Grain-oriented electrical steel sheet and method for refining magnetic domain thereof

Abstract

In one embodiment of the present invention, a magnetic domain refinement method for a grain-oriented electrical steel sheet includes a step of superimposing light spots of two or more kinds of laser light having different light spot shapes and then irradiating the same to form a groove.

Description

Technical Field

[0001] One embodiment of the present invention relates to a grain-oriented electrical steel sheet and a method for refining its magnetic domains. More specifically, one embodiment of the present invention relates to a grain-oriented electrical steel sheet and a method for refining its magnetic domains, which ensures sufficient groove depth by irradiating the steel sheet surface with two or more superimposed lasers, while greatly reducing molten byproducts such as hill-up and sputter, thereby exhibiting excellent iron loss characteristics. Background Technology

[0002] Grain-oriented electrical steel sheets possess excellent magnetic properties and are commonly used as core materials for transformers. The manufacture of these sheets involves a rolling and annealing process specific to electrical steel sheet manufacturing, forming a {110} pattern across the entire sheet. <001> Orientation-recrystallized Gaussian texture.

[0003] To address climate change, global efforts are increasingly strengthening the accounting of greenhouse gas emissions. For transformer cores, the factors influencing greenhouse gas emission accounting are directly related to the efficiency of transformers using electrical steel sheets. Furthermore, the iron losses and magnetic flux density of the electrical steel sheets, i.e., their magnetic properties, play a crucial role in transformer core efficiency.

[0004] The magnetic flux density of electrical steel sheets is determined by the degree of aggregation of easily magnetized crystal axes in the crystal structure, i.e., the higher the crystal orientation, the higher the magnetic flux density. Therefore, the manufacturing process of electrical steel sheets may have a significant impact.

[0005] According to the IEC 60404-3 standard, for the iron loss of electrical steel sheets, the W17 / 50 [W / kg] value measured when a 50Hz magnetic field is applied at a maximum magnetic flux density of 1.7T is called the guaranteed iron loss value of the core material, and this value is used as the standard for measuring the iron loss of electrical steel sheets. However, in transformer design, the W15 / 50 [W / kg] value measured when a relatively lower maximum magnetic flux density of 1.5T is applied at a 50Hz magnetic field is also used. In transformers, the lower this iron loss value, the better the efficiency.

[0006] Therefore, for electrical steel sheets, the higher the magnetic flux density and the lower the iron loss, the better they can be used as transformer cores with high efficiency. Of the two, magnetic flux density and iron loss, iron loss is considered a more important indicator because, with the general improvement in the manufacturing processes of electrical steel sheets, the technology to ensure high magnetic flux density has developed to a level sufficient to support transformer efficiency.

[0007] Such iron losses are divided into eddy current losses and hysteresis losses. Hysteresis losses decrease with increasing magnetic flux density; therefore, in grain-oriented electrical steel sheets, eddy current losses play a crucial role in controlling total iron losses. Eddy current losses are further divided into classical eddy current losses and anomalous eddy current losses. Classical eddy current losses are directly proportional to the thickness of the steel sheet; therefore, the thinner the steel sheet, the smaller the classical eddy current losses. Thus, controlling anomalous eddy current losses has become an important technique for reducing iron losses.

[0008] Among these iron losses, eddy current losses decrease as the spacing between the magnetic walls of the 180° magnetic domains, which are the magnetic domains of the rolling direction, narrows. Therefore, iron losses can be reduced by refining the magnetic domains of the electrical steel sheet.

[0009] Domain refinement in electrical steel sheets refers to the process of applying physical stimulation to grains composed of a single magnetic domain, causing them to separate into multiple magnetic domains. Domain refinement methods can include laser irradiation, electron beam irradiation, plasma treatment, etching, or roll forming. Furthermore, based on whether the domain refinement effect is maintained after stress-relief annealing (SRA), it is classified into permanent domain refinement and temporary domain refinement.

[0010] In magnetic domain refinement technology, the technique that maintains the domain refinement effect even after stress-relief annealing (SRA) improves iron loss is called permanent magnetic domain refinement technology. Examples of permanent magnetic domain refinement techniques include laser methods targeting cold-rolled steel sheets or steel sheets that have undergone secondary recrystallization, surface transfer methods using rotating wedge-shaped cutter rollers (groove transcription), and etching methods that form grooves through electrochemical etching in a solution. Surface transfer methods use rotating cutter rollers to form grooves; therefore, when the steel sheet thickness increases or decreases beyond a critical value, the applied load changes, making it difficult to maintain the durability of the cutter rollers and thus difficult to precisely control the groove depth at high speeds. Chemical etching methods form grooves through the anodic reaction of the steel sheet in a solvent, making high-speed groove formation difficult. For laser methods, when forming grooves by local melting of steel plates, a high-power oscillator is required to achieve high-speed groove formation. Furthermore, hill-ups generated near the grooves need to be removed by physical or chemical methods. Therefore, it is necessary to clean the grooves with a brush after formation or to introduce processes such as coating with oxides before formation. Summary of the Invention

[0011] (a) Technical problems to be solved One embodiment of the present invention provides an oriented electrical steel sheet and a method for refining its magnetic domains. More specifically, one embodiment of the present invention provides an oriented electrical steel sheet and a method for refining its magnetic domains, which ensures sufficient groove depth by irradiating the steel sheet surface with two or more superimposed lasers, while greatly reducing molten byproducts such as hill-up and sputter, thereby exhibiting excellent iron loss characteristics.

[0012] (II) Technical Solution In one embodiment of the present invention, the magnetic domain refinement method for oriented electrical steel sheets includes the step of superimposing the light spots of two or more lasers with different light spot shapes to irradiate and form grooves.

[0013] The laser includes a first laser and a second laser, and the first spot of the first laser beam and the second spot of the second laser beam can be superimposed by more than 10%.

[0014] The laser includes a first laser and a second laser, and the energy density of the first laser beam can be 1.1 to 4.0 times that of the second laser beam.

[0015] The first and second lasers can be selected from CO2 lasers, fiber lasers, YAG lasers, ruby ​​lasers, sapphire lasers, disk lasers, diode lasers, or UV lasers.

[0016] The first and second lasers can each have a power of 10 to 2000W.

[0017] The first laser and the second laser can have different wavelengths.

[0018] At the superposition position, the interval between the irradiation time of the first laser beam and the irradiation time of the second laser beam can be less than 16ms.

[0019] The groove can be a linear shape that extends in a direction intersecting the rolling direction.

[0020] The depth of the trench can be 5 to 15% of the thickness of the electrical steel plate.

[0021] The length direction of the groove can form an angle of 75 to 105° with the rolling direction.

[0022] The grooves can be formed intermittently, from 2 to 10, along the rolling direction perpendicular to the electrical steel sheet.

[0023] (III) Beneficial Effects According to one embodiment of the present invention, by using superimposed laser for optimal magnetic domain refinement, the magnetism can be further improved, while the generation of molten byproducts such as bulges and spatters on the surface of the steel plate can be effectively suppressed.

[0024] According to one embodiment of the present invention, using a long-wavelength laser can easily achieve high average power and ensure the reliability of the processing line, while simultaneously irradiating a short-wavelength laser to minimize the formation of magnetic domains, thereby effectively improving magnetism. Attached Figure Description

[0025] Figure 1 This is a graph showing the light absorption rate of the steel plate according to the laser wavelength.

[0026] Figure 2 This is a schematic diagram illustrating a magnetic domain refinement concept that utilizes superimposed lasers to form trenches according to an embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram illustrating a superimposed laser spot according to an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram illustrating a superimposed laser spot according to yet another embodiment of the present invention.

[0029] Figure 5 This is a schematic diagram illustrating a case where laser light is applied twice with a time interval, rather than superimposed, according to an embodiment of the present invention. Detailed Implementation

[0030] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below can also be described as a second part, component, region, layer, or segment.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in the specification can specifically refer to a feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, and / or components.

[0032] If one part is described as being on top of another part, then other parts may exist directly on top of or in between the other part. If one part is described as being directly on top of another part, then no other parts exist in between.

[0033] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0034] The embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0035] In one embodiment of the present invention, the depth of the trench is sufficiently ensured by irradiating the surface of the electrical steel plate with superimposed laser light, while suppressing the formation of molten byproducts such as bulges and spatters on the surface of the steel plate, so as to impart excellent iron loss characteristics.

[0036] One embodiment of the present invention includes the step of superimposing the light spots of two or more lasers with different light spot shapes to form a groove.

[0037] As one of the methods to improve iron loss in grain-oriented electrical steel sheets, the method of using lasers to form grooves on the surface of the steel sheet to refine magnetic domains is favored.

[0038] For the magnetic domain refinement process of grain-oriented electrical steel sheets, such as Figure 2 As shown, the laser travels and irradiates along a direction intersecting the rolling direction (RD direction), thereby forming the groove 10. The groove can have a dotted or continuous linear groove shape. Figure 2 The image illustrates a linear groove. A linear or linear groove refers not only to solid lines, but also to discontinuous lines such as dashed or broken lines, and also to grooves that are microscopically serrated but macroscopically straight, thus substantially encompassing all grooves that form a linear shape.

[0039] Creating grooves in a steel plate using a laser involves irradiating the steel plate with a laser to melt and vaporize a portion of it, leaving the melted and vaporized portion as a groove shape.

[0040] At this point, the depth of the trench is proportional to the energy density (power density) of the laser per unit time, and is also affected by the laser absorption rate of the steel plate surface.

[0041] However, when irradiated with a laser, the depth of the groove increases with the total laser irradiation energy. But when the energy irradiated onto the steel plate exceeds the required value, molten byproducts such as bulges and spatter will remain on the surface of the steel plate, which will have an adverse effect on the magnetism and therefore needs to be suppressed. Therefore, when irradiating with a laser, it is preferable to irradiate a large amount of energy with a high energy absorption rate over a very narrow area for a short time.

[0042] Furthermore, the interaction conditions between the laser beam and the steel plate are influenced by the characteristics of the laser and its absorptivity on the steel plate. The absorptivity is affected by the surface roughness of the steel plate, its temperature, the absorption characteristics of the steel plate surface, and the laser wavelength. However, when the manufacturing conditions of the steel plate remain constant across its entire surface, the surface roughness, temperature, and absorption characteristics of the steel plate remain constant. In this case, the absorptivity of the laser beam on the steel plate depends on the laser wavelength.

[0043] In other words, when the manufacturing conditions of the steel plate are constant, the laser absorption rate is affected by the laser wavelength. For example... Figure 1 As shown, the laser absorption rate of the steel plate is approximately 35 to 40% for short wavelengths (e.g., YAG or fiber lasers at 1.06 μm) and approximately 5 to 10% for long wavelengths (e.g., CO2 lasers at 10.6 μm), which is relatively low.

[0044] As mentioned above, in the process of refining magnetic domains by laser in oriented electrical steel sheets, using short-wavelength lasers is more efficient than using long-wavelength lasers in order to ensure stable iron loss characteristics.

[0045] On the other hand, sometimes an insulating coating, mainly composed of phosphate and silicon dioxide, is formed on the surface of electrical steel sheets targeted for magnetic domain refinement treatment, with a thickness ranging from a few micrometers to tens of micrometers. These coatings exhibit relatively low absorption rates for short-wavelength lasers (e.g., 1.06 μm YAG or fiber lasers), but higher absorption rates for long-wavelength lasers (e.g., 10.6 μm CO2 lasers). Therefore, the thickness of the insulating coating needs to be considered under long-wavelength laser conditions, but can be considered less under short-wavelength laser conditions compared to long-wavelength laser conditions.

[0046] As mentioned above, short-wavelength lasers and long-wavelength lasers have different characteristics. Therefore, when short-wavelength lasers and long-wavelength lasers are used simultaneously, the advantages of each laser in magnetic domain refinement are given priority, without producing side effects, thereby causing a multiplicative (synergistic) effect.

[0047] The term "superimposed laser" here refers to the use of two or more lasers with different spot shapes to irradiate the steel plate surface, where the spot of one laser beam on the steel plate surface is partially or entirely located within the spot of another laser beam. Therefore, in one embodiment of the invention, superimposed lasers with different wavelengths include not only cases where the spot of one laser beam is completely superimposed on the spot of another laser beam, but also all cases of partial superimposition. On the other hand, regarding irradiation time, when a time interval exists, the steel plate surface will cool rapidly during that interval, making it difficult to obtain the effect of superimposed laser irradiation. Therefore, it is preferable to irradiate two or more lasers simultaneously; specifically, the interval between the irradiation time of the first laser beam and the irradiation time of the second laser beam can be less than 16 ms. Figure 3 This is an example of partially superimposed illumination of the first laser beam 21 and the second laser beam 22. Figure 4 This is an example of completely superimposing the first laser beam 21 and the second laser beam 22. As mentioned above, Figure 5 The condition where laser beams do not overlap at a specific moment is defined as non-overlapping irradiation when the time interval between irradiating a specific location exceeds 16ms.

[0048] In one embodiment of the present invention, the light spot refers to the light spot on the surface of the steel plate. Figure 3 The diagram schematically shows the first spot of the first laser beam 21 and the second spot of the second laser beam 22.

[0049] The first spot of the first laser beam and the second spot of the second laser beam overlap by more than 10%. "More than 10%" refers to the width of the overlapped area. W With the width B of the first laser beam 1W The width B of the second laser beam 2W The ratio of the width of the smaller laser beam. Figure 3 The width B of the first laser beam 1W In the case of smaller values, the superposition ratio can be O. W / B 1W Perform the calculation.

[0050] The width of a laser beam refers to the length of the laser beam in the direction perpendicular to the length of the trench (or the direction of laser irradiation, X direction) (Y direction). The length of a laser beam refers to the length of the laser beam in the direction of the length of the trench (or the direction of laser irradiation, X direction). Figure 3 The length B of the first laser beam is shown in the figure. 1L The length B of the second laser beam 2L .

[0051] Figure 4The diagram schematically shows that the first spot of the first laser beam 21 is located within the second spot of the second laser beam 22, and the superposition ratio is calculated to be 100%.

[0052] On the other hand, in one embodiment of the invention, the groove has an inverted bell shape by irradiating superimposed laser light.

[0053] The first and second lasers can be selected from CO2 lasers, fiber lasers, YAG lasers, ruby ​​lasers, sapphire lasers, disk lasers, diode lasers, or UV lasers.

[0054] More specifically, the first laser A, which is a short-wavelength laser, can be a laser with a relatively short wavelength, such as fiber (Er-Fiber, Yb-Fiber, Tm-Fiber) lasers, YAG (Nd:YAG, Yb:YAG) lasers, ruby ​​lasers, and sapphire lasers. Furthermore, this first laser can also be a disk laser (1.03 μm), a diode laser (0.808 to 0.980 μm), or a UV laser (0.150 to 0.355 μm).

[0055] Furthermore, the second laser, which can be a long-wavelength laser, can be a laser with a wavelength relatively longer than the short-wavelength laser. For example, a CO2 laser is preferred as the second laser. However, if a UV laser (0.150~0.355μm) is used as the first laser, which is a short-wavelength laser, then any laser can be used as the second laser, as long as its wavelength is longer than that of the first laser. In this case, for example, when a UV laser (0.150 to 0.355μm) is used as the first laser, a YAG laser can also be used as the second laser.

[0056] In the following text, taking the case of using a fiber laser as the first laser with a short wavelength and a CO2 laser as the second laser with a long wavelength as examples, the magnetic domain refinement method using superimposed laser 30 will be described in further detail.

[0057] The fiber laser used as the primary laser employs a short wavelength with relatively high laser absorption rate on steel plates, thus allowing the incident energy sufficient to form a trench to irradiate a narrow area for a shorter time. Furthermore, the fiber laser, as the primary laser, has a narrow incident energy range, which minimizes the formation of molten byproducts. However, irradiating only the primary laser is insufficient to deliver enough energy to form a trench.

[0058] On the other hand, for the CO2 laser used as a second laser, the average power can be high, ranging from several hundred watts to several kilowatts or more, depending on the steel plate speed. Therefore, the CO2 laser as a second laser is suitable as a preheating method. However, the CO2 laser as the second laser B has a low laser absorption rate on the steel plate, so excessive energy is required to form the groove using the CO2 laser alone, which will generate a large amount of molten byproducts in the process.

[0059] Therefore, a fiber laser with a relatively short wavelength is used as the first laser and as the main laser for forming the trench, while a CO2 laser with a relatively long wavelength is used as an auxiliary laser for preheating.

[0060] In this case, by refining the magnetic domains, 180° magnetic domains (opposite magnetic poles of willow leaf domains) are formed in the surface direction due to magnetoelastic energy, and 90° magnetic domains are formed in the thickness direction to reduce magnetoelastic energy, thereby narrowing the spacing between the magnetic domains and ultimately reducing abnormal eddy current losses.

[0061] The main laser is preferably positioned in an area where the beam intensity of the auxiliary laser cross-section is greater than 25%. More preferably, the main laser should be positioned in an area where the beam intensity of the auxiliary laser cross-section is greater than 30%. When the main laser position on the final steel plate surface is located in an area where the beam intensity of the auxiliary laser cross-section is greater than 25%, the laser absorption rate of the main laser can be maximized. That is to say, when it is located in an area where the beam intensity is less than 25%, there is a disadvantage that the laser absorption rate of the steel plate surface cannot be significantly improved by the main laser.

[0062] As described above, in the magnetic domain refinement method according to an embodiment of the present invention, a short-wavelength fiber laser is used as the first laser, while a long-wavelength CO2 laser is used as the second laser, thereby forming trenches 10 of sufficient depth and minimizing the formation of molten byproducts.

[0063] At this point, the fiber laser spot, which serves as the short-wavelength first laser, irradiates the surface of the steel plate and preferably has an approximately circular shape, with a diameter (B) W1 0B L1 The width (B) can range from 5 to 500 μm. Furthermore, for fiber laser spot size, its width (B)... W1 The length is 5 to 500 μm, while the length (B) L1 It can also be the length of the CO2 laser spot used as a second laser, which is either below or above the length of the spot.

[0064] When the beam width B of the optical fiber used as the first laser W1When the beam width is reduced to less than 5 μm, the energy density is concentrated in a narrow region, which may lead to degradation of magnetic flux density and iron loss, and complicates the optical system structure. Furthermore, when the beam width B of the fiber used as the first laser... W1 When the size increases to over 500 μm, the width of the grooves along the length of the steel plate increases, leading to the formation of numerous molten byproducts such as bulges and spatter, which may result in a decrease in magnetic flux density. More specifically, the width and length of the light spot can range from 10 to 100 μm.

[0065] On the other hand, the spot of the CO2 laser, which serves as a long-wavelength second laser, irradiating the surface of the steel plate is preferably elliptical, with a beam width B. 2W The beam length is 100 to 400 μm. 2L The wavelength ranges from 0.4 to 20 mm. Furthermore, the spot size of long-wavelength CO2 lasers can also be circular with a radius of 100 μm or more.

[0066] In order to increase the CO2 beam width B of the second laser 2W When the size is kept within 100μm, the mirror optical system becomes as complex as fiber lasers, and therefore is not ideal. When it becomes larger than 400μm, a large number of molten byproducts such as bulges and spatters are formed, which may lead to a decrease in magnetic flux density.

[0067] The reason for limiting the spot size of the CO2 laser as a long-wavelength second laser, as described above, is that when the laser is irradiated at high speed onto the surface of a high-speed moving steel plate, the effect range of the laser beam acting on the steel plate is taken into account.

[0068] The superimposed use of lasers according to an embodiment of the present invention will be described in further detail.

[0069] like Figure 3 and Figure 4 As shown, the superposition of the first laser beam 21 and the second laser beam 22 on the final steel plate surface refers to controlling the spot size of the first laser beam 21 and the spot size of the second laser beam 22 to superimpose them. That is, for the laser spot 20 irradiating the steel plate surface, as... Figure 4 As shown, when the first laser beam 21 is completely located within the range of the larger second laser beam 22 from a planar perspective, this is called beam "superposition," as... Figure 3 As shown, this further includes a portion of the first laser beam 21 located within the range of the second laser beam 22, also referred to as beam "overlap". Further, as... Figure 5As shown, when the laser beams are not superimposed at a specific moment, they are considered not superimposed. However, for a specific location, if the interval between the irradiation time of the first laser beam and the irradiation time of the second laser beam is less than 16ms, they are considered to be irradiated simultaneously. If this time range is exceeded, the steel plate surface will cool rapidly, making it difficult to fully obtain the effect of superimposed laser irradiation. The time interval refers to the distance from when the second laser (or the first laser) irradiates until the width O of its superimposed area reaches the point where the first laser (or the second laser) travels. W The time it takes to reach its maximum. Figure 5 In the case where, at a specific moment, the laser beams do not overlap, but the first laser beam 21 moves to the dashed circle within 16ms, thereby overlapping and irradiating the position irradiated by the second laser beam 22, this is also considered as overlapping irradiation.

[0070] In one embodiment of the present invention, for the oscillation mode of the laser beam used, both the first laser and the second laser are preferably continuous wave lasers that generate laser light continuously, but pulsed lasers can also be used.

[0071] The energy density of the first laser beam can be 1.1 to 4.0 times that of the second laser beam. As mentioned earlier, the higher energy density of the first laser beam allows for the application of higher energy to a narrower area, resulting in deeper trenches and reducing molten byproducts. Conversely, the relatively lower energy density of the second laser beam allows for the application of lower energy to a larger area, thereby increasing the absorption rate of the first laser beam.

[0072] Furthermore, regarding the quality of the laser beams used, both the first and second lasers preferably use the Gaussian mode of TEM00, but the multi-transverse mode of TEMmn can also be used.

[0073] However, for the heterogeneous wavelength superimposed laser beam 20 irradiating the surface of the steel plate according to an embodiment of the present invention, the formation of the groove can be minimized in the length direction of the steel plate, while the depth of the groove can be increased. Therefore, there is no specific limitation on the beam shape or beam quality of each laser.

[0074] The first and second lasers each have a power of 10 to 2000 W. More specifically, the first laser has a power of 1000 to 2000 W, and the second laser has a power of 100 to 700 W. These power ranges for each laser are proposed when the steel plate travels at a speed of 10 to 30 meters per minute (mpm). The laser power can be optimally controlled according to the steel plate's travel speed, and the power can also exceed these ranges depending on the steel plate's travel speed.

[0075] When the laser beam 30, which is a superposition of the first and second lasers as described above, is irradiated onto the surface of the steel plate, the interval between them (i.e., the interval between the grooves in the steel plate rolling direction) can be 2 to 10 mm, the angle between the rolling direction and the laser travel direction (groove length direction, X direction) can be 75 to 105°, and the scanning speed is preferably 0.1 to 300 m / s (sec).

[0076] At this point, the electrical steel sheet used can be cold-rolled sheet, steel sheet after one recrystallization annealing, or steel sheet after two recrystallization annealing.

[0077] In addition, when the irradiation interval of the superimposed laser beam 20 irradiating the steel plate surface is too narrow (less than 2 mm), the influence of the heat-affected zone increases, and the magnetic flux density and iron loss deteriorate. When the irradiation interval is 10 mm or more, the thermal shock effect used to ensure the magnetic domain refinement effect is reduced, making it difficult to achieve the desired effect.

[0078] Furthermore, when irradiating the surface of the steel plate with the superimposed laser beam 20, the irradiation can be performed from a direction perpendicular to or inclined to the rolling direction of the steel plate. The angle between the rolling direction and the laser travel direction (groove length direction, X direction) can be 75 to 105°. If the angle exceeds this range, the desired magnetic domain refinement effect may not be produced.

[0079] In addition, the scanning speed of the superimposed laser is the same as the traveling speed of the steel plate. When the traveling speed increases, the scanning speed needs to be even faster. Therefore, it is preferably 0.1 to 300 m / s, which refers to the value exemplified under the condition of 15 m / min.

[0080] On the other hand, such as Figure 3 and Figure 4 As shown, this indicates that the first and second laser beams are simultaneously superimposed, excluding... Figure 5 The time intervals shown indicate that superimposed irradiation is performed. Simultaneous irradiation means that the interval between the irradiation time of the first laser beam and the irradiation time of the second laser beam at a specific location is less than 16ms. If this time range is exceeded, the steel plate surface will cool rapidly, making it difficult to achieve the effect of superimposed laser irradiation. The time interval refers to the period after the second laser (or the first laser) is irradiated, during which the first laser (or the second laser) travels until the width O of its superimposed area is reached. W The time it takes to reach its maximum.

[0081] The groove can be a linear shape that extends in a direction intersecting the rolling direction.

[0082] The depth of the trench can be 5 to 15% of the thickness of the electrical steel plate.

[0083] The length direction of the groove can form an angle of 75 to 105° with the rolling direction.

[0084] The grooves can be formed intermittently, from 2 to 10, along the rolling direction perpendicular to the electrical steel sheet. On the other hand, when grooves are formed by irradiating the surface of the electrical steel sheet with a superimposed laser according to an embodiment of the present invention, the W17 / 50 iron loss improvement rate of such steel sheet is preferably 5.0% or more. More specifically, it is preferably 9% or more.

[0085] The following describes in detail a method for manufacturing an oriented electrical steel sheet according to an embodiment of the present invention.

[0086] Manufacturing of cold-rolled steel sheets To manufacture oriented electrical steel sheets, a slab of the electrical steel sheet substrate is first manufactured.

[0087] As long as the easily magnetized axes are aligned in a certain direction, thus possessing the function of electrical steel sheets, there are no further restrictions on the chemical composition and microstructure of the slab. However, to illustrate, the chemical composition of the slab is as follows.

[0088] The composition, by mass%, includes the following components: C: less than 0.08% and excluding 0%; Si: 1.0~6.5%; Mn: 0.005~3.0%; any one or more of Nb, V, and Ti: less than 0.070% in total; any one or more of Cr, Sn, and Sb: less than 2.5% in total; Al: less than 2.0% and excluding 0%; any one or more of P and S: less than 0.100% in total and excluding 0%; Cu and Sn: less than 1.0% in total; rare earth elements and other impurities: less than 0.2% in total, with the balance consisting of Fe.

[0089] (C: below 0.08% and excluding 0%) Carbon (C) is an unavoidable element in steel, but it causes magnetic aging, leading to a deterioration of magnetic properties. Therefore, it is preferable to control its content to an appropriate level. If the C content in the steel sheet is too low, phase transformation will not occur sufficiently during the manufacturing process, resulting in an uneven microstructure and an unstable secondary recrystallization structure. Conversely, if the C content is too high, carbides will become coarse during manufacturing, leading to excessive precipitation and insufficient decarburization. Consequently, the aggregation degree of the Gaussian texture decreases, potentially disrupting the secondary recrystallization texture. Therefore, the C content in the steel sheet is below 0.08%, and more preferably 0.001 to 0.040%.

[0090] (Si: 1.0~6.5%) Silicon (Si) is a fundamental component of grain-oriented electrical steel sheets, playing a role in increasing the resistivity of the steel and reducing iron loss. If the content is less than 1.0%, the resistivity decreases, eddy current losses increase, and iron loss characteristics deteriorate, rendering the effect of Si addition unattainable. If the content is above 6.5%, the brittleness of the steel sheet increases and the toughness decreases, potentially leading to sheet fracture during rolling. Furthermore, nitride formation cannot be fully achieved during the manufacturing process, and sufficient grain suppression force required for secondary recrystallization during the final high-temperature annealing process cannot be ensured. Therefore, a Si content of 1.0–6.5% is preferred.

[0091] (Mn: 0.005~3.0%) Manganese (Mn) increases resistivity and reduces eddy current losses, thereby lowering total iron losses. Manganese is an important element; it not only reacts with sulfur in the base steel state to form Mn-based sulfides, but also reacts with nitrogen introduced during nitriding treatment along with silicon to form (Al, Si, Mn)N precipitates. This inhibits the growth of primary recrystallized grains, inducing secondary recrystallization and affecting the surface quality of the final product. However, if the Mn content is too low, the surface quality of the final product may deteriorate. Furthermore, if the Mn content is too high, the austenite phase fraction increases significantly, disrupting the Gaussian texture, reducing magnetic flux density, and causing excessive oxide layer formation during decarburization annealing, which may hinder decarburization. Therefore, a Mn content of 0.005–3.0% is preferred.

[0092] (Any one or more of Nb, V, and Ti: total less than 0.05%) Niobium (Nb), vanadium (V), and titanium (Ti) are elements that react with C and N to form precipitates during the manufacturing process. However, if too much is added, it will remain in the steel plate after secondary recrystallization annealing, thereby reducing the magnetic properties of the steel plate. Therefore, it is preferable to control the total content of one or more elements selected from Nb, V, and Ti to below 0.05%.

[0093] (Cr, Sn, Sb: any one or more of the following: total less than 2.5%) The purpose of adding chromium (Cr) is to promote the formation of Gaussian texture to reduce iron loss, while the purpose of adding Sn is to inhibit grain growth and ultimately increase magnetic flux density. Additionally, antimony (Sb) acts as a grain boundary segregant, thereby inhibiting grain growth and stabilizing secondary recrystallization. All three elements are interrelated to the formation of secondary recrystallization structures; therefore, it is preferable that the combined content of Sn, Sb, and Cr be controlled to below 2.5%.

[0094] (A1: 2.0% or less and 0% excluded) In addition to forming Al-based nitrides precipitated during the manufacturing process, aluminum (Al) introduces nitrogen (N) during the nitriding treatment in the primary recrystallization process, which combines with Al, Si, and Mn existing in the steel in a solid solution state to form (Al, Si, Mn)N and AlN nitrides, thus acting as a strong grain growth inhibitor. However, if the Al content is too high, the precipitates become uneven, and the formation of secondary recrystallization becomes unstable, resulting in a decrease in the magnetic properties of the steel sheet. Therefore, it is preferable to add less than 2.0%.

[0095] (If any one or more of P and S: the total is less than 0.1% and excluding 0%) Phosphorus (P) segregates at grain boundaries, hindering grain boundary movement and also playing an auxiliary role in suppressing grain growth. If too much sulfur (S) is added, the formation of secondary recrystallization becomes unstable. Furthermore, P and S are elements that are unavoidably added during the manufacturing process of electrical steel sheets; it is preferable to control the combined P and S content to below 0.1%.

[0096] (Cu+Sn: less than 0.1% in total) Copper (Cu) is partially dissolved within the grains, thus improving the grain texture. If the Cu+Sn content is too high, segregation will occur at the grain boundaries, and a liquid phase may form at high temperatures. Therefore, it is preferable to control the total Cu and Sn content to below 0.1%.

[0097] (Rare earth elements and other impurities: total less than 0.2%) The grain-oriented electrical steel sheet according to one embodiment of the present invention may include rare earth elements such as cerium (Ce) or praseodymium (Pr) and other impurities. Even if some rare earth elements and impurities are included, their total content is preferably less than 0.2%. Rare earth elements and unavoidable impurities refer to impurities intentionally added or unavoidably mixed in during the steelmaking and manufacturing processes of the grain-oriented electrical steel sheet. Since unavoidable impurities are well-known, specific descriptions are omitted. In one embodiment of the present invention, the addition of elements is not excluded in addition to the aforementioned alloy composition, and various elements may be included within the scope of the technical concept of the present invention. When further adding elements, Fe is substituted for the balance.

[0098] Next, the steel plate with the aforementioned composition is continuously cast into a slab, then hot-rolled using conventional methods, and selectively annealed as needed, followed by cold rolling to produce a thickness in the range of 0.1~0.5 mm. Cold rolling can be performed in a single cold rolling operation or in two or more cold rolling operations with intermediate annealing.

[0099] [Single recrystallization annealing] The aforementioned cold-rolled steel sheet undergoes a single recrystallization annealing process via simultaneous decarburization and nitriding, or decarburization followed by nitriding. When single recrystallization annealing is performed via simultaneous decarburization and nitriding, the deformed cold-rolled structure undergoes recrystallization during the annealing process, and decarburization annealing occurs simultaneously. Therefore, this process is carried out in a mixed gas environment containing nitrogen, hydrogen, and moisture. Alternatively, in the case of decarburization followed by nitriding, a nitriding treatment using ammonia to introduce nitrogen ions into the steel sheet can be performed after decarburization.

[0100] While simultaneously decarburizing and nitriding, the cold-rolled steel sheet charged into the furnace is controlled to have an ambient gas dew point temperature of 40-70°C in the 700-900°C range and a surface Fe2SiO4 / SiO2 ratio of 0.5-3.0, thereby forming an oxide layer on the surface of the electrical steel sheet.

[0101] [Secondary recrystallization annealing] Next, after coating the surface of the electrical steel sheet with an annealing agent whose basic component is MgO, it is heated to above 1000℃ for a long period of homogenous annealing to initiate secondary recrystallization, thereby forming a {110} surface of the steel sheet that is parallel to the rolling surface and <001> A Gaussian-oriented texture with its direction parallel to the rolling direction. A glass-like coating layer including forsterite is formed on the surface of the steel sheet through a final high-temperature annealing process as described above, while secondary recrystallization occurs inside the steel sheet.

[0102] [Form an insulating coating] After coating the steel sheet that has undergone secondary recrystallization with a single or composite insulating coating solution of colloidal silica and metal phosphate, it is then annealed to form an insulating coating layer on the surface of the electrical steel sheet with a glass coating layer.

[0103] The method for forming this insulating coating layer is not particularly limited and can be any method. As an example, the insulating coating layer can be formed by coating an insulating coating solution comprising phosphates. For this insulating coating solution, a coating solution comprising colloidal silica and metal phosphates is preferred. In this case, the metal phosphate can be Al phosphate, Mg phosphate, or a combination thereof, and the content of Al, Mg, or the combination thereof relative to the weight of the insulating coating solution can be 15% by weight or more.

[0104] [Trench formation and domain refinement] The methods for trench formation and domain refinement are as described above, and therefore detailed descriptions are omitted. Domain refinement can be performed after cold rolling, after a first recrystallization annealing, after a second recrystallization annealing, or after forming an insulating coating, as described in the aforementioned processes. More specifically, it can be performed after cold rolling and before the first recrystallization annealing.

[0105] The present invention will be further described in detail below through specific embodiments. However, the following embodiments are merely illustrative of the present invention, and the present invention is not limited to the following embodiments.

[0106] Experimental Example 1 Cold-rolled steel sheets with a thickness of 0.20 mm are manufactured using slabs with the compositions shown in Table 1 below, through hot rolling and cold rolling. In Table 1, % represents weight%.

[0107] Table 1 At a steel plate moving speed of 0.83 m / s, a fiber laser was used as the main laser, and a CO2 laser was used as the auxiliary laser. The final fiber laser beam on the steel plate had a width (in the rolling direction) of 10 μm, forming an elliptical beam. The CO2 laser formed an elliptical beam with a width of 150 μm, and the centers of the laser beams were aligned. By simultaneously irradiating the steel plate along its width, linear grooves with an average depth of 20 μm were formed at 3 mm intervals.

[0108] For steel plates with grooves formed by laser irradiation, after decarburization and nitriding, a surface insulating coating is formed by coating with MgO, high-temperature annealing, and planarization annealing. Then, after stress-relief annealing heat treatment, the magnetic properties of the steel plate are measured using a single-sheet tester (SST). The original plate is the cold-rolled plate closest to the groove formation area. After decarburization, nitriding, high-temperature annealing, and planarization annealing to form a surface insulating coating, it undergoes stress-relief annealing heat treatment, and the magnetic properties are measured using a single-sheet tester, thereby determining the iron loss and magnetic flux density of the original plate.

[0109] Table 2 As shown in Table 2, under the superposition of the first laser and the second laser, the appropriate iron loss improvement effect could not be obtained.

[0110] Experiment Example 2 The procedure was carried out in the same manner as in Example 1, except that the laser irradiation interval was changed to 2.5 mm, and the beam superposition ratio was changed as shown in Table 3. In Comparative Example 4, the second laser was irradiated after a 1-second interval following the first laser irradiation.

[0111] Table 3 As shown in Table 3, it can be confirmed that iron loss can be improved when the first and second lasers are superimposed. On the other hand, it can be confirmed that iron loss deteriorates and insulation deteriorates when a single laser is used or when the laser is irradiated for a longer period of time.

[0112] This invention is not limited to the embodiments described herein, and can be manufactured in various different ways. Those skilled in the art will understand that this invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

[0113] [Explanation of reference numerals in the attached figures] 100: Oriented grain electrical steel sheet; 10: Groove 20: Laser spot; 21: First laser spot 22: Second laser spot

Claims

1. A method for refining magnetic domains in a grain-oriented electrical steel sheet, comprising: The step of superimposing the light spots of two or more lasers with different light spot shapes to form a groove.

2. The method for refining magnetic domains in oriented electrical steel sheets according to claim 1, wherein, The laser includes a first laser and a second laser, wherein the first spot of the first laser beam and the second spot of the second laser beam are superimposed by more than 10%.

3. The method for refining magnetic domains in oriented electrical steel sheets according to claim 1, wherein, The laser includes a first laser and a second laser, wherein the energy density of the first laser beam is 1.1 to 4.0 times that of the second laser beam.

4. The method for refining magnetic domains in oriented electrical steel sheets according to claim 1, wherein, The laser includes a first laser and a second laser, wherein the first laser and the second laser are selected from CO2 lasers, fiber lasers, YAG lasers, ruby ​​lasers, sapphire lasers, disk lasers, diode lasers, or UV lasers.

5. The method for refining magnetic domains in oriented electrical steel sheets according to claim 1, wherein, The laser includes a first laser and a second laser, each with a power of 10 to 2000W.

6. The method for refining magnetic domains in oriented electrical steel sheets according to claim 1, wherein, The laser includes a first laser and a second laser, which have different wavelengths.

7. The method for refining magnetic domains in oriented electrical steel sheets according to claim 1, wherein, The laser includes a first laser and a second laser, and at the superposition position, the interval between the irradiation time of the first laser beam and the irradiation time of the second laser beam is less than 16ms.

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