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, in weight %: 1.5-4.5% of Si; 0.1-2.0% of Al; and 0.1-2.0% Mn, the remainder being Fe and inevitable impurities. The sheet comprises an oxide layer that is inward of the surface, wherein the length of a discontinuous part of the oxide layer, where the thickness of the oxide layer, in a cross section comprising the rolling direction of the steel sheet, is 2nm or less, is 5 to 500nm per 200µm in the rolling direction.

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 magnetism is improved by controlling the dew point and tension during an annealing process prior to cold rolling to form an appropriate oxide layer on the surface of the steel sheet.

[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. A commonly used criterion for evaluating the characteristics of non-oriented electrical steel sheets used in motors is W15 / 50, which is the core loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. However, for non-oriented electrical steel sheets with a thickness of 0.35mm or less used in eco-friendly vehicle drive motors, magnetic properties are often important at low fields of 1.0T or less and high frequencies of 400Hz or higher, so the characteristics of non-oriented electrical steel sheets are often evaluated using W10 / 400.

[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] However, when high-resistivity alloying elements such as Si, Al, Mn, and Cr are added in large quantities, the problem of low magnetic flux density arises. In particular, the use of materials with high magnetic flux density is essential for materials requiring continuous weight reduction, such as eco-friendly electric vehicle drive motors.

[0007] To this end, a method for improving properties by thinning hot-rolled steel was proposed, and a method for improving magnetism by including high Al and performing double annealing and double rolling was proposed. In addition, a method for thinning hot-rolled steel using a thin slab manufacturing method was proposed.

[0008] However, the method of reducing the thickness of hot-rolled plate is difficult to mass-produce due to the increase in rolling load in the general hot-rolling process, and although some improvement in magnetism is confirmed through the addition of high Al and the two-time annealing and two-time rolling processes {110} <001> As the Goss aggregate structure also develops, the circumferential characteristics of the motor deteriorate and surface defects due to high Al addition also increase significantly.

[0009] 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 enhances magnetism by forming an appropriate oxide layer on the surface of the steel sheet by controlling the dew point and tension during an annealing process prior to cold rolling.

[0010] 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%, the remainder being Fe and unavoidable impurities, and includes an oxide layer existing from the surface toward the inside, and the length of a cut portion of the oxide layer in which the thickness of the oxide layer is 2 nm or less in a cross-section including the rolling direction of the steel sheet is 5 to 500 nm per 200 μm in the rolling direction.

[0011] The thickness of the oxide layer can be 15 to 50 nm.

[0012] 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: 0.004 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0013] 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.

[0014] 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%).

[0015] 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%).

[0016] The density of nitride particles with a particle size of 10 to 200 nm is 4 / ㎛ in a cross-section at a depth of 100 nm from the surface. 2 It could be as follows:

[0017]

[0018] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a hot-rolled steel sheet by hot-rolling a slab containing, by weight %, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder including Fe and inevitable impurities; and manufacturing the steel sheet at a dew point of -70 to -40°C and a pressure of 3.0 to 5.0 kgf / mm 2It includes a pre-cold rolling annealing step of applying tension and annealing; 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.

[0019] 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: 0.004 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0020] 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.

[0021] 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%).

[0022] 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%).

[0023] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains.

[0024] A step of pre-cold rolling the hot-rolled sheet may be further included prior to the pre-cold rolling annealing step.

[0025] The reduction ratio in the preliminary cold rolling stage can be 25 to 65%.

[0026] The cracking temperature in the annealing step prior to cold rolling can be 800 to 1100°C.

[0027] In the step of manufacturing cold rolled sheets, the reduction ratio can be 55 to 70%.

[0028] 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.

[0029] A non-oriented electrical steel sheet according to one embodiment of the present invention has further improved magnetic properties without causing surface deterioration.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0036] 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.

[0037] 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.

[0038] 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.

[0039]

[0040] 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.

[0041] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0042]

[0043] Si: 1.5 to 4.5 wt%

[0044] 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 4.2 wt%.

[0045]

[0046] Al: 0.1 to 2.0 wt%

[0047] 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 0.2 to 1.6 wt%. Even more specifically, it may be included in an amount of 0.3 to 1.5 wt%.

[0048]

[0049] Mn: 0.1 to 2.0 wt%

[0050] 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 1.6 wt%. More specifically, it may be included in an amount of 0.3 to 1.5 wt%.

[0051]

[0052] 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: 0.004 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0053] P: 0.1 wt% or less

[0054] 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%.

[0055] C: 0.005 wt% or less

[0056] 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%.

[0057] S: 0.005 wt% or less

[0058] 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%.

[0059] Ti: 0.004 wt% or less

[0060] 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.

[0061] N: 0.005 wt% or less

[0062] 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%.

[0063]

[0064] 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.

[0065] Sn and Sb

[0066] 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%.

[0067] Bi, Pb, Ge, and As

[0068] When added, bismuth (Bi), lead (Pb), germanium (Ge) and arsenic (As) segregate at grain boundaries, thereby relieving stress concentration at grain boundaries during cold rolling, and thus reducing stress concentration in the subsequent recrystallization annealing process. <111> / ND By suppressing the recrystallization of the grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained. However, if they are included in excessive amounts, segregation may occur in large quantities, inhibiting grain growth and lowering the magnetic flux density and iron loss.

[0069]

[0070] 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%).

[0071] Cu: 0.005 to 0.200 wt%

[0072] 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%.

[0073] Cr: 0.01 to 0.50 wt%

[0074] 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%.

[0075] Ni: 0.05 wt% or less

[0076] 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.

[0077] Zn: 0.01 wt% or less

[0078] 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%.

[0079] Co: 0.05 wt% or less

[0080] 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.

[0081]

[0082] 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%).

[0083] Mo: 0.030 wt% or less

[0084] 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%.

[0085] B: 0.0050 wt% or less

[0086] 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%.

[0087] V: 0.0050 wt% or less

[0088] 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%.

[0089] Ca: 0.0050 wt% or less

[0090] 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.

[0091] Nb: 0.0050 wt% or less

[0092] 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%.

[0093] Zr: 0.0050 wt% or less

[0094] 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%.

[0095] Te: 0.0100 wt% or less

[0096] 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%.

[0097] Mg: 0.0050 wt% or less

[0098] 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%.

[0099]

[0100] 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).

[0101]

[0102] As described above, in one embodiment of the present invention, by appropriately controlling the alloy composition of the steel plate and appropriately forming an oxide layer on the surface of the steel plate, magnetism can be improved.

[0103] 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.

[0104] As shown in Fig. 1, it includes an oxide layer (10) existing from the surface of a non-oriented electrical steel sheet (100) toward the inside.

[0105] An oxide layer (10) can be formed when oxygen penetrates into the steel sheet during the manufacturing process of the electrical steel sheet.

[0106] The oxide layer (10) is defined as a portion where oxygen exists on the surface of the steel plate at 20 wt% or more. The detection and thickness of the oxide layer (10) can be determined by processing the TD surface of the specimen with FIB, observing it with TEM, and performing EDS analysis, and determining the portion where oxygen contains 20 wt% or more as the 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 formed may be removed. In order to reduce measurement errors depending on the location, the specimen may be measured at a minimum length of 200 ㎛ in the RD direction, and the average value may be measured.

[0107] As shown in Fig. 1, there is an oxide layer break with a thickness of 2 nm or less in the cross-section including the rolling direction of the steel plate, and the length of this break (DC L ) may be 5 to 500 nm per 200 μm in the rolling direction. As shown in Fig. 1, there may be multiple oxide layer breaks within the specimen, in which case the sum of the lengths of all oxide layer breaks may be included in the aforementioned range. If the length of the oxide layer break is too short, the thickness of the oxide layer may increase overall, and an uneven shape may be generated at the interface between the oxide layer and the base material, which may cause problems in the magnetic properties. If the length of the oxide layer break is too long, the formation of fine nitrides in the region of 100 nm or less in the center of the base material in the oxide layer may be promoted, which may cause problems in the magnetic properties. More specifically, the length of the break (DC L ) may be 50 to 400 nm per 200 μm in the rolling direction. The measurement and determination of the disconnection portion can be performed in the same manner as the measurement and determination method of the oxide layer described above.

[0108] The oxide layer (10) and the oxide layer break can be appropriately formed by controlling the dew point and tension 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.

[0109] The thickness of the oxide layer (10) may be 15 to 50 nm. If the thickness of the oxide layer (10) is too thin, Al enrichment within the oxide layer (10) may not be properly achieved, and the aforementioned AlN suppression effect may not be sufficiently achieved. If the thickness of the oxide layer (10) is too thick, a large amount of oxygen may penetrate into the steel sheet, resulting in poor magnetism. More specifically, the thickness of the oxide layer (10) may be 20 to 30 nm.

[0110] The oxide layer (10) may contain 20 wt% or more of Al due to the surface concentration of Al. More specifically, it may contain 20 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 (10) 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).

[0111] As mentioned above, the formation of nitrides near the surface is suppressed due to the presence of the oxide layer (10). Specifically, the density of nitrides with a particle size of 10 to 200 nm is 4 / ㎛ in the cross section from the surface to a depth of 100 nm. 2 It can be as follows. The grain size and number density of nitride can be measured based on the cross-section (TD plane) perpendicular to the rolling direction (TD direction) of the steel plate. The measurement method is to prepare a specimen using the replica method and observe it with a TEM. The grain size is assumed to be the diameter of an imaginary circle with the same area as the area occupied by the nitride.

[0112] As described above, in one embodiment of the present invention, by appropriately controlling the steel component and appropriately forming an oxide layer, 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 12.5 W / Kg. In addition, the magnetic flux density (B50) may be more than 1.67 T. 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 12.0 W / kg. More specifically, it may be 10.5 to 11.5 W / kg. The magnetic flux density (B50) may be 1.68 T to 1.75 T.

[0113]

[0114] 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 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.

[0115] Below, each step is explained in detail.

[0116] First, the slab is hot rolled.

[0117] 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.

[0118] 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.

[0119] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0120] 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.

[0121] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet may be 0.8 to 2.0 mm. In the step of producing the hot-rolled sheet, the finishing rolling temperature may be 800°C or higher. Specifically, it may be 800 to 1000°C. The hot-rolled sheet may be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled sheet may be 0.9 to 1.8 mm.

[0122] After manufacturing a hot-rolled steel sheet, subsequent steps can be performed while the scale remaining on the hot-rolled steel sheet remains. That is, after hot rolling, scale removal processes such as pickling, shot blasting, or surface grinding can be omitted, and subsequent steps can be performed. By performing cold rolling without the pickling process, friction between the rolling work rolls and the steel sheet increases, so that shear deformation is simultaneously applied in addition to plane deformation during rolling, and a specific orientation develops during recrystallization annealing. In one embodiment of the present invention, scale refers to a portion on the surface of the steel sheet where elements such as Fe, Al, and Si combine with oxygen to form a phase different from that of the base metal. Remaining scale means that at least 1 μm of scale remains on the hot-rolled sheet. In this case, the scale thickness refers to the sum of the scale thicknesses formed on both surfaces of the steel sheet. If the remaining scale thickness is too thin, the effect due to the scale residue may not be fully exerted. Even if the scale thickness is thicker, the effect is not improved, and there is a problem of a reduced yield of the steel sheet. More specifically, scales with a thickness of 0.1 to 1 μm may remain.

[0123] 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.

[0124] 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.

[0125] Preliminary cold rolling can be performed at a reduction ratio of 25 to 65% 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 0.5 to 1.5 mm. More specifically, the reduction ratio can be 30 to 60% and the thickness can be 0.8 to 1.3 mm.

[0126] 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.

[0127] 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.

[0128] As mentioned above, the preliminary cold rolling step can be omitted if necessary.

[0129] Next, in the annealing step prior to cold rolling, a hot-rolled steel sheet or a preliminary cold-rolled sheet is annealed. In one embodiment of the present invention, by controlling the dew point and tension in the annealing step prior to cold rolling, an oxide layer (10) can be appropriately formed.

[0130] Specifically, the dew point may be between -70 and -40°C. If the dew point is too low, the oxide layer of the final product may become excessively fractured, or a large amount of fine nitrides may form near the surface, which may cause problems with the magnetic properties. If the dew point is too high, an excessively thick oxide layer may form, or fine oxide particles may form near the surface, which may cause problems with the magnetic properties. More specifically, the dew point may be between -65 and -45°C. More specifically, the dew point may be the dew point for the atmosphere during the cracking process.

[0131] Also, 3.0 to 5.0 kgf / mm 2 The tension can be applied. If the tension is too low, the shape of the steel plate cannot be sufficiently corrected, which may cause excessive partial oxidation layer formation on the final product plate, which may cause problems with the magnetic properties. If the tension is too high, excessive oxidation layer breakage may be formed on the final product plate, which may cause problems with the magnetic properties. More specifically, the tension should be 3.3 to 4.7 kgf / mm. 2 It can be. Tension can be the tension measured between the Bridle Rolls at the entrance and exit of the annealing furnace, and can be measured using a load cell.

[0132] The soaking temperature during the annealing stage prior to cold rolling can range from 800 to 1100°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 830 to 1080°C. The soaking time may range from 30 to 300 seconds.

[0133] 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.

[0134] 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 55 to 70%. 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 the direction can be promoted, and the grains can become finer, which can cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 58 to 67%. 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.

[0135] 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 -50°C to -10°C.

[0136] 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 drop sharply. More specifically, annealing can be performed at a temperature of 900 to 1050°C. The soaking time may be 10 to 300 seconds.

[0137] 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.

[0138] 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.

[0139]

[0140] 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.

[0141]

[0142] Example 1

[0143] A slab was manufactured with the components listed in Table 1 and containing the remainder Fe and unavoidable impurities. This was heated to 1150°C and hot-rolled at a finishing temperature of 950°C to manufacture a hot-rolled sheet having the thickness listed in Table 2. Specimen No. A1 was pickled to completely remove scale on the hot-rolled sheet, and scale removal was omitted for the remaining specimens.

[0144] Afterwards, the hot-rolled sheet was preliminarily cold-rolled under the conditions of Table 2, omitting annealing, and annealed before cold rolling, and then cold-rolled to a final thickness of 0.25 mm. The cold-rolled steel sheet was annealed at a soaking temperature of 1000°C for 100 seconds.

[0145] The magnetic flux density and iron loss were measured in the rolling direction and the direction perpendicular to the rolling direction using a single sheet tester by cutting 5 sheets of 60 mm width × 60 mm length for each specimen, and the average values ​​were presented.

[0146] At this time, W 10 / 400 is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. B 50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0147] The oxide layer and nitride properties were analyzed by TEM by taking images of the TD surface of the FIB-processed specimen along the RD direction for a length of 300 μm or more, and the chemical composition was analyzed by EDS. The nitride density of 10 to 200 nm particles in the cross-section from the surface to a depth of 100 nm was 4 particles / μm. 2 If exceeded, ○, 4 / ㎛ 2 If it is below, it is marked with X.

[0148] Specimen numberSiAlMnCSNTiNbV(%)(%)(%)(ppm)(ppm)(ppm)(ppm)(ppm)(ppm)A12.701.60.7281416111915A22.701.60.728131323172 1A32.701.60.720181824819A42.701.60.7131817171810A52.701.60.7171614141616A62.701.60.7244317171714A72.701. 60.7261313111313A82.701.60.7141416141418B13.300.61.6137314121123B23.300.61.63513159139B33.300.61.6163292 41910B43.300.61.6172012142021B53.300.61.6131313171318B63.300.61.6281716141715B73.300.61.6294214131817B83. 300.61.6311318181313C13.750.21.668199241920C23.750.21.6211611212316C33.750.21.6291712231412C43.750.21.62 188171818C53.750.21.631451391411C63.750.21.6281516131512C73.750.21.625171671715C83.750.21.6274217141418D1 4.200.50.22298118923D24.200.50.2171611121611D34.200.50.2143510122113D44.200.50.291614141614D54.200.50.21 61716161717D64.200.50.2213320151821D74.200.50.2161720101724D84.200.50.2311312131313D94.200.50.22188171818

[0149] Specimen numberHot rolled plate thickness (mm)Thickness after preliminary cold rolling (mm)Preliminary cold reduction ratio (%)Annealing temperature before cold rolling (℃)Annealing dew point before cold rolling (℃)Annealing tension before cold rolling (kgf / mm) 2) Cold rolling reduction ratio (%) A10.960.6335750-553.560 A22.080.6370950-554.560 A31.560.63601000-803.560 A41.541.00351050-554.575 A51.560.6360850-553.560 A60.960.6335950-554.560 A70.960.63351000-553.560 A81.560.63601050-554.560 B11.140.6345850-554.560B21.140.6345950-556.060B30.910.50451000-554.550B41.140.63451150-553.560B51 .140.6345850-554.560B61.140.6345950-553.560B71.140.63451000-554.560B81.140.63451050-553.560C11.590 .7155850-553.565C21.100.7135750-554.565C31.100.71351000-552.065C41.590.71551050-554.565C51.100.71 35850-553.565C61.590.7155950-554.565C71.590.71551000-553.565C81.100.71351050-554.565D11.590.715585 0-554.565D20.890.7120950-553.565D31.590.71551000-304.565D41.590.71551050-553.565D51.590.7155850-5 54.565D61.590.7155950-553.565D71.590.71551000-554.565D81.590.71551050-553.565D91.590.715595000.365

[0150] Specimen number Oxide layer thickness (nm) Oxide layer break length (nm) Nitride density (units / ㎛) 2)W10 / 400(W / kg)B50(Tesla)A15200○12.81.66A230800○13.01.64A35200○13.01. 64A4401300○12.81.65A540100×11.21.68A630200×11.21.68A730200×11.11.68A 840200×11.31.68B15300○13.01.66B2401300○13.11.66B370200○13.01.64B480200○13.21.65B540100×11.31.68B630100×11.31.68B740200×11.11.68B840200×11 .21.68C15300○13.21.66C25300○13.21.64C370100○13.11.66C440300×11.31.68 C530200×11.21.68C630200×11.21.68C730300×11.31.68C840300×11.21.68D1510 0○12.91.66D280100○12.91.64D380300○12.81.65D440200×11.11.68D540200×11.31.68D640200×11.11.68D730100×11.11.68D840300×11.21.68D91500×12.91.64

[0151] 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, and the oxide layer characteristics are appropriately formed have excellent iron loss and magnetic flux density.

[0152] On the other hand, if the steel component is not properly controlled, the process conditions are not properly controlled, and the oxide layer is not properly formed, it can be confirmed that the iron loss and magnetic flux density are inferior.

[0153]

[0154] 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.

[0155] [Explanation of symbols]

[0156] 100: Non-oriented electrical steel sheet, 10; Oxide layer

Claims

1. Contains Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder includes Fe and inevitable impurities. 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 2 nm or less in a cross-section including the rolling direction of the steel sheet and a length of a cut portion of the oxide layer of 5 to 500 nm per 200 ㎛ in the rolling direction.

2. In paragraph 1, A non-oriented electrical steel sheet having a thickness of the oxide layer of 15 to 50 nm.

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: 0.005 wt% or less (excluding 0%), Ti: 0.004 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, 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%).

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, The density of nitride particles with a particle size of 10 to 200 nm is 4 / ㎛ in the cross section at a depth of 100 nm from the surface. 2 Below is the non-oriented electrical steel sheet.

8. 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; The above steel plate has a dew point of -70 to -40℃ and a pressure of 3.0 to 5.0 kgf / mm 2 An annealing step prior to cold rolling in which tension is applied and annealed; 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 above cold rolled sheet; A method for manufacturing a non-oriented electrical steel sheet comprising:

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: 0.005 wt% or less (excluding 0%), Ti: 0.004 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 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%).

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, wherein the subsequent steps are performed while the scale remaining on the hot-rolled steel sheet remains after manufacturing the hot-rolled steel sheet.

14. In paragraph 8, 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 25 to 65% in the preliminary cold rolling step.

16. In paragraph 8, 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 800 to 1100°C.

17. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet having a reduction ratio of 55 to 70% in the step of manufacturing the cold rolled sheet.

18. In paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the cold rolled sheet annealing step 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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