Online repairing method and welding system for cracks of high-temperature resistance tape

Abstract

The invention provides an online repair method for cracks of a high-temperature resistance tape and a welding system, and belongs to the technical field of welding repair. The repairing method comprises the following steps that a crack area is cleaned, a groove is machined, then gradient preheating is conducted on base metal, the gradient preheating comprises a stress relief preheating stage and a grain boundary reconstruction preheating stage, and the highest preheating temperature reaches 980-1050 DEG C; a composite welding wire composed of a nickel base alloy bottom layer and an austenitic stainless steel surface layer is adopted, under the two-way protection of inert gas, a pulse current mode is adopted for conducting welding on the preheated groove by more than three layers, and the interlayer temperature is always kept within the range of 950-1050 DEG C; and after welding is completed, laser remelting treatment is immediately carried out on a welding seam, and then furnace controlled slow cooling is carried out. Through the synergistic effect of three-stage preheating, a composite welding wire structure, bidirectional inert gas protection and a laser remelting process, the repairing quality of the high-temperature resistance tape is improved.

Description

Technical Field

[0001] This application relates to the field of welding repair technology, and in particular to an online repair method and welding system for high-temperature resistor band cracks. Background Technology

[0002] The resistance band of a high-temperature annealing furnace / electric furnace is a key component in a high-temperature environment, used to convert electrical energy into heat energy. Therefore, its materials and structure have certain special characteristics and need to be made of materials that are resistant to high temperatures, corrosion, and have high electrical conductivity.

[0003] In continuous silicon steel annealing production lines, resistance bands, as key heating elements, operate in high-temperature environments (typically exceeding 800℃, with some requiring up to 1200℃) for extended periods, enduring cyclic thermal expansion and contraction as well as mechanical vibration. This makes them highly susceptible to axial cracks and even breakage. Due to the prolonged operation of the high-temperature annealing furnace, resistance bands are easily affected by multiple factors, including high temperature, current, and environmental corrosion, leading to cracking, breakage, and short circuits. Timely repair or replacement is crucial. Existing repair techniques suffer from the following drawbacks: ① Ordinary arc welding easily induces secondary embrittlement; ② Improper matching of dissimilar materials results in low interfacial bonding strength; ③ Lack of effective pretreatment measures leads to stress concentration in the weld structure. These problems result in short service life for repaired resistance bands, and frequent downtime for replacement severely impacts production efficiency. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide an online repair method and welding system for high-temperature resistor strip cracks. The repair method is applicable to the repair of resistor strips with crack depth ≤ 1 / 3 of the strip thickness, and the resistance deviation after repair is ≤ ±2%.

[0005] Specifically, the first aspect of this application provides an online repair method for cracks in high-temperature resistance bands, used to repair iron-chromium-aluminum resistance bands operating in an annealing furnace, comprising the following steps: Pretreatment steps: Clean the cracked area and process the bevel, then perform gradient preheating on the base material. The gradient preheating includes a stress relief preheating stage and a grain boundary reconstruction preheating stage, with the highest preheating temperature reaching 980-1050℃. Composite welding steps: Using a composite welding wire consisting of a nickel-based alloy bottom layer and an austenitic stainless steel top layer, the preheated groove is welded in more than 3 layers under bidirectional inert gas protection using a pulsed current mode, with the interpass temperature always maintained within the range of 950-1050℃. Post-processing steps: Immediately after welding, the weld is laser remelted and then slowly cooled in the furnace.

[0006] Furthermore, the gradient preheating is as follows: First, raise the temperature to 500-650℃ and hold for 5-8 minutes to remove moisture; Then raise the temperature to 800-900℃ and hold for 8-12 minutes to eliminate work hardening of the base material; Finally, the temperature is raised to 980-1050℃ and held for 15-20 minutes to achieve grain boundary migration and reconstruction.

[0007] Furthermore, the pulse current mode is as follows: base current 60-80A, peak current 140-160A, voltage 18-22V, and pulse frequency 1.5-2.5Hz.

[0008] Furthermore, in the composite welding wire, the nickel-based alloy bottom layer is Inconel 625 nickel-based welding wire, and the austenitic stainless steel surface layer is ER308L or ER309L type welding wire.

[0009] Furthermore, the inert gas bidirectional protection is as follows: the front protective gas flow rate is 20-30 L / min, and the back protective gas flow rate is 10-20 L / min; the inert gas is a mixture of argon and helium, wherein the volume percentage of helium is 15%-20%.

[0010] Furthermore, the laser power density of the laser remelting process is 2.0 × 10⁻⁶. 4 W / cm 2 Up to 5.0×10 4 W / cm 2 The scanning speed is 5-15 mm / s.

[0011] Furthermore, the cooling rate of the furnace-controlled slow cooling is ≤5℃ / min until the temperature drops below 400℃.

[0012] Furthermore, after the post-processing step, the process includes: mechanically grinding the remelted weld and spraying a high-temperature resistant ceramic coating, followed by eddy current testing and resistance uniformity verification.

[0013] A second aspect of this application provides a dedicated welding system for the method, comprising: An integrated platform equipped with a pulse welding power supply, a water-cooled welding torch, a wire feeding mechanism, and a laser remelting head; A temperature control subsystem, including an infrared thermometer, a heating device, and a PID controller connected to them, forms a closed-loop control loop for accurately maintaining the preheating temperature and the interlayer temperature of the weld. A gas protection subsystem includes a front protective gas path and a back protective liner with a gas channel and a copper foil reflector.

[0014] Furthermore, the laser remelting head is a galvanometer-type laser scanning head, which is fixed on the same moving actuator as the welding torch to achieve continuous welding and remelting operations.

[0015] The present invention has the following beneficial effects: (1) This invention effectively reduces thermal stress generated during welding by employing a gradient preheating process, thereby improving the overall performance of the welded joint. The design of the composite welding wire solves the problem of low bonding strength at the interface of dissimilar materials, significantly enhancing the crack resistance and corrosion resistance of the weld. Laser remelting technology is used to treat the weld, further optimizing its microstructure and improving its density and uniformity. Furthermore, the application of furnace-controlled slow cooling avoids residual stress concentration caused by rapid cooling, thus extending the service life of the repaired resistor band. This invention is simple to operate and suitable for online repair scenarios under various high-temperature environments, possessing high practical value and promising prospects for wider application.

[0016] (2) Firstly, by precisely controlling the preheating temperature, this invention can reduce the difference in thermal expansion coefficients between the high-alloy resistance band and the base material, effectively alleviating the tendency to peel off due to the difference in thermal expansion coefficients during welding and ensuring the strength of the weld. Secondly, precise control of welding parameters, such as welding current, voltage, and welding speed, can make the morphology and solidification process of the molten pool more stable, reduce high-temperature oxidation, thereby avoiding slag inclusion defects and improving the quality of the weld. Finally, reasonable protection methods, such as using appropriate shielding gas during welding, can effectively reduce the oxygen content in the welding area, reduce the generation of residual stress, thereby avoiding secondary cracking and extending the service life of the resistance band. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0018] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0019] The first aspect of this application provides an online repair method for high-temperature resistance band cracks, used to repair iron-chromium-aluminum resistance bands operating in an annealing furnace, comprising the following steps: Pretreatment steps: Clean the cracked area and process the bevel, then perform gradient preheating on the base material. The gradient preheating includes a stress relief preheating stage and a grain boundary reconstruction preheating stage, with the highest preheating temperature reaching 980-1050℃. Composite welding steps: Using a composite welding wire consisting of a nickel-based alloy bottom layer and an austenitic stainless steel top layer, the preheated groove is welded in more than 3 layers under bidirectional inert gas protection using a pulsed current mode, with the interpass temperature always maintained within the range of 950-1050℃. Post-processing steps: Immediately after welding, the weld is laser remelted and then slowly cooled in the furnace.

[0020] The pretreatment steps described above include mechanically creating a V-shaped bevel on the base material of the resistor strip to be repaired, with the bevel angle set at 30°-60° and the depth adjusted according to the crack width and base material thickness, typically controlled between 2-4 mm; followed by ultrasonic cleaning. Then, a gas-fired spray gun is used for localized gradient preheating to the maximum preheating temperature of 980-1050℃, monitored in real-time with an infrared thermometer, and the holding time is ≥15 minutes; a special polishing tool is used to remove oxide scale and impurities within a 30mm radius on both sides of the crack, exposing a metallic luster; the cleaned area is then pre-purged with argon gas to replace air and create an inert environment.

[0021] This invention effectively reduces thermal stress during welding and improves the overall performance of the welded joint by employing a special gradient preheating process. The composite welding wire design solves the problem of low interfacial bonding strength in dissimilar material welding, significantly enhancing the weld's crack resistance and corrosion resistance. Laser remelting technology further optimizes the weld microstructure, improving its density and uniformity. Furthermore, the application of controlled slow cooling in the furnace avoids residual stress concentration caused by rapid cooling, thereby extending the service life of the repaired resistor strip. This invention is simple to operate, applicable to various online repair scenarios in high-temperature environments, and has high practical value and promising prospects for wider application.

[0022] In this embodiment, the gradient preheating is as follows: First, raise the temperature to 500-650℃ and hold for 5-8 minutes to remove moisture; Then raise the temperature to 800-900℃ and hold for 8-12 minutes to eliminate work hardening of the base material; Finally, the temperature is raised to 980-1050℃ and held for 15-20 minutes to achieve grain boundary migration and reconstruction.

[0023] Through gradual heating and heat preservation via gradient preheating, the internal stress of the resistance band base material is fully released, while avoiding abrupt changes in microstructure caused by rapid heating, thus creating ideal thermodynamic conditions for subsequent composite welding. This preheating method not only improves the toughness of the welded joint but also effectively suppresses the tendency of cracks to propagate during the welding process, ensuring the long-term stability of the repair layer. Temperature control in this application employs infrared thermometry combined with PID closed-loop control.

[0024] In this embodiment, a DC reverse polarity welding method is employed. The pulse current mode is as follows: base current 60-80A, peak current 140-160A, pulse frequency 1.5-2.5Hz. The welding voltage is 18-22V. This application uses a pulse current modulation mode, which enables precise energy control during the welding process. This ensures sufficient penetration to form a reliable weld joint while avoiding overheating that could degrade the base material. The periodic changes in the pulse current induce periodic stirring in the molten pool, helping to reduce porosity and inclusions, and improving weld purity and mechanical properties. Simultaneously, this mode effectively reduces welding spatter, improves the working environment, and enhances welding efficiency.

[0025] In this embodiment, a pulsed current mode is used to perform multi-layer (more than 3 layers) multi-pass welding on the preheated bevel. The thickness of each layer is controlled at 1.5-2.5 mm, and the width of a single weld bead is controlled at 8-10 mm. The interpass temperature is not lower than 950℃. By precisely controlling the matching relationship between the wire feed speed and the welding current, a smooth droplet transition is ensured, avoiding defects such as incomplete fusion or burn-through. During the welding process, an oscillating welding torch technique is used, with an oscillation amplitude of 3-5 mm and a frequency synchronized with the pulsed current, allowing the weld metal to fully fuse and form a uniform and dense fish-scale texture. The interpass temperature is monitored in real time by an infrared thermometer. When the temperature drops below 950℃, the heating device is immediately activated to compensate for the temperature drop, ensuring that the interpass temperature is always maintained within the process window of 950-1050℃, preventing grain coarsening or hydrogen-induced cracking due to temperature fluctuations. During multi-layer welding, the arc start point and arc end point of each weld bead are staggered by more than 50 mm to avoid stress concentration at the joint. After welding is completed, the weld area should be immediately covered with asbestos cloth to reduce thermal stress caused by rapid cooling and create stable initial conditions for subsequent laser remelting.

[0026] In this embodiment, the composite welding wire consists of an Inconel 625 nickel-based alloy bottom layer and an ER308L or ER309L type welding wire for the austenitic stainless steel surface layer. A gradient annealing treatment is applied to the transition zone between the two layers. The composite welding wire has a diameter of 1.6-2.0 mm. The gradient annealing treatment of the composite welding wire, through precise control of the annealing temperature and time, ensures a good metallurgical bond between the nickel-based alloy and the austenitic stainless steel, avoiding brittle phases and crack defects that are prone to occur in traditional dissimilar material welding.

[0027] The composite welding wire combines the high-temperature strength of nickel-based alloys with the oxidation resistance of austenitic stainless steel through a unique double-layer structure design. The nickel-based alloy bottom layer (Inconel 625) provides excellent high-temperature corrosion resistance and creep resistance, effectively resisting thermal erosion in working environments up to 1200℃; the austenitic stainless steel surface layer (ER308L / ER309L) forms a dense oxide film, preventing oxygen from diffusing into the weld. Atomic-level diffusion bonding is achieved between the two layers through gradient annealing, eliminating the lack of fusion defects commonly found in dissimilar metal welding.

[0028] In this embodiment, the inert gas bidirectional protection is as follows: the front shielding gas flow rate is 20-30 L / min, and the back shielding gas flow rate is 10-20 L / min; the inert gas is a mixture of argon and helium, wherein the helium volume percentage is 15%-20%, and the gas purity is ≥99.999%. The bidirectional inert gas protection technology effectively isolates the welding area from air, preventing high-temperature oxidation and nitriding contamination. Argon, as the basic shielding gas, provides a stable inert environment; the addition of helium significantly improves arc stiffness and heat input efficiency, enhancing the penetration of the molten pool. When the helium percentage is controlled at 15%-20%, it ensures sufficient fusion at the weld root and avoids shielding layer disorder caused by gas density differences. This mixed gas configuration reduces the oxygen content of the weld metal to below 0.003% and the nitrogen content to below 0.002%, significantly improving the weld's oxidation resistance and high-temperature creep strength. Through a two-way gas path design, the front protection ensures the surface smoothness of the molten pool, while the back protection prevents the base material from overheating and oxidizing, together forming a fully enclosed welding heat-affected zone protection system.

[0029] In this embodiment, after welding, laser surface remelting is performed, and the laser power density of the laser remelting process is 2.0 × 10⁻⁶. 4 W / cm 2 Up to 5.0×10 4 W / cm 2The scanning speed is 5-15 mm / s. Laser surface remelting treatment uses a high-energy laser beam to form a micro-molten pool on the weld surface, utilizing the rapid solidification effect to refine the grain structure and eliminate microscopic defects such as porosity and inclusions generated during welding. This process achieves uniform modification of the weld surface by precisely controlling the matching relationship between laser power density and scanning speed, ensuring that the base material does not overheat. During laser remelting, the molten pool existence time is controlled within the range of 0.5-2 seconds, ensuring sufficient metallurgical reaction while avoiding excessive expansion of the heat-affected zone. The surface roughness Ra value of the treated weld decreases, and a dense amorphous oxide film is formed, effectively blocking the contact between high-temperature gases and the substrate.

[0030] In this embodiment, the cooling rate of the furnace-controlled slow cooling is ≤5℃ / min until the temperature drops below 400℃.

[0031] This slow cooling method effectively avoids residual stress concentration and grain coarsening caused by rapid cooling by precisely controlling the cooling process. A cooling rate of ≤5℃ / min reduces residual stress in the weld zone while maintaining grain refinement. As the temperature drops below 400℃, orderly phase transformation and reorganization occur within the metal, forming a stable microstructure. A closed-loop control system consisting of an infrared thermometer and the heating device can correct cooling curve deviations in real time, ensuring the stability of the entire slow cooling process. This process significantly improves the fatigue resistance of the repaired resistance band under high-temperature cyclic loading.

[0032] In this embodiment, after the post-processing step, the method further includes: mechanically grinding the remelted weld and spraying a high-temperature resistant ceramic coating, followed by eddy current testing and resistance uniformity verification.

[0033] When mechanically grinding the remelted weld, 240-400 mesh silicon carbide sandpaper should be used to gradually remove the 0.1-0.3 mm oxide layer on the surface of the laser-remelted layer, while controlling the surface roughness Ra≤1.6μm to provide an ideal substrate for subsequent coating adhesion. The high-temperature resistant ceramic coating uses an alumina-yttrium oxide stabilized composite material, deposited via atmospheric plasma spraying. The coating thickness is controlled within the range of 80-120 μm, with a porosity ≤3%. This coating can form a dense alumina protective film at 1200℃, effectively isolating oxygen penetration and increasing the weld's oxidation resistance life to 2-3 times that of traditional processes. Eddy current testing uses a differential probe with a frequency of 500kHz, scanning along the weld longitudinally at a speed of 5 mm / s, which can detect crack defects with a diameter ≥0.3 mm. Resistance uniformity verification is performed by measuring the weld area resistance using a four-terminal method, requiring a deviation of ≤±2% from the base material resistance to ensure uniform current distribution when the repaired resistance band operates in the annealing furnace.

[0034] A second aspect of this application provides a dedicated welding system for the method, comprising: An integrated platform equipped with a pulse welding power supply, a water-cooled welding torch, a wire feeding mechanism, and a laser remelting head; A temperature control subsystem, including an infrared thermometer, a heating device, and a PID controller connected to them, forms a closed-loop control loop for accurately maintaining the preheating temperature and the interlayer temperature of the weld. A gas protection subsystem includes a front protective gas path and a back protective liner with a gas channel and a copper foil reflector.

[0035] Furthermore, the laser remelting head is a galvanometer-type laser scanning head, which is fixed on the same moving actuator as the welding torch to achieve continuous welding and remelting operations.

[0036] The dedicated welding system integrates a pulsed welding power supply, a water-cooled welding torch, a wire feeding mechanism, and a galvanometer-type laser scanning head, achieving seamless integration of composite welding and laser remelting processes. The water-cooled welding torch features a copper alloy nozzle design, coupled with a 360° rotating gas hood to ensure uniform inert gas protection coverage. The wire feeding mechanism is equipped with a dual-roller drive system, using a pressure sensor to adjust the wire feeding torque in real time, achieving a composite welding wire delivery accuracy of ±0.1mm. The temperature control subsystem's PID controller dynamically adjusts the heating device's power output based on interpass temperature data from an infrared thermometer. When temperature fluctuations exceed ±5℃, an automatic compensation mechanism is triggered to ensure the stability of the 950-1050℃ process window. The gas protection subsystem's back protective gasket uses a copper foil reflector to evenly guide the protective gas to the weld root, working in conjunction with the argon-helium mixed gas (18% helium) in the front gas path to form a bidirectional inert gas barrier. This system can control the weld oxygen content below 0.0025% and the nitrogen content below 0.0018%, significantly superior to traditional single-sided protection processes. The galvanometer-type laser scanning head employs dynamic focusing technology, achieving linear scanning speeds of 5-15 mm / s through a Galvo scanning mirror, in conjunction with a 2.0×10... 4 -5.0×10 4 W / cm 2 The adjustable power density allows for surface remelting of the weld without overheating the base material.

[0037] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0038] Example 1 An online repair method for cracked high-temperature resistors includes the following steps: Pretreatment steps: Clean the cracked area and cut a 60° V-shaped bevel. Then, use an infrared thermometer and PID-controlled heating blanket for three-stage preheating. First, raise the temperature to 600°C and hold for 5 minutes; then raise the temperature to 850°C and hold for 10 minutes; finally, raise the temperature to 1000°C and hold for 15 minutes. The interpass temperature is always maintained within the range of 950-1050°C. Composite welding steps: A composite welding wire consisting of a nickel-based alloy base layer (Inconel 625) and an austenitic stainless steel surface layer (ER308L) is used. Bidirectional shielding with Ar + 20% He inert gas is employed, with a front shielding gas flow rate of 25 L / min and a back shielding gas flow rate of 15 L / min. At least three layers of welding are performed on the preheated bevel using a pulsed current mode. The pulsed current mode has the following parameters: base current 60A, peak current 160A, and pulse frequency 2Hz. The welding voltage is 20V, the welding speed is 10cm / min, and the interpass overlap rate is ≥30%. Post-processing steps: Immediately after welding, the weld surface is subjected to laser remelting treatment with a laser power density of 3.5 × 10⁻⁶. 4 W / cm 2 After being slowly cooled to 400°C in the furnace, it is then removed from the furnace and sprayed with a high-temperature ceramic coating.

[0039] Performance testing: Eddy current testing is performed. After passing the test, the machine is installed for life testing (operating temperature 1150℃, power on and off cycle).

[0040] Example 2 An online repair method for cracked high-temperature resistors includes the following steps: Pretreatment steps: Clean the cracked area and cut a 60° V-shaped bevel. Then, use an infrared thermometer and PID-controlled heating blanket for three-stage preheating. First, raise the temperature to 600°C and hold for 8 minutes; then raise the temperature to 850°C and hold for 12 minutes; finally, raise the temperature to 1000°C and hold for 20 minutes. The interpass temperature is always maintained in the range of 950-1050°C. Composite welding steps: A composite welding wire consisting of a nickel-based alloy base layer (Inconel 625) and an austenitic stainless steel surface layer (ER309L) is used. Bidirectional shielding with Ar + 15% He inert gas is employed, with a front shielding gas flow rate of 22 L / min and a back shielding gas flow rate of 12 L / min. At least three layers of welding are performed on the preheated bevel using a pulsed current mode. The pulsed current mode has the following parameters: base current 60A, peak current 160A, and pulse frequency 2Hz. The welding voltage is 20V, the welding speed is 10cm / min, and the interpass overlap rate is ≥30%. Post-processing steps: Immediately after welding, the weld surface is subjected to laser remelting treatment with a laser power density of 4.0 × 10⁻⁶. 4 W / cm 2 After being slowly cooled to 400°C in the furnace, it is then removed from the furnace and sprayed with a high-temperature ceramic coating.

[0041] Performance testing: Eddy current testing is performed. After passing the test, the machine is installed for life testing (operating temperature 1150℃, power on and off cycle).

[0042] Example 3 An online repair method for cracked high-temperature resistors includes the following steps: Pretreatment steps: Clean the cracked area and cut a 60° V-shaped bevel. Then, use an infrared thermometer and PID-controlled heating blanket for three-stage preheating. First, raise the temperature to 550°C and hold for 6 minutes; then raise the temperature to 820°C and hold for 8 minutes; finally, raise the temperature to 980°C and hold for 18 minutes. The interpass temperature is always maintained in the range of 950-1050°C. Composite welding steps: A composite welding wire consisting of a nickel-based alloy base layer (Inconel 625) and an austenitic stainless steel surface layer (ER308L) is used. Bidirectional shielding with Ar + 25% He inert gas is employed, with a front shielding gas flow rate of 28 L / min and a back shielding gas flow rate of 18 L / min. At least three layers of welding are performed on the preheated bevel using a pulsed current mode. The pulsed current mode has the following parameters: base current 60A, peak current 160A, and pulse frequency 2Hz. The welding voltage is 20V, the welding speed is 10cm / min, and the interpass overlap rate is ≥30%. Post-processing steps: Immediately after welding, the weld surface is subjected to laser remelting treatment with a laser power density of 2.5 × 10⁻⁶. 4 W / cm 2 After being slowly cooled to 400°C in the furnace, it is then removed from the furnace and sprayed with a high-temperature ceramic coating.

[0043] Performance testing: Eddy current testing is performed. After passing the test, the machine is installed for life testing (operating temperature 1150℃, power on and off cycle).

[0044] Example 4 An online repair method for cracked high-temperature resistors includes the following steps: Pretreatment steps: Clean the cracked area and cut a 60° V-shaped bevel. Then, use an infrared thermometer and PID-controlled heating blanket for three-stage preheating. First, raise the temperature to 650°C and hold for 5 minutes; then raise the temperature to 880°C and hold for 10 minutes; finally, raise the temperature to 1020°C and hold for 15 minutes. The interpass temperature is always maintained within the range of 950-1050°C. Composite welding steps: A composite welding wire consisting of a nickel-based alloy base layer (Inconel 625) and an austenitic stainless steel surface layer (ER308L) is used. Bidirectional shielding with Ar + 20% He inert gas is employed, with a front shielding gas flow rate of 25 L / min and a back shielding gas flow rate of 15 L / min. At least three layers of welding are performed on the preheated bevel using a pulsed current mode. The pulsed current mode has the following parameters: base current 60A, peak current 160A, and pulse frequency 2Hz. The welding voltage is 20V, the welding speed is 10cm / min, and the interpass overlap rate is ≥30%. Post-processing steps: Immediately after welding, the weld surface is subjected to laser remelting treatment with a laser power density of 5.0 × 10⁻⁶. 4 W / cm 2 After being slowly cooled to 400°C in the furnace, it is then removed from the furnace and sprayed with a high-temperature ceramic coating.

[0045] Performance testing: Eddy current testing is performed. After passing the test, the machine is installed for life testing (operating temperature 1150℃, power on and off cycle).

[0046] Comparative Example 1 This comparative example is basically the same as Example 1, except that the composite welding wire is replaced with pure ER308L.

[0047] Comparative Example 2 This comparative example is basically the same as Comparative Example 1, except that it does not perform three-stage preheating, uses unidirectional pure Ar protection gas, has a frontal protection gas flow rate of 15L / min, and does not perform laser remelting.

[0048] Comparative Example 3 This comparative example is basically the same as Comparative Example 2, except that it is preheated to 500℃.

[0049] Comparative Example 4 This comparative example is basically the same as Example 1, except that the layer temperature is 600°C.

[0050] Comparative Example 5 This comparative example is basically the same as Example 1, except that pure Ar is used as the protective gas.

[0051] Experimental Case Performance tests were conducted on Examples 1-4 and Comparative Examples 1-5, and the results are shown in Table 1.

[0052] Table 1 Performance test results of Examples 1-4 and Comparative Examples 1-5

[0053] As shown in Table 1, the eddy current testing pass rate of Examples 1 to 4 all reached over 95%, with an average lifespan between 5850 and 6480 hours. The welding lifespan was equivalent to 85% to 94% of that of new parts, significantly better than the comparative examples. Example 2, using ER309L surface composite welding wire with optimized preheating parameters, exhibited the best fatigue resistance, with an average lifespan of 6480 hours. Comparative Example 1, lacking a composite welding wire structure, suffered from decreased high-temperature oxidation resistance, resulting in a 38% reduction in average lifespan compared to Example 1. Comparative Example 2, lacking three-stage preheating and laser remelting, showed numerous pores and cracks in the weld zone, causing its average lifespan to plummet to 850 hours, only 12% of that of new parts. Comparative Example 3, although using single preheating, failed to achieve sufficient metallurgical bonding, resulting in limited performance improvement. Comparative Example 4, due to excessively low interpass temperature leading to grain coarsening, experienced a 53% decrease in average lifespan compared to Example 1. Comparative Example 5, using pure Ar shielding gas, showed severe backside oxidation, resulting in a 27% reduction in average lifespan compared to Example 1. Experimental results show that the synergistic effect of three-stage preheating, composite welding wire structure, bidirectional inert gas protection, and laser remelting process is the key technical element to ensure the quality of high-temperature resistance band repair.

[0054] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An online repair method for cracked high-temperature resistance bands, used to repair iron-chromium-aluminum resistance bands operating in an annealing furnace, characterized in that, Includes the following steps: Pretreatment steps: Clean the cracked area and process the bevel, then perform gradient preheating on the base material. The gradient preheating includes a stress relief preheating stage and a grain boundary reconstruction preheating stage, with the highest preheating temperature reaching 980-1050℃. Composite welding steps: Using a composite welding wire consisting of a nickel-based alloy bottom layer and an austenitic stainless steel top layer, the preheated groove is welded in more than 3 layers under bidirectional inert gas protection using a pulsed current mode, with the interpass temperature always maintained within the range of 950-1050℃. Post-processing steps: Immediately after welding, the weld is laser remelted and then slowly cooled in the furnace.

2. The online repair method for cracked high-temperature resistors according to claim 1, characterized in that, The gradient preheating is as follows: First, raise the temperature to 500-650℃ and hold for 5-8 minutes to remove moisture; Then raise the temperature to 800-900℃ and hold for 8-12 minutes to eliminate work hardening of the base material; Finally, the temperature is raised to 980-1050℃ and held for 15-20 minutes to achieve grain boundary migration and reconstruction.

3. The online repair method for cracked high-temperature resistors according to claim 1, characterized in that, The pulse current mode is as follows: base current 60-80A, peak current 140-160A, voltage 18-22V, pulse frequency 1.5-2.5Hz.

4. The online repair method for cracked high-temperature resistors according to claim 1, characterized in that, In the composite welding wire, the nickel-based alloy bottom layer is Inconel 625 nickel-based welding wire, and the austenitic stainless steel surface layer is ER308L or ER309L type welding wire.

5. The online repair method for cracked high-temperature resistors according to claim 1, characterized in that, The inert gas bidirectional protection is as follows: the front protective gas flow rate is 20-30 L / min, and the back protective gas flow rate is 10-20 L / min; the inert gas is a mixture of argon and helium, wherein the volume percentage of helium is 15%-20%.

6. The online repair method for cracked high-temperature resistors according to claim 1, characterized in that, The laser power density of the laser remelting process is 2.0 × 10⁻⁶. 4 W / cm 2 Up to 5.0×10 4 W / cm 2 The scanning speed is 5-15 mm / s.

7. The online repair method for cracked high-temperature resistors according to claim 1, characterized in that, The furnace-controlled slow cooling rate is ≤5℃ / min until the temperature drops below 400℃.

8. The method according to claim 1, characterized in that, Following the post-processing steps, the process also includes: mechanically grinding the remelted weld and spraying a high-temperature resistant ceramic coating, followed by eddy current testing and resistance uniformity verification.

9. A dedicated welding system for implementing the method according to any one of claims 1-8, characterized in that, include: An integrated platform equipped with a pulse welding power supply, a water-cooled welding torch, a wire feeding mechanism, and a laser remelting head; A temperature control subsystem, including an infrared thermometer, a heating device, and a PID controller connected to them, forms a closed-loop control loop for accurately maintaining the preheating temperature and the interlayer temperature of the weld. A gas protection subsystem includes a front protective gas path and a back protective liner with a gas channel and a copper foil reflector.

10. The dedicated welding system according to claim 9, characterized in that, The laser remelting head is a galvanometer-type laser scanning head, which is fixed on the same moving actuator as the welding torch to achieve continuous welding and remelting operations.

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