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, by wt%, 1.5 to 5.0% Si, 0.1 to 2.0% Al, 0.1 to 2.0% Mn, 0.005 to 0.1% Cu, 0.0003 to 0.007% S and 0.0005 to 0.01% Mg, with the balance being Fe and inevitable impurities, wherein the average particle diameter of sulfides in a surface portion going from the surface of the steel sheet to 1 / 4 of the thickness of the steel sheet is 0.8 to 2.0 µm, and the average particle diameter of sulfides in a central portion going from more than 1 / 4 of the thickness of the steel sheet from the surface thereof to 1 / 2 of the thickness of the steel sheet from the surface thereof is 2.0 to 5.0 µm.

Description

Non-oriented electrical steel sheet and method of manufacturing the same

[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 sulfides are appropriately formed in the thickness direction by controlling sulfide-forming elements such as Cu, Mg, and S, and the atmosphere during stress relief annealing (hereinafter also referred to as SRA), thereby obtaining excellent iron loss characteristics.

[0002] Non-oriented electrical steel is primarily used in motors that convert electrical energy into mechanical energy, and excellent magnetic properties are required to achieve high efficiency in this process. In particular, with the recent rise in interest in eco-friendly vehicles driven by motors instead of internal combustion engines, the demand for non-oriented electrical steel used as core materials for drive motors is increasing, and to meet this demand, non-oriented electrical steel with excellent magnetic properties and strength is required.

[0003] The magnetic properties of non-oriented electrical steel are primarily evaluated based on iron loss and magnetic flux density. Iron loss refers to the energy loss occurring at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. Lower iron loss allows for the manufacture of motors with higher energy efficiency under the same conditions, whereas higher magnetic flux density enables motor miniaturization or reduced copper loss. Therefore, by utilizing non-oriented electrical steel with low iron loss and high magnetic flux density, drive motors with excellent efficiency and torque can be produced, 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 motor's operating conditions. A general criterion for evaluating the characteristics of non-oriented electrical steel sheets used in motors is W, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz. 15 / 50It is widely used. However, for non-oriented electrical steel sheets with a thickness of 0.35 mm or less used in drive motors for eco-friendly vehicles, magnetic properties at low fields of 1.0 T or less and high frequencies of 400 Hz or higher are often important, so W 10 / 400 The characteristics of non-oriented electrical steel sheets are often evaluated based on iron loss.

[0005] In addition, in cases where high rotation is required for motors, such as in eco-friendly vehicles, strength characteristics capable of withstanding such high rotation are also required.

[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 obtains excellent iron loss characteristics by appropriately forming sulfides in the thickness direction by controlling sulfide-forming elements such as Cu, Mg, and S and the atmosphere during stress relief annealing.

[0007] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cu: 0.005 to 0.1%, S: 0.0003 to 0.007% and Mg: 0.0005 to 0.01%, and the remainder being Fe and unavoidable impurities.

[0008] The average particle size of the sulfide in the surface portion from the surface of the steel plate to 1 / 4 of the steel plate thickness is 0.8㎛ to 2.0㎛, and the average particle size of the sulfide in the center portion from the surface of the steel plate to more than 1 / 4 to 1 / 2 of the steel plate thickness is 2.0㎛ to 5.0㎛.

[0009] The occupancy area of ​​the sulfide on the surface is 0.002% to 0.012%, and the occupancy area of ​​the sulfide in the center is 0.03% to 0.115%.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less, C: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0011] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, respectively or in their combined amount.

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, and Te: 0.01 wt% or less.

[0014] The yield strength before stress relief annealing can be 500 MPa or more.

[0015] After stress relief annealing, iron loss (W10 / 400) can be 13W / kg or less.

[0016] 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 comprising, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cu: 0.005 to 0.1%, S: 0.0003 to 0.007% and Mg: 0.0005 to 0.01%, and the remainder being Fe and unavoidable impurities; manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; a cold-rolled sheet annealing step for annealing the cold-rolled sheet; and a stress-relieving annealing step for the annealed cold-rolled sheet.

[0017] In the stress relief annealing step, the atmosphere may contain 0.1 to 20 volume% of H2 and 0.2 to 19 volume% of CO.

[0018] The slab may further include one or more of P: 0.1 wt% or less, C: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0019] The slab may further contain 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, either individually or in their combined amount.

[0020] The slab may further include one or more of Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

[0021] The slab may further include one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, and Te: 0.01 wt% or less.

[0022] During the annealing stage of the cold-rolled sheet, the cracking temperature can be 600 to 820℃.

[0023] The tension applied to the steel sheet during the cold-rolled sheet annealing stage is 0.1 to 1.5 kgf / mm 2 It could be.

[0024] A core according to one embodiment of the present invention comprises the aforementioned non-oriented electrical steel sheet.

[0025] An electric motor according to one embodiment of the present invention includes the aforementioned core.

[0026] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent iron loss characteristics.

[0027] 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 electric motors.

[0028] In particular, it can be usefully utilized as a stator for motors.

[0029] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0030] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of "comprising" specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0031] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0032] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0033] In one embodiment of the present invention, the meaning of including additional elements is that the remainder of iron (Fe) is replaced by an amount of the additional element.

[0034] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined.

[0035] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0036]

[0037] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cu: 0.005 to 0.1%, S: 0.0003 to 0.007% and Mg: 0.0005 to 0.01%, and the remainder being Fe and unavoidable impurities.

[0038] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0039] Si: 1.5 to 5.0 wt%

[0040] Silicon (Si) plays a role in increasing the resistivity of the material to lower iron loss and increasing strength through solid solution strengthening. If too little Si is added, the effect of improving iron loss and strength may be insufficient. If too much Si is added, the hardness of the material increases, which may result in inferior productivity and stamping performance. Therefore, Si may be included in an amount of 1.5 to 5.0 weight%. More specifically, it may be included in an amount of 2.0 to 4.5 weight%. Even more specifically, it may be included in an amount of 2.5 to 3.7 weight%.

[0041] Al: 0.1 to 2.0 wt%

[0042] Aluminum (Al) plays a role in increasing the resistivity of the material to lower iron loss, improve rollingability, and enhance workability during cold rolling. If too little Al is added, it may be difficult to obtain the effect of reducing high-frequency iron loss, and the precipitation temperature of AlN may be lowered, leading to the formation of fine nitrides that may degrade magnetism. If too much Al is added, excessive nitrides may be formed, degrading 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 weight%. More specifically, it may be included in an amount of 0.2 to 1.8 weight%. Even more specifically, it may be included in an amount of 0.3 to 1.5 weight%.

[0043] Mn: 0.1 to 2.0 wt%

[0044] Manganese (Mn) plays a role in improving iron loss by increasing the resistivity of the material and forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic degradation; if too much Mn is added, fine MnS is excessively precipitated and the magnetic domain structure changes, which can adversely affect iron loss. Therefore, Mn may be included in an amount of 0.1 to 2.0 weight%. More specifically, it may be included in an amount of 0.2 to 1.8 weight%. Even more specifically, it may be included in an amount of 0.3 to 1.5 weight%.

[0045] Cu: 0.005 to 0.100 wt%

[0046] Copper (Cu) plays a role in forming sulfides together with Mn. If more Cu is added, high-temperature brittleness due to Cu segregation occurs, which may form cracks during continuous casting or hot rolling. If less is added, fine precipitation of (Cu · Mn)S may occur, which may degrade magnetism. More specifically, it may contain 0.005 to 0.085 weight% of Cu.

[0047] S: 0.0003 to 0.0070 wt%

[0048] Sulfur (S) can form fine precipitates, such as MnS and CuS, which can degrade magnetic properties and hot workability. More specifically, it may contain 0.0005 to 0.0060 weight% of S.

[0049] Mg: 0.0005 to 0.0100 wt% or less

[0050] Magnesium (Mg) is an element that primarily combines with S to form sulfides and can affect the surface oxide layer of the base iron. Therefore, Mg may be included in an amount of 0.0050 wt% or less. The lower limit is not specifically limited, but it may be 0.0001 wt% due to steelmaking costs. That is, Mg may be included in an amount of 0.0005 to 0.0100 wt%. More specifically, it may be included in an amount of 0.0007 to 0.0070 wt%.

[0051] The average particle size of the sulfide in the surface portion from the surface of the steel plate up to 1 / 4 of the steel plate thickness may be 0.80㎛ to 2.00㎛, and the average particle size of the sulfide in the center portion from the surface of the steel plate up to more than 1 / 4 to 1 / 2 of the steel plate thickness may be 2.00㎛ to 5.00㎛.

[0052] Due to desulfurization by stress relief annealing at the surface, the average particle size of the sulfide at the surface and the center may differ. If the particle size of the sulfide at the surface is too small, it may hinder magnetization at the surface, causing a problem of inferior magnetic properties. If the particle size of the sulfide at the surface is too large, the crystal grains may become coarse, causing a problem of inferior iron loss. More specifically, the average particle size of the sulfide at the surface may be 0.85 μm to 1.99 μm.

[0053] In one embodiment of the present invention, sulfide refers to a particle formed by the aggregation of S elements within the steel composition. The particle size of the sulfide can be determined by assuming a virtual circle equal to the area occupied by the sulfide and determining the particle size of that circle. The average particle size refers to the arithmetic mean particle size. The average particle size can be measured by observing a cross-section including the thickness direction of the steel plate under a microscope. More specifically, it can be measured based on a cross-section (TD plane) that cuts in the rolling vertical direction (TD). More specifically, it can be obtained by continuously measuring two or more non-overlapping specimens for a specimen with an area of ​​4 mm × t mm (where t is the thickness of the steel plate) or more.

[0054] In the core, an appropriate level of desulfurization does not occur, so the average particle size of the sulfide may be coarser compared to the surface. If the particle size of the sulfide in the core is too small, fine precipitates may interfere with magnetization, causing a problem of inferior magnetic properties. If the particle size of the sulfide in the core is too large, a problem may arise where optimal iron loss cannot be secured due to coarse crystal grains. More specifically, the average particle size of the sulfide in the core may be 2.20㎛ to 4.20㎛.

[0055] The occupancy area of ​​the sulfide on the surface may be 0.002 to 0.012%. If the occupancy area of ​​the sulfide is too small due to excessive desulfurization on the surface, a problem of deterioration in surface quality may occur. If the occupancy area of ​​the sulfide is too large due to insufficient desulfurization, a problem of deterioration in magnetism may occur. More specifically, the occupancy area of ​​the sulfide on the surface may be 0.003 to 0.010%.

[0056] The sulfide occupancy area in the center may be 0.030 to 0.115%. If the sulfide occupancy area is too small, a problem may arise where the magnetic properties become inferior due to grain coarsening. If the sulfide occupancy area is too large, the magnetization behavior becomes unfavorable, which may lead to a problem where the magnetic properties become inferior. More specifically, the sulfide occupancy area in the center may be 0.035 to 0.115%.

[0057] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of P: 0.1 wt% or less (excluding 0%), C: 0.005 wt% or less (excluding 0%), Ti: 0.005 wt% or less (excluding 0%), and N: 0.005 wt% or less (excluding 0%).

[0058] P: 0.1 wt% or less

[0059] Phosphorus (P) not only plays a role in increasing the resistivity of the material but can also improve magnetic flux density as a grain boundary segregation element. However, if too much P is added, it increases the brittleness of the steel sheet, resulting in poor weldability. More specifically, it may contain 0.0001 to 0.0500 weight% of P. More specifically, it may contain 0.0010 to 0.0200 weight% of P.

[0060] C: 0.005 wt% or less

[0061] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, which can impede grain boundary or domain wall movement and degrade magnetic properties. More specifically, it may contain 0.0001 to 0.003 weight% of C.

[0062] Ti: 0.005 wt% or less

[0063] Titanium (Ti) has a very strong tendency to form precipitates in steel and can degrade iron loss by forming fine carbides, nitrides, or sulfides within the base material, thereby inhibiting grain growth and domain wall movement. More specifically, it may contain 0.0001 to 0.0030 weight% of Ti.

[0064] N: 0.005 wt% or less

[0065] Nitrogen (N) not only forms fine AlN precipitates inside the base material but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall movement, which can worsen iron loss. More specifically, it may contain 0.0001 to 0.0030 weight% of N.

[0066] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, respectively or in their combined amount.

[0067] Sn

[0068] Tin (Sn) can be added to improve magnetism because it plays a role in improving the texture of the material and suppressing surface oxidation by segregating at grain boundaries and surfaces. If too much Sn is added, grain boundary segregation becomes severe, leading to deterioration of surface quality and an increase in hardness, which may cause fracture of the cold-rolled sheet and a decrease in rollability. Specifically, 0.005 to 0.200 weight% of Sn may be further included. More specifically, 0.010 to 0.080 weight% may be further included.

[0069] Sb

[0070] Antimony (Sb) can be additionally added to improve magnetism because it plays a role in improving the texture of the material and suppressing surface oxidation by segregating at grain boundaries and surfaces. If too much Sb is added, grain boundary segregation becomes severe, leading to deterioration of surface quality and increased hardness, which may cause cold-rolled sheet fracture and reduce rollability. Specifically, 0.005 to 0.200 weight% of Sb may be additionally included. More specifically, 0.010 to 0.080 weight% may be additionally included.

[0071] Bi, Pb, Ge, and As

[0072] When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are added, they segregate at grain boundaries, alleviating stress concentration at grain boundaries during cold rolling, which in the subsequent recrystallization annealing process <111> By suppressing the recrystallization of / ND orientation grains, magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained; however, if included in excessive amounts, a large amount of segregation occurs, which inhibits grain growth and may actually result in inferior magnetic flux density and iron loss.

[0073]

[0074] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0075] Cr: 0.01 to 0.50 wt%

[0076] Chromium (Cr) plays a role in improving iron loss by increasing resistivity. If too little Cr is added, the effect of increasing resistivity may not be sufficient. If too much Cr is included, magnetic flux density may decrease. More specifically, 0.050 to 0.20 weight% of Cr may be included.

[0077] Ni: 0.05 wt% or less

[0078] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a harmful effect on magnetism. More specifically, it may contain 0.001 to 0.03 weight percent of Ni.

[0079] Zn: 0.01 wt% or less

[0080] If the content of zinc (Zn) is excessive, it can act as an impurity and impair magnetism. Therefore, Zn may be added within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 weight%.

[0081] Co: 0.05 wt% or less

[0082] Cobalt (Co) does not form fine precipitates that reduce the magnetism of steel sheets, but it increases high-temperature strength, which can cause the coil shape to be defective after hot rolling.

[0083] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more 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%), and Te: 0.0100 wt% or less (excluding 0%).

[0084] Mo: 0.030 wt% or less

[0085] If molybdenum (Mo) is added in excess, it may suppress the segregation of segregated elements, thereby reducing the texture improvement effect. Therefore, Mo may be included in an amount of 0.03 weight% or less. The lower limit is not specifically limited, but since it plays a role in improving the texture by segregating at the surface and grain boundaries, it may be included in an amount of 0.001 weight% or more. More specifically, Mo may be included in an amount of 0.001 to 0.010 weight%. Even more specifically, Mo may be included in an amount of 0.005 to 0.010 weight%.

[0086] B: 0.0050 wt% or less

[0087] If an excessive amount of boron (B) is added, it may cause deterioration of magnetic properties through the formation of inclusions within the steel. Therefore, B may be included in an amount of 0.005 weight% or less. The lower limit is not specifically limited, but it may be 0.0001 weight% due to steelmaking costs. More specifically, B may be included in an amount of 0.0001 to 0.0030 weight%.

[0088] V: 0.0050 wt% or less

[0089] Vanadium (V) has a very strong tendency to form precipitates in steel and degrades iron loss by forming fine carbides or nitrides inside the base material, thereby inhibiting grain growth and domain wall movement. Therefore, the V content may be 0.0050 wt% or less. The lower limit is not specifically limited, but it may be 0.0003 wt% due to steelmaking costs. That is, V may be included in 0.0003 to 0.0050 wt%. More specifically, V may be included in 0.0003 to 0.0030 wt%.

[0090] Ca: 0.0050 wt% or less

[0091] Calcium (Ca) has a very strong tendency to form precipitates within the steel and degrades iron loss by forming fine sulfides inside the base material, thereby inhibiting grain growth and domain wall movement.

[0092] Nb: 0.0050 wt% or less

[0093] Niobium (Nb) has a very strong tendency to form precipitates in steel and degrades iron loss by forming fine carbides or nitrides within the base material, thereby inhibiting grain growth and domain wall movement. Therefore, the Nb content may be 0.0050 wt% or less. The lower limit is not specifically limited, but it may be 0.0003 wt% due to steelmaking costs. That is, it may contain 0.0003 to 0.0050 wt% of Nb. More specifically, it may contain 0.0003 to 0.0030 wt% of Nb.

[0094] Zr: 0.0050 wt% or less

[0095] If an excessive amount of zirconium (Zr) is added, it may cause deterioration of magnetic properties through the formation of inclusions within the steel. Therefore, Zr may be included in an amount of 0.005 weight% or less. The lower limit is not specifically limited, but it may be set to 0.0001 weight% due to steelmaking costs. That is, Zr may be included in an amount of 0.0001 to 0.0050 weight%. More specifically, it may be included in an amount of 0.0005 to 0.0030 weight%.

[0096] Te: 0.0100 wt% or less

[0097] Tellurium (Te) can be added to prevent the oxide layer, which is fractured during rolling, from being pressed into the base material and to detach it, as it diffuses into the oxide layer on the surface of the hot-rolled coil, increases the coefficient of friction between the oxide layer and the rolling work roll, and increases hardness by concentrating beneath the oxide layer. If the amount of Te added is too small, the effect may be negligible. If too much Te is added, the oxide layer detaches easily, causing the base material to come into direct contact with the work roll, which reduces the above effect, and excessive deformation bands may be generated within the steel sheet during cold rolling, leading to the development of a {111} / ND texture that is unfavorable to magnetism. More specifically, it may contain 0.0001 to 0.007 weight% of tellurium.

[0098] The remainder comprises Fe and unavoidable impurities. The unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets; as this is widely known in the field, a detailed description is 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. If additional elements are included, they replace the remainder, Fe.

[0099] In one embodiment of the present invention, the strength characteristics are excellent. The strength characteristics are characteristics prior to stress relief annealing. Specifically, the yield strength prior to stress relief annealing may be 500 MPa or higher. More specifically, it may be 550 to 1050 MPa.

[0100] As described above, in one embodiment of the present invention, the magnetic properties after stress relief annealing are excellent, and in particular, the high-frequency iron loss is excellent. At this time, the stress relief annealing conditions may be 760 to 880°C and 30 minutes to 3 hours. More specifically, the cracking temperature may be 770 to 860°C and 45 minutes to 90 minutes. More specifically, the cracking temperature may be 800°C and 1 hour.

[0101] Specifically, in one embodiment of the present invention, the iron loss (W) of a non-oriented electrical steel sheet based on a thickness of 0.30 mm 10 / 400 ) may be 13.0W / Kg or less. Iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0T is induced at a frequency of 400 Hz. More specifically, the iron loss (W of non-oriented electrical steel) 10 / 400 ) can be 9.0 to 12.5 W / kg.

[0102]

[0103] 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 comprising, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cu: 0.005 to 0.1%, S: 0.0003 to 0.007% and Mg: 0.0005 to 0.01%, and the remainder being Fe and unavoidable impurities; manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; a cold-rolled sheet annealing step for annealing the cold-rolled sheet; and a stress-relieving annealing step for the annealed cold-rolled sheet.

[0104]

[0105] Below, each step is explained in detail.

[0106] First, the slab is hot-rolled.

[0107] As the alloy composition of the slab has been explained in the aforementioned section on the alloy composition of non-oriented electrical steel sheets, a redundant explanation is omitted. Since the alloy composition does not substantially change during the manufacturing process of non-oriented electrical steel sheets, the alloy composition of the non-oriented electrical steel sheets and the slab is substantially the same.

[0108] Specifically, the slab comprises, in weight percent, Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cu: 0.005 to 0.1%, S: 0.0003 to 0.007% and Mg: 0.0005 to 0.01%, and the remainder is Fe and unavoidable impurities.

[0109] As other additional elements have been explained in the alloy composition of non-oriented electrical steel sheets, redundant explanations are omitted.

[0110] The slab can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1200°C or lower. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab may be re-dissolved and then finely precipitated during hot rolling and annealing, which can inhibit grain growth and reduce magnetism.

[0111] Next, a hot-rolled plate is manufactured by hot-rolling a slab. The thickness of the hot-rolled plate may be 1.0 to 4.5 mm. In the step of manufacturing the hot-rolled plate, the finish rolling temperature may be 800°C or higher. Specifically, it may be 800 to 1000°C. The hot-rolled plate may be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled plate may be 1.5 to 4.3 mm.

[0112] After manufacturing the hot-rolled steel sheet, an additional step of annealing the hot-rolled sheet may be included. At this time, the cracking temperature may be 800 to 1100°C. If the annealing temperature is too low, a recrystallization structure is not formed or grows finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, magnetic properties may actually deteriorate, and rolling workability may worsen due to deformation of the sheet shape. More specifically, the temperature range may be 830 to 1080°C. The cracking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0113] Next, a cold-rolled sheet is manufactured by cold-rolling a hot-rolled steel sheet. At this time, cold rolling can be performed with a reduction rate of 40 to 85%. If the reduction rate is too low, the deformation energy accumulated in the rolled steel sheet is small, making it difficult to recrystallize during the subsequent annealing process. As a result, the rolled structure remains, which may cause problems in improving magnetic flux density and iron loss. Conversely, if the reduction rate is too high, during the subsequent annealing process <111> / ND orientation. Recrystallization of the grains is promoted and the grains become finer, which may result in problems such as reduced magnetic flux density and increased iron loss. More specifically, the reduction ratio may be 60 to 75%. For the cold rolling step, a tandem cold rolling mill that continuously cold-rolls the steel sheet using multiple rolling stands or a reverse rolling mill that discontinuously cold-rolls using 12 or more rolling rolls may be used. The final rolled thickness may be 0.1 mm to 0.35 mm.

[0114] The step of manufacturing cold-rolled sheets can be performed once or two or more times with intermediate annealing in between.

[0115] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. In one embodiment of the present invention, the cracking temperature during the annealing of the cold-rolled sheet is set low to form a large number of unrecrystallized cells, thereby improving strength. Specifically, the cracking temperature may be 600 to 820°C. If the cracking temperature is too low, an appropriate level of stress relief and recrystallization is not secured, which may result in a problem where the magnetic properties deteriorate. If the cracking temperature is too high, the strength may decrease. More specifically, it may be 610 to 780°C.

[0116] The tension applied to the steel sheet during the cold-rolled sheet annealing stage is 0.10 to 1.50 kgf / mm 2 It may be. If the tensile strength is too low, the surface of the steel sheet may deteriorate due to friction with the annealing furnace. If the tensile strength is too high, sheet breakage may occur during annealing, leading to production constraints. More specifically, the tensile strength is 0.20 to 1.35 kgf / mm² 2 It can be. Tension can be measured with a tension meter at the inlet or outlet side of the annealing furnace.

[0117] After annealing a cold-rolled sheet, the area occupied by unrecrystallization within the steel sheet may be 5% or more. Unrecrystallization can be measured based on a cross-section including the thickness direction (ND direction) of the steel sheet. More specifically, it can be measured based on a cross-section (TD plane) cut in the rolling perpendicular direction (TD direction). The unrecrystallization fraction can be determined by EBSD. If the area occupied by unrecrystallization is too small, the effect of improving iron loss during the stress relief annealing process may not be sufficient. More specifically, the area occupied by unrecrystallization within the steel sheet may be 5% to 100%. More specifically, it may be 30% to 100%.

[0118] After annealing the cold-rolled sheet, an insulating film can be formed. The insulating film can be treated with organic, inorganic, or organic-inorganic composite films, and it is also possible to treat it with other insulating coating materials.

[0119] After the annealing of the cold-rolled sheet, stamping and lamination into a motor shape may be performed; at this time, stress is applied to the steel sheet, which may degrade its magnetism. In one embodiment of the present invention, stress can be removed through a stress-relief annealing step, thereby further enhancing the magnetism.

[0120] In the stress relief annealing step, the atmosphere may contain 0.1 to 20.0 volume% of H2 and 0.2 to 19.0 volume% of CO. H2 and CO serve as an anti-oxidation and desulfurization agent during stress relief annealing. If too little H2 and CO are included, a problem of oxidation may occur. If too much H2 and CO are included, a problem of degraded magnetism may occur due to excessive desulfurization. More specifically, it may contain 1.0 to 10.0 volume% of H2 and 1.5 to 15.0 volume% of CO.

[0121] In the stress relief annealing stage, the cracking temperature may be 760 to 880°C. If the cracking temperature is too low, it is difficult to achieve sufficient improvement in iron loss. If the cracking temperature is too high, the magnetic flux density may instead be degraded. More specifically, in the stress relief annealing stage, the cracking temperature may be 770 to 860°C. The time may be 30 minutes to 3 hours. More specifically, it may be 45 minutes to 90 minutes.

[0122] A core according to one embodiment of the present invention comprises the aforementioned non-oriented electrical steel sheet.

[0123] The aforementioned core may be a rotor or a stator. More specifically, it may be a stator.

[0124] An electric motor according to one embodiment of the present invention includes the aforementioned core.

[0125]

[0126] The present invention will be explained in more detail below through examples. However, these examples are merely for illustrating the invention and the invention is not limited thereto.

[0127]

[0128] Examples

[0129] A slab was prepared with the composition of Table 1 and the remainder being Fe and unavoidable impurities. It was heated to 1130°C and hot-rolled at a finishing temperature of 950°C to produce a hot-rolled plate with a thickness of 1.8 mm.

[0130] Subsequently, the hot-rolled plate was annealed at 1030 ℃ for 100 seconds and cold-rolled to a final thickness of 0.20 mm. The cold-rolled steel plate was cold-rolled for 60 seconds under the temperature and tension conditions summarized in Table 2 below.

[0131] Subsequently, annealing was performed at 800°C for 1 hour, assuming stress relief annealing. At this time, the volume ratio of H2 and CO in the atmosphere was adjusted as shown in Table 2 below.

[0132] The sulfide characteristics of the surface and center of the TD plane of the manufactured non-oriented electrical steel sheet were observed and analyzed using SEM, and the results are shown in Table 3.

[0133] For each specimen before and after stress relief annealing, 5 specimens with a width of 60 mm × length of 60 mm × number of sheets were cut and measured using a single sheet tester, and the values ​​were presented.

[0134] At this time, W 10 / 400 is the iron loss when a magnetic flux density of 1.0T is induced at a frequency of 400Hz.

[0135] Classification SiMnAlCuMgS13.00.81.10.0810.00260.005122.80.31.70.0400.00110.000633.60.50.50.0690.00130.003042.51.60.80.0470.00220.004353.40.40.70.0850.00360.005863.30 .40.40.0480.00520.001873.70.60.30.0050.00140.000983.20.70.70.0210.00080.002093.61.30.50.0300.00430.0032102.71.51.40.0400.00670.0052113.50.50.70.0030.01100 .0020123.50.50.70.1520.01430.0051133.10.20.80.064-0.0060143.10.20.80.0430.01350.0057153.50.41.10.0420.00910.0002163.50.41.10.0300.00440.0076173.20.60.90.0 750.00340.0011183.20.60.90.0140.00220.0021193.41.30.70.0710.00540.0060203.41.30.70.0310.00860.0003213.40.81.20.0630.00120.0061223.40.81.20.0050.00180.0037

[0136] Classification Cold-rolled sheet thickness Cold-rolled sheet annealing cracking temperature (°C) Tension (kgf / mm²) 2H2 Concentration (Volume%) during SRA CO Concentration (Volume%) during SRA 10.256500.84 1.97.82 0.256500.803.96.53 0.256900.287.32 24 0.276800.34 1.79.95 0.277800.603.72.46 0.276100.329.81 0.47 0.306151.313.812.78 0.307300.583.71 0.29 0.206600.224.014.91 00.206700.536.18.81 10.257800.8 73.610.312Unavailable130.257201.021.08.6140.257201.021.01.6150.256600.786.76.6160.256600.786.712.9170.256100.073.011.5180.258301.723.02.3190.206500.49-6.6200.206500.4923.49.5210.207701.085.9-220.207701.085.919.7

[0137] Classification Surface Sulfide Average Particle Size (㎛) Surface Sulfide Area Ratio (%) Core Sulfide Average Particle Size (㎛) Core Sulfide Area Ratio (%) SRA Total Yield Strength (MPa) SRA Total Iron Loss W10 / 400 (W / kg) SRA Post-Iron Loss W10 / 400 (W / kg) Remarks 10.9 0.0 10 3.7 20.0 8 0 9 8 5 47.8 10.9 Invention Example 2 1.9 7 0.0 7 3.0 10.0 5 7 9 8 3 46.2 11.1 Invention Example 3 0.8 7 0.0 3 3.1 4 0.0 4 9 9 5 0 41.3 11.2 Invention Example 4 1.6 20.0 5 2.2 5 0.1 1 2 9 3 2 43.5 11.0 Invention Example 5 1.0 10.0 10 2.4 9 0.0 3 3 5 8 0 2 7.0 11.6 Invention Example 6 1.1 6 0.0 7 3.9 5 0 .115104753.112.4 Invention Example 71.990.0072.380.09799658.212.2 Invention Example 81.200.0054.160.05480442.412.2 Invention Example 91.940.0072.500.03993040.210.1 Invention Example 101.100.0052.690.10691436.79.8 Invention Example 110.620.0010.630.02753843.813.2 Comparative Example 12 Work Comparison Example 1 30.48 0.00 10.5 20.02 260 434.5 14.3 Comparison Example 1 42.2 20.018 4.88 0.138 616 35.3 13.7 Comparison Example 1 50.72 0.00 10.6 40.0199 3746.3 13.5 Comparison Example 1 63.40 0.02 43.77 0.1609 3747.5 13.5 Comparison Example 1 70.85 0.01 02.2 40.076 105 252.7 11.5 Invention Example 18 1.9 20.00 7 2.7 20.08 546 216.8 11.4 Invention Example 19 2.4 00.02 42.3 60.12 5978 42.4 13.1 Comparative Example 2 00.5 20.00 10.7 60.015 991 43.2 13.0 Comparative Example 2 12.7 20.01 63.1 20.14 667 24.2 13.4 Comparative Example 2 20.5 90.00 10.6 40.02 666 423.8 13.1 Comparative Example

[0138] As shown in Tables 1 to 3, when the atmosphere conditions during steel composition and stress relief annealing are properly controlled, sulfides are properly formed on the surface and in the center, and it can be confirmed that the iron loss after stress relief annealing is excellent.

[0139] On the other hand, if the steel composition does not adequately contain sulfide-forming elements such as Cu, Mg, and S, or if the atmosphere is not properly controlled during the stress relief annealing process, sulfides are not properly formed in the surface and core, and it can be confirmed that the iron loss after stress relief annealing is inferior.

[0140] In addition, among the invention examples, it can be confirmed that iron loss is even better when the cracking temperature and tension are appropriately controlled during the annealing of the cold-rolled plate.

[0141]

[0142] The present invention is not limited to the embodiments described above but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without altering the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. In weight%, comprising Si: 1.5 to 5.0%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cu: 0.005 to 0.1%, S: 0.0003 to 0.007% and Mg: 0.0005 to 0.01%, and the remainder comprising Fe and unavoidable impurities, The average particle size of the sulfide in the surface portion from the surface of the steel plate to 1 / 4 of the steel plate thickness is 0.8 to 2.0 μm, and Non-oriented electrical steel sheet having an average sulfide particle size of 2.0 to 5.0 μm in the center from the surface of the steel sheet to more than 1 / 4 to 1 / 2 of the steel sheet thickness.

2. In Paragraph 1, The occupancy area of ​​the sulfide on the above surface is 0.002 to 0.012%, and A non-oriented electrical steel sheet having a sulfide occupancy area of ​​0.03 to 0.115% in the above-mentioned center.

3. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of P: 0.1 wt% or less, C: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

4. In Paragraph 1, A non-oriented electrical steel sheet further comprising 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, either individually or in their combined amount.

5. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less, Zn: 0.01 wt% or less, and Co: 0.05 wt% or less.

6. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, V: 0.0050 wt% or less, Ca: 0.0050 wt% or less, Nb: 0.0050 wt% or less, Zr: 0.005 wt% or less, and Te: 0.01 wt% or less.

7. In Paragraph 1, Non-oriented electrical steel sheet with a yield strength of 500 MPa or more before stress relief annealing.

8. In Paragraph 1, Non-oriented electrical steel sheet having an iron loss (W10 / 400) of 13 W / kg or less after stress relief annealing.

9. A core comprising the non-oriented electrical steel sheet described in paragraph 1.

10. An electric motor comprising the core described in paragraph 9.