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 includes, in wt%, Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, and REM: 0.001 to 0.007%, with the balance being Fe and inevitable impurities.

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, an embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same that may improve high-frequency iron loss by controlling the contents of Se, Sn, and REM among the alloy compositions in the steel sheet.[Background Art]

[0002] Recently, as disasters caused by climate change increase, countries around the world are announcing roadmaps for achieving carbon neutrality by 2050. 'The total amount of carbon emissions in 2020 reached 39 billion tons, of which internal combustion engines accounted for 24%, or 9.4 billion tons. Therefore, there is a strong demand to achieve carbon neutrality in this field 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 driving motors in new mobility are to increase driving range and improve top speed. This is directly related to the low core loss characteristics of electrical steel sheets. If the core loss of electrical steel sheets is low, efficiency may be further improved, thereby increasing the driving range. Therefore, high-frequency low core loss characteristics of electrical steel sheets are essential, and for this purpose, the electrical steel sheets typically contain a large amount of Si and add a large amount of elements such as Al, Mn, and Cr to secure the high-frequency low core loss. However, in addition to the method of lowering the core loss by adding a large amount of specific resistance elements such as Si, Al, Mn, and Cr, it is necessary to improve material properties by lowering anisotropy in the material.[Disclosure] [Technical Problem]

[0003] An embodiment of the present invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, an embodiment of the present invention provide a non-oriented electrical steel sheet and a method for manufacturing the same that may improve high-frequency iron loss by controlling the contents of Se, Sn, and REM among the alloy compositions in the steel sheet.[Technical Solution]

[0004] A non-oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%, Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, and REM: 0.001 to 0.007%, with the balance being Fe and inevitable impurities.

[0005] The non-oriented electrical steel sheet according to the embodiment of the present invention may satisfy Equation 1: 30 ≤ Se / Sn × REM ≤ 140

[0006] (In Equation 1, [Se], [Sn], and [REM] represent the content (wt%) of Se, Sn, and REM, respectively.)

[0007] The non-oriented electrical steel sheet according to the embodiment of the present invention may further include at least one of C, N, S, Ti, Nb, and V, each in an amount of 0.005 wt% or less.

[0008] The non-oriented electrical steel sheet according to the 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%, P: 0.08 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

[0009] The non-oriented electrical steel sheet according to the embodiment of the present invention may further include 0.200 wt% or less of one or more of Bi, Pb, Ge, and As, individually or in a combined amount.

[0010] The non-oriented electrical steel sheet according to the embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

[0011] The non-oriented electrical steel sheet according to the embodiment of the present invention may have a specific resistance of 50 µΩ•cm or more.

[0012] The non-oriented electrical steel sheet according to the embodiment of the present invention may have an average grain size of 30 to 140 µm.

[0013] The non-oriented electrical steel sheet according to the embodiment of the present invention may have an area fraction of grains having a grain size of 30% to 170% of the average grain size of 70% or more.

[0014] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: hot-rolling a slab including, in wt%, Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, and REM: 0.001 to 0.007%, with the balance being Fe and inevitable impurities, to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0015] The slab may further include at least one of C, N, S, Ti, Nb, and V, each in an amount of 0.005 wt% or less.

[0016] The slab may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, P: 0.08 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

[0017] The slab may further include 0.200 wt% or less (excluding 0%) in each or a combined amount of one or two or more of Bi, Pb, Ge, and As.

[0018] The slab may further include at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0019] During the cold-rolled sheet annealing step, at an inlet side of an annealing furnace, a difference between a maximum tension and a minimum tension for a length of 2,000 mm in a rolling direction of the cold-rolled sheet may be 0.017 kgf / mm 2< or less.

[0020] An average tension at the inlet side of the annealing furnace may be 0.07 to 0.5 kgf / mm 2< .

[0021] A maximum temperature of an annealing furnace in the cold-rolled sheet annealing step may be 875 to 1000 °C.

[0022] A soaking time in the cold-rolled sheet annealing step may be 25 to 60 seconds.[Advantageous Effects]

[0023] A non-oriented electrical steel sheet according to an embodiment of the present invention may have more excellent characteristics by improving iron loss anisotropy by optimizing the amount of elements added that segregate or precipitate at grain boundaries.

[0024] A non-oriented electrical steel sheet according to an embodiment of the present invention may have more excellent characteristics by controlling the variation of annealing tension in a cold-rolled sheet annealing process, thereby uniformly managing the grain size and improving iron loss anisotropy.

[0025] Ultimately, the non-oriented electrical steel sheet according to an embodiment of the present invention contributes to the manufacture of environmentally-friendly automobile motors, high-efficiency home appliance motors, and super premium-grade electric motors.[Mode for Invention]

[0026] It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or sections, they are not limited thereto. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Therefore, a first part, component, area, layer, or section to be described below may be referred to as second part, component, area, layer, or section within the range of the present invention.

[0027] The technical terms used herein are to simply mention a particular embodiment and are not meant to limit the present invention. An expression used in the singular encompasses an expression of the plural, unless it has a clearly different meaning in the context. In the specification, it is to be understood that the terms such as "including", "having", etc., are intended to indicate the existence of specific features, regions, numbers, stages, operations, elements, components, and / or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, regions, numbers, stages, operations, elements, components, and / or combinations thereof may exist or may be added.

[0028] When referring to a part as being "on" or "above" another part, it may be positioned directly on or above the other part, or another part may be interposed therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.

[0029] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of art to which the present invention belongs. Terms defined in commonly used dictionaries are further interpreted as having meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as having idealized or very formal meanings unless defined otherwise.

[0030] Unless otherwise stated, % represents wt%, and 1 ppm is 0.0001 wt%.

[0031] In embodiments of the present invention, inclusion of an additional element means replacing the remaining iron (Fe) by an additional amount of the additional elements.

[0032] The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure.

[0033] In an embodiment of the present invention, iron loss anisotropy is improved by controlling the Se, Sn, and REM content in the alloy composition within the steel sheet and optimizing the addition amount of elements that segregate or precipitate at grain boundaries.

[0034] A non-oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%, Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, REM: 0.001 to 0.007%, and the balance of Fe and inevitable impurities.

[0035] First, the reason for limiting the components of the non-oriented electrical steel sheet will be described.Si: 2.8 to 4.0 wt%

[0036] Silicon (Si) serves to increase the specific resistance of the material and reduce iron loss, so it must be added in relatively large amounts. If too little Si is added, an effect of improving high-frequency iron loss may be insufficient. If Si is added in too large amounts, the hardness of the material increases, which is undesirable because it deteriorates productivity and punching performance. More specifically, Si may be included in an amount of 3.0 to 3.7 wt%.Al: 0.5 to 1.7 wt%

[0037] Aluminum (Al) serves to increase the specific resistance of the material and reduce iron loss, so it must be added in a large amount. If too little Al is added, it is ineffective in reducing high-frequency iron loss and fine nitrides may form, which may deteriorate magnetism. If too much Al is added, it can cause problems by changing the properties of mold flux during the continuous casting process, which may significantly reduce productivity. More specifically, Al may be included in an amount of 0.7 to 1.5 wt%.Mn: 0.3 to 2.0 wt%

[0038] Manganese (Mn) improves the iron loss by increasing the specific resistance of the material and serves to form a sulfide. If too little Mn is added, fine MnS may precipitate, which may deteriorate the magnetism. If too much Mn is added, it may promote the formation of

[111] texture, which is unfavorable for magnetism, and cause a rapid decrease in magnetic flux density. Specifically, Mn may be included in an amount of 0.5 to 1.5 wt%.Specific Resistance: 50 µΩ·cm or more

[0039] The higher the specific resistance, the better for reducing eddy current loss in a high-frequency rotating machine, but if it is too high, the magnetic flux density may be degraded. In an embodiment of the present invention, the specific resistance may be calculated from "13.25 + 11.3×([Si]+[Al]+[Mn] / 2)". Wherein [Si], [Al], and [Mn] represent the contents (wt%) of Si, Al, and Mn, respectively. The higher the specific resistance, the more it plays a role in lowering iron loss. If the specific resistance is too low, the iron loss is poor and it is difficult to use it as a high-efficiency motor. More specifically, the specific resistance may be in the range of 50 to 90 µΩ·cm. More specifically, the specific resistance may be in the range of 60 to 85 µΩ·cm.Se: 0.0005 to 0.0050 wt%, Sn: 0.005 to 0.060 wt%, REM: 0.001 to 0.007 wt%

[0040] Selenium (Se), tin (Sn), and rare earth elements (REM) may be segregated or precipitated at grain boundaries. They may complex precipitate with each other to form SeSn intermetallic compounds, or they may complex precipitate as sulfides. Respective elements interact with each other within these ranges to maximize segregation effects, and outside these ranges, they precipitate as intermetallic compounds or sulfides, affecting magnetism. If one or more of Se, Sn, and REM are included in amounts less than the corresponding range, the desired effect may not be obtained. If one or more of Se, Sn, and REM are included in amounts exceeding the corresponding range, a large amount of segregation or precipitation occurs, which may degrade iron loss. More specifically, Se may be included in the range of 0.0010 to 0.0030 wt%, Sn in the range of 0.010 to 0.050 wt%, and REM in the range of 0.003 to 0.005 wt%.

[0041] In an embodiment of the present invention, the rare earth element (REM) means a total of 17 elements, which are 15 elements with atomic numbers 57 to 71 and 2 elements of Sc and Y, and when two or more elements are included, the REM content means the sum of the two or more elements.

[0042] In an embodiment of the present invention, Equation 1 may be satisfied. 30 ≤ Se / Sn × REM ≤ 140

[0043] (In Equation 1, [Se], [Sn], and [REM] represent the content (wt%) of Se, Sn, and REM, respectively.)

[0044] Equation 1 shows the correlation between Se, Sn, and REM at which the segregation effect is maximized through interaction.

[0045] A non-oriented electrical steel sheet according to an 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%, P: 0.08 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.Cu: 0.005 to 0.200 wt%

[0046] Copper (Cu) serves to form sulfides together with Mn. If Cu is added further, if too little Cu is added, CuMnS may be finely precipitated and magnetism may be degraded. If too much Cu is added, high temperature brittleness occurs, which may form cracks during casting or hot rolling. Specifically, Cu may be included in an amount of 0.01 to 0.10 wt%.Cr: 0.010 to 0.50 wt%

[0047] Chromium (Cr) serves to improve iron loss by increasing specific resistance. If too little Cr is added, an effect of specific resistance may not be sufficient. If too much Cr is included, the magnetic flux density may deteriorate. More specifically, when Cr is further included, 0.050 to 0.20 wt% of Cr may be included.P at 0.08 wt% or less

[0048] Phosphorus (P) is concentrated on the surface and serves to control the fraction of the internal oxide layer. If the addition amount of P is too small, it may be difficult to form a uniform internal oxide layer. If the addition amount of P is too large, the melting point of Si-based oxides may change, and the internal oxide layer may be rapidly formed. Therefore, the content of P may be controlled within the above-mentioned range. More specifically, P may be included in an amount of 0.005 to 0.07 wt%.Sb: 0.06 wt% or less

[0049] Antimony (Sb) is added as a segregating element at grain boundaries to suppress nitrogen diffusion through grain boundaries, suppress {111} texture that is detrimental to magnetism, and increase favorable {100} texture, thereby improving magnetic properties. If too much Sb is added, grain growth is hindered, which reduces magnetism and results in poor rolling properties. Therefore, Sb may be added within the above-mentioned range. More specifically, it may be included in an amount of 0.005 to 0.060 wt%. More specifically, it may be included in an amount of 0.01 to 0.05 wt%.Ni: 0.05 wt% or less

[0050] Nickel (Ni) may react with impurity elements to form fine sulfides, carbides, and nitrides, which may have a detrimental effect on magnetism. More specifically, Ni may be included in an amount of 0.001 to 0.03 wt%.Zn: 0.01 wt% or less

[0051] If the content of zinc (Zn) is excessive, it may act as an impurity and deteriorate magnetism. Therefore, Zn may be further added within the above-mentioned range. More specifically, it may be included in an amount of 0.001 to 0.005 wt%.

[0052] A non-oriented electrical steel sheet according to an embodiment of the present invention may further include 0.200 wt% or less of one or more of Bi, Pb, Ge, and As, individually or in a combined amount.

[0053] The aforementioned elements, when additionally added, segregate at grain boundaries, thereby alleviating stress concentration at grain boundaries during cold rolling, thereby suppressing recrystallization of <111> / / ND oriented grains in the subsequent recrystallization annealing process, thereby improving the magnetic flux density. If these are added appropriately, the aforementioned effects may be additionally obtained, but if they are included in too much, a large amount of segregation may occur, inhibiting grain growth and resulting in lower magnetic flux density and iron loss. More specifically, it may further include 0.0001 to 0.200 wt% of each or a combined amount of one or more of Bi, Pb, Ge, and As. More specifically, it may further include 0.001 to 0.100 wt%. It may further include 0.005 to 0.050 wt%.

[0054] A non-oriented electrical steel sheet according to an embodiment of the present invention may further include at least one of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

[0055] Since these may react with C, S, N, and the like, which are inevitably included, to form fine carbides, nitrides, or sulfides, which may adversely affect magnetism, the upper limit may be limited as described above.Other Impurities

[0056] In addition to the aforementioned elements, inevitably mixed impurities such as carbon (C), sulfur (S), nitrogen (N), titanium (Ti), niobium (Nb), and vanadium (V) may be included.

[0057] C, N, and Ti may be limited because they form carbonitrides and hinder magnetic domain movement, and S may form sulfides and thus lower grain growth, which may limit its upper limit. Each of these elements may be included in an amount of 0.0040 wt% or less.

[0058] N combines with Ti, Nb, and V to form nitrides and plays a role in reducing grain growth.

[0059] C reacts with N, Ti, Nb, and V to form fine carbides, which hinder grain growth and magnetic domain movement.

[0060] S forms sulfides, which degrade grain growth.

[0061] As described above, when impurity elements are further included, one or more of C, S, N, Ti, Nb, and V may be included at 0.005 wt% or less each.

[0062] A non-oriented electrical steel sheet according to an embodiment of the present invention may have an average grain size of 30 to 140 µm. When the average grain size is appropriately adjusted, magnetism may be further improved. In an embodiment of the present invention, the grain size may be measured on a plane parallel to the sheet surface. More specifically, it may be measured at a thickness ranging from 1 / 4t to 3 / 4t with respect to the total thickness t of the steel sheet. The grain size is determined by assuming a virtual circle with an area equal to the grain area, and the diameter of this circle is taken as the grain size. The average grain size can be measured by dividing the area of the measurement target by the number of grains within that area. More specifically, the non-oriented electrical steel sheet according to an embodiment of the present invention may have an average grain size of 50 to 100 µm. The grain size may be observed using an optical microscope, and the grain size distribution may be measured using SEM-EBSD.

[0063] A non-oriented electrical steel sheet according to an embodiment of the present invention may have an area fraction of grains having a grain size of 30% to 170% of the average grain size of 70% or more.

[0064] The grain size within the non-oriented electrical steel sheet has a distribution, and when the grain size is uniformly formed, the iron loss may be improved and anisotropy may be reduced. In particular, it is best to adjust the grain size so that it is similar to the average grain size. To this purpose, it is helpful to reduce the tension deviation during annealing, and it is also helpful to reduce the tension magnitude during annealing. This will be specifically described in the manufacturing method of the non-directional electrical steel sheet described later. More specifically, the non-oriented electrical steel sheet may have an area fraction of grains with a grain size of 30% to 170% of the average grain size of 85% to 95%.

[0065] A non-oriented electrical steel sheet according to an embodiment of the present invention has excellent high-frequency iron loss, and particularly excellent high-frequency iron loss at a 60-degree angle with respect to the rolling direction. Specifically, the iron loss (W 10 / 400 ) in the rolling direction of the non-oriented electrical steel sheet may be 11.0 W / kg or less. The iron loss (W 10 / 400 ) is iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz. More specifically, the iron loss (W 10 / 400 ) in the rolling direction of the non-oriented electrical steel sheet may be 9.0 to 10.5 W / kg. In addition, the iron loss (W 10 / 400 ) in a direction forming a 60-degree angle with the rolling direction of the non-oriented electrical steel sheet may be 14.0 W / kg or less. More specifically, the iron loss (W 10 / 400 ) in a direction forming a 60 degree angle with the rolling direction may be 11.0 to 13.0 W / kg.

[0066] The ratio (W60 10 / 400 / WRD 10 / 400 ) of iron loss (W60 10 / 400 ) in a direction forming a 60-degree angle with the rolling direction to iron loss (WRD 10 / 400 ) in the rolling direction of the non-oriented electrical steel sheet according to an embodiment of the present invention may be 1.27 or less. Specifically, it may be 1.10 to 1.25. When this ratio is low, the driving distance may be increased and the maximum speed may be increased when manufactured as a driving motor.

[0067] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: hot-rolling a slab including, in wt%, Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, REM: 0.001 to 0.007%, and the balance of Fe and inevitable impurities to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

[0068] Hereinafter, each step will be specifically described.

[0069] First, the slab is manufactured. The reason for limiting the addition ratio of each composition in the slab is the same as the reason for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated description will be omitted. Since the slab composition is not substantially changed during manufacturing processes including hot rolling, hot-rolled sheet annealing, cold rolling, and cold-rolled sheet annealing to be described later, the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially the same.

[0070] The slab may be heated before the step of manufacturing the hot-rolled sheet. Specifically, the slab is fed into a heating furnace and heated to 1100 to 1,250°C. When heated at a temperature exceeding 1,250°C, a precipitate may be redissolved, and it may be finely precipitated after the hot-rolling.

[0071] The heated slab is hot-rolled to 2 to 2.3 mm to manufacture a hot-rolled sheet. In the step of manufacturing the hot-rolled sheet, a finish rolling temperature may be 800 to 1,000 °C.

[0072] After the step of manufacturing the hot-rolled sheet, hot-rolled-sheet-annealing the hot-rolled sheet may be further included. In this case, a temperature of the hot-rolled-sheet-annealing may be 850 to 1150 °C. If the temperature of the hot-rolled sheet annealing is lower than 850°C, there is little effect of increasing the magnetic flux density because the structure does not grow, or finely grows, and if the temperature of the annealing exceeds 1,150°C, magnetic properties are rather deteriorated, and rolling workability may be deteriorated due to deformation of a shape of the sheet. Specifically, the annealing temperature may be 950 to 1,125 °C. More specifically, the annealing temperature of the hot-rolled steel is 900 to 1,100°C. The hot-rolled sheet annealing is performed in order to increase the orientation favorable to magnetism as required, and it may be omitted.

[0073] Next, the hot-rolled sheet is pickled and then cold-rolled to have a predetermined sheet thickness. Although It may be applied differently depending on the thickness of the hot-rolled sheet, but the cold-rolling may be performed so that the final thickness thereof becomes 0.2 to 0.65 mm, by applying a reduction ratio of 70 to 95 %. To match the reduction ratio, one cold rolling or two or more cold rollings with intermediate annealing may be performed.

[0074] The cold-rolled sheet is subjected to cold-rolled sheet annealing.

[0075] During the cold-rolled sheet annealing step, at the inlet side of the annealing furnace, the difference between the maximum tension and the minimum tension for a length of 2,000 mm in the rolling direction of the cold-rolled sheet may be 0.017 kgf / mm2 or less.

[0076] Tension is applied to the steel sheet using bridle rolls at the inlet and outlet of the annealing furnace for cold-rolled steel sheets. In this case, it is ideal to apply a uniform tension in the length direction of the steel plate, but it is practically difficult to continuously maintain this uniformly due to various reasons such as slip between the bridle roll and the steel sheet, speed fluctuations of the hearth roll inside the annealing furnace, and thermal expansion of the steel sheet due to heating. In an embodiment of the present invention, it has been found that a difference in grain size occurs due to the difference in tension applied to the steel sheet, and by minimizing the difference between the maximum tension and the minimum tension, high-frequency core loss may be improved. To reduce the tension deviation, methods such as minimizing slip between the bridle roll and the steel sheet and speed synchronization considering the speed of the hearth roll in the annealing furnace and the thermal expansion of the steel sheet may be used. More specifically, at the inlet side of the annealing furnace, the difference between the maximum tension and the minimum tension for a length of 2,000 mm in the rolling direction of the cold-rolled sheet may be 0.001 to 0.015 kgf / mm 2< .

[0077] The average tension applied to the steel sheet at the inlet side of the annealing furnace may be 0.07 to 0.5 kgf / mm 2< . Since the anisotropy of iron loss may increase if the average tension is excessively applied, the upper limit thereof may be adjusted as described above. More specifically, it may be 0.1 to 0.5 kgf / mm 2< .

[0078] In the cold-rolled sheet annealing step, the maximum temperature of the annealing furnace can be 875 to 1,000°C. If the maximum temperature of the annealing furnace is too high, defects such as surface micro-dents increase, and grain growth may increase, which may deteriorate the uniformity of grain size. More specifically, the maximum temperature of the annealing furnace may be 900 to 997°C.

[0079] The soaking time is the time after the soaking temperature is reached that the temperature remains uniform without fluctuation. The soaking time may be 25 to 60 seconds. More specifically, it may be 30 to 50 seconds.

[0080] Next, a step of forming an insulating layer may be further included. The method of forming the insulating layer is widely known in the field of non-oriented electrical steel sheet technology, so a detailed description thereof is omitted.

[0081] Hereinafter, preferred examples of the present invention and comparative examples will be described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.Example 1

[0082] A slab was manufactured with the composition shown in Table 1 below. C, S, N, Ti, Nb, and V, other than those listed in Table 1, were all controlled to 0.003 wt% or less, and the balance was Fe. REM included Ce, Y, and Sc.

[0083] The slab was heated to 1,150°C and hot-finished rolled at 850°C to manufactured a hot-rolled sheet with a thickness of 2.0 mm. The hot-rolled hot-rolled sheet was annealed at 1,100°C for 4 minutes and then pickled. Subsequently, cold rolling was performed to manufacture a 0.25 mm cold-rolled sheet, and cold-rolled sheet annealing was performed under the conditions summarized in Table 2 below.

[0084] For each specimen, the iron loss was measured by cutting 5 specimens of 60 mm width × 60 mm length × number of sheets using a single sheet tester in a direction forming a 60-degree angle with the rolling direction.

[0085] The grain size was examined using an optical microscope, and the grain size distribution was measured using SEM-EBSD.

[0086] The tension was measured using a load cell as the force applied to the bridle roll. (Table 1)ClassificationSiAlMnCuCrSpecific ResistanceSeSnREM[Equation 1]13.60.60.30.050.40650.0030.080.0021923.40.90.30.070.20650.00020.0070.0012933.11.20.30.150.20660.0020.060.0013343.80.50.50.150.50680.0060.020.00215053.51.30.50.150.08720.0010.0150.0016763.11.70.50.200.01720.00250.0030.00327872.81.51.20.050.08690.0010.0060.0028383.10.61.20.070.08630.0050.0150.0065693.40.71.20.070.15680.0010.0150.00167103.20.71.80.070.08680.0030.040.0003250112.90.51.80.070.08630.0010.0150.00167123.31.61.80.010.08790.0030.030.00250133.21.61.80.090.08790.0010.020.0086143.11.10.80.010.01650.0010.0060.00283153.21.11.40.010.01700.0010.0150.00167162.81.40.90.0990.469690.00140.0340.00141172.91.70.90.0690.263720.00410.030.003638183.01.61.30.1090.194740.00190.0570.001130193.11.20.30.0900.197650.00490.0060.0064128203.21.11.70.0930.158730.00070.0060.00339213.31.70.90.1780.422780.00170.0060.0024118223.40.61.30.1650.339690.00230.0450.001632233.50.50.80.1540.472670.00360.0310.003434243.61.11.70.0580.218780.00240.0520.001238253.70.51.50.0890.019700.00250.0180.004531263.81.00.70.1750.482750.00320.0270.003435273.91.41.50.0990.297840.00340.0180.005236284.00.61.00.1430.482740.00440.0290.004434292.71.21.50.1390.268680.00260.0340.002235304.11.31.80.0760.28860.00330.0220.002952313.50.41.40.0200.036660.00160.0410.001233323.11.82.00.0270.436830.00330.0480.001740333.01.30.20.0930.386660.0040.0270.0011135342.81.32.10.1210.421750.00470.0520.002241352.80.10.30.0100.010480.00410.0560.001939363.71.41.10.0930.103780.00030.0050.001833373.91.71.40.0780.132860.00650.0550.002547384.00.50.50.1930.162690.0010.0030.006551393.70.51.70.1500.365730.00350.0650.001341402.80.51.80.1100.034620.00170.0520.000747412.81.41.70.1400.482740.00420.0170.007533422.91.31.80.1110.251730.00430.0070.0021280433.01.51.40.1500.154740.00130.0550.00318444.00.51.00.1640.164720.00290.0420.001546453.00.51.00.1660.427620.00110.0120.001465462.90.90.50.1440.335620.00280.0120.005940472.81.01.10.0920.42650.00360.0070.0051101483.51.22.00.1590.244800.00220.0350.001252493.31.31.30.0270.246740.00470.0250.006230502.91.71.60.1900.436780.00260.0320.001174 (Table 2) ClassificationAnnealing Maximum Temperature (°C)Soaking Time (seconds)Tension at Inlet Side of AnnealingTension deviation (kgf / mm 2< )Average Grain Size (µm)0.3-1.7 AreaFurnace (kg / mm 2< )Fraction (%)1950450.20.01371552970450.20.01584673980450.20.016103784980450.30.00799625975450.30.00984846950450.30.00561617945450.30.00671758950450.30.01868639950450.40.012747810950450.40.010586611985450.40.020696512945450.40.009728213950450.30.009596314990450.60.0111258715985450.40.0161158116968360.40.017857517967410.30.017928118965360.30.015758419916550.30.009687920965440.30.016838321947570.20.013658822916460.20.013688123934550.50.009958324936450.250.0161239025962440.50.0141308426912300.20.012968327915310.50.011917528958550.10.010787829986400.40.012687930990480.40.016597831949420.40.013687432934350.40.016577533996470.40.010877834914320.40.011597235916590.30.014758136940390.30.012746837912460.40.015796238982520.40.009926539963580.40.0091206840929370.40.0111156341952450.50.011986542907480.50.012927543915570.50.0099784441050420.40.0081678645850550.40.012158746990680.40.0131457547937200.40.016207248917600.70.009896549993560.050.010886850940350.40.0188567 (Table 3) ClassificationW10 / 400 Rolling Direction (W / kg)W10 / 400 60 Degree Direction (W / kg)W10 / 400 Ratio111.214.51.29210.914.91.37310.312.51.21411.915.31.29510.212.11.19611.215.21.36710.812.91.19812.115.61.29910.512.11.151012.716.81.321112.515.51.24129.511.51.211311.414.91.311410.314.61.42159.911.91.21610.712.61.181710.511.81.121810.211.61.141910.812.41.152010.911.91.092110.412.51.202210.613.11.242310.212.81.25249.811.21.14259.411.81.26269.7111.13279.210.81.17289.411.21.192911.214.51.293011.714.91.273111.614.91.283211.715.21.303312.516.21.303412.616.41.303513.417.21.283612.716.41.293712.416.81.353811.815.91.353911.714.91.274011.515.31.334111.715.91.364211.915.71.324312.616.31.294412.716.51.304512.716.51.30461216.41.374711.715.91.364812.415.91.284911.915.21.285011.515.41.34

[0087] As shown in Table 1 to Table 3, it can be confirmed that the alloy component precipitation characteristics are appropriately controlled, and the iron loss and iron loss anisotropy are improved.

[0088] When the tension deviation is adjusted during the cold-rolled sheet annealing, it can be confirmed that the grain distribution is formed consistently and the iron loss and anisotropy of iron loss are further improved.

[0089] The present invention may be embodied in many different forms, and should not be construed as being limited to the disclosed embodiments. In addition, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the technical spirit and essential features of the present invention. Therefore, it is to be understood that the above-described embodiments are for illustrative purposes only, and the scope of the present invention is not limited thereto.

Claims

1. A non-oriented electrical steel sheet comprising, in wt%: Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, and REM: 0.001 to 0.007%, with the balance being Fe and inevitable impurities.

2. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet satisfies Equation 1: 30 ≤ Se / Sn × REM ≤ 140 (In Equation 1, [Se], [Sn], and [REM] represent the content (wt%) of Se, Sn, and REM, respectively.)3. The non-oriented electrical steel sheet of claim 1, further comprising at least one of C, N, S, Ti, Nb, and V, each in an amount of 0.005 wt% or less.

4. The non-oriented electrical steel sheet of claim 1, further comprising at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, P: 0.08 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

5. The non-oriented electrical steel sheet of claim 1, further comprising 0.200 wt% or less in each or a combined amount of one or two or more of Bi, Pb, Ge, and As.

6. The non-oriented electrical steel sheet of claim 1, further comprising at least one of Mo: 0.03 wt% or less, B: 0.0050 wt% or less, Ca: 0.0050 wt% or less, and Mg: 0.0050 wt% or less.

7. The non-oriented electrical steel sheet of claim 1, wherein the non-oriented electrical steel sheet has a specific resistance of 50 µΩ•cm or more.

8. The non-oriented electrical steel sheet of claim 1, wherein an average grain size is 30 to 140 µm.

9. The non-oriented electrical steel sheet of claim 1, wherein an area fraction of grains having a grain size of 30% to 170% of an average grain size is 70% or more.

10. A method for manufacturing a non-oriented electrical steel sheet, comprising: hot-rolling a slab including, in wt%, Si: 2.8 to 4.0%, Al: 0.5 to 1.7%, Mn: 0.3 to 2.0%, Se: 0.0005 to 0.005%, Sn: 0.005 to 0.06%, and REM: 0.001 to 0.007%, with the balance being Fe and inevitable impurities, to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and annealing the cold-rolled sheet.

11. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein the slab further includes at least one of C, N, S, Ti, Nb, and V, each in an amount of 0.005 wt% or less.

12. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein the slab further includes at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, P: 0.08 wt% or less, Sb: 0.06 wt% or less, Ni: 0.05 wt% or less, and Zn: 0.01 wt% or less.

13. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein the slab further includes 0.200 wt% or less (excluding 0%) in each or a combined amount of one or two or more of Bi, Pb, Ge, and As.

14. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein the slab further includes at least one of Mo: 0.03 wt% or less (excluding 0%), B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

15. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein during the cold-rolled sheet annealing step, at an inlet side of an annealing furnace, a difference between a maximum tension and a minimum tension for a length of 2000 mm in a rolling direction of the cold-rolled sheet is 0.017 kgf / mm2 or less.

16. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein an average tension at the inlet side of the annealing furnace is 0.07 to 0.5 kgf / mm2.

17. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein a maximum temperature of an annealing furnace in the cold-rolled sheet annealing step is 875 to 1000 °C.

18. The method for manufacturing the non-oriented electrical steel sheet of claim 10, wherein a soaking time in the cold-rolled sheet annealing step is 25 to 60 seconds.

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