Laser scribing method for low iron loss grain-oriented silicon steel sheet and grain-oriented silicon steel sheet

Abstract

In the present invention, a laser scribing method for a grain-oriented silicon steel sheet is disclosed. When performing surface laser scribing on a grain-oriented silicon steel sheet using this laser scribing method, a plurality of focused spots are formed on the surface of the grain-oriented silicon steel sheet in a laser beam splitting manner corresponding to each length position in the rolling direction of the grain-oriented silicon steel sheet. The plurality of focused spots are distributed in the width direction of the grain-oriented silicon steel sheet, and an energy gap region exists between two focused spots. Here, the dimension b of each focused spot in the width direction of the grain-oriented silicon steel sheet is larger than the dimension a of each focused spot in the length direction of the grain-oriented silicon steel sheet. Accordingly, in the present invention, a grain-oriented silicon steel sheet produced by using the laser scribing method in the present invention is further disclosed. With this grain-oriented silicon steel sheet, the iron loss of the grain-oriented silicon steel is reduced and the loss of the surface coating is avoided.

Description

Technical Field

[0001] Technical Field The present invention relates to a manufacturing process of grain-oriented silicon steel, and particularly to a method for laser scribing grain-oriented silicon steel sheets.

Background Art

[0002] Background In recent years, as global energy and environmental problems have become increasingly prominent, countries around the world generally raise the energy consumption standards of various energy-consuming devices and reduce their ineffective energy consumption. For example, in the power transmission system, the losses caused by transformers account for about 40% of the total system losses. The core of grain-oriented silicon steel is a core component of the transformer, and its losses account for about 20% of the total losses.

[0003] The losses caused by the core are usually called iron losses. Therefore, reducing the iron losses of grain-oriented silicon steel used to prepare the transformer core has great economic and social benefits.

[0004] As is well known, grain-oriented silicon steel is named because the direction of the internal particle arrangement is almost the same as the rolling direction of the steel sheet. In grain-oriented silicon steel sheets, since the particle arrangement direction is in the easy magnetization direction, the higher the particle orientation degree, the better the magnetic properties of the silicon steel sheet, which appear as higher magnetic induction and lower iron losses. In the particles of grain-oriented silicon steel, there exists a magnetic domain structure generated by the spontaneous magnetization of ferromagnetic substances. The magnetic moments of each atom in each magnetic domain are spontaneously arranged in parallel to form a 180° magnetic domain parallel to the easy magnetization direction of the particle {110}<100>. Adjacent magnetic domains are 180° opposite to each other, and there exists a magnetic wall consisting of dozens to hundreds of atomic layers between them. In the process of magnetization, the magnetic moments in adjacent magnetic domains are arranged in the same direction by the movement of the magnetic wall, thereby realizing the magnetic conduction performance. Therefore, the magnetic domain structure is the result of the principle of minimum energy action and is also a basic factor affecting the steel loss, magnetic induction and magnetostriction characteristics of grain-oriented silicon steel.

[0005] The magnetic conductivity performance of silicon steel sheets appears as magnetic induction generally represented by B8, which is the magnetic flux density (T) of the silicon steel sheet under an excitation magnetic field of 800 A / m; the iron loss is P, which is the non-effective electrical energy (W / kg) consumed by the magnetization of the silicon steel sheet when the magnetic flux density in the strip reaches 1.7 T under an AC excitation magnetic field of 50 Hz. 17 / 50 It should be noted that it is generally represented by this.

[0006] From the current prior art, it is known that the iron loss of grain-oriented silicon steel sheets includes three parts: hysteresis loss, eddy current loss, and abnormal eddy current loss. Hysteresis loss is the energy loss caused by the hysteresis phenomenon in magnetic materials during the magnetization and demagnetization processes, where factors such as inclusions, crystal defects, internal stress, and crystal orientation that impede the movement of magnetic walls cause the magnetic induction intensity to lag behind the change in magnetic field strength, resulting in the inhibition of the change in magnetic flux. Eddy current loss is the energy loss caused by eddy currents induced by the change in magnetic flux due to the alternating magnetization of grain-oriented silicon steel sheets, which is related to the conductivity and thickness of the grain-oriented silicon steel sheets. Abnormal eddy current loss is the energy loss caused by the different structures of magnetic domains in grain-oriented silicon steel sheets during magnetization, which is mainly affected by the width of the magnetic domains.

[0007] Currently, there are three main methods to improve the performance of grain-oriented silicon steel: (1) controlling the secondary recrystallization structure of the finished product by metallurgical means, thereby improving the orientation degree of grain-oriented silicon steel and reducing the iron loss; (2) forming a tension coating on the surface of grain-oriented silicon steel to subdivide the magnetic domains and reduce the iron loss; (3) scribing the surface of grain-oriented silicon steel by means such as laser, electron beam, mechanical, and electrochemical to form linear stress or strain, thereby subdividing the magnetic domains and reducing the iron loss.

[0008] Among these three methods, the above method (3) has received the most attention and has now become one of the research hotspots in this field. The principle of reducing iron loss by subdividing magnetic domains through scribing in the above method (3) is briefly explained as follows: There is a magnetic domain structure inside the particles of grain-oriented silicon steel. When there is no external magnetic field condition, the magnetic domains inside the grain-oriented silicon steel are mainly 180° magnetic domains arranged antiparallel. The width of one magnetic domain can usually reach from dozens of microns to several millimeters. There is a transition layer of dozens to hundreds of atomic layers between adjacent magnetic domains, which is called the magnetic wall. In the magnetization process, under the drive of the external magnetic field, the magnetic moment rotates, and adjacent magnetic domains combine with each other through the movement of the magnetic wall, thereby realizing the magnetic conduction function. At the same time, due to the difference in the magnetic domain structure in different regions during the movement of the magnetic wall, micro eddy currents are generated in the micro region, thereby generating an eddy current loss called the abnormal eddy current loss Pa of the grain-oriented silicon steel.

[0009] The abnormal eddy current loss Pa is directly related to the inherent magnetic domain structure of the grain-oriented silicon steel, and it can be seen that it is more directly related to the magnetic domain width of the grain-oriented silicon steel. Therefore, by reducing the magnetic domain width, the abnormal eddy current loss Pa can be effectively reduced. The abnormal eddy current loss Pa accounts for a large proportion of the total loss of the grain-oriented silicon steel. Especially for thin-gauge grain-oriented silicon steel with a thickness of 0.23 mm or less, the abnormal eddy current loss Pa can account for more than 40%. Therefore, by using scribing to subdivide the magnetic domains of the grain-oriented silicon steel, that is, reducing the magnetic domain width, the abnormal eddy current loss can be effectively reduced, thereby reducing the overall iron loss of the grain-oriented silicon steel.

[0010] Currently, the scribing technology for the surface of grain-oriented silicon steel to subdivide magnetic domains and reduce the steel loss of grain-oriented silicon steel can be divided into two categories according to the scribing effect:

[0011] One is to use a laser, plasma beam, electron beam, etc. to form a linear thermal stress region at a certain distance on the surface of the oriented silicon steel, thereby forming a score (scribed mark) that cannot withstand stress relief annealing, thereby reducing the width of the main magnetic domain and reducing the iron loss. Since the linear thermal stress disappears due to stress relief annealing, the products manufactured in this way are generally used to manufacture laminated core transformers that do not require stress relief annealing. The other is to form a score that can withstand stress relief annealing. The basic solution is to form a linear strain region or groove on the surface of the oriented silicon steel by mechanical gear rollers or electrochemical corrosion, etc., to reduce the width of the 180° magnetic domain, thereby reducing the iron loss. Since the strain region does not change even after stress relief annealing, the products manufactured in this way can be used to manufacture wound core transformers that require stress relief annealing.

[0012] For example, CN1216072A, published on May 5, 1999, titled "Oriented electromagnetic steel sheet having excellent magnetic properties, and method and apparatus for manufacturing the same", discloses a method for laser heat-resistant scribing of oriented silicon steel without damaging the film on the surface of the silicon steel by controlling the spot size, energy density and other parameters of the incident laser to realize a stress region having a large and deep closed magnetic domain region, thereby reducing the iron loss and magnetic strain of the oriented silicon steel.

[0013] As another example, CN101528951A, published on September 9, 2009, titled "One-way electromagnetic steel sheet excellent in iron loss characteristics", discloses a one-way electromagnetic steel sheet excellent in iron loss characteristics. In this patent, further considering the stress distribution state formed by laser scribing, and finely controlling the integral value of the compressive residual stress generated by laser irradiation of the steel sheet, thereby improving the iron loss improvement rate of laser scribing. However, as a technical solution, since the determination of the residual stress depends on an offline detection method such as X-ray diffraction, the detection cycle time is relatively long, so there are still certain difficulties in actual large-scale production.

[0014] As another example, CN102477484A, which was published on May 30, 2012 and titled "High-Speed Laser Scribing Method", discloses a high-speed laser scribing method that simultaneously scribes the upper and lower surfaces of a strip steel at equal intervals in a staggered pattern to ensure the uniformity of the iron loss improvement effect brought about by scribing. However, it should be noted that the scribing of the upper and lower surfaces requires precise control of the vibration of the strip steel, and the spatial layout for this purpose is relatively complex, so the implementation of this technical solution is relatively difficult.

[0015] However, as a result of intensive research, the inventors of the present invention have found that when laser scribing is performed using laser irradiation to form local stress, the temperature of a local area on the surface of the steel plate rises due to heat absorption. The thermal conductivity of silicon steel is isotropic, so it is very difficult to obtain a thermal stress region that is deep in the thickness direction of the steel plate and narrow in width in the rolling direction.

[0016] In the prior art, laser scribing usually uses a laser spot having an elliptical shape, and the major axis of the elliptical spot is controlled to coincide with the scanning direction and substantially coincide with the direction perpendicular to the rolling direction of the steel plate, thereby obtaining a longer residence time and raising the temperature of a local area of the steel plate to a range sufficient to cause a magnetic domain refinement effect. However, regardless of whether a continuous laser or a pulsed laser is used, the heat generated by laser irradiation always accumulates rapidly. If the residence time of laser irradiation is too long, a better iron loss reduction effect can be obtained, but due to the excessively high temperature, the problem of coating damage inevitably exists, which increases the risk of short-circuit failure of the transformer during use. If the residence time of laser irradiation is too short, the coating is not damaged, but the effect of reducing the iron loss achieved by laser scribing is limited.

[0017] Therefore, in order to solve the problems existing in the prior art, the inventors propose a new laser scribing method with controllable temperature rise to effectively improve and reduce the iron loss of grain-oriented silicon steel without damaging the surface coating of the steel sheet.

Summary of the Invention

Means for Solving the Problems

[0018] Summary One object of the present invention is to provide a method for laser scribing a grain-oriented silicon steel sheet. The method for laser scribing of the present invention optimizes the conventional process by using a beam splitting laser focusing scanning method, which can further improve the subdivision of magnetic domains and reduce the iron loss without damaging the surface coating of the grain-oriented silicon steel. The grain-oriented silicon steel sheet manufactured by the laser scribing method has the characteristics of low iron loss and coating breakage resistance, and can be used for manufacturing energy-saving transformers for ultra-high voltage power transmission networks. The laser scribing method can be expected to have a wide range of applications.

[0019] To achieve the above object, the present invention provides a method for laser scribing a grain-oriented silicon steel sheet including the following: when laser scribing the surface of the grain-oriented silicon steel sheet, forming a plurality of focused spots (or focal spots) on the surface of the grain-oriented silicon steel sheet by splitting the laser beam corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet, where the plurality of focused spots are arranged along the width direction of the grain-oriented silicon steel sheet and have an energy gap region between each other, and where the dimension b of each focused spot in the width direction of the grain-oriented silicon steel sheet is larger than the dimension a in the length direction of the grain-oriented silicon steel sheet.

[0020] In this specification, "corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet" refers to a position where the laser focusing spot extends in the width direction of the steel with respect to the rolling direction of the steel sheet and is elongated, and the position where the scribed line is to be formed is scanned in the form of this long light spot.

[0021] In the current prior art, there are three main methods in the field for reducing the iron loss and vibration noise level of grain-oriented silicon steel sheets: (1) Metallurgical method: By optimizing the composition system and process parameters, a complete secondary recrystallized structure is obtained and the degree of orientation is increased; (2) Tension control: By improving the tension of the surface coating of the substrate and subdividing the magnetic domains, the iron loss and magnetostriction are reduced; (3) Surface scribing: By means such as lasers, electron beams, and plasmas, continuous or discontinuous scribing lines are applied at regular intervals along the rolling direction on the surface of the silicon steel, and stress or strain is applied to subdivide the magnetic domains and reduce the iron loss.

[0022] In recent years, by using metallurgical techniques, the degree of orientation has been improved to a very high level, and the average orientation deviation angle of the particles in Hi-B steel is less than 5°. Also, the tension coating and surface scribing technologies have matured and are commercially available, and grain-oriented silicon steel sheets with good magnetic properties have been obtained.

[0023] However, with the development of the world economy and the increase in population, people's requirements for the living environment are becoming increasingly high. Therefore, further improvement in energy efficiency to reduce unnecessary losses is being demanded. For the oriented silicon steel used to manufacture the core material of the energy-saving transformer in the power grid, it is necessary to further reduce the iron loss. The laser scribing technology that has been used so far forms local thermal stress by laser irradiation, thereby narrowing the width of the magnetic domain and reducing the iron loss. In the actual use process, high laser energy introduces more heat, which has a better effect on subdividing the magnetic domain and reducing the iron loss. Therefore, in order to improve the high iron loss, it is necessary to introduce higher laser energy. However, excessive laser energy may damage the silicate and phosphate coatings on the surface of the oriented silicon steel, increasing the risk of interlayer conduction during use. That is, in order not to damage the surface coating of the oriented silicon steel, low laser energy is required. In order to prevent damage to the surface coating of the oriented silicon steel, in the laser scribing technology currently used for commercial applications, the heat introduction by the laser is limited, and the iron loss reduction effect is generally about 10% - 15%. It is very difficult to further reduce the iron loss.

[0024] Therefore, the inventors have addressed the contradiction between the iron loss improvement effect of the oriented silicon steel and the laser energy required not to damage its surface coating, and have innovatively devised a new composite laser scribing method to further improve the iron loss reduction effect without damaging the surface coating of the oriented silicon steel.

[0025] In the present invention, the inventors have carefully studied the temperature rise phenomenon generated by the irradiation of the steel plate surface during the laser scribing process, and found that the temperature of the local micro-region on the steel plate surface continuously rises by continuous laser irradiation. When the temperature of this region rises to the damage threshold of the surface coating, the surface coating of the steel plate is also damaged by the excessive temperature.

[0026] In recent years, researchers in this field have proposed the use of beam shaping to form a spot focused on the surface of a steel sheet into an ellipse or a rectangle having a longer length in the laser scanning direction. This solution effectively disperses the laser energy and avoids excessive temperature rise in local regions caused by excessive energy concentration. At the same time, the elongation of the spot size in the scanning direction lengthens the laser irradiation time (i.e., residence time) in local micro-regions, which can effectively diffuse the heat generated by irradiation to the surrounding regions of the local micro-regions, forming a heat stress zone with a larger width in the rolling direction and a deeper depth in the thickness direction, which is advantageous for domain refinement and achieves significant results. However, in this solution, local micro-regions on the surface of silicon steel still continue to receive heat from laser irradiation, and at the same time, due to the high running speed of the production line and the high laser scanning speed that matches the running speed, which is usually 100 m / s or even 200 m / s or more, and the residence time is in microseconds, the problem that the insulating film on the surface is easily damaged due to excessive temperature rise still remains.

[0027] To solve this problem, the inventors have designed a laser scribing method of the present invention that uses a beam splitting method to split an incident light beam into a plurality of beams and strictly controls the interval in the laser scanning direction of the condensed spots thus formed and the energy distribution of each light spot, thereby realizing the control of the temperature rise on the surface of the steel sheet caused by laser irradiation, forming a larger heat stress region within the thickness range of the steel sheet, which can not only increase the iron loss improvement rate of the directional silicon steel sheet before scribing to more than 15%, but also avoid damage to the thin film on the surface of the steel sheet caused by excessive temperature rise.

[0028] Preferably, in the method for laser scribing the directional silicon steel sheet of the present invention, the condensed spot is elliptical or rectangular.

[0029] In the above technical solution of the present invention, the focused spot formed by the laser can be realized by a combination of one or more means such as a diffraction beam splitter or a polarization beam splitter, and the shape of the formed focused spot may be elliptical or rectangular.

[0030] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet, the total length D of a plurality of focused spots extending in the width direction of the grain-oriented silicon steel sheet is ≦80 mm.

[0031] In the above technical solution of the present invention, since the heat conduction of the grain-oriented silicon steel sheet is isotropic, if the total residence time of the laser is too long, heat will diffuse over a wider range in the rolling direction of the steel sheet, thereby forming a larger thermal stress region, which not only increases the hysteresis loss but also reduces the magnetic induction. Therefore, the extended total length of the plurality of formed focused spots needs to be controlled within a certain range, thereby limiting the total residence time within a certain range. As a result of repeated experiments, the present inventors have determined that the extended total length of a plurality of focused spots arranged along the width direction of the grain-oriented silicon steel sheet can preferably be controlled to be ≦80 mm. When the total length exceeds 80 mm, the hysteresis loss increases, and as a result, the total loss increases and the magnetic induction B8 decreases.

[0032] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, the grain-oriented silicon steel sheet has a dimension a of 10 to 100 μm along its length direction.

[0033] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, the grain-oriented silicon steel sheet has a dimension b of ≦8 mm along its width direction. When the dimension b exceeds 8 mm, it is difficult to control the total length of the light spots, and a long residence time causes heat accumulation and destruction of the surface coating.

[0034] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet, the ratio of the length ds of the energy gap region between the preceding focused spot and the subsequent focused spot to the length of the preceding focused spot in the laser scanning direction is between 0.5 and 2.

[0035] In the above technical solution of the present invention, the size of the energy gap region between the focused spots also directly affects the temperature drop formed during scanning. The ratio of the energy gap region between each focused spot and the next focused spot to the length of the focused spot is controlled between 0.5 and 2. If the ratio is less than 0.5, it is difficult to achieve effective temperature reduction, and the surface coating of the grain-oriented silicon steel cracks; if the ratio is greater than 2, the temperature reduction is too large, and it is difficult for the subsequent focused spot to maintain the surface temperature of the steel sheet within the range where sufficient thermal stress is generated, and the effects of magnetic domain refinement and iron loss reduction cannot be obtained.

[0036] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, the output density p of each focused spot is 1000 - 3000 W / mm 2 is.

[0037] In the above technical solution of the present invention, in order to achieve the purpose of reducing iron loss without damaging the surface coating, the value range of the output density p of the laser focused spot is further controlled. When the output density exceeds 3000 W / mm 2 , excessive large energy will damage the surface coating of the grain-oriented silicon steel sheet; and when the output density is less than 1000 W / mm 2 , the laser energy is too low, and it is difficult to form an effective thermal stress zone on the surface of the grain-oriented silicon steel sheet. Therefore, it is insufficient to achieve the magnetic domain refinement effect, and the iron loss improvement rate is low.

[0038] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, along the laser scanning direction, the output density ratio of the subsequent condensing spot to the preceding condensing spot is 0.75 to 0.95.

[0039] The inventors repeated experiments and determined that the output density ratio of the subsequent condensing spot to the preceding condensing spot is 0.75 to 0.95. If the ratio is lower than 0.75, the energy carried by the subsequent condensing spot is too small, and the surface temperature of the steel sheet begins to gradually decrease after the first laser spot scanning, making it difficult to form an effective thermal stress zone and limiting the effect of domain refinement for reducing iron loss; if the ratio is higher than 0.95, the energy carried by the subsequent condensing spot is too large, and the surface temperature of the steel sheet gradually rises and still reaches the damage threshold of the surface coating.

[0040] Preferably, in the method for laser scribing the grain-oriented silicon steel sheet of the present invention, the plurality of condensing spots are formed by at least one of a diffraction beam splitter and a polarization beam splitter.

[0041] Another object of the present invention is to provide a grain-oriented silicon steel sheet having low iron loss and coating breakage resistance characteristics, which can be used for manufacturing an energy-saving transformer for an ultra-high voltage power transmission network and has a very wide application prospect.

[0042] To achieve the above object, the present invention provides a grain-oriented silicon steel sheet manufactured by the laser scribing method of the present invention.

[0043] When manufacturing the grain-oriented silicon steel sheet of the present invention, first, steel containing a certain amount of silicon is subjected to ironmaking, steelmaking, and continuous casting, then subjected to a hot rolling process, and subsequently subjected to a single cold rolling process or two cold rolling processes with intermediate annealing to roll the steel into a silicon steel sheet having a target thickness.

[0044] Next, the produced silicon steel sheet is subjected to decarburization annealing to form a primary recrystallized steel sheet having an oxide coating on the surface; after coating with a magnesium oxide release agent, the silicon steel sheet is subjected to high-temperature annealing, and a silicon steel sheet having a Goss texture is formed by secondary recrystallization, and the oxide film on the surface reacts with the release agent to form a magnesium silicate bottom layer. Thereafter, the silicon steel sheet is subjected to hot rolling, flattening, annealing, coating and baking processes, and then laser scribing of the present invention is applied to the surface of the steel sheet to produce a finished grain-oriented silicon steel sheet.

[0045] Preferably, in the manufacturing method of the present invention, the improvement rate of iron loss before scribing of the grain-oriented silicon steel increases by 15% or more.

[0046] Compared with the prior art, the method and the grain-oriented silicon steel sheet for laser scribing the low-iron-loss grain-oriented silicon steel sheet of the present invention have the following beneficial effects:

[0047] In the present invention, the inventors design a novel laser scribing method that can form a thermal stress zone by using an optimized laser scribing method, thereby controlling the temperature rise of the steel sheet, and reducing the iron loss of the grain-oriented silicon steel sheet without damaging the surface coating on the scribed area.

[0048] When applying the laser scribing method of the present invention, by adopting a laser beam splitting method, a plurality of focused spots are formed on the surface of the steel sheet, and the output density of each focused spot is controlled between 1000 and 3000 W / mm 2 ; corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet, the ratio of the energy gap region in the scanning direction to the length of the corresponding focused spot is controlled between 0.5 and 2; at the same time, along the laser scanning direction, the output density ratio of the subsequent focused spot to the preceding focused spot is controlled between 0.75 and 0.95.

[0049] According to the laser scribing method of the present invention, since there is an energy gap between the condensing spots of the laser beam splitting, it is possible to effectively avoid the continuous temperature rise on the surface of the steel sheet caused by the continuous accumulation of laser heat radiation. Therefore, while ensuring the integrity of the coating in the minute region where the surface is scribed, the effect of reducing iron loss by magnetic domain subdivision is improved, and the improvement rate of iron loss of the steel sheet relative to before scribing increases to 15% or more. The low iron loss grain-oriented silicon steel sheet thus manufactured can be used for manufacturing an energy-saving transformer for an extra-high voltage power transmission network and has broad application prospects.

Brief Description of the Drawings

[0050]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0051] Detailed Description The laser scribing method of the low iron loss grain-oriented silicon steel sheet of the present invention and the grain-oriented silicon steel sheet will be further described and described below in conjunction with the drawings and specific embodiments. However, these descriptions and descriptions do not unduly limit the technical solution of the present invention.

[0052] FIG. 1 is a schematic diagram showing the laser scribing method of the present invention that forms a focused spot using laser beam splitting and scans the surface of a steel sheet.

[0053] FIG. 2 is a schematic diagram showing that the focused spot of the present invention is focused on the surface of the steel sheet.

[0054] As can be seen from FIGS. 1 and 2, these figures are schematic diagrams showing the laser scribing method of the present invention that forms a plurality of focused spots on the surface of a steel sheet using laser beam splitting.

[0055] In the present invention, after splitting the incident laser beam, a plurality of focused spots 1, 2, 3......n - 1, n are formed on the surface of the steel sheet, and the lengths of the focused spots in the laser scanning direction (i.e., the width direction of the grain-oriented silicon steel sheet) are b1, b2, b3......b n-1 、b n respectively, and the plurality of focused spots are arranged along the width direction of the grain-oriented silicon steel sheet and have energy gap regions between them, and the lengths of the energy gap regions are ds1, ds2, ds3......ds n-1 respectively. The sum of the lengths of the focused spots in the width direction of the grain-oriented silicon steel sheet is the total spot length D.

[0056] In the present application, the "preceding focused spot" and the "subsequent focused spot" refer to any two adjacent focused spots along the laser scanning direction. For example, when the laser scanning direction starts from spot 1 in FIG. 2, spot 1 is the "preceding focused spot", and spot 2 is the "subsequent focused spot". Similarly, for spot 2 and spot 3, spot 2 is the "preceding focused spot", and spot 3 is the "subsequent focused spot", and so on.

[0057] In this embodiment, the length of the focused spot in the direction perpendicular to the laser scanning direction (i.e., the length direction of the oriented silicon steel sheet) can be set to a uniform value a. Of course, in some other embodiments, the lengths of the different focused spots in the direction perpendicular to the laser scanning direction may be different, but they all need to satisfy the range of the laser output density required by the present invention. Under normal production conditions, the laser scanning speed is very fast, reaching 100 m / s or more, and the full-width scanning of a steel sheet with a width of about 1 m takes only less than 0.01 seconds. Therefore, in order to simplify the spatial layout during production, usually, the laser scanning direction is made substantially the same as the width direction of the steel sheet.

[0058] It should be noted that the present inventors have also carefully studied the process of temperature rise on the silicon steel surface during laser scribing, and the results are shown in FIG. 3. FIG. 3 schematically shows the relationship between the irradiation time and the temperature change in a local micro-region on the surface of the steel sheet when the steel sheet is scribed by the laser scribing method of the present invention and the conventional laser scribing method.

[0059] In the relationship diagram 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.

[0060] Referring to Fig. 3, when using the conventional laser scribing method, since the local micro-region on the surface of the steel plate is continuously irradiated with the laser, the temperature in that region continuously rises, reaches the peak value within the residence time range of the laser irradiation, and then the temperature in that region gradually decreases. On the other hand, when using the laser scribing method devised by the inventors of the present invention, since there is a certain interval between adjacent focused spots, a certain energy gap region is formed between the focused spots. Therefore, the temperature of the local micro-region on the surface of the steel plate decreases to a certain extent, and the energy of the subsequent focused spot is lower than that of the preceding focused spot. The temperature of the irradiation region is always controlled below the damage threshold of the surface coating. At the same time, the total residence time becomes longer, heat diffusion occurs in a wider range, so thermal stress is formed in a wider region, and an improvement effect on iron loss can be obtained.

[0061] Based on the above principle, it can be determined that the control parameters directly related to the effect of the present invention include the following: the focused spot sizes a and b, the output density p of each focused spot, the focused spot gap ds, and the total spot length D (refer to Fig. 2) directly related to the total laser residence time. It should be noted that by splitting a single laser beam of a continuous laser or a pulsed laser used in the prior art into a plurality of laser beams to form a plurality of focused spots having an energy gap region ds between them, the heat accumulated in the scribing region on the surface of the steel plate during laser scribing can be reduced. Regarding the output density p of each focused spot, the focused spot gap ds, and the total spot length D directly related to the total laser residence time, they can be selected within any preferred range as long as the continuous temperature rise of the steel plate surface caused by the continuous accumulation of laser heat radiation during the formation of the scribed line during laser scribing is effectively avoided.

[0062] Compared with the prior art, the focused spot designed in the present invention has a smaller size a in the rolling direction of the steel plate (i.e., the length direction of the grain-oriented silicon steel), thereby reducing the diffusion of laser irradiation heat in the rolling direction and avoiding an increase in hysteresis loss. Theoretically, the smaller the size a, the better the effect of the present invention. However, in actual industrial production, since the laser scanning range needs to cover the entire width of the steel plate, usually 900 mm or even larger, a longer focal length is required. Also, in order to prevent the focus shift phenomenon caused by the variation in the strip shape, a certain degree of depth of focus is required to cover the focus shift deviation caused by the variation in the strip shape and the sway of the strip. Therefore, the lower limit of the size a of the focused spot is restricted by the optical system and should not be less than 10 μm. If the size a of the focused spot is smaller than this value, the complexity of the optical system will increase significantly, and in order to complete laser scribing over the entire width direction of the plate, it is necessary to arrange multiple lasers simultaneously in the width direction of the plate. According to the research of the present inventors, the upper limit of the size a of the focused spot in the rolling direction is preferably set to 100 μm. If this value is exceeded, heat will diffuse in the rolling direction, the thermal stress zone will increase in the region near the score (scribed mark) in the rolling direction, and the hysteresis loss will increase. The total loss will not decrease further, and the magnetic induction B8 will also decrease.

[0063] In the present invention, after the incident laser is split by a diffraction beam splitter and a polarization beam splitter, a plurality of focused spots are formed on the surface of the grain-oriented silicon steel plate. The focused spots are usually elliptical and have a spot size b in the laser scanning direction (i.e., the width direction of the grain-oriented silicon steel plate) that is larger than the size a in the rolling direction, thereby dispersing the laser energy as much as possible and preventing the formation of excessive output density and damage to the surface coating.

[0064] It should be noted that in the present invention, the output density p of the focused spot can be an average value defined as follows:

[0065]

Number

[0066] Here, P0 is the total output of the laser (W); n is the number of condensing spots; and S is the area of the condensing spot (mm 2 ). When the condensing spot is an ellipse, the calculation formula for the area S of the condensing spot can be expressed as follows:

[0067]

Number

[0068] In some other embodiments, the laser can also form a rectangular spot through a beam shaper, and it should be noted that the long side of the rectangle is b extending along the width direction of the steel plate, and the short side of the rectangle is a extending along the rolling direction of the steel plate (i.e., the length direction of the oriented silicon steel sheet). These embodiments where the condensing spot is rectangular are also within the scope of the present invention and will not be described in detail here.

[0069] In the present invention, in order to achieve the purpose of reducing iron loss without damaging the surface coating, it is necessary to strictly control the output density p of the laser condensing spot. When the output density p exceeds 3000 W / mm 2 , the surface coating is damaged by excessive laser energy; when the output density p is less than 1000 W / mm 2 , the laser energy is too low, and it is difficult to form an effective thermal stress zone on the surface of the oriented silicon steel sheet. Therefore, it is insufficient to achieve the magnetic domain refinement effect, and the iron loss improvement rate is low. Therefore, in practice, it is necessary to control the output density of each condensing spot between 1000 and 3000 W / mm 2 .

[0070] In the present invention, after splitting the laser beam, the gap between adjacent focused spots causes a certain temperature drop in the relevant area, which can avoid damage to the surface coating due to excessive temperature in the scanning area. Therefore, it is necessary to control the output distribution ratio between the subsequent focused spot and the preceding focused spot as well as the size ds of the energy gap region.

[0071] By repeating the experiment, the inventors have determined that the output density ratio of the subsequent focused spot to the preceding focused spot is 0.75 to 0.95, that is,

[0072]

Number

[0073] the range of should be 0.75 to 0.95.

[0074]

Number

[0075] When the value of is lower than 0.75, the energy carried by the subsequent focused spot is too little, and the surface temperature of the steel plate begins to gradually decrease after the first laser spot scanning. Therefore, it is difficult to form an effective thermal stress zone, and the effect of magnetic domain refinement to reduce iron loss is not significant.

[0076]

Number

[0077] When the value of is higher than 0.95, the energy carried by the subsequent focused spot is too large, and the surface temperature of the steel plate gradually rises and still reaches the damage threshold of the surface coating.

[0078] The size ds of the energy gap region between the light-collecting spots also directly affects the temperature drop that occurs during scanning. The ratio of the length of the energy gap region between each light-collecting spot and the next light-collecting spot to the length of the focused spot in the scanning direction should be controlled between 0.5 and 2, that is,

[0079] [Number]

[0080] the range should be 0.5 to 2.

[0081] [Number]

[0082] if the value of [Number] is less than 0.5, it is difficult to form an effective temperature drop, and cracks will occur in the surface coating of the grain-oriented silicon steel;

[0083] [Number]

[0084] if the value of [Number] is greater than 2, the temperature drop is too large, and it is difficult for the subsequent light-collecting spot to maintain the surface temperature of the steel sheet within a range where sufficient thermal stress can be generated, and it is impossible to achieve the effect of magnetic domain refinement and iron loss reduction.

[0085] Therefore, the total extended length of the plurality of formed light-collecting spots needs to be controlled within a certain range, and thus the total residence time is limited within a certain range. As a result of repeated experiments, the inventors determined that the total extended length of the plurality of light-collecting spots arranged along the width direction of the grain-oriented silicon steel sheet can preferably be controlled to be ≤ 80 mm. If the total length exceeds 80 mm, the hysteresis loss increases, and as a result, the total loss increases and the magnetic induction B8 decreases.

[0086] Furthermore, due to the isotropic heat transfer of the grain-oriented silicon steel sheet, if the total residence time of the laser is too long, heat will diffuse over a wider range in the rolling direction of the steel sheet, forming a larger thermal stress zone, which should be noted that it increases the hysteresis loss and decreases the magnetic induction. Also, the total extended length of the plurality of focused spots needs to be controlled within a certain range, and thus the total residence time is restricted within a certain range. As a result of repeated experiments, the inventors determined that the total extended length D of the plurality of focused spots in the width direction of the grain-oriented silicon steel sheet is preferably controlled to be ≦80 mm. When the total length exceeds 80 mm, the hysteresis loss increases, and as a result, the total loss increases and the magnetic induction B8 decreases.

[0087] In the present invention, the calculation formula for the total extended length D of the plurality of focused spots is as follows:

[0088]

Equation

[0089] FIG. 4 schematically shows a system configuration diagram of an optical path system for implementing the laser scribing method of the present invention.

[0090] In FIG. 4, as an example, an optical path system for implementing the laser scribing method of the present invention is shown, and other systems can also be used to achieve the spectral focusing effect required by the present invention, and these systems are also within the scope of the present invention. In the optical path shown in FIG. 4, the laser beam 8 is emitted from the laser 1, passes through the reflecting mirrors 2 and 3, and then passes through the beam shaping system 4 to form a beam having an elliptical energy distribution. Then, it passes through the diffraction grating element 5 to form a plurality of beams, which pass through the scanning focusing mirror 6 and quickly scan the surface of the grain-oriented silicon steel sheet 7 to form a scribing stress zone 9.

[0091] Regarding the laser light source, there are no special restrictions in the present invention. The lasers commonly used in the art are continuous lasers with a wavelength of 1066 nm. Other lasers can also be used to achieve the object of the present invention and will not be described in detail herein.

[0092] Hereinafter, the technical solution of the present invention will be described by specific examples, and the beneficial effects brought about by the laser scribing method devised by the present inventors will be shown.

[0093] Examples 1 - 7 and Comparative Examples 1 - 2 The oriented silicon steel sheets of Examples 1 - 7 and Comparative Examples 1 - 2 were manufactured by the following steps: (1) Subject the oriented silicon steel to ironmaking, steelmaking, continuous casting, and hot rolling, then cold roll it to a final thickness of 0.22 mm, and after decarburizing annealing at 850 °C, coat the surface of the oriented silicon steel with an MgO separating agent to form a surface oxide layer, then roll it into a steel coil, and hold it for 20 hours under high-temperature annealing conditions of 1200 °C, then wash and dry the unreacted residual MgO on the surface, and apply an insulating coating on the surface of the oriented steel sheet; (2) Laser scribe one side of the oriented silicon steel along its transverse direction.

[0094] When laser scribing the surface of the oriented silicon steel sheet, a plurality of focused spots are formed on the surface of the oriented silicon steel sheet by splitting the laser beam corresponding to each length position along the rolling direction of the oriented silicon steel sheet; the plurality of focused spots are arranged along the width direction of the oriented silicon steel sheet and have an energy gap region between them; the dimension b of each focused spot along the width direction of the oriented silicon steel sheet is larger than the dimension a along the length direction of the oriented silicon steel sheet.

[0095] During laser scribing, the dimension a is controlled to be 10 - 100 μm; corresponding to each length position along the rolling direction of the oriented silicon steel sheet, the total length D of a plurality of focused spots arranged along the width direction of the oriented silicon steel sheet is controlled to be ≤ 80 mm; the ratio ds / b of the length ds of the energy gap region in the scanning direction to the corresponding length b of the focused spot is controlled to be between 0.5 and 2; the output density of each focused spot is controlled to be 1000 - 3000 W / mm 2 and; along the laser scanning direction, the output density ratio of a subsequent focused spot to a preceding focused spot is controlled to be 0.75 - 0.95.

[0096] As the laser used in Examples 1 - 7 and Comparative Examples 1 - 2, a continuous single - mode fiber laser with a wavelength of 1066 nm was used, and a customized diffractive optical element was used to split the light beam into sub - beams with different parameters, and then the surface of the steel sheet was scanned to form a scribing stress band. Here, it should be noted that in the comparative example, no diffractive optical element was used for light splitting, and the output density was adjusted by adjusting the laser output.

[0097] The laser scribing process adopted in the present invention is carried out after the final annealing of the oriented silicon steel. Therefore, in the present invention, there is no particular limitation on the oriented silicon steel sheet, and in actual applications, it is not limited to the oriented silicon steel sheet manufactured by the above process.

[0098] The process parameters of the oriented silicon steel sheets in Examples 1 - 7 and Comparative Examples 1 - 2 in the above process are shown in Table 1.

[0099]

Table 1

[0100] The magnetic induction (B8) and iron loss (P of the oriented silicon steel sheets in Examples 1 - 7 and Comparative Examples 1 - 2 17 / 50was tested before and after laser scribing by using the method described in GB / T 13789-2008, and the lengths in the rolling direction and the transverse direction of the samples prepared in the examples and comparative examples were controlled to be 500 mm, and thus the magnetic flux density B8 of the grain-oriented silicon steel under an excitation magnetic field of 800 A / m and the reactive electric energy P consumed by magnetization when the magnetic flux density reached 1.7 T under an alternating current excitation magnetic field of 50 Hz 17 / 50 were measured. Furthermore, the degree of coating damage in the scribed areas of the grain-oriented silicon steel sheets of Examples 1 to 7 and Comparative Examples 1 to 2 was also tested, and the related test results are shown in Table 2 below.

[0101]

Table 2

[0102] As can be seen from Table 2 above, the grain-oriented silicon steel sheets after laser scribing in Examples 1 to 7 have good iron loss and magnetic properties, their surface coatings are not damaged, and the reduction of iron loss due to magnetic domain refinement is remarkable. Compared with before scribing, the iron loss improvement rate can reach 15% or more.

[0103] On the other hand, for the grain-oriented silicon steel sheet after laser scribing in Comparative Example 1, by adjusting the laser output, a high iron loss improvement effect was achieved, but its coating was damaged due to heat accumulation; when laser scribing was performed on the grain-oriented silicon steel sheet in Comparative Example 2, the laser output was reduced. The coating on the surface of the scribed steel sheet was complete, but the iron loss improvement effect was low.

[0104] It should be noted that the embodiments shown above are merely illustrative of the present invention and should not be construed as limiting the present invention thereto. Any changes or modifications that can be directly derived or easily conceived by those skilled in the art from the disclosure of this application should be considered to be within the scope of the present invention.

Claims

1. A method for laser scribing a grain-oriented silicon steel sheet, comprising forming a plurality of focused spots on the surface of the grain-oriented silicon steel sheet by splitting a laser beam corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet when laser scribing the surface of the grain-oriented silicon steel sheet, wherein the plurality of focused spots are arranged along the width direction of the grain-oriented silicon steel sheet and have an energy gap region ds therebetween, and wherein the dimension b of each focused spot along the width direction of the grain-oriented silicon steel sheet is larger than the dimension a along the length direction of the grain-oriented silicon steel sheet.

2. The method for laser scribing a grain-oriented silicon steel sheet according to claim 1, wherein the focused spots are elliptical or rectangular.

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

4. The method for laser scribing a grain-oriented silicon steel sheet according to claim 1, wherein the focused spots have a dimension a along the length direction of the grain-oriented silicon steel sheet of 10 to 100 μm, preferably 40 to 80 μm.

5. The method for laser scribing a grain-oriented silicon steel sheet according to claim 1, wherein the focused spots have a dimension b along the width direction of the grain-oriented silicon steel sheet of 3 to 8 mm, preferably 4 to 6 mm.

6. The method for laser scribing a grain-oriented silicon steel sheet according to claim 1, wherein the ratio of the length ds of the energy gap region between a preceding focused spot and a subsequent focused spot to the length of the preceding focused spot in the laser scanning direction corresponding to each length position along the rolling direction of the grain-oriented silicon steel sheet is between 0.5 and 2, preferably between 0.7 and 1.

3.

7. The output density p of each light-collecting spot is 1000 to 3000 W / mm 2 A method for laser scribing a directional silicon steel sheet according to claim 1, wherein the output density p of each light-collecting spot is 1000 to 3000 W / mm

8. The method for laser scribing a grain-oriented silicon steel sheet according to claim 1, wherein the output density ratio of a subsequent focused spot to a preceding focused spot along the laser scanning direction is 0.75 to 0.

95.

9. A method for laser scribing a directional silicon steel sheet according to claim 1, wherein a plurality of focused spots are formed using at least one of a diffraction beam splitter and a polarization beam splitter.

10. A method for laser scribing a directional silicon steel sheet according to claim 2, wherein a focused spot having an elliptical or rectangular shape is formed by a beam shaper.

11. A directional silicon steel sheet comprising a score generated by the method according to any one of claims 1 to 9.

12. The directional silicon steel sheet according to claim 11, wherein the improvement rate of the iron loss of the directional silicon steel sheet before scribing is increased to 15% or more.

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