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 comprises, by wt%, 1.5-4.5% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, and the remainder of Fe and inevitable impurities, wherein the area fraction of <111> / ND crystal grains is 30% or less, the sum of the area fractions of <110> / ND crystal grains and <100> / ND crystal grains is 28% or more, and the ratio of the area fraction of <100> / ND> crystal grains to the area fraction of <110> / ND crystal grains is 0.4 or more. Here, <111> / ND, <110> / ND, and <100> / ND indicate crystal grains of which the <111>, <110>, and <100> axes are parallel to the normal direction (ND) of the rolling surface of the steel sheet, with an angle of 15 degrees or less.

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, wherein the magnetism is improved by developing a specific aggregate structure by controlling the heating rate in an annealing process prior to cold rolling.

[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] A common method for improving the magnetic properties of non-oriented electrical steel is to add alloying elements such as Si, Al, and Mn. These alloying elements increase the steel's resistivity, reducing eddy current losses and lowering overall core loss. Furthermore, these alloying elements act as substitutional elements in the steel, strengthening it and increasing its strength. However, increasing the amount of Si, Al, and Mn alloying elements results in lower magnetic flux density and increased brittleness. Beyond a certain level, cold rolling becomes impossible, making commercial production impossible. In particular, thinner electrical steel sheets exhibit superior high-frequency core loss, but the resulting brittleness can be a critical issue. The maximum combined Si, Al, and Mn content for commercial production is known to be approximately 4.5 wt%. Optimizing the content of trace elements beyond this level can produce premium non-oriented electrical steel with superior magnetism and strength.

[0006] Methods for improving magnetic properties by controlling the grain structure of non-oriented electrical steel sheets are also widely used. Texture control is a method for promoting the development of crystal orientations favorable for magnetism and suppressing crystal orientations unfavorable to magnetism during the process of deforming, recovering, and recrystallizing a material through various methods. It is known that crystal orientations with {001} planes are favorable for magnetism, while crystal orientations with {111} planes are unfavorable. Many methods are known for selectively developing several crystal orientations by varying the manufacturing conditions of non-oriented electrical steel sheets.

[0007] When non-oriented electrical steel sheets are produced through a double-rolling and double-annealing process, the {111} / ND crystal orientation, which is unfavorable to magnetism, can be suppressed, and crystal orientations such as {001} / ND, which are favorable to magnetism, can be strengthened. The above process is well known to be excellent in improving the texture, but compared to the existing single-rolling method, the manufacturing cost increases somewhat due to the addition of cold rolling and intermediate annealing processes, and the surface oxide layer formation behavior is unstable during the annealing and cold rolling processes, so there is a problem that the magnetic properties deteriorate due to additional formation of precipitates on the surface layer or uneven formation of the surface oxide layer, and therefore, there were limitations in applying it to actual mass production processes.

[0008] 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, wherein the non-oriented electrical steel sheet has improved magnetism by developing a specific aggregate structure by controlling the heating rate in an annealing process prior to cold rolling.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities. <111> / ND The area fraction of crystal grains is 30% or less, <110> / ND crystal grains and <100> / The sum of the area fractions of ND crystal grains is 28% or more, <110> / ND for the area fraction of crystal grains <100> / ND The ratio of the area fraction of crystal grains is 0.4 or more.

[0010] At this time, <111> / ND, <110> / ND and <100> / ND is the crystal grain <111> , <110> and <100> It refers to a crystal grain whose axis is parallel to the normal direction of the rolling surface of the steel plate (ND direction) at an angle of 15° or less.

[0011] It includes an oxide layer existing from the surface to the inside, and the thickness of the oxide layer may be 200 nm or less.

[0012] The maximum length of the oxide layer break portion having an oxide layer thickness of 5 nm or less in a cross-section including the rolling direction of the steel plate may be 750 nm or less per 100 μm in the rolling direction.

[0013] The number of precipitates per unit area (P) in the center exceeding 1 / 20 to 1 / 2 of the total thickness I ) The number of precipitates per unit area (P) on the surface of the steel plate up to 1 / 20 of the total thickness S ) may be less than 1.2.

[0014] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0015] 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.

[0016] 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%).

[0017] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 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%).

[0018]

[0019] 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: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; a cold-rolling pre-annealing step of annealing the hot-rolled steel sheet; a step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0020] It includes a first heating step of heating the steel sheet to 750°C at a heating rate of 22°C / sec or less before the annealing step prior to cold rolling, and a second heating step of heating the steel sheet to a temperature exceeding 750°C and up to the cracking temperature at a heating rate of 28°C / sec or more.

[0021] The slab may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0022] 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.

[0023] 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%), and Zn: 0.01 wt% or less (excluding 0%).

[0024] The slab may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 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%), Co: 0.05 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0025] A step of pre-cold rolling the hot-rolled sheet may be further included prior to the annealing step prior to cold rolling.

[0026] The reduction ratio in the preliminary cold rolling stage can be 30 to 80%.

[0027] The cracking temperature in the annealing step prior to cold rolling can be 850 to 1010°C.

[0028] The annealing step before cold rolling is performed at a dew point of -50 to -10℃ and a pressure of 0.2 kgf / mm. 2 3.0kgf / mm 2 The tension is applied and annealing can be performed in a mixed gas atmosphere of hydrogen and nitrogen containing 0.1 to 50 volume% of hydrogen gas.

[0029] In the process of manufacturing cold rolled sheets, the reduction ratio can be 40 to 85%.

[0030] The cold rolled sheet annealing step can be performed at a soaking temperature of 850 to 1100°C in an atmosphere with a dew point of 0°C or lower.

[0031] A non-oriented electrical steel sheet according to one embodiment of the present invention has further improved magnetic properties without causing surface deterioration.

[0032] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the manufacture of eco-friendly automobile motors, high-efficiency home appliance motors, and super-premium-grade electric motors.

[0033] Figure 1 is a drawing schematically illustrating a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0034] FIG. 2 is a drawing schematically illustrating a cut portion in a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0039] 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.

[0040] 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.

[0041] 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.

[0042]

[0043] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities.

[0044] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0045]

[0046] Si: 1.5 to 4.5 wt%

[0047] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and enhances strength through solid solution strengthening. If too little Si is added, the iron loss and strength improvement effects may be insufficient. If too much Si is added, the material becomes brittle, leading to a sharp decline in rolling productivity and the formation of a surface oxide layer and oxides that are detrimental to magnetism. Therefore, Si may be included in an amount of 1.5 to 4.5 wt%. More specifically, it may be included in an amount of 2.0 to 4.3 wt%. Even more specifically, it may be included in an amount of 2.5 to 4.0 wt%.

[0048]

[0049] Al: 0.1 to 2.0 wt%

[0050] Aluminum (Al) increases the resistivity of the material, thereby reducing iron loss, and enhances strength through solid solution strengthening. If too little Al is added, fine nitrides may form, making it difficult to achieve the effect of improving magnetism. If too much Al is added, excessive nitrides may form, deteriorating magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. Therefore, Al may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.3 to 1.5 wt%. Even more specifically, it may be included in an amount of 0.5 to 1.0 wt%.

[0051]

[0052] Mn: 0.1 to 2.0 wt%

[0053] Manganese (Mn) improves iron loss by increasing the resistivity of the material and plays a role in forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic deterioration, and if too much Mn is added, fine MnS is excessively precipitated and promotes the formation of {111} texture, which is unfavorable for magnetism, resulting in a rapid decrease in magnetic flux density. Therefore, Mn may be included in an amount of 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.2 to 1.5 wt%. More specifically, it may be included in an amount of 0.3 to 1.0 wt%.

[0054]

[0055] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0056] P: 0.1 wt% or less

[0057] Phosphorus (P) is a grain boundary segregation element that can improve magnetic flux density, but if added in too large a quantity, it increases the brittleness of the steel plate, resulting in poor weldability. More specifically, P may be included in an amount of 0.0001 to 0.0500 wt%.

[0058] C: 0.005 wt% or less

[0059] 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%.

[0060] S: 0.005 wt% or less

[0061] Sulfur (S) can form fine precipitates, MnS and CuS, which can deteriorate magnetic properties and hot workability. More specifically, S can be included in an amount of 0.0001 to 0.0030 wt%.

[0062] Ti: 0.005 wt% or less

[0063] Titanium (Ti) has a strong tendency to form precipitates within the steel, and can deteriorate iron loss by forming fine carbides, nitrides, or sulfides within the parent material, thereby inhibiting grain growth and domain wall migration. More specifically, it can contain 0.0001 to 0.003 wt% of Ti.

[0064] N: 0.005 wt% or less

[0065] Nitrogen (N) not only forms fine AlN precipitates within the base material, but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall migration, thereby worsening iron loss. More specifically, N may be included in an amount of 0.0001 to 0.0030 wt%.

[0066]

[0067] 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.

[0068] Sn and Sb

[0069] 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%.

[0070] Bi, Pb, Ge, and As

[0071] 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 orientation 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.

[0072]

[0073] 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%).

[0074] Cu: 0.005 to 0.200 wt%

[0075] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu · Mn)S may occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement may occur, leading to cracks during rolling or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.10 wt%.

[0076] Cr: 0.01 to 0.50 wt%

[0077] 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%.

[0078] Ni: 0.05 wt% or less

[0079] 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.

[0080] Zn: 0.01 wt% or less

[0081] 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%.

[0082] Co: 0.05 wt% or less

[0083] 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.

[0084]

[0085] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 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%).

[0086] Mo: 0.030 wt% or less

[0087] 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%.

[0088] B: 0.0050 wt% or less

[0089] 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%.

[0090] V: 0.0050 wt% or less

[0091] 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%.

[0092] Ca: 0.0050 wt% or less

[0093] Calcium (Ca) has a strong tendency to form precipitates within the steel, and forms fine sulfides within the parent material, which inhibits grain growth and domain wall movement, thereby deteriorating iron loss.

[0094] Nb: 0.0050 wt% or less

[0095] 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%.

[0096] Zr: 0.0050 wt% or less

[0097] 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%.

[0098] Te: 0.0100 wt% or less

[0099] 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 roll, and concentrates under the oxide layer to improve hardness. Therefore, it can be added to remove the oxide layer that is broken during rolling without being pressed into the base metal. 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 roll, reducing the effect, and excessive deformation bands are generated in the steel sheet during cold rolling, which is unfavorable for magnetism. <111> / ND aggregate structure can be developed. More specifically, it can contain 0.0001 to 0.007 wt% of tellurium.

[0100] Mg: 0.0050 wt% or less

[0101] 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%.

[0102]

[0103] 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).

[0104]

[0105] As described above, in one embodiment of the present invention, by appropriately controlling the alloy composition of the steel plate and developing a specific aggregate structure, magnetism can be improved.

[0106] A non-oriented electrical steel sheet according to one embodiment of the present invention <111> / ND The area fraction of crystal grains is 30% or less, <110> / ND crystal grains and <100> / The sum of the area fractions of ND crystal grains is 28% or more, <110> / ND for the area fraction of crystal grains <100> / ND The ratio of the area fraction of crystal grains is 0.4 or more.

[0107] At this time, <111> / ND, <110> / ND and <100> / ND is each grain size <111> , <110> and <100> It refers to a crystal grain whose axis is parallel to the normal direction of the rolling surface of the steel plate (ND direction) at an angle of 15° or less.

[0108] <111> / ND crystal grains are crystal grains that are unfavorable to magnetization, so minimizing their fraction is advantageous to magnetism. <111> / The area fraction of ND crystal grains is 30.0% or less. More specifically, it may be 10.0 to 30.0%.

[0109] <110> / ND crystal grains and <100> / ND crystal grains <111> / ND It is easier to magnetize than crystal grains, and securing as many of these crystal grains as possible is advantageous for magnetization. <110> / ND crystal grains and <100> / The sum of the area fractions of ND crystal grains is 28.0% or more. More specifically, <110> / ND crystal grains and <100> / The sum of the area fractions of the ND crystal grains can be 29.0 to 75.0%.

[0110] <110> / ND crystal grains and <100> / ND Among the crystal grains <100> / ND crystal grains are more advantageous for magnetism. <110> / ND for the area fraction of crystal grains <100> / ND The ratio of the area fraction of crystal grains ( <100> / ND / <110> / ND) can be set to 0.40 or higher. More specifically, <100> / ND / <110> / ND can be set to 0.80 to 3.00.

[0111] <111> / ND, <110> / ND and <100> / ND The grain fraction can be measured using an EBSD measurement device from TSL equipped on a JEOL Scanning Electron Microscope (model number JSM-7200F) that includes the rolling direction of the steel sheet. Area fraction refers to the ratio of the area occupied by grains of a specific orientation to the total area of ​​the steel sheet measured by electron backscatter diffraction (EBSD). The range within 15° means that the angle between the vertical axis of the surface of the steel sheet and any plane that includes the orientation is within 15°, and can be measured using the crystal orientation analysis program (OIM) of TSL's EBSD. More specifically, the steel sheet is cut parallel to the sheet thickness direction, and the crystal orientation of the grains is analyzed through electron backscatter diffraction (EBSD) measurement at the center of the cut surface. The measurement interval is 2㎛ and the total measurement area can be 3000㎛ × 3000㎛.

[0112] Figure 1 shows a schematic diagram of a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0113] As shown in Fig. 1, a non-oriented electrical steel plate (100) includes a surface portion (20) extending from the surface of the steel plate to 1 / 20 of the total thickness inward based on a cross-section including the thickness direction (ND direction) and a central portion (10) extending from more than 1 / 20 to 1 / 2 of the total thickness. In Fig. 1, for convenience, the surface portion (20) is shown to exist only on one side, but the surface portion (20) exists on both sides.

[0114] In one embodiment of the present invention, by appropriately controlling the ratio of precipitates present in the central portion (10) and the surface portion (20), the magnetic properties can be improved without causing deterioration of the surface portion of the non-oriented electrical steel sheet.

[0115] Specifically, the number of precipitates per unit area (P) in the center (10) I ) for the surface (20) per unit area of ​​the precipitate (P) S ) ratio (P S / P I ) may be 1.20 or less. If this ratio is too high, it means that there are a lot of precipitates on the surface (20) or too few precipitates on the center (10). If there are a lot of precipitates on the surface (20), the magnetism of the surface (20) is deteriorated due to the many precipitates, and ultimately the magnetism of the entire non-oriented electrical steel sheet (100) is deteriorated. If there are too few precipitates on the center (10), grain growth is promoted inside, the microstructure becomes non-uniform, and the problem of increased iron loss may occur. More specifically, the number of precipitates per unit area of ​​the center (10) (P I ) for the surface (20) per unit area of ​​the precipitate (P) S ) ratio (P S / P I ) can be between 0.95 and 1.19.

[0116] In one embodiment of the present invention, the precipitate means a particle formed by the agglomeration of elemental components existing in the electrical steel sheet. More specifically, it means a particle formed by combining at least one element among Si, Al, Mn, Ti, Nb, Cu, and Zr with at least one element among C, N, S, and O. The precipitate has a thickness of at least 200 μm with respect to a cross-section including the thickness direction (ND direction), and more specifically, a plane perpendicular to the steel sheet rolling direction (TD plane). 2 The area can be measured by observing it through TEM. Since precipitates with a particle size of less than 0.03 μm do not have a significant effect on magnetism, they are excluded from the ratio calculation. In this case, the particle size refers to the diameter of an imaginary circle having the same area as the area occupied by the precipitate. As described later, an oxide layer (30) may exist on the surface layer of the surface portion (20), but the oxide layer (30) is excluded from the calculation of the precipitate density (both the measured area and the number of precipitates are excluded).

[0117] More specifically, the precipitate density of the surface (20) is 0.5 / ㎛. 2 2.5 pieces / ㎛ 2 And the density of precipitates in the center (10) is 0.3 / ㎛. 2 2.5 pieces / ㎛ 2 It could be.

[0118] Figure 2 shows a schematic diagram of a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0119] As shown in Fig. 2, it includes an oxide layer (30) existing from the surface of the non-oriented electrical steel sheet (100) toward the inside.

[0120] An oxide layer (30) can be formed when oxygen penetrates into the steel sheet during the manufacturing process of the electrical steel sheet.

[0121] The oxide layer (30) is defined as a portion containing 0.01 wt% of oxygen from the surface of the steel plate toward the inside. The detection and thickness of the oxide layer (30) can be determined by processing the TD surface of the specimen with FIB and observing it with a TEM, and determining that the portion containing 0.01 wt% or more of oxygen is an oxide layer. At this time, the steel plate sample may be a sample in which no insulating film is formed, or a sample in which an insulating film is removed if formed. In order to reduce measurement errors depending on the location, the specimen may be measured 20 times or more at intervals of 1 μm or more in the TD direction with a length of at least 200 μm in the RD direction, and the average value may be measured.

[0122] The thickness of the oxide layer (30) may be 200 nm or less. If the thickness of the oxide layer (30) is too thick, a large amount of oxygen may penetrate into the steel plate, which may result in poor magnetism. More specifically, the thickness of the oxide layer (30) may be 5 to 190 nm. The thickness of the oxide layer (30) may be the average thickness of the oxide layer (30) in the measured specimen.

[0123] As shown in Fig. 2, there is a break in the oxide layer with a thickness of 5 nm or less in the cross-section including the rolling direction of the steel plate, and the maximum length of this break (DC L ) may be less than 750 nm per 100 um in the rolling direction. If the maximum length of the oxide layer disconnection is too long, additional oxidation and nitriding may occur at the disconnected area, which may increase the iron loss. More specifically, the maximum length of the disconnection (DC L ) can be 0.01 to 730 nm per 100 um in the rolling direction. More specifically, the maximum length of the disconnection (DC L ) can be 100 to 720 nm per 100 um in the rolling direction. The measurement and judgment of the disconnection can be performed in the same manner as the measurement and judgment method of the oxide layer described above.

[0124] The oxide layer (30) and the oxide layer break portion can be appropriately formed by appropriately controlling conditions during the annealing process prior to cold rolling. A more specific method will be described later in relation to the method for manufacturing a non-oriented electrical steel sheet.

[0125] The oxide layer (30) may contain 40 wt% or more of Al due to the surface concentration of Al. More specifically, it may contain 50 to 60 wt% of Al. The remaining alloy components other than Al and O are the same as the alloy components of the non-oriented electrical steel sheet described above. Since the thickness of the oxide layer (30) is very thin compared to the thickness of the entire non-oriented electrical steel sheet (100), it has practically no effect on the alloy components of the non-oriented electrical steel sheet (100).

[0126]

[0127] As described above, in one embodiment of the present invention, by appropriately controlling the steel component and appropriately forming precipitates according to thickness, the magnetism can be improved. Specifically, the iron loss (W) of a non-oriented electrical steel sheet based on a thickness of 0.25 mm 10 / 400 ) may be less than 13.0 W / Kg. In addition, the magnetic flux density (B 50 ) can be 1.66T or more. Iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. Magnetic flux density (B 50 ) means the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, the iron loss (W) of non-oriented electrical steel sheet 10 / 400 ) may be 10.0 to 12.5 W / kg. More specifically, it may be 10.5 to 13.5 W / kg. The magnetic flux density (B50) may be 1.66 T to 1.75 T.

[0128]

[0129] 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 annealing the hot-rolled steel sheet before cold rolling; a step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0130] Below, each step is explained in detail.

[0131] First, the slab is hot rolled.

[0132] 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.

[0133] Specifically, the slab contains Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, with the remainder being Fe and unavoidable impurities.

[0134] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0135] 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.

[0136] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 1.0 to 4.5 mm. In the step of producing the hot-rolled sheet, the finishing rolling temperature can be 800°C or higher. Specifically, it can be 800 to 1000°C. The hot-rolled sheet can be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled sheet can be 1.5 to 4.3 mm.

[0137] In one embodiment of the present invention, after manufacturing a hot-rolled steel sheet, a pre-cold rolling annealing step for annealing the hot-rolled steel sheet may be performed immediately. Alternatively, a pre-cold rolling annealing step for annealing the pre-cold rolled steel sheet may be performed after performing preliminary cold rolling on the hot-rolled steel sheet.

[0138] Preliminary cold rolling is distinguished from cold rolling, which will be described later, in that it is the first rolling stage of the process of rolling to an intermediate thickness rather than the final product thickness, then performing intermediate annealing, and then cold rolling to the final product thickness.

[0139] Preliminary cold rolling can be performed at a reduction ratio of 30 to 80% to improve final cold rolling productivity and grain size in the final product sheet. Furthermore, if rolling productivity is not a consideration, the present invention also allows preliminary cold rolling to be performed in a reverse mill. The preliminarily cold rolled sheet can have a thickness of 0.3 to 1.5 mm. More specifically, the reduction ratio can be 60 to 75% and the thickness can be 0.6 to 1.3 mm.

[0140] The preliminary cold rolling reduction can be calculated as (steel thickness before rolling - steel thickness after rolling) / steel thickness before rolling. If the reduction ratio is too low in the preliminary cold rolling stage, the rolling load increases during the final cold rolling, which reduces productivity and increases the final reduction ratio, which causes fine grains. <111> / ND This can lead to problems that promote directional recrystallization. Conversely, if the reduction ratio is too high, the cold rolling load increases and the possibility of plate fracture increases.

[0141] The pre-cold rolling step can be performed at a temperature of 60 to 300°C. This temperature can be raised naturally by friction between the steel sheet and the rolling rolls, or by external heating. If the temperature is too low, the rolling load increases significantly, and the steel sheet may slip between the rolling rolls instead of being rolled, resulting in problems such as twisting. If the temperature is too high, a thick oxide layer may form on the steel sheet surface, which can deteriorate magnetism and cause problems such as ignition of the rolling oil. More specifically, it is preferably performed at a temperature of 70 to 250°C. The aforementioned temperature refers to the temperature of the steel sheet.

[0142] As mentioned above, the preliminary cold rolling step can be omitted if necessary.

[0143] Next, in the annealing step prior to cold rolling, the hot-rolled steel sheet or the preliminary cold-rolled steel sheet is annealed. In one embodiment of the present invention, by controlling the heating rate, dew point, and tension in the annealing step prior to cold rolling, the aggregate structure and oxide layer (30) within the steel sheet can be appropriately formed.

[0144] It includes a first heating step of heating the steel sheet to 750°C at a heating rate of 22°C / sec or less before the annealing step prior to cold rolling, and a second heating step of heating the steel sheet to a temperature exceeding 750°C and up to the cracking temperature at a heating rate of 28°C / sec or more.

[0145] The first heating step can be a step of heating the temperature range from 100℃ to 750℃. In this range, it is necessary to heat at a heating rate of 22℃ / sec or less. If the heating rate is faster than this, it may have a negative effect on magnetism. <111> / ND aggregate organization can be developed. More specifically, the heating rate of the first heating stage can be 10 to 20°C / sec. The heating rate during the first heating stage can vary, and the aforementioned heating rate refers to the average heating rate within the temperature range of the first heating stage. The temperature standard can be based on the surface temperature of the steel plate.

[0146] The second heating stage is the step of increasing the temperature from 750℃ to the soaking temperature of the annealing stage before cold rolling. If necessary, the temperature can be increased to a higher temperature than the soaking temperature, but the heating rate can be limited to reaching the soaking temperature. The second heating stage can be increased at a rate of 28℃ / sec or more. If the heating rate is insufficient, <100> / ND development may be inhibited. More specifically, in the second heating stage, the temperature can be increased at a heating rate of 30 to 500°C / sec.

[0147] And, in the annealing step before cold rolling, it is preferable to perform the annealing in a hydrogen-nitrogen mixed gas atmosphere containing at least 0.1 vol% of hydrogen. If the hydrogen content is low, an oxide layer may be additionally formed during heat treatment, which may remain in the final product and cause an increase in iron loss. A higher hydrogen content is advantageous in suppressing the oxide layer, but if used excessively, it may become a factor in the process load. Therefore, it is preferable to perform the annealing in a mixed gas atmosphere containing 0.1 to 50 vol% of hydrogen gas. More specifically, in the annealing step before cold rolling, the annealing can be performed in a mixed gas atmosphere of hydrogen and nitrogen gas containing 3 to 30 vol% of hydrogen gas in the atmospheric gas.

[0148] Additionally, the annealing step prior to cold rolling may have a dew point of -50°C to -10°C. If the dew point is too low, a fine oxide layer may form, and numerous cracks in the surface oxide layer may occur during cold rolling. If the dew point is too high, a thick oxide layer may form, which may have a negative impact on the magnetic properties. More specifically, the dew point may be -50°C to -20°C. More specifically, the dew point may be the dew point for the atmosphere during the cracking process.

[0149] Also, 0.20 kgf / mm 2 3.00 kgf / mm 2can be applied to the tension. If the tension is too low, annealing may not occur properly. If the tension is too high, <111> / ND is generated in large numbers, and numerous oxide layer breaks may occur. More specifically, the tension is 0.30 to 1.00 kgf / mm. 2 It can be. More specifically, the tension can be the tension measured at the exit of the annealing furnace, and can be measured using a tension meter measuring device.

[0150] The soaking temperature in the annealing stage prior to cold rolling can be 850 to 1010°C. If the annealing temperature is too low, recrystallized structures may not form or grow finely, resulting in a small increase in magnetic flux density. If the annealing temperature is too high, magnetic properties may deteriorate, and deformation of the plate shape may deteriorate rolling workability. More specifically, the temperature range may be 900 to 1005°C. The soaking time may be 30 to 1000 seconds.

[0151] The annealing before cold rolling described above can be performed in vertical continuous annealing equipment or horizontal continuous annealing equipment. If scale removal is omitted after hot rolling, scale removal can be performed after annealing before cold rolling. If scale remains in the final non-oriented electrical steel sheet, it can impair magnetism. Furthermore, if cold rolling is performed with remaining scale, the scale can form uneven marks on the surface where it is pressed or removed, which can deteriorate the operational stability and magnetic properties of the motor. After pickling, the scale may be completely removed or may remain less than 0.01㎛ in thickness. Pickling refers to all physical and chemical descaling methods, not just pickling. Pickling methods can include pickling, shot blasting, or surface grinding.

[0152] After annealing before cold rolling, the average grain size of the steel sheet can be 75 to 200 ㎛. If the average grain size is too small, <111> / ND is generated in large numbers, and the magnetism may be inferior. If the average grain size is too large, the cold rolling property is inferior, and the oxide layer thickness also increases while the grains grow significantly, which may deteriorate the iron loss. More specifically, after annealing before cold rolling, the average grain size of the steel sheet may be 80 to 195 ㎛. The average grain size can be obtained from the average area of ​​the number of grains included in the specimen for the cross-section of the steel sheet. The grain size can be obtained from the diameter of a circle having the same area as the area.

[0153] Next, the annealed steel sheet is cold rolled to produce a cold rolled sheet. At this time, cold rolling can be performed at a reduction ratio of 40 to 85%. 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 grains in the direction of orientation is promoted, and the grains become finer, which can cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 60 to 75%. The cold rolling step can be performed using 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 the steel sheet using 12 or more rolling rolls. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0154] Next, the cold-rolled sheet is annealed. The cold-rolled sheet annealing step can be performed in an atmosphere with a dew point temperature below 0°C. More specifically, the annealing can be performed in an atmosphere with a dew point temperature of -80 to -10°C.

[0155] The cold-rolled sheet annealing step can be performed at a soaking temperature of 850 to 1100°C. If the soaking temperature is too low, grain growth may not be sufficient, resulting in increased hysteresis loss and deteriorated iron loss. If the soaking temperature is too high, eddy current loss may increase and magnetic flux density may decrease rapidly. More specifically, annealing can be performed at a temperature of 900 to 1050°C. The soaking time may be 10 to 300 seconds.

[0156] During the cold-rolled sheet annealing process, all (i.e., more than 99%) of the processed structure formed during the cold rolling stage can be recrystallized.

[0157] After cold-rolled sheet annealing, an insulating film can be formed. The insulating film can be treated with organic, inorganic, or organic-inorganic composite films, and can also be treated with other insulating film agents.

[0158]

[0159] 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.

[0160]

[0161] Example

[0162] A slab containing 3.5% Si, 0.8% Al, 0.4% Mn, and other impurities by weight was manufactured. This was heated to 1150℃ and hot-rolled at a finishing temperature of 900℃ to manufacture a hot-rolled sheet having a thickness of 2.0 mm. The hot-rolled hot-rolled sheet was pickled, then preliminarily cold-rolled to a thickness of 0.8 mm, and annealed before cold rolling under the conditions of the first heating rate (100℃ to 750℃), the second heating rate (750℃ to the soaking temperature), the soaking temperature, the dew point, and the tension in Table 1. At this time, the annealing was heat treated in an atmosphere of a hydrogen and nitrogen mixture containing 5 vol% hydrogen. Subsequently, the annealed steel sheet was cold-rolled to a thickness of 0.25 mm, and then final recrystallization annealing was performed for 100 seconds under the conditions of a dew point of -50℃ and a soaking temperature of 1000℃.

[0163] The main characteristics of each specimen that went through the manufacturing process are summarized in Table 1.

[0164] The average grain size after annealing before cold rolling was measured using an EBSD measuring device from TSL equipped with a JEOL Scanning Electron Microscope (model number JSM-7200F).

[0165] The thickness of the oxide layer was measured at least 20 times at intervals of at least 1 μm in the area containing 5 wt% or more of Al and 3 wt% or more of O on the surface of the parent material when the TD surface of the specimen was processed with FIB and observed with TEM, and the average value was indicated.

[0166] The maximum length of the oxide layer disconnection is the maximum value measured in the rolling direction at the part where the oxide layer is not continuous but disconnected and the base material is exposed when the Al-containing oxide layer is observed in the rolling direction for 100 μm or more through TEM.

[0167] Analysis of precipitates by thickness within the steel plate was performed through TEM measurement at 200 um for the surface and center. 2The ratio of the number of precipitates with a diameter of 0.03 um or more in the area was obtained.

[0168] <111> / ND, <110> / ND and <100> / ND grain fraction was measured using an EBSD measurement device from TSL equipped on a JEOL Scanning Electron Microscope (model number JSM-7200F) on a cross-section including the rolling direction of the steel sheet. The error angle was set to 15°, and the measurement was performed using the orientation analysis program (OIM) of TSL EBSD. The steel sheet was cut parallel to the sheet thickness direction, and the crystal orientation of the grains was analyzed through electron backscatter diffraction (EBSD) measurement at the center of the cut surface. The measurement interval was 2 ㎛, and the total measurement area was 3000 ㎛ × 3000 ㎛.

[0169] Magnetic properties such as magnetic flux density and iron loss were measured by cutting 60 mm wide × 60 mm long × 5 sheets of each specimen and measuring the rolling direction and the direction perpendicular to the rolling with a single sheet tester, and the average value is shown. Here, W10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, and B50 means the magnetic flux density of the steel sheet induced in a magnetic field of 5000 A / m.

[0170] Classification 1 Heating rate 2 Heating rate Crack temperature Dew point Tension Average grain size (℃ / sec) (℃ / sec) (℃) (℃) (kgf / mm) 2)(um)A0120301000-400.80119A0230301000-400.80105A0325301000-400.8098A0415301020-400.80150A0515301000-400.09열처리실패A0615301000-400.8095A0720501000-403.20100A0820501000-400.8088A0920501000-400.80106A1020251000-400.30194A11201001000-400.30122A1220100970-400.30116A1320250970-400.50109A1420500950-400.50101A1520150830-400.5068A1615150950-400.80131A1715150950-400.80118A1815150950-400.80124A1915150950-90.80131A2015150950-400.80118A2115150950-600.80124

[0171] division <111> / ND (area%) <110> / ND (area%) <100> / ND (area%) <110> / ND+ <100> / ND (area%) <100> / ND / <110> / NDA0125.212.317.529.81.42A0230.511.312.523.81.11A0329.815.86.222.00.39A0422.514.218.532.71.30A05-----A0621.810.422.532.92.16A0731.512.315.728.01.28A0819.518.215.433.60.85A0923.719.122.441.51.17A1033.510.815.926.71.47A1124.811.925.837 .72.17A1223.115.420.836.21.35A1318.414.725.139.81.71A1415. 811.829.441.22.49A1534.822.78.731.40.38A1629.412.721.834.51 .72A1728.510.523.333.82.22A1827.111.727.138.82.32A1929.412. 721.834.51.72A2028.510.523.333.82.22A2127.111.727.138.82.32

[0172] Oxide layer thickness (nm)Maximum length of oxide layer break (nm)Precipitate ratio (P S / P I)W10 / 400B50Remarks (W / kg)(Tesla)A01504501.0012.11.66Inventive materialA02504001.1014.11.64Comparative materialA03503301.1913.91.65Comparative materialA042207101.2514.51.64Comparative materialA05---- -Comparative material A06682501.1211.51.68Inventive material A0718010251.3814.41.63Comparative material A081151201.0811.81.67Inventive material A09534801.1510.51.69Inventive material A10754301.0513.61.64Comparative material A1158 4001.1010.91.69Inventive material A121753301.1911.31.68Inventive material A131357101.0910.51.69Inventive material A141202001.0510.21.71Inventive material A151502501.1214.71.63Comparative material A161103001.11 11.31.68Inventive material A17301201.0210.11.69Inventive material A18534801.0910.91.68Inventive material A192503801.1813.11.65Comparative material A20301201.0210.11.69Inventive material A21358501.2814.21.64Comparative material

[0173] As shown in Tables 1 to 3, it can be confirmed that the remaining invention examples, in which the steel components are appropriately controlled, the process conditions are appropriately controlled, a specific aggregate structure is developed, and the thickness-specific precipitate and oxide layer characteristics are appropriately formed, have excellent iron loss and magnetic flux density.

[0174] On the other hand, if the process conditions are not properly controlled, a specific aggregate structure is not developed, or the precipitates and oxide layers by thickness are not properly formed, it can be confirmed that the iron loss and magnetic flux density are inferior.

[0175]

[0176] 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.

[0177]

[0178] [Explanation of symbols]

[0179] 100: Non-oriented electrical steel sheet, 10; Surface area,

[0180] 20: center, 30: oxide layer

Claims

1. Contains Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities. <111> / The area fraction of ND crystal grains is 30% or less, <110> / ND crystal grains and <100> / The sum of the area fractions of ND crystal grains is 28% or more, <110> / ND The area fraction of the crystal grains <100> / Non-oriented electrical steel sheet having an area fraction ratio of ND crystal grains of 0.4 or more. (step, <111> / ND, <110> / ND and <100> / ND is the crystal grain <111> , <110> and <100> (It refers to grains whose axis is parallel to the rolling surface normal direction (ND direction) of the steel plate at an angle of less than 15°.) 2. In paragraph 1, Contains an oxide layer that exists from the surface to the inside, A non-oriented electrical steel sheet having a thickness of the oxide layer of 200 nm or less.

3. In paragraph 2, A non-oriented electrical steel sheet having a maximum length of a fracture of an oxide layer of 5 nm or less in a cross-section including the rolling direction of the steel sheet and 750 nm or less per 100 um in the rolling direction.

4. In paragraph 1, The number of precipitates per unit area (P) in the center exceeding 1 / 20 to 1 / 2 of the total thickness I ) The number of precipitates per unit area (P) on the surface of the steel plate from the surface to the inside up to 1 / 20 of the total thickness S ) Non-oriented electrical steel sheet having a ratio of 1.2 or less.

5. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 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: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 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. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities; An annealing step prior to cold rolling for annealing the above hot-rolled steel sheet; A step for manufacturing cold rolled steel sheets by cold rolling an annealed steel sheet, and A cold rolled sheet annealing step for annealing the cold rolled sheet; A first heating step for heating the steel sheet to 750°C at a heating rate of 22°C / sec or less before the annealing step prior to the above cold rolling, and A method for manufacturing a non-oriented electrical steel sheet, comprising a second heating step of heating at a heating rate of 28°C / sec or more to a temperature exceeding 750°C and up to a cracking temperature.

10. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

11. In paragraph 9, 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.

12. In paragraph 9, 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%).

13. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), V: 0.0050 wt% or less (excluding 0%), Ca: 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%).

14. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet further comprising a step of preliminarily cold rolling a hot-rolled sheet prior to the above-mentioned pre-cold rolling annealing step.

15. In paragraph 14, A method for manufacturing a non-oriented electrical steel sheet having a reduction ratio of 30 to 80% in the preliminary cold rolling step.

16. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the cracking temperature in the annealing step prior to the above cold rolling is 850 to 1010°C.

17. In paragraph 9, The annealing step prior to the above cold rolling is performed at a dew point of -50 to -10°C and a pressure of 0.2 kgf / mm. 2 Within 3.0kgf / mm 2 A method for manufacturing a non-oriented electrical steel sheet by applying tension and annealing.

18. In paragraph 9, A method for manufacturing a non-oriented electrical steel sheet having a reduction ratio of 40 to 85% in the step of manufacturing the cold rolled sheet.

19. In paragraph 9, The above cold rolled sheet annealing step is a method for manufacturing a non-oriented electrical steel sheet, in which the annealing is performed at a soaking temperature of 850 to 1100°C in an atmosphere having a dew point of 0°C or lower.

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