Method of laser scripting of textured silicon steel plate

Abstract

FIELD: mechanical engineering.SUBSTANCE: method for laser scribing a textured silicon steel plate includes forming a plurality of focused light spots corresponding to each position along the length along the rolling direction of the textured silicon steel plate, on the surface of the textured silicon steel plate by splitting a laser beam during laser scribing of said surface of the textured silicon steel plate. The spots of the specified set of focused light spots are located along the width direction of the textured silicon steel plate and between adjacent spots there is an energy-forbidden zone region. The size of each focused light spot along the width direction of the textured silicon steel plate is larger than the size along the length direction of the textured silicon steel plate. The ratio of the power densities of the subsequent focused light spot to the previous focused light spot in the direction of laser scanning is 0.75-0.95, and the power density (p) of each focused light spot is 1000-3000 W / mm2.EFFECT: preventing the loss of the surface coating of the plate and reducing the loss in the textured silicon steel.8 cl, 4 dwg, 7 tbl

Description

[0001] Field of technology to which the invention relates

[0002] The present invention relates to a process for producing textured silicon steel, and in particular to a method for laser scribing a textured silicon steel plate.

[0003] Technology Level

[0004] In recent years, as global energy and environmental issues become increasingly prominent, countries around the world have generally raised energy consumption standards for various types of power-consuming equipment to reduce reactive energy consumption. For example, in a power transmission system, transformer-related losses account for approximately 40% of total system losses. The grain-oriented silicon steel core is the main component of a transformer, and its losses account for approximately 20% of total losses.

[0005] The losses associated with a silicon steel core are commonly referred to as steel losses. Therefore, reducing losses in grain-oriented silicon steels used to make transformer cores has significant economic and social benefits.

[0006] As is well known, grain-oriented silicon steel is so named due to the orientation of its internal grains, which roughly coincides with the rolling direction of the steel plate. For grain-oriented electrical steel plate, due to the grain orientation being in the easy magnetization direction, the higher the grain orientation, the better the magnetic properties of the silicon steel plate, resulting in higher magnetic induction and lower losses in the steel. Within the grains of grain-oriented silicon steel, there are magnetic domain structures caused by the spontaneous magnetization of ferromagnets. The magnetic moments of each atom in each magnetic domain are spontaneously aligned parallel, forming a 180° magnetic domain, which is parallel to the easy magnetization direction of the grain {110} <100> .Adjacent magnetic domains are 180° opposed to each other, and between them exists a magnetic domain wall consisting of tens to hundreds of atomic layers. During magnetization, the magnetic moments in adjacent magnetic domains are aligned by the displacement of the magnetic domain wall, resulting in magnetic conductivity. Thus, the structure of magnetic domains is a result of the minimum energy operating mode principle and is the main factor influencing steel losses, magnetic induction, and magnetostrictive properties of grain-oriented silicon steel.

[0007] It should be noted that the magnetic conductivity property of silicon steel sheet is expressed as magnetic induction, which is generally denoted as B8, is the magnetic flux density (T) of silicon steel sheet under an exciting magnetic field of 800 A / m; the core loss of the transformer is generally denoted as P 17 / 50, that is, the ineffective electrical energy (W / kg) consumed for magnetizing a sheet of silicon steel when the magnetic flux density in the strip steel reaches 1.7 T with an exciting field of alternating current with a frequency of 50 Hz.

[0008] According to the prior art, steel losses (textured silicon steel sheets) include three components: hysteresis losses, eddy current losses, and abnormal eddy current losses. Hysteresis losses are energy losses caused by the hysteresis phenomenon in magnetic materials during magnetization and demagnetization. This phenomenon occurs when the magnetic induction intensity lags behind the change in magnetic field intensity due to factors such as inclusions, crystal defects, internal stresses, and crystal orientation, which impede the movement of domain walls, leading to difficulty changing the magnetic flux.Eddy current losses are energy losses caused by eddy currents, which in turn are caused by the local electromotive force induced by the change in magnetic flux during alternating magnetization of a grain-oriented silicon steel plate. They are related to the conductivity and thickness of the grain-oriented silicon steel plate. Anomalous eddy current losses are energy losses caused by the different magnetic domain structures of the grain-oriented silicon steel plate during magnetization, primarily influenced by the width of the magnetic domains.

[0009] At present, there are three main methods for improving the performance of grain-oriented silicon steel: (1) adjusting the secondary recrystallization structure of the finished product by metallurgical methods, thereby improving the degree of orientation and reducing the loss in steel of grain-oriented silicon steel; (2) forming a tension coating on the surface of grain-oriented silicon steel to refine the magnetic domains and reduce the loss in steel; (3) scribing the surface of grain-oriented silicon steel by laser, electron beam, mechanical, electrochemical and other means to form linear stress or tension, thereby refining the magnetic domains and reducing the loss in steel.

[0010] Among these three methods, the above method (3) has received the most attention and is currently one of the hot spots for research in this field. The principle of reducing steel loss by refining magnetic domains using scribing in the above method (3) is briefly described below: there is a magnetic domain structure within the grains of textured silicon steel. Under the conditions of no external field, the magnetic domains inside the textured silicon steel are mainly 180° magnetic domains arranged in a reverse parallel direction. The width of a single magnetic domain can usually reach tens of micrometers or even several millimeters. Between adjacent magnetic domains, there is a transition layer of tens to hundreds of atomic layers, which is called a magnetic domain wall.During magnetization, the magnetic moment rotates under the influence of an external field, and the displacement of magnetic domain walls causes adjacent magnetic domains to merge with each other, thereby implementing magnetic conductivity. At the same time, differences in the magnetic domain structures in different regions during magnetic domain wall displacement generate micro-eddy currents in these micro-regions, thereby generating eddy current losses, known as anomalous eddy current losses (Pa) for grain-oriented silicon steel.

[0011] It can be seen that the anomalous eddy current loss Pa is directly related to the inherent magnetic domain structure of grain-oriented silicon steel, which in turn is directly related to the magnetic domain width of grain-oriented silicon steel. Therefore, reducing the magnetic domain width can effectively reduce the anomalous eddy current loss Pa. The anomalous eddy current loss Pa accounts for a large proportion of the total loss of grain-oriented silicon steel, especially for thin-sheet grain-oriented silicon steel with a thickness of 0.23 mm or less, for which the anomalous eddy current loss Pa can account for more than 40%. Therefore, using scribing to refine the magnetic domains of grain-oriented silicon steel, that is, reducing the magnetic domain width, can effectively reduce the anomalous eddy current loss, thereby reducing the overall loss of grain-oriented silicon steel.

[0012] At present, the technology of scribing on the surface of textured silicon steel to improve magnetic domains and reduce steel loss, textured silicon steel can be divided into two categories according to the scribing effect:

[0013] One of them is to form notches (scribed marks) that are not resistant to stress relief annealing using laser, plasma beam, electron beam, and other means to form linear thermal stress regions at a certain distance on the surface of grain-oriented silicon steel, thereby reducing the width of the main magnetic domain and reducing iron loss. Since the linear thermal stress disappears after stress relief annealing, the resulting product is generally used for the manufacture of laminated-core transformers that do not require stress relief annealing. Another technology is to form notches that are resistant to stress relief annealing, and its main solution is to form linear deformation regions or grooves on the surface of grain-oriented silicon steel using mechanical toothed rollers, electrochemical corrosion, and other methods., to reduce the width of 180° magnetic domains, thereby reducing losses in the steel. Since the deformation regions remain unchanged after stress-relief annealing, the resulting product can be used to manufacture transformers with tape cores, which require stress-relief annealing.

[0014] For example, document CN 1216072 A, published on May 5, 1999, and entitled “Grain-oriented electrical steel sheets with excellent magnetic properties and a method and apparatus for producing the same,” describes a method for laser heat-resistant scribing of grain-oriented silicon steel without damaging the films on the surface of the silicon steel, by adjusting the spot size, energy density and other parameters of the incident laser beam to obtain a stress region with a large and deep closed domain region, thereby reducing steel loss and magnetostriction of the grain-oriented silicon steel.

[0015] As another example, document CN 101528951 A, published on September 9, 2009 and titled "Grain-Oriented Electrical Steel Sheet with Excellent Active Power Loss Characteristics," discloses a grain-oriented electrical steel sheet with excellent steel loss characteristics. The patent further discusses the stress distribution state formed by laser scribing and precisely controls the integral value of the compressive residual stress generated by laser irradiation of the steel sheet, thereby increasing the degree of improvement in steel loss due to laser scribing.However, in this technical solution, since the determination of residual stress depends on traditional stress detection methods such as X-ray diffraction analysis, the measurement cycle is quite long in time, so this method still faces certain difficulties in actual large-scale production.

[0016] As another example, document CN 102477484 A, published on May 30, 2012 and entitled "Method for High-Speed ​​Laser Notching," discloses a method for high-speed laser scribing in which the upper and lower surfaces of a steel strip are simultaneously scribed in a staggered pattern at equal intervals to ensure uniformity of the steel loss improvement effect achieved by scribing. However, it should be noted that scribing the upper and lower surfaces requires high-precision vibration control of the steel strip, and therefore the spatial arrangement is quite complex, making the implementation of this technical solution quite challenging.

[0017] However, the present inventors discovered through extensive research that when laser scribing is performed using laser irradiation to generate localized stress, the surface temperature of the steel plate in localized areas will increase due to heat absorption. The thermal conductivity of silicon steel is isotropic, making it very difficult to create a thermal stress region that is deep in the thickness direction of the steel plate and narrow in width in the rolling direction.

[0018] In the prior art, laser scribing typically uses an elliptical laser spot. The long axis of the elliptical spot is adjusted to match the scanning direction and roughly correspond to the direction perpendicular to the rolling direction of the steel plate. This allows for a longer exposure time and increases the temperature of localized areas of the steel plate to a range sufficient to achieve magnetic domain refinement. However, regardless of whether a continuous-wave laser or a pulsed laser is used, the heat generated by laser irradiation will always accumulate rapidly.If the laser exposure time is too long, although the best iron loss reduction effect may be achieved, the coating will inevitably be damaged due to excessive heat, increasing the risk of transformer short-circuiting during operation. If the laser exposure time is too short, the coating will not be damaged, but the iron loss reduction effect achieved by laser scribing will be limited.

[0019] Therefore, in order to solve the problem existing in the prior art, the inventors of the present invention propose a new laser scribing method with controlled temperature increase to effectively improve, i.e., reduce, the loss in textured silicon steel without damaging the surface coating of the steel plate.

[0020] Disclosure of the essence of the invention

[0021] One of the objectives of the present invention is to provide a method for laser scribing a textured silicon steel plate. The laser scribing method has been optimized from previous processes using a laser focusing scanning method and beam splitting, which can further improve magnetic domain refinement to reduce steel loss without losing the surface coating of the textured silicon steel. The textured silicon steel plate produced by the laser scribing method has low steel loss and resistance to coating failure and can be used to manufacture energy-saving transformers for ultra-high-voltage networks. The laser scribing method has wide application prospects.

[0022] In order to achieve the above object, the present invention provides a method for laser scribing a textured silicon steel plate, including: forming a plurality of focused light spots (or focused spots) on the surface of the textured silicon steel plate by splitting a laser beam corresponding to each position along the length along the rolling direction of the textured silicon steel plate, when laser scribing the surface of said textured silicon steel plate, wherein the spots of said plurality of focused light spots are arranged along the width direction of the textured silicon steel plate and there is an energy band gap region between adjacent spots,wherein the size "b" of each focused light spot in the width direction of the textured silicon steel plate is larger than the size "a" in the longitudinal direction of the textured silicon steel plate.

[0023] In this document, the phrase "corresponding to each position along the length along the rolling direction of the textured silicon steel plate" refers to a position where the focused laser spot is stretched and elongated in the width direction of the steel, compared with the rolling direction of the steel plate, and this is a position where the scribing line to be formed is scanned by such an elongated light spot.

[0024] In the current prior art, there are three main methods in the art for reducing the steel loss and vibration noise of textured silicon steel plate: (1) metallurgical method: by optimizing the composition system and process parameters, an ideal secondary recrystallization structure is obtained and the orientation degree is increased; (2) tension control: by improving the tension of the surface coating of the substrate and refining the magnetic domains, the steel loss and magnetostriction are reduced; (3) surface scribing: by using laser, electron beam, plasma, etc., continuous or discontinuous scribing lines are applied at a certain spacing on the surface of silicon steel along the rolling direction, and stress or strain is applied to refine the magnetic domains and reduce the steel loss.

[0025] In recent years, through the use of metallurgical methods, the grain orientation degree has been improved to a very high level, and the average grain orientation deviation angle in Hi-B steel is less than 5°. Tensile stress coating and surface scribing technologies have also been developed and commercially applied, producing textured silicon steel plates with good magnetic properties.

[0026] However, with the development of the global economy and population growth, people's demands on their living environment are becoming increasingly stringent. This requires further improvements in energy efficiency to reduce unnecessary losses. For grain-oriented silicon steel, used to manufacture the core material for energy-saving transformers in power transmission networks, core losses must be further reduced. The laser scribing technology currently in use generates localized thermal stress through laser irradiation, thereby reducing the width of magnetic domains to reduce losses in the steel. In actual use, high laser energy introduces more heat, which has a better effect on reducing magnetic domains and reducing losses in the steel. Therefore, to reduce high losses in the steel, higher laser energy is required.However, excessive laser energy can damage the silicate and phosphate coatings on the surface of textured silicon steel, increasing the risk of interlayer conductivity during operation. Therefore, low laser energy is required to prevent damage to the surface coating of textured silicon steel. To prevent damage to the surface coating of textured silicon steel, laser scribing technologies currently limit the heat input from the laser in commercial applications, typically reducing steel loss by about 10% to 15%. Further reductions in steel loss are very difficult.

[0027] Therefore, the inventors innovatively developed a new laser scribing combination method to resolve the contradiction between the effect of improving the steel loss performance of textured silicon steel and the laser energy required to keep its surface coating intact, so as to further improve the effect of reducing steel loss without damaging the surface coating of textured silicon steel.

[0028] In the present invention, the inventors thoroughly studied the temperature rise phenomenon caused by irradiation of the steel plate surface during the laser scribing process. They found that the temperature of a local microregion on the steel plate surface continuously increases due to continuous laser irradiation. When the temperature of this region rises to the damage threshold for the surface coating, the surface coating of the steel plate is also destroyed due to the excessive temperature.

[0029] In recent years, researchers in this field have proposed using beam shaping to shape the spot focused on the surface of a steel plate into an elliptical or rectangular shape with a large extension in the laser scanning direction. This solution effectively dissipates laser energy and avoids excessive temperature rise in localized areas caused by excessive energy concentration. At the same time, expanding the spot size in the scanning direction increases the laser irradiation time (i.e., dwell time) in localized microregions. This can effectively dissipate the heat generated by irradiation into the surrounding areas, forming a thermal stress zone that is wide in the rolling direction and deep in the thickness direction. This is favorable for magnetic domain refinement and achieving significant results.However, with this solution, localized microregions on the silicon steel surface continue to receive heat continuously from the laser irradiation. At the same time, due to the high speed of the production line and the high laser scanning speed corresponding to the operating speed—typically 100 m / s or even 200 m / s or more—the dwell time is mere microseconds. Therefore, the problem of the insulating film on the surface being easily damaged by excessive temperature increases still exists.

[0030] To solve this problem, the inventors developed a laser scribing method in the present invention, which uses a beam splitting method to divide an incident light beam into multiple beams, and the spacing of the focused light spots thus formed in the scanning direction of the laser and the energy distribution of each light spot are strictly controlled, so as to realize control over the temperature rise on the surface of the steel plate caused by laser irradiation, forming a large thermal stress region in the thickness range of the steel plate, which can not only improve the steel loss rate of the textured silicon steel plate by up to 15% or more compared with that before scribing, but also avoid damage to the thin film on the surface of the steel plate caused by excessive temperature rise.

[0031] Preferably, in the method for laser scribing a textured silicon steel plate according to the present invention, the focused light spots are elliptical or rectangular.

[0032] In the above technical solution of the present invention, the focused light spot formed by the laser can be realized by a combination of one or more means such as a diffraction beam splitter and a polarization beam splitter, and the shape of the formed focused light spots can be elliptical or rectangular.

[0033] Preferably, in the method for laser scribing a textured silicon steel plate according to the present invention, the total length D of a plurality of focused light spots corresponding to each position along the length along the rolling direction of the textured silicon steel plate, extending in the width direction of the textured silicon steel plate, is ≤80 mm, preferably 38 ≤ D ≤ 60 mm.

[0034] In the above technical solution of the present invention, due to the isotropic heat transfer of the textured silicon steel plate, if the total holding time under laser irradiation is too long, the heat will be dissipated over a larger range in the rolling direction of the steel plate, thereby forming a larger thermal stress zone. This not only increases hysteresis loss but also reduces magnetic induction. Therefore, the developed total length of the plurality of formed focused light spots must be controlled within a certain range so that the total holding time is limited to a certain range. After repeated experiments, the inventors determined that the developed total length of the plurality of focused light spots arranged along the width direction of the textured silicon steel plate can be preferably controlled to be ≤80 mm.When the total length exceeds 80mm, the hysteresis loss increases, resulting in an increase in the total loss and a decrease in the magnetic flux density B8.

[0035] Preferably, in the laser scribing method of a textured silicon steel plate according to the present invention, the textured silicon steel plate has a dimension "a" along its length direction of 10-100 μm, preferably 40-80 μm.

[0036] In the laser scribing method for a textured silicon steel plate according to the present invention, the textured silicon steel plate preferably has a dimension b along its width direction of ≤8 mm, preferably 4-6 mm. If the dimension b exceeds 8 mm, the overall length of the light spots will be difficult to control, and prolonged exposure to irradiation will lead to heat accumulation and destruction of the surface coating.

[0037] Preferably, in the method for laser scribing a textured silicon steel plate according to the present invention, corresponding to each position along the length along the rolling direction of the textured silicon steel plate, the ratio of the length ds of the energy-forbidden zone region between the pre-focus spot and the post-focus spot to the length of the pre-focus spot in the laser scanning direction is from 0.5 to 2, preferably 0.7-1.3.

[0038] In the above-mentioned technical solution of the present invention, the size of the energy gap region between the focused light spots also has a direct impact on the temperature reduction during scanning. The ratio of the energy gap region between each focused light spot and the next focused light spot to the length of said focused light spot is controlled within the range of 0.5-2. If the ratio is lower than 0.5, it is difficult to achieve effective temperature reduction, and the surface coating of the textured silicon steel will crack; if the ratio is higher than 2, the temperature reduction is too great, and it is difficult for the next focused light spot to maintain the surface temperature of the steel plate in the range where sufficient thermal stress is generated, and the effect of refining magnetic domains and reducing steel loss cannot be achieved.

[0039] Preferably, in the laser scribing method of a textured silicon steel plate according to the present invention, the power density p of each focused light spot is 1000-3000 W / mm 2 .

[0040] In the above technical solution of the present invention, in order to achieve the goal of reducing steel loss without damaging the surface coating, the range of power density values ​​p of the focused laser light spot is also controlled. When the power density exceeds 3000 W / mm 2 , excessively large energy will cause damage to the surface coating of the textured silicon steel plate; and when the power density is below 1000W / mm 2, the laser energy is too small, and it is difficult to form an effective thermal stress zone on the surface of the textured silicon steel plate, so it is not enough to achieve the effect of refining the magnetic domains, and the improvement rate of the loss index in the steel is low.

[0041] Preferably, in the method for laser scribing a textured silicon steel plate according to the present invention, along the laser scanning direction, the ratio of the power density of the subsequent focused light spot to the previous focused light spot is 0.75-0.95.

[0042] Through repeated experiments, the inventors found that the ratio of the power density of the subsequent focused light spot to the previous focused light spot is 0.75-0.95. When this ratio is lower than 0.75, the energy transferred by the subsequent focused spot is too small, and the surface temperature of the steel plate gradually decreases after the initial scanning of the laser spot, making it difficult to form an effective thermal stress zone, and the effect of refining the magnetic domains in reducing steel loss is limited; and when the ratio is higher than 0.95, the energy transferred by the subsequent focused spot is too large, and the surface temperature of the steel plate gradually increases, eventually reaching the damage threshold of the surface coating.

[0043] Preferably, in the method for laser scribing a textured silicon steel plate according to the present invention, a plurality of focused light spots are formed using a diffraction beam splitter and / or a polarization beam splitter.

[0044] Another object of the present invention is to provide a grain-oriented silicon steel plate which has the characteristics of low iron loss and resistance to coating failure, and can be used for the manufacture of energy-saving transformers for ultra-high voltage networks and has very broad application prospects.

[0045] In order to achieve the above object, the present invention provides a textured silicon steel plate which is produced by the laser scribing method of the present invention.

[0046] When producing the grain-oriented silicon steel plate of the present invention, steel with a certain amount of silicon can first be produced through the following processes: iron smelting, steel smelting and continuous casting, then a hot rolling process, followed by one cold rolling process or two cold rolling processes with intermediate annealing to roll the steel into silicon steel plates with a predetermined thickness.

[0047] Then, the produced silicon steel plate is subjected to decarburization annealing to form a primarily recrystallized steel plate with an oxide film on the surface. After applying a magnesium oxide release agent, the silicon steel plate is subjected to high-temperature annealing to form a Gaussian-textured silicon steel plate through secondary recrystallization, and the oxide film on the surface reacts with the release agent to form a lower magnesium silicate layer. After this, the silicon steel plate is subjected to hot stretching, leveling, annealing, coating, and baking processes. Then, the surface of the steel plate is laser-scribed according to the present invention to obtain a finished textured silicon steel plate.

[0048] Preferably, in the manufacturing method of the present invention, the improvement rate of the loss in the grain-oriented silicon steel, compared with the rate before scribing, is increased to 15% or more.

[0049] Compared with the prior art, the laser scribing method of a low steel loss textured silicon steel plate and the textured silicon steel plate of the present invention have the following advantageous effects:

[0050] In the present invention, the inventors develop a new laser scribing method in which an optimized laser scribing method is used to form a thermal stress zone so that the temperature rise of the steel plate can be controlled and the loss in the textured silicon steel plate can be reduced without damaging the surface coating in the areas that are subjected to scribing.

[0051] When applying the laser scribing method of the present invention, a plurality of focused light spots are formed on the surface of a steel plate by using a laser beam splitting method, and the power density of each focused light spot is controlled in the range of 1000 to 3000 W / mm 2 ; the ratio of the energy-forbidden zone area to the corresponding focused light spot corresponding to each position along the length in the rolling direction of the textured silicon steel plate, along the length in the scanning direction, is controlled in the range of 0.5 - 2; at the same time, along the laser scanning direction, the ratio of the power density of the subsequent focused light spot to the previous focused light spot is controlled in the range of 0.75-0.95.

[0052] According to the laser scribing method of the present invention, the continuous increase in the surface temperature of a steel plate caused by the continuous accumulation of laser thermal radiation can be effectively prevented by the existence of energy gaps between focused light spots due to laser beam splitting. Therefore, while ensuring the integrity of the coating in the microregion where the surface is scribed, the effect of reducing steel loss by refining magnetic domains is improved, and the improvement in steel loss increases to 15% or more compared to the loss before scribing. The textured silicon steel plate produced in this way with low steel loss can be used for the manufacture of energy-saving transformers for ultra-high-voltage networks and has wide application prospects.

[0053] Brief description of drawings

[0054] Fig. 1 is a diagram of a laser scribing method according to the present invention, which uses laser beam splitting to form focused spots and scan the surface of a steel plate.

[0055] Fig. 2 is a schematic diagram showing that a focused light spot according to the present invention is focused on the surface of a steel plate.

[0056] Fig. 3 is a schematic graph showing the relationship between the irradiation time and the change in temperature of a local microregion on the surface of a steel plate when the steel plate is scribed by the laser scribing method according to the present invention and the conventional laser scribing method.

[0057] Fig. 4 is a system architecture diagram showing an optical path formation system for implementing a laser scribing method according to the present invention.

[0058] Detailed description of the invention

[0059] The laser scribing method for a low-loss grain-oriented silicon steel plate and the grain-oriented silicon steel plate according to the present invention will be further explained and described below in conjunction with the drawings and specific embodiments of the invention. However, the explanation and description do not unduly limit the technical solutions of the present invention.

[0060] Fig. 1 is a schematic drawing showing a laser scribing method according to the present invention using laser beam splitting to form focused light spots and scan the surface of a steel plate.

[0061] Fig. 2 is a schematic diagram showing focused light spots of the present invention focusing on the surface of a steel plate.

[0062] In Fig. 1 and Fig. 2, it can be seen that these figures are diagrams showing the laser scribing method of the present invention using laser beam splitting to form a plurality of focused light spots on the surface of a steel plate.

[0063] In the present invention, after splitting the incident laser beam, a plurality of focused light spots 1, 2, 3……n-1, n are formed on the surface of the steel plate, and the length of the focused light spots in the laser scanning direction (i.e., in the width direction of the textured silicon steel plate) is b1, b2, b3……b n-1 , b n accordingly, a plurality of focused light spots are arranged along the width direction of the textured silicon steel plate and have a forbidden energy band region of length ds1, ds2, ds3……ds between adjacent spots n-1respectively. The sum of the lengths of the focused light spots in the width direction of the textured silicon wafer is the total length D of the spots.

[0064] In this application, "previous focus spot" and "post-focus spot" refer to the spots of any two adjacent focus spots along the laser scanning direction. For example, if the laser scanning direction starts from spot 1 in Fig. 2, spot 1 is the "previous focus spot," and spot 2 is the "post-focus spot." Similarly, for spot 2 and spot 3, spot 2 is the "previous focus spot," and spot 3 is the "post-focus spot," etc.

[0065] In this embodiment, the lengths of the focused light spots in the direction perpendicular to the laser scanning direction (i.e., in the length direction of the textured silicon steel sheet) can be set to the same value "a". Of course, in some other embodiments, the lengths of different focused light spots in the direction perpendicular to the laser scanning direction may be different, but they all must meet the range of laser power density required in the present invention. Under normal production conditions, the laser scanning speed is very high, reaching 100 m / s or more, and scanning the entire width of a steel plate with a width of about 1 m takes only 0.01 s or less. Therefore, in order to simplify the spatial arrangement during the production process, the laser scanning direction is generally made approximately the same as the width direction of the steel plate.

[0066] It should be noted that the inventors also studied in detail the process of increasing the surface temperature of silicon steel during laser scribing, and the result is shown in Fig. 3. Fig. 3 schematically shows the relationship between the irradiation time and the change in temperature of a local microregion on the surface of a steel plate when the steel plate is scribed by the laser scribing method of the present invention and the conventional laser scribing method.

[0067] In the dependence graph shown in Fig. 3, the laser scribing method of the present invention corresponds to the solid line in Fig. 3, and the conventional laser scribing method corresponds to the dotted line in Fig. 3.

[0068] Referring to Fig. 3, it can be seen that when using the conventional laser scribing method, since a local microregion on the surface of the steel plate is continuously irradiated with a laser, the temperature in this region continuously increases and reaches a peak value in the range of the laser irradiation time, and then the temperature in this region gradually decreases. On the other hand, when using the laser scribing method developed by the inventors of the present invention, due to the presence of a certain interval between adjacent focused spots, a certain energy band gap region is formed between the focused spots. Therefore, the temperature of the local microregion on the surface of the steel plate decreases to a certain extent, and the energy of the subsequent focused spot is lower than the energy of the previous focused spot.The temperature of the irradiated area is always controlled to ensure it remains below the damage threshold of the surface coating. At the same time, the overall exposure time is increased, heat diffusion occurs over a wider range, and thermal stress is generated over a larger area, resulting in an improvement in the loss parameters of the steel.

[0069] Based on the above principle, it can be determined that the controlled parameters directly related to the effect of the present invention include: the sizes of the focused spot, a and b, the power density of each focused spot, p, the band gap of the focused spots, ds, and the total length of the light spots, D, which is directly related to the total duration of laser irradiation (see Fig. 2). It should be noted that by splitting one laser beam of a continuous laser or a pulsed laser used in traditional technologies into several laser beams to form several focused spots with energy band gap regions, ds, between adjacent spots, it is possible to reduce the accumulated heat in the scribing region on the surface of the steel plate during laser scribing.With respect to the power density p of each focused spot, the forbidden zone between the focused spots ds, and the total length D of the spots directly related to the total duration of laser irradiation, they can be selected in any preferred range, as long as the continuous increase in the surface temperature of the steel plate caused by the continuous accumulation of laser thermal radiation is effectively prevented while the scribed line is formed during laser scribing.

[0070] Compared with the prior art, the focused spot formed in the present invention has a smaller dimension "a" in the rolling direction of the steel plate (i.e., in the length direction of the grain-oriented silicon steel) to reduce the diffusion of laser irradiation heat in the rolling direction and avoid an increase in hysteresis loss. Theoretically, the smaller the dimension "a," the better the effect of the present invention. However, in actual industrial production, since the laser scanning range must cover the entire width of the steel plate, typically 90 mm or more, a longer focal length is required. Furthermore, to prevent defocusing caused by shape fluctuations in the steel strip, a certain focal depth is required that is sufficient to cover the defocus deviation caused by shape fluctuations in the plate and the shaking of the steel strip.Therefore, the lower limit of the focused spot size "a" is limited by the optical system and must be no less than 10 μm. When the focused spot size "a" is smaller than this value, the complexity of the optical system increases significantly, requiring multiple lasers to be simultaneously positioned in the width direction of the wafer to achieve laser scribing across the entire wafer in the width direction. According to the inventors' research, the upper limit of the focused spot size "a" in the rolling direction is preferably set at 100 μm. If this value is exceeded, heat will dissipate in the rolling direction, the thermal stress zone will increase in the areas near the notches (scribing marks) in the rolling direction, and hysteresis losses will increase. Overall losses will not decrease further, and the magnetic induction B8 will also decrease.

[0071] In the present invention, after incident laser light is split by a diffraction beam splitter and a polarization beam splitter, a plurality of focused light spots are formed on the surface of a textured silicon steel plate. The focused light spots are generally elliptical in shape, and the spot size b in the laser scanning direction (i.e., in the width direction of the textured silicon steel plate) is assumed to be larger than the size a in the rolling direction, so as to make the laser energy as dispersed as possible and prevent the formation of excessive power density and damage to the surface coating.

[0072] It should be noted that in the present invention, the power density p of the focused light spot may be an average value, which is defined as follows:

[0073]

[0074] where P0 is the total output power (W) of the laser; n is the number of focused spots, and S is the area (mm 2 ) focused spots. When the focused spots are elliptical, the formula for calculating the area S of the focused spots can be expressed as:

[0075]

[0076] It should be noted that in some other embodiments, the laser can also form rectangular spots using a beam former, and the long side of the rectangle is the value b, extending along the width direction of the steel plate, and the short side of the rectangle is the value a, extending along the rolling direction of the steel plate (i.e., the length direction of the textured silicon steel plate). These embodiments, in which the focused spots are rectangular, are also within the scope of the present invention and will not be described in detail here.

[0077] In order to achieve the goal of reducing steel loss without damaging the surface coating, the present invention requires strict control of the laser focal spot power density p. When the power density p exceeds 3000 W / mm 2 , excessive laser energy will cause damage to the surface coating; when the power density p is below 1000 W / mm 2 The laser energy is too low, making it difficult to form an effective thermal stress zone on the surface of the textured silicon steel sheet. Therefore, it is insufficient to achieve the effect of magnetic domain refinement, and the improvement rate of steel loss is low. Therefore, in practical applications, it is necessary to control the power density of each focal spot to be within the range of 1000-3000 W / mm. 2 .

[0078] In the present invention, after splitting the laser beam, the gap between adjacent focused spots will cause a certain temperature drop in the corresponding region, which can prevent damage to the surface coating due to excessive temperature in the scanning region. Therefore, it is necessary to control the power distribution ratio between subsequent focused spots and previous focused spots, as well as the size of the energy band gap ds.

[0079] Through repeated experiments, the inventors determined that the ratio of the power densities of subsequent focused spots to the previous focused spots is 0.75-0.95, that is, the range should be 0.75-0.95. When the value Below 0.75, the energy transferred by the subsequent focused spot is too small, and the surface temperature of the steel plate begins to gradually decrease after scanning by the initial laser spot, so it is difficult to form an effective thermal stress zone, and the effect of magnetic domain refinement in reducing steel loss is insignificant; when the value exceeds 0.95, the energy transferred by the subsequent focused spot is too large, the surface temperature of the steel plate gradually increases, and the damage threshold of the surface coating will still be reached.

[0080] The size of the energy band gap region ds between the focused spots also has a direct impact on the temperature reduction generated during scanning. The ratio of the length of the energy band gap region between each focused spot and the next focused spot to the length of the focused spot in the scanning direction should be controlled within 0.5-2, i.e., the range should be 0.5-2. When the value below 0.5, it is difficult to form an effective temperature reduction, and the surface coating of textured silicon steel will crack; and when the value above 2, the temperature decrease is too large, and it is difficult for the subsequent focused spot to maintain the surface temperature of the steel plate in the range that can generate sufficient thermal stress, and it is impossible to achieve the effects of refining magnetic domains and reducing steel loss.

[0081] Therefore, the total unfolded length of the plurality of focused light spots must be adjusted within a certain range to limit the total holding time. After repeated experiments, the inventors determined that the total unfolded length of the plurality of focused light spots arranged along the width direction of the textured silicon steel plate can be controlled to be preferably ≤80 mm. When the total length exceeds 80 mm, hysteresis loss increases, resulting in increased overall loss and a decrease in magnetic flux density B8.

[0082] Furthermore, it should be noted that due to the isotropic heat transfer of grain-oriented silicon steel sheets, if the total holding time during laser irradiation is too long, heat will be dissipated over a larger range in the rolling direction of the steel plate, forming a larger thermal stress zone, which will increase hysteresis loss and reduce magnetic flux density. The developed total length of the plurality of focused light spots must be controlled within a certain range to limit the total holding time. After repeated experiments, the inventors determined that the developed total length D of the plurality of focused light spots in the width direction of the grain-oriented silicon steel sheet should be controlled to preferably be ≤80 mm. When the total length exceeds 80 mm, the hysteresis loss will increase, resulting in an increase in the total loss and a decrease in magnetic flux density B8.

[0083] In the present invention, the calculation formula for the expanded total length D of a plurality of focused light spots is as follows:

[0084]

[0085] Fig. 4 schematically shows the architecture diagram of the optical path system for implementing the laser scribing method according to the present invention.

[0086] Figure 4 illustrates an optical path system for implementing the laser scribing method according to the present invention as an example. In addition, other systems can also be used to achieve the spectral focusing effect required in the present invention, and these systems are also included in the scope of the present invention. In the optical path shown in Figure 4, the laser beam 8 is emitted from the laser 1, passes through the reflector 2, the reflector 3, and then passes through the beam forming system 4 to form a beam with an elliptical energy distribution. Then, it passes through the diffraction spectroscopic element 5 to form multiple beams, which pass through the scanning focusing mirror 6 and quickly scan the surface of the textured silicon steel plate 7 to form a stress zone 9 during scribing.

[0087] There are no particular limitations regarding the use of a laser source in this invention. A commonly used laser in this field is a continuous-wave laser with a wavelength of 1066 nm. Other lasers can also be used to achieve the objective of the present invention and are not described in detail herein.

[0088] Next, the technical solution of the present invention will be illustrated with specific examples showing the beneficial effects provided by the laser scribing method developed by the authors of the present invention.

[0089] Examples 1-7 and Comparative Examples 1-2

[0090] The grain-oriented silicon steel sheets in Examples 1-7 and Comparative Examples 1-2 were produced through the following steps:

[0091] (1) producing grain-oriented silicon steel through the following processes: iron smelting, steel making, continuous casting, hot rolling and then cold rolling to a final thickness of 0.22mm, and after decarburization annealing at 850°C, applying an insulating agent MgO on the surface of the grain-oriented silicon steel to form a surface oxide layer, then rolling the steel into a coil and soaking under high-temperature annealing conditions of 1200°C for 20 hours, then cleaning and drying the unreacted residual MgO on the surface and applying an insulating coating on the surface of the grain-oriented steel plate;

[0092] (2) Laser scribing textured silicon steel on one side along the transverse direction.

[0093] When laser scribing the surface of a textured silicon steel plate, a plurality of focused spots are formed on the surface of the textured silicon steel plate by splitting a laser beam corresponding to each position along the length along the rolling direction of the textured silicon steel plate, these plurality of focused light spots are arranged along the width direction of the textured silicon steel plate, and there are energy band gap regions between adjacent spots; the dimension b of each focused light spot along the width direction of the textured silicon steel plate is larger than the dimension a along the length direction of the textured silicon steel plate.

[0094] During laser scribing, the dimension "a" is controlled to be 10-100 μm; the total length D corresponding to each length position along the rolling direction of the textured silicon steel plate of the plurality of focused light spots arranged along the width direction of the textured silicon steel plate is controlled to be ≤80 mm; the ratio ds / b of the length ds of the energy band gap region to the corresponding length b of the focused light spot in the scanning direction is controlled in the range of 0.5-2; the power density of each focused light spot is controlled to be in the range of 1000-3000 W / mm 2 ; and the ratio of the power density of the subsequent focused light spot to the power density of the previous focused light spot along the laser scanning direction is adjusted to be 0.75-0.95.

[0095] It should be noted that the laser used in Examples 1-7 and Comparative Examples 1-2 was a continuous-wave single-mode fiber laser with a wavelength of 1066 nm, a tunable diffractive optical element was used to split the light beam into secondary beams with different parameters, and the surface of the steel plate was scanned to form a stress zone by scribing, while in the Comparative Examples, a diffractive optical element was not used to split the light, and the power density was adjusted by adjusting the output power of the laser.

[0096] The laser scribing process adopted in the present invention is performed after the final annealing of the grain-oriented silicon steel. Therefore, the present invention places no particular limitations on the grain-oriented silicon steel plate, and in actual applications, it is not limited to grain-oriented silicon steel plates produced according to the above process.

[0097] The process parameters of the grain-oriented silicon steel sheets in Examples 1-7 and Comparative Examples 1-2 in the above process are shown in Table 1.

[0098] Table 1

[0099]

[0100] Magnetic conductivity (B8) and losses (P 17 / 50) in the steel for the grain-oriented silicon steel plates of Examples 1 to 7 and Comparative Examples 1 to 2 were tested using the method described in GB / T 13789-2008 before and after laser scribing; the length in the rolling direction and transverse direction of the specimens prepared in the Examples and Comparative Examples was controlled to be 500 mm, to measure the magnetic flux density B8 value of the grain-oriented silicon steel under excitation with a magnetic field of 800 A / m, and the non-productive electric power P 17 / 50 , consumed due to magnetization when the magnetic flux density under the influence of the 50 Hz AC magnetic field reaches 1.7 T. In addition, the degree of damage to the coating in the scribed areas of the grain-oriented silicon steel plates of Examples 1-7 and Comparative Examples 1-2 was also tested, and the corresponding test results are shown in the following Table 2.

[0101] Table 2

[0102]

[0103] Table 2 above shows that the textured silicon steel plates after laser scribing in Examples 1–7 have good steel loss and magnetic conductivity, their surface coating is intact, and there is a significant reduction in steel loss due to magnetic domain refinement. Compared with before scribing, the improvement (i.e., reduction) in steel loss can reach 15% or more.

[0104] On the other hand, the textured silicon steel sheet after laser scribing in Comparative Example 1 achieved a higher improvement effect in iron loss by adjusting the laser power, but its coating was damaged due to heat accumulation. Consequently, when laser scribing was performed on the textured silicon steel plate in Comparative Example 2, the laser power was reduced. Although the coating on the surface of the steel sheet after scribing was complete, the improvement effect (i.e., reduction) in iron loss was weak.

[0105] It should be noted that the above embodiments are merely illustrative of the present invention, and the present invention should not be construed as limited to these embodiments. Any changes or variations that can be directly obtained or easily devised by those skilled in the art from the disclosure in this application should be considered within the scope of the present invention.

Claims

1. A method for laser scribing a textured silicon steel plate, which comprises forming a plurality of focused light spots corresponding to each position along the length along the rolling direction of the textured silicon steel plate on the surface of the textured silicon steel plate by splitting a laser beam during laser scribing of said surface of the textured silicon steel plate, wherein the spots of said plurality of focused light spots are arranged along the width direction of the textured silicon steel plate and between adjacent spots there is an energy-forbidden zone region (ds), wherein the size (b) of each focused light spot along the width direction of the textured silicon steel plate is larger than the size (a) along the length direction of the textured silicon steel plate,wherein the ratio of the power densities of the subsequent focused light spot to the previous focused light spot in the direction of laser scanning is 0.75-0.95, and the power density (p) of each focused light spot is 1000-3000 W / mm, 2 .

2. A method for laser scribing a textured silicon steel plate according to claim 1, wherein the focused light spots are elliptical or rectangular.

3. The method for laser scribing a textured silicon steel plate according to claim 1, wherein the total length, D, of said plurality of focused light spots corresponding to each position in the rolling direction of the textured silicon steel plate, extending in the width direction of the textured silicon steel plate, satisfies the relationship: 18 mm ≤ D ≤ 80 mm, preferably 38 ≤ D ≤ 60 mm.

4. The method for laser scribing a textured silicon steel plate according to claim 1, wherein the size (a) of the focused light spots along the length direction of the textured silicon steel plate is 10-100 μm, preferably 40-80 μm.

5. The method for laser scribing a textured silicon steel plate according to claim 1, wherein the size (b) of the focused light spots along the width direction of the textured silicon steel plate is 3-8 mm, preferably 4-6 mm.

6. A method for laser scribing a textured silicon steel plate according to claim 1, wherein the ratio of the length (ds) of the region of the energy forbidden zone between the prior focusing spot and the subsequent focusing spot to the length of the prior focusing spot in the laser scanning direction, corresponding to each position along the length along the rolling direction of the textured silicon steel plate, is 0.5-2, preferably 0.7-1.

3.

7. A method for laser scribing a textured silicon steel plate according to claim 1, wherein said plurality of focused light spots are formed using a diffraction beam splitter and / or a polarization beam splitter.

8. A method for laser scribing a textured silicon steel plate according to claim 2, wherein the elliptical or rectangular shape of the focused light spots is formed using a beam former.

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