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%, 1.5-6.0% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, and 0.002-0.100% of Cu, with the remainder comprising Fe and inevitable impurities, wherein the ratio (AlMAX / Al5µm) of AlMAX, which is the maximum Al content when the content of Al is measured in the thickness direction from the surface of the steel sheet to a point 5 µm inside the steel sheet, to Al5µm, which is the Al content at the point 5 µm inside the steel sheet from the surface of the steel sheet, is 4.0 or less, and the number of ridges having a width of at least 2 mm and a length of at least 10 mm is 5 or less per 300 mm x 300 mm area.

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 simultaneously exhibits excellent appearance and magnetic properties by appropriately controlling steel composition and scale removal conditions to suppress surface aluminum enrichment and the occurrence of linear defects.

[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 silicon (Si), aluminum (Al), and manganese (Mn). However, these elements are strong oxidizers and can form stable oxide or nitride scales on the surface during the manufacturing process, adversely affecting the surface quality of the product. This can result in deterioration of the steel sheet's appearance, as well as the adhesion of the insulating coating and the strength of the steel sheet's lamination.

[0006] 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 both excellent appearance and magnetic properties by appropriately controlling steel composition and scale removal conditions to suppress surface aluminum enrichment and the occurrence of linear defects.

[0007] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 6.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and Cu: 0.002 to 0.100%, the remainder being Fe and unavoidable impurities, and the Al content at a point 5 ㎛ inside the steel sheet from the surface of the steel sheet is Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content AlMAX The ratio of (Al MAX / Al 5㎛ ) is 4.0 or less, and there are 5 or fewer unevennesses with a width of 2 mm or more and a length of 10 mm or more per 300 mm × 300 mm area.

[0008] According to one embodiment of the present invention, a non-oriented electrical steel sheet may have 5 or fewer Al aggregates having a particle diameter of 500 nm or more per 100 μm of the steel sheet length in a region from the surface of the steel sheet to 5 μm inside the steel sheet.

[0009] 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: 0.010 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0010] 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.

[0011] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of 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%).

[0012] 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%).

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention includes an insulating film positioned on the surface of the steel sheet, and the whiteness of the surface of the insulating film is 50 or more.

[0014]

[0015] 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 6.0%, Al: 0.1 to 2.0%, Mn: 2.0% or less (excluding 0%), and Cu: 0.002 to 0.100%, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; a first annealing step of annealing the hot-rolled steel sheet; a scale removal step of removing scale from the first-annealed steel sheet; a step of cold-rolling the scale-removed steel sheet to manufacture a cold-rolled sheet; and a second annealing step of annealing the cold-rolled sheet.

[0016] The scale removal step includes spraying coolant having a pH of 4.0 to 8.5 onto the steel plate surface and polishing it with a brush.

[0017] 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: 0.010 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0018] 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.

[0019] The slab may further include at least one of Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0020] 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%).

[0021] The scale remaining on the surface of the steel plate before the first annealing step may be 5% by area or less, and the surface roughness (Ra) may be 3.0㎛ or less.

[0022] Prior to the first annealing step, a step of removing scale by immersing in a 15 to 30 wt% acid aqueous solution for 30 to 150 seconds may be further included.

[0023] Before the first annealing step, a preliminary cold rolling step for cold rolling the hot-rolled steel sheet may be further included, and the first annealing step may anneal the preliminary cold-rolled steel sheet.

[0024] The first annealing step can be performed in an atmosphere containing 3% by volume or more of hydrogen and at a temperature of 870 to 1050°C.

[0025] The scale removal step may further include a step of immersing in a 5 to 20 wt% acid aqueous solution for 2 to 30 seconds.

[0026] After the scale removal step, Al content at 5㎛ inside the steel sheet from the steel sheet surface Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content Al MAX The ratio of (Al MAX / Al 5㎛ ) may be less than 10.0.

[0027] After the scale removal step, the surface roughness of the steel plate may be 1.5㎛ or less.

[0028] The second annealing step can be performed in an atmosphere containing 10 to 50 volume% of hydrogen and at a temperature of 900 to 1050°C.

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent surface quality and electromagnetic properties at the same time.

[0030] A non-oriented electrical steel sheet according to one embodiment of the present invention has a high surface whiteness due to reduced residual oxide on the surface and excellent adhesion of the insulating coating.

[0031] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to improving the performance of an eco-friendly vehicle drive motor.

[0032] Because it has high magnetic anisotropy, high torque can be obtained when manufactured into automobile motors.

[0033] Figure 1 shows a TEM cross-section of a steel plate manufactured in Invention Example 10.

[0034] Figure 2 shows the Al component map of the steel plate manufactured in Invention Example 10.

[0035] Figure 3 is a graph showing the Al content analyzed using GDS for the steel plate manufactured in Invention Example 10.

[0036] Figure 4 is a drawing showing the shape of the surface of a steel plate manufactured in Invention Example 10, and a graph showing the surface outline along the horizontal axis of the drawing.

[0037] Figure 5 shows a TEM cross-section of the steel plate manufactured in Comparative Example 8.

[0038] Figure 6 shows the Al component map of the steel plate manufactured in Comparative Example 8.

[0039] Figure 7 is a graph showing the Al content analyzed using GDS for the steel plate manufactured in Comparative Example 8.

[0040] Figure 8 is a drawing showing the shape of the surface of the steel plate manufactured in Comparative Example 8, and a graph showing the surface outline along the horizontal axis of the drawing.

[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: 1.5 to 6.0%, Al: 0.1 to 2.0%, Mn: 2.0% or less, and Cu: 0.002 to 0.100%, 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: 1.50 to 6.00 wt%

[0053] Silicon (Si) increases the resistivity of the material, thereby reducing iron loss, and increases 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, which drastically reduces rolling productivity and may form a surface oxide layer and oxides that are harmful to magnetism. Therefore, Si may be included in an amount of 1.50 to 6.00 wt%. More specifically, it may be included in an amount of 2.00 to 5.95 wt%. More specifically, it may be included in an amount of 2.10 to 4.50 wt%.

[0054]

[0055] Al: 0.1 to 2.0 wt%

[0056] Aluminum (Al) increases the resistivity of the material, thereby reducing iron loss and improving rollability, and plays a role in improving workability during cold rolling. If too little Al is added, it may be difficult to achieve the effect of reducing high-frequency iron loss, and the precipitation temperature of AlN may be lowered, which may cause fine nitride formation, which may reduce magnetism. If too much Al is added, excessive nitride formation may deteriorate magnetism, 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 0.1 to 2.0 wt%. More specifically, it may be included in an amount of 0.15 to 1.7 wt%. Even more specifically, it may be included in an amount of 0.2 to 1.6 wt%.

[0057]

[0058] Mn: 2.00 wt% or less

[0059] Manganese (Mn) increases the resistivity of the material, improving iron loss and promoting sulfide formation. Excessive addition of Mn increases brittleness during slab and hot rolling. More specifically, Mn may be included in an amount of 0.01 to 2.00 wt%, and even more specifically, 0.05 to 1.80 wt%.

[0060]

[0061] Cu: 0.002 to 0.100 wt%

[0062] Copper (Cu) is effective in suppressing the formation of oxides and nitrides by concentrating on the surface of the steel sheet under a specific range of hot rolling process conditions and annealing processes. It also has the effect of weakening the adhesion between the scale formed on the surface and the steel sheet, thus facilitating descaling. Adding copper reduces oxides and nitrides on the surface and increases the grain size of the steel sheet, thereby increasing the magnetic flux density of the product and reducing core loss. However, if the Cu content is too low, it is difficult to achieve the above effects. Furthermore, if too much is added, descaling becomes uneven as it concentrates and concentrates in specific areas of the steel sheet surface, which can lead to surface defects. More specifically, the Cu content may be 0.002 to 0.050 wt%.

[0063]

[0064] 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: 0.010 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0065] P: 0.1 wt% or less

[0066] Phosphorus (P) not only plays a role in increasing the resistivity of a material, but also can improve the magnetic flux density as a grain boundary segregation element. However, if too much P is added, 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 0.0900 wt%. More specifically, P may be included in an amount of 0.0010 to 0.0750 wt%.

[0067] C: 0.0050 wt% or less

[0068] 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 may be included in an amount of 0.0001 to 0.0035 wt%. More specifically, C may be included in an amount of 0.0010 to 0.0045 wt%.

[0069] S: 0.0100 wt% or less

[0070] Sulfur (S) can form fine precipitates, MnS and CuS, which can deteriorate magnetic properties and hot workability. More specifically, S may be included in an amount of 0.0001 to 0.0080 wt%. More specifically, S may be included in an amount of 0.0005 to 0.0078 wt%.

[0071] Ti: 0.0050 wt% or less

[0072] 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 base metal, thereby inhibiting grain growth and domain wall migration. More specifically, Ti may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, Ti may be included in an amount of 0.0005 to 0.0030 wt%.

[0073] N: 0.0050 wt% or less

[0074] 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 0.0050 wt%. More specifically, N may be included in an amount of 0.0005 to 0.0045 wt%.

[0075]

[0076] 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.

[0077] Sn

[0078] Tin (Sn) can be added to improve magnetism by segregating at grain boundaries and surfaces, improving the material's aggregate structure and suppressing surface oxidation. Excessive addition of Sn can exacerbate grain boundary segregation, deteriorating surface quality, and increasing hardness, potentially leading to fracture of cold-rolled sheets and reduced rollability. Specifically, Sn can be added in an amount of 0.001 to 0.200 wt%.

[0079] Sb

[0080] Antimony (Sb) can be added additionally to enhance magnetism, as it improves the material's texture by segregating at grain boundaries and surfaces and suppresses surface oxidation. Excessive addition of Sb can exacerbate grain boundary segregation, deteriorating surface quality and increasing hardness, potentially leading to fracture of cold-rolled sheets and reduced rollability. Specifically, Sb can be further included in an amount of 0.001 to 0.200 wt%.

[0081] Bi, Pb, Ge, and As

[0082] 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.

[0083]

[0084] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of 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%).

[0085] Cr: 0.01 to 0.50 wt%

[0086] 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 0.010 to 0.20 wt%.

[0087] Ni: 0.05 wt% or less

[0088] 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.

[0089] Zn: 0.01 wt% or less

[0090] 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%.

[0091] Co: 0.05 wt% or less

[0092] 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.

[0093]

[0094] 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%).

[0095] Mo: 0.030 wt% or less

[0096] 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%.

[0097] B: 0.0050 wt% or less

[0098] 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%.

[0099] V: 0.0050 wt% or less

[0100] 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%.

[0101] Ca: 0.0050 wt% or less

[0102] 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.

[0103] Nb: 0.0050 wt% or less

[0104] 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%.

[0105] Zr: 0.0050 wt% or less

[0106] 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%.

[0107] Te: 0.0100 wt% or less

[0108] 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%.

[0109] Mg: 0.0050 wt% or less

[0110] 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%.

[0111]

[0112] 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).

[0113]

[0114] As described above, in one embodiment of the present invention, by appropriately controlling the alloy composition of the steel plate and suppressing Al enrichment and linear defect occurrence on the surface, the appearance characteristics and magnetic characteristics can be improved simultaneously.

[0115] Al content at 5㎛ inside the steel plate from the steel plate surface Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content Al MAX The ratio of (Al MAX / Al 5㎛ ) is 4.0 or less. By adjusting this ratio, the appearance and insulation coating adhesion and iron loss characteristics can be improved. If this ratio is too large, the above characteristics may be deteriorated. More specifically, the Al content at a point 5㎛ inside the steel sheet from the steel sheet surface Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content Al MAX The ratio of (Al MAX / Al 5㎛) may be 1.0 to 3.5. More specifically, it may be 1.5 to 3.3. As an example of a method for evaluating the enriched Al, it can be analyzed using a glow discharge spectrometer. In one embodiment of the present invention, the GDS850A model of Leco can be used for the analysis of the glow discharge spectrometer. At this time, the measurement can be made under the conditions of 700KV of acceleration voltage and 30mA of current. Even if the manufacturer or acceleration voltage of the glow discharge spectrometer is changed, the relative change of Al according to the depth is similar, so the same standard can be applied. The steel plate surface means the outermost surface of the steel plate, and when an insulating film is additionally present on the steel plate surface, it means the surface of the steel plate with the insulating film removed. The interface between the insulating film and the steel plate surface is determined as the point where the Fe content changes rapidly.

[0116] In addition, in one embodiment of the present invention, there may be 5 or fewer unevennesses having a width of 2 mm or more and a length of 10 mm or more per 300 mm x 300 mm area. In one embodiment of the present invention, a portion where a protrusion or groove of 1 μm or more is formed compared to the surface of the steel plate is called an unevenness. If the width and length of the unevenness are greater than a certain size, the appearance and the adhesion of the insulating coating may be deteriorated. The unevenness described above can be measured based on the surface of the steel plate substrate when there is no insulating film, or on the surface of the insulating film when an insulating film exists on the steel plate substrate. The unevenness can be measured using a 3D measuring device capable of measuring the shape of a circle. More specifically, there may be 4 or fewer unevennesses per 300 mm x 300 mm area.

[0117] In addition, in one embodiment of the present invention, there are 5 or fewer Al aggregates having a particle size of 500 nm or more per 100 μm of the steel sheet in an area from the surface of the steel sheet to 5 μm inside the steel sheet. These Al aggregates are evaluated as a type of defect and have a negative effect on the appearance, insulation coating adhesion, and iron loss characteristics. Therefore, it is necessary to suppress the formation of Al aggregates having a particle size of 500 nm or more as much as possible. More specifically, the number of Al aggregates having a particle size of 500 nm or more may be 0.0 to 4.0 per 100 μm of the steel sheet. The Al aggregates can be determined as oxides and nitrides of Al. When observing a cross-section including the thickness direction of the steel sheet using TEM, the Al aggregates can be evaluated using an Al element map. The particle size of the Al aggregates can be obtained as the average value of the horizontal and vertical axes of the Al element map.

[0118] In one embodiment of the present invention, an insulating film is provided on a surface of a steel sheet, and the whiteness of the surface of the insulating film may be 50 or higher. The higher the whiteness, the easier it is to observe defects on the surface of the steel sheet, which is advantageous for surface quality control. In other words, the more residual oxides there are on the surface, the lower the whiteness. Therefore, the degree of residual oxides can be easily determined by the whiteness. More specifically, the whiteness may be 51 to 65. The whiteness can be measured using a CM-3700D from Minolta. Since the measurement values ​​are similar in other devices, the measuring device is not limited.

[0119] In one embodiment of the present invention, the iron loss (W) of the non-oriented electrical steel sheet 10 / 400 ) may be less than 12.5 W / Kg. 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. More specifically, the iron loss (W) of non-oriented electrical steel sheet 10 / 400 ) may be 10.0 to 12.0 W / kg. In one embodiment of the present invention, the iron loss may be expressed based on a thickness of 0.20 mm.

[0120]

[0121] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes the steps of hot-rolling a slab to manufacture a hot-rolled steel sheet; a first annealing step of annealing the hot-rolled steel sheet; a scale removal step of removing scale from the first-annealed steel sheet; a step of cold-rolling the scale-removed steel sheet to manufacture a cold-rolled sheet; and a second annealing step of annealing the cold-rolled sheet.

[0122]

[0123] Below, each step is explained in detail.

[0124] First, the slab is hot rolled.

[0125] 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.

[0126] Specifically, the slab contains, by weight %, Si: 1.5 to 6.0%, Al: 0.1 to 2.0%, Mn: 2.0% or less, and Cu: 0.002 to 0.100%, with the remainder being Fe and unavoidable impurities.

[0127] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0128] The slab can be heated before hot rolling. The heating temperature of the slab is not limited, but it can be heated to 1000 to 1180℃. If the slab heating temperature is too low, problems with hot-rollability may occur. If the slab heating temperature is too high, the growth of oxides containing Si may accelerate, and the concentration of Cu on the surface of the base steel may not occur.

[0129] Next, the slab is hot rolled to produce a hot-rolled plate.

[0130] After rough rolling to a thickness of 30 mm to 60 mm, hot-rolled products with a thickness of 0.8 mm to 2.7 mm can be produced through finish rolling. If the rough rolling thickness is too thick, the latent heat on the steel plate surface is large, and the rolling speed is slowed, which increases the growth of scale during rolling, which is detrimental to the descaling of the hot-rolled coil. On the other hand, if the rough rolling thickness is too thin, the cooling of the steel material is accelerated, which may reduce the rollability. More specifically, it can be 35 mm to 55 mm.

[0131] At this time, after rough rolling, the scale can be removed. For example, a method of removing the scale from the surface by mechanical means is to spray high-pressure water to remove the scale by the impact. If too much time passes after rough rolling, the temperature of the surface decreases, and the adhesion of the scale becomes stronger. In this case, scale removal is not easy. The temperature of the material immediately after rough rolling should be 950℃ or higher and less than 1,050℃, and it is necessary to remove the scale within 25 seconds after rough rolling. If the temperature of the material is too low, the scale growth rate is low, but the surface is cooled, making scale removal difficult. If the temperature is too high, the scale growth rate is excessive, causing internal oxidation to develop and increasing residual oxides on the surface. Therefore, rough rolling can be completed within the above temperature range and scale can be removed within 25 seconds. In one embodiment of the present invention, the scale is an oxide or a nitride.

[0132] The hot-rolled sheet thickness can be 0.8 to 2.7 mm. More specifically, the hot-rolled sheet thickness can be 1.60 to 2.30 mm.

[0133] In the process of manufacturing hot-rolled sheets, the finishing rolling temperature may be 800°C or higher. Specifically, it may be 870 to 950°C. The hot-rolled sheets may be coiled at a temperature of 550°C or higher.

[0134] After the step of manufacturing a hot-rolled steel sheet, a step of removing scale may be further included. If scale remains, the scale will be incorporated into the base steel during the cold rolling process, causing the surface of the final non-oriented electrical steel sheet to become rough and cause point defects, etc. In addition, the scale remaining in the final non-oriented electrical steel sheet will deteriorate the electromagnetic properties, such as reducing the iron loss. Therefore, the scale of the hot-rolled steel sheet must be appropriately removed. In the present invention, the method of removing scale may be a mechanical method using a brush or shot peening, or a chemical method using an aqueous hydrochloric acid (HCl) solution. According to one aspect of the present invention, in the shot blast treatment, the average diameter of the metal balls used may be 1 to 100 ㎛, the operating speed of the steel sheet may be controlled to 50 to 150 mpm (meters per minute), or the metal balls at 300 to 3,000 kg / min may be controlled to collide with the surface of the steel sheet. When using a hydrochloric acid aqueous solution, scale can be removed by immersing in a 15 to 30 wt% acid aqueous solution for 30 to 150 seconds. More specifically, immersion can be performed for 70 to 140 seconds.

[0135] Through scale removal, the oxide remaining on the steel sheet surface before the first annealing step can be reduced to 5.0 area% or less, and the surface roughness can be reduced to 3.0㎛ or less. If the pickling is too excessive, the surface roughness increases, which can cause fracture during cold rolling. If the pickling is too light, the oxide remaining on the surface increases, which can lead to aluminum enrichment and aluminum agglomeration on the surface. More specifically, the oxide remaining on the surface of the hot-rolled steel sheet can be reduced to 1.0 to 4.8 area%. In addition, the surface roughness can be reduced to 0.5 to 2.8㎛. One way to confirm the area of ​​the residual scale is through observation with a scanning electron microscope (SEM). The SEM observation mode is set to a backscattered electron detector, and photographs are taken at a magnification of 50x or 100x. At this time, the base iron and the oxide can be clearly distinguished by the difference in brightness, with the oxide appearing relatively dark. The captured images can be analyzed using an image analyzer to measure the area ratio of residual oxide. In hot-rolled steel sheets, the observation locations of residual scale can be measured at at least three locations, including the center of the sheet and points corresponding to one-quarter of the width from both ends.

[0136] The method of measuring illuminance follows ISO4287-1997 and its equivalent standards, and the cut-off value is based on 2.5㎛.

[0137] Next, the hot-rolled steel sheet is subjected to a first annealing. It is also possible to perform preliminary cold rolling on the hot-rolled steel sheet without performing a hot-rolled steel sheet annealing before the annealing.

[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, performing a first annealing, and then cold rolling to the final product thickness.

[0139] Preliminary cold rolling can be performed at a reduction ratio of 40 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 0.30 to 1.50 mm. More specifically, the reduction ratio can be 50 to 78% and the thickness can be 0.40 to 1.00 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> Problems that promote orientation recrystallization may arise. Conversely, if the reduction ratio is too high, the cold rolling load increases and the possibility of plate breakage increases. The cold rolling mill can be a tandem cold mill with four to six rows, or a Z-mill or Sendzimir mill, but there are no specific limitations.

[0141] Next, in the first annealing step, hot-rolled steel sheets (if preliminary cold rolling is not performed) or preliminary cold-rolled steel sheets are annealed.

[0142] At this time, the temperature can be annealed at 870 to 1050℃. If the temperature is too low, the magnetism of the final electrical steel sheet may be damaged. If the temperature is too high, it may cause fracture during cold rolling. Before the preliminary cold rolling step or before the step of manufacturing the cold-rolled sheet (if the preliminary cold rolling is omitted), the average crystal grain size of the steel sheet may be 180㎛ or less. More specifically, it may be 50 to 180㎛.

[0143] The first annealing step can be performed in an atmosphere containing at least 3% by volume of hydrogen. This can be performed in an atmosphere that suppresses oxides. The remainder is nitrogen. Furthermore, the dew point can be -20°C or lower. More specifically, the hydrogen content can be 3 to 30% by volume. The dew point can be -30°C or lower.

[0144] After the first annealing step, scale is removed from the first-annealed steel sheet. There are limits to the ability to suppress oxide growth during the first annealing step. Therefore, scale removal after the first annealing step can improve the appearance of the steel sheet.

[0145] In one embodiment of the present invention, a step of spraying a coolant having a pH of 4.0 to 8.5 onto a steel plate surface and polishing it with a brush is included. The structure of the brush is not particularly limited as long as it is a structure capable of removing scale from the steel plate. Specifically, the brush structure is such that a SiC abrasive mixed with nylon is combined into threads, and a cylindrical brush is brought into close contact with the upper and lower surfaces of the steel plate and rotated to remove oxides on the surface. The roughness (mesh) of the SiC abrasive, the thickness of the threads, the method of focusing the threads, etc. can be freely changed according to the purpose. For example, the roughness (mesh) of the SiC abrasive can be used in the range of 40 to 120, the diameter of the threads can be 0.3 to 2.0 mm, and the focusing method can be such that 8 to 15 threads can be combined as a single unit, and the focused threads can be attached to a cylindrical cylinder to form a cylindrical brush. Brushing can be performed 1 to 6 times. More specifically, this can be performed one to three times. If the brush is repeatedly used, the surface roughness of the steel sheet increases, which can cause the sheet to break during the cold rolling process described later. The number of brushes can be calculated based on a cylindrical brush rotation speed of 2,000 RPM (Rounds Per Minute), a steel sheet passing speed of 100 MPM (Meters Per Minute), and one brush cycle.

[0146] Because excessive frictional heat can be generated when the brush polishes the steel plate surface, coolant is sprayed onto the brush and the steel plate surface. The acid-base (pH) of the coolant should be within the range of 4.0 to 8.5. If the acid-base (pH) exceeds this range, stains may appear on the steel plate, which can affect the final product.

[0147] The step of removing scale may additionally include a chemical scale removal step along with brush polishing. More specifically, the step of immersing in a 5 to 20 wt% acid aqueous solution for 2 to 30 seconds may be further included. At this time, the acid aqueous solution may be hydrochloric acid. The temperature of the acid solution may be 40 to 96°C. The acid aqueous solution may additionally include an inhibitor to protect the base iron, and the inhibitor may be included in an amount of 0.1 wt% or less. The treatment with the acid aqueous solution may be performed either before or after the brush treatment, but may be performed after the brush treatment.

[0148] After scale removal, Al content at 5㎛ inside the steel plate from the steel plate surface Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content Al MAX The ratio of (Al MAX / Al 5㎛ ) may be less than 10.0. The ratio (Al MAX / Al 5㎛ ) is too large, it means that the surface scale is not sufficiently removed, which may deteriorate the surface quality. More specifically, it can be 1.5 to 9.7.

[0149] The surface roughness after scale removal can be 1.5㎛ or less. Scale removal removes the rough surface irregularities, so the average roughness decreases somewhat or remains similar to the pre-scale removal level. However, if scale removal is excessive and the surface roughness becomes excessive, it hinders rollability in the subsequent rolling process and poses a risk of sheet breakage. More specifically, the surface roughness after scale removal can be 0.5 to 1.3㎛.

[0150]

[0151] Again, returning to the description of the manufacturing method of non-oriented electrical steel sheet, after descaling, the annealed steel sheet is cold rolled to manufacture a cold-rolled sheet.

[0152] Cold rolling mills can be tandem cold mills with four to six rows, or Z-mills or Sendzimir mills. The type of rolling mill and rolling method are not specific. The final rolled thickness can range from 0.1 mm to 0.35 mm.

[0153] Next, in the second annealing step, the cold-rolled sheet is annealed. The second annealing step can be annealed at 900 to 1050°C. If the soaking temperature is too low, the grains may not grow sufficiently, which may lead to increased hysteresis loss and deterioration of iron loss. More specifically, the annealing can be performed at a temperature of 920 to 1020°C. The second annealing step can be soaked for 50 to 120 seconds.

[0154] The atmosphere may contain 10 to 50 volume percent hydrogen and the remainder nitrogen, and the dew point may be below -10°C.

[0155] During the cold-rolled sheet annealing process, all (i.e., more than 99%) of the processed grain structure formed during the cold rolling process can be recrystallized. More specifically, the average grain size can be 100 to 200 µm. If the average grain size is too small, it is difficult to achieve appropriate magnetic properties. Even if the average grain size is larger, no additional magnetic enhancement occurs.

[0156] 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.

[0157] In order to increase the flatness and improve the workability of the electrical steel sheet manufactured above, a stress-relieving heat treatment may be additionally performed at a temperature of 750 to 950°C. However, since the scale remaining during the manufacture of the electrical steel sheet is in a stable state, it does not affect the size or distribution of oxides or nitrides formed on the surface.

[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 1

[0162] Table 1 and the remaining iron and unavoidable impurities were used to produce a 250 mm thick slab. This was maintained at 1120°C for 60 minutes. The slab was rolled to 40 mm using a rough rolling mill, and the temperature after passing through the rough rolling mill was 1020°C. After 23 seconds of rough rolling, the scale was removed using high-pressure water at 150 bar, and finish rolling was performed to produce a 2.0 mm thick hot-rolled steel sheet in the form of a coil. The temperature immediately after finish rolling was 912°C, and the temperature when made into a coil was 630°C.

[0163] Descaling of hot-rolled coils was performed using a hydrochloric acid solution in an 18 wt% HCl aqueous solution at 80°C for 100 seconds, except for Comparative Example 6, which was performed for 60 seconds. Inventive Examples 4 and Comparative Examples 4 and 13 were subjected to a shot blast treatment followed by a pickling treatment for 100 seconds. At this time, the shot blast was performed using metal balls with an average diameter of 400 μm, the steel sheet passing speed was 50 MPM, and the metal ball collision rate was 3,000 kg / min. In Comparative Example 13, scale removal was repeated twice.

[0164] Afterwards, preliminary cold rolling was performed to a thickness of 0.9 mm, and first annealing was performed in an H2 atmosphere at the temperature listed in Table 2 below. Thereafter, scale was removed through the number of brushings and cooling water supply listed in Table 2 below. After brushing, additional scale was removed for the hydrochloric acid concentration and time listed in Table 2. Cold rolling was performed after scale removal. The thickness after final rolling was 0.2 mm.

[0165] After performing the second annealing at 970℃ for 30 seconds, the insulating coating was applied as a resin coating with a thickness of 0.5㎛.

[0166] Al MAX / Al 5㎛ The measurement was performed using Leco's GDS850A model under conditions of 700 KV acceleration voltage and 30 mA current.

[0167] Al agglomerates were measured by observing a cross-section including the thickness direction of the steel plate using TEM.

[0168] One way to determine the scale area of ​​hot-rolled steel sheets is through observation using a scanning electron microscope (SEM). Using a backscattered electron detector, the SEM's observation mode is used to capture images at 50x or 100x magnification, which are then analyzed and measured.

[0169] Whiteness was measured using a colorimeter called Minolta CM3700D.

[0170]

[0171] CSiMnCuAlNPSOther elementsInvention example 10.00225.910.620.0300.700.00380.00450.0078-Invention example 20.00412.500.070.0400.700.00430.00550.0042-Invention example 30.00253.000.180.0500.700.00260.00700.0017-Invention example 40.00154.500.800.0020.500.00420.00800.0027Ni 0.002 invention example 50.003 53.500.500.02 50.700.001 50.01 200.001 9 Ni 0.002, Sn 0.001 invention example 60.002 52.500.500.01 00.550.003 70.07 500.003 3 Sb 0.002 invention example 70.00213.600.350.0501.920.00340.06000.0035- invention example 80.00193.700.320.0070.820.00190.00700.0040- invention example 90.00193.700.320.0070.820.00190.00700.0040- invention example 100.00193.700.320.0070.8 20.00190.00700.0040-Invention Example 110.00193.700.320.0070.820.00190.00700.0040-Comparative Example 10.00506.501.800.0401.200.00180.00710.0042-Comparative Example 20.00374.502.100.0300.800.00250.00860.0014-Comparative Example 30.00453 .700.500.0010.500.00360.01190.0035-Comparative Example 40.00433.500.400.1350.800.00200.01170.0005-Comparative Example 50.00212.200.300.0302.100.00200.00730.0014-Comparative Example 60.00193.700.320.0070.820.00190.00700.00 40-Comparative Example 70.00193.700.320.0070.820.00190.00700.0040-Comparative Example 80.00193.700.320.0070.820.00190.00700.0040-Comparative Example 90.00193.700.320.0070.820.00190.00700.0040-Comparative Example 100.00193.700.320.0070.820.00190.00700.0040-Comparative Example 110.00193.700.320.0070.820.00190.00700.0040-Comparative Example 120.00193.700.320.0070.820.00190.00700.0040-Comparative Example 130.00193.700.320.0070.820.00190.00700.0040-.

[0172] Hot-rolled surface residual oxide (area%)Hot-rolled surface roughness (Ra, ㎛)First annealing temperature (℃)H2 in atmosphere (volume%)Number of brushesCooling water (pH)HCl concentration (%), time (sec)Cold-rolled surface roughness (Ra)after scale removalAl after scale removal MAX / Al 5㎛Invention Example 14.81.9920301 times 4.210%, 5 seconds 0.84.8 Invention Example 23.01.697051 times 8.310%, 5 seconds 1.36.0 Invention Example 33.51.497041 times 6.510%, 5 seconds 1.07.0 Invention Example 44.81.999041 times 6.510%, 5 seconds 0.95.8 Invention Example 54.71.097031 times 6.510%, 5 seconds 1.09.6 Invention Example 63.11.097032 times 6.510%, 5 seconds 1.06.4 Invention Example 73.21.1880102 times 6.518%, 10 seconds 1.26.1 invention example 82.7 0.99 30 33 times 6.2-1.05.1 invention example 92.7 0.91, 05 0 33 times 6.25%, 60 seconds 1.07.3 invention example 102.7 0.99 30 32 times 6.218%, 10 seconds 1.24.7 invention example 112.7 0.99 70 33 times 6.218%, 10 seconds 0.93.0 comparison example 15.8 9705---1.121.5Comparative Example 2---------Comparative Example 34.51.097031 times6.2-0.911.5Comparative Example 43.91.81,04051 times6.2-1.112.5Comparative Example 54.50.89703---1.231.5Comparative Example 611.50.99703---1.136.0Comparative Example 72.70.91,0703---0.937.0Comparative Example 82.70.99702---0.926.4Comparative Example 92.70.99303---0.916.7Comparative Example 102.70.997031 times3.915%, 10 seconds 0.79.1 Comparison Example 112.7 0.99 70 31 times 8.915%, 10 seconds 0.97.3 Comparison Example 122.7 0.99 70 35 times 6.218%, 35 seconds 1.71.1 Comparison Example 130.03.5-----`-

[0173] Number of Al agglomeratesAl after second annealing MAX / Al 5㎛Number of irregularities, whiteness, invention example 101.8065, invention example 232.3161, invention example 313.2260, invention example 401.8162, invention example 521.6462, invention example 631.9265, invention example 723.3166, invention example 832.7167, invention example 912.2363, invention example 1012.0268, invention example 1111.7071, comparative example 17 5.4649 Comparative Example 2----Comparative Example 3 74.1653 Comparative Example 4 54.4551 Comparative Example 5 96.1744 Comparative Example 6 126.5943 Comparative Example 7 76.0847 Comparative Example 8 65.5848 Comparative Example 9 32.5655 Comparative Example 10 34.2358 Comparative Example 11 44.5457 Comparative Example 12----Comparative Example 13----

[0174] As shown in Tables 1 to 3, when the steel component is appropriately controlled and the process conditions are appropriately controlled to suppress Al enrichment and defect occurrence on the surface, it can be confirmed that the surface characteristics are excellent and the magnetism is excellent.

[0175] Comparative Example 1 contained an excessive amount of Si, so a large amount of residual oxide was present in the hot-rolled sheet, and Al concentration and defects occurred in large numbers.

[0176] Comparative Example 2 contained too much Mn, so the surface of the steel sheet cracked during the hot rolling process, and rolling was stopped.

[0177] Comparative examples 3 and 4 are cases where the Cu content was not properly controlled, resulting in numerous Al enrichments and defects.

[0178] Comparative examples 5 to 9 are cases where scale removal was not performed after the first annealing, and Al enrichment and numerous defects occurred.

[0179] Comparative examples 10 and 11 are cases where the pH of the cooling water was not properly controlled during the scale removal process, and Al concentration occurred in large quantities, and stains occurred after the insulating film was formed.

[0180] Comparative Example 12 is a case where scale removal was performed multiple times using a brush, and after scale removal, the roughness was so high that plate breakage occurred during the subsequent cold rolling process.

[0181] In Comparative Example 13, excessive scale removal occurred during the scale removal process after hot rolling, resulting in a large roughness on the surface of the hot-rolled sheet, which resulted in sheet breakage during the subsequent preliminary cold rolling process.

[0182]

[0183] Figures 1 to 4 show the TEM cross-section, composition map, and GDS analysis results of the steel sheet manufactured in Inventive Example 10, as well as the results of a three-dimensional shape analysis of the product surface. As can be seen in Figures 1 to 4, it can be confirmed that Al is only partially concentrated at the boundary of the base steel sheet within the insulating film, and is not concentrated within the base steel sheet. This can also be clearly confirmed in Figure 3. In addition, as shown in Figure 4, it can be confirmed that the occurrence of linear unevenness is suppressed.

[0184] On the other hand, Figs. 5 to 8 show the TEM cross-section, composition map, and GDS analysis results of the steel sheet manufactured in Comparative Example 10. As can be seen in Figs. 5 to 8, Al is concentrated in large quantities near the boundary with the insulating film in the base steel sheet, and in particular, it can be confirmed that aggregates are formed in an elliptical shape of about 1.5 ㎛ in the horizontal direction and about 500 nm in the vertical direction. In addition, the GDS results also show that Al MAX / Al 5㎛ It can be confirmed that the Al is excessively concentrated, with a ratio of approximately 5.5. In addition, it can be confirmed by the occurrence of numerous linear irregularities.

[0185]

[0186] 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. Contains Si: 1.5 to 6.0% by weight, Al: 0.1 to 2.0%, Mn: 2.0% or less (excluding 0%), and Cu: 0.002 to 0.100%, and the remainder includes Fe and inevitable impurities. Al content at 5㎛ inside the steel plate from the steel plate surface Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content Al MAX The ratio of (Al MAX / Al 5㎛ ) is 4.0 or less, Non-oriented electrical steel sheet with 5 or fewer unevennesses, each with a width of 2 mm or more and a length of 10 mm or more per 300 mm × 300 mm area.

2. In paragraph 1, Non-oriented electrical steel sheet having no more than 5 Al agglomerates with a particle size of 500 nm or more per 100 ㎛ of sheet length in a region extending from the surface of the sheet to a depth of 5 ㎛ inside the sheet.

3. 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: 0.010 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

4. 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.

5. In paragraph 1, Non-oriented electrical steel sheet further comprising at least one of 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%).

6. 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%).

7. In paragraph 1, A non-oriented electrical steel sheet comprising an insulating film positioned on the surface of the steel sheet, and having a whiteness of the surface of the insulating film of 50 or higher. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 6.0% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% (excluding 0%)2.0% or less, and Cu: 0.002 to 0.100%, with the remainder being Fe and unavoidable impurities; A first annealing step for annealing the above hot-rolled steel plate; A scale removal step for removing scale from a first annealed steel plate; A step for manufacturing cold rolled sheets by cold rolling descaled steel sheets, and A second annealing step for annealing the cold rolled sheet is included; The above scale removal step is a method for manufacturing a non-oriented electrical steel sheet, including a step of spraying cooling water having a pH of 4.0 to 8.5 on the surface of the steel sheet and polishing it with a brush.

9. In paragraph 8, 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: 0.010 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

10. In paragraph 8, 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.

11. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of 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%).

12. In paragraph 8, 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%).

13. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet having a scale remaining on the surface of the steel sheet before the first annealing step of 5 area% or less and a surface roughness (Ra) of 3.0 ㎛ or less.

14. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet further comprising, prior to the first annealing step, a step of removing scale by immersing in a 15 to 30 wt% acid aqueous solution for 30 to 150 seconds.

15. In paragraph 8, Prior to the first annealing step, a preliminary cold rolling step for cold rolling the hot rolled steel sheet is further included, A method for manufacturing a non-oriented electrical steel sheet, wherein the first annealing step is to anneal a preliminarily cold-rolled steel sheet.

16. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the first annealing step is performed in an atmosphere containing 3 volume% or more of hydrogen and at a temperature of 870 to 1050°C.

17. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the above scale removal step further comprises a step of immersing in a 5 to 20 wt% acid aqueous solution for 2 to 30 seconds.

18. In paragraph 8, After the above scale removal step, Al content at a point 5 μm inside the steel plate from the steel plate surface Al 5㎛ When measuring the Al content in the thickness direction from the steel plate surface to 5㎛ inside the steel plate, the maximum Al content Al MAX The ratio of (Al MAX / Al 5㎛ ) A method for manufacturing a non-oriented electrical steel sheet having a molecular weight of 10.0 or less.

19. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet having a surface roughness of 1.5 ㎛ or less after the above scale removal step.

20. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the second annealing step is performed in an atmosphere containing 10 to 50 volume% of hydrogen and at a temperature of 900 to 1050°C.

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