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

Abstract

According to one embodiment of the present invention, a method for refining magnetic domains of a grain-oriented steel sheet comprises a step of forming grooves by overlapping and emitting beam spots of two or more types of lasers having different beam spot shapes.

Description

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

[0001] One embodiment of the present invention relates to a grain-oriented electrical steel sheet and a method for refining the magnetic domain thereof. More specifically, one embodiment of the present invention relates to a grain-oriented electrical steel sheet having excellent iron loss characteristics and a method for refining the magnetic domain thereof, wherein two or more types of overlapping lasers are irradiated onto the surface of the steel sheet to sufficiently secure groove depth while at the same time drastically reducing melting byproducts such as hill-up sputtering.

[0002] Grain-oriented electrical steel sheets have excellent magnetic properties and are commonly used as core material for transformers. The production of grain-oriented electrical steel sheets involves a unique rolling and annealing process unique to the electrical steel manufacturing process, resulting in {110} <001> The Goss aggregate structure, which is re-arranged in the direction of the direction, is formed throughout the steel plate.

[0003] To address climate change, the world is steadily strengthening greenhouse gas emission grading standards. For transformer cores, the factors affecting greenhouse gas emission grading are directly related to the efficiency of transformers using electrical steel. Furthermore, the efficiency of transformer cores is significantly influenced by the core loss and magnetic flux density of the electrical steel, i.e., its magnetic properties.

[0004] The magnetic flux density of electrical steel sheets is higher when the crystal orientation, that is, the degree to which the crystal axes that are easy to magnetize are gathered in the crystal structure, is high, so the manufacturing process of electrical steel sheets can have a significant effect.

[0005] According to the IEC60404-3 standard, the core loss of electrical steel is the W17 / 50 [W / kg] value measured when a magnetic field with a frequency of 50 Hz is applied at a maximum magnetic flux density of 1.7 T, and this value is called the guaranteed core loss of the core material, and this value is used as a measure of the core loss of the electrical steel. However, when designing a transformer, the W15 / 50 [W / kg] value measured when a magnetic field with a frequency of 50 Hz is applied at a maximum magnetic flux density of 1.5 T, which is lower than this, is also used. In a transformer, the efficiency is evaluated as better when this core loss value is lower.

[0006] Therefore, electrical steel sheets with higher magnetic flux density and lower core loss can be used as efficient transformer cores. Among these, core loss is considered a more important indicator, as the manufacturing process for electrical steel sheets has been standardized upward, and the process technology for achieving high magnetic flux density has developed to a level that can support transformer efficiency.

[0007] This iron loss is divided into eddy current loss and hysteresis loss, and hysteresis loss tends to decrease when the magnetic flux density is high, so eddy current loss plays an important role in controlling the overall iron loss in grain-oriented electrical steel sheets. Among the iron losses, eddy current loss is divided into classical eddy current loss and abnormal eddy current loss, and classical eddy current loss is proportional to the thickness of the steel sheet, so classical eddy current loss decreases as the steel sheet becomes thinner. Therefore, controlling abnormal eddy current loss is established as an important technology for reducing iron loss.

[0008] Among these iron losses, eddy current loss is reduced as the magnetic domain wall spacing of the 180° magnetic domain in the rolling direction is narrowed, so iron loss can be reduced by refining the magnetic domain of the electrical steel sheet.

[0009] In electrical steel, domain refinement refers to the process of physically stimulating a single domain to separate it into multiple domains. Domain refinement can be achieved through laser irradiation, electron beam irradiation, plasma treatment, etching, or roll pressing. Depending on whether the domain refinement effect persists after stress relief annealing (SRA), the process is categorized as permanent domain refinement or temporary domain refinement.

[0010] Among the magnetic domain refinement technologies, the technology that can secure the magnetic domain refinement effect even after the stress relief annealing (SRA) heat treatment for iron loss improvement is called permanent magnetic domain refinement technology. Permanent magnetic domain refinement technology includes a laser method for cold-rolled sheets or steel sheets that have completed secondary recrystallization, a groove transfer method using a rotating wedge-shaped knife roll, and an etching method that forms grooves using electrochemical etching in a solution. Since the surface transfer method forms grooves using a rotating knife roll, it is difficult to maintain roll durability due to changes in the applied load when the steel sheet thickness exceeds a critical value, making it difficult to precisely control the groove depth at high speeds. In addition, chemical etching forms grooves through an anodic reaction of the steel sheet in a solvent, making it difficult to form grooves at high speeds. When the laser method forms a groove by partially melting the steel plate, it requires a high-power generator for high-speed groove formation, and because the hill-up that occurs around the groove is removed by physical or chemical methods, it is necessary to use a brush after groove formation or introduce a process of applying oxide, etc. before groove formation.

[0011] In one embodiment of the present invention, a grain-oriented electrical steel sheet and a method for refining the magnetic domain thereof are provided. More specifically, in one embodiment of the present invention, by irradiating the surface of the steel sheet with two or more overlapping lasers to sufficiently secure the depth of the groove while at the same time drastically reducing melting byproducts such as hill-up sputtering, a grain-oriented electrical steel sheet having excellent iron loss characteristics and a method for refining the magnetic domain thereof are provided.

[0012] In one embodiment of the present invention, a method for refining a magnetic domain of a directional electrical steel sheet includes a step of forming a groove by overlapping and irradiating beam spots of two or more types of lasers having different beam spot shapes.

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

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

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

[0016] The first laser and the second laser may each have an output power of 10 to 2000 W.

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

[0018] At the overlapping position, the interval between the time at which the first laser beam is irradiated and the time at which the second laser beam is irradiated may be 16 ms or less.

[0019] The groove may be in the form of a line extending in a direction intersecting the rolling direction.

[0020] The depth of the groove may be 5 to 15% of the thickness of the electrical steel sheet.

[0021] The longitudinal direction of the groove may form an angle of 75 to 105° with respect to the rolling direction.

[0022] The grooves can be formed intermittently in numbers of 2 to 10 along the vertical rolling direction of the electrical steel sheet.

[0023] According to one embodiment of the present invention, by performing optimal magnetic domain refinement using an overlapping laser, magnetism can be further improved while at the same time sufficiently suppressing the generation of molten by-products such as hill-up sputtering on the surface of a steel plate.

[0024] According to one embodiment of the present invention, it is possible to easily increase the average output power by using a long-wavelength laser and secure the reliability of the processing line, and at the same time, by simultaneously irradiating a short-wavelength laser, the magnetic domains can be formed to a minimum, thereby effectively improving the magnetism.

[0025] Figure 1 is a graph showing the optical absorption rate of steel plates according to laser wavelength.

[0026] FIG. 2 is a schematic diagram illustrating the concept of domain refinement for forming grooves using an overlapping laser according to one embodiment of the present invention.

[0027] FIG. 3 is a schematic diagram showing a beam spot of an overlapping laser according to one embodiment of the present invention.

[0028] FIG. 4 is a schematic diagram showing a beam spot of an overlapping laser according to another embodiment of the present invention.

[0029] Figure 5 is a schematic diagram showing a case where lasers are irradiated twice at a time interval rather than overlapping lasers according to one embodiment of the present invention.

[0030] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0032] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0033] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0034] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0035] In one embodiment of the present invention, the purpose is to provide excellent iron loss characteristics by irradiating the surface of an electrical steel sheet with an overlapping laser to sufficiently secure the depth of a groove while suppressing the formation of molten by-products such as hill-up and sputter existing on the surface of the steel sheet.

[0036] One embodiment of the present invention includes a step of forming a groove by overlapping and irradiating beam spots of two or more types of lasers having different beam spot shapes.

[0037] One of the preferred methods for improving iron loss in oriented electrical steel sheets is to refine magnetic domains by forming grooves on the surface of the steel sheet using a laser.

[0038] The domain refinement process of the grain-oriented electrical steel sheet forms a groove (10) by irradiating the laser in a direction crossing the rolling direction (RD direction), as illustrated in Fig. 2. The groove may have a point-like or continuous linear groove shape, and Fig. 2 exemplifies a linear groove. Here, the linear or linear groove includes not only a solid line but also a dotted or broken line that continues intermittently, and also includes a zigzag shape when viewed microscopically but a straight line when viewed macroscopically, and includes all grooves that form a linear shape.

[0039] Groove formation in steel plates by laser is achieved by melting and vaporizing a portion of the steel plate by laser irradiation, and the melted and vaporized portion remains in the shape of a groove.

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

[0041] However, the depth of the groove increases as the total laser irradiation energy increases during laser irradiation. However, if energy exceeding the required amount is irradiated to the steel plate, molten byproducts such as heel-up and sputtering remain on the steel plate surface, which adversely affect magnetism and therefore need to be suppressed. Therefore, when irradiating with a laser, it is desirable to irradiate a large amount of energy to the smallest possible area for a short period of time with a high energy absorption rate.

[0042] Furthermore, the interaction conditions between the laser beam and the steel plate are affected by the characteristics of the laser and the absorption rate of the laser beam on the steel plate. The absorption rate of the laser beam is affected by the surface roughness of the steel plate, the temperature of the steel plate, the absorption characteristics of the steel plate surface, and the laser wavelength. However, when the manufacturing conditions of the steel plate are constant across the entire surface, the surface roughness, temperature, and absorption characteristics of the steel plate surface will be constant, and in this case, the absorption rate of the laser beam on the steel plate will depend on the laser wavelength.

[0043] That is, when the manufacturing conditions of the steel plate are constant, the laser absorption rate is affected by the wavelength of the laser. As shown in Fig. 1, the laser absorption rate of the steel plate is approximately 35 to 40% when the wavelength is short (e.g., YAG or Fiber laser with a wavelength of 1.06 ㎛), while it is relatively low at approximately 5 to 10% when the wavelength is long (e.g., CO2 laser with a wavelength of 10.6 ㎛).

[0044] In this way, in the process of refining the magnetic domains of oriented electrical steel sheets using a laser, it is more efficient to use a short-wavelength laser than to use a long-wavelength laser to secure stable iron loss characteristics.

[0045] Meanwhile, the surface of electrical steel sheets subject to domain refinement treatment sometimes has an insulating film, several to several tens of micrometers thick, mainly composed of phosphate and silica. This film absorbs relatively little laser beam from short-wavelength lasers (e.g., 1.06 micrometers YAG or Fiber lasers), but exhibits high absorption from long-wavelength lasers (e.g., 10.6 micrometers CO2 lasers). As a result, while the thickness of the insulating film must be considered for long-wavelength lasers, the thickness of the insulating film needs to be considered less for short-wavelength lasers than for long-wavelength lasers.

[0046] As described above, short-wavelength and long-wavelength lasers have different characteristics. Therefore, when short-wavelength and long-wavelength lasers are used simultaneously and superimposed, the advantages of each laser for domain refinement are prioritized without adverse side effects, resulting in a synergistic effect.

[0047] Here, using overlapping lasers means that two or more lasers with different beam spot shapes are used to irradiate the surface of the steel plate, and the spot of one laser beam formed on the surface of the steel plate is partially or completely located within the spot of another laser beam. Therefore, in one embodiment of the present invention, the overlapping lasers with different wavelengths include not only the case where the spot of one laser beam is completely overlapped and overlapped within the spot of another laser beam, but also all cases where some are partially overlapped. Meanwhile, if there is a time interval for the irradiation time, the surface of the steel plate cools rapidly during the interval, making it difficult to obtain the effect of the overlapping laser irradiation. Therefore, it is preferable to irradiate two or more lasers simultaneously, and specifically, the interval between the irradiation time of the first laser beam and the irradiation time of the second laser beam may be 16 ms or less. FIG. 3 shows an example in which the first laser beam (21) and the second laser beam (22) are partially overlapped and irradiated, and FIG. 4 shows an example in which the first laser beam (21) and the second laser beam (22) are fully overlapped and irradiated. As mentioned above, Fig. 5 is a case where the laser beams do not overlap at a specific point in time, and if the interval between the irradiation times to a specific location exceeds 16 ms, it is defined as not being irradiated by overlapping.

[0048] In one embodiment of the present invention, a beam spot means a beam spot on the surface of a steel plate. Fig. 3 schematically illustrates a first beam spot of a first laser beam (21) and a second beam spot of a second laser beam (22).

[0049] The first beam spot of the first laser beam and the second beam spot of the second laser beam overlap by 10% or more. 10% or more means the width (B) of the first laser beam 1W ) and the width of the second laser beam (B 2W ) for the width of the overlapping region (O W ) means the ratio of the width of the first laser beam (B). In Fig. 3, the width of the first laser beam (B1W ) is small, and in this case the overlap ratio is O W / B 1W can be calculated as

[0050] The width of the laser beam is the length of the laser beam in the direction perpendicular to the groove length direction (or laser irradiation direction, X direction) (Y direction). The length of the laser beam is the length of the laser beam in the groove length direction (or laser irradiation direction, X direction). In Fig. 3, the length of the first laser beam (B 1L ) and the length of the second laser beam (B 2L ) was displayed.

[0051] In Fig. 4, it is schematically shown that the first beam spot of the first laser beam (21) exists within the second beam spot of the second laser beam (22), and in this case, the overlap ratio is calculated as 100%.

[0052] Meanwhile, in one embodiment of the present invention, the groove has a shape in which the bell is turned upside down by irradiation with an overlapping laser.

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

[0054] More specifically, the first laser (A), which is a short-wavelength laser, can use a laser with a relatively short wavelength, such as an optical fiber (Er-Fiber, Yb-Fiber, Tm-Fiber) laser, a YAG (Nd:YAG, Yb:YAG) laser, a ruby ​​laser, or a sapphire laser. In addition, 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) can also be used as the first laser.

[0055] And as the second laser, which is a long-wavelength laser, a laser with a relatively longer wavelength than a short-wavelength laser can be used. For example, a CO2 laser is preferable as the second laser. However, if a UV laser (0.150 to 0.355 μm) is used as the first short-wavelength laser, any laser with a longer wavelength than the first laser can be used as the second laser. For example, if a UV laser (0.150 to 0.355 μm) is used as the first laser, a YAG laser can be used as the second laser.

[0056] Hereinafter, a method for domain refinement using a superposition laser (30) will be described in more detail, taking as an example the case where a fiber laser is used as the first laser with a short wavelength and a CO2 laser is used as the second laser with a long wavelength.

[0057] The primary laser, a fiber laser, uses a short wavelength with relatively high absorption by the steel plate. This allows it to irradiate the groove-forming energy to a narrow area for a short period of time. Furthermore, the narrow energy range of the primary laser, a fiber laser, minimizes the formation of melt byproducts. However, the primary laser alone cannot provide sufficient energy for groove formation.

[0058] Meanwhile, the second laser, a CO2 laser, can operate at an average output of several hundred watts to several kilowatts or more, depending on the sheet metal speed. Therefore, the second laser, a CO2 laser, is suitable for a type of preheating function. However, the second laser (B), a CO2 laser, has a low absorption rate in the sheet metal. Therefore, forming a groove using the CO2 laser alone requires excessive energy, which leads to the formation of a large amount of melting byproducts.

[0059] Accordingly, a fiber laser with a relatively short wavelength is used as the primary laser for groove formation, and a CO2 laser with a relatively long wavelength is used as an auxiliary laser that acts as a kind of preheating.

[0060] In this case, a 180° magnetic domain (opposite magnetic pole of the lancet magnetic domain) is formed in the surface direction by magnetoelastic energy due to domain refinement, and a 90° magnetic domain is formed to reduce the magnetoelastic energy in the plate thickness direction, thereby narrowing the gap between the magnetic domains and ultimately reducing the abnormal eddy current loss.

[0061] It is preferable that the main laser be positioned in an area where the beam intensity of the auxiliary laser cross-section is at least 25% of that of the auxiliary laser cross-section. More preferably, the main laser be positioned in an area where the beam intensity of the auxiliary laser cross-section is at least 30% of that of the auxiliary laser cross-section. When the main laser position on the final steel plate surface is positioned in an area where the beam intensity of the auxiliary laser cross-section is at least 25% of that of the auxiliary laser cross-section, the laser absorption rate of the main laser can be maximized. In other words, when the main laser is positioned in an area where the beam intensity is less than 25% of that of the auxiliary laser cross-section, there is a disadvantage in that the laser absorption rate of the steel plate surface by the main laser cannot be significantly increased.

[0062]

[0063] As described above, a method for refining a magnetic domain according to one embodiment of the present invention uses a short-wavelength fiber laser as a first laser and simultaneously uses a long-wavelength CO2 laser as a second laser to form a groove (10) of sufficient depth while minimizing the formation of molten by-products.

[0064] At this time, the beam spot of the fiber laser, which is the first short-wavelength laser irradiated on the surface of the steel plate, is preferably close to a circle, and its diameter (B W1 , B L1 ) can be 5 to 500 ㎛. In addition, the beam spot of the fiber laser has a width (B W1) is 5 to 500 ㎛ and its length (B L1 ) can be used with a length less than or greater than the length of the CO2 laser beam spot, which is the second laser.

[0065] The beam width (B) of the first laser, the optical fiber W1 ) is reduced to less than 5㎛, the energy density is concentrated in a narrow area, which may cause magnetic flux density and iron loss inferiority, and the optical system structure becomes complicated. In addition, the beam width (B) of the first laser, the optical fiber W1 ) increases by more than 500㎛, the groove width in the longitudinal direction of the steel plate increases, and a large number of melting byproducts such as hill-up and sputter are formed, which may result in a decrease in magnetic flux density. More specifically, the width and length of the beam spot may be 10 to 100㎛.

[0066] Meanwhile, the beam spot of the CO2 laser, a second long-wavelength laser irradiated on the surface of the steel plate, has a beam width (B 2W ) is 100 to 400 ㎛, and the beam length (B 2L ) is preferably an ellipse with a radius of 0.4 to 20 mm. In addition, the beam spot of a long-wavelength CO2 laser can also be used as a circle with a radius of 100 ㎛ or more.

[0067] The second laser, CO2 beam width (B 2W ) is not desirable to form within 100㎛ because the mirror optical system becomes complicated, such as in a fiber laser. If it becomes larger than 400㎛, a large number of melting byproducts such as hill-up and sputtering may be formed, resulting in a decrease in magnetic flux density.

[0068] The reason for limiting the size of the beam spot of the CO2 laser, which is a long-wavelength second laser, is to consider the range within which the effect of the laser beam acting on the steel plate is maintained when scanning the surface of the steel plate moving at high speed at high speed.

[0069] A case of using lasers in an overlapping manner according to one embodiment of the present invention will be described in more detail.

[0070] As shown in FIGS. 3 and 4, using the first laser beam (21) and the second laser beam (22) to overlap on the final steel plate surface means that the beam spot of the first laser beam (21) and the beam spot of the second laser beam (22) are controlled to overlap. That is, when the laser beam spots (20) irradiated on the steel plate surface are completely positioned anywhere within the range of the second laser beam (22) with a large beam spot when viewed in a plan view, as shown in FIG. 4, the beams are said to be “overlapping”, and as shown in FIG. 3, it means that the beams are “overlapping” even when the first laser beam (21) is partially positioned within the range of the second laser beam (22). Furthermore, when the laser beams do not overlap at a specific point in time, as shown in FIG. 5, they are considered not to be overlapped. However, if the interval between the time at which the first laser beam is irradiated and the time at which the second laser beam is irradiated to a specific location is 16 ms or less, they are considered to be irradiated simultaneously. If this time range is exceeded, the surface of the steel plate cools rapidly, making it difficult to sufficiently obtain the effect of overlapping lasers. The time interval is the width (O) of the overlap area after the second laser (or the first laser) is irradiated and the first laser (or the second laser) advances. W ) means the time until the point where the maximum is reached. In the case of Fig. 5, the laser beams are not overlapped for a specific point in time, but if the first laser beam (21) moves to the dotted circle within 16 ms and overlaps and irradiates the position irradiated by the second laser beam (22), it is considered to have overlapped and irradiated.

[0071] In one embodiment of the present invention, the laser beam oscillation mode is preferably a continuous wave laser that continuously generates laser light for both the first laser and the second laser, but a pulse laser may also be used.

[0072] The energy density of the first laser beam may be 1.1 to 4.0 times that of the second laser beam. As described above, the high energy density of the first laser beam allows for high energy to be applied to a narrow area, thereby forming deep grooves with less melt byproducts. In addition, the energy density of the second laser beam is relatively low, allowing for low energy to be applied to a large area, thereby increasing the absorption rate of the first laser beam.

[0073] Also, the quality of the laser beam used is, for both the first and second lasers, the Gaussian mode of TEM 00 is preferable, but the multi-mode (multi transverse mode) of TEMmn can also be used.

[0074] However, since the overlapping laser beams (20) of different wavelengths irradiated on the surface of the steel plate according to one embodiment of the present invention can form the depth of the grooves deep while minimizing the formation of grooves in the longitudinal direction of the steel plate, the beam shape or beam quality of each laser is not specifically limited.

[0075] The first laser and the second laser may each have an output of 10 to 2000 W. More specifically, the output of the first laser may be 1000 to 2000 W, and the output of the second laser may be 100 to 700 W. The output range of each laser indicates the laser output conditions when the steel sheet progresses at a speed of 10 to 30 mpm, and the output value of the laser can be optimally controlled according to the progress speed of the steel sheet, and the output value may also fall outside the above range depending on the progress speed of the steel sheet.

[0076] When the laser beam (30) in which the first laser and the second laser are overlapped as described above is irradiated onto the surface of the steel plate, the interval (i.e., the interval in the steel plate rolling direction between the grooves) can be 2 to 10 mm, the angle between the rolling direction and the laser propagation direction (groove length direction, X direction) can be 75 to 105°, and the scanning speed is preferably 0.1 to 300 m / sec.

[0077] The electrical steel sheet used at this time can be a cold-rolled sheet, a steel sheet after primary recrystallization annealing, or a steel sheet after secondary recrystallization annealing.

[0078] And if the irradiation interval of the overlapping laser beam (20) irradiated on the surface of the steel plate is too narrow, less than 2 mm, the effect of the heat affected zone becomes large, and the magnetic flux density and iron loss become inferior, and if the irradiation interval is 10 mm or more, the thermal shock effect for securing the magnetic domain refinement effect is reduced, making it difficult to achieve the effect.

[0079] In addition, when irradiating the overlapping laser beam (20) onto the surface of the steel plate, the irradiation may be performed in a direction perpendicular or inclined to the steel plate rolling direction, and the angle between the rolling direction and the laser propagation direction (groove length direction, X direction) may be 75 to 105°. If this angle range is exceeded, the required magnetic domain refinement effect may not be achieved.

[0080] And, since the scanning speed of the overlapping laser should be the same as the plate progress speed, the scanning speed should be faster as the progress speed increases, so 0.1 to 300 m / sec is preferable, and this speed means the value exemplified under the condition of 15 mpm.

[0081] Meanwhile, as shown in FIGS. 3 and 4, it means that the first laser beam and the second laser beam are irradiated simultaneously and overlapped, and irradiated with a time interval as shown in FIG. 5 is excluded. Simultaneously irradiating means that the interval between the time at which the first laser beam is irradiated and the time at which the second laser beam is irradiated for a specific position is 16 ms or less. If this time range is exceeded, the surface of the steel plate cools rapidly, making it difficult to sufficiently obtain the effect of irradiating with overlapping lasers. The time interval refers to the time at which the first laser (or second laser) advances after irradiating the second laser (or first laser), and the width (O) of the overlapping area W ) means the time until it reaches its maximum.

[0082] The groove may be in the form of a line extending in a direction intersecting the rolling direction.

[0083] The depth of the groove may be 5 to 15% of the thickness of the electrical steel sheet.

[0084] The longitudinal direction of the groove may form an angle of 75 to 105° with respect to the rolling direction.

[0085] The grooves may be formed in a continuous manner in the number of 2 to 10 along the vertical rolling direction of the electrical steel sheet. Meanwhile, when forming grooves by irradiating the surface of the electrical steel sheet according to one embodiment of the present invention with an overlapping laser, it is preferable that the W17 / 50 iron loss improvement rate of the steel sheet be 5.0% or more. More specifically, it is preferable that it be 9% or more.

[0086] Hereinafter, a method for manufacturing a directional electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0087] [Manufacturing of cold rolled steel sheets]

[0088] To manufacture oriented electrical steel sheets, slabs of electrical steel sheet substrate are first manufactured.

[0089] The chemical composition and metal structure of a slab are not specifically limited as long as the magnetization axis is aligned in a certain direction and functions as an electrical steel plate. However, by way of example, the chemical composition of a slab is as follows.

[0090] Mass % C: 0.08% or less (excluding 0%), Si: 1.0 to 6.5%, Mn: 0.005 to 3.0%, (sum of any one or more of Nb, V, Ti); 0.070% or less, (sum of any one or more of Cr, Sn, Sb): 2.5% or less, Al: 2.0% or less (excluding 0%), (sum of any one or more of P, S): 0.100% or less (excluding 0%), (sum of Cu and Sn): 1.0% or less, rare earth elements and other impurities totaling 0.2% or less, the remainder being Fe.

[0091] (C: 0.08% or less (excluding 0%))

[0092] Carbon (C) is an element that is inevitably mixed into steel, but it is desirable to control the content to an appropriate level because it worsens magnetic properties due to magnetic aging. If the content of C in the steel sheet is too low, phase transformation may not occur sufficiently during the manufacturing process, making the microstructure of the steel sheet non-uniform, which may ultimately lead to unstable secondary recrystallization. On the other hand, if too much C is included, carbides become coarse and the amount of precipitation is excessive during the manufacturing process, resulting in insufficient decarburization, which may lower the degree of integration of the Goss grain structure and damage the secondary recrystallization grain structure. Therefore, the C content of the steel sheet is 0.08% or less, and more preferably 0.001 to 0.040%.

[0093] (Si: 1.0 ~ 6.5 %)

[0094] Silicon (Si) is a basic component of grain-oriented electrical steel sheets and plays a role in reducing iron loss by increasing the resistivity of the steel sheet. If it is less than 1.0%, the resistivity decreases, which increases eddy current loss and deteriorates iron loss characteristics, making it impossible to expect the effect of Si addition. If it is 6.5% or more, the brittleness of the steel sheet increases and the toughness decreases, which may cause sheet fracture during the rolling process. In addition, nitrides are not sufficiently formed during the manufacturing process, making it difficult to secure sufficient grain restraint necessary for secondary recrystallization during the final high-temperature annealing process. Therefore, Si is preferably 1.0 to 6.5%.

[0095] (Mn: 0.005 ~ 3.0%)

[0096] Manganese (Mn) has the effect of reducing the overall iron loss by increasing the resistivity and reducing the eddy current loss, and it not only reacts with sulfur in the annealed state to form manganese sulfides, but also reacts with nitrogen introduced through nitriding with silicon to form (Al,Si,Mn)N precipitates, thereby inhibiting the growth of primary recrystallized grains and causing secondary recrystallization, and is an important element that affects the surface quality of the final product. However, if too little Mn is included, the surface quality of the final product may deteriorate. In addition, if too much Mn is included, the austenite phase fraction increases significantly, damaging the Goss texture, reducing the magnetic flux density, and forming an excessive oxide layer during decarburization annealing, which may hinder decarburization. Therefore, Mn is preferably 0.005 to 3.0%.

[0097] (Total of any one of Nb, V, and Ti: 0.05% or less)

[0098] Niobium (Nb), vanadium (V), and titanium (Ti) are elements that react with C and N during the manufacturing process to form precipitates. However, if too much is added, they remain in the steel sheet even after the secondary recrystallization annealing, which reduces the magnetic properties of the steel sheet. Therefore, it is desirable to control the total amount of at least one element selected from among Nb, V, and Ti to 0.05% or less.

[0099] (Total of any one of Cr, Sn, Sb: 2.5% or less)

[0100] Chromium (Cr) is added to promote the formation of Goss grain structure and reduce iron loss, and Sn is added to suppress grain growth, ultimately improving magnetic flux density. Antimony (Sb) segregates at grain boundaries, suppressing grain growth and stabilizing secondary recrystallization. Since these three elements are all interrelated with the formation of secondary recrystallization structure, it is desirable to control the total content of Sn, Sb, and Cr to less than 2.5%.

[0101] (Al: 2.0% or less (excluding 0%))

[0102] Aluminum (Al) acts as a strong grain growth inhibitor by forming nitrides in the form of (Al, Si, Mn)N and AlN by combining with N introduced through nitriding during the primary recrystallization process and Al, Si, and Mn present in solid solution in the steel, in addition to the Al-based nitrides precipitated during the manufacturing process. However, if too much Al is included, the precipitates become uneven, making the secondary recrystallization unstable and degrading the magnetic properties of the steel sheet. Therefore, it is recommended to add less than 2.0%.

[0103] (Sum of any one of P and S: 0.1% or less (excluding 0%))

[0104] Phosphorus (P) plays a supporting role by segregating at grain boundaries, hindering grain boundary movement and simultaneously suppressing grain growth. Excessive addition of sulfur destabilizes secondary recrystallization. Furthermore, P and S are elements inevitably added during the manufacturing process of electrical steel sheets, and it is desirable to control the combined P and S content to less than 0.1%.

[0105] (Cu + Sn total: 0.1% or less)

[0106] Copper (Cu) plays a role in improving the grain structure as it is partially dissolved in the grains. If the Cu + Sn content is excessive, it may segregate at the grain boundaries and form a liquid phase at high temperatures. Therefore, it is desirable to control the total amount of Cu and Sn to less than 0.1%.

[0107] (Total of rare earth elements and other impurities is 0.2% or less)

[0108] 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, and it is preferable that the total amount of any rare earth elements and impurities contained is 0.2% or less. Rare earth elements and inevitable impurities refer to impurities that are intentionally added or inevitably mixed in during the steelmaking and manufacturing of grain-oriented electrical steel sheets. Since inevitable impurities are widely known, a detailed description thereof is omitted. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are further included, they are included in place of the remainder, Fe.

[0109] Next, a steel plate having the above composition is manufactured into a slab by continuous casting, then heated in a conventional manner, hot-rolled, optionally hot-rolled, and then cold-rolled to manufacture a thickness in the range of 0.1 to 0.5 mm. Here, cold rolling may be performed once or twice or more times with intermediate annealing in between.

[0110] [1st recrystallization annealing]

[0111] The cold-rolled steel sheets described above undergo primary recrystallization annealing through the simultaneous decarburization or post-decarburization nitriding processes. In the case of primary recrystallization annealing using simultaneous decarburization, the structure of the cold-rolled steel sheet deformed during the annealing process undergoes decarburization annealing, including recrystallization. This process is performed in a mixed gas atmosphere containing nitrogen, hydrogen, and moisture. Furthermore, in the case of post-decarburization nitriding, a nitriding treatment can be performed using ammonia gas to introduce nitrogen ions to the steel sheet after decarburization.

[0112] When performing simultaneous decarbonization, the cold rolled steel sheet loaded into the furnace is heated to 700 to 900°C, the dew point temperature of the atmospheric gas is set to 40 to 70°C, and the surface Fe2SiO4 / SiO2 ratio is controlled to 0.5 to 3.0 to form an oxide layer on the surface of the electrical steel sheet.

[0113] [Second recrystallization annealing]

[0114] Then, an annealing agent based on MgO is applied to the surface of the electrical steel sheet, and the temperature is raised to 1,000℃ or higher to cause secondary recrystallization by long-term crack annealing, so that the {110} plane of the steel sheet is parallel to the rolling surface. <001> The Goss orientation is formed as a grain structure parallel to the rolling direction. Through this final high-temperature annealing process, a glassy film containing forsterite is formed on the surface of the steel sheet, and secondary recrystallization is formed inside the steel sheet.

[0115] [Insulating film formation]

[0116] For a steel sheet on which secondary recrystallization has occurred, an insulating coating layer is formed on the surface of the electrical steel sheet by coating it with a single or composite insulating coating solution of colloidal silica and metal phosphate and then annealing it to form a glass film layer.

[0117] The method for forming such an insulating film layer may be used without particular limitation, and for example, the insulating film layer may be formed by applying an insulating coating solution containing phosphate. It is preferable that the insulating coating solution use a coating solution containing colloidal silica and a metal phosphate. In this case, the metal phosphate may be Al phosphate, Mg phosphate, or a combination thereof, and the content of Al, Mg, or a combination thereof relative to the weight of the insulating coating solution may be 15 wt% or more.

[0118] [Groove formation and domain refinement treatment]

[0119] Since the groove formation and domain refinement methods have been previously described, a detailed description will be omitted. Domain refinement treatment can be performed during the aforementioned processes: after cold rolling, after primary recrystallization annealing, after secondary recrystallization annealing, or after insulating film formation. More specifically, it can be performed after cold rolling and before primary recrystallization annealing.

[0120] The present invention will be described in more detail below through specific examples. However, these examples are intended merely to illustrate the present invention and are not intended to limit the present invention.

[0121]

[0122] Experimental Example 1

[0123] A 0.20 mm thick cold rolled steel plate was manufactured using a slab having the composition shown in Table 1 below through hot rolling and cold rolling. In Table 1, % means weight %.

[0124] C(%)Si(%)Mn(%)Cr(%)Sn(%)Sb(%)Al(%)Balance0.053.5180.1030.1130.06990.0190.003Fe

[0125] At a 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 beam size of the fiber laser finally formed on the plate was an elliptical beam with a width (in the rolling direction) of 10 μm, and the CO2 laser formed an elliptical beam with a width of 150 μm. By aligning the centers of the laser beams and irradiating the laser in the width direction of the plate simultaneously, linear grooves with an average depth of 20 μm were formed at 3 mm intervals.

[0126] The steel plate formed grooves by laser irradiation was subjected to decarburization, MgO coating, high-temperature annealing, and flattening annealing to form a surface insulation coating layer. Afterwards, the steel plate was subjected to stress relief annealing heat treatment, and the magnetism of the steel plate was measured using a single sheet tester (SST). The original plate was subjected to decarburization, high-temperature annealing, and flattening annealing on the cold-rolled plate closest to the groove formation area to form a surface insulation coating layer, and then stress relief annealing heat treatment was performed. The magnetism was measured using a single sheet magnetometer to measure the core loss and magnetic flux density of the original plate.

[0127]

[0128] 1st laser 2nd laser Groove non-formation Groove formation Iron loss improvement rate (%) Electrical insulation (mA) Oscillation type / beam quality Output (W) Output (W) W 17 / 50 (W / kg)B8(T)W 17 / 50 (W / kg) B8(T) Example 1 Continuous wave 1 200 8 00 0.73 1 9 1 3 0.63 1 9 1 1 3 7 8 Example 2 Pulse wave (15 kHz) 1 200 8 00 0.73 1 9 1 3 0.62 1 9 1 1 1 5 1 9 Example 3 Gaussian (M2=1.05) 1 200 8 00 0.73 1 9 1 4 0.62 1 9 1 0 1 5 1 1 0 Example 4 Multi-mode (M2=12.2) 1 200 8 00 0.73 1 9 1 3 0.63 1 9 1 1 1 3 7 1 0

[0129] As shown in Table 2, when the first and second lasers were superimposed, no appropriate iron loss improvement could be obtained.

[0130]

[0131] Experimental Example 2

[0132] The same procedure as Example 1 was followed, but the laser irradiation interval was changed to 2.5 mm, and the beam overlap ratio was changed as shown in Table 3 below. In Comparative Example 4, a second laser was irradiated after the first laser irradiation with an interval of 1 second.

[0133] 1st laser 2nd laser Overlap ratio (%) Groove not formed Groove formed Iron loss improvement rate (%) Electrical insulation (mA) Output (W) Output (W) W 17 / 50 (W / kg)W 17 / 50 (W / kg)W 17 / 50 (W / kg)B8(T)Example 51200800250.731.9140.691.9135.510Example 61200800300.731.9140.681.9136.89Example 71200800500.731.9150.651.91211.011Example 812008001000.731.9150.631.91113.78Comparative Example 11200--0.731.9230.741.925-1.467Comparative Example 2-800-0.731.9200.761.900-4.1350Comparative Example 3-2000-0.731.9200.781.875-6.8670Comparative example 41200800-0.731.9200.741.923-1.475

[0134] As shown in Table 3, when the first and second lasers are superimposed, it can be confirmed that iron loss improvement can be achieved. On the other hand, when a single laser is used or when the lasers are irradiated for a long period of time, iron loss actually deteriorates and insulation is inferior.

[0135]

[0136] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0137] [Explanation of symbols]

[0138] 100: Oriented electrical steel sheet, 10: Groove,

[0139] 20: Laser beam spot, 21: First laser beam spot,

[0140] 22: Second laser beam spot

Claims

1. A method for refining a magnetic domain of a directional electrical steel sheet, comprising a step of forming a groove by overlapping and irradiating beam spots of two or more lasers having different beam spot shapes.

2. In paragraph 1, A method for refining a magnetic domain of a directional electrical steel sheet, wherein the laser comprises a first laser and a second laser, and a first beam spot of the first laser beam and a second beam spot of the second laser beam overlap by 10% or more.

3. In paragraph 1, A method for refining a magnetic domain of a directional electrical steel sheet, wherein the laser comprises a first laser and a second laser, and the energy density of the first laser beam is 1.1 to 4.0 times the energy density of the second laser beam.

4. In paragraph 1, A method for refining a magnetic domain of a directional electrical steel sheet, wherein the laser comprises a first laser and a second laser, and the first laser and the second laser are selected from among a CO2 laser, a fiber laser, a YAG laser, a ruby ​​laser, a sapphire laser, a disk laser, a diode laser, or a UV laser.

5. In paragraph 1, A method for refining a magnetic domain of a directional electrical steel sheet, wherein the laser comprises a first laser and a second laser, and the first laser and the second laser each have an output of 10 to 2000 W.

6. In paragraph 1, A method for refining magnetic domains of a directional electrical steel sheet, wherein the laser comprises a first laser and a second laser, and the first laser and the second laser have different wavelengths.

7. In paragraph 1, A method for refining a magnetic domain of a directional electrical steel sheet, wherein the laser comprises a first laser and a second laser, and, at the overlapping position, the interval between the time at which the first laser beam is irradiated and the time at which the second laser beam is irradiated is 16 ms or less.

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