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 percent, 1.5-5.0% Si, 0.1-3.0% Al, and 0.1-3.0% Mn, with the balance being Fe and inevitable impurities, and, in a cross-section taken in the thickness direction of the steel sheet, the surface portion extending from the surface to one-quarter of the total thickness has a grain-size standard deviation of 45-55 µm, and the central portion extending from beyond one-quarter to one-half of the thickness has a grain-size standard deviation of 50-70 µm.

Description

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

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, wherein the standard deviation of the crystal grain size at the surface and center of the steel sheet is controlled by adjusting the cooling rate and the tension applied to the steel sheet during the cooling process after hot-rolled sheet annealing and cold-rolled sheet annealing, thereby improving ultra-high frequency iron loss.

[0002] Non-oriented electrical steel sheets are used as core materials in rotating equipment such as motors and generators, as well as in stationary equipment such as small transformers, and play an important role in determining the energy efficiency of electrical equipment.

[0003] The magnetic properties of non-oriented electrical steel sheets are primarily evaluated based on iron loss and magnetic flux density. Iron loss refers to the energy loss occurring in the iron core of devices such as motors, transformers, and generators at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. It is desirable to have low iron loss and high magnetic flux density. This is because when electricity is applied to the iron core to induce a magnetic field, lower iron loss reduces energy loss as heat, allowing for the manufacture of motors with higher energy efficiency under the same conditions. Conversely, higher magnetic flux density enables the induction of a larger magnetic field with the same amount of energy, and allows for motor miniaturization or reduction of copper loss. Therefore, using non-oriented electrical steel sheets with low iron loss and high magnetic flux density enables the production of motors with excellent efficiency and torque. This extends the operating time using the same power and allows for increased motor output through higher torque.

[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] For non-oriented electrical steel sheets with a thickness of 0.35 mm or less used in drive motors for eco-friendly vehicles, magnetic properties are often important at low fields of 1.0 T or less and high frequencies of 400 to 800 Hz or higher. Therefore, the characteristics of non-oriented electrical steel sheets are often evaluated using W10 / 400 and W10 / 800 iron losses. As the rotational speed of eco-friendly vehicle drive motors increases, the required frequency band also rises, making iron losses at several kHZ important.

[0006] Meanwhile, as disasters caused by climate change increase, countries around the world are announcing carbon neutrality roadmaps. Internal combustion engines account for a significant portion of total carbon emissions, and there is a strong demand to achieve carbon neutrality in this sector through the electrification of internal combustion engines. To this end, electrification is progressing rapidly in the mobility sector, led by electric vehicles. The characteristics required for drive motors in new mobility are to increase driving range and top speed. To achieve this, while the low iron loss and high magnetic flux density characteristics of electrical steel sheets are important, iron loss at ultra-high frequencies is critical.

[0007] One embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, which improves ultra-high frequency iron loss by controlling the standard deviation of the crystal grain size at the surface and center of the steel sheet through controlling the cooling rate and the tension applied to the steel sheet during the cooling process after hot-rolled sheet annealing and cold-rolled sheet annealing.

[0008] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities, and with respect to a cross-section including the thickness direction of the steel sheet, the standard deviation of the grain size in the surface portion up to 1 / 4 of the total thickness is 45 to 55 μm, and the standard deviation of the grain size in the center portion up to more than 1 / 4 to 1 / 2 is 50 to 70 μm.

[0009] The difference between the standard deviation of the grain size at the surface and the standard deviation of the grain size at the center may be 10 to 20 μm.

[0010] The average grain size at the surface may be 60 to 75 μm, and the average grain size at the center may be 70 to 90 μm.

[0011] 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, S: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0012] 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.

[0013] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cu: 0.005 to 0.2 wt%, 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.

[0014] 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.

[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: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities; a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; 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] The hot-rolled sheet annealing step involves cooling to 730°C after cracking at a cooling rate of 5 to 15°C / second, with a tensile strength of 0.5 to 2.5 MPa during cooling, and the cold-rolled sheet annealing step involves cooling to 730°C after cracking at a cooling rate of 15 to 30°C / second, with a tensile strength of 2.0 to 4.5 MPa during cooling.

[0017] The difference between the cooling rate after the hot-rolled plate annealing step and the cooling rate after the cold-rolled plate annealing step can be 10 to 25℃ / second.

[0018] The difference between the tensile strength when cooling after the annealing step of the hot-rolled plate and the tensile strength when cooling after the annealing step of the cold-rolled plate may be 1.5 to 4.0 MPa.

[0019] The slab may further include one or more of P: 0.1 wt% or less, C: 0.005 wt% or less, S: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0020] 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.

[0021] The slab may further include one or more of Cu: 0.005 to 0.2 wt%, 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.

[0022] 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.

[0023] In the hot-rolled plate annealing stage, it can be annealed at a cracking temperature of 930 to 1100°C.

[0024] In the cold-rolled sheet annealing stage, it can be annealed at a cracking temperature of 940 to 990°C.

[0025] A non-oriented electrical steel sheet according to one embodiment of the present invention has improved ultra-high frequency iron loss and can be usefully utilized as an iron core for high-speed motors. More specifically, it can be usefully utilized as an iron core for new mobility drive motors.

[0026] FIG. 1 is a schematic diagram showing a cross-section of a non-oriented electrical steel sheet according to one embodiment of the present invention.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0031] 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.

[0032] 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.

[0033] 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.

[0034]

[0035] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, in weight%, Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities.

[0036] Below, we will explain the reason for limiting the composition of non-oriented electrical steel sheets.

[0037] Si: 1.5 to 5.0 wt%

[0038] Silicon (Si) plays a role in increasing the resistivity of the material to lower iron loss and increasing strength through solid solution strengthening. If too little Si is added, the effect of improving iron loss and strength may be insufficient. If too much Si is added, the brittleness of the material increases, which can drastically reduce rolling productivity and form surface oxide layers and oxides that are harmful to magnetism. Therefore, Si may be included in an amount of 1.5 to 5.0 weight%. More specifically, it may be included in an amount of 2.0 to 4.5 weight%. Even more specifically, it may be included in an amount of 3.00 to 3.60 weight%.

[0039]

[0040] Al: 0.1 to 3.0 wt%

[0041] Aluminum (Al) plays a role in increasing the resistivity of the material to lower iron loss and increasing strength through solid solution strengthening. If too little Al is added, fine nitrides may form, making it difficult to obtain the effect of improving magnetism. If too much Al is added, nitrides are excessively formed, degrading magnetism and causing problems in all processes, such as steelmaking and continuous casting, which can significantly reduce productivity. More specifically, it may contain 0.3 to 2.5 weight% of Al. More specifically, it may contain 0.4 to 2.0 weight%. More specifically, it may contain 0.5 to 1.5 weight%.

[0042]

[0043] Mn: 0.1 to 3.0 wt%

[0044] Manganese (Mn) plays a role in improving iron loss by increasing the resistivity of the material and forming sulfides. If too little Mn is added, fine sulfides are formed, causing magnetic degradation; if too much Mn is added, fine MnS is excessively precipitated, 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 0.1 to 3.0 weight%. More specifically, it may be included in an amount of 0.2 to 2.5 weight%. Even more specifically, it may be included in an amount of 0.3 to 2.0 weight%.

[0045]

[0046] 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, S: 0.005 wt% or less, Ti: 0.005 wt% or less, and N: 0.005 wt% or less.

[0047] P: 0.1 wt% or less

[0048] Phosphorus (P) can improve magnetic flux density as a grain boundary segregation element, but if added in excessive amounts, it increases the brittleness of the steel sheet and impairs weldability. More specifically, it may contain 0.0001 to 0.0500 weight% of P.

[0049] C: 0.005 wt% or less

[0050] Carbon (C) can cause magnetic aging and combine with other impurity elements to form carbides, which can impede grain boundary or domain wall movement and degrade magnetic properties. More specifically, it may contain 0.0001 to 0.003 weight% of C.

[0051] S: 0.005 wt% or less

[0052] Sulfur (S) can form fine precipitates, such as MnS and CuS, which can worsen magnetic properties and hot workability. More specifically, it may contain 0.0001 to 0.0030 weight% of S.

[0053] Ti: 0.005 wt% or less

[0054] 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 0.003 weight% of Ti.

[0055] N: 0.005 wt% or less

[0056] Nitrogen (N) not only forms fine AlN precipitates inside the base material but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and domain wall movement, which can worsen iron loss. More specifically, it may contain 0.0001 to 0.0030 weight% of N.

[0057]

[0058] 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.

[0059] Sn and Sb

[0060] Tin (Sn) and antimony (Sb) play a role in suppressing the development of {111} orientations, which degrade magnetism by segregating at the grain boundaries during the initial stage of final recrystallization annealing. If too much Sn and Sb are added, it can hinder the recovery and growth of coarse elongated band structures and degrade surface quality. Therefore, one or more of Sn and Sb may be added within the aforementioned range. More specifically, it may contain 0.005 to 0.200 wt% of Sn or 0.005 to 0.200 wt% of Sb. More specifically, it may contain 0.010 to 0.150 wt% of Sn or 0.010 to 0.150 wt% of Sb.

[0061] Bi, Pb, Ge, and As

[0062] 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 the / ND orientation crystal grains, the magnetic flux density is improved. If these are added appropriately, the aforementioned effects can be additionally obtained, but if they are included in too much, a large amount of segregation occurs, which suppresses crystal grain growth and may result in inferior magnetic flux density and iron loss. More specifically, one or more of Bi: 0.005 to 0.200 wt%, Pb: 0.005 to 0.200 wt%, Ge: 0.005 to 0.200 wt%, and As: 0.005 to 0.200 wt% may be further included. More specifically, one or more of Bi: 0.010 to 0.150 wt%, Pb: 0.010 to 0.150 wt%, Ge: 0.010 to 0.150 wt%, and As: 0.010 to 0.150 wt% may be further included.

[0063]

[0064] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), Zn: 0.01 wt% or less (excluding 0%), and Co: 0.05 wt% or less (excluding 0%).

[0065] Cu: 0.005 to 0.200 wt%

[0066] 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 can form cracks during continuous casting or hot rolling. More specifically, it may contain 0.01 to 0.10 weight% of Cu.

[0067] Cr: 0.01 to 0.50 wt%

[0068] 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.

[0069] Ni: 0.05 wt% or less

[0070] 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.

[0071] Zn: 0.01 wt% or less

[0072] 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%.

[0073] Co: 0.05 wt% or less

[0074] 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.

[0075]

[0076] 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: 0.0050 wt% or less, Te: 0.0100 wt% or less, and Mg: 0.0050 wt% or less.

[0077] Mo: 0.030 wt% or less

[0078] 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%.

[0079] B: 0.0050 wt% or less

[0080] 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%.

[0081] V: 0.0050 wt% or less

[0082] 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%.

[0083] Ca: 0.0050 wt% or less

[0084] 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.

[0085] Nb: 0.0050 wt% or less

[0086] 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.

[0087] Zr: 0.0050 wt% or less

[0088] 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%.

[0089] Te: 0.0100 wt% or less

[0090] 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.

[0091] Mg: 0.0050 wt% or less

[0092] 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%.

[0093]

[0094] 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.

[0095] Figure 1 schematically shows a cross-section of a steel plate according to one embodiment of the present invention.

[0096] As shown in FIG. 1, a non-oriented electrical steel sheet (100) according to one embodiment of the present invention includes a surface portion (20) from the surface to 1 / 4 of the total thickness and a center portion (10) from more than 1 / 4 to 1 / 2 with respect to a cross-section including the thickness direction of the steel sheet. The surface portion (20) may exist near both surfaces.

[0097] The standard deviation of the grain size in the surface portion (20) may be 45 to 55 μm. It is preferable that the standard deviation of the grain size in the surface portion (20) be small, but since the deviation becomes large when annealing for a short time with commercial annealing equipment, it is better to maintain it constant. If the standard deviation of the grain size in the surface portion (20) is too large, there are many large grain sizes, and high-frequency iron loss may be inferior. More specifically, the standard deviation of the grain size in the surface portion (20) may be 47 to 52 μm.

[0098] The standard deviation of the grain size in the center (10) may be 50 to 70 μm. It would be better if the standard deviation of the grain size in the center (10) were too small, but a small and constant standard deviation cannot be obtained with high-temperature short-time annealing in commercial facilities. If the standard deviation of the grain size in the center (10) is too large, there may be a problem with low-frequency iron loss. More specifically, the standard deviation of the grain size in the center (10) may be 55 to 65 μm.

[0099] The standard deviation can specifically be the population standard deviation. More specifically, for n grains, it can be calculated using the following formula.

[0100]

[0101] Gs i is the grain size of the i-th grain, and Gs is the average grain size.

[0102] The grain size and standard deviation can be calculated by observing the grain size in the relevant part using an electron microscope at a magnification of 30 to 150 and using a computer program. The grain size of the surface part is observed and calculated in the area from the surface to a thickness of 1 / 4 t by photographing the TD plane, and the center part is observed in the ND plane, but the grain size is observed and calculated after polishing from the surface layer to a thickness of 1 / 2 t.

[0103] The grain size can be determined by assuming a circle with an area equal to the area occupied by the grains in the cross-section of the steel plate and determining the diameter of that circle. The cross-section to be measured at the surface was measured on the plane perpendicular to the rolling direction (TD plane) to include small grains in the surface, and the cross-section to be measured at the center was measured after grinding the ND plane (a plane perpendicular to both the rolling direction and the rolling vertical direction) to half the thickness.

[0104] The difference between the standard deviation of the grain size at the surface portion (20) and the standard deviation of the grain size at the center (10) can be 10 to 20 μm. If the difference in standard deviation is too large, there may be a problem in that uniform magnetism cannot be secured. More specifically, the difference between the standard deviation of the grain size at the surface portion (20) and the standard deviation of the grain size at the center (10) can be 12 to 18 μm. The standard deviation of the grain size at the surface portion (20) can be smaller than the standard deviation of the grain size at the center (10).

[0105] The average grain size at the surface portion (20) may be 60 to 75 μm, and the average grain size at the center (10) may be 70 to 90 μm. More specifically, the average grain size at the surface portion (20) may be 60 to 70 μm, and the average grain size at the center (10) may be 75 to 85 μm. The average of the average grain size can be calculated as a numerical average.

[0106] A non-oriented electrical steel sheet according to one embodiment of the present invention may have a resistivity of 58 μΩ·cm or higher. While a higher resistivity is preferable for reducing eddy current losses in high-frequency rotating machines, if it becomes too large, the magnetic flux density may be inferior. In one embodiment of the present invention, the resistivity can be calculated from 13.25 + 11.3 × ([Si] + [Al] + [Mn] / 2). The elements in brackets represent the weight percent of each element, and if the corresponding element is not included, it is calculated as 0.

[0107]

[0108] As previously stated, in one embodiment of the present invention, ultra-high frequency iron loss can be improved. Specifically, W 13 / 800 It may be 59.5 W / kg or less. More specifically, W 13 / 800 It can be 20 to 59.1 W / kg. Also, W 13 / 60 It may be 1.82 W / kg or less. More specifically, W 13 / 60 It can be 1.60 to 1.75 W / kg.

[0109] Iron loss can be measured by cutting five specimens of 60mm width × 60mm length × number of sheets for each specimen, measuring the rolling direction and the rolling perpendicular direction using a single sheet tester, and calculating the average value. At this time, W 13 / 800 ε is the iron loss when a magnetic flux density of 1.3T is induced at a frequency of 800Hz. W 13 / 60 is the iron loss when a magnetic flux density of 1.3T is induced at a frequency of 60Hz.

[0110]

[0111] 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 hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; 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.

[0112] Below, each step is explained in detail.

[0113] First, the slab is hot-rolled.

[0114] 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.

[0115] Specifically, the slab contains Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0% by weight, and the remainder is Fe and unavoidable impurities.

[0116] As other additional elements have been explained in the alloy composition of non-oriented electrical steel sheets, redundant explanations are omitted.

[0117] The slab may be heated before hot rolling. The heating temperature of the slab is not limited, but the slab may be heated to 1200°C or lower. If the heating temperature of the slab is too high, precipitates within the slab may be re-dissolved and then finely precipitated, which may adversely affect magnetism. If the re-heating temperature is too low, hot rolling may be difficult. More specifically, it may be heated to a temperature of 1050 to 1200°C.

[0118] Next, a hot-rolled plate is manufactured by hot-rolling a slab. The thickness of the hot-rolled plate may be 1.0 to 4.5 mm. In the step of manufacturing the hot-rolled plate, the finish rolling temperature may be 800°C or higher. Specifically, it may be 800 to 1000°C. The hot-rolled plate may be coiled at a temperature of 600°C or higher. More specifically, the thickness of the hot-rolled plate may be 1.5 to 4.3 mm.

[0119] 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 930 to 1100°C. If the annealing temperature is too low, a recrystallization structure is not formed or grows finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, magnetic properties may actually deteriorate, and rolling workability may worsen due to deformation of the sheet shape. More specifically, the temperature range may be 950 to 1080°C. The cracking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0120] In one embodiment of the present invention, after cracking during annealing of a hot-rolled plate, it may be cooled to 730°C at a cooling rate of 5.0 to 15.0°C / second, and the tensile strength during cooling may be 0.5 to 2.5 MPa. If the cooling rate is too slow, it may cause problems due to low productivity. If the cooling rate is too fast, the shape may deteriorate due to thermal shock, and rolling productivity may be deteriorated. If the tensile strength during cooling is too weak, meandering may occur during continuous annealing, making it difficult to pass through the plate. If the tensile strength during cooling is too high, problems such as width shrinkage and plate breakage may occur, resulting in deteriorated productivity. More specifically, after cracking, it may be cooled to 730°C at a cooling rate of 5.0 to 10.0°C / second, and the tensile strength during cooling may be 0.5 to 1.5 MPa.

[0121] Next, a cold-rolled sheet is manufactured by cold-rolling a hot-rolled steel sheet. In the step of manufacturing the cold-rolled sheet, the reduction ratio may be 75 to 90%. If the reduction ratio is too low, additional rolling is required to obtain an appropriate final thickness, and productivity may be inferior. If the reduction ratio is too high, a texture unfavorable to magnetism is formed, and iron loss may be inferior. More specifically, in the step of manufacturing the cold-rolled sheet, the total reduction ratio may be 77 to 88%.

[0122] After cold rolling, the thickness may be 0.10 to 0.35 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 ultra-high frequency iron loss. More specifically, the thickness may be 0.15 to 0.30 mm.

[0123] In one embodiment of the present invention, cold rolling can be performed in a single step without intermediate annealing.

[0124] In the annealing stage of the cold-rolled sheet, the cracking temperature may be 940 to 990°C. If the annealing temperature is too low, it is difficult to obtain appropriate magnetic properties. Conversely, if the annealing temperature is too high, surface defects may occur and high-frequency iron loss may deteriorate. More specifically, the annealing stage of the cold-rolled sheet may be 950 to 980°C. The cracking time may be 30 seconds to 300 seconds.

[0125] In one embodiment of the present invention, the cold-rolled sheet is cooled to 730°C at a cooling rate of 15 to 30°C / second after cracking during annealing, and the tensile strength during cooling may be 2.0 to 4.5 MPa. If the cooling rate is too slow, the annealing productivity is too low, which may cause problems in terms of manufacturing costs. If the cooling rate is too fast, the shape may be degraded, and edge waves may occur. If the tensile strength during cooling is too weak, meandering may occur within the annealing furnace, which may cause problems in terms of difficulty in passing the sheet. If the tensile strength during cooling is too strong, residual stress remains, which may cause problems in terms of degrading iron loss. More specifically, the sheet is cooled to 730°C at a cooling rate of 15 to 25°C / second after cracking, and the tensile strength during cooling may be 2.0 to 3.5 MPa.

[0126] The difference between the cooling rate after the hot-rolled plate annealing stage and the cooling rate after the cold-rolled plate annealing stage may be 10 to 25°C / second. If the speed difference is too small, annealing productivity becomes too low, which may cause problems in terms of production costs. If the speed difference is too large, plate shape control becomes difficult, which may cause problems with rollability. The cooling rate after cold-rolled plate annealing may be faster than the cooling rate after hot-rolled plate annealing.

[0127] The difference between the tensile strength during cooling after the annealing stage of the hot-rolled plate and the tensile strength during cooling after the annealing stage of the cold-rolled plate may be 1.5 to 4.0 MPa. If the tensile strength difference is too small, it may cause problems in terms of fracture occurrence during the production of the hot-rolled plate annealing. If the tensile strength difference is too large, it may cause problems in terms of shape control due to width shrinkage, etc. The tensile strength after the annealing of the cold-rolled plate may be greater than the tensile strength after the annealing of the hot-rolled plate.

[0128] 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.

[0129]

[0130] 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.

[0131]

[0132] Examples

[0133] A slab containing the components and other impurities listed in Table 1 below was manufactured. In addition to the components listed in Table 1, C, S, N, and Ti were all controlled to be 0.003 wt% or less. The slab was heated to 1150°C and hot-rolled at a finishing temperature of 850°C to produce a hot-rolled plate. The hot-rolled plate was annealed for 4 minutes at the temperature listed in Table 1 below, then cooled at the cooling rate and tension listed in Table 1 below, and subsequently pickled. Afterward, it was cold-rolled to produce a thickness of 0.25 mm. During cold rolling, the annealing of the cold-rolled plate was carried out for 90 seconds at the temperature listed in Table 1 below, and cooled at the cooling rate and tension listed in Table 1.

[0134] The average grain size and standard deviation of the grain size were calculated for the manufactured steel plate using SEM-EBSD on a plane perpendicular to the TD direction.

[0135] 1.3 The permeability, iron loss (W13 / 800) and iron loss (W13 / 60) at T were measured as the average of the rolling direction and the rolling vertical direction using a single sheet tester.

[0136] Classification SiAlMn Hot-rolled plate annealing crack temperature (°C) Cooling rate after hot-rolled plate annealing (°C / sec) Tension during cooling after hot-rolled plate annealing (MPa) Cold-rolled plate annealing crack temperature (°C) Cooling rate after cold-rolled plate annealing (°C / sec) Tension during cooling after cold-rolled plate annealing (MPa) 13.4 1.2 0.5 980 7.3 0.8 945 16 2.3 23.7 0.7 1.1 10 20 8.4 1.5 987 25 3.8 33.8 0.5 0.7 10 50 6.7 1.2 9 60 20 4.1 43.2 1.5 1.8 10 0 5.5 1.8 9 50 18 2.9 5 3.3 1.1 1.7 10 80 10.8 2.3 9 70 25 3.5 6 2.8 1.7 2.5 9 60 12.10.6980274.272.71.62.795010.72.1965222.582.52.22.19909.41.5955193.693.61.41.410107.80.9975242.8103.20.70.5103013.42.2985283.9112.70.82.110003.01.3960214.5123. 70.50.4105016.70.7945172.1133.20.61.2107011.10.3987163.2143.80.70.4109010.43.2960212.3153.11.61.710707.52.2950103.7163.01.91.510806.71.2970354.1173.31.40.710106 .90.8980181.5183.41.20.510508.92.1965175.7193.11.40.393013.51.9955212.9203.60.60.6110012.40.7975283.4213.70.30.4102012.11.5940244.2222.90.71.2103010.11.8990192.8

[0137] Classification Productivity and Passability Surface Average Particle Size (㎛) Surface Standard Deviation (㎛) Center Average Particle Size (㎛) Center Standard Deviation (㎛) Permeability at 1.3T High-frequency Iron Loss (W13 / 800) Low-frequency Iron Loss (W13 / 60) 1 Good 62477552523057.41.65 Example 2 Good 63497261530056.11.59 Example 3 Good 66517558630056.71.68 Example 4 Good 68517866680057.11.71 Example 5 Good 71507957691058.41.69 Example 6 Good 6648735367105 7.11.81 Example 7 Good 71538167681058.11.78 Example 8 Good 65497555598057.41.75 Example 9 Good 63487665635056.81.62 Example 10 Good 73548868612058.41.74 Example 11 Inferior Productivity 81678375489060.41.88 Comparative Example 12 Inferior Sales Performance 78 607575481061.21.87 Comparative Example 13 Inferiority in Mail-order Sales 77597872489059.71.86 Comparative Example 14 Inferiority in Productivity 72577071495062.71.88 Comparative Example 15 Inferiority in Productivity 70567281482061.71.95 Comparative Example 16 Inferiority in Mail-order Sales 75627977475060.41.86 Comparative Example 17 Inferiority in Mail-order Sales 776275 71489059.81.86 Comparative Example 18 Inferior Productivity 82617674420062.41.95 Comparative Example 19 Good 61457050537059.11.82 Example 20 Good 75559070579058.41.77 Example 21 Good 70508060564057.91.76 Example 22 Good 70518265612058.11.64 Example

[0138] As shown in Tables 1 and 2, when the steel composition is properly controlled and the cooling rate and tension during cold-rolled sheet annealing are properly controlled along with the cooling rate and tension during hot-rolled sheet annealing, the grain size of the surface and center is properly formed, resulting in excellent magnetism. On the other hand, when the process conditions are not properly controlled, the grain size of the surface and center is not properly controlled, and the magnetism is inferior.

[0139] Among the examples, it can be confirmed that the magnetism is even better when the hot-rolled plate annealing temperature and the cold-rolled plate annealing temperature are appropriately controlled.

[0140]

[0141] 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.

[0142] [Explanation of the symbol]

[0143] 100: Non-oriented electrical steel sheet 10: Center

[0144] 20 : Surface

Claims

1. In weight%, it comprises Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 3.0%, and the remainder being Fe and unavoidable impurities, and For a cross-section including the thickness direction of the steel plate, the standard deviation of the grain size at the surface up to 1 / 4 of the total thickness is 45 to 55 μm, and Non-oriented electrical steel sheet having a standard deviation of grain size of 50 to 70 μm in the center from more than 1 / 4 to 1 / 2.

2. In Paragraph 1, Non-oriented electrical steel sheet having a difference of 10 to 20 μm between the standard deviation of grain size at the surface and the standard deviation of grain size at the center.

3. In Paragraph 1, A non-oriented electrical steel sheet having an average grain size of 60 to 75 μm at the surface and an average grain size of 70 to 90 μm at the center.

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, S: 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 Cu: 0.005 to 0.2 wt%, 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.

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