A laser cladding repair method for a long-life structure of a flange furnace bottom plate

Abstract

The application discloses a laser cladding repair method for a flange furnace bottom disc of a long-service-life structure and belongs to the field of plating technology for metal materials, and aims at the green manufacturing plan of super-high-grade oriented silicon steel and comprises the following steps: performing state evaluation and pretreatment on a working surface of a bottom disc after a service cycle is completed, confirming whether the working surface is a primary service surface or a secondary service surface; pre-preparing three kinds of functional powders of substrate regeneration, A-surface thermal fatigue resistance and B-surface high-thermal-conductivity oxidation resistance; firstly, cladding a substrate regeneration layer on a surface of a substrate to reset a microstructure; secondly, selectively cladding an A-surface or a B-surface functional layer according to the attribute of the working surface to form a gradient repair structure; and finally, performing post-heat treatment. Through the differential powder system and the repair strategy, the application solves the different failure problems of the primary and secondary service surfaces and significantly improves the repair quality and the whole life cycle of the bottom disc, realizes life doubling after single repair and guarantees the product quality uniformity of the bearing silicon steel coil.

Description

Technical Field

[0001] This invention relates to the field of metal plating technology, and more particularly to a laser cladding repair method for a long-life flange furnace chassis. Background Technology

[0002] Cold-rolled grain-oriented silicon steel is the core material for manufacturing the cores of electromagnetic equipment such as power transformers and reactors. Its final performance is highly dependent on the high-temperature bell-type annealing process. In this process, the flange furnace base, as a key supporting component that bears tens of tons of silicon steel coils, must maintain excellent load-bearing capacity, structural stability, and uniform heat conduction at a high temperature of 1200℃ for a period of up to one week.

[0003] like Figure 2 As shown, for the green manufacturing of ultra-high grade grain-oriented silicon steel, the performance of cold-rolled grain-oriented silicon steel is directly related to the heating uniformity of the silicon steel coil, and is a key process equipment affecting the consistency of product magnetic properties, yield, and production efficiency. For example... Figure 2 As shown, the single-sided furnace bottom platen, which was commonly made of Q235-B carbon steel in the early days, has problems such as high-temperature creep, thermal fatigue and severe oxidation, resulting in rapid deformation and cracking and short service life (about 5-6 months), which can no longer meet the needs of high-quality and high-efficiency production.

[0004] To extend service life, existing technologies have proposed a double-sided symmetrical furnace chassis made of heat-resistant stainless steel SUS309S, and introduced laser cladding repair technology. This structural design allows the first side (A side) to be flipped and used as the second side (B side) after a certain service cycle, theoretically doubling the service life; at the same time, laser cladding is used to repair damage to the working surface, aiming to form a "use-flip-repair" cyclical regeneration mode.

[0005] However, this approach still faces significant limitations in practical applications: while the double-sided structure extends the overall service life before the first flip, the concentrated heat input introduced during the laser cladding repair process leads to the deterioration of the heat-affected zone (HAZ) of the substrate. Furthermore, the damage mechanisms of sides A and B differ due to their different service histories, and the homogeneous cladding material cannot specifically adapt to these differences. Multiple repairs further exacerbate the accumulation of tissue damage in the HAZ, accelerating the overall performance degradation and resulting in an actual service life far below the design expectations of the double-sided structure. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a laser cladding repair method for a long-life flange furnace chassis.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: a laser cladding repair method for a long-life flange furnace chassis, comprising:

[0008] S1. Conduct condition assessment and surface pretreatment on the working surface of the flange furnace chassis that has completed its service cycle to determine whether the surface attribute is the first service surface or the second service surface, i.e., surface A or surface B.

[0009] S2. Pre-fabricate three types of cladding powders, including: substrate regeneration powder, A-side repair powder, and B-side repair powder; wherein, the substrate regeneration powder is used to reset the microstructure of the heat-affected zone; the A-side repair powder is used to enhance the thermal fatigue resistance of the A-side; and the B-side repair powder is used to enhance the thermal conductivity and oxidation resistance of the B-side.

[0010] S3. On the pretreated substrate surface, a layer of the substrate regeneration powder is first deposited using laser cladding technology to form a substrate regeneration cladding layer;

[0011] S4. Based on the surface properties of the surface to be repaired, select the corresponding A-side repair powder or B-side repair powder, and perform laser cladding on the substrate regenerated cladding layer to construct a directional reinforced main cladding layer with thermal fatigue resistance or high thermal conductivity and oxidation resistance, respectively.

[0012] S5. Perform post-heat treatment on the cladding area and put the repaired chassis back into service.

[0013] The flange furnace chassis is a double-sided symmetrical disc structure made of heat-resistant austenitic stainless steel. Its upper and lower surfaces are surface A and surface B, respectively. During service, surface A bears the load before surface B.

[0014] In a preferred embodiment of the present invention, the status assessment in step S1 includes defect screening and attribute determination. The defect screening adopts a combined detection method of eddy current detection and optical profilometry. When a microcrack with a depth ≥0.3mm or a local plastic deformation ≥0.5mm is detected on the working surface, the repair process is triggered. If ultrasonic testing detects an internal crack with a depth greater than 4-8mm, the chassis is determined to be unqualified for repair.

[0015] In a preferred embodiment of the present invention, the attribute determination in step S1 is achieved by identifying a preset laser marking mark on the non-load-bearing area of ​​the flange furnace chassis. The mark includes the chassis number, service surface type and service status. The marking information can be linked to a central database to achieve full life cycle traceability.

[0016] In a preferred embodiment of the present invention, the recycled substrate powder is Fe-based, and its chemical composition by weight percentage includes: Ti 1.5-2.5%, Zr 0.8-1.2%, Al 0.4-0.8%, B 0.10-0.30%, Y 0.05-0.15%, C 0.03-0.10%, with the balance being Fe and unavoidable impurities; the thickness of the recycled substrate cladding layer is 0.25-0.35 mm.

[0017] In a preferred embodiment of the present invention, the A-side repair powder is Fe-Cr-Ni based, and its chemical composition by weight percentage includes: Nb 2.2-3.2%, Mo 1.5-2.5%, W 0.8-1.8%, V 0.5-1.0%, C 0.10-0.20%, N 0.04-0.10%, Cr 20-25%, Ni 10-15%, with the balance being Fe; the A-side repair powder is used to construct a directionally strengthened main cladding layer with thermal fatigue resistance.

[0018] In a preferred embodiment of the present invention, the B-side repair powder is Fe-based, and its chemical composition by weight percentage includes: Cu 7.0-11.0%, Ag 1.0-2.5%, Si 1.0-2.0%, Mg 0.2-0.6%, Ce 0.05-0.25%, Cr 18-22%, Ni 8-12%, with the balance being Fe; the B-side repair powder is used to construct a directionally strengthened main cladding layer with high thermal conductivity and antioxidant function.

[0019] In a preferred embodiment of the present invention, when the laser cladding deposition substrate regenerated powder is performed, a laser with an output power of 2500-2800W is used, the spot diameter is 3.5-4.5mm, the scanning speed is 7-10mm / s, and the overlap rate of adjacent scanning passes is 35%-45%.

[0020] In a preferred embodiment of the present invention, the directional strengthening main cladding layer is a single-layer structure with a thickness of 1.1-1.3 mm; when repairing surface A, surface A repair powder with a particle size range of 53-150 μm is used; when repairing surface B, surface B repair powder with a particle size range of 45-125 μm is used.

[0021] In a preferred embodiment of the present invention, the post-heat treatment is carried out in a protective atmosphere furnace, heated to 850°C at a heating rate of 2-5°C / min, held at that temperature for 4 hours, then cooled to 400°C at a cooling rate of 1-2°C / min, and finally air-cooled to room temperature.

[0022] In a preferred embodiment of the present invention, the surface pretreatment includes sandblasting and vacuum heating. The sandblasting uses brown corundum particles with a particle size of 0.8-1.2 mm, a blasting pressure of 0.6 MPa, a blasting angle of 75°, and treats the surface until the surface roughness Ra is 3.2-6.3 μm. The vacuum heating is carried out under an argon protective atmosphere, heated to 300°C at a heating rate of 5°C / min, held at that temperature for 2 hours, and then naturally cooled to room temperature.

[0023] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0024] This invention, by strictly distinguishing the essential differences between the A and B sides of the flange furnace chassis in terms of service time and substrate condition, designs a differentiated gradient repair system using substrate regeneration powder, A-side repair powder, and B-side repair powder. Before each repair, the microstructure of the heat-affected zone is actively reset, and then a specific functional layer is applied based on the surface properties. The A side, as the first-time damaged surface, is primarily affected by thermomechanical fatigue, while the B side, as a secondary service surface, has pre-damaged substrate and focuses more on thermal conductivity and oxidation resistance. This achieves a dynamic and precise match between the repair strategy and the actual failure risk at different stages throughout the component's life cycle. In contrast to existing technologies that use homogenized repair methods treating the repair area as an independent locality and simply using the same powder, leading to the repair thermal cycle superimposing damage on the original fragile structure and creating a vicious cycle, this invention's precise matching ensures that each repair effectively corrects the performance shortcomings of a specific surface.

[0025] This invention first deposits a layer of substrate regeneration powder on the surface of a pretreated substrate. During laser cladding, elements such as titanium, zirconium, boron, aluminum, and yttrium form nanoscale borides and nitrides, strongly pinning grain boundaries and dislocations, thus resetting the microstructure of the heat-affected zone (HAZ). This breaks the intergenerational accumulation of thermal damage caused by grain boundary embrittlement and carbide aggregation from previous service, purifies the harmful grain boundary environment, and provides a novel, uniform, and tough metallurgical bonding interface for subsequent functional layers. It avoids the superposition of new damage on the existing fragile HAZ during the repair thermal cycle, preventing a vicious cycle of repair-embrittlement-re-repair. This resetting mechanism lays a reliable foundation for the performance of subsequent functional layers.

[0026] This invention designs functionally specific cladding powders for surfaces A and B. The surface A repair powder is rich in niobium, molybdenum, tungsten, and vanadium, forming a high-hardness carbonitride reinforcing phase, focusing on resistance to thermal fatigue. The surface B repair powder is rich in copper, silver, silicon, magnesium, and cerium, forming a high thermal conductivity phase and a self-healing oxide film, focusing on thermal conductivity and oxidation resistance. These directionally reinforced main cladding layers are constructed on top of the substrate regeneration layer, forming a gradient performance transition zone from high functionality on the surface to high toughness on the bottom, synergistically strengthening the service performance of each surface. Surface A achieves excellent resistance to crack initiation and propagation, resisting the initial high-temperature heavy-load impact; surface B achieves efficient thermal conduction and durable oxidation protection, compensating for the performance degradation of the substrate. This synergistic reinforcement, combined with the regeneration effect of the substrate regeneration layer, achieves a three-dimensional improvement in material properties during laser cladding repair.

[0027] This invention integrates condition assessment, substrate regeneration, functional repair, and post-heat treatment into a single, life-cycle repair system deeply integrated with the dual-sided, sequentially serving structure. It not only considers the immediate damage during each repair but also proactively addresses the historical condition of the substrate and future service requirements through ultrasonic flaw detection and a life assessment model. Differentialized, gradient repair fully utilizes the component's potential lifespan. The flange furnace chassis maintains high performance even after multiple repairs, extending its overall service life and reducing the cost of replacing expensive heat-resistant alloys. Compared to existing technologies that employ homogeneous repair methods or neglect substrate condition, this invention ensures the chassis continues to perform effectively during alternating dual-sided service. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of a preferred embodiment of the present invention;

[0030] Figure 2 This is a side view of the flange furnace chassis of the present invention;

[0031] Figure 3 This is a surface view of the flange furnace chassis of the present invention;

[0032] In the diagram: 1. Flange furnace base; 2. Annular heat conduction groove; 3. Central through hole. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0035] Application Overview:

[0036] This invention addresses the flange furnace chassis used in the high-temperature annealing process of cold-rolled grain-oriented silicon steel, and particularly relates to the problem of improving its lifespan in scenarios of alternating double-sided service and laser cladding repair.

[0037] The A-side defined in this application is the first service surface of the flange furnace chassis, referring to the surface of the double-sided symmetrical disc-shaped heat-resistant austenitic stainless steel matrix that is arranged upwards and directly supports the silicon steel coil when it is first put into the high-temperature bell-type annealing process, whether brand new or after complete repair; the core feature is priority in service sequence.

[0038] B side is the secondary service surface of the flange furnace chassis. It refers to the original downward-facing surface that is put into use after A side has completed a full service cycle and is flipped over by a flipping device. Its core feature is that the base material has been pre-damaged.

[0039] Because of the fundamental differences in the thermal history and damage mechanism between surface A and surface B, the damage on surface A is driven by both external load and initial high-temperature exposure, which jointly induces and propagates fatigue cracks. On the other hand, when surface B is put into use, the surface has already undergone a complete thermal cycle and the microstructure has degraded to a certain extent. Subsequent failure of surface B is more related to decreased thermal conductivity, weakened oxidation resistance, and crack initiation on the already weakened microstructure. The homogeneous laser cladding repair technology in the current technology leads to the continuous deterioration of the microstructure in the heat-affected zone after repair, ultimately causing the chassis to fail before reaching its theoretical lifespan.

[0040] Conventional laser cladding repair follows the principles of defect filling and surface performance restoration, with the technical logic starting from treating the repair area as a local part independent of the overall component's historical state. When applied to a double-sided structure with a clear time-series service characteristic, as described in this invention, simply using the same powder for repair not only fails to correct the existing structural defects in the B-side matrix, but the concentrated heat input introduced during the repair process itself will also superimpose new and uncontrollable thermal cycles on the original HAZ, leading to continuous weakening of grain boundaries and aggregation of brittle phases, forming a vicious cycle.

[0041] This invention proposes a differentiated gradient repair system that is deeply integrated with the structural characteristics of dual-sided sequential service. Before each repair, the HAZ below the repair area is actively regenerated. Then, based on the completely different damage-dominant mechanisms and service requirements of sides A and B, functionally specific cladding powders are designed and applied respectively. In principle, this achieves dynamic and precise matching between the repair strategy and the actual failure risk at different stages of the component's entire life cycle.

[0042] Exemplary method:

[0043] like Figure 1 As shown, a laser cladding repair method for a long-life flange furnace chassis includes:

[0044] S1. Conduct condition assessment and surface pretreatment on the working surface of the flange furnace chassis that has completed its service cycle to determine whether the surface attribute is the first service surface or the second service surface, i.e., surface A or surface B.

[0045] S2. Pre-fabricate three types of cladding powders, including: substrate regeneration powder, A-side repair powder, and B-side repair powder; wherein, the substrate regeneration powder is used to reset the microstructure of the heat-affected zone; the A-side repair powder is used to enhance the thermal fatigue resistance of the A-side; and the B-side repair powder is used to enhance the thermal conductivity and oxidation resistance of the B-side.

[0046] S3. On the pretreated substrate surface, a layer of the substrate regeneration powder is first deposited using laser cladding technology to form a substrate regeneration cladding layer;

[0047] S4. Based on the surface properties of the surface to be repaired, select the corresponding A-side repair powder or B-side repair powder, and perform laser cladding on the substrate regenerated cladding layer to construct a directional reinforced main cladding layer with thermal fatigue resistance or high thermal conductivity and oxidation resistance, respectively.

[0048] S5. Perform post-heat treatment on the cladding area and put the repaired chassis back into service.

[0049] The long-life structural flange furnace chassis 1 of the present invention is a core support and heat conduction component designed for cold-rolled grain-oriented silicon steel to support silicon steel coils weighing tens of tons in a high-temperature bell-type annealing process at a temperature of up to about 1200°C.

[0050] like Figure 3 As shown, the main body, or base, of the flange furnace chassis 1 adopts a double-sided symmetrical disc structure and is made of heat-resistant austenitic stainless steel base.

[0051] The main chemical composition of the material is: C 0-0.08 wt%, Si 0-1wt%, Mn 0-2wt%, P 0-0.045wt%, S 0-0.030wt%, Ni 12.0-14.0-wt%, Cr 22.0-24.0-wt%, with the balance being Fe and unavoidable impurity elements. Silicon and manganese, as common alloying elements and deoxidizers, ensure good metallurgical quality of the material while avoiding negative impacts on high-temperature plasticity or weldability. The high nickel content ensures that the matrix maintains a stable single-phase face-centered cubic austenitic structure throughout the entire range from room temperature to service temperature. The high chromium content preferentially forms a dense and strongly adherent chromium oxide protective film on the material surface. This film can greatly delay further corrosion of the matrix in high-temperature oxidizing atmospheres and is the key to the material's excellent oxidation resistance.

[0052] like Figure 2As shown, in terms of shape, the flange furnace base plate 1 is generally disc-shaped with an outer diameter of 1800±200mm, a central through hole 3 with a diameter of 150±20mm, and a total thickness of 150±10mm. The upper and lower surfaces of the plate, namely surface A and surface B, are both machined with concentric annular heat-conducting grooves 2, with a groove depth of 5.0±0.2mm, a groove width of 8.0±0.3mm, and a spacing between adjacent grooves of 25.0±0.5mm.

[0053] The annular heat-conducting groove 2 forms a channel that is conducive to protecting gas flow, promoting the uniform distribution and renewal of the atmosphere in the furnace, and avoiding uneven carburization or decarburization caused by local atmosphere stagnation. The annular heat-conducting groove 2 increases the effective contact area between the chassis and the silicon steel coil and divides the continuous contact surface into multiple annular contact bands, which helps to distribute the huge static load more evenly and reduce contact compressive stress. The alternating structure of the groove ridge and groove bottom guides the path of heat transfer from the chassis to the steel coil, mitigating the difference in contact thermal resistance caused by the coil's own winding gap or slight unevenness.

[0054] In addition, eight positioning pin holes are evenly distributed around the circumference of the plate, with a hole diameter of Φ25H7 and a center distance of 750±1mm from the center of the plate. These holes are used to cooperate with the positioning pins of the furnace support base to achieve precise assembly. The upper surface of the plate, defined as surface A, and the lower surface, defined as surface B, are completely mirror-symmetrical, with identical annular heat conduction groove 2 patterns, identical surface finish requirements, and identical mechanical load-bearing potential.

[0055] However, in terms of service, the flange furnace chassis 1 has a strict time sequence distinction: side A is the initial service side, that is, when the brand new or fully repaired flange furnace chassis 1 is first loaded into the furnace, side A must face upward so that it directly contacts and bears the newly loaded silicon steel coil, and withstands the full load and thermal shock of the first complete high-temperature annealing cycle.

[0056] After side A successfully completes a service cycle typically lasting seven to eight months and rolls off the production line, the chassis is not scrapped. Instead, it is flipped over entirely at the maintenance station using a hydraulic tilting device. After flipping, side B, which was originally facing down, now faces up and is activated as a secondary service surface to bear the load for the next cycle. Physically, this increases the number of usable load-bearing surfaces of a component from one to two, theoretically doubling the potential service life of the material.

[0057] As the surface undergoing its first service, the damage to surface A mainly stems from the direct effects of the first high-temperature heavy load. The damage mechanism is dominated by thermomechanical fatigue, meaning that the initiation and propagation of cracks caused by creep and alternating thermal stress at high temperatures are the main contradictions.

[0058] When side B was put into use, its physical state was completely different from that of the brand-new side A: although the surface of side B did not bear direct load, its base material had undergone the same long-term, overall high-temperature exposure throughout the entire service life of side A.

[0059] The matrix below side B has undergone a complete thermal history and irreversible microstructural evolution. For example, the grains may have grown slightly, carbides may have a preliminary tendency to precipitate at the grain boundaries, and there may be a residual stress field inside due to uneven thermal expansion and phase transformation constraints. Its high-temperature mechanical and physical properties may have degraded to some extent from the initial peak value.

[0060] Therefore, the failure risk after the B side is activated will be different from that of the A side, and is more likely to be related to the insufficient performance of the aged substrate under secondary load, as well as the additional thermal stress that may be caused by a slight decrease in thermal conductivity.

[0061] Determining whether it is side A, which is in its first service sequence, or side B, which has already undergone a complete thermal history, is the starting point for subsequent selection of differentiated materials and implementation of processes.

[0062] Step S1 includes two stages: condition assessment and surface pretreatment.

[0063] Condition assessment is made through a life assessment model based on damage mechanics theory; the life assessment model calculates the cumulative damage degree by collecting FBG sensor data at key locations on the furnace bottom in real time, thereby achieving quantitative prediction of life.

[0064] The life assessment formula is: ,in, The cumulative damage level over time t; The equivalent strain rate is derived from the strain tensor measured by the FBG sensor through mechanical formulas. Let be the integral variable, representing any moment during service, and t be the actual service time of the furnace chassis. This represents the allowable equivalent strain rate of the furnace bottom plate matrix material at a service temperature of 1200℃.

[0065] When the system determines a certain area When the value is ≥0.85, the region is considered to have entered a critical damage state, triggering a repair warning.

[0066] After a complete service cycle, in addition to relying on the aforementioned damage model for early warning, the system also conducts a comprehensive surface condition inspection of the furnace chassis working surface; if microcracks with a depth ≥ 0.3 mm or local plastic deformation ≥ 0.5 mm are detected on the surface, the system will automatically trigger the repair process.

[0067] After the flange furnace chassis 1 completes a full service cycle, its working surface is evaluated.

[0068] If microcracks with a depth ≥0.3mm or local plastic deformation ≥0.5mm are detected on the surface, the repair process is initiated; the repair decision algorithm automatically generates path planning instructions for laser cladding repair based on the specific location, depth and surface morphology characteristics of the damage.

[0069] Before repair, the system uses a confocal laser displacement sensor installed at the end of the robotic arm to perform a 3D scan of the damaged area and acquire high-precision point cloud data. Subsequently, the central control unit calls a pre-stored geometric reconstruction algorithm to generate a CAD model of the area to be repaired, and performs Boolean difference operations with the original design model to accurately calculate the volume and contour boundary of the material to be filled, providing precise path instructions for subsequent laser cladding.

[0070] After defect screening is completed, the second step is attribute determination, that is, confirming whether the working surface to be evaluated is surface A or surface B. This is the cornerstone of the differentiated repair logic of this application, but on a geometrically symmetrical double-sided structure, it is impossible to distinguish them by appearance alone.

[0071] In a preferred embodiment, before the flange furnace chassis 1 is manufactured or put into initial use, a unique identification code and service status mark are laser-marked on its non-load-bearing sidewalls or near the locating pin holes, or in other locations that do not affect functionality; for example, ID-001-A-0, where ID-001 is the chassis number, A represents side A, and 0 represents the initial state. Whenever this side completes a service cycle and enters the maintenance workshop, personnel or an automatic identification system first scans this mark.

[0072] The system automatically updates the status according to preset logic: if A-0 is scanned, it is determined that the A side has entered its first service and will soon enter the first repair process of the A side, and the identifier is automatically updated to A-1; if B-1 is scanned, it is determined that the B side has entered its second service and will enter the second repair process of the B side, and the identifier is updated to B-2, and so on.

[0073] All historical data can be linked to a central database, enabling full lifecycle traceability.

[0074] Using a suitable ultrasonic probe, scan the disk surface, especially below areas where surface cracks have been detected, and in stress concentration areas such as near the root of the heat conduction groove after coupling.

[0075] Ultrasonic waves propagate in a straight line in a homogeneous material, but are reflected when they encounter internal defects such as cracks or inclusions. By analyzing the location, amplitude, and shape of the reflected echo, the depth, equivalent size, and nature of the internal defect can be determined.

[0076] This invention sets a repair safety red line: if ultrasonic testing detects internal cracks with a depth greater than 4-8mm, especially those defects that have a tendency to expand and may connect to become through cracks, the system automatically determines that the chassis is not eligible for repair and must be directly and forcibly scrapped.

[0077] In step S1, the repair surface is pretreated;

[0078] The surface oxide scale and deposits are removed by sandblasting. The sandblasting medium is brown corundum particles with a particle size of 0.8-1.2mm. The blasting pressure is 0.6MPa and the blasting angle is 75°. The treatment time continues until the surface roughness Ra reaches 3.2-6.3μm.

[0079] The workpiece was then placed in a vacuum heating furnace and heated to 300°C at a heating rate of 5°C / min under an argon protective atmosphere. It was then held at that temperature for 2 hours to eliminate surface-adsorbed moisture and residual stress, and then allowed to cool naturally to room temperature.

[0080] Step S2, based on the understanding of the different failure mechanisms, performance shortcomings and matrix conditions of surface A and surface B, designs and prefabricates three sets of dedicated cladding powder systems that are both clearly defined in terms of chemical composition and metallurgical function and work together with each other.

[0081] In existing repair techniques, the heat from laser cladding creates a new heat-affected zone (HAZ) beneath the functional layer. For the chassis of this invention, this new HAZ will spatially overlap with a historical HAZ within the substrate that is present due to previous service and is characterized by grain boundary embrittlement, carbide aggregation, and residual stress.

[0082] Traditional powders, such as SUS309S powder which is close to the matrix, are powerless against this. The cladding process is equivalent to burning the already fatigued and aged matrix surface again. The newly generated thermal stress and structural stress will be selectively released at the original fragile grain boundaries, leading to further cracking of the grain boundaries and accelerated aggregation of brittle phases.

[0083] Each repair makes the interface area more fragile, creating a vicious cycle of repair-fragility-re-repair-more-fragility, until the interface becomes completely unusable.

[0084] The three types of specialized cladding powders are substrate recycling powder, A-side repair powder, and B-side repair powder.

[0085] In step S2, the recycled powder of the substrate is not used to directly undertake the service function, but to form a special transition layer on the surface of the pretreated substrate during the first deposition of laser cladding;

[0086] By intervening in the microstructure of the heat-affected zone (HAZ), which is inevitably generated during the laser cladding process and carries the entire history of damage from previous service, the intergenerational accumulation of thermal damage is interrupted, the deteriorated microstructure is reset, and the harmful grain boundary environment is purified, thereby providing a new, uniform, and tough metallurgical bonding interface for the subsequent functional repair layer.

[0087] The recycled powder substrate is iron (Fe) based, but key functions are achieved through a variety of microalloying elements, including:

[0088] Titanium (Ti) and zirconium (Zr), wherein the Ti content is 1.5-2.5 wt% and the Zr content is 0.8-1.2 wt%. Ti and Zr are strong carbonitride forming elements, but in this invention, their more important role is in combination with boron (B).

[0089] During the extremely rapid heating and cooling process of the laser molten pool, Ti and Zr react in situ with B to form TiB2 and ZrB2; these borides have extremely high hardness, melting point and thermal stability.

[0090] TiB2 and ZrB2 are dispersed at the nanoscale, less than 100 nm.

[0091] These nanoparticles act as tiny rivets, effectively anchoring austenite grain boundaries and dislocations, strongly hindering grain boundary migration and dislocation slip and climb.

[0092] During the cladding thermal cycle, the grains in the HAZ that may have coarsened due to previous service cannot continue to grow. Instead, they are significantly refined under the pinning and recrystallization effects of the nanophase. Fine grain strengthening is one of the most effective means to simultaneously improve the strength and toughness of the material, which restores good matrix toughness to the repaired area.

[0093] Aluminum (Al) and boron (B) are present, with Al content of 0.4-0.8 wt% and B content of 0.10-0.30 wt%. In addition to deoxidizing and purifying the molten pool, Al can also combine with trace amounts of nitrogen in the molten pool or protective gas to form AlN nanoparticles.

[0094] AlN also possesses high thermal stability and good hardness, and in synergy with TiB2 and ZrB2, it further enhances the effect of nanophase dispersion strengthening.

[0095] In addition to forming borides, element B atoms also tend to cluster at grain boundaries, which can purify grain boundaries and form stable compounds with harmful impurity elements clustered at grain boundaries or change their distribution, thereby reducing the tendency of grain boundary embrittlement.

[0096] During the repair thermal cycle, TiB2, ZrB2, and AlN can effectively prevent the coarsened grains in the historical HAZ from continuing to grow, and can even induce abnormal recrystallization, breaking down and refining the coarse grains into uniform and fine new grains, forming a nanoparticle network. Similarly, when microcracks that are trying to propagate encounter the nanoparticle network, their propagation paths are forced to deflect, bypass, or bifurcate, consuming a large amount of energy, thereby significantly improving the fracture toughness of the material.

[0097] Yttrium (Y), with a content of 0.05-0.15 wt%, is a rare earth element with extremely low solid solubility in austenite. During solidification and cooling, it strongly segregates at grain boundaries and phase interfaces. The enrichment of Y at grain boundaries can, on the one hand, physically hinder grain boundary migration and further suppress grain growth; on the other hand, Y is highly reactive and can preferentially react with impurities such as oxygen and sulfur at grain boundaries to form high-melting-point spherical compounds, thereby avoiding impurity precipitation and significantly improving the bonding strength of grain boundaries and resistance to high-temperature oxidation and corrosion.

[0098] Carbon (C), with a content of 0.03-0.10 wt%, provides the necessary carbon to form small amounts of carbides with some Ti and Zr, participating in nanophase composite strengthening; it also prevents excessive carbon from combining with chromium in the matrix to form coarse Cr during subsequent service or repair thermal cycles. 23 C6 or Cr7C3 type carbides precipitate continuously at grain boundaries.

[0099] Through the combined action of elements such as Ti, Zr, B, Al, and Y, a new cladding layer is formed, and the ultra-high density nanophase and grain boundary purification effect generated by these elements actively and forcibly reconstruct the microstructure of the underlying HAZ.

[0100] In step S2, the A-side repair powder is the first surface to be damaged. Its damage is not simply wear or corrosion, but rather, during the initial experience of a drastic temperature rise from room temperature to 1200°C and the long-term exposure to maximum static load, the material simultaneously faces high-temperature creep, plastic deformation, and alternating thermal stress caused by temperature fluctuations. The failure mode is mainly manifested as the initiation and steady-state propagation of thermomechanical fatigue cracks.

[0101] Existing technologies using cobalt-based or nickel-based high-temperature alloy powders have acceptable high-temperature strength, but two problems are prominent: first, the difference in thermal expansion coefficients with the austenitic stainless steel matrix may lead to large interfacial stress; second, the strengthening phase will undergo over-aging and coarsening at 1200℃ for a long time, resulting in performance degradation; if ordinary iron-chromium-nickel powder is used, the high-temperature strength is simply insufficient to resist initial creep.

[0102] The A-side repair powder introduces a large number of second-phase reinforcing particles with high thermal stability and high hardness. Through dispersion reinforcement and fine grain reinforcement, it greatly hinders dislocation movement and pins crack tips, thereby delaying the accumulation of fatigue damage.

[0103] The A-side repair powder is based on Fe-Cr-Ni, and key reinforcement is achieved by adding a variety of strong carbonitride forming elements:

[0104] Niobium (Nb) and vanadium (V), with Nb content of 2.2-3.2 wt% and V content of 0.5-1.0 wt%; Nb and V are the main elements for forming MC-type carbides and nitrides; they have a very strong affinity for C and N, and will form very fine and dispersed (Nb,V)(C,N) composite phases during the solidification of the molten pool and subsequent cooling process.

[0105] The MC phase has extremely high melting point and hardness, remaining stable even at 1200℃ and not easily coarsening or dissolving. It effectively pins dislocations, hindering their slip and climb at high temperatures, significantly improving the material's high-temperature yield strength and creep resistance.

[0106] Molybdenum (Mo) and tungsten (W) are used, with Mo content ranging from 1.5 to 2.5 wt% and W content ranging from 0.8 to 1.8 wt%. Mo and W are refractory metals with significant solid solution strengthening effects. They are dissolved in the austenitic matrix, which can improve the bonding force of matrix atoms and enhance high-temperature strength.

[0107] More importantly, given a certain amount of carbon, they tend to form M6C or M... 23 C6-type carbides. Although these carbides are slightly less stable than the MC phase, at appropriate concentrations, they can form a multi-scale, multi-type composite reinforcing phase system with the MC phase. The M6C phase is usually slightly larger, but it can still effectively hinder dislocations. The addition of Mo and W also increases the recrystallization temperature of the matrix through solid solution, making the microstructure more stable at high temperatures.

[0108] The powder contains carbon (C) and nitrogen (N), with C content of 0.10-0.20 wt% and N content of 0.04-0.10 wt%. If the C and N content is too low, sufficient volume fraction of reinforcing carbonitrides cannot be formed, resulting in insufficient reinforcing effect. If the C and N content is too high, the carbides may become excessively coarse and precipitate continuously along the grain boundaries, which may impair toughness and fatigue resistance.

[0109] Chromium (Cr) and nickel (Ni) are used, with Cr content of 20-25 wt% and Ni content of 10-15 wt%. Maintaining a high Cr and Ni content is to ensure that the cladding layer itself has good high-temperature oxidation and corrosion resistance, so that it can form a protective oxide film when it is in direct contact with the furnace atmosphere as a surface layer.

[0110] The main challenge for surface materials is resisting the combined damage caused by cyclic thermal stress and static mechanical loads. This requires surface materials to possess extremely high high-temperature instantaneous strength and creep strength to resist plastic deformation; and excellent resistance to crack initiation and propagation to extend fatigue life.

[0111] The A-side repair powder achieves dispersion strengthening through a high volume fraction of MC / M6C composite reinforcing phase. The abundant, fine, hard, and thermally stable second-phase particles are one of the most effective means of improving high-temperature strength. The A-side repair powder achieves toughening through synergistic reinforcement of the second phase and fine grain structure. The rapid solidification characteristic of laser cladding itself is conducive to the formation of fine dendrites or cellular crystals. The pinning effect of the reinforcing phase further inhibits grain growth. Fine grain structure not only improves strength but, more importantly, increases the total grain boundary area, requiring more energy for crack propagation. Simultaneously, fine grains also promote uniform stress distribution, reducing local stress concentration and thus significantly inhibiting the initiation of thermal fatigue cracks.

[0112] The A-side repair powder is fused onto the regenerated substrate layer, which has already been reset and refined in grain size. This allows the reinforcement effect to be built on a strong and tough substrate, avoiding the risk of interface failure caused by the direct bonding of the reinforcement layer and the fragile HAZ.

[0113] In step S2, the design of the B-side repair powder is completely different from that of the A-side repair powder.

[0114] Since the substrate beneath side B was already in a pre-damaged state after undergoing a complete thermal history and experiencing performance degradation when it was first activated, the repair of side B was not intended to further enhance its potential to resist extreme mechanical fatigue, as the initial heavy load was already borne by side A. Instead, it was to specifically compensate for the performance shortcomings of the substrate, namely, to significantly improve the thermal conductivity of the surface layer to compensate for the decline in the thermal conductivity of the substrate and ensure a uniform thermal field; at the same time, it greatly enhanced the oxidation resistance and environmental corrosion resistance of the surface layer, providing a more robust protective barrier for the already slightly damaged substrate and blocking the path of rapid oxidation erosion inward along the grain boundaries.

[0115] The chemical content of the B-side repair powder is:

[0116] The composite material contains copper (Cu) and silver (Ag), with Cu content ranging from 7.0 to 11.0 wt% and Ag content from 1.0 to 2.5 wt%. While Cu and Ag have limited solid solubility in iron-based austenite, during the rapid solidification process of laser cladding, they are distributed in the austenite matrix in extremely fine and dispersed forms as Cu / Ag-rich intermetallic compounds or pure metallic phases. Cu and Ag are excellent electrical and thermal conductors. The introduction of these highly thermally conductive phases can significantly improve the overall thermal conductivity of the composite material. Electrons are the primary carriers of heat conduction in metals, and the Cu / Ag phase provides an efficient electron conduction channel.

[0117] Higher surface thermal conductivity means that heat can be transferred from the furnace to the bottom of the silicon steel coil more quickly and evenly, effectively offsetting the increased temperature difference at the bottom that may be caused by the decay of the thermal conductivity of the substrate, and fundamentally preventing watermark edge defects.

[0118] Silicon (Si) and magnesium (Mg) are present, with Si content ranging from 1.0 to 2.0 wt% and Mg content ranging from 0.2 to 0.6 wt%. Both Si and Mg are strong oxide film forming elements.

[0119] In a high-temperature oxidizing atmosphere, Si and Mg exhibit a stronger tendency to oxidize than chromium in the matrix. Si oxidizes to form SiO2, and Mg oxidizes to form MgO. These two oxides can fuse together at high temperatures, forming a dense, continuous, and well-bonded SiO2-MgO composite oxide film on the outermost surface of the cladding layer.

[0120] The SiO2-MgO composite oxide film has an extremely low oxygen ion diffusion coefficient, which can effectively block the diffusion of oxygen inward and metal ions outward. Its protective effect is even better than that of a simple Cr2O3 film in some temperature ranges.

[0121] More importantly, the SiO2-MgO system exhibits a certain degree of fluidity at high temperatures. If microcracks develop in the oxide film due to thermal stress or mechanical action, these cracks can self-heal through viscous flow or diffusion at high temperatures, resealing the cracks and restoring their protective function. This provides dynamic and durable oxidation protection for the B-side during long-term secondary service.

[0122] Cerium (Ce), with a content of 0.05-0.25wt%, is a rare earth element with multiple functions: First, similar to Y in recycled powder, Ce can segregate at grain boundaries, purify grain boundaries, and improve the oxidation resistance of grain boundaries.

[0123] Secondly, and more importantly, Ce can significantly improve the adhesion and structure of oxide films. 4+ or Ce 3+ Ion infiltration into the SiO2-MgO composite oxide film can reduce the growth stress of the oxide film, improve the adhesion between the film and the metal substrate, and prevent the oxide film from peeling off.

[0124] Meanwhile, Ce can refine the grains of the oxide film, making its structure more compact and further reducing the oxidation rate. The addition of Ce enables the SiO2-MgO composite oxide film to achieve the highest level of protection and reliability in engineering applications.

[0125] Iron (Fe) is the base element, with appropriate amounts of Cr and Ni, with Cr content ranging from 18-22 wt% and Ni content from 8-12 wt%; this ensures basic heat resistance and metallurgical bonding with the regenerated layer. Since the main protection relies on a special oxide film, the dependence on Cr is relatively reduced, which also provides room for designs with high Cu content.

[0126] The core challenge of side B is ensuring thermal conductivity and long-term environmental stability on an aged substrate. Due to high-temperature exposure, the thermal conductivity of the side B substrate has decreased. By cladding a layer of material rich in a highly thermally conductive metallic phase onto the surface, a thermal channel is connected in parallel along the heat dissipation path.

[0127] Heat is transferred from the furnace and preferentially spreads rapidly laterally through this highly thermally conductive surface layer, forming a uniform temperature field, before being transferred downwards to the silicon steel coil. This effectively compensates for the loss of thermal conductivity in the substrate, representing a proactive and functional compensation strategy.

[0128] The grain boundaries of the substrate on the B-side may have been weakened due to previous thermal history, making them more susceptible to rapid oxidation and corrosion. By forming a dense oxide film with advanced oxidation tendency and self-healing properties on the surface, this film preferentially forms and adheres firmly, actively resisting oxidation and protecting the underlying substrate, especially the fragile grain boundaries, thus blocking the path of oxidation along the grain boundaries. The addition of Ce ensures the strength and durability of the composite oxide film.

[0129] The B-side repair powder is clad onto the regenerated layer of the substrate, which has also been re-restored. The regenerated layer has purified and strengthened the grain boundaries of the B-side substrate surface, which provides a better starting point for the excellent oxidation resistance of the B-side repair layer; at the same time, the refined microstructure of the regenerated layer is also conducive to the uniform dispersion of the Cu / Ag phase and avoids agglomeration.

[0130] Using the same reinforcing powder for side B as for side A would be completely wrong with current technology. High-hardness carbonitride reinforcement offers no benefit in terms of relative thermal conductivity improvement; it may even slightly reduce thermal conductivity by introducing more phase interfaces. Furthermore, its oxidation resistance primarily relies on Cr, and its protective effect is significantly reduced in grain boundary regions where the matrix is ​​already Cr-depleted.

[0131] The B-side repair powder of this invention is based entirely on the actual physical and chemical needs of the B-side. It uses a high thermal conductivity phase to solve the problem of heat transfer uniformity and a self-healing special oxide film to solve the problem of long-term environmental stability. It is a solution that is completely complementary to the A-side repair powder in terms of function.

[0132] Step S2 completes the core construction of the material system of the present invention, and prefabricates three special cladding powders with different functions and synergistic effects. The synergy of the three powders constitutes a dynamic and three-dimensional material solution for failure risks at different stages of the entire life cycle of the component.

[0133] After the powder system is prepared, the repair process enters the critical physical realization stage.

[0134] In step S3, a layer of substrate regeneration powder is first deposited on the pretreated substrate surface using laser cladding technology to form a substrate regeneration cladding layer;

[0135] A fiber-coupled semiconductor laser or disk laser is used as the energy source, with an output power of 2500-2800W. If the power is too low, the input energy is insufficient, making it impossible to achieve complete metallurgical fusion between the powder and the matrix, which can easily lead to incomplete fusion defects, and the molten pool temperature is insufficient to drive the necessary in-situ reaction; if the power is too high, the molten pool will overheat, which may lead to accelerated element burn-off, violent convection in the molten pool causing compositional inhomogeneity, and excessive heat input making the heat-affected zone too wide, thus negating the grain refinement effect.

[0136] The spot diameter is typically controlled between 3.5 and 4.5 mm. Dry and clean substrate recycled powder is delivered to the laser spot action area at a precise rate using either off-axis or coaxial powder feeding.

[0137] The scanning speed is 7-10 mm / s, and there is an overlap rate of 35% to 45% between adjacent scanning passes to ensure that the entire repair area is completely and uniformly covered and to avoid the formation of unfused grooves.

[0138] When the laser beam irradiates the substrate surface and forms a molten pool, the fed substrate regenerated powder is instantly melted and strongly mixed with the molten thin substrate material, the depth of which is 0.1-0.3 mm.

[0139] Within this high-temperature molten pool, the metallurgical reaction designed in step S2 occurs rapidly:

[0140] When Ti, Zr, and B atoms in the molten pool meet, TiB2 and ZrB2 crystal nuclei are formed in non-equilibrium under extremely high supercooling. Simultaneously, Al atoms combine with trace amounts of N dissolved in the molten pool to form AlN.

[0141] Due to the extremely rapid cooling rate, these compounds do not have enough time to grow and form ultrafine dispersed phases with a size of 50 to 150 nanometers in the rapidly solidifying metal matrix. Moreover, their distribution is not random, but tends to precipitate at the solidification front and at the phase interface of subsequent solid-state phase transitions.

[0142] The rapid solidification of the molten pool itself forms fine dendrites or cellular structures. More importantly, in the semi-molten zone at the edge of the molten pool, i.e., the new HAZ in this repair, the original grains coarsened during previous service are heated to near their melting point. During the subsequent rapid cooling, the recrystallization process in these areas is strongly pinned by the newly formed nano-TiB2, ZrB2, and AlN particles located at the grain boundaries.

[0143] During the later stages of solidification, the surface-active element Y and the remaining B atoms strongly segregate to the newly formed austenite grain boundaries, reacting with low-melting-point harmful impurities such as S and P that may be present at the grain boundaries to form stable, spherical high-melting-point compounds.

[0144] The substrate regenerated cladding layer formed through the above process has a thickness of 0.25-0.35 mm.

[0145] Step S4: Based on the surface properties of the surface to be repaired, select the corresponding A-side repair powder or B-side repair powder, and perform laser cladding on the substrate regenerated cladding layer to construct a directional reinforced main cladding layer with thermal fatigue resistance or high thermal conductivity and oxidation resistance, respectively.

[0146] This step uses the same high-precision laser cladding system as step S3, but the key process parameters are adjusted to adapt to the physical properties of the repair powders on sides A and B, and the corresponding powder feeding chambers are switched.

[0147] The system first reads the surface attribute code input in step S1, the identity determination step, and automatically calls the corresponding process parameter database and powder formula.

[0148] If the current repair surface is surface A, then surface A repair powder will be used; surface A repair powder is spherical alloy powder with a particle size range of 53-150μm.

[0149] The chemical composition is as follows: Nb 2.5-3.0 wt%, Mo 1.8-2.2 wt%, W 1.0-1.5 wt%, V 0.6-0.9 wt%, C 0.12-0.18 wt%, N 0.05-0.08 wt%, with the balance being Fe;

[0150] Under the action of high-energy laser, powder rich in Nb, Mo, W, V, C and N enters the molten pool and mixes with the surface of the micro-melted substrate regenerated layer.

[0151] Under conditions of extremely high supersaturation and rapid cooling in the molten pool, strong carbonitride forming elements Nb and V preferentially combine with C and N, precipitating extremely fine primary MC-type (Nb,V)(C,N) phases at interdendritic and grain boundaries via heterogeneous nucleation. These phases typically range in size from 0.5 to 2.0 micrometers and are distributed in a diffuse, granular manner.

[0152] Mo and W partially dissolve in the austenitic matrix, resulting in significant solid solution strengthening, while the other part forms M6C-type carbides with C, serving as secondary strengthening phases.

[0153] These high-melting-point, high-hardness second phases form a rigid framework network in the cladding layer with a volume fraction of 8% to 12%, making it extremely difficult for dislocations to move at high temperatures and significantly improving creep resistance.

[0154] The fine austenite grains formed by laser rapid solidification are well integrated with the regenerated layer, providing a foundation for excellent toughness. The dispersed hard carbonitride phase plays multiple roles: under alternating thermal stress, they can effectively disperse stress concentration and hinder the initiation of microcracks; when cracks propagate, these hard particles force the crack tip to deflect, bypass, or be bridged, greatly increasing the energy consumption for crack propagation and significantly reducing the crack propagation rate.

[0155] The cladding heat of the functional layer on side A will form a new HAZ below it, but this HAZ is built on the substrate regeneration layer that has been reset.

[0156] The fine grains and clean grain boundaries of the regenerated layer provide a stable starting point for this thermal cycle, avoiding the accumulation of damage on fragile tissues.

[0157] The interface between the two surfaces achieves metallurgical bonding, forming a gradient performance transition zone from high hardness and high fatigue resistance on the surface to high toughness and stable structure on the underlying surface, which together resists the severe impact of the first service of the A-side.

[0158] When the system determines that the current repair is for side B, side B repair powder is used. The side B repair powder is a spherical alloy powder with a particle size range of 45-125 μm and a chemical composition of: Cu 8.0-10.0 wt%, Ag 1.5-2.0 wt%, Si 1.2-1.8 wt%, Mg 0.3-0.5 wt%, Ce 0.1-0.2 wt%, with the balance being Fe.

[0159] During the cladding process, Cu and Ag form an electron-rich metallic phase. When powder with high Cu and Ag content enters the molten pool, due to their limited solid solubility in iron-based austenite, most of Cu and Ag precipitate uniformly and diffusely in the austenite dendrites as nano- to submicron-sized Cu / Ag eutectic phases or pure metal particles during rapid solidification.

[0160] Meanwhile, Si and Mg preferentially form a dense SiO2-MgO composite oxide film in a high-temperature oxidizing environment, and Ce element promotes the self-healing ability of this oxide film; and effectively inhibits the oxidation corrosion rate of the B side during secondary service through the anti-oxidation film.

[0161] The high thermal conductivity of the B-side repair layer solves the problem of temperature difference at the bottom of the silicon steel coil that may be caused by the thermal attenuation of the substrate, thus physically ensuring the uniformity of product quality.

[0162] The directional strengthening main cladding layer on both sides A and B has a single layer thickness of 1.1-1.3 mm to ensure sufficient service life without affecting the overall structural rigidity. The cladding process must be carried out under a tight inert atmosphere, especially for powder containing easily oxidized elements on side B.

[0163] In step S5, after the cladding is completed, the repaired area undergoes post-heat treatment.

[0164] The workpiece is placed in a protective atmosphere furnace and slowly heated to 850°C at a rate of 2°C / min-5°C / min, held at that temperature for 4 hours, and then slowly cooled to 400°C at a rate of 1°C / min-2°C / min, and then air-cooled to room temperature. This heat treatment promotes the full release of residual stress in the cladding layer and promotes the moderate coarsening of the carbonitride phase to optimize toughness, while stabilizing the structure of the anti-oxidation film.

[0165] During the heat preservation stage, the material undergoes creep, and the dislocations at the micro level rearrange and slip, which fully relaxes and homogenizes the macroscopic residual tensile stress generated during the cladding process, preventing it from becoming a crack source during service.

[0166] For the A-side repair layer, this heat treatment induces a moderate coarsening of the dispersed MC / M6C carbonitrides. By adjusting the average size from 0.5-2.0 μm in the deposited state to 1.0-2.5 μm, the phase interface can be reduced without significantly sacrificing strength, optimizing the material's toughness and making it more resistant to impact. Simultaneously, this process stabilizes the composition and distribution of the carbonitrides, ensuring that their performance does not degrade during long-term high-temperature service.

[0167] This heat treatment is crucial for the B-side repair layer.

[0168] On the one hand, it provides kinetic conditions for the diffusion and selective oxidation of elements such as Si, Mg, and Ce, which helps to initially form a thin and dense SiO2-MgO-CeO layer on the surface before it is put into service. x Composite oxide films provide pre-protection.

[0169] On the other hand, heat treatment can stabilize the distribution of Cu / Ag-rich phases in the matrix and eliminate micro-component segregation that may be caused by rapid solidification, ensuring the uniformity and stability of high thermal conductivity.

[0170] Example 1: A laser cladding repair method for a long-life flange furnace chassis, comprising:

[0171] An evaluation was conducted on a flange furnace chassis 1 that had completed its service life. Scanning the laser markings on the sidewalls confirmed that side A (marked A-1) and side B (marked B-1) had both completed one service life cycle. Inspection of both working surfaces revealed microcracks with a depth ≥0.3mm. The system determined that both sides A and B required repair.

[0172] Surfaces A and B were pretreated separately. Surface oxide scale was removed using sandblasting with 1.0mm brown corundum particles as the blasting medium, at a pressure of 0.6MPa and an angle of 75°, until the surface roughness Ra was 4.8μm. The workpiece was then placed in a vacuum furnace and heated to 300℃ at a rate of 5℃ / min under argon protection, held at that temperature for 2 hours, and then allowed to cool naturally to room temperature.

[0173] Substrate recycled powder: Chemical composition (wt%): Ti 2.0, Zr 1.0, Al 0.6, B 0.20, Y 0.10, C 0.065, balance Fe.

[0174] A-side repair powder: Chemical composition (wt%): Nb 2.7, Mo 2.0, W 1.3, V 0.75, C 0.15, N 0.07, Cr 22.5, Ni 12.5, balance Fe.

[0175] B-side repair powder: Chemical composition (wt%): Cu 9.0, Ag 1.75, Si 1.5, Mg 0.4, Ce 0.15, Cr 20.0, Ni 10.0, balance Fe.

[0176] For the pretreated A-side and B-side substrates, the same parameters are used to deposit the substrate regeneration layer.

[0177] The process parameters are as follows: laser output power 2650W, spot diameter 4.0mm, substrate regeneration powder is fed by off-axis powder feeding method, powder feeding rate 15g / min, scanning speed 8.5mm / s, and overlap rate 40%.

[0178] A substrate regeneration cladding layer with a thickness of 0.3 mm was formed in the damaged areas of both sides A and B to be repaired.

[0179] For side A: Laser cladding is performed on the substrate regeneration cladding layer of side A using side A repair powder.

[0180] Process parameters: laser power 2650W, spot diameter 4.0mm, powder feeding rate 12g / min, scanning speed 8.5mm / s, overlap rate 40%.

[0181] The thickness of a single cladding layer is approximately 1.2 mm, and multiple cladding layers are applied until the repair area on side A is completely filled.

[0182] For side B: Laser cladding is performed on the substrate regeneration cladding layer of side B using side B repair powder.

[0183] Process parameters: laser power 2650W, spot diameter 4.0mm, powder feeding rate 12g / min, scanning speed 8.5mm / s, overlap rate 40%.

[0184] The thickness of a single cladding layer is approximately 1.2 mm, and multiple layers of cladding are applied until the repair area on side B is completely filled.

[0185] The workpiece with the A and B sides cladding repair completed is placed in a protective atmosphere furnace for heat treatment.

[0186] The temperature was increased to 850℃ at a rate of 3.5℃ / min and held for 4 hours.

[0187] It was then slowly cooled to 400°C at a rate of 1.5°C / min, and finally air-cooled to room temperature.

[0188] This heat treatment is applied to both the repaired areas on side A and side B.

[0189] Example 2: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here, but the differences are as follows:

[0190] The titanium (Ti) content in the recycled powder of the substrate is 1.5 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2700W, powder feeding rate 14g / min.

[0191] Example 3: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here, but the differences are as follows:

[0192] The titanium (Ti) content in the recycled powder of the substrate is 2.5 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2600W, powder feeding rate 16g / min.

[0193] Example 4: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0194] The boron (B) content in the recycled powder of the substrate is 0.15 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2700W, powder feeding rate 14g / min.

[0195] Example 5: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here, but the differences are as follows:

[0196] The boron (B) content in the recycled powder of the substrate is 0.25 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2600W, powder feeding rate 16g / min.

[0197] Example 6: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0198] The niobium (Nb) content in the A-side repair powder is 2.2 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted to: powder feeding rate 11 g / min.

[0199] Example 7: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0200] The niobium (Nb) content in the A-side repair powder is 3.2 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2700W, powder feeding rate 13g / min.

[0201] Example 8: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0202] The carbon (C) content in the A-side repair powder is 0.12 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted to: powder feeding rate 11 g / min.

[0203] Example 9: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0204] The carbon (C) content in the A-side repair powder is 0.18 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2700W, powder feeding rate 13g / min.

[0205] Example 10: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0206] The copper (Cu) content in the B-side repair powder is 7.5 wt%, and the remaining components and contents are the same as in Example 1. The process parameters remain unchanged, namely, laser output power of 2650 W and powder feeding rate of 12 g / min.

[0207] Example 11: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0208] The copper (Cu) content in the B-side repair powder is 10.5 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2600W, powder feeding rate 11g / min, and the cladding process is carried out under an inert atmosphere with an oxygen content of less than 50ppm.

[0209] Example 12: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0210] The silicon (Si) content in the B-side repair powder is 1.2 wt%, and the remaining components and contents are the same as in Example 1. The process parameters remain unchanged, namely, laser output power of 2650 W and powder feeding rate of 12 g / min.

[0211] Example 13: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here; the differences are as follows:

[0212] The silicon (Si) content in the B-side repair powder is 1.8 wt%, and the remaining components and contents are the same as in Example 1. The corresponding process parameters are adjusted as follows: laser output power 2600W, powder feeding rate 11g / min, and the cladding process is carried out under an inert atmosphere with an oxygen content of less than 50ppm.

[0213] Comparative Example 1: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here, but the differences are as follows:

[0214] No surface property determination is performed (i.e., no distinction is made between surface A and surface B), and throughout the entire repair process, all surfaces to be repaired (including surface A after the first service and surface B after the second service) are laser clad with a single, general-purpose iron-chromium-nickel alloy powder with a composition similar to the base material SUS309S.

[0215] The general-purpose powder has the following chemical composition (wt%): Cr 23.0, Ni 13.0, Mn 1.5, Si 0.8, C 0.06, with the balance being Fe. During repair, the substrate regeneration layer is not pre-deposited; instead, the general-purpose powder is directly fused onto the pre-treated substrate surface to form a functional layer.

[0216] Comparative Example 2: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here, but the differences are as follows:

[0217] In step S3, the deposition of substrate regenerated powder is omitted. On the pretreated substrate surface, the corresponding A-side repair powder or B-side repair powder is directly selected according to the surface properties (A-side or B-side) for laser cladding to construct a functional layer.

[0218] Comparative Example 3: A laser cladding repair method for a long-life flange furnace chassis. The similarities to Example 1 will not be repeated here, but the differences are as follows:

[0219] In step S2, the chemical compositions of the A-side repair powder and the B-side repair powder are interchanged. That is, for the A-side which requires resistance to thermal fatigue, the B-side repair powder (high Cu, Ag, containing Si, Mg, Ce) designed in Example 1 is used for cladding; for the B-side which requires high thermal conductivity and oxidation resistance, the A-side repair powder (high Nb, Mo, W, containing V, C, N) designed in Example 1 is used for cladding.

[0220] Adjusting equipment parameters such as laser power and powder feeding rate when repairing cladding powders with different formulations is a key measure to address the differences in the physicochemical properties of the materials themselves in order to achieve optimal metallurgical bonding and performance.

[0221] This experiment mainly studies the influence of material ratio on the process window.

[0222] Experimental Example 1: Example 1 and Comparative Examples 1-3 were selected to make a horizontal comparison between the complete strategy of the present invention and three typical defective strategies. The performance degradation after multiple repair-service cycles was simulated to verify the fundamental advantages of the strategy of the present invention.

[0223] Performance indicators: yield strength (overall load-bearing capacity), crack density (degree of damage accumulation), thermal conductivity (B-side function retention).

[0224] By simulating long-term use under actual working conditions, the retention rate and damage status of the core performance of the repaired area were compared after three complete "service → evaluation → repair" cycles under different overall repair strategies, in order to prove the long-term effectiveness of the complete strategy of the present invention.

[0225] Table 1

[0226]

[0227] The data from Experiment 1 clearly demonstrate the long-term performance differences between different repair strategies. The repaired area of ​​the complete strategy of this invention exhibited the highest high-temperature yield strength, the lowest crack density, and the best thermal conductivity after three cycles, demonstrating superior overall performance. The performance of the three defect strategies showed a stepwise decline, with the traditional homogeneous repair strategy performing the worst in all indicators, followed by the strategy without a regeneration layer, while the functional mismatch strategy failed to function properly due to incorrect directional selection.

[0228] From a fundamental perspective, the reason for this performance ranking lies in the different logics by which each strategy addresses the nature of component damage. The strategy of this invention first resets the microstructure of the deteriorated heat-affected zone through a substrate regeneration layer, interrupting the intergenerational transmission of damage and providing a robust foundation for subsequent functional layers. Then, it applies specific functional compensation to address the different failure mechanisms on both sides, achieving a precise dynamic match between repair and requirements. Traditional homogeneous repair ignores the differences between history and requirements, and its repair behavior itself exacerbates tissue deterioration. While the strategy without a regeneration layer is correct in direction, the functional layer is directly built on the fragile historical damage area, making the interface a weak point. The functional mismatch strategy completely deviates from physical requirements, using high thermal conductivity materials to combat mechanical fatigue and high-strength materials to compensate for thermal conductivity attenuation, making its failure inevitable.

[0229] Experimental Example 2: Examples 1-13 were selected to longitudinally verify the changes in the core performance of the repair layer after fine-tuning the key components of the three special powders within the scope of the claims, within the framework of the present invention.

[0230] Table 2

[0231]

[0232] The data from Experiment 2 validated the effective window for parameter optimization within the system of this invention. All embodiments with adjustments to key components maintained excellent core performance indicators and exhibited reasonable normal distribution fluctuations around the central optimal value. For example, the hardness of surface A changed regularly with the increase or decrease of the reinforcing element content, and the thermal diffusivity of surface B also increased or decreased accordingly with the adjustment of the thermally conductive element content. The interfacial bonding strength of all schemes remained high, indicating reliable bonding of the repair layer.

[0233] The material system design of this invention possesses inherent tolerance and synergy. Each key element is assigned a specific metallurgical functional role; for example, titanium and boron are used to form nanophases to pin grain boundaries, niobium and carbon are used to constitute high-temperature strengthening phases, and copper and silver are designed to construct efficient thermal channels. Therefore, performance fluctuates within a high-performance range without systematic failure. This demonstrates that the claimed scope is not arbitrarily defined but is based on a scientific composition-structure-property relationship, ensuring the repeatability and engineering applicability of the method.

[0234] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A laser cladding repair method for a long-life flange furnace chassis, characterized in that, include: S1. Conduct condition assessment and surface pretreatment on the working surface of the flange furnace chassis that has completed its service cycle to determine whether the surface attribute is the first service surface or the second service surface, i.e., surface A or surface B. S2. Pre-fabricate three types of cladding powders, including: substrate regeneration powder, A-side repair powder, and B-side repair powder; wherein, the substrate regeneration powder is used to reset the microstructure of the heat-affected zone; the A-side repair powder is used to enhance the thermal fatigue resistance of the A-side; and the B-side repair powder is used to enhance the thermal conductivity and oxidation resistance of the B-side. S3. On the pretreated substrate surface, a layer of the substrate regeneration powder is first deposited using laser cladding technology to form a substrate regeneration cladding layer; S4. Based on the surface properties of the surface to be repaired, select the corresponding A-side repair powder or B-side repair powder, and perform laser cladding on the substrate regenerated cladding layer to construct a directional reinforced main cladding layer with thermal fatigue resistance or high thermal conductivity and oxidation resistance, respectively. S5. Perform post-heat treatment on the cladding area and put the repaired chassis back into service. The flange furnace chassis is a double-sided symmetrical disc structure made of heat-resistant austenitic stainless steel matrix, with its upper and lower surfaces being surface A and surface B, respectively. During service, surface A bears the load before surface B. The recycled substrate powder is Fe-based, and its chemical composition by weight percentage includes: Ti 1.5-2.5%, Zr 0.8-1.2%, Al 0.4-0.8%, B 0.10-0.30%, Y 0.05-0.15%, C 0.03-0.10%, with the balance being Fe and unavoidable impurities; the thickness of the recycled substrate cladding layer is 0.25-0.35 mm. The A-side repair powder is Fe-Cr-Ni based, and its chemical composition by weight percentage includes: Nb 2.2-3.2%, Mo 1.5-2.5%, W 0.8-1.8%, V 0.5-1.0%, C 0.10-0.20%, N 0.04-0.10%, Cr 20-25%, Ni 10-15%, with the balance being Fe; the A-side repair powder is used to construct a directionally strengthened main cladding layer with thermal fatigue resistance. The B-side repair powder is Fe-based, and its chemical composition by weight percentage includes: Cu 7.0-11.0%, Ag 1.0-2.5%, Si 1.0-2.0%, Mg 0.2-0.6%, Ce 0.05-0.25%, Cr 18-22%, Ni 8-12%, with the balance being Fe. The B-side repair powder is used to construct a directionally reinforced main cladding layer with high thermal conductivity and oxidation resistance.

2. The laser cladding repair method for a long-life flange furnace chassis according to claim 1, characterized in that: The status assessment in step S1 includes defect screening and attribute determination. Defect screening adopts a combined detection method of eddy current detection and optical profilometer. When microcracks with a depth ≥0.3mm or local plastic deformation ≥0.5mm are detected on the working surface, the repair process is triggered. If ultrasonic testing detects internal cracks with a depth greater than 4-8mm, the chassis is deemed ineligible for repair.

3. The laser cladding repair method for a long-life flange furnace chassis according to claim 2, characterized in that: The attribute determination in step S1 is achieved by identifying the preset laser marking marks on the non-load-bearing area of ​​the flange furnace chassis. The marks include the chassis number, service surface type and service status. The marking information can be linked to the central database to achieve full life cycle traceability.

4. The laser cladding repair method for a long-life flange furnace chassis according to claim 1, characterized in that: When laser cladding is used to deposit regenerated powder on the substrate, a laser with an output power of 2500-2800W is used, the spot diameter is 3.5-4.5mm, the scanning speed is 7-10mm / s, and the overlap rate between adjacent scanning passes is 35%-45%.

5. The laser cladding repair method for a long-life flange furnace chassis according to claim 1, characterized in that: The directional reinforced main cladding layer is a single-layer structure with a thickness of 1.1-1.3 mm. When repairing side A, side A repair powder with a particle size range of 53-150 μm is used; when repairing side B, side B repair powder with a particle size range of 45-125 μm is used.

6. The laser cladding repair method for a long-life flange furnace chassis according to claim 1, characterized in that: The post-heat treatment is carried out in a protective atmosphere furnace, where the temperature is raised to 850°C at a heating rate of 2-5°C / min, held for 4 hours, cooled to 400°C at a cooling rate of 1-2°C / min, and finally air-cooled to room temperature.

7. The laser cladding repair method for a long-life flange furnace chassis according to claim 1, characterized in that: The surface pretreatment includes sandblasting and vacuum heating. The sandblasting uses brown corundum particles with a particle size of 0.8-1.2 mm, a spraying pressure of 0.6 MPa, a spraying angle of 75°, and a surface roughness Ra of 3.2-6.3 μm. The vacuum heating is carried out under an argon protective atmosphere, with a heating rate of 5 °C / min to 300 °C, and after holding at that temperature for 2 hours, it is naturally cooled to room temperature.

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