steel sheet, it is possible to coarsely precipitate sulfides to minimize magnetic deterioration caused by S. Specifically, the average particle size of the sulfides in the steel sheet may be 1 to 10 μm. Sulfides refer to particles in which the S element is aggregated and clumped together. In other words, they refer to a portion in which sulfur is contained in a larger amount than the content of the base material of the steel sheet. In one embodiment of the present invention, the sulfides are particles in which the aggregated particle size is at least 1 nm and S is contained in excess of the content in the base material of the steel sheet when measured with a scanning electron microscope (SEM). The cross-section for measuring the sulfides is not particularly limited, but may be a normal plane (TD plane) in the rolling vertical direction (TD direction) of the steel sheet. The particle size of the sulfides refers to the diameter of an imaginary circle having the same area as the area occupied by the sulfides. The average particle size of the sulfides can be analyzed using an image analysis program using an image obtained through TEM or SEM and EDS. To reduce the deviation according to the measurement location, measurements are made at intervals of 10 μm × 10 μm for specimens with an area of ​​5 mm × 5 mm or more, and the average value for the total number of sulfides can be obtained.

[0117] In addition to S, sulfide may contain one or more of Ca, Mn, Al, and Cu. In addition to the above-mentioned elements, it is also possible to precipitate complexly with C, N, and O. That is, sulfide may contain precipitates represented by (Ca, Mn, Al, Cu)(S, C, N, O). In this case, (A, B) means single or complex precipitation of A and B. More specifically, sulfide may contain one or more of CaS, MnS, and CuS.

[0118] If the average particle size of the sulfide is too small, it may not only deteriorate the magnetic quality by hindering the movement of the magnetic domain, but also inhibit the growth of the crystal grains, resulting in inferior magnetism. If the average particle size of the sulfide is too large, the crystal grain growth is promoted, but the movement of the magnetic domains is hindered due to the stress field formed at the interface between the sulfide and the matrix metal, which may result in inferior magnetism. More specifically, the average particle size of the sulfide may be 1.1 to 8.0 ㎛. More specifically, the average particle size of the sulfide may be 2.0 to 7.5 ㎛.

[0119]

[0120] According to one embodiment of the present invention, the non-oriented electrical steel sheet may have an average grain size of 50 to 80 μm within the steel sheet. If the average grain size is too small, iron loss may be deteriorated due to an excessive increase in hysteresis loss. If the average grain size is too large, iron loss may be deteriorated due to an excessive increase in eddy current loss. More specifically, the average grain size within the steel sheet may be 50 to 80 μm. It may be 50 to 75 μm.

[0121] A non-oriented electrical steel sheet according to an embodiment of the present invention has excellent magnetic flux density and high-frequency iron loss. Specifically, a non-oriented electrical steel sheet according to an embodiment of the present invention has excellent iron loss (W 10 / 400 ) is 10.5 W / Kg or less, and the magnetic flux density (B 50 ) may be 1.59T or more.

[0122] B 50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0123] W 10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz.

[0124] In one embodiment of the present invention, B 50 and W 10 / 400The values ​​measured in the rolling direction (RD direction) and the rolling vertical direction (TD direction) are averaged and shown. More specifically, the non-oriented electrical steel sheet according to one embodiment of the present invention has a core loss (W 10 / 400 ) is 9.0 to 10.5 W / Kg, and the magnetic flux density (B 50 ) can be 1.59T to 1.65T.

[0125]

[0126] 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 steel sheet; a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet.

[0127] Below, each step is explained in detail.

[0128] First, the slab is hot rolled.

[0129] The alloy composition of the slab has been described in the alloy composition of the previously mentioned non-oriented electrical steel sheet, so a duplicate description will be omitted. Since the alloy composition does not substantially change during the manufacturing process of the non-oriented electrical steel sheet, the alloy composition of the non-oriented electrical steel sheet and the slab are substantially identical.

[0130] Specifically, the slab contains, in wt%, Si: 2.6 to 4.5%, Al: 0.0005 to 2.5%, Mn: 0.05 to 2.5%, S: 0.0051 to 0.0100%, and Ca: 0.0002 to 0.0100%, with the remainder being Fe and unavoidable impurities.

[0131] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0132]

[0133] The slab can be manufactured using 80 wt% or less of blast furnace molten iron and 20 wt% or more of iron scrap. Iron scrap contains a large amount of sulfur compared to blast furnace molten iron, which can cause a large amount of precipitates such as sulfides to be precipitated. In one embodiment of the present invention, by adding an appropriate amount of Ca, the particle size of the precipitates can be appropriately controlled, thereby reducing the negative impact on magnetism and uniformly growing the crystal grain size to improve magnetism.

[0134] Slabs can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1200℃ or lower. If the slab heating temperature is too high, precipitates such as AlN and MnS present within the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, inhibiting grain growth and reducing magnetism.

[0135] Next, the slab is hot-rolled to produce a hot-rolled sheet. The hot-rolled sheet may have a thickness of 1.0 to 4.5 mm. In one embodiment of the present invention, a preliminary cold-rolling step may be additionally included before cold rolling, so that even if the hot-rolled sheet is relatively thick, a non-oriented electrical steel sheet of an appropriate thickness can be produced. More specifically, the thickness of the hot-rolled sheet may be 1.5 to 3.5 mm.

[0136] The step of manufacturing the hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher.

[0137] If the hot rolling finishing temperature is too low, the rolling load increases, which reduces the hot rolling workability. In addition, a lot of deformation structures remain in the hot rolled steel sheet, which can cause an increase in the rolling load during the subsequent preliminary cold rolling process. In addition, during the intermediate annealing, deformation structures are removed. <111> / ND The recrystallization of the orientation grains is promoted, resulting in a lower magnetic flux density. Therefore, the higher the hot rolling finishing temperature, the better, and more specifically, finishing rolling at a temperature of 860 to 1000°C is preferable.

[0138] The step of manufacturing a hot-rolled sheet may include a step of performing water cooling after a time of 0.1 seconds or more after finish rolling.

[0139] After the finishing rolling, cooling is performed for coiling. When water cooling is performed immediately after the finishing rolling (i.e., within less than 0.1 seconds), the steel sheet may be rapidly cooled, causing deformation and residual stress, making coiling difficult. In addition, in terms of microstructure, the deformation stress after the finishing rolling is not released and remains, causing an increase in the rolling load and micro-stress in the subsequent cold rolling stage. <111> / ND may cause recrystallization of the orientation. Therefore, it is necessary to maintain the hot-rolled deformation structure for more than 0.1 seconds immediately after the hot-rolled finishing rolling to allow recovery and recrystallization, thereby reducing the rolling load during the subsequent preliminary cold rolling. <111> / ND suppresses the formation of azimuth recrystallization grains. More specifically, water cooling can be performed after 0.3 to 5.0 seconds, and even more specifically, water cooling can be performed after 0.5 to 3.0 seconds.

[0140] The step of manufacturing a hot rolled sheet may include a coiling step at a temperature of 600 to 800°C. A rough rolling step may also be included before the finish rolling step.

[0141] If the temperature during the coiling stage is controlled too low, the recovery and recrystallization of the hot-rolled deformation structure will not occur well, and the cooling load will increase in order to quickly cool the steel sheet to a low temperature, which may make it difficult to coil the supercooled coil. On the other hand, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during coiling, which may cause thicker scale formation and the problem of intergranular oxidation. Intergranular oxidation of hot-rolled sheets promotes intergranular corrosion during the subsequent pickling process, which increases the possibility of surface stripe defects and may cause severe wear of the rolling rolls. Therefore, it is recommended that the coiling temperature be 600 to 800℃, and more specifically, coiling can be performed at 600 to 750℃.

[0142] After manufacturing hot-rolled steel sheets, hot-rolled sheet annealing can be performed before cold rolling. The soaking temperature during hot-rolled sheet annealing can be 800 to 1200℃. If the annealing temperature is too low, the recrystallized structure may not be formed or may grow finely, which will have little effect on increasing the magnetic flux density. If the annealing temperature is too high, the magnetic properties may actually deteriorate, and the rolling workability may deteriorate due to deformation of the plate shape. More specifically, the temperature range can be 830 to 1170℃. The soaking time can be 15 to 180 seconds. Hot-rolled sheet annealing can also be omitted if necessary.

[0143] Returning to the description of the manufacturing method of non-oriented electrical steel sheet, cold-rolled steel sheet is cold-rolled to produce cold-rolled steel sheet. At this time, cold rolling can be performed at a reduction ratio of 30 to 80%. If the reduction ratio is too low, the accumulated strain energy in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which can cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it can cause problems in the subsequent annealing process. <111> / ND The recrystallization of the orientation grains is promoted and the grains become finer, which may cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 40 to 70%. The thickness can be 0.1 mm to 0.5 mm. More specifically, it can be 0.15 to 0.35 mm. The cold rolling step can use a tandem cold rolling mill that continuously cold rolls the steel sheet using multiple rolling stands, or a reverse rolling mill that discontinuously cold rolls using 12 or more rolling rolls.

[0144] Next, the cold rolled sheet is annealed.

[0145] The cold rolled sheet annealing step can be performed in a mixed gas and 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.

[0146] The cold-rolled sheet annealing step can be performed at a temperature of 900°C to 1100°C for 60 to 300 seconds. In one embodiment of the present invention, although annealing is performed at a relatively high temperature, since sulfides are appropriately precipitated, the grain size is prevented from growing significantly, thereby preventing magnetic deterioration caused by this. In addition, by annealing at a high temperature in a state where sulfides are appropriately precipitated, the grains can grow uniformly. If the annealing temperature is too low or the annealing time is too short, the grains may not grow sufficiently, and the iron loss may be degraded due to an excessive increase in hysteresis loss. If the annealing temperature is too high or the annealing time is too long, the grains may grow too large, and the iron loss may be degraded due to an excessive increase in eddy current loss. More specifically, the cold-rolled sheet annealing step can be performed at a temperature of 950°C to 1050°C for 120 to 240 seconds.

[0147] After the cold-rolled sheet annealing step, a step of forming an insulating film may be further included to ensure insulation and corrosion resistance of the steel sheet. Since the insulating film is widely known, a detailed description thereof will be omitted.

[0148] The present invention will be described in more detail below through examples. However, these examples are intended only to illustrate the present invention and are not intended to limit the present invention.

[0149]

[0150] Example 1

[0151] Slabs containing the alloy components and residual Fe and unavoidable impurities summarized in Tables 1 and 2 were manufactured, heated to 1180°C, and hot-rolled to a thickness of 2.3 mm. The hot-rolled sheet was heated to a temperature of 1000°C and then water-cooled. The steel product annealed by the hot-rolled sheet was pickled and rolled once to a thickness of 0.2 mm. The cold-rolled sheet was maintained at a temperature of 1000°C for 180 seconds to perform cold-rolled sheet annealing.

[0152] Iron loss W after machining of magnetic measurement specimen 10 / 400 and magnetic flux density B 50 The results were measured and shown in Table 2 below.

[0153] The magnetic properties were measured using an Epstein tester by preparing Epstein specimens at each angle, and the average results in the rolling direction and the direction perpendicular to the rolling are summarized in Table 3 below.

[0154] Sulfides were measured using a scanning electron microscope (SEM) in a 5 mm × 5 mm area at 10 μm × 10 μm intervals, and the results are summarized in Table 3.

[0155] The average grain size was measured using a scanning electron microscope (SEM) and is summarized in Table 3.

[0156] (wt%)SiMnAlSCaCa / SInventive material 13.681.1671.2010.00510.00060.12Inventive material 23.091.3271.7150.00530.00080.15Inventive material 33.951.2540.8900.00620.00120.19Inventive material 43.321.4931.3980.00660.00170.26Inventive material 53.811.0421.1330.00730.00220.30Inventive material 63.411.1841.4650.00 750.00260.35Inventive material 73.901.4590.8350.00850.00340.40Inventive material 84.140.9100.8670.00880.00400.45Inventive material 92.661.4672.0710.00920.00420.46Inventive material 103.690.9841.2780.00980.00450.46Comparative material 12.821.0452.1260.00500.00010.02Comparative material 23.530.8271.5200.00610.0 0030.05Comparative material 33.731.0371.2130.00750.00060.08Comparative material 43.510.8181.5410.00830.00050.06Comparative material 53.091.3191.7130.00910.00060.07Comparative material 63.081.0671.8540.00990.00080.08Comparative material 72.781.3751.9950.00500.00240.48Comparative material 83.611.0411.3360.00610.00320.5 2Comparative material 92.811.0982.1070.00750.00450.60Comparative material 103.851.3980.9170.00830.00660.80Comparative material 113.591.0331.3570.00910.00730.80Comparative material 123.821.1441.0750.00990.00790.80Comparative material 132.500.9100.8670.00880.00400.45Comparative material 143.411.1841.4650.02480.01170.47

[0157] (wt%)CNPCuSnNiMoInventive Material 10.00360.00220.010.010.058--Inventive Material 20.00360.00180.010.010.056-0.01Inventive Material 30.00310.00500.010.020.063--Inventive Material 40.00340.00260.010.010.056--Inventive Material 50.00360.00400.010.020.0630.05-Inventive Material 60.00390.00140 .010.020.062-0.04Inventive 70.00370.00320.010.010.057--Inventive 80.00470.00400.010.020.065--Inventive 90.0030.00420.010.010.058--Inventive 100.00410.00460.010.010.065--Comparative 10.00460.00380.010.010.059--Comparative 20.00360.00140.010. 010.064--Comparative Material 30.00420.00400.010.020.064--Comparative Material 40.00370.00160.010.020.059--Comparative Material 50.00420.00500.010.020.062--Comparative Material 60.00350.00450.010.020.064--Comparative Material 70.00360.00270.010.020.059--Comparative Material 80.00370.00500.010.010.063- -Comparative material 90.00380.00190.010.010.065--Comparative material 100.00350.00370.010.010.064--Comparative material 110.00490.00260.010.020.058--Comparative material 120.00410.00190.010.010.058--Comparative material 130.0030.00420.010.010.058--Comparative material 140.00390.00140.010.020.062-0.04

[0158] Sulfide average grain size (㎛)Average crystal grain size (㎛)W 10 / 400(W / kg) B50 (Tesla) Inventive 11.168 9.81.60 Inventive 22.167 9.91.60 Inventive 33.85 69.21.64 Inventive 44.07 310.01.62 Inventive 53.66 810.41.62 Inventive 64.25 49.11.61 Inventive 76.85 310.41.61 Inventive 86.95 19.21.64 Inventive 96.05 29.21.62 Inventive 105.55 89.61.62 Comparative 10.04 810.01.56 Comparative 20.12 212.91.55 B Textbook 30.045 12.41.57 Comparative Material 40.02 412.61.59 Comparative Material 50.048 12.91.55 Comparative Material 60.042 12.51.57 Comparative Material 713.57 811.91.58 Comparative Material 813.68 011.41.59 Comparative Material 911.58 012.11.55 Comparative Material 1012.27 711.61.57 Comparative Material 1112.69 012.01.57 Comparative Material 1210.78 311.61.57 Comparative Material 136.95 713.11.52 Comparative Material 1416.46 312.91.53

[0159] As shown in Tables 1 to 3, it can be confirmed that examples in which the steel component is appropriately controlled and the grain size of sulfide and crystal grains is appropriately formed have excellent iron loss and magnetic flux density.

[0160] On the other hand, Comparative Materials 1 to 12 and Comparative Material 14 do not contain Ca or S properly, so that sulfides are formed too finely or in too excessive amounts, and as a result, crystal grains do not grow properly, resulting in iron loss W. 10 / 400 and magnetic flux density B 50 This appeared to be inferior.

[0161] Comparative material 13 has too little Si added, resulting in iron loss W 10 / 400 and magnetic flux density B 50 This appeared to be inferior.

[0162]

[0163] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A non-oriented electrical steel sheet containing Si: 2.6 to 4.5% by weight, Al: 0.0005 to 2.5%, Mn: 0.05 to 2.5%, S: 0.0051 to 0.0100%, and Ca: 0.0002 to 0.0100%, with the remainder being Fe and unavoidable impurities.

2. In paragraph 1, A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] 0.09 ≤ [Ca] / [S] ≤ 0.50 (However, in Equation 1, [Ca] and [S] represent the contents (weight%) of Ca and S, respectively.) 3. In paragraph 1, Non-oriented electrical steel sheet having an average particle size of sulfide in the steel sheet of 1 to 10 ㎛ 4. In paragraph 3, The above sulfide is a non-oriented electrical steel sheet containing at least one of Ca, Mn, Al, and Cu.

5. In paragraph 1, A non-oriented electrical steel sheet further comprising at least one of P: 0.002 to 0.02 wt%, C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

6. In paragraph 1, A non-oriented electrical steel sheet further comprising 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As.

7. In paragraph 1, A non-oriented electrical steel sheet further comprising at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

8. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of Mo: 0.05 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

9. In paragraph 1, Non-oriented electrical steel sheet having an average grain size of 50 to 80 ㎛ within the steel sheet.

10. In paragraph 1, Iron Hand(W 10 / 400 ) is less than 10.5 W / Kg, and the magnetic flux density (B 50 ) Non-oriented electrical steel sheet having a strength of 1.59T or higher 11. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 2.6 to 4.5%, Al: 0.0005 to 2.5%, Mn: 0.05 to 2.5%, S: 0.0051 to 0.0100%, and Ca: 0.0002 to 0.0100% by weight, with the remainder being Fe and unavoidable impurities; A step of manufacturing a cold rolled sheet by cold rolling the hot rolled steel sheet above, and A cold rolled sheet annealing step for annealing the above cold rolled sheet; A method for manufacturing a non-oriented electrical steel sheet comprising:

12. In paragraph 11, The above slab is a method for manufacturing a non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] 0.09 ≤ [Ca] / [S] ≤ 0.50 (However, in Equation 1, [Ca] and [S] represent the contents (weight%) of Ca and S, respectively.) 13. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of P: 0.002 to 0.02 wt%, C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

14. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further contains 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As.

15. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

16. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Mo: 0.05 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Nb: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

17. In paragraph 11, The above slab is a method for manufacturing a non-oriented electrical steel sheet using 80 wt% or less of molten iron and 20 wt% or more of iron scrap.

18. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the cracking temperature in the above cold rolled sheet annealing step is 900 to 1100°C.