A processing method of high-strength butt welding flange

Abstract

The application discloses a processing method of high-strength butt-welding flanges, and belongs to the field of flange processing. The method comprises the following steps: S1. Low-carbon medium-alloy aluminum plate is used as raw material, directional deformation treatment is performed on the raw material through a temperature control roller forging process, and a forged blank with a grain refinement structure is obtained; S2. The forged blank is subjected to plasma preheating treatment; S3. The forged blank after the preheating treatment is placed into a multi-zone temperature difference control forging die, and one-time forming is performed through a high-frequency precision hot forging technology; S4. The flange blank is subjected to solid solution treatment and controlled cooling treatment, and then multi-stage slow cooling furnace is used to realize stage-by-stage temperature control cooling; S5. Double-sided high-precision numerical control processing is performed on the flange blank by using a low-residual-stress precision turning device, and the finished flange with an inner hole deviation of less than ±0.03 mm and an end face perpendicularity deviation of less than 0.02 mm is obtained; and S6. The finished flange is subjected to low-temperature gas nitriding treatment. The method has the beneficial effects of improving the compactness of the flange blank, improving the yield strength and ductility, improving the welding reliability, avoiding repeated machining correction in the traditional process, and being particularly suitable for high-pressure occasions.

Description

Technical Field

[0001] This invention relates to the field of flange processing, and more specifically, to a processing method for high-strength weld neck flanges. Background Technology

[0002] High-strength weld neck flanges, as key components in aerospace, have undergone a gradual evolution in their manufacturing methods, from traditional forging to precision forming and automated control technologies. Early weld neck flanges primarily relied on free forging or die forging, a simple process but with significant fluctuations in dimensional accuracy and mechanical properties. Subsequently, the introduction of hot die forging, isothermal forging, and heat treatment processes significantly improved the uniformity of flange microstructure and strength stability. In the 21st century, advanced manufacturing technologies such as CNC machining, laser cutting, and automated welding have been widely applied, greatly improving the processing efficiency, precision, and consistency of flanges, meeting the requirements of harsh operating conditions such as high pressure and high temperature. Furthermore, with the development of materials science, the application of new materials such as corrosion-resistant high-strength aluminum alloys has also driven the widespread use of high-performance flanges.

[0003] However, current high-strength weld neck flange manufacturing technology still faces a prominent problem: while ensuring high strength and high precision, it is difficult to simultaneously achieve low cost and green manufacturing. Complex processes, high-temperature treatments, and the use of high-end materials result in high energy consumption and low material utilization. The manufacturing process also generates a large amount of waste and heat treatment pollution, which hinders its widespread adoption in the low-to-mid-end market and the achievement of green manufacturing goals. Summary of the Invention

[0004] The purpose of this invention is to provide a processing method for high-strength weld neck flanges to solve the problems mentioned in the background art: it is difficult to simultaneously ensure high strength and high precision while achieving low cost and green manufacturing. Complex processes, high-temperature treatment, and the use of high-end materials result in high processing energy consumption, low material utilization, and the generation of a large amount of waste and heat treatment pollution during processing, which restricts its popularization in the low-to-mid-end market and the achievement of green manufacturing goals.

[0005] Technical solution: The processing method of the high-strength butt-welding flange includes the following steps: S1. Select low-carbon medium-alloy aluminum plates with a yield strength of not less than 350MPa, and after surface rust removal, cutting and stress-relieving annealing pretreatment, perform multi-pass directional deformation treatment by temperature-controlled roll forging. The roll forging temperature is controlled at 1000-1100℃. Apply radial and axial stress by alternating longitudinal and transverse roll pressing to generate a uniform fibrous structure along the flange circumference, while refining the grain to 5-10μm, and finally obtain a pre-forged billet with isotropic strength distribution.

[0006] S2. The pre-forged billet is subjected to rapid plasma beam preheating treatment in an oxidation-free atmosphere. The heating zone is maintained between 850 and 950°C under the protection of high-purity argon gas for 10 to 20 minutes, so that a small thermal gradient is formed between the surface and the interior of the billet, reducing the internal stress in the subsequent hot forging process and ensuring that no oxide film or metal decarburization layer is generated.

[0007] S3. The preheated forging blank is subjected to high-frequency precision hot forging. A multi-cavity combined mold and an intelligent zone heating system are used to control the temperature distribution of the outer edge, middle and core areas of the mold cavity respectively, and the temperature difference is controlled to not exceed 100℃. The deformation rate is controlled in the range of 0.5~2mm / s, and the pressing time is 20~45 seconds. This achieves simultaneous dense forming of the flange neck and the annular flange area, and obtains a flange blank with an average dimensional tolerance of less than ±0.05mm and a density of not less than 98%.

[0008] S4. Transfer the hot forged flange blank into a temperature-controlled resistance furnace for solution heat treatment. Set the temperature to 1000-1080℃ and hold for 1.5-3 hours. Then, use a segmented slow cooling process to slowly cool the blank to room temperature. The cooling rate is controlled at 20℃ / min in the first stage, 10℃ / min in the second stage, and no more than 5℃ / min in the final stage. S5. The heat-treated flange blank is machined in sequence, including double-end face turning, inner hole boring, outer diameter precision turning and end face precision milling. The machining allowance for each process is set to not exceed 0.1mm. The cutting tools are made of carbide or CBN material. The spindle runout is controlled within 0.005mm. The final internal and external dimensional tolerances are controlled within ±0.03mm, the end face perpendicularity error is less than 0.02mm, and the surface roughness Ra is less than 0.4μm. Specifically, the flange blank undergoes solution heat treatment at a temperature of 1000–1080℃ for 1.5–3 hours; a three-stage slow cooling method is employed. The first stage involves cooling the temperature from 1080℃ to 800℃ at a uniform rate in a temperature-controlled furnace. The second stage involves cooling the temperature from 800℃ to 500℃ using high-purity argon gas, with a temperature difference of ≤15℃ / min. The third stage involves cooling from 500℃ to room temperature using intermittent water mist with a particle size of 50–80 μm, spraying once every 10 seconds, for a total duration not exceeding 15 minutes. This method controls tissue evolution and reduces internal stress and deformation.

[0009] S6. The machined flange is subjected to low-temperature gas nitriding treatment. The treatment temperature range is 480-520℃, the ratio of ammonia to hydrogen in the atmosphere is 3:1, the flow rate is kept stable at 100-150mL / min, and the nitriding time is set to 4-6 hours. The surface nitrogen content gradient distribution is achieved through a three-stage treatment method of layer-by-layer heating, isothermal diffusion and constant temperature heat preservation. Finally, a nitrided layer with a thickness of 0.3-0.6mm and a hardness between 800-950HV is formed, which has high wear resistance and high fatigue strength.

[0010] Preferably, the S1 temperature-controlled roll forging adopts a combined multi-pass roll forging path planning process. In the first pass, the axial reduction is 12% to 15% of the material thickness, and in subsequent passes, it is reduced to 5% to 8%. After each pass, the uniformity of the thermal field in the workpiece deformation zone is maintained by adjusting the roll spacing and roll temperature, preventing the concentration of central stress from causing uneven plasticity or the initiation of microcracks. The material structure gradually extends to a fibrous form along the processing direction, effectively suppressing the formation of columnar crystals and coarse grains, and significantly improving the matching degree of mechanical properties along the radial and axial directions, forming continuous and consistent metal flow lines and balanced deformation characteristics.

[0011] Preferably, after each pass, the forging billet is sent into the induction heating zone for a second heating. The temperature rise is maintained in the range of 95% to 98% of the initial roll forging temperature, the induction frequency is set to 8 to 12 kHz, and the heating time is controlled in the range of 45 to 90 seconds. This thermal compensation process avoids cooling lag in the core area of ​​the billet and prevents the internal and external temperature difference caused by premature cooling of the surface layer. This maintains the overall deformation coordination, suppresses the occurrence of uneven structure, thermal fatigue and stress rebound, and improves the subsequent forging forming quality and grain size consistency.

[0012] Preferably, in the plasma beam preheating treatment, the preheating scan adopts a spiral concentric circle wiring method, the scanning step is set to 2 mm, the scanning rate is 50 mm / s, high-purity argon gas is output from the nozzle annular distribution structure at a constant flow rate of 150 mL / min, the nozzle is kept 10-12 mm away from the workpiece surface, and the plasma arc beam width is 4-6 mm. By controlling the above process parameters, a heating zone with a heat-affected zone depth of no more than 0.5 mm is formed on the surface of the billet, while the metal surface oxide layer is controlled below 10 nm to inhibit oxide film growth and carbon migration, and avoid cracks or local peeling caused by surface embrittlement during subsequent forging.

[0013] Preferably, in the high-frequency precision hot forging process, electromagnetic induction heating is used to set the heating power ratio of the outer edge, middle section and center of the mold to 3:2:1, respectively. The temperature of each mold cavity area is stabilized at 880℃, 920℃ and 950℃, respectively. At the same time, the mold surface is coated with a high-temperature thermally conductive ceramic coating with a thickness of not less than 1.5mm to improve the heat field distribution efficiency. The forging rate is controlled at 0.8mm / s, the pressing duration is 40 seconds, and the pressure is maintained above 120MPa when the mold is closed. This forms a dense and defect-free neck structure, the ring thickness error is controlled within ±0.05mm, and the compression ratio reaches more than 1.8, effectively enhancing the overall mechanical consistency and service life of the weld flange.

[0014] Preferably, after hot forging and pressing, the mold is kept closed for 10 seconds, and a constant pressure load is applied to cause secondary micro-plastic deformation of the metal at high temperature, which promotes grain boundary migration and microstructure compaction, and further reduces microcracks or residual porosity caused by rapid unloading. Then, it is cooled in an inert atmosphere of 0.3 MPa at a controlled rate of 10 °C / min until the temperature drops below 700 °C, and then transferred to a slow cooling furnace for further cooling, finally obtaining a high-density flange forging with uniform structure, no stress concentration at the edges, and micro-porosity of less than 0.1%.

[0015] Preferably, the segmented slow cooling includes three stages. In the first stage, the temperature is slowly reduced from 1080°C to 800°C, with uniform temperature control in the holding furnace to ensure sufficient transformation of austenite into pearlite or bainite. In the second stage, the temperature is reduced from 800°C to 500°C, switching to high-purity argon gas cooling, with the gas temperature maintained in the range of room temperature to 300°C, and the cooling rate reduced to 15°C / min through continuous ventilation. In the third stage, the temperature is reduced from 500°C to room temperature, switching to intermittent water mist assisted cooling, with the water mist particle size controlled at 50-80 μm, the spray frequency interval set to once every 10 seconds, and the total spraying time not exceeding 15 minutes. This establishes a stable microstructure evolution path, reduces the formation of internal stress, and ultimately obtains a heat-treated structure with a gentle hardness gradient and no precipitate agglomeration.

[0016] Preferably, the machining steps adopt a five-axis linkage machining process, the cutting tool is a carbide circular arc tool with a diameter of 4-8mm, the spindle speed is set to 1500-1800rpm, the feed rate is 0.2-0.4mm / rev, the machining path is generated by the CAD / CAM system with minimum interference trajectory, and the trajectory overlap is set to be no less than 30%. The end face machining adopts a staggered bidirectional milling mode to improve the flatness consistency. After each process, in-situ dimension inspection is performed, and the parts with errors exceeding ±0.03mm are re-finished. Finally, the inner hole size deviation of the flange is controlled within ±0.02mm, and the end face flatness is less than 0.01mm, ensuring sufficient contact and minimal deformation of the flange welding surface.

[0017] Preferably, the nitriding process uses a dynamic alternating ammonia and hydrogen atmosphere. In the initial stage, a mixed gas with a volume ratio of 3:1 is introduced and maintained for 1 hour. Then, every 60 minutes, the atmosphere is switched to pure hydrogen for 10 minutes, and then the original mixed gas ratio is restored. This cycle is repeated 6 times. The nitriding temperature is kept constant at 500°C, and the total treatment time does not exceed 6 hours. The thickness of the nitrided layer is controlled within the range of 0.35 to 0.5 mm by metallographic microscopy. The nitrogen concentration gradient is stable, and a fine diffusion layer and composite phase layer structure are formed on the surface. The Vickers hardness gradually transitions to the level of the core matrix material, while avoiding grain boundary embrittlement and the formation of low-toughness zones, significantly enhancing the flange's thermal shock resistance and fatigue resistance.

[0018] Compared with the prior art, the advantages of this invention are: (1) By combining plasma beam preheating with temperature-controlled roll forging, internal shrinkage cavities and inclusions are effectively eliminated, and the density of the flange blank is improved.

[0019] (2) The heat treatment process precisely controls the microstructure transformation to obtain fine and uniform tempered sorbite, thereby improving yield strength and ductility.

[0020] (3) The microstructure of the welded joint is continuously transitioned, avoiding the problems of weld softening or hardening and brittleness, and improving the reliability of welding.

[0021] (4) The molding size is controlled by a temperature control and deformation feedback mechanism throughout the process, avoiding repeated machining corrections in traditional processes. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall process of a high-strength butt-welding flange processing method according to the present invention; Detailed Implementation

[0023] For examples, please refer to Figure 1 The processing method for a high-strength weld neck flange includes the following steps: A method for processing a high-strength weld neck flange includes the following steps: S1. Select low-carbon medium alloy aluminum plates with a yield strength of not less than 350MPa, perform surface rust removal, cutting and stress relief annealing pretreatment, and then perform multi-pass directional deformation treatment by temperature-controlled roll forging. The roll forging temperature is controlled at 1000~1100℃. Apply radial and axial stress by alternating longitudinal and transverse roll pressing to generate a uniform fibrous structure along the flange circumference of the material, while refining the grain to 5~10μm, and finally obtain a pre-forged billet with isotropic strength distribution. Specifically, low-carbon medium-alloy aluminum sheets with a yield strength of not less than 350 MPa are selected. The medium-alloying elements are selected from one or more of Cr, Mo, Ni, and V, and the alloy content is controlled between 0.5% and 1.5%. The thickness of the aluminum sheet is not less than 30 mm. The aluminum sheet is mechanically shot-peened to remove rust, and then cut to the target shape using plasma cutting equipment. After that, it is subjected to stress-relieving annealing treatment at 650–700℃ for 1–2 hours.

[0024] S2. The pre-forged billet is subjected to rapid plasma beam preheating treatment in an oxidation-free atmosphere. The heating zone is maintained at 850-950°C under the protection of high-purity argon for 10-20 minutes, so that a small thermal gradient is formed between the surface and the interior of the billet, reducing the internal stress in the subsequent hot forging process and ensuring that no oxide film or metal decarburization layer is generated. Specifically, a spiral concentric scanning path is adopted, with a step size of 2 mm, a scanning rate of 50 mm / s, a nozzle distance of 10–12 mm from the surface, an argon flow rate of 150 mL / min, and the depth of the heat-affected zone controlled to be ≤0.5 mm and the surface oxide layer ≤10 nm to prevent metal decarburization and surface embrittlement.

[0025] S3. The preheated forging blank is subjected to high-frequency precision hot forging. A multi-cavity combined mold and an intelligent zone heating system are used to control the temperature distribution of the outer edge, middle and core areas of the mold cavity respectively, and the temperature difference is controlled to not exceed 100℃. The deformation rate is controlled in the range of 0.5~2mm / s, and the pressing time is 20~45 seconds. This achieves simultaneous dense forming of the flange neck and the annular flange area, and obtains a flange blank with an average dimensional tolerance of less than ±0.05mm and a density of not less than 98%. Specifically, an electromagnetic induction heating mold is used, with the mold cavity divided into an outer edge, middle section, and central area. The heating power ratio is set to 3:2:1, and the temperatures of each area are 880℃, 920℃, and 950℃, respectively. The mold surface is coated with a high-temperature thermally conductive ceramic layer with a thickness of ≥1.5mm to improve thermal uniformity. The pressure when the mold is closed is ≥120MPa.

[0026] S4. Transfer the hot forged flange blank into a temperature-controlled resistance furnace for solution heat treatment. Set the temperature to 1000-1080℃ and hold for 1.5-3 hours. Then, use a segmented slow cooling process to slowly cool the blank to room temperature. The cooling rate is controlled at 20℃ / min in the first stage, 10℃ / min in the second stage, and no more than 5℃ / min in the final stage. S5. The heat-treated flange blank is machined in sequence, including double-end face turning, inner hole boring, outer diameter precision turning and end face precision milling. The machining allowance for each process is set to not exceed 0.1mm. The cutting tools are made of carbide or CBN material. The spindle runout is controlled within 0.005mm. The final internal and external dimensional tolerances are controlled within ±0.03mm, the end face perpendicularity error is less than 0.02mm, and the surface roughness Ra is less than 0.4μm. Specifically, the flange blank undergoes solution heat treatment at a temperature of 1000–1080℃ for 1.5–3 hours; a three-stage slow cooling method is employed. The first stage involves cooling the temperature from 1080℃ to 800℃ at a uniform rate in a temperature-controlled furnace. The second stage involves cooling the temperature from 800℃ to 500℃ using high-purity argon gas, with a temperature difference of ≤15℃ / min. The third stage involves cooling from 500℃ to room temperature using intermittent water mist with a particle size of 50–80 μm, spraying once every 10 seconds, for a total duration not exceeding 15 minutes. This method controls tissue evolution and reduces internal stress and deformation.

[0027] S6. The machined flange is subjected to low-temperature gas nitriding treatment. The treatment temperature range is 480-520℃, the ratio of ammonia to hydrogen in the atmosphere is 3:1, the flow rate is kept stable at 100-150mL / min, and the nitriding time is set to 4-6 hours. The surface nitrogen content gradient distribution is achieved through a three-stage treatment method of layer-by-layer heating, isothermal diffusion and constant temperature heat preservation. Finally, a nitrided layer with a thickness of 0.3-0.6mm and a hardness between 800-950HV is formed, which has high wear resistance and high fatigue strength.

[0028] S1 temperature-controlled roll forging adopts a combined multi-pass roll forging path planning process. In the first pass, the reduction along the axial direction is 12% to 15% of the material thickness. In subsequent passes, the reduction is successively reduced to 5% to 8%. After each pass, the uniformity of the thermal field in the workpiece deformation zone is maintained by adjusting the roll spacing and roll temperature. This prevents the concentration of central stress from causing uneven plasticity or the initiation of microcracks. The material structure gradually extends to a fibrous form along the processing direction, effectively suppressing the formation of columnar crystals and coarse grains, and significantly improving the matching degree of mechanical properties along the radial and axial directions, forming continuous and consistent metal flow lines and uniform deformation characteristics in all directions.

[0029] After each pass, the forging billet is sent into the induction heating zone for a second heating. The temperature rise is maintained in the range of 95% to 98% of the initial roll forging temperature. The induction frequency is set to 8 to 12 kHz, and the heating time is controlled in the range of 45 to 90 seconds. This thermal compensation process avoids cooling lag in the core area of ​​the billet and prevents the internal and external temperature difference caused by premature cooling of the surface layer. This maintains the overall deformation coordination, suppresses the occurrence of uneven structure, thermal fatigue and stress rebound, and improves the subsequent forging forming quality and grain size consistency.

[0030] In the plasma beam preheating process, the preheating scan adopts a spiral concentric loop wiring method, with a scanning step size of 2 mm and a scanning rate of 50 mm / s. High-purity argon gas is output from the nozzle annular distribution structure at a constant flow rate of 150 mL / min. The nozzle is kept 10–12 mm away from the workpiece surface, and the plasma arc beam width is 4–6 mm. By controlling the above process parameters, a heating zone with a heat-affected zone depth of no more than 0.5 mm is formed on the surface of the billet. At the same time, the oxide layer on the metal surface is controlled to be below 10 nm, which inhibits oxide film growth and carbon migration, and avoids cracks or local peeling caused by surface embrittlement during subsequent forging.

[0031] In the high-frequency precision hot forging process, electromagnetic induction heating is used to set the heating power ratio of the outer edge, middle section and center of the mold to 3:2:1, respectively. The temperature of each mold cavity area is stabilized at 880℃, 920℃ and 950℃, respectively. At the same time, the mold surface is coated with a high-temperature thermally conductive ceramic coating with a thickness of not less than 1.5mm to improve the heat field distribution efficiency. The forging rate is controlled at 0.8mm / s, the pressing duration is 40 seconds, and the pressure is maintained above 120MPa when the mold is closed. This results in a dense and defect-free neck structure, the ring thickness error is controlled within ±0.05mm, and the compression ratio reaches more than 1.8, effectively enhancing the overall mechanical consistency and service life of the weld flange.

[0032] After hot forging, the die is kept closed for 10 seconds. A constant pressure load is applied to cause secondary micro-plastic deformation of the metal at high temperature, which promotes grain boundary migration and microstructure compaction, and further reduces microcracks or residual porosity caused by rapid unloading. Then, the metal is cooled at a controlled rate of 10℃ / min in an inert atmosphere of 0.3MPa until the temperature drops below 700℃. The metal is then transferred to a slow cooling furnace for further cooling, ultimately obtaining a high-density flange forging with uniform structure, no stress concentration at the edges, and a microporosity of less than 0.1%.

[0033] The segmented slow cooling process consists of three stages. In the first stage, the temperature is slowly reduced from 1080℃ to 800℃ using uniform temperature control within a holding furnace to ensure sufficient transformation of austenite into pearlite or bainite. In the second stage, the temperature is reduced from 800℃ to 500℃, switching to high-purity argon gas cooling, with the gas temperature maintained between room temperature and 300℃. The cooling rate is reduced to 15℃ / min through continuous ventilation. In the third stage, the temperature is reduced from 500℃ to room temperature, switching to intermittent water mist assisted cooling. The water mist particle size is controlled between 50 and 80 μm, the spray frequency is set to once every 10 seconds, and the total spraying time does not exceed 15 minutes. This establishes a stable microstructure evolution path, reduces the formation of internal stress, and ultimately obtains a heat-treated structure with a gentle hardness gradient and no precipitate agglomeration.

[0034] The machining process employs a five-axis linkage machining process, using carbide circular arc cutters with a diameter of 4–8 mm. The spindle speed is set to 1500–1800 rpm, and the feed rate is 0.2–0.4 mm / rev. The machining path is generated using a CAD / CAM system with minimal interference, and the overlap of the paths is set to be no less than 30%. The end face machining adopts an interlaced bidirectional milling mode to improve flatness consistency. In-situ dimensional inspection is performed after each process, and any parts with an error exceeding ±0.03 mm are re-finished. Ultimately, the inner hole size deviation of the flange is controlled within ±0.02 mm, and the end face flatness is less than 0.01 mm, ensuring sufficient contact and minimal deformation of the flange welding surface.

[0035] The nitriding process uses a dynamic alternating ammonia and hydrogen atmosphere. In the initial stage, a mixed gas with a volume ratio of 3:1 is introduced and maintained for 1 hour. Then, every 60 minutes, the atmosphere is switched to pure hydrogen and kept at a constant temperature for 10 minutes before returning to the original mixed gas ratio. This cycle is repeated 6 times. The nitriding temperature is kept constant at 500℃, and the total treatment time does not exceed 6 hours. The thickness of the nitrided layer is controlled within the range of 0.35 to 0.5 mm by metallographic microscopy. The nitrogen concentration gradient is stable, and a fine diffusion layer and composite phase layer structure are formed on the surface. The Vickers hardness gradually transitions to the level of the core matrix material, while avoiding grain boundary embrittlement and the formation of low-toughness zones. This significantly enhances the flange's thermal shock resistance and fatigue resistance.

[0036] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for processing a high-strength butt-welding flange, characterized in that, The processing method for a high-strength weld neck flange includes the following steps: S1. Low-carbon medium-alloy aluminum plates with a yield strength of not less than 350MPa are selected. After surface rust removal, cutting, and stress-relieving annealing pretreatment, multi-pass directional deformation treatment is carried out using temperature-controlled roll forging. The roll forging temperature is controlled at 1000-1100℃. Radial and axial stresses are applied by alternating longitudinal and transverse roll pressing, so that the material generates a uniform fibrous structure along the flange circumference, and the grain is refined to 5-10μm, finally obtaining a pre-forged billet with isotropic strength distribution. The temperature-controlled roll forging in S1 adopts a combined multi-pass roll forging path planning process. The first pass reduces the material thickness by 12%-15% along the axial direction, and the subsequent passes reduce it to 5%-8% in turn. The roll spacing and roll temperature are adjusted after each pass. S2. The pre-forged billet is subjected to rapid plasma beam preheating in an oxidation-free atmosphere. The heating zone is maintained at 850-950°C under the protection of high-purity argon gas for 10-20 minutes. This creates a small thermal gradient between the surface and interior of the billet, reducing internal stress in the subsequent hot forging process and ensuring the absence of oxide film or decarburized metal layer formation. In the S2 plasma beam preheating process, the preheating scan uses a spiral concentric loop wiring method, with a scanning step size of 2 mm and a scanning rate of 50 mm / s. High-purity argon gas is output from the nozzle annular distribution structure at a constant flow rate of 150 mL / min. The nozzle is kept 10-12 mm away from the workpiece surface, and the plasma arc beam width is 4-6 mm. This forms a heating zone with a heat-affected zone depth of no more than 0.5 mm on the surface of the billet, while controlling the metal surface oxide layer to below 10 nm to inhibit oxide film growth and carbon migration. S3. The preheated forging blank is subjected to high-frequency precision hot forging. A multi-cavity combined mold and an intelligent zone heating system are used to control the temperature distribution of the outer edge, middle and core areas of the mold cavity respectively, and the temperature difference is controlled to not exceed 100℃. The deformation rate is controlled in the range of 0.5~2mm / s, and the pressing time is 20~45 seconds. This achieves simultaneous dense forming of the flange neck and the annular flange area, and obtains a flange blank with an average dimensional tolerance of less than ±0.05mm and a density of not less than 98%. S4. Transfer the hot forged flange blank into a temperature-controlled resistance furnace for solution heat treatment. Set the temperature to 1000-1080℃ and hold for 1.5-3 hours. Then, use a segmented slow cooling process to slowly cool the blank to room temperature. The cooling rate is controlled at 20℃ / min in the first stage, 10℃ / min in the second stage, and no more than 5℃ / min in the final stage. S5. The heat-treated flange blank is machined in sequence, including double-end face turning, inner hole boring, outer diameter precision turning and end face precision milling. The machining allowance for each process is set to not exceed 0.1mm. The cutting tools are made of carbide or CBN material. The spindle runout is controlled within 0.005mm. The final internal and external dimensional tolerances are controlled within ±0.03mm, the end face perpendicularity error is less than 0.02mm, and the surface roughness Ra is less than 0.4μm. S6. The machined flange is subjected to low-temperature gas nitriding treatment. The treatment temperature range is 480-520℃, the ratio of ammonia to hydrogen in the atmosphere is 3:1, the flow rate is kept stable at 100-150mL / min, and the nitriding time is set to 4-6 hours. The surface nitrogen content gradient distribution is achieved through a three-stage treatment method of layer-by-layer heating, isothermal diffusion and constant temperature heat preservation. Finally, a nitrided layer with a thickness of 0.3-0.6mm and a hardness between 800-950HV is formed, which has high wear resistance and high fatigue strength.

2. The processing method for a high-strength weld neck flange according to claim 1, characterized in that, In the multi-pass roll forging, after each pass is completed, the forging billet is sent into the induction heating zone for a second heating. The temperature recovery is maintained in the range of 95% to 98% of the initial roll forging temperature, the induction frequency is set to 8 to 12 kHz, and the heating time is controlled in the range of 45 to 90 seconds.

3. The processing method for a high-strength weld neck flange according to claim 1, characterized in that, The S3 high-frequency precision hot forging process employs electromagnetic induction heating, setting the heating power ratio of the outer edge, middle section, and center of the mold to 3:2:1, respectively. The temperatures of each mold cavity area are stabilized at 880℃, 920℃, and 950℃, respectively. Simultaneously, the mold surface is coated with a high-temperature thermally conductive ceramic coating with a thickness of not less than 1.5mm. The forging rate is controlled at 0.8mm / s, the pressing duration is 40 seconds, and the pressure is maintained above 120MPa when the mold is closed. This results in a dense, defect-free neck structure, with the ring thickness error controlled within ±0.05mm, and a compression ratio of over 1.

8.

4. The processing method for a high-strength weld neck flange according to claim 3, characterized in that, After hot forging, the die is kept closed for 10 seconds, and a constant pressure load is applied to cause secondary micro-plastic deformation of the metal at high temperature. Then, it is cooled in an inert atmosphere of 0.3 MPa at a controlled rate of 10℃ / min until the temperature drops below 700℃. Then it is transferred to a slow cooling furnace to continue cooling, and finally a high-density flange forging with uniform structure, no stress concentration at the edges, and micro porosity of less than 0.1% is obtained.

5. The processing method for a high-strength butt-welding flange according to claim 1, characterized in that, The S4 segmented slow cooling system comprises three stages. In the first stage, the temperature is slowly reduced from 1080℃ to 800℃ using uniform temperature control within a holding furnace, allowing the austenite metal to fully transform into pearlite or bainite. In the second stage, the temperature is reduced from 800℃ to 500℃, switching to high-purity argon gas cooling, with the gas temperature maintained between room temperature and 300℃. Continuous ventilation is used to maintain a cooling rate of 15℃ / min. In the third stage, the temperature is reduced from 500℃ to room temperature, switching to intermittent water mist assisted cooling. The water mist particle size is controlled between 50 and 80 μm, the spray frequency is set to once every 10 seconds, and the total spraying time does not exceed 15 minutes. This establishes a stable microstructure evolution path, reduces the formation of internal stress, and ultimately obtains a heat-treated structure with a gentle hardness gradient and no precipitate agglomeration.

6. The processing method for a high-strength butt-welding flange according to claim 1, characterized in that, The S5 machining process employs a five-axis linkage machining technology. The cutting tool is a carbide circular arc tool with a diameter of 4-8mm. The spindle speed is set to 1500-1800rpm, and the feed rate is 0.2-0.4mm / rev. The machining path is generated by the CAD / CAM system with minimum interference trajectory and the trajectory overlap is set to be no less than 30%. The end face machining adopts an interlaced bidirectional milling mode. After each process, in-situ dimensional inspection is performed. Parts with errors exceeding ±0.03mm are re-finished. Finally, the inner hole size deviation of the flange is controlled within ±0.02mm, and the end face flatness is less than 0.01mm.

7. The processing method for a high-strength weld neck flange according to claim 1, characterized in that, The S6 nitriding treatment uses a dynamic alternating ammonia and hydrogen atmosphere process. In the initial stage, a mixed gas with a volume ratio of 3:1 is introduced and maintained for 1 hour. Then, every 60 minutes, the atmosphere is switched to pure hydrogen and kept at a constant temperature for 10 minutes. The original mixed gas ratio is then restored, and this cycle is repeated 6 times. The nitriding temperature is kept constant at 500℃, and the total treatment time does not exceed 6 hours. The thickness of the nitrided layer is controlled within the range of 0.35 to 0.5 mm by metallographic microscopy analysis.

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