Electrical steel sheet and manufacturing method therefor

Abstract

In an electrical steel sheet according to an embodiment of the present invention, in a cross section in the thickness direction of the steel sheet, an average ratio of the major axis to minor axis of crystal grains is 1 to 2.3, and a ratio of crystal grains having an orientation within 15° from the {110}<001> orientation is 20 area% or more.

Description

Electrical steel sheet and method of manufacturing the same

[0001] One embodiment of the present invention relates to an electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to an axial motor electrical steel sheet with excellent magnetic properties and processability by appropriately controlling the grain shape, and a method for manufacturing the same.

[0002] Non-oriented electrical steel is used as a core material in rotating machinery such as motors and generators, as well as in stationary machinery such as small transformers, playing a crucial role in determining the energy efficiency of electrical equipment. Recently, stricter motor efficiency regulations have led to a significant increase in the use of high-efficiency motors. To improve the efficiency of these motors, it is necessary to reduce iron losses or copper losses. These iron and copper losses are significantly influenced by the magnetic properties of the electrical steel used as the motor core material. Therefore, motor manufacturers are increasingly using electrical steel with low iron losses instead of conventional steel with high iron losses. To reduce copper losses, methods such as lowering the design magnetic flux density or reducing the excitation current at the design flux are used; however, to utilize the latter method, it is necessary to increase the magnetic flux density of the electrical steel. In particular, electrical steel with high magnetic flux density offers the advantage of enhancing torque, which allows motors with frequent on / off cycles to generate high output quickly. To manufacture electrical steel sheets with high magnetic flux density, the silicon content must be lowered; however, a low silicon content—an element that increases resistivity—presents a problem of high iron loss. Therefore, there is a need to develop electrical steel sheets with characteristics of low iron loss and high magnetic flux density.

[0003] From a structural perspective of the motor, the torque in a radial motor is typically generated in proportion to the product of the square of the rotor diameter and the length of the cylindrical stator. Therefore, to increase the torque, the length of the motor's cylindrical stator is increased, which leads to the problem of an increase in the overall volume of the motor.

[0004] Unlike conventional radial motor structures, the stator and rotor of an axial flux motor are arranged parallel to each other in the axial direction. Magnetic force is transmitted axially through the stator to the rotor, generating torque, and the magnitude of the torque is proportional to the cube of the diameter of the cylindrical rotor. In other words, it is a structure capable of generating high torque even in a small space. Since the magnetic force generated by the current applied to the stator is transmitted axially to the rotor magnets, the application of magnetic materials with particularly excellent unidirectional magnetic properties is required.

[0005] The electrical steel sheet described in the Korean patent (KR10-1605791 B1) can be used in axial motors due to its excellent magnetic flux density and iron loss; however, because its grain shape is columnar, there is a high possibility of defects in the cutting edge during punching. When manufacturing motors using electrical steel sheets, the product is processed by punching; however, plastic deformation and residual stress inevitably occur at the cutting edge during this process. The resulting plastic deformation causes non-uniformity in the lamination of the electrical steel sheets, while residual stress degrades magnetic properties. To improve performance in processing steps that include such punching, an electrical steel sheet with excellent processability is required. Generally, it is known that materials with smaller grain sizes are advantageous for punchability, but materials with larger grain sizes are advantageous in terms of magnetic properties.

[0006] One embodiment of the present invention relates to an electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an axial motor electrical steel sheet with excellent magnetic properties and processability by appropriately controlling the grain shape, and a method for manufacturing the same.

[0007] An electrical steel sheet according to one embodiment of the present invention has, in a cross-section in the thickness direction of the steel sheet, a ratio of the major axis to the average minor axis of the grains of 1 to 2.3, and {110} <001> The proportion of grains with an orientation within 15° of the orientation is 20% or more of the area.

[0008] In a cross-section in the thickness direction of the steel plate, the average grain size of the crystal grains may be 50 to 100 μm.

[0009] On the surface of the steel plate, among all the crystal grains, crystal grains with a ratio (D2 / D1) of the diameter of the circumscribed circle (D1) and the diameter of the inscribed circle (D2) of 0.5 or more may have an area of ​​70% or more.

[0010] In weight percent, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder may contain Fe and unavoidable impurities.

[0011] Mn: 0.1 wt% or less and S: 0.005 wt% or less may be further included.

[0012] A method for manufacturing an electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot rolling a slab to produce a hot-rolled steel sheet; first cold rolling the hot-rolled steel sheet to produce a first cold-rolled sheet; intermediate annealing the first cold-rolled sheet; second cold rolling the first cold-rolled sheet to produce a second cold-rolled sheet; and a cold-rolled sheet annealing step for annealing the second cold-rolled sheet.

[0013] The intermediate annealing step includes a heating step and a cracking step, and the difference in dew point temperature between the heating step and the cracking step (heating step-cracking step) may be 10 to 45°C.

[0014] The heating step is a step of heating the temperature of the steel plate from 50°C to the cracking temperature, and the dew point temperature may be 30 to 80°C.

[0015] The cracking stage is a cracking stage at a cracking temperature of 800 to 1100°C, and the dew point temperature may be 25 to 75°C.

[0016] The slab contains, in weight percent, Si: 0.3% to 7.0%, C: 0.01% to 0.4%, and the remainder being Fe and unavoidable impurities.

[0017] The slab may further contain Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0018] After the step of manufacturing a hot-rolled steel sheet, the method further includes a hot-rolled sheet annealing step for annealing the hot-rolled sheet, and the hot-rolled sheet annealing step can be performed at a temperature of 850℃ to 1000℃ and a dew point temperature of 0℃ or lower.

[0019] The cold-rolled sheet annealing step can be performed at a temperature of 850°C to 1200°C and a dew point temperature of 0°C or lower.

[0020] According to one embodiment of the present invention, the magnetism in the rolling direction is excellent, so it can be usefully utilized as an iron core for an axial motor.

[0021] According to one embodiment of the present invention, it has excellent machinability and can be usefully utilized as an iron core for an axial motor.

[0022] In addition, since it can be manufactured through a continuous process, manufacturing time can be relatively shortened and productivity can be improved.

[0023] Figure 1 is a photograph of a cross-section of an electrical steel sheet manufactured in Example 1, observed through an optical microscope.

[0024] Figure 2 is a photograph showing the surface of the electrical steel sheet manufactured in Example 1 through EBSD analysis.

[0025] Figure 3 is a photograph showing the surface of an electrical steel sheet for an axial motor manufactured in Example 1 analyzed by the Orientation Distribution Function (ODF).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[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]

[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] An electrical steel sheet for an axial motor according to one embodiment of the present invention has, in a cross-section in the thickness direction of the steel sheet, a ratio of the major axis to the average minor axis of the grains of 1 to 2.3, and {110} <001> The proportion of grains with an orientation within 15° of the orientation is 20% or more of the area.

[0036] First, an electrical steel sheet for an axial motor according to one embodiment of the present invention comprises Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

[0037] Si: 0.3 to 7.0 wt%

[0038] Silicon (Si) improves iron loss by lowering the magnetic anisotropy of electrical steel sheets and increasing resistivity. If the Si content is too low, iron loss becomes inferior, and if it is too high, brittleness increases. More specifically, the composition may contain 1.0 to 3.0% Si.

[0039] C: 0.15 wt% or less

[0040] Since a process is required for carbon (C) to escape from the center to the surface layer so that Goss grains in the surface layer diffuse to the center during intermediate decarburization annealing, the carbon content in the slab may be 0.010 to 0.400 weight%. More specifically, the carbon content in the slab may be 0.100 to 0.300 weight%. In addition, the carbon content in the steel sheet after the decarburization annealing step completed may be 0.150 weight% or less. More specifically, it may be 0.100 weight% or less. More specifically, it may be 0.065 weight% or less.

[0041] An electrical steel sheet for an axial motor according to one embodiment of the present invention may further include Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0042] Mn and S form MnS precipitates, which hinder the growth of Goss grains diffusing into the center during the decarburization process. Therefore, it is preferable not to add Mn and S. However, considering the amount inevitably incorporated during the steelmaking process, Mn and S in the slab and steel sheet after the non-oxidizing annealing step can be controlled to Mn: 0.1 wt% or less and S: 0.005 wt% or less, respectively. More specifically, Mn: 0.0001 to 0.0500 wt% and S: 0.0001 to 0.0030 wt% may be included. More specifically, Mn: 0.0010 to 0.0300 wt% may be included.

[0043] The remainder comprises Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of electrical steel sheets; as this is widely known in the field, a detailed explanation is omitted. Specifically, since components such as Al, N, Ti, Mg, and Ca react with oxygen in the steel to form oxides, it is necessary to strongly suppress their presence; thus, each component can be managed to a level of 0.005 weight% or less. 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.

[0044]

[0045] In one embodiment of the present invention, in a cross-section in the thickness direction of the steel plate, the ratio of the major axis to the average minor axis of the grain is 1.00 to 2.30. By adjusting the ratio of the major axis to the minor axis to be low in this way, sufficient processability required for the manufacture of an axial motor can be secured. A cross-section in the thickness direction of the steel plate refers to a cross-section that includes the thickness direction of the steel plate. More specifically, it may be a plane perpendicular to the rolling direction (RD plane) or a plane perpendicular to the rolling direction (TD plane). More specifically, it may be a plane perpendicular to the rolling direction (TD plane).

[0046] The ratio of the major axis to the minor axis refers to the ratio of lengths (major axis / minor axis) when the longest axis passing through the center of a grain is designated as the major axis and the shortest axis as the minor axis. The center of the grain can be determined as the center of the smallest circle containing all the grains. The average refers to the numerical average of the number of grains. The grain shape can be observed through an optical microscope, and the ratio of the major axis to the minor axis of the average grain can be calculated by measuring the lengths of the major and minor axes of each grain from an image of the TD plane of the specimen observed with an optical microscope and determining the average value of the major axis length / minor axis length. More specifically, it may be between 1.50 and 2.15.

[0047] If the ratio of the major axis to the average minor axis of the grain is too large, it is difficult to sufficiently secure the desired workability. This ratio can be achieved by performing decarburization in only a single annealing process during the manufacturing of electrical steel sheets. A detailed explanation of this will be provided in the description of the electrical steel sheet manufacturing method.

[0048] An electrical steel sheet for an axial motor according to one embodiment of the present invention is {110} <001> The proportion of grains having an orientation within 15° of the orientation (Goss grains) is 20.0 area% or more. In this case, the measurement reference plane is not limited and, specifically, may be a plane parallel to the rolling plane (ND plane). The fraction of Goss grains contributes to improving high-frequency iron loss. More specifically, Goss ({110} <001> The fraction of ) crystal grains may be 21.0 to 95.0 area%. More specifically, Goss({110} <001> The fraction of crystal grains may be 21.0 to 35.0 area%. The area of ​​crystal grains having the corresponding orientation in the cross-section of the steel plate is calculated and considered as the area fraction.

[0049] In one embodiment of the present invention, the effect may be manifested by the unique manufacturing process and the unique microstructure generated by the manufacturing process, rather than by the alloy components of the electrical steel sheet for an axial motor.

[0050] In a cross-section in the thickness direction of the steel plate, the average grain size may be 50 to 100 μm. As previously mentioned, if the average grain size is too small, it is difficult to obtain appropriate magnetic properties. Conversely, if the average grain size is too large, workability may decrease. More specifically, the average grain size may be 52 to 80 μm. The average grain size refers to the number average grain size. The average grain size refers to the diameter of a virtual circle having the same area as the grain. By counting the number of grains within a specific area, the average grain size can be calculated from the average area of ​​the grains.

[0051] On the surface of the steel plate, there may be 70% or more of the area of ​​grains in which the ratio (D2 / D1) of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) is 0.5 or greater. Here, the circumscribed circle refers to the smallest circle among the imaginary circles surrounding the outside of the grain, and the inscribed circle refers to the largest circle among the imaginary circles contained within the grain.

[0052] In the texture of the electrical steel sheet for an axial motor according to one embodiment of the present invention, the crystal grains on the surface grow into the interior of the steel sheet, so round-shaped crystal grains are formed on the surface of the steel sheet. As such, due to the crystal grain shape according to one embodiment of the present invention, superior magnetism can be obtained. More specifically, among the total crystal grains on the surface of the steel sheet, crystal grains in which the ratio (D2 / D1) of the circumscribed circle diameter (D1) to the inscribed circle diameter (D2) is 0.5 or greater may be 80% or more of the area.

[0053] In one embodiment of the present invention, the grain shape of the surface is due to the short duration of decarburization annealing and non-oxidation annealing. If the annealing is performed for a long duration of 30 minutes or more through decarburization annealing and subsequent batch annealing, the diameter (D1) of the circumscribed circle becomes significantly larger than that of the inscribed circle (D2), so the ratio cannot be greater than 0.5. Here, the circumscribed circle refers to the smallest circle among the imaginary circles surrounding the outside of the grain, and the inscribed circle refers to the largest circle among the imaginary circles contained within the grain. The grain shape can be analyzed using a computer program after observing the surface (ND surface) of the steel plate with an optical microscope and the observed photograph.

[0054]

[0055] In this way, by appropriately adjusting the steel composition of the steel plate and appropriately forming the texture, excellent magnetic properties and workability are achieved simultaneously. Specifically, the average magnetic flux density (B) in the rolling direction and the rolling perpendicular direction 50 ) can be 1.820T or higher. . In addition, the average iron loss (W in the rolling direction and the rolling vertical direction) 15 / 50 ) may be 2,500 W / kg or less. In addition, the average iron loss (W in the rolling direction and the direction perpendicular to rolling) 10 / 400 ) may be 15.00 W / kg or less. More specifically, the magnetic flux density (B) in the rolling direction 50 ) can be 1.821 to 1.910 T. In addition, the average iron loss (W in the rolling direction and the rolling perpendicular direction) 15 / 50) can be 1.800 to 1.990 W / kg. In addition, the average iron loss (W in the rolling direction and the rolling perpendicular direction) is 10 / 400 ) can be 11.00 to 14.70 W / kg. In this case, the measurement reference thickness for iron loss can be 0.23 mm.

[0056] When burrs are generated at the sheared cross-section of the core material during motor core manufacturing, empty spaces are created when the core material is laminated, leading to an increase in porosity. This increase in porosity causes a decrease in the performance of the motor core. Furthermore, unlike general radial motors, axial motors can achieve maximum efficiency only when the direction of magnetic flux generation is axial. If the core lamination is inaccurate, the direction of magnetic flux generation in the core material changes slightly, which can also affect motor efficiency. For this reason, processability is an essential property required to utilize electrical steel sheets as axial motors. In one embodiment of the present invention, processability was determined to be satisfactory when the length of the generated burr was measured and the thickness was 50 μm or less.

[0057]

[0058] A method for manufacturing an electrical steel sheet for an axial motor according to one embodiment of the present invention comprises the steps of: manufacturing a hot-rolled steel sheet by hot-rolling a slab; manufacturing a first cold-rolled sheet by first cold-rolling the hot-rolled steel sheet; intermediately annealing the first cold-rolled sheet; manufacturing a second cold-rolled sheet by second cold-rolling the first cold-rolled sheet; and annealing the second cold-rolled sheet.

[0059] First, the slab is hot-rolled.

[0060] The slab may contain, in weight percent, Si: 0.3% to 7.0%, C: 0.01% to 0.4%, and the remainder being Fe and unavoidable impurities.

[0061] The slab may further contain Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0062] The description of the steel composition of the slab is the same as the description of the electrical steel sheet for axial motors mentioned above, so the redundant description is omitted. Except for C, the steel composition of the steel sheet may be substantially the same as the steel composition of the slab.

[0063] The slab may be heated before hot rolling. The slab heating temperature may be 1050°C to 1350°C, which is higher than the conventional heating temperature. When the temperature is high during slab reheating, there is a problem in that the hot-rolled structure becomes coarse, which adversely affects magnetism. However, the method for manufacturing an electrical steel sheet according to one embodiment of the present invention has a higher carbon content than conventional methods, so the hot-rolled structure does not become coarse even if the slab reheating temperature is high, and by reheating at a higher temperature than in the conventional case, it is advantageous during hot rolling. However, when the reheating temperature is high, the solubility of precipitates such as TiN and AlN increases, and when cooling, a large number of fine precipitates are distributed, which hinders the growth of crystal grains on the surface.

[0064] Hot rolling can be used to produce a hot-rolled plate with a thickness of 1.3 to 4.3 mm by applying an appropriate rolling reduction rate at the final cold rolling stage so that it can be manufactured to the final product thickness. More specifically, it can be manufactured to a thickness of 1.5 to 4.0 mm.

[0065] The hot rolling finish rolling temperature may be 750°C to 1050°C. If the hot rolling finish rolling temperature is too high, surface defects occur, which degrades quality. In addition, if the finish rolling temperature is too low, the rolling load increases, which reduces sheet throughput and lowers productivity. More specifically, it may be 800°C to 1030°C.

[0066] The winding temperature can be 600℃ or lower.

[0067] After hot rolling, the process may further include a step of annealing the hot-rolled steel sheet. At this time, the annealing of the hot-rolled sheet may or may not include a decarburization process. Specifically, the annealing of the hot-rolled sheet may be performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or lower. More specifically, the annealing may be performed at a dew point temperature of -70°C to 70°C.

[0068] In one embodiment of the present invention, by annealing a hot-rolled sheet at a dew point temperature of 20°C or lower, the grain shape in the thickness direction of the steel sheet can be appropriately controlled. For example, if the dew point temperature is set high during the hot-rolled sheet annealing step to cause excessive decarburization, the grain length in the thickness direction of the steel sheet increases significantly, and it may be difficult to appropriately secure the ratio of the major axis to the minor axis of the electrical steel sheet produced at the end. More specifically, the hot-rolled sheet can be annealed at a dew point temperature of -30°C to 0°C.

[0069] After annealing the hot-rolled plate, pickling can be performed. The annealing of the hot-rolled plate may be omitted if necessary.

[0070]

[0071] Next, cold rolling is performed to manufacture cold-rolled steel sheets.

[0072] Accordingly, cold rolling can be performed at a reduction ratio of 50% to 80%. More specifically, it can be 55% to 75%. Through this, a cold-rolled steel sheet with a final thickness of 0.2 to 2.0 mm can be manufactured.

[0073] It is known that in the manufacturing process of oriented electrical steel sheets, cold rolling is effective when performed once with a high reduction rate of nearly 90%. This is because it creates an environment favorable for grain growth for only the Goss grains among the primary recrystallized grains. However, since the method for manufacturing an electrical steel sheet for an axial motor according to one embodiment of the present invention does not utilize abnormal grain growth of Goss orientation grains and instead diffuses the Goss grains in the surface layer generated by decarburization annealing and multiple cold rollings inward, it is advantageous to form a large number of Goss orientation grains distributed in the surface layer.

[0074] Therefore, when cold rolling is performed at a reduction rate of 50% to 80%, a large number of Goss textures may be formed in the surface layer. More specifically, it may be 55% to 75%.

[0075] Next, the cold-rolled steel sheet is subjected to intermediate annealing. At this time, the intermediate annealing step includes a heating step and a cracking step. In one embodiment of the present invention, decarburization is efficiently achieved by controlling the dew points in the heating step and the cracking step differently.

[0076] First, the heating step involves heating the steel plate from 50°C to the cracking temperature. During the heating step, the dew point temperature needs to be set higher than that of the cracking step described later, ranging from 30 to 80°C. This allows for the primary removal of carbon from the surface of the material during the initial heating stage, thereby improving decarburization efficiency. Subsequently, residual carbon is uniformly diffused and removed from the surface during the process, maximizing the decarburization effect.

[0077] Specifically, the difference in dew point temperature between the heating stage and the cracking stage (heating stage-cracking stage) may be 10 to 45°C. If the difference is too small, or if the dew point temperature in the cracking stage is too high, decarburization may not proceed smoothly, and thus, sufficient improvement in magnetism may not be achieved. More specifically, the difference in dew point temperature between the heating stage and the cracking stage (heating stage-cracking stage) may be 10 to 44°C. To prevent the atmosphere gases from mixing with each other in the heating stage and the cracking stage, the heating stage and the cracking stage may be performed physically separated, or a separator may be installed to prevent the atmospheres in the heating stage and the cracking stage from mixing.

[0078] If the dew point temperature during the heating step is too low, decarburization may not occur sufficiently, and conversely, if it is too high, surface oxidation may occur, which may inhibit decarburization. More specifically, the dew point temperature during the heating step may be 35 to 78°C. The heating step may be performed for 30 seconds to 3 minutes.

[0079] The cracking stage is a stage of annealing at the cracking temperature. The cracking temperature may be 800°C to 1100°C. If the cracking temperature is too low, sufficient decarburization and internal diffusion of Goss grains may not occur. If the cracking temperature is too high, surface oxidation may occur, which may cause problems in inhibiting decarburization. More specifically, the cracking temperature may be 840°C to 1020°C. The cracking stage can be distinguished from the heating stage by the fact that the instantaneous change in the steel plate temperature is 1°C / second or less.

[0080] During the cracking stage, the dew point temperature needs to be set to 25 to 75°C, which is lower than that of the aforementioned heating stage. If the dew point temperature during the heating stage is too low, decarburization may not occur sufficiently, and conversely, if it is too high, problems may arise due to surface oxidation. More specifically, the dew point temperature during the heating stage may be 25 to 70°C. The cracking stage may be performed for 30 seconds to 5 minutes.

[0081] After intermediate annealing, the carbon content in the steel sheet may be 0.15 weight% or less.

[0082] Next, the steel sheet that has completed intermediate annealing is subjected to secondary cold rolling. Since the secondary cold rolling is identical to the primary cold rolling, a detailed explanation is omitted. Through secondary cold rolling, the thickness of the steel sheet can be manufactured to 0.10 to 0.50 mm.

[0083] The aforementioned intermediate annealing step and secondary cold rolling step may be repeated two or more times. However, in one embodiment of the present invention, if repeated two or more times, the grain shape in the thickness direction of the steel plate may not be properly controlled. Accordingly, the intermediate annealing step and secondary cold rolling step may be performed only once.

[0084] Next, the steel sheet is cold-rolled and annealed. The cold-rolled sheet annealing step can be performed at a temperature of 850°C to 1200°C and a dew point temperature of 0°C or lower.

[0085] If the cracking temperature is too low, grain growth may not occur sufficiently, and it may be difficult to secure magnetism. If the cracking temperature is too high, surface defects may occur. More specifically, the cracking temperature may be 900 to 1100°C. More specifically, annealing may be performed at a dew point temperature of -70°C to 0°C.

[0086] In one embodiment of the present invention, by annealing a cold-rolled sheet at a dew point temperature of 0°C or lower, the grain shape in the thickness direction of the steel sheet can be appropriately controlled. For example, if decarburization is performed by setting the dew point temperature high during the cold-rolled sheet annealing step, the grain length in the thickness direction of the steel sheet increases, and it may be difficult to appropriately secure the ratio of the major axis to the minor axis of the electrical steel sheet produced at the end. Annealing can be performed in an atmosphere of 99 volume% or more hydrogen.

[0087] The annealing step of the cold-rolled sheet can be performed for 30 seconds to 5 minutes. Grain growth can be sufficiently achieved within the aforementioned time range.

[0088] After the first cold rolling step, the process up to the cold-rolled sheet annealing step can be performed as a continuous process. A continuous process means that there is no batch process, such as winding the steel sheet into a coil for annealing. As previously mentioned, a continuous process is possible because the intermediate annealing step or the cold-rolled sheet annealing step is completed within a few minutes or less.

[0089] Specific embodiments of the present invention are described below. However, the following embodiments are merely specific examples of the present invention, and the present invention is not limited to the following embodiments.

[0090]

[0091] Examples

[0092] A slab containing Si:2.0% and C:0.101% by weight, with the remainder being Fe and unavoidable impurities, is heated at a temperature of 1270°C, then undergoes rough rolling and finish rolling, followed by hot rolling at a finishing rolling temperature of 950°C, hot-rolled sheet annealing at 930°C for 3 minutes at a dew point temperature of 15°C, first cold rolling, intermediate annealing under the manufacturing conditions of Table 1, second cold rolling, and cold-rolled sheet annealing in that order. After the second cold rolling, the thickness was 0.23 mm.

[0093] The average grain size, average aspect ratio, GOSS area ratio, magnetic flux density, iron loss (W10 / 50), iron loss (W10 / 400), and machinability of the fabricated specimens were measured and are shown in Table 2.

[0094] The microstructure of the specimens was observed in the plane perpendicular to the thickness direction (TD plane). The average grain size was analyzed using commercial TSL OIM Analysis software after observing the microstructure with EBSD, and the GOSS area ratio was determined based on the EBSD measurement results regarding the crystals with respect to the rolling direction. <100> A texture was obtained in which the orientations are parallel and the {110} planes of the crystal are parallel to the rolled plane. The deviation was limited to within 15°. The average aspect ratio was calculated by measuring the lengths of the major and minor axes of each grain from images of the TD plane of the specimen observed under an optical microscope.

[0095] The magnetic flux density (B50) and iron loss (W15 / 50, W10 / 400) were measured using Brockhaus magnetic measuring equipment in a direction parallel to the rolling direction. The magnetic flux density (B50) was measured under conditions of a frequency of 50 Hz and a magnetic field magnitude of 5000 A / m, and the W15 / 50 iron loss was measured under conditions of a frequency of 50 Hz and a magnetic flux density of 1.5 T. Additionally, the W10 / 400 iron loss was measured under conditions of a frequency of 400 Hz and a magnetic flux density of 1.0 T.

[0096] Machinability was determined by measuring the length of the burr generated after shear processing using a scanning electron microscope (SEM), and indicating X (failure) if the length was 50 μm or more, and O (pass) if it was less than 50 μm.

[0097] Specimen Intermediate Annealing Conditions Cold Rolled Plate Annealing Conditions Heating Zone Cracking Zone Residual C Content (wt.%) Annealing Temperature (°C) Dew Point Temperature (°C) Annealing Time (s) Heating Zone Dew Point Annealing Cracking Zone Dew Point Annealing Temperature (°C) Temperature (°C) Time (s) Temperature (°C) Temperature (°C) Time (s) 190 256 628 48 44 175 0.01 810 20-206 528 95 4258 86 232 16 20.02 79 82-158 139 127 268 88 128 16 80.00 99 52-109 249 216 87 29 105 11 7 20.01 11 04 2-128 25 100 338 68 98 725 1 920.0621011-18686102178751011671980.0211025-8657908655852621680.183940-20988892566289481650.127850-207198955768870481550.10199758621088065885891720.35810245572119155462880561630.113968-1666128913266876531620.1421023-1864

[0098] Specimen Residual C Content (wt.%) Microstructure Magnetic Machinability Remarks Solid Grain Average Grain Size (㎛) Average Aspect Ratio Goss Fraction Magnetic Flux Density (T, B50) Iron Loss (W / kg, W15 / 50) Iron Loss (W / kg, W10 / 400) 10.0186 11.813 0.31.902 1.854 13.200 Example 1 20.02658 1.6828.11.890 1.857 13.310 Example 2 30.00852 1.5727.31.887 1.875 13.570 Example 3 40.01178 1.5428.91.895 1.801 12.520 Example 4 50.06062 1.9126.81.867 1.910 13.870 Example 5 60.02067 2.132 4.21.82 11.985 14.64O Example 6 70.182221.55 10.81.76 24.99 121.34O Comparative Example 1 80.125 281.73 12.41.78 63.39 218.91O Comparative Example 2 90.08 46 82.62 28.71.91 13.62 119.55X Comparative Example 3 100.152 55 2.42 21.51.82 42.60 416.05X Comparative Example 4 110.110 501.72 18.71.78 43.15 117.81O Comparative Example 5 120.139 651.89 13.81.76 93.28 718.04O Comparative Example 6

[0099] As shown in Tables 1 and 2, when process conditions are properly controlled, it can be confirmed that the texture of the steel sheet is properly formed and that both magnetic properties and workability are excellent.

[0100] On the other hand, it can be confirmed that in Comparative Examples 1 and 2, the dew point is not properly controlled during the intermediate annealing stage, decarburization is not properly performed, and as a result, the magnetic properties are inferior.

[0101] Comparative Examples 3 and 4 are examples in which decarburization was performed in a high dew point atmosphere during the cold-rolled sheet annealing process. Although the magnetic properties are at a level equivalent to the inventive example, it can be confirmed that the machinability is inferior and therefore not suitable for use as an axial motor.

[0102] Comparative Examples 5 and 6 are cases where the dew point temperature of the cracking zone during the intermediate annealing process is at an equivalent or higher level than that of the heating zone, and it can be confirmed that decarburization is not properly carried out and, as a result, the magnetic properties are inferior.

[0103] In addition, Figure 1 shows a photograph of a cross-section of an electrical steel sheet for an axial motor manufactured in Example 1, observed through an optical microscope. As shown in Figure 1, the electrical steel sheet for an axial motor according to one embodiment of the present invention forms grains of an appropriate shape, which contributes to improved processability.

[0104] In FIG. 2, the surface of the electrical steel sheet for an axial motor manufactured in Example 1 is shown through EBSD analysis. As shown in FIG. 2, the electrical steel sheet for an axial motor according to one embodiment of the present invention has grains of an appropriate shape formed on its surface, which contributes to the improvement of magnetism.

[0105] In FIG. 3, the surface of the electrical steel sheet for an axial motor manufactured in Example 1 is analyzed using the Orientation Distribution Function (ODF). As shown in FIG. 3, the electrical steel sheet for an axial motor according to one embodiment of the present invention can appropriately secure Goss grains, which contributes to the improvement of magnetism.

[0106]

[0107] The present invention is not limited to the above embodiments and / or examples 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 changing the technical concept or essential features of the invention. Therefore, the embodiments and / or examples described above should be understood as illustrative in all respects and not restrictive.

Claims

1. In a cross-section in the thickness direction of the steel plate, the ratio of the major axis to the average minor axis of the grains is 1 to 2.3, and {110} <001> Electrical steel sheet having a ratio of grains with an orientation within 15° of the orientation of 20% or more of the area.

2. In Paragraph 1, Electrical steel sheet having an average grain size of 50 to 100 μm in the cross-section in the thickness direction of the steel sheet.

3. In Paragraph 1, An electrical steel sheet having 70% or more of the area of ​​grains on the surface of the steel sheet in which the ratio (D2 / D1) of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) is 0.5 or greater.

4. In Paragraph 1, Electrical steel sheet comprising, in weight percent, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

5. In Paragraph 4, Electrical steel sheet further containing Mn: 0.1 wt% or less and S: 0.005 wt% or less.

6. A step of manufacturing a hot-rolled steel sheet by hot-rolling a slab; A step of manufacturing a primary cold-rolled plate by primary cold-rolling the above hot-rolled steel plate; Step of intermediate annealing the above primary cold-rolled sheet; A step of manufacturing a second cold-rolled plate by second cold-rolling the above first cold-rolled plate and It includes a cold-rolled sheet annealing step for annealing the above secondary cold-rolled sheet, and The above intermediate annealing step includes a heating step and a cracking step, and A method for manufacturing an electrical steel sheet in which the difference in dew point temperature (heating step-cracking step) between the heating step and the cracking step is 10 to 45℃.

7. In Paragraph 6, The above heating step is a step of heating the temperature of the steel plate from 50℃ to the cracking temperature, and a method for manufacturing an electrical steel plate having a dew point temperature of 30 to 80℃.

8. In Paragraph 6, A method for manufacturing an electrical steel sheet in which the cracking step is a cracking step at a cracking temperature of 800 to 1100℃ and the dew point temperature is 25 to 75℃.

9. In Paragraph 6, A method for manufacturing an electrical steel sheet in which the above slab comprises, in weight percent, Si: 0.3% to 7.0%, C: 0.01% to 0.4%, and the remainder being Fe and unavoidable impurities.

10. In Paragraph 9, A method for manufacturing an electrical steel sheet, wherein the above slab further comprises Mn: 0.1 wt% or less and S: 0.005 wt% or less.

11. In Paragraph 6, A method for manufacturing an electrical steel sheet, comprising a step of manufacturing the hot-rolled steel sheet followed by a step of annealing the hot-rolled sheet, wherein the hot-rolled sheet annealing step is performed at a temperature of 850°C to 1000°C and a dew point temperature of 0°C or lower.

12. In Paragraph 6, The above cold-rolled sheet annealing step is a method for manufacturing an electrical steel sheet by annealing at a temperature of 850°C to 1200°C and a dew point temperature of 0°C or lower.

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