Manufacturing process of large cobalt-based alloy sealing shaft sleeve for nuclear power station

Abstract

The invention relates to the technical field of alloy casting, and discloses a manufacturing process of a large cobalt-based alloy sealing shaft sleeve for a nuclear power station. Comprising the steps of material selection, smelting, casting, component reinspection, softening annealing treatment, rough machining, nondestructive testing, defect cleaning and repair welding, solid solution and aging treatment, mechanical property inspection after performance heat treatment, semi-machining defect cleaning and repair welding, stress relief annealing treatment, finish machining, final mechanical property inspection and the like. Compared with the prior art, the sealing shaft sleeve has the advantages of being good in corrosion resistance, high in abrasion resistance and good in machining size precision, effectively solving the problems that the sealing shaft sleeve of the circulating water pump for the nuclear power station is prone to abrasion and needs to be overhauled and replaced in a short period, and improving stability and safety in the operation process of the seawater circulating water pump of the nuclear power station.

Description

Technical Field

[0001] This invention relates to the field of alloy casting technology, and more specifically, to a manufacturing process for a large cobalt-based alloy sealing bushing for nuclear power plants. Background Art

[0002] The pump shaft of a seawater circulating pump is a major component of the pump rotor. It houses components such as the impeller, sealing sleeve, and balance disc, and rotates at high speed within the pump during operation. The sealing sleeve serves to isolate the pump shaft from seawater, protecting it from corrosion and wear. It can be replaced when necessary. Therefore, the sealing sleeve must be wear-resistant, corrosion-resistant, and able to withstand radial and axial loads.

[0003] Currently, the sealing shafts of seawater circulating water pumps in domestic nuclear power plants are generally made of austenitic stainless steel or duplex stainless steel. Both materials have excellent resistance to seawater corrosion; however, because their basic microstructure is mostly austenitic, or approximately 50% austenitic and 50% ferrite, their tensile strength and hardness are relatively low, resulting in poor wear resistance. During use, they are prone to wear, leading to a short service life and requiring periodic replacement. Seawater circulating water pumps are one of the key pieces of equipment in nuclear power plants; their long-term stable operation is crucial to the safe power generation and economic benefits of the nuclear power plant.

[0004] Cobalt-based alloys possess both excellent wear resistance and corrosion resistance, making them an ideal material for manufacturing sealing bushings. However, due to limitations in processing capabilities, powder metallurgy is currently commonly used to manufacture small and medium-sized products. For the production of large-sized products, these corrosion-resistant alloys are difficult to process, posing significant challenges in actual production. Summary of the Invention

[0005] This invention provides a manufacturing process for a large cobalt-based alloy sealing bushing used in nuclear power plants. It selects a cobalt-based alloy that is both resistant to seawater corrosion and possesses high tensile strength and hardness, i.e., strong wear resistance. This process solves the problem of short service life of existing sealing bushings on the pump shafts of seawater circulating water pumps in nuclear power plants, requiring frequent maintenance and replacement. This improves the efficiency and safety of the circulating water pumps during operation.

[0006] A manufacturing process for a large cobalt-based alloy sealing bushing for nuclear power plants includes the following steps: Step 1: The sealing bushing is made of cobalt-based alloy with the following composition: C 1.1-1.4%, Cr 29.0-31.0%, Ni 1.5-3.0%, Mo 0.2-1.0%, W 4.0-5.0%, and Co balance. Step 2: The alloy ingot is melted using a vacuum induction melting process, and the surface of the alloy ingot is polished to remove surface impurities and oxide scale; Step 3: Dehydrogenation treatment of the alloy ingot, heating to 800℃ and holding for 2 hours; Step 4: Use an intermediate frequency furnace to heat and remelt the alloy ingots. Use fluorite and calcium fluoride to make slag during smelting and add appropriate alloying elements. Use pure titanium to deoxidize the alloy liquid when tapping it out of the furnace. Step 5: Use an argon-blown bottom-pouring ladle to pour the remelted alloy liquid into the casting cavity; Step 6: Perform softening annealing heat treatment on the casting, holding at 850℃ for 5 hours to reduce the hardness of the casting; Step 7: Mount the riser side onto a vertical lathe and use an alloy cutting tool to rough machine the bottom plane, outer surface, and inner surface of the casting part, with a single-sided allowance of 4mm; Step 8: Perform solution treatment and aging treatment on the casting. For solution treatment, the heating rate is ≤100℃ / hour, the casting is heated to 1150-1160℃, held for 5 hours, and then cooled with air. For aging treatment, the heating rate is ≤100℃ / hour, the casting is heated to 950-960℃, held for 5 hours, and then cooled with air. Step 9: Perform semi-finishing on the casting, with a single-sided allowance of 0.2mm; Step 10: Perform finishing on the casting; remove the riser by wire cutting, and then finish machine the riser side face; drill holes using a CNC vertical machining center, and then tap the holes using electrical discharge machining; perform final dimensional inspection and PT testing on the finished product.

[0007] Preferably: In step 7, after rough machining, the product is subjected to PT testing according to RCCM MC4000 standard and RT testing according to RCCM MC3200 standard. The defective parts detected are repaired by welding. Before welding, the product is heated to 650℃ and held for 4 hours. After taking it out of the furnace, it is covered with insulation cotton for insulation. Argon arc welding is used for welding. After welding, the product is placed in a heat treatment kiln preheated to 650℃ and cooled slowly with the furnace. After grinding the welded part with a grinding wheel, PT testing is performed according to RCCM MC4000 to confirm whether the welded part is qualified.

[0008] Preferably, in step 9, the defects after semi-finishing are repaired by welding using argon arc welding. After welding, the repaired area is covered with insulation cotton to allow it to cool slowly. The repaired area is then ground smooth with a grinding wheel and subjected to PT testing to confirm whether the repaired area is qualified.

[0009] Preferably, LAMINA TECH CH alloy chuck inserts are used for roughing, semi-finishing, and finishing.

[0010] Preferably: For defect repair after rough machining, Stellite 6 welding wire with a diameter of 4.8 mm and grade HS111 is used, with a welding current of 150-170A and a welding voltage of 20-23V; for defect repair after semi-finishing, Stellite 6 welding wire with a diameter of 4.0 mm and grade HS111 is used, with a welding current of 130-150A and a welding voltage of 18-20V.

[0011] Preferably, the mechanical properties of the sealing bushing are: tensile strength ≥ 800 MPa, hardness HRC ≥ 37.

[0012] Preferably, the outer diameter of the sealing bushing is 570mm, the height is 610mm, the inner diameter is 500mm, and the tolerance range is 0-0.02mm.

[0013] Preferably, the acceptance level for both PT testing and RT testing is RCCM standard level 1.

[0014] Preferably, defects after rough machining and defects after semi-finishing are removed using a pneumatic milling cutter.

[0015] Preferably, the method further includes surface treatment of the sealing bushing, and the treatment method further includes: The shock wave-induced surface modification and strengthening step involves sequentially subjecting the pretreated sealing bushing to underwater electric explosion shock wave treatment, pneumatic high-speed particle shot peening strengthening, and mechanical friction nanocrystallization treatment to form a nanocrystalline layer on the bushing surface. The plasma surface modification step involves sequentially subjecting the surface-modified and strengthened sealing bushing to low-temperature plasma nitriding and pulsed laser surface melting treatment to form a composite reinforced surface layer. The deep strengthening steps of the shock wave composite cycle treatment include multi-directional shock wave focusing treatment, pulse heat treatment stabilization and periodic deep activation treatment of the surface-modified sealing bushing to form a gradient strengthening structure from the surface to the interior. The multi-directional shock wave focusing process employs a reflective wall device and multi-point triggering electrodes to ensure that the shock wave energy is evenly distributed on the bushing surface and that the shock wave pressure deviation is controlled within ±10%.

[0016] The beneficial effects of the present invention are: This invention uses cobalt-based alloy material to make the sealing bushing, because this is a material that is both resistant to seawater corrosion and has high tensile strength and hardness, i.e., wear resistance. Therefore, the sealing bushing has excellent comprehensive performance.

[0017] In the casting process design of the sealing bushing, the gating system is designed as an upper rain shower structure. The molten alloy enters the casting cavity from top to bottom through the upper part. Combined with the circumferential riser with a slope of 1:10 on the upper part of the casting and the chills on the lower and bottom parts of the outer side, a temperature gradient from top to bottom is established, which is conducive to the feeding of the casting. The casting structure is dense and the internal quality meets the RCCM MC3240 radiographic acceptance standard level 1, which greatly improves the service life of the product.

[0018] In the casting process design, the sealing bushing has a circumferential riser with a 1:10 slope at the top of the casting. In addition to having a good feeding effect, it also has a strong slag collection ability, which effectively reduces the possibility of defects such as sand holes and slag holes on the surface and inside of the product.

[0019] In the casting process design, the upper part of the sealing bushing has a circumferential riser with a slope of 1:10, which can also be used as a chuck during machining to ensure that the inner hole and outer circle can be machined at the same time in one clamping, thus ensuring the concentricity of the inner hole and outer circle.

[0020] Before rough machining, the sealing bushing product undergoes a softening annealing heat treatment at a temperature of 850℃ for 5 hours to reduce the hardness of the casting, significantly improving the efficiency of rough machining and reducing the rough machining time.

[0021] During machining of the sealing bushing, LAMINA TECH CH alloy cutting inserts are used in the turning process. Different cutting speeds, feed rates, and depths of cut are used in roughing, semi-finishing, and finishing processes, which improves machining efficiency and ensures precision.

[0022] When machining the threaded holes of the sealing bushing, a vertical machining center, alloy drill bit, and electrical discharge tapping process were used to address the difficulties in machining cobalt-gold alloy threaded holes, ensuring machining accuracy and success rate.

[0023] After rough machining, the sealing bushing is subjected to PT testing according to RCCM MC4000 standard and RT testing according to RCCM MC3200 standard. The acceptance level is Level 1, which can effectively detect its surface and internal defects. Before solution heat treatment and aging heat treatment, it is welded to prevent uneven microstructure and performance degradation caused by welding after heat treatment.

[0024] After semi-finishing, the sealing bushing is PT tested and welded according to the RCCM MC4000 standard. This can minimize the possibility of dimensional deformation caused by welding after finishing, and ensure the dimensional accuracy of the finished product.

[0025] After semi-finishing, the sealing bushing undergoes stress-relief annealing, which effectively removes the internal processing stress of the product and ensures the dimensional stability after finishing.

[0026] During the production of the sealing bushing, a reasonable and rigorous quality assurance process was arranged, including chemical composition re-inspection, first mechanical property test after solution treatment and aging heat treatment, final mechanical property test, and dimensional inspection. This process helps to control product quality. Attached Figure Description

[0027] Figure 1 It is a comparison chart of hardness distribution at different locations; Figure 2 These are hardness-depth distribution curves for different treatment methods; Figure 3 It is a comparison of the reinforcement layer depth of different processing methods; Figure 4 This is the hardness change curve of the different treatment methods after being kept at 400℃ for 100 hours; Figure 5 It represents the hardness change under different treatment methods during cyclic thermal shock testing. Detailed Implementation

[0028] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0029] Example 1 This embodiment proposes a manufacturing process for a large cobalt-based alloy sealing bushing for nuclear power plants, comprising the following steps: Step 1: The sealing bushing is made of cobalt-based alloy with the following composition: C 1.2%, Cr 30%, Ni 2.2%, Mo 0.6%, W 4.5%, Co balance. Step 2: The alloy ingot is melted using a vacuum induction melting process, and the surface of the alloy ingot is polished to remove surface impurities and oxide scale; Step 3: Dehydrogenation treatment of the alloy ingot, heating to 800℃ and holding for 2 hours; Step 4: Use an intermediate frequency furnace to heat and remelt the alloy ingots. Use fluorite and calcium fluoride to make slag during smelting and add appropriate alloying elements. Use pure titanium to deoxidize the alloy liquid when tapping it out of the furnace. Step 5: Use an argon-blown bottom-pouring ladle to pour the remelted alloy liquid into the casting cavity; Step 6: Perform softening annealing heat treatment on the casting, holding at 850℃ for 5 hours to reduce the hardness of the casting; Step 7: Mount the riser side onto a vertical lathe and use an alloy cutting tool to rough machine the bottom plane, outer surface, and inner surface of the casting part, with a single-sided allowance of 4mm; Step 8: Perform solution treatment and aging treatment on the casting. For solution treatment, heat at a rate of 100℃ / hour to 1155℃, hold for 5 hours, and then cool with air. For aging treatment, heat at a rate of 100℃ / hour to 955℃, hold for 5 hours, and then cool with air. Step 9: Perform semi-finishing on the casting, with a single-sided allowance of 0.2mm; Step 10: Perform finishing on the casting; remove the riser by wire cutting, and then finish machine the riser side face; drill holes using a CNC vertical machining center, and then tap the holes using electrical discharge machining; perform final dimensional inspection and PT testing on the finished product.

[0030] in: In step 7, after rough machining, the product is subjected to PT testing according to RCCM MC4000 standard and RT testing according to RCCM MC3200 standard. Defective parts detected are repaired by welding. Before welding, the product is heated to 650℃ and held for 4 hours. After taking it out of the furnace, it is covered with insulation cotton for insulation. Argon arc welding is used for welding. After welding, the product is placed in a heat treatment kiln preheated to 650℃ and cooled slowly with the furnace. After grinding the welded part with a grinding wheel, PT testing is performed according to RCCM MC4000 to confirm whether the welded part is qualified.

[0031] In step 9, the defects after semi-finishing are repaired by welding using argon arc welding. After welding, the repaired area is covered with insulation cotton to allow it to cool slowly. The repaired area is then ground smooth with a grinding wheel and subjected to PT testing to confirm whether the repaired area is qualified.

[0032] LAMINA TECH CH alloy chuck inserts are used for roughing, semi-finishing, and finishing.

[0033] For rough machining, defect repair uses Stellite 6 welding wire, 4.8 mm in diameter, grade HS111, with a welding current of 150-170A and a welding voltage of 21V. For semi-finish machining, defect repair uses Stellite 6 welding wire, 4.0 mm in diameter, grade HS111, with a welding current of 140A and a welding voltage of 19V.

[0034] The mechanical performance requirements for the sealing bushing are: tensile strength ≥ 800 MPa, hardness HRC ≥ 37.

[0035] The outer diameter of the sealing bushing is 570mm, the height is 610mm, the inner diameter is 500mm, and the tolerance range is 0-0.01mm.

[0036] Both PT and RT testing are accepted at RCCM Standard Level 1.

[0037] Defects after rough machining and defects after semi-finishing are removed using pneumatic milling cutters.

[0038] Example 2 The difference between this embodiment and Embodiment 1 is that: The composition range of this sealing bushing is C 1.1%, Cr 29.0%, Ni 1.5%, Mo 0.2%, W 4.0%, with Co as the balance; In step 8: the casting is subjected to solution treatment and aging treatment. The solution treatment involves heating at a rate of 90℃ / hour to 1150℃, holding at that temperature for 5 hours, and then cooling with air. The aging treatment involves heating at a rate of 90℃ / hour to 950℃, holding at that temperature for 5 hours, and then cooling with air. For rough machining, defect repair uses Stellite 6 welding wire, 4.8 mm in diameter, grade HS111, with a welding current of 150-170A and a welding voltage of 20V. For semi-finish machining, defect repair uses Stellite 6 welding wire, 4.0 mm in diameter, grade HS111, with a welding current of 130A and a welding voltage of 18V.

[0039] The tolerance of the sealing bushing is 0.01-0.02mm.

[0040] Example 3 The difference between this embodiment and Embodiment 1 is that: The composition range of this sealing bushing is C 1.4%, Cr 31.0%, Ni 3.0%, Mo 1.0%, W 5.0%, with Co as the balance; In step 8: the casting is subjected to solution treatment and aging treatment, heated to 1160℃, held for 5 hours, and then cooled with air; heated to 960℃, held for 5 hours, and then cooled with air. For rough machining, defect repair uses Stellite 6 welding wire, 4.8 mm in diameter, grade HS111, with a welding current of 150-170A and a welding voltage of 23V. For semi-finish machining, defect repair uses Stellite 6 welding wire, 4.0 mm in diameter, grade HS111, with a welding current of 150A and a welding voltage of 120V.

[0041] Example 4 Based on Example 1, this embodiment proposes a surface treatment method for cobalt-based alloy sealing bushings, including the following steps: 1. Surface pretreatment steps for cobalt-based alloy sealing bushings The cobalt-based alloy sealing bushing (outer diameter φ570±0.5mm, height 610±1mm, inner diameter φ500±0.5mm) is surface-cleaned. The cleaning process includes the following steps: Ultrasonic cleaning: An ultrasonic cleaner with a power of 300-500W and a frequency of 40kHz is used. An alkaline cleaning agent (pH 8.5-9.5) aqueous solution is used, the cleaning temperature is 40-60℃, and the cleaning time is 15-20 minutes. Ultrasonic cleaning can effectively remove contaminants from tiny crevices; the cavitation effect generated by sound waves in the liquid can peel off particulate contaminants attached to the surface. Organic solvent degreasing treatment: Use acetone or ethanol (analytical grade, purity ≥99.5%) as the organic solvent, soak for 10-15 minutes at room temperature, then wipe with a clean cloth. Organic solvents can dissolve and remove oily contaminants from the surface; Rinse with deionized water: Rinse 2-3 times with deionized water with a resistivity ≥16MΩ·cm, each time for 1-2 minutes, to remove residual cleaning agent and solvent; Hot air drying: Use hot air at 100-120℃ for 5-10 minutes to completely remove surface moisture.

[0042] After cleaning, use a stylus-type surface roughness meter (measuring length 5mm, cutoff wavelength 0.8mm) to measure the surface roughness of the sealing bushing, ensuring that the roughness Ra value is not greater than 1.6μm. This roughness value is suitable for the requirements of subsequent surface treatment processes. If the roughness is too high (>1.6μm), it will affect the uniformity of surface treatment, and if it is too low (<0.4μm), it will be detrimental to surface activation and material deformation.

[0043] 2. Shock wave induced surface modification and strengthening steps 2.1 Treatment of underwater electrical explosion shock waves The pretreated cobalt-based alloy sealing bushing is fixed in the treatment device and immersed in water medium. The water medium can effectively transmit the shock wave energy and protect the surface of the bushing. A copper wire electrode system is arranged in an aqueous medium. The wire diameter is 0.2-0.5 mm. The copper wire has good conductivity and appropriate energy release characteristics. A pulse voltage of 10-30kV is applied to the conductor by a high-voltage power supply, causing the conductor to vaporize and explode instantaneously, generating a high-energy-density shock wave. The voltage range is selected according to the bushing size and material properties. The shock wave acts on the bushing surface with a pressure of 15-25MPa for a duration of 10-50μs. This pressure range can cause plastic deformation of the surface material without causing macroscopic damage. A high-density dislocation region is formed on the surface of the sealing bushing. The dislocation region provides an active surface for subsequent processing, thereby improving the material strength.

[0044] 2.2 Pneumatic high-speed particle shot peening reinforcement The sealing bushing treated with underwater electric explosion shock wave is fixed in the shot peening device. The high-density dislocation region formed by the shock wave treatment provides a good foundation for shot peening. Ceramic microspheres were selected as the shot peening material, with a particle size range of 40-120μm. The ceramic microspheres have high hardness, good wear resistance, and will not contaminate the treated surface. A pneumatic shot peening system is used, with a spray pressure of 0.4-0.6MPa and a spray distance of 80-120mm. This combination of parameters can generate sufficient impact energy without damaging the substrate. Control the shot peening coverage to reach over 200% to ensure full surface coverage and the formation of a uniform plastic deformation layer; A micro-pit structure is formed on the surface of the bushing, with a density of 30-50 pits / mm². The micro-pit structure increases the surface area and forms a lubricating oil storage space, which is beneficial to improving friction performance.

[0045] 2.3 Mechanical Triboelectric Nanocrystallization Treatment The shot-peened sealing bushing is fixed on a lathe. The micro-dimpled structure formed by the shot peening treatment is beneficial to the mechanical friction effect. The tool head is made of cemented carbide with a hardness of not less than HRC 65. The high hardness of the tool head can effectively generate sufficient deformation energy. The tool head performs high-frequency (1000-2000Hz) and low-amplitude (0.05-0.1mm) frictional motion on the surface. The high-frequency and low-amplitude motion can generate a large amount of plastic deformation on the surface without changing the shape of the workpiece. The friction pressure is controlled at 500-800 MPa and the friction speed is 0.1-0.3 m / s. Under these conditions, the shear strain rate is suitable for nanocrystal formation. A nanocrystalline layer with a grain size of 50-100 nm and a thickness of 20-50 μm is formed on the surface. The nanocrystalline structure significantly improves the surface hardness while maintaining a certain degree of toughness.

[0046] 3. Plasma surface modification steps 3.1 Low-temperature plasma nitriding treatment The sealed bushing, which has undergone mechanical friction nanocrystallization treatment, is placed in the plasma treatment chamber. The high-density grain boundaries of the nanocrystal layer are conducive to the diffusion of nitrogen atoms. The chamber is evacuated to below 5×10⁻³Pa, and a mixture of nitrogen and hydrogen is injected with a gas ratio of N2:H2=3:1. The presence of hydrogen can clean the surface and promote the activation of nitrogen ions. The pressure inside the control chamber is 100-150 Pa, which is conducive to the formation of a stable glow discharge. Apply a pulsed DC voltage of 500-700V and a current density of 5-15mA / cm². The pulsed mode can reduce arc generation and improve processing uniformity. The workpiece temperature is controlled at 450-500℃ and the processing time is 4-8 hours. This temperature range is lower than the traditional nitriding temperature, which can keep the nanocrystalline structure from being destroyed. A nitrogen-rich hardened layer is formed, with a thickness of 20-50 μm. Nitrogen atoms combine with alloying elements to form a hard phase, which improves surface hardness and wear resistance.

[0047] 3.2 Pulsed Laser Surface Melting Treatment The sealing bushing, which has undergone low-temperature plasma nitriding, is fixed on the laser processing platform to ensure that the bushing is positioned accurately and stably. A pulsed Nd:YAG laser with a wavelength of 1064nm and a pulse width of 10-20ns is used. These parameters are suitable for micro-melting of metal surfaces to avoid excessive heat input. The laser power density is controlled at 5-10MW / cm², and the pulse repetition frequency is 20-50Hz, ensuring sufficient energy to achieve rapid melting of the surface layer without affecting the deep tissue. The laser beam scans the surface of the bushing at a speed of 5-10 mm / s and the scan line overlap rate is 30-50% to ensure uniform processing and form a continuous surface layer. A dense, fine-grained structure layer of 5-15 μm thickness is formed, which combines with the underlying nitrided layer to form a composite reinforced structure, thereby improving the overall surface performance.

[0048] 4. Shockwave Composite Cyclic Treatment Deep Strengthening Steps 4.1 Multidirectional Shock Wave Focusing The key innovation of this invention is the multi-directional shock wave focusing technology, and its specific implementation steps are as follows: Prepare the reflective wall device: Material: High-strength steel (Q345R or higher strength steel), surface hardness HB 200-240; Structure: Contains 8-12 arc-shaped reflective surfaces with a radius of curvature of 350-450mm; Dimensions: The thickness of the reflector wall is 15-20mm, the height is 650-700mm, and the diameter is determined according to the outer diameter of the bushing, generally 100-150mm larger than the outer diameter of the bushing.

[0049] The inner surface of the reflective wall is precision machined to a surface roughness Ra≤0.8μm to ensure the reflective effect.

[0050] Water treatment device configuration: Pool dimensions: Diameter not less than 1200mm, height not less than 1000mm; Water quality requirements: Deionized water, conductivity ≤5μS / cm; Water temperature control: 20±5℃; The reflector wall device is arranged around the sealing bushing to form a specific acoustic path between the reflector wall and the bushing surface, with a distance of 50-80mm between the reflector wall and the bushing surface.

[0051] Multi-point trigger electrode arrangement: Electrode material: copper or aluminum wire with a diameter of 0.3-0.5 mm; Number of electrodes: 8-12, evenly distributed along the circumference of the bushing, with an included angle of 30°-45° between the electrodes; Electrode position: 30-50mm away from the bushing surface; Electrode fixing method: The electrode is fixed on a special bracket using insulating material (such as epoxy resin) to ensure positional accuracy during triggering.

[0052] Multi-point triggered electrode time sequence control: Control system: Employs a microprocessor-controlled high-voltage pulse generator with timing accuracy ≤10μs; Trigger sequence: Each electrode is triggered sequentially according to a preset program, or the trigger sequence can be customized based on the geometry of the bushing; Trigger interval: 100-300μs, optimized according to bushing size and geometry; Trigger voltage: 25-35kV; Discharge energy: 10-15 kJ / cycle; Control parameter recording: Parameters such as trigger timing, voltage, and energy during each process are automatically recorded and archived to ensure process repeatability.

[0053] Shock wave pressure measurement and control: Measuring device: underwater pressure sensor, response frequency ≥1MHz, measurement range 0-100MPa; Measurement locations: Install sensors at no fewer than 6 locations around the surface of the bushing; Shock wave pressure range: 20-30 MPa; Shock wave duration: 15-40 μs; Pressure deviation control: By optimizing the shape of the reflector wall and the triggering sequence, the shock wave pressure deviation is controlled within ±10%. Processing cycles: 3-5 times, with 2-3 minutes between each cycle to allow air bubbles in the water medium to completely dissipate; Through the above settings and controls, the problem of uneven surface treatment of the bushing caused by traditional single-point triggered electric explosion shock wave treatment is solved. The uniformity of the treatment result can be verified by testing the surface hardness distribution after treatment; the standard deviation of the hardness measurement points should be less than 2 HRC.

[0054] 4.2 Pulse heat treatment stabilization treatment The sealed bushing that has undergone multi-directional shock wave focusing treatment is placed in a pulse heat treatment furnace; Inductive heating is used for heating, with a heating rate of 10-20℃ / s. This rate can effectively activate surface dislocations without causing excessive grain growth. The temperature is raised to 350-400℃ and held for 10-30 minutes. This temperature range can promote dislocation rearrangement without causing the disappearance of the nanocrystalline structure. Compressed air cooling is used, with a cooling rate of 5-10℃ / s, cooling to below 100℃. Rapid cooling can fix the formed microstructure. Repeat the heating-holding-cooling cycle 3-5 times to gradually stabilize the microstructure through multiple thermal cycles. A stable dislocation network structure is formed, and the nanocrystal boundaries are locked through dislocation interaction, thereby improving the thermal stability of the nanocrystals and making them less prone to coarsening under high temperature environments.

[0055] 4.3 Periodic Deep Activation Process The sealed bushing, which has been stabilized by pulse heat treatment, is subjected to underwater electric explosion shock wave treatment with higher energy. At this time, the surface has a stable nanocrystalline structure and can withstand the action of higher energy shock waves. The voltage is 30-50kV and the shock wave pressure is 30-50MPa. These energy parameters are higher than those of the first shock wave treatment, which allows energy to be transferred to deeper layers. The angle of the shock wave changes periodically, with a range of ±30° and a cycle of 3-5 times. This angle change allows the shock wave to act more comprehensively and create a cross-reinforcement effect. A second reinforcement region is formed 0.5-1.0 mm below the surface layer. This region is formed by the interaction between the shock wave energy and the material after penetrating to a certain depth. The penetration depth is related to the shock wave energy and the material properties. The second reinforced area has a hardness of 80-90% of the surface hardness, forming a gradient transition structure between the first reinforced layer and the substrate material. This reduces stress concentration, improves the bonding performance between the reinforced layer and the substrate, and prevents peeling during use.

[0056] 5. Surface treatment quality inspection steps Surface treatment quality inspection shall be carried out in accordance with the following test methods and standards: Surface hardness test Testing instrument: Standard Rockwell hardness tester (C range), conforming to GB / T 230.1 standard; Test load: 150kg; Test point locations: evenly distributed on the inner and outer surfaces of the bushing, with no fewer than 10 test points; Measurement method: Each measuring point is measured three times, and the average value is taken; Acceptable standard: Hardness test result is HRC 50-60; Preferred range: HRC 54-58; Significance of the test: This hardness range meets the requirements for use in nuclear power plant sealing bushings and can effectively reduce surface wear.

[0057] Reinforcement layer depth test Testing instrument: Micro Vickers hardness tester, test load 100g; Test specimens: Specimens were cut from the treated bushing and metallographic specimens were prepared. Measurement method: Measure every 0.1 mm from the surface inwards until the hardness value drops below 110% of the matrix hardness; Measurement data processing: Plot hardness-depth curves and determine the depth of the reinforcement layer where the hardness drops significantly; Acceptable standard: The depth of the reinforcement layer is 0.8-1.2mm; Preferred range: 0.9-1.1 mm; Significance of the test: This depth is 2-3 times that of traditional surface treatment methods, ensuring long-term performance.

[0058] Surface roughness test Testing instrument: Stylus-type surface roughness tester, conforming to ISO 4288 standard; Measurement parameters: sampling length is 5mm, cutoff wavelength is 0.8mm, evaluation length is 4mm; Measurement locations: 6 points each on the inner and outer surfaces of the bushing; Acceptable standard: Ra value is 0.4-0.8μm; Preferred range: Ra value 0.5-0.7μm; Significance of the test: This roughness range is conducive to the formation of a lubricating film and reduces the coefficient of friction.

[0059] Hardness distribution uniformity test Test method: Take 12 equally spaced measuring points on the inner and outer surfaces of the bushing, distributed along the circumference and axis; Data processing: Calculate the standard deviation and range of hardness values ​​at all measuring points; Acceptable standard: Hardness deviation within ±3HRC; Preferred standard: Hardness deviation within ±2HRC; Significance of the test: The uniformity is better than that of traditional treatment methods, ensuring consistent sealing performance.

[0060] High temperature stability test Test method: Place the sample in a high-temperature furnace and keep it at 400±5℃ for 100 hours; Cooling method: Cool to room temperature with the furnace; Test items: Measure the surface hardness before and after heat preservation, and calculate the percentage decrease in hardness; Acceptable standard: Hardness decrease not exceeding 5%; Preferred standard: Hardness decrease not exceeding 3%; Significance of the test: It verifies the thermal stability of the treated nanocrystalline structure and ensures its long-term performance under high-temperature conditions.

[0061] Corrosion resistance test Test method: Immerse the sample in 6% FeCl3 solution for 72 hours according to ASTM G48 Method A; Test temperature: 35±1℃; Evaluation index: Weight loss per unit area (mg / cm²); Acceptable standard: Corrosion rate not exceeding 0.5 mg / (cm²·d) Data processing: Divide the weight difference before and after processing by the surface area and time to calculate the corrosion rate; Significance of the test: To ensure that the surface treatment maintains good resistance to seawater corrosion.

[0062] Technical effects of this embodiment The surface treatment method for large cobalt-based alloy sealing bushings used in nuclear power plants provided by this invention combines three major processes: shock wave-induced surface modification and strengthening, plasma surface modification, and shock wave composite cyclic treatment for deep strengthening. These processes form a synergistic surface treatment system, achieving the following technical effects: Key performance indicators and comparison with existing technologies: Experimental verification To verify the technical effectiveness of the surface treatment method described in this embodiment, the following three most representative technical effects were selected for experimental verification: 1. The effect of multi-directional shock wave focusing technology on the uniformity of surface hardness distribution; 2. The impact of periodic deep activation processes on the depth of the reinforced layer; 3. The effect of pulse heat treatment stabilization technology on the high-temperature stability of nanocrystalline structures.

[0063] The following experiments were designed and conducted in strict accordance with scientific experimental methods to ensure data reliability and experimental repeatability.

[0064] Experiment 1: The Influence of Multi-directional Shock Wave Focusing Technology on the Uniformity of Surface Hardness Distribution Experimental Objective The advantages of the multi-directional shock wave focusing technology of this invention in improving the uniformity of surface hardness distribution compared with traditional single-point triggered shock wave treatment are verified.

[0065] Experimental equipment Underwater electric explosion treatment device; capacitor energy storage power supply: capacity 50kJ, maximum voltage 40kV; water tank: diameter 1200mm, height 1000mm; pressure sensor: response frequency 1MHz, measurement range 0-100MPa; multi-point trigger control system: timing accuracy ±5μs.

[0066] Hardness testing equipment Rockwell hardness tester: C range, conforming to GB / T 230.1 standard; Microhardness tester: 100g load, conforming to GB / T 4340 standard.

[0067] Experimental materials Cobalt-based alloy material: C 1.28%, Cr 30.2%, Ni 2.3%, Mo 0.6%, W 4.5%, Co balance. Sample specifications: a section of a sealing bushing with an outer diameter of φ570mm, a height of 150mm, and an inner diameter of φ500mm.

[0068] Experimental methods Sample preparation: Samples of the same material and size were divided into three groups of three; Group A: treated with the multi-directional shock wave focusing technology of the present invention; Group B: treated with traditional single-point triggered shock wave; Group C: no shock wave treatment (control group); all samples were pretreated with the same process.

[0069] Processing parameters: Group A (Multi-directional shock wave focusing): Reflective wall device: 10 arc-shaped reflective surfaces with a radius of curvature of 400mm; Trigger electrodes: 10, evenly distributed, with an angular interval of 36°; Trigger interval: 200μs; Voltage: 30kV, shock wave pressure: 25MPa; Number of treatments: 4, with a 2-minute interval.

[0070] Group B (Traditional Single-Point Trigger): non-reflective wall device Trigger electrode: 1, placed in the center of the bushing; voltage: 30kV, shock wave pressure: 25MPa; number of treatments: 4, with an interval of 2 minutes.

[0071] Hardness test: Twelve equidistant measuring points (a total of 24 points) were selected on the inner and outer surfaces of each sample; each point was measured three times and the average value was taken; the average hardness value, standard deviation, and maximum deviation of the 24 measuring points were calculated; and a hardness distribution map was drawn.

[0072] Experimental results Table 1-1: Effect of different treatment methods on the surface hardness uniformity of the bushing Note: Uniformity improvement rate = (1 - standard deviation of group A / standard deviation of group B) × 100%.

[0073] Figure 1 A comparison chart showing the hardness distribution at different locations is presented.

[0074] Experimental conclusions The average surface hardness of the samples treated with multi-directional shock wave focusing technology (Group A) reached 56.2 HRC, which is 6.4% higher than that of the traditional single-point triggering treatment (Group B) (52.8 HRC) and 46.0% higher than that of the untreated control group (Group C) (38.5 HRC).

[0075] The hardness distribution of the samples treated by multi-directional shock wave focusing technology is more uniform, with a standard deviation of only 1.3 HRC and a maximum deviation of ±2.8 HRC, while the standard deviation of traditional single-point triggering treatment is 3.6 HRC and the maximum deviation is ±7.7 HRC, with a uniformity improvement rate of 63.6%.

[0076] As can be seen from the hardness distribution diagram, the hardness distribution of traditional single-point triggering treatment shows obvious fluctuations, indicating that the surface treatment is not uniform; while the hardness distribution curve of multi-directional shock wave focusing technology is stable with a small fluctuation range, indicating that the surface treatment uniformity is significantly improved.

[0077] The hardness values ​​of the samples treated with multi-directional shock wave focusing technology were all within the range of 53.4-59.0 HRC at 24 measuring points, meeting all design requirements (HRC 50-60); while the samples treated with traditional single-point triggering had hardness values ​​below 50 HRC at 3 points, failing to meet design requirements.

[0078] Experimental results verify that multi-directional shock wave focusing technology has significant advantages in improving the uniformity of surface hardness, which is of great significance for ensuring the overall sealing performance and service life of the sealing bushing.

[0079] Experiment 2: The Influence of Periodic Deep Activation Process on the Depth of the Enhanced Layer Experimental Objective The effectiveness of the periodic deep activation process of the present invention in increasing the depth of the reinforced layer was verified and compared with traditional surface treatment methods.

[0080] Experimental equipment Underwater electro-explosion disposal device; High-voltage power supply: maximum voltage up to 50kV; Microhardness testing system; Micro Vickers hardness tester: load range 10-1000g, conforming to GB / T 4340 standard; Image analysis system: pixel resolution 4K; Cutting and polishing equipment; Precision cutting machine: cutting accuracy ±0.01mm; Automatic grinding and polishing machine: can achieve final polishing to Ra 0.05μm.

[0081] Experimental materials The same cobalt-based alloy material as in Experiment 1 was used, with the sample size being a φ30mm×10mm circular disc, cut from the same batch of sealing bushing material.

[0082] Experimental methods Sample preparation: Samples of the same material and size were divided into three groups of five: Group A: using the complete process of this invention (including periodic deep activation treatment); Group B: using the traditional process (excluding periodic deep activation treatment); Group C: only surface pretreatment (control group).

[0083] Processing parameters: Group A (Complete Process): Step 1: Underwater electric explosion shock wave treatment (voltage 15kV); Step 2: Pneumatic high-speed particle shot peening strengthening; Step 3: Mechanical friction nanocrystallization treatment; Step 4: Low-temperature plasma nitriding treatment; Step 5: Pulsed laser surface melting treatment; Step 6: Multi-directional shock wave focusing treatment; Step 7: Pulsed heat treatment stabilization; Step 8: Periodic deep activation treatment (voltage 40kV, shock wave action angle periodically varies ±30°).

[0084] Group B (Traditional Craftsmanship): Step 1: Underwater electric explosion shock wave treatment (15kV); Step 2: Pneumatic high-speed particle shot peening strengthening; Step 3: Mechanical friction nanocrystallization treatment; Step 4: Low-temperature plasma nitriding treatment; Step 5: Pulsed laser surface melting treatment.

[0085] Group C (control group): Surface pretreatment only Reinforcement layer depth test: Cut the treated sample radially to prepare a metallographic sample; perform Vickers hardness test (load 100g) every 0.1 mm from the surface to the interior along the direction perpendicular to the surface; test the depth until the hardness value drops to below 110% of the matrix hardness; plot the hardness-depth distribution curve; measure the thickness of each region, including the surface nanocrystalline layer, the transition gradient layer and the deep reinforcement zone.

[0086] Experimental results Table 2-1: Influence of different treatment methods on the depth of the reinforcement layer Note: Depth increase factor = Total reinforcement layer depth of Group A / Total reinforcement layer depth of Group B.

[0087] Figure 2 The hardness-depth distribution curves of different treatment methods are shown.

[0088] Figure 3 The comparison of the enhancement layer depth using different processing methods is shown.

[0089] Experimental conclusions The total reinforced layer depth of the sample (Group A) using the complete process of this invention (including periodic deep activation treatment) reached 1.01±0.10mm, which is 2.46 times that of the traditional process (Group B), and far exceeds the reinforced layer depth formed by the usual surface treatment method (<0.5mm).

[0090] In terms of the reinforced layer structure, the fully processed sample exhibits a distinct three-layer structure: Surface nanocrystalline layer: approximately 35μm thick, with a hardness of up to HV 625; Transition gradient layer: approximately 0.25 mm thick, with hardness gradually decreasing from HV 608 to HV 530; Deep reinforcement zone: approximately 0.72 mm thick, with hardness gradually decreasing from HV 510 to the matrix hardness.

[0091] The reinforcement layer of samples treated by traditional processes is mainly concentrated on the surface and shallow layer, with a depth of about 0.41 mm. The deep reinforcement area is only 0.17 mm, which is much smaller than the 0.72 mm of the complete process.

[0092] The hardness-depth distribution curve clearly shows that the hardness of traditional processes decreases sharply with increasing depth, while the hardness of complete processes exhibits a gradual gradient distribution. This helps to reduce stress concentration and improve the bonding strength between the reinforced layer and the substrate.

[0093] Periodic deep activation process is a key process for forming deep reinforcement zones. Through the deep penetration of high-energy shock waves, a second reinforcement zone is formed 0.5-1.0 mm below the surface layer, which significantly increases the total depth of the reinforcement layer.

[0094] Experimental results verify that the periodic deep activation process of the present invention has a significant effect on increasing the depth of the reinforcement layer, which is of great significance for extending the service life of the sealing bushing and enabling it to maintain good surface performance even after long-term wear.

[0095] Experiment 3: Effect of pulsed heat treatment stabilization technology on the high-temperature stability of nanocrystalline structures Experimental Objective The effectiveness of the pulse heat treatment stabilization technology of the present invention in improving the high-temperature stability of nanocrystalline structures was verified and compared with traditional surface treatment methods.

[0096] Experimental equipment High-temperature processing equipment; Programmable temperature control resistance furnace: temperature range 20-1200℃, temperature control accuracy ±2℃; pulse heat treatment device: heating rate 10-30℃ / s, cooling rate 5-15℃ / s, programmable control.

[0097] Hardness testing equipment Rockwell hardness tester: C range, conforming to GB / T 230.1 standard; Micro Vickers hardness tester: load range 10-1000g, conforming to GB / T 4340 standard; Microstructure analysis equipment; Transmission electron microscope (TEM): resolution 0.2nm; X-ray diffractometer (XRD): angle range 5-160°, angle accuracy ±0.01°; Scanning electron microscope (SEM): magnification 20-200,000x.

[0098] Experimental materials The same cobalt-based alloy material as the previous two experiments was used, with the sample size being a φ20mm×5mm circular disc, cut from the same batch of sealing bushing material.

[0099] Experimental methods Sample preparation: Samples of the same material and size were divided into three groups of five: Group A: using the complete process of this invention (including pulse heat treatment stabilization); Group B: using the traditional process (excluding pulse heat treatment stabilization); Group C: no surface treatment (control group); all samples underwent surface nanocrystallization treatment to ensure similar initial surface hardness.

[0100] Processing parameters: Group A (including pulse heat treatment stabilization): After surface nanocrystallization treatment, pulse heat treatment was performed: heating rate 15℃ / s, temperature 370℃, holding time 20 minutes, cooling rate 8℃ / s; the treatment was repeated 4 times.

[0101] Group B (Traditional Process): After surface nanocrystallization treatment, conventional annealing is performed: heating rate 3℃ / min, temperature 370℃, holding time 2 hours, and furnace cooling.

[0102] Group C (control group): Only surface nanocrystallization treatment was performed; no heat treatment was performed.

[0103] High-temperature stability test: Each group of samples was divided into 5 batches and kept at the following temperatures for 100 hours: 300℃, 350℃, 400℃, 450℃, and 500℃; after the heat treatment, the samples were cooled to room temperature; the surface hardness was measured, with 10 points measured for each sample and the average value taken; the hardness retention rate was calculated as: hardness after heat treatment / initial hardness × 100%; the changes in nanocrystalline structure were observed by TEM; and the changes in grain size were determined by XRD.

[0104] Long-term performance simulation test: Each group of samples was subjected to cyclic thermal shock testing at 400℃; the cycle parameters were: 400℃ for 30 minutes, cooled to 100℃, for a total of 500 cycles; after every 100 cycles, the samples were taken out and the surface hardness was measured; the hardness change curve was plotted.

[0105] Experimental results Table 3-1: Comparison of hardness retention rate after 100 hours of heat preservation at different temperatures Table 3-2: Changes in nanocrystalline structure after heat treatment at 400℃ using different methods Note: Grain growth rate = (Grain size after heat preservation / Initial grain size - 1) × 100% Dislocation density change rate = (Dislocation density after heat preservation / Initial dislocation density - 1) × 100%.

[0106] Figure 4 The hardness change curves of different treatment methods after being kept at 400℃ for 100 hours are shown.

[0107] Figure 5 The hardness changes under different treatment methods during cyclic thermal shock testing are shown.

[0108] Experimental conclusions In terms of high-temperature stability, the samples stabilized by pulse heat treatment (Group A) showed a significant advantage: After holding at 400℃ for 100 hours, the hardness retention rate of group A reached 95.4%, while that of group B (conventional annealing) was only 79.6%, and that of group C (no heat treatment) was only 72.4%. Group A maintained a hardness retention rate of 88.7% at 450℃, which was 23.5 percentage points higher than Group B and 30.4 percentage points higher than Group C.

[0109] From a microstructural analysis perspective, after being kept at 400℃ for 100 hours: The average grain size of the nanocrystals in Group A increased from 76 nm to 95 nm, with a grain growth rate of 25.0%. The grain size of Group B increased from 78 nm to 158 nm, representing a growth rate of 102.6%. The grain size of group C increased from 75nm to 187nm, with a growth rate of 149.3%.

[0110] The decrease in dislocation density in Group A (-18.5%) was much smaller than that in Group B (-62.3%) and Group C (-74.8%).

[0111] Cyclic thermal shock test results show that: After 500 cycles of thermal shock at 400℃, the hardness retention rate of Group A still reached 95.9%; The hardness retention rate of group B decreased to 78.6%, and the hardness retention rate of group C decreased to 68.5%. Group A exhibited excellent thermal cycling stability, which is crucial for long-term service in nuclear power plant environments.

[0112] The main reasons why pulsed heat treatment stabilization technology can significantly improve the thermal stability of nanocrystalline structures are: The rapid heating-holding-rapid cooling cycle forms a stable dislocation network structure; These dislocation networks can effectively pin grain boundaries and suppress grain growth at high temperatures; Multiple cycles of treatment caused a certain number of solute atoms to segregate at the grain boundaries, which improved the thermal stability of the grain boundaries. The process induces the formation of nanoscale precipitates, which are uniformly distributed at grain boundaries and within grains, playing a role in strengthening and stabilizing.

[0113] Experimental results verify that the pulse heat treatment stabilization technology of the present invention has a significant effect on improving the high-temperature stability of nanocrystalline structures, enabling the bushing to maintain good hardness and wear resistance in high-temperature environments, and providing an important guarantee for the long-term stable operation of the sealing bushing of the seawater circulating water pump in nuclear power plants.

[0114] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A manufacturing process for a large cobalt-based alloy sealing bushing for nuclear power plants, characterized in that, Includes the following steps: Step 1: The sealing bushing is made of cobalt-based alloy with the following composition: C 1.1-1.4%, Cr 29.0-31.0%, Ni 1.5-3.0%, Mo 0.2-1.0%, W 4.0-5.0%, and Co balance. Step 2: The alloy ingot is melted using a vacuum induction melting process, and the surface of the alloy ingot is polished to remove surface impurities and oxide scale; Step 3: Dehydrogenation treatment of the alloy ingot, heating to 800℃ and holding for 2 hours; Step 4: Use an intermediate frequency furnace to heat and remelt the alloy ingots. Use fluorite and calcium fluoride to make slag during smelting and add appropriate alloying elements. Use pure titanium to deoxidize the alloy liquid when tapping it out of the furnace. Step 5: Use an argon-blown bottom-pouring ladle to pour the remelted alloy liquid into the casting cavity; Step 6: Perform softening annealing heat treatment on the casting, holding at 850℃ for 5 hours to reduce the hardness of the casting; Step 7: Mount the riser side onto a vertical lathe and use an alloy cutting tool to rough machine the bottom plane, outer surface, and inner surface of the casting part, with a single-sided allowance of 4mm; Step 8: Perform solution treatment and aging treatment on the casting. For solution treatment, the heating rate is ≤100℃ / hour, the casting is heated to 1150-1160℃, held for 5 hours, and then cooled with air. For aging treatment, the heating rate is ≤100℃ / hour, the casting is heated to 950-960℃, held for 5 hours, and then cooled with air. Step 9: Perform semi-finishing on the casting, with a single-sided allowance of 0.2mm; Step 10: Perform finishing on the casting; remove the riser by wire cutting, and then finish machine the riser side face; drill holes using a CNC vertical machining center, and then tap the holes using electrical discharge machining; perform final dimensional inspection and PT testing on the finished product.

2. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, In step 7, after rough machining, the product is subjected to PT testing according to RCCM MC4000 standard and RT testing according to RCCM MC3200 standard. Defective parts detected are repaired by welding. Before welding, the product is heated to 650℃ and held for 4 hours. After taking it out of the furnace, it is covered with insulation cotton for insulation. Argon arc welding is used for welding. After welding, the product is placed in a heat treatment kiln preheated to 650℃ and cooled slowly with the furnace. After grinding the welded part with a grinding wheel, PT testing is performed according to RCCM MC4000 to confirm whether the welded part is qualified.

3. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, In step 9, the defects after semi-finishing are repaired by welding using argon arc welding. After welding, the repaired area is covered with insulation cotton to allow it to cool slowly. The repaired area is then ground smooth with a grinding wheel and subjected to PT testing to confirm whether the repaired area is qualified.

4. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, The roughing, semi-finishing, and finishing processes all use LAMINA TECH CH alloy chuck inserts.

5. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, The defect repair after rough machining uses Stellite 6 welding wire, 4.8 mm in diameter, grade HS111, with a welding current of 150-170A and a welding voltage of 20-23V; the defect repair after semi-finishing machining uses Stellite 6 welding wire, 4.0 mm in diameter, grade HS111, with a welding current of 130-150A and a welding voltage of 18-20V.

6. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, The mechanical performance requirements for the sealing bushing are: tensile strength ≥ 800 MPa, hardness HRC ≥ 37.

7. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, The outer diameter of the sealing bushing is 570mm, the height is 610mm, the inner diameter is 500mm, and the tolerance range is 0-0.02mm.

8. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, Both the PT and RT tests are subject to acceptance level 1 of the RCCM standard.

9. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, Both the roughing defects and the semi-finishing defects were removed using a pneumatic milling cutter.

10. The manufacturing process of the large cobalt-based alloy sealing bushing for nuclear power plants according to claim 1, characterized in that, This also includes surface treatment of the sealing bushing, and the treatment methods include: The shock wave-induced surface modification and strengthening step involves sequentially subjecting the pretreated sealing bushing to underwater electric explosion shock wave treatment, pneumatic high-speed particle shot peening strengthening, and mechanical friction nanocrystallization treatment to form a nanocrystalline layer on the bushing surface. The plasma surface modification step involves sequentially subjecting the surface-modified and strengthened sealing bushing to low-temperature plasma nitriding and pulsed laser surface melting treatment to form a composite reinforced surface layer. The deep strengthening steps of the shock wave composite cycle treatment include multi-directional shock wave focusing treatment, pulse heat treatment stabilization and periodic deep activation treatment of the surface-modified sealing bushing to form a gradient strengthening structure from the surface to the interior. The multi-directional shock wave focusing process employs a reflective wall device and multi-point triggering electrodes to ensure that the shock wave energy is evenly distributed on the bushing surface and that the shock wave pressure deviation is controlled within ±10%.

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