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 1.5-5.0 wt% of Si, 0.1-3.0 wt% of Al, and 0.1-2.5 wt% of Mn, with the balance being Fe and inevitable impurities, wherein the ratio of the number of oxides in a 1 / 8 to 1 / 4 region of the total thickness in the sheet thickness direction to the number of oxides in a 3 / 8 to 1 / 2 region thereof is 0.82 or less.

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 generation of oxides in the thickness direction of the steel sheet is controlled by adjusting the temperature and reduction rate between passes during the cold rolling process, 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 that improves ultra-high frequency iron loss by controlling oxide generation in the thickness direction of the steel sheet through controlling the temperature and reduction rate between passes.

[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 2.5%, the remainder being Fe and unavoidable impurities, and the ratio of the number of oxides in the 1 / 8 to 1 / 4 region to the number of oxides in the 3 / 8 to 1 / 2 region of the total thickness in the thickness direction of the steel sheet is 0.82 or less.

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention may have an average length of oxides of 17 to 77 μm and an average thickness of 2 to 8 μm.

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

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

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include one or more of 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.

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

[0014] 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 2.5%, and the remainder being Fe and unavoidable impurities; a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0015] The step of manufacturing a cold-rolled sheet includes multiple rolling passes of five or more, and in the 3rd to 5th pass, the minimum temperature of the steel sheet is 85°C or higher, and in the 3rd to 5th pass, the reduction rate is 50% or higher.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] In the step of manufacturing cold-rolled sheets, the total reduction rate may be 75 to 90%.

[0021] In the cold-rolled sheet annealing stage, the heating rate in the temperature range of 350 to 550℃ can be 15 to 35℃ / second.

[0022] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following Equation 1.

[0023] [Equation 1]

[0024] ([RT 3-5 ]×[RR 3-5]) / ([HR]×[TR]) ≤ 4.0

[0025] (From Equation 1 [RT 3-5 ] refers to the lowest temperature (°C) of the steel plate in the 3rd to 5th passes, and [RR 3-5 ] represents the reduction rate (%) in the 3rd to 5th passes, [HR] represents the heating rate (°C / sec) in the temperature range of 350 to 550°C during the cold-rolled sheet annealing stage, and [TR] represents the total reduction rate (%) during the cold-rolled sheet manufacturing stage.

[0026] 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.

[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 2.5%, 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, causing a sharp decrease in rolling productivity and potentially forming a surface oxide layer 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%. More specifically, it may be included in an amount of 3.00 to 3.60 weight%. More specifically, it may be included in an amount of 3.05 to 3.59 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, excessive nitrides are 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 0.5 to 1.0 weight%. More specifically, it may contain 0.5 to 1.5 weight%. More specifically, it may contain 0.59 to 1.35 weight%.

[0042]

[0043] Mn: 0.1 to 2.5 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 2.5 weight%. More specifically, it may be included in an amount of 0.2 to 2.0 weight%. More specifically, it may be included in an amount of 0.3 to 1.7 weight%. More specifically, it may be included in an amount of 0.45 to 1.54 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 segregating 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 degrade 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 0.007 to 0.150 wt% of Sn or 0.007 to 0.150 wt% of Sb. More specifically, it may contain 0.007 to 0.045 wt% of Sn or 0.007 to 0.037 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] A non-oriented electrical steel sheet according to one embodiment of the present invention has a number of oxides (O) in a region of 3 / 8 to 1 / 2 of the total thickness in the thickness direction of the steel sheet. 3 / 8-1 / 2 With respect to ), the number of oxides (O) in the 1 / 8 to 1 / 4 region 1 / 8-1 / 4 The ratio of )(O 1 / 8-1 / 4 / O 3 / 8-1 / 2 ) may be 0.82 or less. The above ratio means that a large amount of oxide is generated in the interior of the steel sheet (3 / 8 to 1 / 2 region) compared to the surface region (1 / 8 to 1 / 4 region). As a result of the large amount of oxide being formed in the 3 / 8 to 1 / 2 region in this way, ultra-high frequency iron loss can be improved due to the skin effect. More specifically, the ratio of the number of oxides (O 1 / 8-1 / 4 / O 3 / 8-1 / 2 ) may be 0.50 to 0.81. More specifically, the ratio of the number of oxides (O 1 / 8-1 / 4 / O 3 / 8-1 / 2 ) can be 0.59 to 0.81.

[0096] In one embodiment of the present invention, oxides can be measured based on a cross-section including the thickness direction (ND direction) of the steel plate. More specifically, they can be measured based on a plane perpendicular to the steel plate rolling direction (TD plane). More specifically, oxides can be measured by polishing a specimen measuring 30 mm by 30 mm by 30 mm and observing 100 fields of view under a microscope at a magnification of 100x, and counting the number of oxides observed in each field of view. The classification of oxides and other measurement methods may be based on ASTM E 45 method D.

[0097] Number of oxides (O) in the region of 3 / 8 to 1 / 2 of the total thickness in the steel plate thickness direction 3 / 8-1 / 2 ) does not significantly affect ultra-high frequency iron loss; rather, when formed in large numbers, it is advantageous as it can suppress oxide formation in the 1 / 8 to 1 / 4 region. Specifically, the number of oxides (O) in the 3 / 8 to 1 / 2 region of the total thickness in the steel plate thickness direction. 3 / 8-1 / 2 ) can be 70 to 180 pieces / (30mm × 30mm). More specifically, it can be 80 to 175 pieces / (30mm × 30mm). More specifically, it can be 86 to 172 pieces / (30mm × 30mm).

[0098] Number of oxides (O) in the region of 1 / 8 to 1 / 4 of the total thickness in the steel plate thickness direction 1 / 8-1 / 4 ) has a significant impact on ultra-high frequency iron loss. While it is desirable to suppress oxide formation on the surface as much as possible, oxides are inevitably formed due to the penetration of oxygen during the steel composition and manufacturing process within the steel plate. In one embodiment of the present invention, ultra-high frequency iron loss can be improved by suppressing the number of oxides on the surface as much as possible.

[0099] Specifically, the number of oxides (O) in the region of 1 / 8 to 1 / 4 of the total thickness in the steel plate thickness direction. 1 / 8-1 / 4) can be 30 to 140 pieces / (30mm × 30mm). More specifically, it can be 53 to 121 pieces / (30mm × 30mm).

[0100] In one embodiment of the present invention, the oxide may have an average length of 17 to 77 μm and an average thickness of 2 to 8 μm. In one embodiment of the present invention, a relatively large amount of oxide is formed in the 3 / 8 to 1 / 2 region, and accordingly, the shape of the oxide is also formed in an approximately elliptical shape.

[0101] In one embodiment of the present invention, the length of the oxide refers to the longest axis passing through the center of the oxide in a cross-section including the thickness direction of the steel plate. The thickness of the oxide refers to the length of the axis perpendicular to the aforementioned longest axis. The average refers to the average of the number of oxides.

[0102] A non-oriented electrical steel sheet according to one embodiment of the present invention may have an average grain size of 50 to 150 μm. If the average grain size is too small, high-frequency iron loss is poor, and if the average grain size is too large, magnetic flux density is poor. More specifically, the average grain size may be 60 to 130 μm.

[0103] The average grain size can be measured by observing the ND plane at 1 / 8 of the total thickness when using EBSD. It is the area-based average grain size used in TSL, and the measurement area can be the average value measured over an area of ​​3mm × 3mm or larger.

[0104] 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. More specifically, the resistivity may be 58 to 80 μΩ·cm or higher.

[0105] As previously stated, in one embodiment of the present invention, ultra-high frequency iron loss can be improved. Specifically, W 1 / 10000 It can be 28.5 W / kg. More specifically, W 1 / 10000 It may be 20 to 27.5 W / kg. More specifically, it may be 22.5 to 26.7 W / kg.

[0106] 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 1 / 10000 is the iron loss when a magnetic flux density of 0.1T is induced at a frequency of 10,000Hz.

[0107] Also, magnetic flux density (B 50 ) may be 1.66T or higher. More specifically, the magnetic flux density (B50) may be 1.66T to 1.75T. B50 refers to the magnetic flux density of the steel plate induced in a magnetic field of 5000A / m.

[0108] In one embodiment of the present invention, the yield strength may be 400 MPa to 500 MPa. In one embodiment of the present invention, it is used as an iron core for a motor with a high rotational speed, and for this purpose, it is necessary to secure an appropriate yield strength.

[0109]

[0110] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises: a step of manufacturing a hot-rolled steel sheet by hot-rolling a slab; a step of manufacturing a cold-rolled sheet by cold-rolling the hot-rolled steel sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0111] Below, each step is explained in detail.

[0112] First, the slab is hot-rolled.

[0113] 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.

[0114] Specifically, the slab contains Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 2.5% by weight, and the remainder is Fe and unavoidable impurities.

[0115] As other additional elements have been explained in the alloy composition of non-oriented electrical steel sheets, redundant explanations are omitted.

[0116] 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.

[0117] 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.

[0118] After manufacturing the hot-rolled steel sheet, an additional step of annealing the hot-rolled sheet may be included. At this time, the cracking temperature may be 800 to 1150°C. If the annealing temperature is too low, a recrystallization structure is not formed or grows finely, resulting in a small increase in magnetic flux density; if the annealing temperature is too high, magnetic properties may actually deteriorate, and rolling workability may worsen due to deformation of the sheet shape. More specifically, the temperature range may be 830 to 1100°C. The cracking time may be 30 to 300 seconds. The hot-rolled sheet annealing step may also be omitted.

[0119] Next, a hot-rolled steel sheet is cold-rolled to produce a cold-rolled sheet. At this time, the step of producing the cold-rolled sheet includes five or more rolling passes. A pass refers to the number of times the steel sheet passes through the rolling rolls. More specifically, in one embodiment of the present invention, the cold rolling may include five to eight passes.

[0120] In one embodiment of the present invention, the minimum temperature of the steel plate in the 3rd to 5th passes is 85°C or higher. If the minimum temperature of the steel plate in the 3rd to 5th passes is low, it promotes the formation of (111) planes that are unfavorable to magnetism and has an adverse effect on iron loss. More specifically, the minimum temperature of the steel plate in the 3rd to 5th passes may be 87°C to 120°C. More specifically, the minimum temperature of the steel plate in the 3rd to 5th passes may be 88°C to 106°C.

[0121] In one embodiment of the present invention, the reduction rate in the 3rd to 5th passes may be 50% or more. If the reduction rate is too low, it promotes the formation of (111) planes that are unfavorable to magnetism and has an adverse effect on iron loss. More specifically, the reduction rate in the 3rd to 5th passes may be 51% to 70%. More specifically, the reduction rate in the 3rd to 5th passes may be 51% to 68%. The reduction rate can be calculated as ([thickness of steel plate before passing the 3rd pass] - [thickness of steel plate after passing the 5th pass]) / [thickness of steel plate before passing the 3rd pass] × 100.

[0122] In the stage of manufacturing the cold-rolled sheet, the total reduction rate may be 75 to 90%. The total reduction rate can be calculated from the thickness of the steel sheet before cold rolling and the thickness after cold rolling. If the reduction rate is too low, additional rolling is required to obtain an appropriate final thickness, and productivity may be inferior. If the reduction rate is too high, a texture unfavorable to magnetism is formed, and iron loss may be inferior. More specifically, in the stage of manufacturing the cold-rolled sheet, the total reduction rate may be 77 to 88%. More specifically, it may be 79 to 87%.

[0123] 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.

[0124] In one embodiment of the present invention, cold rolling can be performed in a single step without intermediate annealing.

[0125] Next, the cold-rolled sheet is annealed. During the cold-rolled sheet annealing stage, the heating rate may be 15 to 35°C / second in the temperature range of 350 to 550°C. If the heating rate is too low, the formation of a texture unfavorable to magnetism is promoted. If the heating rate is too high, surface oxidation problems and excessive oxide formation on the surface layer may occur due to surface overheating caused by rapid heating. More specifically, the heating rate may be 16 to 33°C / second in the temperature range of 350 to 550°C.

[0126] In the annealing stage of the cold-rolled sheet, the cracking temperature can be 750°C to 1050°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 can be 800°C to 1000°C.

[0127] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following Equation 1.

[0128] [Equation 1]

[0129] ([RT 3-5 ]×[RR 3-5 ]) / ([HR]×[TR]) ≤ 4.0

[0130] (From Equation 1 [RT 3-5 ] refers to the lowest temperature (°C) of the steel plate in the 3rd to 5th passes, and [RR 3-5 ] represents the reduction rate (%) in the 3rd to 5th passes, [HR] represents the heating rate (°C / sec) in the temperature range of 350 to 550°C during the cold-rolled sheet annealing stage, and [TR] represents the total reduction rate (%) during the cold-rolled sheet manufacturing stage.

[0131] When Equation 1 is satisfied, a texture favorable to magnetism is created, and at the same time, oxides of different thicknesses are appropriately formed, ultimately improving ultra-high frequency iron loss. More specifically, the left side of Equation 1 may be 1.5 to 3.7. More specifically, the left side of Equation 1 may be 1.56 to 3.46.

[0132] 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.

[0133]

[0134] 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.

[0135]

[0136] Examples

[0137] 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 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 at 1100°C for 4 minutes and then pickled. Subsequently, it was cold-rolled to produce a thickness of 0.25 mm. At this time, the minimum temperature of the steel plate and the reduction ratio during the 3rd to 5th passes were controlled as shown in the table below, and the total reduction ratio was controlled as shown in the table. During cold rolling, the annealing of the cold-rolled plate was performed at 965°C for 90 seconds. At this time, the heating rate in the temperature range of 350 to 550°C was controlled as shown in the table.

[0138] Oxide was measured by polishing a specimen measuring 30 mm by 30 mm and observing 100 fields of view under a microscope at a magnification of 100x, and adding up the number of oxides observed in each field of view, based on ASTM E 45 method D. Iron loss was measured using a Single Sheet Tester at a magnetization force of 0.1 T and 10,000 Hz.

[0139] Classification (Weight%) SiAlMnSnSb 13.57 0.78 0.84 0.009 0.029 23.11 0.59 0.45 0.017 0.037 33.55 0.34 0.55 0.03 0.018 43.51 0.75 0.45 0.03 50.008 53.45 0.86 0.67 0.0140 .00763.591.251.450.0250.01573.050.791.850.0550.01783.241.521.470.0590.02493.271.111.540.0310.027103.372.330.450.0250.018113.391. 170.250.0350.033123.492.240.860.0550.037133.560.950.810.0450.031143.270.982.240.0450.028153.311.190.780.0280.027163.221.870.970. 0570.029173.482.661.220.0460.027182.882.111.440.0350.021193.671.951.780.0510.021203.471.350.460.0240.027213.321.250.780.0070.025

[0140] Resistivity (μΩ·cm) Total Reduction (TR, %) 3-5 Pass Minimum Temperature (RT3-5, ℃) 3-5 Pass Reduction (RR3-5, %) 350 - 550℃ Heating Rate (HR, ℃ / sec) Equation 1 Left-hand side value 167818851163.462587910663263.253607788522222.70464798055183.09566869561232.93676929752163.43767879550.3124.58875889548192.73971879762272.561080868751331.56116686895825 2.401283729669224.181369849768243.271474879862213.3315698210458184.0916768110651371.8017908010753312.2918788310755282.531987859557242.652070849359262.512169869752193.09

[0141] Classification Number of oxides in the 3 / 8 to 1 / 2 region Number of oxides in the 1 / 8 to 1 / 4 region Oxide number ratio W 1 / 10000 (W / kg) Remarks 1 10 27 5 0.7 4 2 2.5 Invention Example 2 8 6 5 3 0.6 2 2 3.7 Invention Example 3 2 1 120 5 0.9 7 2 9.7 Comparative Example 4 1 9 5 18 2 0.9 3 3 1.2 Comparative Example 5 1 5 4 12 1 0.7 9 2 4.5 Invention Example 6 1 7 2 18 9 1.1 0 3 1.5 Comparative Example 7 2 20 2 3 4 1.0 6 2 9.7 Comparative Example 8 2 35 2 4 7 1.0 5 2 8.6 Comparative Example 9 1 6 7 12 1 0.7 2 2 2.5 Invention Example 10 1 14 6 7 0.5 9 2 3.4 Invention Example 1 12 35 2 200.94 29.7 Comparative Example 12 182 187 1.03 31.5 Comparative Example 13 12086 0.72 23.8 Inventive Example 14 189 207 1.10 30.7 Comparative Example 15 175 196 1.12 31.5 Comparative Example 16 199 207 1.04 30.8 Comparative Example 17 188 196 1.04 31.5 Comparative Example 18 201 191 0.95 29.4 Comparative Example 19 199 187 0.94 28.7 Comparative Example 201 32 107 0.81 23.9 Inventive Example 2 11 1588 0.77 26.7 Inventive Example

[0142] As shown in Tables 1 to 3, when the steel composition is appropriately controlled and process conditions such as the steel sheet temperature, reduction rate, total reduction rate, and heating rate during cold rolling annealing are appropriately controlled, it can be confirmed that oxides are properly formed and ultra-high frequency iron loss is excellent.

[0143] On the other hand, if process conditions are not properly controlled, a relatively large amount of oxide is generated on the surface, and it can be confirmed that the ultra-high frequency iron loss is inferior.

[0144]

[0145] The present invention is not limited to the embodiments described above but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without altering the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. In weight%, it comprises Si: 1.5 to 5.0%, Al: 0.1 to 3.0%, Mn: 0.1 to 2.5%, and the remainder being Fe and unavoidable impurities, and A non-oriented electrical steel sheet in which the ratio of the number of oxides in the 1 / 8 to 1 / 4 region to the number of oxides in the 3 / 8 to 1 / 2 region of the total thickness in the thickness direction of the steel sheet is 0.82 or less.

2. In Paragraph 1, Non-oriented electrical steel sheet having an average oxide length of 17 to 77 μm and an average thickness of 2 to 8 μm.

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

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

5. In Paragraph 1, A non-oriented electrical steel sheet further comprising one or more of 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.

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