Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention comprises, by wt%, 1.5-4.5% of Si, 0.1-2.0% of Al, 0.1-2.0% of Mn, 0.002-0.03% of at least one from among Mo, V and Nb, and the balance of Fe and inevitable impurities, and, in order of grain size, the ratio of the average grain diameter of coarse grains of 0-25% to the average grain diameter of fine grains of 75-100% is 6.5 or less.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[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, which improves magnetism by appropriately forming grain sizes within the steel sheet by appropriately controlling the thermal history during cooling of the steel sheet in an annealing process prior to cold rolling.

[0002] Recently, with the increasing number of disasters caused by climate change, countries around the world are announcing roadmaps for carbon neutrality by 2050. Total carbon emissions in 2020 will reach 39 billion tons, of which internal combustion engines will account for 24%, or 9.4 billion tons. Therefore, there is a strong demand to achieve carbon neutrality in this sector through the electrification of internal combustion engines. To this end, electrification is rapidly progressing in the mobility sector, led by electric vehicles. The key characteristics required for drive motors in new mobility systems are increased driving range and higher top speed. These characteristics are directly related to the low core loss characteristics of electrical steel. Low core loss in electrical steel leads to greater efficiency and longer driving range. Therefore, low high-frequency core loss in electrical steel is essential. To achieve this, electrical steel typically contains large amounts of silicon (Si) and is enriched with elements such as aluminum (Al), manganese (Mn), and chromium (Cr).

[0003] However, when high-resistivity alloying elements such as Si, Al, Mn, and Cr are added in large quantities, the problem of low magnetic flux density arises. In particular, the use of materials with high magnetic flux density is essential for materials requiring continuous weight reduction, such as eco-friendly electric vehicle drive motors.

[0004] 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, wherein the thermal history of the steel sheet during cooling is appropriately controlled in the annealing process prior to cold rolling, thereby forming an appropriate grain size within the steel sheet and thereby improving magnetism.

[0005] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, the remainder being Fe and unavoidable impurities, and the ratio of the average grain size of coarse grains (0 to 25%) to the average grain size of fine grains (75 to 100%) in descending order of grain size is 6.5 or less.

[0006] The density of carbide is 2.5 / ㎛ 2 It could be as follows:

[0007] The average grain size of the crystal grains in the steel plate may be 40 to 150 ㎛.

[0008] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1% or less (excluding 0%), C: 0.005% or less (excluding 0%), S: 0.005% or less (excluding 0%), Ti: 0.005% or less (excluding 0%), and N: 0.005% or less (excluding 0%).

[0009] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0010] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0011] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of B: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0012] A non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following equation 1.

[0013] [Formula 1]

[0014] (B50 L + B50 C ) / 2 ≥1.60

[0015] (However, in Equation 1, B50 L is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 C represents the magnetic flux density (B50, Tesla) measured in the vertical direction of the rolling.)

[0016]

[0017] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, Si: 1.5 to 4.0%, Al: 0.1 to 2.0%, Mn: 0.2 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder being Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; a cold-rolling pre-annealing step of annealing the steel sheet; a cold-rolling step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0018] The annealing step prior to cold rolling includes a step of cracking the steel sheet; a first cooling step of cooling the steel sheet to a first cooling temperature at a first cooling rate; a second cooling step of cooling the steel sheet to a second cooling temperature at a second cooling rate that is 3 to 17°C / sec higher than the first cooling rate; and a first heat-holding step of maintaining the steel sheet within a range of ±10°C of the second cooling temperature for 30 seconds or longer.

[0019] The first cooling temperature may be 580 to 770°C.

[0020] The second cooling temperature may be 280 to 370°C.

[0021] The first cooling rate may be 5 to 20°C / sec, and the second cooling rate may be 10 to 30°C / sec.

[0022] The annealing step prior to cold rolling may further include a third cooling step of cooling to a third cooling temperature after the first heat preservation step.

[0023] The annealing step prior to cold rolling may further include a second heat preservation step, after the third cooling step, of maintaining the third cooling temperature within a range of ±10°C for 30 seconds or longer.

[0024] The third cooling temperature can be 90 to 220°C.

[0025] The third cooling stage may have an average cooling rate of 30 to 50°C / sec.

[0026] A step of pre-cold rolling the hot rolled steel sheet may be further included prior to the pre-cold rolling annealing step.

[0027] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and iron loss in the rolling direction.

[0028] A non-oriented electrical steel sheet according to one embodiment of the present invention has improved cold rolling properties, thereby enhancing productivity.

[0029] Ultimately, the non-oriented electrical steel sheet according to one embodiment of the present invention contributes to the manufacture of eco-friendly automobile motors, high-efficiency home appliance motors, and super-premium motor cores.

[0030] Figure 1 is a schematic diagram of the cooling pattern in the annealing stage prior to cold rolling.

[0031] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0032] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0033] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0034] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0035] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0036] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0037] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0038]

[0039] A non-oriented electrical steel sheet according to one embodiment of the present invention contains, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%.

[0040] First, let's explain the reason for the limitation of the components of non-oriented electrical steel sheets.

[0041]

[0042] Si: : 1.5 to 4.5 wt%

[0043] Silicon (Si) should be added in relatively large amounts because it increases the resistivity of the material and lowers the iron loss. If too little Si is added, the effect of improving the high-frequency iron loss may be minimal. If too much Si is added, the hardness of the material increases, which is not desirable because it lowers productivity and punchability. More specifically, Si may be included in an amount of 2.0 to 4.0 wt%. Even more specifically, Si may be included in an amount of 2.5 to 3.5 wt%.

[0044] Al: 0.1 to 2.0 wt%

[0045] Aluminum (Al) should be added in large quantities because it increases the resistivity of the material and lowers iron loss. 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 may cause problems by changing the properties of the mold flux during the continuous casting process, which may significantly reduce productivity. More specifically, Al may be included in an amount of 0.3 to 1.8 wt%, and even more specifically, Al may be included in an amount of 0.5 to 1.7 wt%.

[0046] Mn: 0.1 to 2.0 wt%

[0047] Manganese (Mn) increases the resistivity of the material, improves iron loss, and forms sulfides. If too little Mn is added, MnS may precipitate finely, which may deteriorate magnetism. If too much Mn is added, it may be detrimental to magnetism. <111> / ND The formation of aggregated structures can be promoted, thereby rapidly reducing the magnetic flux density. More specifically, it can contain 0.3 to 1.8 wt% of Mn. More specifically, it can contain 0.5 to 1.5 wt% of Mn.

[0048] At least one of Mo, V, and Nb: 0.0020 to 0.0300 wt%

[0049] Molybdenum (Mo), vanadium (V), and niobium (Nb) form carbides and complex-precipitate with TiC, thereby causing precipitate coarsening and reducing the number of fine carbides, thereby improving the magnetic flux density. If they are added appropriately, the aforementioned effect can be obtained, but if they are included in too much, a lot of segregation may occur, which may inhibit grain growth and deteriorate the magnetic flux density and iron loss. More specifically, one or more of Mo, V, and Nb may be included in an amount of 0.0030 to 0.0200 wt%. When only one of Mo, V, and Nb is included, each is included in an amount of 0.0020 to 0.0300 wt%. When two or more of Mo, V, and Nb are included, the sum of the contents of each element may be 0.0020 to 0.0300 wt%.

[0050] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.1% or less (excluding 0%), C: 0.003% or less (excluding 0%), S: 0.004% or less (excluding 0%), Ti: 0.003% or less (excluding 0%), and N: 0.003% or less (excluding 0%).

[0051] P: 0.1 wt% or less

[0052] Phosphorus (P) is a grain boundary segregation element that can improve magnetic flux density, but if added in too large a quantity, it increases the brittleness of the steel plate, resulting in poor weldability. More specifically, P may be included in an amount of 0.0001 to 0.0500 wt%.

[0053] C: 0.0050 wt% or less

[0054] Carbon (C) can react with N, Ti, Nb, V, etc. to form fine carbides, which hinder grain growth and domain movement, thereby deteriorating magnetism. In particular, if carbides smaller than 0.05㎛ are present, the movement of magnetic domains becomes difficult, which increases iron loss. Therefore, in one embodiment of the present invention, by optimizing the cooling pattern for controlling the size of carbides during the cooling process of the annealing process before cold rolling, the problem of increased iron loss can be overcome even if some carbides exist in the steel sheet. More specifically, C may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, C may be included in an amount of 0.0010 to 0.0035 wt%.

[0055] S: 0.0050 wt% or less

[0056] Sulfur (S) is an element that forms sulfides such as MnS, and can inhibit grain growth, thereby reducing magnetism. More specifically, S may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, S may be included in an amount of 0.0010 to 0.0030 wt%.

[0057] Ti: 0.0050 wt% or less

[0058] Titanium (Ti) can be limited because it forms carbonitrides and thus hinders domain movement. More specifically, Ti can be included in an amount of 0.0001 to 0.0050 wt%. More specifically, Ti can be included in an amount of 0.0010 to 0.0035 wt%.

[0059] N: 0.0050 wt% or less

[0060] Nitrogen (N) can combine with Ti, Nb, and V to form nitrides and reduce grain growth. More specifically, N may be included in an amount of 0.0001 to 0.0050 wt%. More specifically, N may be included in an amount of 0.0010 to 0.0035 wt%.

[0061]

[0062] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge, and As.

[0063] The aforementioned elements, when added additionally, segregate at grain boundaries and alleviate stress concentration at grain boundaries during cold rolling, thereby reducing the stress concentration at grain boundaries during the subsequent recrystallization annealing process. <111> / ND By suppressing recrystallization of orientation 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 may occur, which may suppress grain growth and result in inferior magnetic flux density and iron loss. More specifically, one or more types of Sn, Sb, Bi, Pb, Ge, and As may be further included in an amount of 0.010 to 0.100 wt%, individually or in combination.

[0064]

[0065] A non-oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%).

[0066] Cu: 0.005 to 0.200 wt%

[0067] Copper (Cu) forms sulfides with manganese (Mn). If too little Cu is added, fine precipitation of (Cu · Mn)S may occur, degrading magnetism. If too much Cu is added, high-temperature embrittlement may occur, leading to cracks during rolling or hot rolling. More specifically, Cu may be included in an amount of 0.01 to 0.10 wt%.

[0068] Cr: 0.01 to 0.50 wt%

[0069] Chromium (Cr) increases resistivity and improves iron loss. If too little Cr is added, the resistivity-enhancing effect may not be sufficient. If too much Cr is added, the magnetic flux density may decrease. More specifically, Cr may be included in an amount of 0.050 to 0.20 wt%.

[0070] Ni: 0.05 wt% or less

[0071] Nickel (Ni) can react with impurity elements to form fine sulfides, carbides, and nitrides, which can have a detrimental effect on magnetism. More specifically, it can contain 0.001 to 0.03 wt% of Ni.

[0072] Zn: 0.01 wt% or less

[0073] Zinc (Zn) can act as an impurity and degrade magnetism if the content is excessive. Therefore, Zn may be added further within the aforementioned range. More specifically, Zn may be included in an amount of 0.001 to 0.005 wt%.

[0074]

[0075] A non-oriented electrical steel sheet according to one embodiment of the present invention 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%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%).

[0076] These can react with C, S, N, etc., which are inevitably included, to form fine carbides, nitrides, or sulfides, which can adversely affect magnetism, so the upper limit can be limited as described above.

[0077] Other impurities

[0078] In addition to the elements described above, impurities that are unavoidably mixed may be included. Unavoidable impurities include impurities mixed during the steelmaking process and the manufacturing process of non-oriented electrical steel sheets. Since these are widely known in the art, a detailed description thereof will be omitted. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. When additional elements are included, they are included to replace the remaining Fe.

[0079]

[0080] In one embodiment of the present invention, a non-oriented electrical steel sheet has a ratio of the average grain size of coarse grains (0 to 25%) to the average grain size of fine grains (75 to 100%) in descending order of grain size, of 6.5 or less.

[0081] Fine grain (GS) ≤75% ) refers to the grains in the lower 75% or less based on grain size. That is, based on grain size, it refers to grains having a smaller grain size of 75 to 100% of the total 100% of the number of grains existing in the measurement area. For example, if there are 100 grains in the measurement area, it refers to the 75th to 100th grains arranged in order of grain size. The measurement reference cross-section is not particularly limited, but can be the normal plane (TD plane) of the rolling vertical direction (TD direction) of the steel plate. In order to reduce deviation due to measurement, the measurement area can be at least the entire thickness × 3 mm, and the number of measurement specimens can be at least 3 for non-overlapping areas. The grain size can be determined as the diameter of a circle having the same area as the corresponding grain.

[0082] Coarse grains (GS) ≥25%) refers to the top 25% or more crystal grains based on grain size. In other words, based on grain size, it refers to the grains with a large grain size of 0 to 25% out of the total 100% of the number of crystal grains existing within the measurement area. For example, when 100 crystal grains exist within the measurement area, it refers to the 1st to 25th crystal grains arranged in order of grain size.

[0083] In one embodiment of the present invention, based on the crystal grain size, the average grain size of coarse crystal grains is 0 to 25% of the average grain size of fine crystal grains to 75 to 100% of the average grain size (GS ≥25% / GS ≤75% ) can be adjusted to 6.5 or less, thereby further improving the magnetism by lowering the area fraction of coarse grains, which are unfavorable to the magnetic properties. More specifically, the ratio of the average grain size of coarse grains of 0 to 25% to the average grain size of fine grains of 75 to 100% (GS ≥25% / GS ≤75% ) can be between 2.0 and 6.0.

[0084] More specifically, the average grain size of fine grains of 75 to 100% (GS ≤75% ) can be 5 to 25㎛. In addition, the average grain size of coarse crystals of 0 to 25% (GS ≥25% ) can be 80 to 300 μm.

[0085] In one embodiment of the present invention, the density of the carbide is 2.5 / ㎛. 2It may be as follows. Carbide means that the carbon component in the steel plate is aggregated and clumped in the form of particles. In other words, it means a portion that contains carbon in greater quantity than the base content of the steel plate. In one embodiment of the present invention, the carbide is determined to be a particle containing a carbon component and having a carbon aggregate particle size of at least 1 nm when measured by TEM (Transmission Electron Microscopy) and EDS (Electrical Dispersive Spectroscopy). The measurement reference cross-section of the carbide is not particularly limited, but may be a normal plane (TD plane) in the rolling vertical direction (TD direction) of the steel plate. The particle size of the carbide means the diameter of an imaginary circle having the same area as the area occupied by the carbide. In one embodiment of the present invention, the carbide may include at least one of Mo, V, and Nb in addition to C.

[0086] If the density of carbides is high, the absolute number of fine carbides increases, which can have a negative effect on iron loss. More specifically, the density of carbides is 0.1 to 2.3 / ㎛. 2 It can be. More specifically, 0.5 to 2.3 / ㎛ 2 It could be.

[0087] In one embodiment of the present invention, the average grain size of the crystal grains within the steel plate may be 40 to 150 μm. If the crystal grain size is too large or too small, it may have a negative effect on magnetism. More specifically, the average grain size of the crystal grains within the steel plate may be 50 to 100 μm.

[0088] In one embodiment of the present invention, the magnetic flux density is excellent in the rolling direction and the rolling vertical direction.

[0089] Specifically, a non-oriented electrical steel sheet according to an embodiment of the present invention can satisfy the following equation 1.

[0090] [Formula 1]

[0091] (B50 L+ B50 C ) / 2 ≥1.60

[0092] (However, B50 in Equation 1 L is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 C represents the magnetic flux density (B50, Tesla) measured in the vertical direction of the rolling.)

[0093] B50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m.

[0094] Equation 1 is a general method for evaluating the magnetic flux density of a non-oriented electrical steel sheet, and means the average value of the magnetic flux density (B50) in the rolling direction (L) and the rolling vertical direction (C). More specifically, the value of Equation 1 may be 1.61 to 1.65.

[0095] In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention may have a core loss (W10 / 400) of 13.5 W / kg or less based on 0.25 mm. W10 / 400 is the core loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz.

[0096]

[0097] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, Si: 1.5 to 4.5%, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder being Fe and unavoidable impurities, to manufacture a hot-rolled steel sheet; a cold-rolling pre-annealing step of annealing the steel sheet; a cold-rolling step of cold-rolling the annealed steel sheet to manufacture a cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the cold-rolled sheet.

[0098] Below, each step is explained in detail.

[0099] First, a slab is manufactured. The reasons for limiting the addition ratio of each component within the slab are the same as those for limiting the composition of the non-oriented electrical steel sheet described above, so a repeated explanation is omitted. Since the composition of the slab does not substantially change during the manufacturing processes described below, such as hot rolling, pre-cold rolling annealing, cold rolling, and cold-rolled sheet annealing, the composition of the slab and the composition of the non-oriented electrical steel sheet are substantially identical.

[0100] Prior to the step of manufacturing hot-rolled plates, the slabs can be heated to 1000°C or higher. Specifically, the slabs are placed in a heating furnace and heated to 1050 to 1250°C. When heated at temperatures exceeding 1250°C, precipitates may be re-dissolved and finely precipitated after hot rolling.

[0101] The heated slab is hot-rolled to a thickness of 3.0 mm or less to produce a hot-rolled steel sheet. In one embodiment of the present invention, a preliminary cold-rolling step may be additionally included before cold rolling, so that even if the hot-rolled sheet is relatively thick, a non-oriented electrical steel sheet of an appropriate thickness can be produced. More specifically, the thickness of the hot-rolled sheet may be 1.5 to 3.0 mm.

[0102] The step of manufacturing the hot rolled sheet may include a step of finish rolling at a temperature of 850°C or higher.

[0103] If the hot rolling finishing temperature is too low, the rolling load increases, which reduces the hot rolling workability. In addition, a lot of deformation structures remain in the hot rolled steel sheet, which can cause an increase in the rolling load during the subsequent preliminary cold rolling process. In addition, during the intermediate annealing, deformation structures are removed. <111> / ND The recrystallization of the orientation grains is promoted, resulting in a lower magnetic flux density. Therefore, the higher the hot rolling finishing temperature, the better, and more specifically, finishing rolling at a temperature of 860 to 1000°C is preferable.

[0104] The step of manufacturing a hot-rolled sheet may include a step of performing water cooling after a time of 0.1 seconds or more after finish rolling.

[0105] After the finishing rolling, cooling is performed for coiling. When water cooling is performed immediately after the finishing rolling (i.e., within less than 0.1 seconds), the steel sheet may be rapidly cooled, causing deformation and residual stress, making coiling difficult. In addition, in terms of microstructure, the deformation stress after the finishing rolling is not released and remains, causing an increase in the rolling load and micro-stress in the subsequent cold rolling stage. <111> / ND may cause recrystallization of the orientation. Therefore, it is necessary to maintain the hot-rolled deformation structure for more than 0.1 seconds immediately after the hot-rolled finishing rolling to allow recovery and recrystallization, thereby reducing the rolling load during the subsequent preliminary cold rolling. <111> / ND suppresses the formation of azimuth recrystallization grains. More specifically, water cooling can be performed after 0.3 to 5.0 seconds, and even more specifically, water cooling can be performed after 0.5 to 3.0 seconds.

[0106] The step of manufacturing a hot rolled sheet may include a coiling step at a temperature of 600 to 800°C. A rough rolling step may also be included before the finish rolling step.

[0107] If the temperature during the coiling stage is controlled too low, the recovery and recrystallization of the hot-rolled deformation structure will not occur well, and the cooling load will increase in order to quickly cool the steel sheet to a low temperature, which may make it difficult to coil the supercooled coil. On the other hand, if the temperature is too high, recovery and recrystallization may be promoted, but additional oxidation by atmospheric oxygen may occur during coiling, which may cause thicker scale formation and the problem of intergranular oxidation. Intergranular oxidation of hot-rolled sheets promotes intergranular corrosion during the subsequent pickling process, which increases the possibility of surface stripe defects and may cause severe wear of the rolling rolls. Therefore, it is recommended that the coiling temperature be 600 to 800℃, and more specifically, coiling can be performed at 600 to 750℃.

[0108] In one embodiment of the present invention, after manufacturing a hot-rolled steel sheet, a pre-cold rolling annealing step for annealing the hot-rolled steel sheet may be performed immediately. Alternatively, a pre-cold rolling annealing step for annealing the pre-cold rolled steel sheet may be performed after performing preliminary cold rolling on the hot-rolled steel sheet.

[0109] Preliminary cold rolling can be performed in a PCM (Pickling & Cold rolling Mill) that includes a pickling process to improve rolling productivity, or in a TCM (Tandem Cold rolling Mill) that only performs cold rolling, and in the final cold rolling productivity and final product plate. <100> / ND In order to improve the crystal grain fraction, it can be performed in the range of a reduction ratio of 20 to 80%. In addition, if rolling productivity is not considered, it is also possible in the present invention to perform preliminary cold rolling in a reverse mill. The preliminary cold-rolled sheet can have a thickness of 0.5 to 1.8 mm. More specifically, the reduction ratio can be 30 to 70% and the thickness can be 0.8 to 1.5 mm.

[0110] Preliminary cold rolling is distinguished from cold rolling, which will be described later, in that it is the first rolling stage of the process of rolling to an intermediate thickness rather than the final product thickness, then performing intermediate annealing, and then cold rolling to the final product thickness.

[0111] The preliminary cold rolling reduction can be calculated as (steel plate thickness before rolling - steel plate thickness after rolling) / steel plate thickness before rolling. If the reduction ratio is too low in the preliminary cold rolling stage, the rolling load increases during the final cold rolling, which reduces productivity and increases the final reduction ratio, which causes fine grains. <111> / ND This can lead to problems that promote directional recrystallization. Conversely, if the reduction ratio is too high, the cold rolling load increases and the possibility of plate fracture increases.

[0112] The step of manufacturing the preliminary cold-rolled sheet can be performed at a temperature of 60 to 300°C. This temperature can be increased naturally by friction between the steel sheet and the rolling rolls, or by external heating. If the temperature is too low, the rolling load will increase significantly, and the steel sheet may slip between the rolling rolls instead of being rolled, resulting in problems such as twisting. If the temperature is too high, silicon and aluminum oxidation may occur on the steel sheet surface, which may deteriorate the magnetism, and the rolling oil may ignite. If the temperature is too high, silicon and aluminum oxidation may occur on the steel sheet surface, which may deteriorate the magnetism, and the rolling oil may ignite. More specifically, the process can be performed at a temperature of 70 to 250°C.

[0113] As mentioned above, the preliminary cold rolling step can be omitted if necessary.

[0114] Next, in the annealing step before cold rolling, hot-rolled steel sheets or preliminary cold-rolled sheets are annealed.

[0115] The soaking temperature during the annealing stage prior to cold rolling can range from 800 to 1200°C. If the annealing temperature is too low, recrystallized structures may not form or grow finely, resulting in a small increase in magnetic flux density. If the annealing temperature is too high, magnetic properties may deteriorate, and deformation of the plate shape may deteriorate rolling workability. More specifically, the temperature range may be 830 to 1170°C. The soaking time may range from 15 to 180 seconds.

[0116] In one embodiment of the present invention, the cooling pattern is controlled in the annealing step before cold rolling, thereby increasing the average grain size ratio of coarse grains to fine grains (GS ≥25% / GS ≤75% ) and carbide density can be controlled.

[0117] Figure 1 schematically illustrates the cooling pattern in the annealing stage prior to cold rolling.

[0118] As shown in Fig. 1, the step of cracking the steel plate includes: a first cooling step (C1) of cooling the steel plate to a first cooling temperature (T1) at a first cooling rate; a second cooling step (C2) of cooling the steel plate to a second cooling temperature at a second cooling rate (T2) that is 3 to 17°C / sec higher than the first cooling rate; and a first heat preservation step (M1) of maintaining the steel plate within a range of ±10°C of the second cooling temperature (T2) for 30 seconds or longer.

[0119] The first cooling step (C1) cools the steel plate from the soaking temperature (T0) to the first cooling temperature (T1) at a first cooling rate. In one embodiment of the present invention, the cooling temperature in the cooling step refers to the average cooling temperature over the entire time of the cold step. In Fig. 1, the cooling rate is expressed as being uniform, but it may vary over time.

[0120] The first cooling temperature (T1) may be 580 to 770°C. If the first cooling temperature (T1) is too low, it means that cooling was performed at the first cooling rate for a long time, which may cause problems in terms of material deformation due to thermal shock and deterioration of magnetic flux density and iron loss due to residual stress resulting therefrom. If the first cooling temperature (T1) is too high, the first cooling step (C1) may be terminated prematurely, forming fine carbides, which may cause problems in terms of magnetic flux density and iron loss. In one embodiment of the present invention, the cooling temperature is based on the plate surface temperature. More specifically, the first cooling temperature (T1) may be 600 to 750°C.

[0121] The first cooling rate may be 5 to 20°C / sec. If the first cooling rate is too slow, problems may arise in that the carbide coarsens, promoting the growth of coarse grains. If the first cooling rate is too fast, problems may arise in that the time required for fine grain growth is not secured. More specifically, the first cooling rate may be 10 to 15°C / sec.

[0122] Next, the second cooling step (C2) cools from the first cooling temperature (T1) to the second cooling temperature (T2) at a second cooling rate. At this time, the second cooling rate is 3 to 17°C / sec higher than the first cooling rate. If the difference between the second cooling rate and the first cooling rate is small, problems may arise in that the overall annealing time increases and carbide growth is promoted. If the difference between the second cooling rate and the first cooling rate is too large, magnetic deterioration may occur due to residual stress formed by rapid cooling. More specifically, the second cooling rate may be 5 to 15°C / sec higher than the first cooling rate.

[0123] The second cooling temperature (T2) may be 280 to 370°C. If the second cooling temperature (T2) is too low, it means that cooling at the second cooling rate is performed for a long time, which may cause problems in terms of an increase in the amount of carbide precipitation. If the second cooling temperature (T2) is too high, the second cooling step (C2) may be terminated prematurely, which may cause problems in terms of insufficient time for fine grain growth. More specifically, the second cooling temperature (T2) may be 300 to 350°C.

[0124] The second cooling rate may be 10 to 30°C / sec. If the second cooling rate is too slow, carbide precipitation may increase. If the second cooling rate is too fast, problems may arise in that residual stress due to rapid cooling increases. More specifically, the second cooling rate may be 15 to 25°C / sec.

[0125] Next, in the first heat retention step (M1), the temperature is maintained within the range of the second cooling temperature (T2) ±10°C for 30 seconds or more. If the holding time of the first heat retention step (M1) is too short, problems may arise in terms of insufficient growth of microcrystalline grains. More specifically, the holding time may be 30 to 600 seconds. More specifically, it may be 60 to 300 seconds.

[0126] After the first insulation step (M1), cooling to room temperature is possible, but additional cooling and insulation may be performed to prevent plate breakage due to material deviation in the width and length directions and shape defects when cooling to room temperature.

[0127] After the first heat preservation step, a third cooling step (C3) for cooling to a third cooling temperature (T3) may be further included.

[0128] The third cooling temperature (T3) may be between 90 and 220°C. If the third cooling temperature (T3) is too low, problems may arise in terms of shape deformation due to rapid cooling. If the third cooling temperature (T3) is too high, problems may arise in terms of poor coating quality due to the coating being performed at high temperatures. More specifically, the third cooling temperature (T3) may be between 100 and 200°C.

[0129] The average cooling rate of the third cooling stage can be 30 to 50°C / s. If the third cooling rate is too slow, productivity may decrease. If the third cooling rate is too fast, problems may arise in terms of material deviation and shape defects due to width-wise and length-wise deviations. More specifically, the third cooling rate can be 35 to 45°C / s.

[0130] The aforementioned pre-cold rolling annealing can be performed in vertical continuous annealing equipment or horizontal continuous annealing equipment. When performing annealing, a pickling operation can be performed to remove any oxide layer that may exist on the steel sheet before annealing using sulfuric acid, hydrochloric acid, or nitric acid. Alternatively, pickling can be performed after annealing to remove any oxide layer remaining on the surface.

[0131] Returning to the description of the method for manufacturing non-oriented electrical steel sheets, cold-rolled sheets are manufactured by cold-rolling an annealed steel sheet. At this time, cold rolling can be performed at a reduction ratio of 30 to 80%. If the reduction ratio is too low, the accumulated strain energy in the rolled steel sheet is small, making it difficult to recrystallize in the subsequent annealing process, and the rolled structure remains, which can cause problems in improving the magnetic flux density and iron loss. On the other hand, if the reduction ratio is too high, it can cause problems in the subsequent annealing process. <111> / ND The recrystallization of the orientation grains is promoted and the grains become finer, which may cause problems such as poor magnetic flux density and increased iron loss. More specifically, the reduction ratio can be 40 to 70%. The thickness can be 0.1 mm to 0.5 mm. More specifically, it can be 0.15 to 0.35 mm. The cold rolling step can use a tandem cold rolling mill that continuously cold rolls the steel sheet using multiple rolling stands, or a reverse rolling mill that discontinuously cold rolls using 12 or more rolling rolls.

[0132]

[0133] Next, the step of annealing the cold rolled sheet can be performed at a temperature range of 600 to 1200℃. If the annealing temperature is too low, <111> / ND orientation grains are accelerated for recrystallization, and the grains become finer, making it difficult to secure excellent magnetic flux density characteristics. If the annealing temperature is too high, the grains grow coarsely, increasing iron loss. In addition, an oxide or nitride layer may form on the steel sheet surface from the annealing atmosphere gas, which also increases iron loss. More specifically, annealing can be performed at 750 to 1100°C.

[0134] After the cold-rolled sheet annealing step, a step of forming an insulating film may be further included to ensure insulation and corrosion resistance of the steel sheet. Since the insulating film is widely known, a detailed description thereof will be omitted.

[0135]

[0136] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0137]

[0138] Example 1

[0139] A slab was manufactured with the composition shown in Table 1 below. The remainder is Fe. The slab was heated to 1150°C, hot-finish rolled at 920°C, and coiled at 650°C to produce a 2.3 mm hot-rolled sheet. Subsequently, the hot-rolled sheet was preliminarily cold-rolled to 1.4 mm. Subsequently, the slab was soaked at 1100°C for 30 seconds, then cooled to 600°C at a cooling rate of 10°C / sec for the first time, cooled to 350°C at a cooling rate of 15°C / sec for the second time, and annealed at 350°C for 240 seconds. Subsequently, it was cooled to 150°C at a cooling rate of 40°C / sec, held at 150°C for 60 seconds, and then cooled to room temperature. Next, the final cold rolling was performed using a reverse rolling mill to a thickness of 0.25 mmt, annealed at a temperature of 900°C for 100 seconds, and then insulation coating treatment was performed.

[0140] The grain size of the steel plate is measured by EBSD and analyzed using the GS (diameter) chart in the OIM software to obtain the ratio of the average grain size of coarse grains to the average grain size of fine grains (GS ≥25% / GS ≤75% ) was measured.

[0141] The carbides of the steel plate were measured by TEM and EDS and are summarized in Table 2 below.

[0142] The magnetic properties were measured using an Epstein tester by preparing Epstein specimens at each angle, and expressed as the average values ​​in the rolling direction and the direction perpendicular to the rolling.

[0143] (% by weight)SiAlMnC(ppm)S(ppm)N(ppm)Ti(ppm)Mo(ppm)V(ppm)Nb(ppm)A12.71.60.770141616155012A22.71.60.732155515201215A32.71.60. 7282021201535135A42.71.60.7166232294012550A52.71.60.720232 6315010720A62.71.60.7251017243015415A72.71.60.720232631555

[0144] Grain size ratioAverage grain size (㎛)Carbide density (units / ㎛) 2 )B50(Tesla)A16.8893.251.58A26.7802.421.59A34.5323.701.57A42.8352.801.58A55.9682.311.63A64.8752.451.62A76.6802.621.59

[0145] As shown in Tables 1 and 2, if the steel composition is not properly included, the crystal grain size ratio is not properly formed and the magnetic flux density is inferior.

[0146]

[0147] Example 2

[0148] A slab was manufactured as shown in Table 3 below. The same procedure as Example 1 was followed, except that the thermal conditions in the annealing before cold rolling were changed as shown in Table 4 below.

[0149] (% by weight)SiAlMnC(ppm)S(ppm)N(ppm)Ti(ppm)Mo(ppm)V(ppm)Nb(ppm)B13.450.71.25616325885--B23.450.71.228222826-- 70B33.450.71.226162314-125-B43.450.71.220152722-10040B53.450.71.23023262310-80B63.450.71.2451520327020-

[0150] Specific cracking temperature (℃)First cooling temperature (℃)First cooling rate (℃ / sec)Second cooling temperature (℃)Second cooling rate (℃ / sec)First heat retention time (sec)Third cooling temperature (℃)Second heat retention time (sec)C1B11000600103501530015060C2B21000600253501530015060C3B3900550103501530015060C4B41000800103201530015060C5B5900600103201530015060C6B6100060015320153 0015060C7B275060010350156015035C8B3850600103501530015060C9B4100060010350153 0015060C10B51100600103501530015060C11B61150600253501530015060C13B31000700103 501530015060C14B41000650103501530015060C16B61000600154502530015060C17B21000 60015360256015060C18B31000600153202530015060C19B4100060015250256015060C20B5 100060015320356015060C21B6100060015320252015030C22B2100060015320256025030C2 3B31000600153202560150120C14B410006001532025608060C16B6100060015320256010020

[0151] Average grain size ratio (㎛) Carbide density (units / ㎛) 2)B50(Tesla) Shape defect occurredC15.8363.811.57XC23.9314.241.58XC34.5383.781.58XC46.9932.321.58XC54.7732.381.61XC64.3622.821.58XC75.8353.611.57XC84.7462.351.63XC95.1642.411.61XC104.91032.431.61XC116.81153.121.59XC134.8722.3 11.62XC144.7612.151.61XC166.8373.081.58XC175.3792.411.61X C184.9752.281.62 9812.421.59OC216.7852.681.59XC226.8852.751.59XC234.2812.451.61XC144.9842.631.58OC165.2832.551.59X

[0152] As can be seen in Tables 3 to 5, when the cooling pattern is appropriately controlled during the annealing process prior to cold rolling, the grain size ratio and carbide density are appropriately controlled, confirming excellent magnetism. On the other hand, when the cooling pattern is not appropriately controlled, the grain size is not properly formed, a large amount of carbide is generated, confirming poor magnetism.

[0153] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Containing Si: 1.5 to 4.5% by weight, Al: 0.1 to 2.0%, Mn: 0.1 to 2.0%, and at least one of Mo, V and Nb: 0.002 to 0.03%, the remainder being Fe and inevitable impurities. A non-oriented electrical steel sheet having a ratio of the average grain size of coarse grains (0 to 25%) to the average grain size of fine grains (75 to 100%) in order of increasing grain size of 6.5 or less. In the first paragraph, The density of carbide is 2.5 / ㎛ 2 Below is the non-oriented electrical steel sheet. In the first paragraph, A non-oriented electrical steel sheet having an average grain size of 40 to 150 ㎛ within the steel sheet. In the first paragraph, Non-oriented electrical steel sheet further containing at least one of P: 0.1% or less (excluding 0%), C: 0.005% or less (excluding 0%), S: 0.005% or less (excluding 0%), Ti: 0.005% or less (excluding 0%), and N: 0.005% or less (excluding 0%). In the first paragraph, A non-oriented electrical steel sheet further comprising 0.005 to 0.200 wt% of each or a combined amount of one or more of Sn, Sb, Bi, Pb, Ge and As. In the first paragraph, A non-oriented electrical steel sheet further comprising at least one of Cu: 0.005 to 0.2 wt%, Cr: 0.01 to 0.5 wt%, Ni: 0.05 wt% or less (excluding 0%), and Zn: 0.01 wt% or less (excluding 0%). In the first paragraph, B: Non-oriented electrical steel sheet further comprising at least one of: 0.0050 wt% or less (excluding 0%), Ca: 0.0050 wt% or less (excluding 0%), Zr: 0.005 wt% or less (excluding 0%), Te: 0.01 wt% or less (excluding 0%), and Mg: 0.0050 wt% or less (excluding 0%). In the first paragraph, A non-oriented electrical steel sheet satisfying the following equation 1. [Formula 1] (B50 L + B50 C ) / 2 ≥1.60 (However, B50 in Equation 1 L is the magnetic flux density (B50, Tesla) measured in the rolling direction, and B50 C represents the magnetic flux density (B50, Tesla) measured in the vertical direction of the rolling.) A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab containing Si: 1.5 to 4.0% by weight, Al: 0.1 to 2.0%, Mn: 0.2 to 2.0%, and at least one of Mo, V, and Nb: 0.002 to 0.03%, with the remainder being Fe and unavoidable impurities; An annealing step prior to cold rolling to anneal the above steel plate; A step for manufacturing cold rolled steel sheets by cold rolling an annealed steel sheet, and A cold rolled sheet annealing step for annealing the above cold rolled sheet; Including, The annealing step before the above cold rolling A step of cracking the above steel plate; A first cooling step of cooling the above steel plate to a first cooling temperature at a first cooling rate; A second cooling step of cooling the steel plate to a second cooling temperature at a second cooling rate that is 3 to 17°C / sec higher than the first cooling rate; and A method for manufacturing a non-oriented electrical steel sheet, comprising a first heat-keeping step of maintaining the second cooling temperature within a range of ±10℃ for 30 seconds or longer. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the first cooling temperature is 580 to 770°C. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the second cooling temperature is 280 to 370°C. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the first cooling rate is 5 to 20°C / sec and the second cooling rate is 10 to 30°C / sec. In Article 9, A method for manufacturing a non-oriented electrical steel sheet, wherein the annealing step prior to the cold rolling further includes a third cooling step of cooling to a third cooling temperature after the first heat preservation step. In Article 13, A method for manufacturing a non-oriented electrical steel sheet, wherein the annealing step prior to the cold rolling further comprises a second heat preservation step of maintaining the temperature within a range of ±10°C of the third cooling temperature for 30 seconds or longer after the third cooling step. In Article 13, A method for manufacturing a non-oriented electrical steel sheet, wherein the third cooling temperature is 90 to 220°C. In Article 13, A method for manufacturing a non-oriented electrical steel sheet, wherein the third cooling step has an average cooling rate of 30 to 50°C / sec. In Article 9, A method for manufacturing a non-oriented electrical steel sheet further comprising a step of preliminarily cold rolling a hot rolled steel sheet prior to the above-mentioned pre-cold rolling annealing step.

Images