Non-oriented electrical steel sheet and method for manufacturing same

Abstract

A non-oriented electrical steel sheet according to an embodiment of the present invention comprises, in weight%, 2.5% or less (excluding 0%) of Si, 1.0% or less of AI, 0.1-2.0% of Mn, 0.0003-0.01% of S, and 0.0150-0.0600% of Cu, with the remainder being Fe and inevitable impurities, wherein the area fraction of sulfides having an aspect ratio of at least 1.5 relative to the total sulfides is 30-80 area%.

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 with improved magnetism through sulfide coarsening via Cu addition and hot-rolled grain growth by controlling residence time in different temperature ranges after coiling, and a method for manufacturing the same.

[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, motors used in the home appliance industry demand high torque and high efficiency characteristics depending on the type of finished product; to meet these requirements, superior non-oriented electrical steel with low iron loss and high magnetic flux density is needed.

[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, motors with excellent efficiency and torque can be produced by using non-oriented electrical steel with low iron loss and high magnetic flux density.

[0004] Depending on the operating conditions of the motor, the characteristics of non-oriented electrical steel sheets that need to be considered also vary. As a general standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors, W15 / 50, which is the iron loss when a 1.5T magnetic field is applied at a commercial frequency of 50Hz, is widely used.

[0005] 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 with improved magnetism through sulfide coarsening via Cu addition and grain growth of the hot-rolled sheet by controlling the residence time according to temperature ranges after coiling, and a method for manufacturing the same.

[0006] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight percent, Si: 2.5% or less (excluding 0%), Al: 1.0% or less, Mn: 0.1 to 2.0%, S: 0.0003 to 0.01%, and Cu: 0.0150 to 0.0600%, and the remainder being Fe and unavoidable impurities.

[0007] The area fraction of sulfides with a ratio of long axis lengths to short axis lengths of 1.5 or greater among all sulfides is 30 to 80 area percent.

[0008] The density of CuS with a major axis length of 200 nm or more is 260 particles / mm³ 2 That is all.

[0009] The density of complex sulfides containing two or more of Cu, Mn, and Ti with a major axis length of 600 nm or more is 130 particles / mm³ 2 It could be more than that.

[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, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0014]

[0015] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises: a step of manufacturing a hot-rolled steel sheet by hot-rolling a slab comprising, in weight%, Si: 2.5% or less (excluding 0%), Al: 1.0% or less, Mn: 0.1 to 2.0%, S: 0.0003 to 0.01% and Cu: 0.0150 to 0.0600%, and the remainder being Fe and unavoidable impurities; a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0016] A method for manufacturing a non-oriented electrical steel sheet, comprising a coiling step for coiling a hot-rolled steel sheet manufactured in a step of manufacturing a hot-rolled steel sheet, wherein in the coiling step, the temperature of the steel sheet at the center in the coil length direction and within 20 mm from the end of the hot-rolled width is maintained at 650°C or higher for 60 seconds or more, and the temperature of the steel sheet is maintained at less than 650°C and 500°C or higher for 1000 seconds or more.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0021] Prior to the step of manufacturing hot-rolled steel sheets, a heating step of heating the slab to 1130 to 1280°C may be further included.

[0022] In the winding stage, the winding start temperature may be 700℃ or higher.

[0023] In one embodiment of the present invention, the non-oriented electrical steel sheet has sulfides formed appropriately, which facilitates the movement of grain boundaries by suppressing peening, thereby allowing grains to grow, and subsequently, during the annealing of the cold-rolled sheet, the iron loss can be improved by suppressing the texture (111) through the induction of recrystallization within the grains.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0028] 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.

[0029] 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.

[0030] 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.

[0031]

[0032] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 2.5% or less (excluding 0%), Al: 1.0% or less, Mn: 0.1 to 2.0%, S: 0.0003 to 0.01% and Cu: 0.0150 to 0.0600%, and the remainder being Fe and unavoidable impurities.

[0033] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0034]

[0035] Si: 2.5 wt% or less

[0036] 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 much Si is added, the saturation density may decrease. Therefore, Si may be included in an amount of 2.50 wt% or less. More specifically, it may be included in an amount of 1.50 wt% or less. More specifically, it may be included in an amount of 0.10 to 1.30 wt%. More specifically, it may be included in an amount of 0.50 to 1.10 wt%.

[0037]

[0038] Al: 1.0 wt% or less

[0039] Aluminum (Al) plays a role in increasing the resistivity of the material to lower iron loss and improve rollability, as well as enhancing workability during cold rolling. If too much Al is added, excessive nitrides may be formed, which can degrade magnetism. Therefore, Al may be included in an amount of 1.0 weight% or less. More specifically, it may be included in an amount of 0.01 to 0.50 weight%. Even more specifically, it may be included in an amount of 0.03 to 0.30 weight%.

[0040]

[0041] Mn: 0.05 to 1.0 wt%

[0042] 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, promoting the formation of a {111} texture that is unfavorable to magnetism, which causes a rapid decrease in magnetic flux density. Therefore, Mn may be included in an amount of 0.05 to 1.0 weight%. More specifically, it may be included in an amount of 0.10 to 0.50 weight%.

[0043]

[0044] S: 0.0003 to 0.0100 wt%

[0045] 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 0.0050 weight% of S. More specifically, it may contain 0.0010 to 0.0030 weight% of S.

[0046] Cu: 0.0150 to 0.0600 wt%

[0047] Copper (Cu) plays a role in forming sulfides together with Mn. If more Cu is added, or if too little is added, (Cu · Mn)S may precipitate finely, which can degrade magnetism. If too much Cu is added, high-temperature brittleness occurs, which may form cracks during continuous casting or hot rolling. More specifically, it may contain 0.0170 to 0.0580 weight% of Cu. More specifically, it may contain 0.0180 to 0.0550 weight% of Cu.

[0048]

[0049] 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.

[0050] P: 0.1 wt% or less

[0051] 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.

[0052] C: 0.005 wt% or less

[0053] 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 0.0035 weight% of C.

[0054] Ti: 0.005 wt% or less

[0055] 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 0.0050 weight% of Ti. More specifically, it may contain 0.0005 to 0.0030 weight% of Ti.

[0056] N: 0.005 wt% or less

[0057] 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 0.0050 weight% of N. More specifically, it may contain 0.0005 to 0.0030 weight% of N.

[0058]

[0059] 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.

[0060] Sn

[0061] 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.

[0062] Sb

[0063] 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.

[0064] Bi, Pb, Ge, and As

[0065] 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.

[0066]

[0067] 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.

[0068] Cr: 0.01 to 0.50 wt%

[0069] 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.

[0070] Ni: 0.05 wt% or less

[0071] 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.

[0072] Zn: 0.01 wt% or less

[0073] 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%.

[0074] Co: 0.05 wt% or less

[0075] 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.

[0076]

[0077] 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, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

[0078] Mo: 0.030 wt% or less

[0079] 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%.

[0080] B: 0.0050 wt% or less

[0081] 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%.

[0082] V: 0.0050 wt% or less

[0083] 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%.

[0084] Ca: 0.0050 wt% or less

[0085] 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.

[0086] Nb: 0.0050 wt% or less

[0087] 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.

[0088] Zr: 0.0050 wt% or less

[0089] 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%.

[0090] Te: 0.0100 wt% or less

[0091] 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.

[0092] Mg: 0.0050 wt% or less

[0093] 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 0.0001 to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 to 0.0030 wt%.

[0094]

[0095] 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.

[0096]

[0097] The area fraction of sulfides having a ratio of long axis lengths to short axis lengths of 1.5 or greater among the total sulfides may be 30 to 80 area percent. If the shape of the sulfides is not appropriate, it inhibits grain growth and hinders the movement of magnetic domains, resulting in inferior magnetic properties. More specifically, it may be 45 to 75 area percent. The sulfides can be measured by observing them with TEM at a magnification of 110,000 times.

[0098] In one embodiment of the present invention, the density of CuS with a major axis length of 200 nm or more is 260 particles / mm² 2 The above applies, and the density of complex sulfides containing two or more of Cu, Mn, and Ti with a major axis length of 600 nm or more is 130 particles / mm³ 2That is all. If the density of sulfides is lower than the described density, a large number of small-sized sulfides will exist within the material, inhibiting grain growth and hindering the movement of magnetic domains, resulting in inferior magnetic properties.

[0099] More specifically, the density of CuS with a major axis length of 200 nm or more is 1,000 to 2,000 particles / mm 2 It may be. The density of a complex sulfide containing two or more of Cu, Mn, and Ti with a major axis length of 600 nm or more is 300 to 1,000 particles / mm³ 2 It could be.

[0100] CuS refers to particles in which the elemental components other than Cu and S fall within the steel composition range of the steel sheet. CuS can be measured across a cross-section including the ND direction of the steel sheet, specifically on the TD vertical plane. CuS can be measured by observing it with a TEM at a magnification of 110,000x. To reduce errors due to measurement location, measurements are taken at least five locations, and the value is obtained as the average. The major axis of a particle refers to the longest length in a specific direction within the area occupied by the particle.

[0101]

[0102] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises: a step of manufacturing a hot-rolled steel sheet by hot-rolling a slab; a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0103]

[0104] Below, each step is explained in detail.

[0105] First, the slab is hot-rolled.

[0106] 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.

[0107] Specifically, the slab contains, in weight percent, Si: 2.5% or less (excluding 0%), Al: 1.0% or less, Mn: 0.1 to 2.0%, S: 0.0003 to 0.01% and Cu: 0.0150 to 0.0600%, and the remainder is Fe and unavoidable impurities.

[0108] As other additional elements have been explained in the alloy composition of non-oriented electrical steel sheets, redundant explanations are omitted.

[0109] The slab can be heated before hot rolling. The heating temperature of the slab is not limited, but the slab can be heated to 1130 to 1280°C. If the slab heating temperature is too low, the hot rolling performance becomes inferior as the strength of the material increases, which may cause productivity problems. If the slab heating temperature is too high, precipitates such as AlN and MnS present in the slab may be re-dissolved and then form fine precipitates during hot rolling and annealing, which may inhibit grain growth and reduce magnetism.

[0110] 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 870 to 950°C. The hot-rolled plate may be coiled at a temperature of 700°C or higher. If the coiling temperature is low, the driving force for grain growth is reduced, and the magnetic quality may be inferior. More specifically, the coiling temperature may be 702 to 780°C.

[0111] During the winding stage, the time during which the temperature of the steel plate located at the center along the coil length direction and within 20 mm from the end of the hot-rolled width is maintained at 650°C or higher is 60 seconds or more, and the time during which the temperature of the steel plate is maintained at less than 650°C and above 500°C is 1000 seconds or more. By appropriately adjusting the residence time in each temperature range after winding, the crystal grains of the hot-rolled plate can be increased, which may result in more favorable magnetic properties. More specifically, during the winding stage, the time during which the temperature of the steel plate located at the center along the coil length direction and within 20 mm from the end of the hot-rolled width is maintained at 650°C or higher may be 70 to 350 seconds. The time during which the temperature of the steel plate is maintained at less than 650°C and above 500°C may be 1500 to 3500 seconds.

[0112] More specifically, the thickness of the hot-rolled plate may be 1.4 to 3.0 mm.

[0113] 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 1150°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 1100°C. The cracking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0114] After annealing of the hot-rolled plate, the average grain size can be 25 to 40 μm.

[0115] Next, a hot-rolled steel sheet is cold-rolled to produce a cold-rolled sheet. In the step of producing the cold-rolled sheet, the total reduction rate may be 75 to 90%. The total reduction rate can be calculated from the thickness of the steel sheet before cold rolling and the thickness after cold rolling. If the reduction rate is too low, additional rolling is required to obtain an appropriate final thickness, and productivity may be inferior. If the reduction rate is too high, a texture unfavorable to magnetism is formed, and iron loss may be inferior. More specifically, in the step of producing the cold-rolled sheet, the total reduction rate may be 77 to 88%.

[0116] After cold rolling, the thickness may be 0.10 to 0.7 mm. If the thickness is too thin, problems may arise in terms of the strength of the steel sheet, and if the thickness is too thick, it may have an adverse effect on iron loss. More specifically, the thickness may be 0.15 to 0.6 mm.

[0117] In one embodiment of the present invention, cold rolling may be performed once without intermediate annealing, or may include two or more cold rollings including intermediate annealing.

[0118] Next, the cold-rolled sheet is annealed in the cold-rolled sheet annealing step. In the cold-rolled sheet annealing step, the cracking temperature may be 750 to 1050°C. If the cracking temperature is too low, the grains may not grow sufficiently, leading to increased hysteresis loss and a problem of deterioration in iron loss. Conversely, if the cracking temperature is too high, surface defects may occur. More specifically, annealing may be performed at a temperature of 800 to 1000°C. The cold-rolled sheet annealing step may be performed for 50 to 120 seconds.

[0119] During the annealing process of the cold-rolled sheet, all (i.e., more than 99%) of the processed structure formed during the cold rolling stage can be recrystallized.

[0120] 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.

[0121]

[0122] 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.

[0123]

[0124] Example 1

[0125] A slab was prepared with a composition containing 0.0020 wt% of S and the remainder being Fe and unavoidable impurities, as shown in Table 1. This was heated to the temperatures listed in Table 1 and hot-rolled at a finishing temperature of 900°C to produce a hot-rolled sheet with a thickness of 2.5 mm. The coiling temperature of the hot-rolled sheet was set as shown in Table 1 below, and subsequently, the residence time for each temperature range was set as shown in Table 1. Afterward, it was cold-rolled to produce a thickness of 0.25 mm. The cold-rolled sheet was annealed at a temperature of 960°C to produce a non-oriented electrical steel sheet.

[0126] The number and size of sulfides were measured at TEM 110,000 magnification in a cross-section perpendicular to the TD direction of the manufactured non-oriented electrical steel sheet and summarized in Table 2 below.

[0127] For magnetic properties such as magnetic flux density and iron loss, five specimens measuring 60 mm in width × 60 mm in length were cut for each sample and tested using a single sheet tester. Magnetic flux density was measured in the rolling direction and perpendicular to the rolling direction, and the results were expressed as the average value. Iron loss was measured in the rolling direction and perpendicular to the rolling direction and expressed as the average. At this time, W 15 / 50 is the iron loss when a magnetic flux density of 1.5T is induced at a frequency of 50Hz, and B50 means the magnetic flux density induced in a magnetic field of 5000A / m.

[0128] Classification Si (wt%) Al (wt%) Mn (wt%) Cu (wt%) Heating Temperature (°C) Winding Temperature (°C) Holding Time at 650°C or Higher (sec) Holding Time at 500°C or Higher and Less Than 650°C (sec) Invention Example 1 0.8 40.2 40.4 70.0 47012277542602562 Invention Example 20.6 00.0 40.2 60.0 53611447371242509 Invention Example 30.8 00.2 50.2 00.0 44412317081931887 Invention Example 40.7 90.0 30.4 00.0 4851245748 3272429 Invention Example 50.870.130.160.042712167141282929 Invention Example 60.730.260.280.031912157222402535 Invention Example 70.790.270.430.018111857492483310 Invention Example 81.080.010.480.04871204738 2202424 Invention Example 90.98 0.06 0.19 0.02741188702744976 Comparative Example 10.03 0.23 0.30 0.047811537703006450 Comparative Example 20.85 0.06 0.06 0.001512417561513049 Comparative Example 30.79 0.24 0.20 0.138212187088 36850 Comparative Example 4 1.1 30.2 00.2 20.0 36812987431862514 Comparative Example 5 1.1 70.2 90.0 50.0 531118765273033 Comparative Example 6 0.8 10.2 30.4 50.0 5481218702482838 Comparative Example 7 1.0 20.1 80.1 90.0 3731228705173896

[0129] Classification Hot-rolled Grain Size (㎛) Longitudinal length ratio 1.5 or greater Area fraction of sulfides (%) CuS 200 nm or larger (pieces / mm²) 2 )Density of complex sulfides larger than 600 nm (pieces / mm²) 2)B50(T)W15 / 50(W / kg) Invention Example 1 397512248631.744.35 Invention Example 2 355015295961.754.58 Invention Example 3 355118225131.754.40 Invention Example 4 375618366911.734.25 Invention Example 5 295011748121.754.37 Invention Example 6 346016699261.724.25 Invention Example 7 354618973211.734.78 Invention Example 8 397316 288991.724.28 Invention Example 9375315764381.724.33 Comparative Example 1386013676691.776.83 Comparative Example 2221387221.705.76 Comparative Example 3215112167701.685.62 Comparative Example 419261390391.695.31 Comparative Example 520467546881.705.13 Comparative Example 6214014827651.705.24 Comparative Example 720469437111.695.31

[0130] As shown in Tables 1 and 2, when the steel composition is appropriately controlled and the residence time for each temperature range after coiling is appropriately controlled, it can be confirmed that the density of coarse sulfides increases and the magnetic properties are excellent.

[0131] On the other hand, if the steel composition is not properly controlled, or if the residence time for each temperature range after winding is not properly controlled, the sulfides are not properly controlled, and it can be confirmed that the magnetism is inferior.

[0132] Among the examples, it can be confirmed that the magnetic properties are even better when both the slab heating temperature and the coiling start temperature conditions are satisfied.

[0133]

[0134] 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: 2.5% or less (excluding 0%), Al: 1.0% or less, Mn: 0.1 to 2.0%, S: 0.0003 to 0.01% and Cu: 0.0150 to 0.0600%, and the remainder comprising Fe and unavoidable impurities, Non-oriented electrical steel sheet having an area fraction of sulfides with a ratio of long axis lengths to short axis lengths of 1.5 or more among the total sulfides of 30 to 80 area percent.

2. In Paragraph 1, The density of CuS with a major axis length of 200 nm or more is 260 particles / mm³ 2 Non-oriented electrical steel sheet of the above type.

3. In Paragraph 1, The density of complex sulfides containing two or more of Cu, Mn, and Ti with a major axis length of 600 nm or more is 130 particles / mm³ 2 Non-oriented electrical steel sheet of the above type.

4. 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.

5. 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.

6. 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.

7. 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, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

8. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab comprising, in weight%, Si: 2.5% or less (excluding 0%), Al: 1.0% or less, Mn: 0.1 to 2.0%, S: 0.0003 to 0.01% and Cu: 0.0150 to 0.0600%, and the remainder being Fe and unavoidable impurities; A step of manufacturing a cold-rolled plate by cold-rolling the above hot-rolled steel plate; and A cold-rolled plate annealing step for annealing the above cold-rolled plate; comprising, It includes a winding step for winding the hot-rolled steel sheet manufactured in the step of manufacturing the hot-rolled steel sheet, and A method for manufacturing a non-oriented electrical steel sheet, wherein, during the winding stage, the temperature of the steel sheet at the center in the coil length direction and within 20 mm from the end of the hot rolling width is maintained at 650°C or higher for 60 seconds or more, and the temperature of the steel sheet is maintained at less than 650°C and 500°C or higher for 1000 seconds or more.

9. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises 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.

10. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises 0.005 to 0.200 weight% of one or more of Sn, Sb, Bi, Pb, Ge, and As, respectively or in their combined amount.

11. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises 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.

12. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further comprises 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, Te: 0.01 wt% or less, and Mg: 0.0050 wt% or less.

13. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet, further comprising a heating step of heating the slab to 1130 to 1280°C prior to the step of manufacturing the hot-rolled steel sheet.

14. In Paragraph 8, A method for manufacturing a non-oriented electrical steel sheet in which the coiling start temperature in the above-mentioned coiling step is 700℃ or higher.