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%, 1.5-5.0% of Si, 0.1-2.0% of Al, and 0.1-2.0% of Mn, with the remainder comprising Fe and inevitable impurities, wherein the ratio (Gsout / Gsin) of the average grain size (Gsout) on the surface of the steel sheet or in a surface layer, which is a region extending at least 1 / 8 and less than 1 / 4 of the total thickness of the steel sheet from the surface of the steel sheet, to the average grain size (Gsin) in an inner layer, which is a region extending 1 / 4-3 / 4 of the total thickness of the steel sheet from the surface of the steel sheet, is 0.60-0.95, and the ratio (Hv1 / 8 / (Hv1 / 2) of the hardness (Hv1 / 8) at the 1 / 8 point (1 / 8t) of the total thickness of the steel sheet from the surface of the steel sheet to the hardness (Hv1 / 2) at the 1 / 2 point (1 / 2t) of the total thickness of the steel sheet from the surface of the steel sheet is at least 1.05.

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 improves both punchability and magnetism by simultaneously controlling the hardness and grain size of the surface layer and inner layer by controlling the heating rate and dew point during the heating process of cold-rolled sheet annealing.

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

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

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

[0005] Meanwhile, manufacturing non-oriented electrical steel sheets into motors involves a process of stamping and laminating the sheets into the motor's shape. If the stamping performance is poor, resulting in an unsmooth cut surface or significant burr formation, this can negatively impact the performance of the final motor.

[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 simultaneously improves both punchability and magnetism by simultaneously controlling the hardness and grain size of the surface layer and inner layer by controlling the heating rate and dew point during the heating process of cold-rolled sheet annealing.

[0007] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, the remainder Fe and inevitable impurities, and has an average grain size (Gs) in the inner layer, which is a region of 1 / 4 to 3 / 4 of the total steel sheet thickness from the steel sheet surface. in ) for the steel plate surface or the surface layer, which is an area from the steel plate surface to the entire steel plate surface, from 1 / 8 to less than 1 / 4 of the total steel plate thickness, the average grain size (Gs) out ) ratio (Gsout / Gs in ) is 0.60 to 0.95, and the hardness (Hv) at 1 / 2 point (1 / 2t) of the total steel plate thickness 1 / 2 ) at 1 / 8 point (1 / 8t) of the total steel plate thickness from the steel plate surface (Hv 1 / 8 ) ratio (Hv 1 / 8 / Hv 1 / 2 ) is 1.05 or higher.

[0008] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0009] [Formula 1]

[0010] [Si] × [Mn] / (4 × [Al]) ≤ 1.0

[0011] (In Equation 1, [Si], [Mn], and [Al] represent the contents (weight %) of Si, Mn, and Al, respectively.)

[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: 0.005 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] Average grain size in the inner layer (Gs) in ) can be 70 to 90㎛.

[0017] Average grain size in the surface layer (Gs) out ) may be 55 to 75 μm.

[0018] Hardness (Hv) at a point half (1 / 2t) of the total thickness of the steel plate from the surface of the steel plate 1 / 2 ) can be 220 to 235 Hv.

[0019] Hardness (Hv) at 1 / 8 point (1 / 8t) of the total thickness of the steel plate from the surface of the steel plate 1 / 8 ) can be 240 to 270 Hv.

[0020] 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, by weight %, 1.5 to 5.0% Si, 0.1 to 2.0% Al, and 0.1 to 2.0% Mn, with the remainder including Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0021] In the step of manufacturing a cold-rolled sheet, a first heating step of heating the cold-rolled sheet in a temperature range of 300°C or more and less than 500°C; a second heating step of heating the cold-rolled sheet in a temperature range of 500 to 700°C, and a soaking step are included, and the following equations 2 and 3 are satisfied.

[0022] [Formula 2]

[0023] HR1 / DP1 ≤ 1.5

[0024] [Formula 3]

[0025] HR2 / DP2 ≥ 6

[0026] (In Equations 2 and 3, HR1 and HR2 are the heating rates (℃ / sec) in the first heating stage and the second heating stage, respectively, and DP1 and DP2 are the dew point temperatures (℃) in the first heating stage and the second heating stage, respectively.)

[0027] Slavs can satisfy the following equation 1.

[0028] [Formula 1]

[0029] [Si] × [Mn] / (4 × [Al] ≤ 1.0

[0030] (In Equation 1, [Si], [Mn], and [Al] represent the contents (weight%) of Si, Mn, and Al in the slab, respectively.)

[0031] The slab may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

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

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

[0034] 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%).

[0035] In the first heating step, the heating rate may be 50°C / sec or less.

[0036] In the first heating stage, the dew point temperature may be 30°C or higher.

[0037] In the second heating step, the heating rate may be 50°C / sec or more.

[0038] In the second heating stage, the dew point temperature may be above 0°C and below 10°C.

[0039] A non-oriented electrical steel sheet according to one embodiment of the present invention can control the burr height during punching to be low while having excellent high-frequency iron loss.

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

[0041] Figure 1 is a schematic diagram schematically showing a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0046] 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.

[0047] 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.

[0048] 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.

[0049]

[0050] A non-oriented electrical steel sheet according to one embodiment of the present invention includes, in wt%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities.

[0051] Below, the reasons for the limitation of the components of non-oriented electrical steel sheets are explained.

[0052]

[0053] Si: 1.5 to 5.0 wt%

[0054] 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's hardness may increase, resulting in poor productivity and punchability. Therefore, the Si content may be 1.5 to 5.0 wt%. More specifically, it may be 2.0 to 4.5 wt%. More specifically, it may be 3.2 to 3.75 wt%.

[0055]

[0056] Al: 0.1 to 2.0 wt%

[0057] 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 0.5 to 1.8 wt%. Even more specifically, it may be included in an amount of 0.7 to 1.5 wt%.

[0058]

[0059] Mn: 0.1 to 2.0 wt%

[0060] 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. If too much Mn is added, fine MnS is excessively precipitated, changing the magnetic domain structure and adversely affecting iron loss. 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 1.8 wt%. Even more specifically, it may be included in an amount of 0.4 to 1.5 wt%.

[0061]

[0062] In one embodiment of the present invention, the resistivity of the non-oriented electrical steel sheet may be 55 μΩ·cm or more. The resistivity is better the larger the resistivity is for reducing eddy current loss in a high-frequency rotating machine, but if it is too large, the magnetic flux density may be inferior. In one embodiment of the present invention, the resistivity can be estimated from the equation 13.25+11.3×([Si]+[Al]+[Mn] / 2+[Cu] / 2+[Cr] / 2). In this case, if Cu and Cr are not included, it can be calculated as 0. More specifically, the resistivity can be 58 to 80 μΩ·cm.

[0063]

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

[0065] [Formula 1]

[0066] [Si] × [Mn] / (4 × [Al]) ≤ 1.00

[0067] (In Equation 1, [Si], [Mn], and [Al] represent the contents (weight %) of Si, Mn, and Al, respectively.)

[0068] Si and Mn cause surface oxidation during high-temperature annealing. If the Si and Mn content is too high compared to the Al content, and the value of Equation 1 exceeds the upper limit, internal oxidation may occur rapidly at a dew point above 0℃, which may rapidly deteriorate the iron loss. More specifically, the value of Equation 1 may be 0.40 to 0.90.

[0069]

[0070] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0071] P: 0.1 wt% or less

[0072] Phosphorus (P) not only plays a role in increasing the resistivity of a material, but also can improve 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 0.0500 wt%. More specifically, P may be included in an amount of 0.0010 to 0.0200 wt%.

[0073] C: 0.005 wt% or less

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

[0075] S: 0.005 wt% or less

[0076] Sulfur (S) can form fine precipitates, MnS and CuS, which can worsen magnetic properties and hot workability. More specifically, S can be included in an amount of 0.0001 to 0.0030 wt%.

[0077] Ti: 0.005 wt% or less

[0078] 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, Ti may be included in an amount of 0.0001 to 0.0030 wt%.

[0079] N: 0.005 wt% or less

[0080] 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%.

[0081]

[0082] 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.

[0083] Sn

[0084] Tin (Sn) can be added to improve magnetism because it improves the material's texture by segregating at grain boundaries and surfaces and plays a role in suppressing surface oxidation. If too much Sn is added, grain boundary segregation becomes severe, which deteriorates the surface quality and increases hardness, which can cause cold-rolled sheet fracture and reduce rollability. Specifically, Sn can be further included in an amount of 0.005 to 0.200 wt%. More specifically, it can be further included in an amount of 0.010 to 0.080 wt%.

[0085] Sb

[0086] Antimony (Sb) can be additionally added to improve magnetism because it improves the material's texture and suppresses surface oxidation by segregating at grain boundaries and surfaces. If too much Sb is added, grain boundary segregation becomes severe, deteriorating surface quality and increasing hardness, which can cause cold-rolled sheet fracture and reducing rollability. Specifically, Sb can be further included in an amount of 0.005 to 0.200 wt%. More specifically, it can be further included in an amount of 0.010 to 0.080 wt%.

[0087] Bi, Pb, Ge, and As

[0088] 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.

[0089]

[0090] 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%).

[0091] Cu: 0.005 to 0.200 wt%

[0092] 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%.

[0093] Cr: 0.01 to 0.50 wt%

[0094] 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%.

[0095] Ni: 0.05 wt% or less

[0096] 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.

[0097] Zn: 0.01 wt% or less

[0098] 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%.

[0099] Co: 0.05 wt% or less

[0100] 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.

[0101]

[0102] 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%).

[0103] Mo: 0.030 wt% or less

[0104] 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%.

[0105] B: 0.0050 wt% or less

[0106] 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%.

[0107] V: 0.0050 wt% or less

[0108] 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%.

[0109] Ca: 0.0050 wt% or less

[0110] 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.

[0111] Nb: 0.0050 wt% or less

[0112] 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%.

[0113] Zr: 0.0050 wt% or less

[0114] 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%.

[0115] Te: 0.0100 wt% or less

[0116] 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%.

[0117] Mg: 0.0050 wt% or less

[0118] 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%.

[0119]

[0120] 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).

[0121]

[0122] As described above, in one embodiment of the present invention, by appropriately controlling the alloy composition of the steel plate and controlling the heating rate and dew point during the heating process of annealing the cold-rolled plate, the hardness and grain size of the surface layer and the inner layer can be controlled simultaneously.

[0123] Figure 1 is a schematic diagram schematically showing a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0124] As shown in Fig. 1, a non-oriented electrical steel sheet (100) according to one embodiment of the present invention has a surface layer (10) in an area of ​​1 / 8 or more and less than 1 / 4 of the total steel sheet thickness from the entire steel sheet surface, and an inner layer (20) in an area of ​​1 / 4 to 3 / 4 of the total steel sheet thickness from the steel sheet surface. As shown in Fig. 1, the surface layer (10) exists on not only one surface but also both surfaces. In this case, the lower surface layer may exist in an area of ​​more than 3 / 4 and less than 7 / 8 of the total steel sheet thickness from the entire steel sheet surface. The inner layer (20) exists between the surface layers (10).

[0125] The average grain size (Gs) in the inner layer (20) in ) for the average crystal grain size (Gs) in the surface layer (10) out ) ratio (Gs out / Gs in ) is 0.60 to 0.95. As the frequency increases, the eddy current flowing on the surface increases due to the skin effect, so it is advantageous to finely control the grain size of the surface layer (10). On the other hand, if the grain size of the surface layer (10) is too small, the magnetism at the commercial frequency (50 Hz) may deteriorate. More specifically, the average grain size (Gs) in the inner layer (20) in ) for the average crystal grain size (Gs) in the surface layer (10) out ) ratio (Gs out / Gs in ) can be between 0.65 and 0.90.

[0126] In one embodiment of the present invention, the crystal grain size can be measured based on a cross-section including the steel plate thickness, more specifically, the TD plane. The number of crystal grains in each region can be measured using an optical microscope, and the area per crystal grain can be measured, thereby determining the crystal grain size. The crystal grain size can be calculated as the diameter of a virtual circle with the same area as the circle.

[0127] The average grain size (Gs) in the inner layer (20) in ) may be 70 to 90 μm. If the inner layer (20) crystal grain size is too small, the iron loss at 50 to 400 Hz may be poor. If the inner layer (20) crystal grain size is too large, the magnetism may be poor at frequencies exceeding 400 Hz. More specifically, the inner layer (20) crystal grain size may be 72 to 88 μm.

[0128] Average grain size (Gs) in the surface layer (10) out ) may be 55 to 75㎛. If the crystal grain size of the surface layer (10) is too small, the magnetism at commercial frequency (50Hz) may deteriorate. This may be a problem in terms of surface finish. If the crystal grain size of the surface layer (10) is too large, the surface processability may deteriorate. More specifically, the crystal grain size of the surface layer (10) may be 56 to 72㎛.

[0129] In one embodiment of the present invention, the hardness (Hv) at the point 1 / 2t of the total steel plate thickness 1 / 2 ) at 1 / 8 point (1 / 8t) of the total steel plate thickness from the steel plate surface (Hv 1 / 8 ) ratio (Hv 1 / 8 / Hv 1 / 2 ) is 1.05 or more. When the hardness of the surface layer (10) is greater than that of the inner layer (20), it helps to reduce the burr height after punching. More specifically, the hardness (Hv) at 1 / 2 point (1 / 2t) of the total steel plate thickness 1 / 2 ) at 1 / 8 point (1 / 8t) of the total steel plate thickness from the steel plate surface (Hv 1 / 8 ) ratio (Hv 1 / 8 / Hv 1 / 2 ) can be between 1.08 and 1.20.

[0130] In one embodiment of the present invention, the hardness value refers to Vickers hardness, and the average value obtained by measuring 5 points at 1 mm intervals in the TD direction was used.

[0131] Hardness (Hv) at a point half (1 / 2t) of the total thickness of the steel plate from the surface of the steel plate 1 / 2 ) can be 220 to 235 Hv. Hardness (Hv 1 / 2 ) is too small, the strength is low and breakage may occur during high-speed rotation. Hardness (Hv) 1 / 2 ) is too large, the material may be too hard and break during processing. More specifically, the hardness (Hv 1 / 2 ) can be 225 to 233 Hv.

[0132] Hardness (Hv) at 1 / 8 point (1 / 8t) of the total thickness of the steel plate from the surface of the steel plate 1 / 8 ) can be 240 to 270 Hv. Hardness (Hv 1 / 8 ) is too small, the surface is softer than the inside, so it is not effective in reducing burrs. Hardness (Hv) 1 / 8 ) is too large, surface fracture may occur excessively. More specifically, the hardness (Hv 1 / 8 ) can be 245 to 265 Hv.

[0133]

[0134] As described above, in one embodiment of the present invention, by controlling the crystal grain size and hardness according to thickness, both the punchability and magnetism can be improved simultaneously.

[0135] Specifically, in one embodiment of the present invention, when punching with a tolerance of 8% and a punching speed of 300 spm (stamping speed per minute), the burr height may be 0.020 μm or less. More specifically, the burr height may be 0.005 to 0.015 μm.

[0136] As described above, in one embodiment of the present invention, the core loss (W) of the non-oriented electrical steel sheet based on a thickness of 0.25 mm 10 / 800 ) may be less than 35.0 W / Kg. Iron loss (W 10 / 800 ) is the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 800 Hz. More specifically, the iron loss (W) of non-oriented electrical steel sheet 10 / 400) may be 30.0 to 35.0 W / kg.

[0137]

[0138] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet.

[0139]

[0140] Below, each step is explained in detail.

[0141] First, the slab is hot rolled.

[0142] 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.

[0143] Specifically, the slab contains Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, with the remainder being Fe and unavoidable impurities.

[0144] As other additional elements have been described in the alloy composition of non-oriented electrical steel sheets, redundant descriptions are omitted.

[0145] 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.

[0146] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be 1.0 to 4.5 mm. In the step of producing the hot-rolled sheet, the finishing rolling temperature can be 800°C or higher. Specifically, it can be 800 to 1000°C. The hot-rolled sheet can be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled sheet can be 1.5 to 4.3 mm.

[0147] After manufacturing a hot-rolled steel sheet, an additional step of annealing the hot-rolled sheet may be included. At this time, the soaking temperature may be 800 to 1100°C. If the annealing temperature is too low, the recrystallized structure may not be formed or may grow finely, thereby reducing the effect of increasing the magnetic flux density. If the annealing temperature is too high, the magnetic properties may deteriorate, and the rolling workability may deteriorate due to deformation of the plate shape. More specifically, the temperature range may be 830 to 1080°C. The soaking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may be omitted.

[0148] Next, the hot rolled steel sheet is cold rolled to produce a cold rolled sheet. At this time, cold rolling can be performed at a reduction ratio of 40 to 85%. If the reduction ratio is too low, the accumulated strain energy in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which can cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it can cause problems in the subsequent annealing process. <111> / ND The recrystallization of the grains in the direction of orientation is promoted, and the grains become finer, which can cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 60 to 75%. The cold rolling step can be performed using a tandem cold rolling mill that continuously cold rolls the steel sheet using multiple rolling stands, or a reverse rolling mill that discontinuously cold rolls the steel sheet using 12 or more rolling rolls. The final rolled thickness can be 0.1 mm to 0.35 mm.

[0149] The process of manufacturing cold rolled sheets can be performed once or twice or more with intermediate annealing in between.

[0150] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. In one embodiment of the present invention, by controlling the heating rate and dew point in a specific temperature range during heating during the cold-rolled sheet annealing, both the punching properties and magnetism can be improved simultaneously.

[0151] Specifically, in the step of manufacturing a cold-rolled sheet, the method includes a first heating step of heating the cold-rolled sheet in a temperature range of 300°C or more and less than 500°C; a second heating step of heating the cold-rolled sheet in a temperature range of 500 to 700°C; and a soaking step, and satisfies the following equations 2 and 3.

[0152] [Formula 2]

[0153] HR1 / DP1 ≤ 1.5

[0154] [Formula 3]

[0155] HR2 / DP2 ≥ 6.0

[0156] (In Equations 2 and 3, HR1 and HR2 are the heating rates (℃ / sec) in the first heating stage and the second heating stage, respectively, and DP1 and DP2 are the dew point temperatures (℃) in the first heating stage and the second heating stage, respectively.)

[0157] In the temperature range of 300℃ or more and less than 500℃, which corresponds to the initial stage of annealing, by slowing down the heating rate and managing the dew point high, Si, Al, and Mn existing inside the material diffuse and concentrate to the surface. In addition, by controlling the heating rate and dew point as in Equation 2, internal oxidation of the material can be suppressed. If the value of Equation 2 is too large, it is difficult to achieve the above-mentioned purpose. More specifically, the value of Equation 2 can be 0.1 to 1.3. In one embodiment of the present invention, the heating rate and dew point in the corresponding temperature range may vary, and in this case, the heating rate and dew point in the corresponding temperature range may be the average heating rate and dew point. The average may be an average over time.

[0158] In the first heating step, the heating rate (HR1) may be 50°C / sec or less. If the heating rate (HR1) is too high, it may be difficult to control the optimal grain size. More specifically, the heating rate (HR1) may be 10 to 48°C / sec.

[0159] In the first heating step, the dew point temperature may be 30°C or higher. If the dew point temperature (DP1) is too low, it may be difficult to finely control surface grain size. More specifically, the dew point temperature (DP1) may be 35 to 65°C.

[0160] In the temperature range of 500 to 700°C, the heating rate is increased and the dew point is controlled to be low, promoting the formation of a magnetically favorable texture. If the value of Equation 3 is too small, the internal oxide layer may become thick, which may adversely affect magnetism. More specifically, the value of Equation 3 may be 8.0 to 35.0.

[0161] In the second heating stage, the heating rate may be 50°C / sec or higher. If the heating rate (HR2) is too low, a problem of low magnetic flux density may occur. More specifically, the heating rate (HR2) may be 55 to 90°C / sec.

[0162] In the second heating step, the dew point temperature may be between 0°C and 10°C. If the dew point temperature (DP2) is too low, an external oxidation layer may develop. If the dew point temperature (DP2) is too high, an internal oxidation layer may develop. More specifically, the dew point temperature (DP2) may be between 2°C and 8°C.

[0163] The cracking temperature during the cracking stage may be between 850 and 1100°C. If the cracking temperature is too low, the grains may not grow sufficiently, which may lead to increased hysteresis loss and deterioration of iron loss. If the cracking temperature is too high, the grains may grow excessively, which may lead to increased eddy current loss. More specifically, the cracking temperature may be between 900 and 1050°C. The cracking time may be between 30 and 120 seconds.

[0164] 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.

[0165] 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.

[0166]

[0167] 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.

[0168]

[0169] Example 1

[0170] A slab was manufactured using the components listed in Table 1 and containing the remainder Fe and unavoidable impurities. The C, S, N, and Ti contents of the slab were all controlled to 0.0025 wt%. The slab was heated to 1150°C and hot-rolled at a finishing temperature of 850°C to manufacture a hot-rolled sheet with a thickness of 2.0 mm.

[0171] Afterwards, the hot-rolled sheet was annealed at 1,100℃ for 4 minutes and then pickled. It was then cold-rolled to a thickness of 0.25 mm. The conditions for the cold-rolled sheet annealing are shown in Table 2, with a soaking zone temperature of 1,000℃ and a soaking time of 60 seconds. The hardness was measured by Vickers hardness, a load of 100 g was applied, and five points were measured at 1 mm intervals to obtain the average value. A small, makeshift mold in the laboratory was used for punching, with a tolerance of 8% and a speed of 300 spm. The burr height was measured using a micrometer. The grain size was determined by averaging the number of grains per corresponding area on the TD plane, and the high-frequency core loss was measured using a single sheet tester.

[0172] Classification SiAlMn Resistivity (μΩ cm) Formula 1 Value 13.40.80.8650.8523.21.10.7660.5133.51.20.8710.5843.51.50.4720.2353.51.21.2730.8863.51.10.8700.6473.20.91.3671.1683.41.01.0 690.8593.61.50.9760.54103.51.51.2770.70113.21.21.1690.73123.31.41.0720.59133.31.40.8710.47143.51.21.1730.80153.60.90.5670.50

[0173]

[0174] Classification 1 Heating stage Heating rate (℃ / sec) 1st heating stage Dew point (℃) HR1 / DP1 2nd heating stage Heating rate (℃ / sec) 2nd heating stage Dew point (℃)HR2 / DP2145351.375612.5249311.652510.4336660.588422.0441570.765513.0555321.767513.4635351.05295.8740321.362610.3825251.052510.4935400.975515.01038450.845411.31148550.95569.21220380.575126.31318610.36988.61415510.358414.51516470.362231.0

[0175] DivisionHv1 / 8(Hv)Hv1 / 2(Hv)Hv1 / 8 / Hv1 / 2Gs out (㎛)Gs in (㎛)Gs out / Gs in Burr height (㎛) W10 / 800 (W / kg) Note 1 25 4 2 2 5 1.1 35 8 7 5 0.7 7 0.0 15 33.8 Invention example 2 23 5 2 2 5 1.0 46 7 6 21.0 8 0.0 21 35.7 Comparative example 3 25 4 2 2 5 1.1 36 27 8 0.7 9 0.0 9 33.1 Invention example 4 25 02 2 7 1. 1071870.820.01434.1 Invention Example 52392301.0473750.970.03435.7 Comparative Example 62342271.0381781.040.02536.7 Comparative Example 72452351.0484870.970.02735.2 Comparative Example 82412341 .0388861.020.03736.1Comparative Example 92612281.1468840.810.01333.7Invention Example 102412351.0378810.960.02835.4Comparative Example 112452311.0670850.820.01132.1Invention Example 12238 2281.0467621.080.02435.2 Comparative Example 132572271.1364810.790.00734.1 Invention Example 142492251.1157720.790.00933.2 Invention Example 152642271.1656840.670.01234.8 Invention Example

[0176] As shown in Tables 1 to 3, it can be confirmed that the invention examples in which the steel components are appropriately controlled, the process conditions are appropriately controlled, and the crystal grain size and hardness by thickness are appropriately controlled have a small burr height and, at the same time, excellent iron loss.

[0177] On the other hand, if the process conditions are not properly controlled and the grain size and hardness by thickness are not properly formed, it can be confirmed that the burr height is high or the iron loss is poor.

[0178]

[0179] 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.

[0180] [Explanation of symbols]

[0181] 100: Non-oriented electrical steel sheet, 10: Surface layer,

[0182] 20: Inner layer

Claims

1. Contains Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the remainder includes Fe and inevitable impurities. The average grain size (Gs) in the inner layer, which is the area from 1 / 4 to 3 / 4 of the total thickness of the steel plate from the surface of the steel plate in ) for the steel plate surface or the surface layer, which is an area from the steel plate surface to the entire steel plate surface, from 1 / 8 to less than 1 / 4 of the total steel plate thickness, the average crystal grain size (Gs) out ) ratio (Gs) out / Gs in ) is 0.60 to 0.95, Hardness (Hv) at 1 / 2t of the total plate thickness 1 / 2 ) at 1 / 8 point (1 / 8t) of the total thickness of the steel plate from the surface of the steel plate. 1 / 8 ) ratio (Hv) 1 / 8 / Hv 1 / 2 ) Non-oriented electrical steel sheet with a coefficient of friction of 1.05 or higher.

2. In paragraph 1, Non-oriented electrical steel sheet satisfying the following equation 1 [Formula 1] [Si] × [Mn] / (4 × [Al]) ≤ 1.0 (In Equation 1, [Si], [Mn], and [Al] represent the contents (weight%) of Si, Mn, and Al, respectively.) 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: 0.005 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, 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 average grain size (Gs) in the inner layer above in ) Non-oriented electrical steel sheet having a thickness of 70 to 90㎛.

8. In paragraph 1, The average grain size (Gs) in the above surface layer in ) Non-oriented electrical steel sheet having a thickness of 55 to 75 μm.

9. In paragraph 1, Hardness (Hv) at a point half (1 / 2t) of the total steel plate thickness from the surface of the steel plate 1 / 2 ) is a non-oriented electrical steel sheet having a hardness of 220 to 235 Hv.

10. In paragraph 1, Hardness (Hv) at 1 / 8 point (1 / 8t) of the total thickness of the steel plate from the surface of the steel plate 1 / 8 ) is a non-oriented electrical steel sheet having a hardness of 240 to 270 Hv.

11. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 5.0% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0% by weight, and the remainder being Fe and unavoidable impurities; A step of manufacturing a cold rolled sheet by cold rolling the hot rolled steel sheet above, and A cold rolled sheet annealing step for annealing the above cold rolled sheet; Including, In the step of manufacturing the cold rolled sheet, a first heating step of heating the cold rolled sheet in a temperature range of 300°C or higher and less than 500°C; A second heating step of heating the cold rolled sheet in a temperature range of 500 to 700°C, and Including the cracking stage, A method for manufacturing a non-oriented electrical steel sheet satisfying the following equations 2 and 3. [Formula 2] HR1 / DP1 ≤ 1.5 [Formula 3] HR2 / DP2 ≥ 6 (In Equations 2 and 3, HR1 and HR2 are the heating rates (℃ / sec) in the first heating stage and the second heating stage, respectively, and DP1 and DP2 are the dew point temperatures (℃) in the first heating stage and the second heating stage, respectively.) 12. In paragraph 11, The above slab is a method for manufacturing a non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] [Si] × [Mn] / (4 × [Al] ≤ 1.0 (In Equation 1, [Si], [Mn], and [Al] represent the contents (in weight%) of Si, Mn, and Al in the slab, respectively.) 13. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), S: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

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

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

16. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further includes at least one of Mo: 0.03 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%).

17. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the heating rate in the first heating step is 50°C / sec or less.

18. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the dew point temperature in the first heating step is 30°C or higher.

19. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the heating rate in the second heating step is 50°C / sec or more.

20. In paragraph 11, A method for manufacturing a non-oriented electrical steel sheet, wherein the dew point temperature in the second heating step is between 0°C and 10°C.

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