Non-oriented electrical steel sheet and method for producing same

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in wt%, 1.5 to 4.5% of Si, 0.1 to 2.0% of Al, and 0.1 to 2.0% of Mn, the remainder comprising Fe and unavoidable impurities, and comprises an oxide layer present in a direction from the surface toward the inside, the thickness of the oxide layer being less than 15 nm, and the thickness of the oxide layer being less than 15 nm. The length of an oxide layer interruption portion in which the thickness of the oxide layer is 2 nm or less in a cross section including the rolling direction in the steel sheet is 5-500 nm per 200 [mu] m in the rolling direction.

Description

TECHNICAL FIELD

[0001] One embodiment of the present application relates to a non-oriented electrical steel sheet and a method of manufacturing the same. In particular, one embodiment of the present application relates to a non-oriented electrical steel sheet and a method of manufacturing the same, in which a proper oxide layer is formed on the surface of the steel sheet by adjusting the dew point and tension in the annealing process before cold rolling, thereby improving the magnetic properties. BACKGROUND

[0002] The non-oriented electrical steel sheet is mainly used for a motor that converts electrical energy into mechanical energy, and in order to exhibit high efficiency in the conversion process, the non-oriented electrical steel sheet needs to have excellent magnetic properties. In particular, in recent years, as environmentally friendly vehicles using a motor instead of an internal combustion engine have been drawing attention, the demand for non-oriented electrical steel sheets used as a driving motor core material has been increasing, and thus non-oriented electrical steel sheets having both excellent magnetic properties and strength are required.

[0003] The magnetic properties of the non-oriented electrical steel sheet are mainly evaluated in terms of iron loss and magnetic flux density. The iron loss refers to energy loss occurring at a specific magnetic flux density and frequency, and the magnetic flux density refers to the degree of magnetization obtained at a specific magnetic field. The lower the iron loss, the higher the energy efficiency of the motor that can be manufactured under the same conditions, and the higher the magnetic flux density, the motor can be downsized or the copper loss can be reduced. Therefore, by using a non-oriented electrical steel sheet having low iron loss and high magnetic flux density, a driving motor having excellent efficiency and torque can be manufactured, thereby enabling an increase in the driving distance and output of the environmentally friendly vehicle.

[0004] Depending on the operating conditions of the motor, the properties of the non-oriented electrical steel sheet that need to be considered also vary. As a conventional standard for evaluating the properties of the non-oriented electrical steel sheet used in a motor, the iron loss W15 / 50 at a commercial frequency of 50 Hz under a magnetic field of 1.5 T is widely used. However, in the non-oriented electrical steel sheet having a thickness of 0.35 mm or less used for a driving motor of an environmentally friendly vehicle, the magnetic properties at a low magnetic field of 1.0 T or less and a high frequency of 400 Hz or more are more important many times, and thus the properties of the non-oriented electrical steel sheet are evaluated in terms of W 10 / 400 Iron loss. In addition, as the rotational speed increases, the strength properties, which are not very important, are also evaluated as important properties.

[0005] In order to improve the magnetic properties of non-oriented electrical steel sheets, a method of adding alloying elements such as Si, Al, Mn, etc. is generally used. By adding these alloying elements, when the electrical resistivity of the steel increases, the eddy current loss decreases, and the total iron loss can be reduced. In addition, the alloying elements are solid-solved in iron as substitution elements to exert a strengthening effect, thereby the strength can be improved. On the other hand, as the addition amount of the alloying elements such as Si, Al, Mn, etc. increases, the magnetic flux density deteriorates, and there is a disadvantage that the brittleness increases, and if a certain amount or more is added, cold rolling cannot be performed, and thus industrial production cannot be performed. In particular, for electrical steel sheets, the thinner the thickness, the better the high-frequency iron loss, and the decrease in rollability due to brittleness becomes a fatal problem. It is known that the maximum value of the sum of the contents of Si, Al, and Mn, which can be industrially produced, is about 4.5% by weight, and in addition thereto, by optimizing the contents of trace elements, the highest grade non-oriented electrical steel sheet having excellent magnetic properties and strength can be produced.

[0006] However, when a large amount of high-resistivity alloying elements such as Si, Al, Mn, Cr, etc. are added, a problem of a decrease in magnetic flux density occurs. In particular, materials for lightweighting which are continuously required for electric vehicle drive motors must use materials having high magnetic flux density.

[0007] For this reason, a method of improving the properties by thinning a hot-rolled sheet has been proposed, and a method of improving the magnetic properties by containing high aluminum and performing two annealing and two rolling processes has been proposed. In addition, a method of achieving hot-rolled thinning by a thin slab manufacturing method has been proposed.

[0008] However, for the method of reducing the thickness of the hot-rolled sheet, in the conventional hot-rolling process, mass production is difficult to achieve due to an increase in rolling load, and the addition of high aluminum and the two annealing and two rolling processes have been confirmed to improve the magnetic properties to some extent, but the {110} <001> Goss texture is also developed at the same time, and thus the axial properties of the motor are deteriorated, and surface defects due to the addition of high aluminum are also greatly increased. SUMMARY

[0009] (I) Technical problem to be solved One embodiment of the present application provides a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, one embodiment of the present application provides a non-oriented electrical steel sheet and a manufacturing method thereof, in which a proper oxidation layer is formed on the surface of the steel sheet by adjusting the dew point and tension in the annealing process before cold rolling, and thus the magnetic properties are improved.

[0010] (II) Technical solution The non-oriented electrical steel sheet according to one embodiment of the present application contains, in weight %, Si: 1.5 to 4.5 %, Al: 0.1 to 2.0 %, Mn: 0.1 to 2.0 %, the balance containing Fe and inevitable impurities, and contains an oxide layer present from the surface in the direction of the interior, the thickness of the oxide layer being less than 15 nm, and the length of the oxide layer interruption portion in the rolling direction in the cross section in the rolling direction in which the thickness of the oxide layer is 2 nm or less is 5 to 500 nm per 200 μm of the rolling direction.

[0011] The non-oriented electrical steel sheet according to one embodiment of the present application can further contain one or more of P: 0.1 % by weight or less except 0 %, C: 0.005 % by weight or less except 0 %, S: 0.005 % by weight or less except 0 %, Ti: 0.004 % by weight or less except 0 %, and N: 0.005 % by weight or less except 0 %.

[0012] The non-oriented electrical steel sheet according to one embodiment of the present application can further contain one or more of Sn, Sb, Bi, Pb, Ge, and As, each or the total of which is 0.005 to 0.200 % by weight.

[0013] The non-oriented electrical steel sheet according to one embodiment of the present application can further contain one or more of Cu: 0.005 to 0.2 % by weight, Cr: 0.01 to 0.5 % by weight, Ni: 0.05 % by weight or less except 0 %, Zn: 0.01 % by weight or less except 0 %, and Co: 0.05 % by weight or less except 0 %.

[0014] The non-oriented electrical steel sheet according to one embodiment of the present application can further contain one or more of Mo: 0.03 % by weight or less except 0 %, B: 0.0050 % by weight or less except 0 %, V: 0.0050 % by weight or less except 0 %, Ca: 0.0050 % by weight or less except 0 %, Nb: 0.0050 % by weight or less except 0 %, Zr: 0.005 % by weight or less except 0 %, Te: 0.01 % by weight or less except 0 %, and Mg: 0.0050 % by weight or less except 0 %.

[0015] The density of nitrides having a particle size of 10 to 200 nm can be 4 / μm 2 The following.

[0016] A manufacturing method of a non-oriented electrical steel sheet according to one embodiment of the present application includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet, the slab containing, in weight %, Si: 1.5 to 4.5 %, Al: 0.1 to 2.0 %, Mn: 0.1 to 2.0 %, the balance containing Fe and inevitable impurities; a cold-rolling pre-annealing step of annealing the steel sheet at a dew point of more than -40 °C and less than -10 °C and under a tension of less than 3.0 kgf / mm 2 more than 3.0 kgf / mm 2 A manufacturing method of a non-oriented electrical steel sheet according to one embodiment of the present application includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet, the slab containing, in weight %, Si: 1.5 to 4.5 %, Al: 0.1 to 2.0 %, Mn: 0.1 to 2.0 %, the balance containing Fe and inevitable impurities; a cold-rolling pre-annealing step of annealing the steel sheet at a dew point of more than -40 °C and less than -10 °C and under a tension of less than 3.0 kgf / mm

[0017] The slab can further contain one or more of P: 0.1 % or less by weight and except 0 %, C: 0.005 % or less by weight and except 0 %, S: 0.005 % or less by weight and except 0 %, Ti: 0.004 % or less by weight and except 0 %, N: 0.005 % or less by weight and except 0 %.

[0018] The slab can further contain one or more of Sn, Sb, Bi, Pb, Ge and As, each or the total of which is 0.005 to 0.200 % by weight.

[0019] The slab can further contain one or more of Cu: 0.005 to 0.2 % by weight, Cr: 0.01 to 0.5 % by weight, Ni: 0.05 % or less by weight and except 0 %, and Zn: 0.01 % or less by weight and except 0 %.

[0020] The slab can further contain one or more of Mo: 0.03 % or less by weight and except 0 %, B: 0.0050 % or less by weight and except 0 %, V: 0.0050 % or less by weight and except 0 %, Ca: 0.0050 % or less by weight and except 0 %, Nb: 0.0050 % or less by weight and except 0 %, Zr: 0.005 % or less by weight and except 0 %, Te: 0.01 % or less by weight and except 0 %, Co: 0.05 % or less by weight and except 0 %, and Mg: 0.0050 % or less by weight and except 0 %.

[0021] After the hot-rolled steel sheet is manufactured, the subsequent steps can be performed in a state in which scale remaining on the hot-rolled steel sheet.

[0022] The method can further include a step of pre-cold-rolling the hot-rolled sheet before the cold-rolling pre-annealing step.

[0023] In the step of pre-cold-rolling, the reduction can be 65 to 80 %.

[0024] The soaking temperature of the cold-rolling pre-annealing step can be 800 to 1100 °C.

[0025] In the process of manufacturing cold-rolled sheets, the reduction rate can be 55% to 70%.

[0026] The annealing process for cold-rolled steel sheets can be carried out at a homogenization temperature of 850 to 1100°C in a dew point atmosphere below 0°C.

[0027] (III) Beneficial Effects According to an embodiment of the present invention, the non-oriented electrical steel sheet does not suffer from surface degradation, thus further improving magnetic properties.

[0028] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention can help manufacture environmentally friendly automotive motors, high-efficiency home appliance motors, and ultra-high-end electric motors. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a cross-section of a non-oriented electrical steel sheet according to an embodiment of the present invention. Detailed Implementation

[0030] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below can also be described as a second part, component, region, layer, or segment.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. As used in the specification, "comprising" can specifically refer to a feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, and / or components.

[0032] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, there are no other parts in between.

[0033] In addition, unless otherwise specified, % means weight, 1 ppm is 0.0001 weight.

[0034] In one embodiment of the present invention, the additional element refers to the additional element replacing the balance of iron (Fe), and the amount of replacement is equivalent to the amount of additional element added.

[0035] Although not otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. For the terms defined in a dictionary, unless specifically defined in the present application, they should be interpreted as having the same meaning as those used in the relevant technical field and the present application, and should not be interpreted in an idealized or overly formal sense.

[0036] Hereinafter, embodiments of the present application will be described in detail so that those skilled in the art to which the present application pertains can easily practice the present application. However, the present application can be implemented in various different ways, and is not limited to the embodiments described herein.

[0037] The non-oriented electrical steel sheet according to one embodiment of the present application contains, in weight %, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the balance containing Fe and inevitable impurities.

[0038] Hereinafter, reasons for the component limitations of the non-oriented electrical steel sheet will be described first.

[0039] Si: 1.5 to 4.5% by weight The role of silicon (Si) is to increase the electrical resistivity of the material, reduce the iron loss, and increase the strength through solid solution strengthening. If Si is added too little, the iron loss and strength improvement effects can be insufficient. If Si is added too much, the brittleness of the material increases, the rolling productivity sharply decreases, and a surface layer oxide layer and oxides that are harmful to the magnetic properties can be formed. Therefore, Si can be contained in an amount of 1.5 to 4.5% by weight. More specifically, it can be contained in an amount of 2.0 to 4.3% by weight. More specifically, it can be contained in an amount of 2.5 to 4.2% by weight.

[0040] Al: 0.1 to 2.0% by weight The role of aluminum (Al) is to increase the electrical resistivity of the material, reduce the iron loss, and increase the strength through solid solution strengthening. If Al is added too little, fine nitrides are formed, and it can be difficult to obtain the magnetic improvement effect. If Al is added too much, too many nitrides are formed, resulting in magnetic degradation, problems in all processes such as steelmaking and continuous casting, and a great decrease in productivity can occur. Therefore, Al can be contained in an amount of 0.1 to 2.0% by weight. More specifically, it can be contained in an amount of 0.2 to 1.6% by weight. More specifically, it can be contained in an amount of 0.3 to 1.5% by weight.

[0041] Mn: 0.1 to 2.0% by weight Manganese (Mn) functions to increase the electrical resistivity of the material, improve the iron loss, and form sulfides. If Mn is added too little, fine sulfides are formed, resulting in magnetic deterioration. If Mn is added too much, too many fine MnS precipitates are formed, promoting the formation of {111} texture, which is not conducive to magnetism, and the magnetic flux density can be sharply reduced. Therefore, Mn can be contained in an amount of 0.1 to 2.0% by weight. More specifically, it can be contained in an amount of 0.2 to 1.6% by weight. More specifically, it can be contained in an amount of 0.3 to 1.5% by weight.

[0042] The non-oriented electrical steel sheet according to one embodiment of the present application can further contain one or more of P: 0.1% by weight or less and excluding 0%, C: 0.005% by weight or less and excluding 0%, S: 0.005% by weight or less and excluding 0%, Ti: 0.004% by weight or less and excluding 0%, N: 0.005% by weight or less and excluding 0%.

[0043] P: 0.1% by weight or less Phosphorus (P) is a grain boundary segregation element, and can increase the magnetic flux density, but if added too much, the brittleness of the steel sheet increases, and the weldability can deteriorate. More specifically, P can be contained in an amount of 0.0001 to 0.0500% by weight.

[0044] C: 0.005% by weight or less Carbon (C) causes magnetic aging, and in combination with other impurity elements, generates carbides, thereby hindering the movement of grain boundaries or magnetic domain walls, and can cause deterioration of magnetic properties. More specifically, C can be contained in an amount of 0.0001 to 0.003% by weight.

[0045] S: 0.005% by weight or less Sulfur (S) forms fine precipitates MnS and CuS, and can cause deterioration of magnetic properties and deterioration of hot rolling workability. More specifically, S can be contained in an amount of 0.0001 to 0.0030% by weight.

[0046] Ti: 0.004% by weight or less Titanium (Ti) has a very strong tendency to form precipitates in steel, and forms fine carbides, nitrides, or sulfides inside the base material, thereby inhibiting grain growth and magnetic domain wall movement, and can cause deterioration of iron loss. More specifically, Ti can be contained in an amount of 0.0001 to 0.003% by weight.

[0047] N: 0.005% by weight or less Nitrogen (N) not only forms fine AlN precipitates inside the base material, but also forms fine precipitates in combination with other impurities, and inhibits grain growth and magnetic domain wall movement, and can cause deterioration of iron loss. More specifically, N can be contained in an amount of 0.0001 to 0.0030% by weight.

[0048] The non-oriented electrical steel sheet according to one embodiment of the present application can further include one or two or more of Sn, Sb, Bi, Pb, Ge, and As, each or the total of which is 0.005 to 0.200% by weight.

[0049] Sn and Sb The roles of tin (Sn) and antimony (Sb) are to segregate at grain boundaries at the initial stage of final recrystallization annealing, thereby suppressing the development of {111} orientation which causes deterioration of magnetic properties. If Sn and Sb are added too much, the recovery and growth of a coarse extended band structure can be hindered, possibly causing deterioration of surface quality. Therefore, one or more of Sn and Sb can be further added within the ranges described above. More specifically, Sn can be included in an amount of 0.005 to 0.200% by weight or Sb can be included in an amount of 0.005 to 0.200% by weight.

[0050] Bi, Pb, Ge, and As When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are further added, they segregate at grain boundaries, relieve stress concentration at grain boundaries at the time of cold rolling, and suppress the recrystallization of <111> / / ND-oriented grains in the recrystallization annealing of subsequent processes, thereby improving the magnetic flux density. When these elements are appropriately added, the effects described above can be further obtained, but if the contents are too much, segregation occurs in large amounts, thereby suppressing grain growth, which can cause deterioration of the magnetic flux density and the iron loss.

[0051] The non-oriented electrical steel sheet according to one embodiment of the present application can further include one or more of Cu: 0.005 to 0.2% by weight, Cr: 0.01 to 0.5% by weight, Ni: 0.05% by weight or less and excluding 0%, Zn: 0.01% by weight or less and excluding 0%, and Co: 0.05% by weight or less and excluding 0%.

[0052] Cu: 0.005 to 0.200% by weight The role of copper (Cu) is to form sulfides together with Mn. When Cu is further added, if it is added too little, (Cu·Mn)S is finely precipitated, which can cause deterioration of magnetic properties. If Cu is added too much, high-temperature brittleness can occur, causing cracks to be formed at the time of continuous casting or hot rolling. More specifically, Cu can be included in an amount of 0.01 to 0.10% by weight.

[0053] Cr: 0.01 to 0.50% by weight The role of chromium (Cr) is to increase the electrical resistivity and improve the iron loss. If Cr is added too little, the effect of increasing the electrical resistivity can be insufficient. If the content of Cr is too much, the magnetic flux density can be decreased. More specifically, Cr can be included in an amount of 0.050 to 0.20% by weight.

[0054] Ni: 0.05% by weight or less Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which can adversely affect the magnetic properties. More specifically, Ni can be included in an amount of 0.001 to 0.03% by weight.

[0055] Zn: 0.01% by weight or less If the zinc (Zn) content is too high, it can cause the magnetic properties to deteriorate as an impurity. Therefore, Zn can be further added within the aforementioned range. More specifically, Zn can be included in an amount of 0.001 to 0.005% by weight.

[0056] Co: 0.05% by weight or less Cobalt (Co) does not form fine precipitates that reduce the magnetic properties of the steel sheet, but increases the high-temperature strength, which can cause the shape of the coiled sheet after hot rolling to be poor.

[0057] The non-oriented electrical steel sheet according to one embodiment of the present application can further include one or more of Mo: 0.03% by weight or less except 0%, B: 0.0050% by weight or less except 0%, V: 0.0050% by weight or less except 0%, Ca: 0.0050% by weight or less except 0%, Nb: 0.0050% by weight or less except 0%, Zr: 0.0050% by weight or less except 0%, Te: 0.0100% by weight or less except 0%, and Mg: 0.0050% by weight or less except 0%.

[0058] Mo: 0.030% by weight or less If molybdenum (Mo) is excessively added, the segregation of segregation elements can be inhibited, which can reduce the texture improvement effect. Therefore, Mo can be included in an amount of 0.03% by weight or less, the lower limit of which is not particularly limited, but can be 0.001% by weight or more since it plays a role in improving the texture by segregating on the surface and grain boundaries. More specifically, Mo can be included in an amount of 0.001 to 0.010% by weight. More specifically, Mo can be included in an amount of 0.005 to 0.010% by weight.

[0059] B: 0.0050% by weight or less If boron (B) is excessively added, inclusions or the like can be formed in the steel, which can cause the magnetic properties to deteriorate. Therefore, B can be included in an amount of 0.005% by weight or less, the lower limit of which is not particularly limited, but can be 0.0001% by weight in terms of steelmaking costs. More specifically, B can be included in an amount of 0.0001 to 0.0030% by weight.

[0060] V: 0.0050% by weight or less Vanadium (V) has a very strong tendency to form precipitates in steel, and forms fine carbides or nitrides inside the base material, inhibiting grain growth and magnetic domain wall movement, thereby causing iron loss deterioration. Therefore, the V content can be 0.0050% by weight or less, the lower limit of which is not particularly limited, but can be 0.0003% by weight due to steelmaking costs. That is, V can be included in an amount of 0.0003 to 0.0050% by weight. More specifically, V can be included in an amount of 0.0003 to 0.0030% by weight.

[0061] Ca: 0.0050% by weight or less Calcium (Ca) has a very strong tendency to form precipitates in steel, and forms fine sulfides inside the base material, inhibiting grain growth and magnetic domain wall movement, thereby causing iron loss deterioration.

[0062] Nb: 0.0050% by weight or less Niobium (Nb) has a very strong tendency to form precipitates in steel, and forms fine carbides or nitrides inside the base material, inhibiting grain growth and magnetic domain wall movement, thereby causing iron loss deterioration. Therefore, the Nb content can be 0.0050% by weight or less, the lower limit of which is not particularly limited, but can be 0.0003% by weight due to steelmaking costs. That is, Nb can be included in an amount of 0.0003 to 0.0050% by weight. More specifically, Nb can be included in an amount of 0.0003 to 0.0030% by weight.

[0063] Zr: 0.0050% by weight or less If zirconium (Zr) is excessively added, inclusions, etc. can be formed in the steel, causing magnetic deterioration. Therefore, Zr can be included in an amount of 0.005% by weight or less, the lower limit of which is not particularly limited, but can be 0.0001% by weight due to steelmaking costs. That is, Zr can be included in an amount of 0.0001 to 0.0050% by weight. More specifically, it can be included in an amount of 0.0005 to 0.0030% by weight.

[0064] Te: 0.0100% by weight or less Tellurium (Te) diffuses to the oxide layer on the surface of the hot-rolled coil, increases the friction coefficient between the oxide layer and the rolling work roll, and is enriched in the lower part of the oxide layer, thereby increasing the hardness. Therefore, tellurium can be added so that the broken oxide layer in the rolling process falls off without being pressed into the base material. If the amount of Te added is too small, the effect can not be significant. If Te is added too much, the oxide layer is easily peeled off, and the base material directly contacts the work roll, thereby reducing the effect, and too many deformation bands are generated in the steel sheet during the cold rolling process, which can cause the {111} / / ND texture to develop, which is not good for magnetic properties. More specifically, tellurium can be included in an amount of 0.0001 to 0.007% by weight.

[0065] Mg: 0.0050% by weight or less Magnesium (Mg) is an element that mainly forms sulfides in combination with S and can affect the surface oxide layer of the base iron. Accordingly, Mg can be contained in 0.0050% by weight or less, the lower limit of which is not particularly limited, but can be 0.0001% by weight due to steelmaking costs. That is, Mg can be contained in 0.0001 to 0.0050% by weight. More specifically, 0.0005 to 0.0030% by weight can be contained.

[0066] The balance includes Fe and inevitable impurities. As for the inevitable impurities, they are impurities mixed in during the steelmaking step and the manufacturing process of the non-oriented electrical steel sheet, which are well known in the art, and thus a detailed description is omitted. In one embodiment of the present application, in addition to the aforementioned alloying components, an increase in elements is not excluded, and various elements can be contained within a range that does not impair the technical idea of the present application. When the additional elements are further contained, a part of the balance of Fe is replaced.

[0067] As described above, in one embodiment of the present application, by appropriately adjusting the alloying components of the steel sheet and appropriately forming the oxide layer on the surface of the steel sheet, the magnetic properties can be improved.

[0068] Figure 1 A schematic view of a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present application is shown in FIG. 1.

[0069] As shown in FIG. 1, the oxide layer 10 can be contained in the non-oriented electrical steel sheet 100. Figure 1

[0070] As for the oxide layer 10, the oxide layer 10 can be formed by the penetration of oxygen into the steel sheet during the manufacturing process of the electrical steel sheet.

[0071] The oxide layer 10 is defined as a portion in which oxygen is 20% by weight or more from the surface of the steel sheet in the inward direction. As for the detection and thickness of the oxide layer 10, when the TD surface of the sample is processed using FIB, observed using TEM, and analyzed using EDS, a portion in which oxygen is 20% by weight or more can be determined as the oxide layer. At this time, the steel sheet sample is not formed with an insulating coating film, or in the case of being formed with an insulating coating film, a sample in which the insulating coating film is removed can be used. In order to reduce the measurement error according to the position, the sample can be measured in a length of at least 200 μm in the RD direction, and the average value thereof can be taken.

[0072] The thickness of the oxide layer 10 can be less than 15 nm. If the thickness of the oxide layer 10 is too thick, oxygen can be largely penetrated into the steel sheet, which can cause deterioration in the magnetic properties. More specifically, the thickness of the oxide layer 10 can be 2 to 13 nm. More specifically, the thickness of the oxide layer 10 can be 3 to 10 nm. The thickness of the oxide layer 10 can be the average thickness of the oxide layer 10 in the measured sample.

[0073] ​like Figure 1 As shown, there exists an oxide layer interruption in the steel plate with a thickness of less than 2 nm on a cross-section in the rolling direction. The length of this interruption is DC. L It can be 5 to 500 nm per 200 μm in the rolling direction. For example... Figure 1 As shown, multiple oxide layer interruptions can exist within the sample. In this case, the sum of the lengths of all oxide layer interruptions falls within the aforementioned range. If the length of the oxide layer interruption is too short, the overall thickness of the oxide layer increases, creating an uneven shape at the interface between the oxide layer and the substrate, which may lead to problems with magnetic properties. If the length of the oxide layer interruption is too long, fine nitrides will be promoted to form in the region below 100 nm from the center of the substrate in the oxide layer, which may also lead to problems with magnetic properties. More specifically, the length of the interruption (DC...) L The value can be 50 to 400 nm per 200 μm in the rolling direction. The measurement and determination of the interrupted portion can be performed using the same method as the aforementioned measurement and determination of the oxide layer.

[0074] The oxide layer 10 and the oxide layer interruption can be properly formed by adjusting the dew point and tension during the pre-rolling annealing process. For a more specific method, it is described below in connection with the manufacturing method of non-oriented electrical steel sheets.

[0075] Due to the surface concentration of Al, the oxide layer 10 can contain more than 20% by weight of Al. More specifically, Al can contain 20 to 60% by weight. Apart from Al and O, the remaining alloy composition is the same as that of the aforementioned non-oriented electrical steel sheet. The oxide layer 10 is very thin relative to the overall thickness of the non-oriented electrical steel sheet 100, and therefore has no substantial impact on the alloy composition of the non-oriented electrical steel sheet 100.

[0076] As described above, the presence of oxide layer 10 suppresses the formation of nitrides near the surface. Specifically, in a cross-section from the surface to a depth of 150 nm to 300 nm, the density of nitride particles with a diameter of 10 to 200 nm can be 4 particles / μm. 2 The particle size and number density of nitrides can be measured based on a cross-section (TD plane) perpendicular to the rolling direction (TD direction) of the steel plate. As a measurement method, after preparing the sample using a replication method, it can be observed using a TEM. For particle size, a virtual circle with an area equal to the area occupied by the nitrides is assumed, and the diameter of this circle is taken as the particle size.

[0077] As described above, in one embodiment of the present invention, magnetism can be improved by appropriately controlling the steel composition and appropriately forming an oxide layer. Specifically, based on a thickness of 0.25 mm, the iron loss (W) of the non-oriented electrical steel sheet is... 10 / 400) can be 12.5 W / Kg or less. In addition, the magnetic flux density (B50) can be 1.67 T or more. The iron loss (W 10 / 400 ) is the iron loss when a magnetic flux density of 1.0 T is excited at a frequency of 400 Hz. The magnetic flux density (B 50 ) is the magnetic flux density induced under a magnetic field of 5000 A / m. More specifically, the iron loss (W 10 / 400 ) of the non-oriented electrical steel sheet can be 10.0 to 12.0 W / kg. More specifically, it can be 10.5 to 11.5 W / kg. The magnetic flux density (B50) can be 1.68 T to 1.75 T.

[0078] A method of manufacturing a non-oriented electrical steel sheet according to one embodiment of the present application includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a cold-rolling pre-annealing step of annealing the steel sheet before cold-rolling; a step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0079] The following will be described in detail by steps.

[0080] First, the slab is hot-rolled.

[0081] As for the alloying components of the slab, the foregoing description of the alloying components of the non-oriented electrical steel sheet applies, and thus repeated description is omitted. The alloying components do not substantially change during the manufacturing process of the non-oriented electrical steel sheet, and thus the alloying components of the non-oriented electrical steel sheet and the slab are substantially the same.

[0082] Specifically, the slab contains, by weight %, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and the balance containing Fe and inevitable impurities.

[0083] As for other additional elements, the foregoing description of the alloying components of the non-oriented electrical steel sheet applies, and thus repeated description is omitted.

[0084] Before the hot-rolling, the slab can be heated. The heating temperature of the slab is not limited, but the slab can be heated to 1200°C or less. If the heating temperature of the slab is too high, the precipitates such as AlN and MnS present in the slab are re-dissolved and then finely precipitated during the hot-rolling and annealing, thereby inhibiting the grain growth, which can cause a decrease in magnetic properties.

[0085] Next, the slab is hot-rolled to manufacture a hot-rolled sheet. The thickness of the hot-rolled sheet can be 1.0 to 4.5 mm. In the step of manufacturing the hot-rolled sheet, the finish rolling temperature can be 800°C or more. Specifically, it can be 800 to 1000°C. For the hot-rolled sheet, coiling can be performed at a temperature of 600°C or more. More specifically, the thickness of the hot-rolled sheet can be 1.5 to 4.3 mm.

[0086] After manufacturing the hot-rolled steel sheet, the subsequent steps can be performed in a state in which scale remaining on the hot-rolled steel sheet. That is, after hot-rolling, the removal of scale such as pickling, shot blasting, or surface grinding, etc. can be omitted, and the subsequent steps can be performed. Since cold-rolling is performed in a state in which the pickling process is omitted, the friction of the work roll with the steel sheet increases, so that in addition to plane deformation, shear deformation is also applied during rolling, and specific orientation develops during recrystallization annealing. In one embodiment of the present application, scale refers to a portion in which elements such as Fe, Al, Si, etc. on the surface of the steel sheet are combined with oxygen to form a phase different from the base material. Scale remaining refers to scale remaining on the hot-rolled sheet having a thickness of at least 1 μm. At this time, the scale thickness refers to the sum of the thicknesses of the scale generated on both surfaces of the steel sheet. If the thickness of the scale remaining is too thin, the effect caused by scale remaining can not be sufficiently exhibited. Even if the thickness of the scale is thicker, the effect does not increase, and there is a problem in that the yield of the steel sheet decreases. More specifically, scale having a thickness of 0.1 to 1 μm can remain.

[0087] In one embodiment of the present application, after manufacturing the hot-rolled steel sheet, a cold-rolling pre-annealing step of annealing the hot-rolled steel sheet can be directly performed. Alternatively, after pre-cold-rolling the hot-rolled steel sheet, a cold-rolling pre-annealing step of annealing the pre-cold-rolled sheet can be performed.

[0088] Pre-cold-rolling is distinguished from the following cold-rolling in that pre-cold-rolling is a rolling step of rolling to an intermediate thickness rather than a final product thickness, and then performing intermediate annealing, and then cold-rolling to the final product thickness.

[0089] For pre-cold-rolling, it can be performed in a reduction range of 65 to 80% to improve the final cold-rolling productivity and the grains in the final product sheet. Meanwhile, if the rolling productivity is not considered, the present application can also perform pre-cold-rolling in a reverse mill. The pre-cold-rolled sheet can have a thickness of 0.3 to 1.5 mm. More specifically, the reduction can be 68 to 78% and the thickness can be 0.6 to 1.3 mm.

[0090] For the pre-cold-rolling reduction, it can be calculated by (thickness of the steel sheet before rolling - thickness of the steel sheet after rolling) / thickness of the steel sheet before rolling. If the reduction is too low in the pre-cold-rolling step, the rolling load increases at the time of final cold-rolling, so that the productivity decreases, the final reduction increases, and there is a problem in that the recrystallization of the fine <111> / ND orientation is promoted. On the other hand, if the reduction is too high, the cold-rolling load increases, and the possibility of sheet breakage also increases.

[0091] The pre-rolling step can be performed at a temperature of 60 to 3000C. For this temperature, the temperature of the steel sheet is naturally increased due to friction between the steel sheet and the rolls or can be increased by external heating. If the temperature is too low, the rolling load is greatly increased, the steel sheet slips between the rolls instead of being rolled, and problems such as twisting can occur. If the temperature is too high, a thick oxide layer is generated on the surface of the steel sheet, the magnetic properties are deteriorated, and problems such as ignition of the rolling oil can occur. More specifically, it is preferable to perform at a temperature of 70 to 2500C. The aforementioned temperature refers to the temperature of the steel sheet.

[0092] As described above, the pre-rolling step can also be omitted as necessary.

[0093] Next, the hot-rolled steel sheet or the pre-rolled sheet is annealed in a cold-rolling pre-annealing step. In one embodiment of the present application, by adjusting the dew point and the tension in the cold-rolling pre-annealing step, the oxide layer 10 can be appropriately formed.

[0094] Specifically, the dew point can be more than -40°C and less than -10°C. If the dew point is too low, the oxide layer discontinuity of the final product is excessively increased or fine nitrides are generated in large amounts near the surface portion, thereby causing problems in the magnetic properties. If the dew point is too high, a too thick oxide layer is formed or fine oxide particles are formed near the surface portion, thereby causing problems in the magnetic properties. More specifically, the dew point can be -35 to -8°C. More specifically, the dew point can be the dew point with respect to the atmosphere during the soaking process.

[0095] In addition, a tension of 1.0 kgf / mm 2 or less and more than 3.0 kgf / mm 2 can be imparted. If the tension is too low, the shape of the steel sheet cannot be sufficiently corrected, and a too much oxide layer is formed locally on the final product sheet, thereby causing problems in the magnetic properties. If the tension is too high, a too much oxide layer discontinuity is formed on the final product sheet, thereby causing problems in the magnetic properties. More specifically, the tension can be 1.3 to 2.7 kgf / mm 2 . The tension can be a tension measured between the Bridle Rolls at the inlet and the outlet of the annealing furnace, and can be measured with a load cell.

[0096] In the cold-rolling pre-annealing step, the soaking temperature can be 800 to 11000C. If the annealing temperature is too low, a recrystallized structure is not formed or fine growth, and the magnetic flux density improvement effect is small, and if the annealing temperature is too high, the magnetic properties are rather decreased, and the rolling workability is deteriorated due to the plate-like deformation. More specifically, the temperature range can be 830 to 10800C. The soaking time can be 30 to 300 seconds.

[0097] For the aforementioned annealing before cold rolling, it can be performed in a vertical continuous annealing apparatus or a horizontal continuous annealing apparatus, etc. If the scale removal after hot rolling is omitted, scale removal can be performed after the annealing before cold rolling. When scale remains in the finally manufactured non-oriented electrical steel sheet, the magnetic properties will be deteriorated. In addition, when cold rolling is performed in a state in which scale remains, the scale is pressed into the surface or a trace of peeling is formed to cause unevenness, which can cause deterioration in the running stability of a motor and magnetic properties. After pickling, the scale can be completely removed or can remain to a thickness of 0.01 μm or less. Pickling refers not only to acid dipping but also to all methods of physical and chemical scale removal. The pickling method can employ acid dipping, sand blasting, or surface grinding.

[0098] Next, the annealed steel sheet is cold-rolled to manufacture a cold-rolled sheet. At this time, cold rolling can be performed at a reduction ratio of 55 to 70%. If the reduction ratio is too low, the deformation energy accumulated in the rolled steel sheet is small, it is difficult to recrystallize in the subsequent annealing process, the rolling structure remains, and thus problems can occur in the improvement of the magnetic flux density and the iron loss. On the other hand, if the reduction ratio is too high, recrystallization of the <111> / / ND-oriented grains is promoted in the subsequent annealing process, the grains also become fine, and problems can occur in which the magnetic flux density deteriorates and the iron loss increases. The reduction ratio can be 58 to 67%. For the cold rolling step, a Tandem cold rolling mill, which continuously cold-rolls a steel sheet using a plurality of rolling stands, or a Reverse mill, which discontinuously cold-rolls using a rolling roll of 12 stages or more, can be used. The final rolling thickness can be 0.1 mm to 0.35 mm.

[0099] Next, the cold-rolled sheet is annealed. For the cold-rolled sheet annealing step, annealing can be performed in a dew point atmosphere of -50 to -10°C. More specifically, annealing can be performed in a dew point temperature atmosphere of -50 to -10°C.

[0100] For the cold-rolled sheet annealing step, annealing can be performed at a soaking temperature of 850 to 1100°C. If the soaking temperature is too low, the grains cannot grow sufficiently, the hysteresis loss increases, and a problem can occur in which the iron loss deteriorates. If the soaking temperature is too high, the eddy current loss increases, and a problem can occur in which the magnetic flux density sharply decreases. More specifically, annealing can be performed at a temperature of 900 to 1050°C. The soaking can be performed for 10 to 300 seconds.

[0101] During the annealing of the cold-rolled sheet, the processing structure formed in the cold rolling step can be recrystallized (i.e., 99% or more).

[0102] After the annealing of the cold-rolled sheet, an insulating coating film can be formed. The insulating coating film can be processed into an organic film, an inorganic film, and an organic-inorganic composite film, or can be processed with other insulating film formers.

[0103] Hereinafter, the present application will be described in further detail by way of examples. However, the following examples are only for illustrating the present application, and the present application is not limited to the following examples.

[0104] Example 1 A slab was manufactured to contain the components shown in Table 1, with the balance containing Fe and unavoidable impurities. The slab was heated to 1150°C, and hot-rolled at a finish temperature of 950°C to manufacture a hot-rolled sheet having a thickness shown in Table 2. For sample No. Al, the scale on the hot-rolled sheet was completely removed by pickling, and the scale removal was omitted for the remaining samples.

[0105] Then, the hot-rolled sheet was annealed, and pre-cold-rolled, annealed before cold-rolled, and cold-rolled under the conditions of Table 2 to reach a final thickness of 0.25 mm. The cold-rolled sheet was annealed at a dew point of -20°C and a soaking temperature of 1000°C for 100 seconds.

[0106] For the magnetic flux density and the iron loss, 60 mm wide x 60 mm long x 5 sheets were cut out at 10° intervals from the rolling direction to the direction perpendicular to the rolling direction, the magnetic flux density and the iron loss were measured for each sample using a single sheet tester, and the average values were shown.

[0107] At this time, W 10 / 400 is the iron loss when a magnetic flux density of 1.0 T is excited at a frequency of 400 Hz. B 50 is the magnetic flux density induced under a magnetic field of 5000 A / m.

[0108] For the oxide layer properties, the TD surface of the sample processed using FIB was photographed using TEM over a length of 300 μm in the RD direction, and the chemical composition was analyzed using EDS.

[0109] For the nitrides, when an area of 200 μm in length in the rolling direction was observed from the surface to a depth of 150 nm to 300 nm in the inner direction using TEM, the number of nitrides was analyzed by image analysis. If the density of nitrides having a particle size of 10 to 200 nm was 4 / μm 2 The following is shown as x if it exceeds 4 / μm 2 and is shown as o.

[0110] [Table 1] [Table 2] [Table 3] As shown in Tables 1 to 3, for the inventive examples in which the oxide layer properties are appropriately formed by appropriately adjusting the steel composition and appropriately adjusting the process conditions, excellent iron loss and magnetic flux density can be confirmed.

[0111] On the other hand, in cases where the steel composition is not appropriately adjusted or the process conditions are not appropriately adjusted, and the oxide layer is not appropriately formed, poor iron loss and magnetic flux density can be confirmed.

[0112] The present application can be implemented in various different ways and is not limited to the embodiments, and it will be understood by those skilled in the art to which the present application pertains that the present application can be implemented by other specific ways without changing the technical idea or essential characteristics of the present application. Therefore, it should be understood that the above-described embodiments are exemplary in all respects and are not restrictive.

[0113] [Explanation of Reference Numerals] 100: non-oriented electrical steel sheet; 10: oxide layer

Claims

1. A non-oriented electrical steel sheet, wherein, By weight percent, the non-oriented electrical steel sheet comprises Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance including Fe and unavoidable impurities. It also contains an oxide layer that extends from the surface inwards. The thickness of the oxide layer is less than 15 nm. The length of the oxide layer interruption in the cross section of the steel plate containing the rolling direction is 5 to 500 nm for every 200 μm of the oxide layer thickness.

2. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; S: less than 0.005% by weight and excluding 0%; Ti: less than 0.004% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

3. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of Sn, Sb, Bi, Pb, Ge and As, with each or their combined content ranging from 0.005 to 0.200 by weight.

4. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

5. The non-oriented electrical steel sheet according to claim 1, wherein, The non-oriented electrical steel sheet further comprises one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

6. The non-oriented electrical steel sheet according to claim 1, wherein, In a cross-section from the surface to a depth of 150 nm to 300 nm, the density of nitride particles with a diameter of 10 to 200 nm is 4 particles / μm. 2 the following.

7. A method for manufacturing a non-oriented electrical steel sheet, comprising: The step of hot rolling a slab to produce a hot-rolled steel sheet, wherein the slab comprises, by weight %: Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, with the balance comprising Fe and unavoidable impurities; The steel plate was subjected to dew points above -40°C and below -10°C, and an application of 1.0 kgf / mm². 2 Above and below 3.0 kgf / mm 2 The pre-annealing step of cold rolling is performed under tension; The steps of cold rolling annealed steel sheets to produce cold-rolled sheets; and The annealing step for the cold-rolled sheet.

8. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The slab further comprises one or more of the following: P: less than 0.1% by weight and excluding 0%; C: less than 0.005% by weight and excluding 0%; S: less than 0.005% by weight and excluding 0%; Ti: less than 0.004% by weight and excluding 0%; N: less than 0.005% by weight and excluding 0%.

9. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The slab also contains one or more of Sn, Sb, Bi, Pb, Ge and As, with each or their combined content ranging from 0.005 to 0.200 by weight.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The slab further comprises one or more of the following: Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: less than 0.05 wt% and excluding 0%, Zn: less than 0.01 wt% and excluding 0%, and Co: less than 0.05 wt% and excluding 0%.

11. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The slab further comprises one or more of the following: Mo: less than 0.03% by weight and excluding 0%; B: less than 0.0050% by weight and excluding 0%; V: less than 0.0050% by weight and excluding 0%; Ca: less than 0.0050% by weight and excluding 0%; Nb: less than 0.0050% by weight and excluding 0%; Zr: less than 0.005% by weight and excluding 0%; Te: less than 0.01% by weight and excluding 0%; and Mg: less than 0.0050% by weight and excluding 0%.

12. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, After the hot-rolled steel sheet is manufactured, subsequent steps are performed while the hot-rolled steel sheet still has residual oxide scale.

13. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, Prior to the pre-annealing step of cold rolling, a step of pre-cold rolling the hot-rolled plate is also included.

14. The method for manufacturing non-oriented electrical steel sheet according to claim 13, wherein, In the pre-cooling rolling step, the reduction rate is 65% to 80%.

15. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The homogenization temperature of the pre-annealing step before cold rolling is 800 to 1100°C.

16. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, In the process of manufacturing the cold-rolled sheet, the reduction rate is 55% to 70%.

17. The method for manufacturing non-oriented electrical steel sheet according to claim 7, wherein, The annealing step of the cold-rolled sheet is carried out in a dew point atmosphere below 0°C at a homogenization temperature of 850 to 1100°C.

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