Processing method of niobium-tungsten alloy forge piece

Abstract

The invention relates to a machining method of a niobium-tungsten alloy forge piece, and belongs to the technical field of high-temperature alloy precision forging. The method comprises the steps of bar heat treatment, free forging, die pre-forming, punching, repairing after punching and the like, particularly, a die provided with an R400 arc transition section is adopted in the punching process, two-section punching and multiple annealing processes are matched, and generation of ring cracks and through cracks is effectively restrained. A guide hole and a limiting structure are arranged before punching, so that the punching stability is improved, and a punching hardening area is repaired through polishing, acid pickling and three-section annealing after punching. The structural integrity, the size consistency and the high-temperature service reliability of the Nb521 alloy forge piece are remarkably improved, and the method is suitable for manufacturing precision components with high requirements for high temperature resistance and strength stability in the aerospace industry, the military industry and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature alloy forging and precision forming, and in particular relates to a processing method of niobium-tungsten alloy forgings. Background Art

[0002] Niobium-tungsten alloy, especially the Nb521 alloy registered under the national military standard (nominal composition: Nb5W2Mo1Zr0.08C), is a high-temperature, high-specific-strength alloy material that combines solid solution strengthening and dispersion precipitation strengthening. It has excellent high-temperature strength, high-temperature creep performance, good weldability and plasticity. In addition, its relatively low density makes it have important application value in key structural components such as aerospace propulsion systems and attitude and orbit control engines.

[0003] Currently, the forging process of Nb521 alloy still faces many technical challenges. The existing process mainly includes ingot melting, extrusion blanking, heat treatment, open die forging, punching forging and other steps. However, the following typical problems exist in the actual production process: If the height-to-diameter ratio of the upsetting forging is too large, it is easy to cause defects such as uneven deformation, work hardening of the head, slip accumulation in the middle, folding, and cracking; The medium-frequency induction heating temperature is relatively low, the material has great resistance to deformation, and the final forging temperature is insufficient, resulting in brittle cracking or incomplete forging of the billet; the punching expansion rate is too large, exceeding the ultimate strength of the material, often leading to annular cracking, causing the entire batch to be scrapped; the mold structure has stress concentration design defects, which easily induces axial cracks at the overlap of tensile stress and sharp angles of the mold; the cumulative deformation and work hardening of multiple punching fires are serious, and the final punching step is prone to form transgranular cracks, affecting the quality and pass rate of the finished product.

[0004] In summary, existing Nb521 alloy forgings suffer from poor process stability, difficulty in crack control, low material utilization, and a low first-pass inspection rate, severely restricting their mass application and engineering promotion. Therefore, a new forming process for special-shaped forgings is urgently needed. By adjusting the forging ratio, hole expansion ratio, heating / annealing process, and die design, the entire process can be optimized to significantly reduce the cracking rate and improve forging quality and production efficiency. Summary of the Invention

[0005] The present invention aims to provide a processing method suitable for Nb521 niobium tungsten alloy special-shaped forgings, and at the same time provide a matching punching die structure to solve the problems of existing Nb521 materials such as easy cracking, severe work hardening, low punching accuracy and high product scrap rate during forging and punching, thereby achieving a significant improvement in product dimensional stability, structural uniformity and high-temperature service reliability.

[0006] To achieve the above object, the present invention provides the following technical solutions: A method for processing a niobium-tungsten alloy forging, wherein the niobium-tungsten alloy is Nb521 and has a nominal composition of Nb5W2Mo1Zr0.08C, comprising the following steps: The following steps are involved: 1) Taking an extruded bar with a diameter of Φ134-145 mm, the extruded bar is subjected to heat straightening, grinding, pickling and annealing treatment, wherein the annealing temperature is 1450° C. and the holding time is 90-120 minutes; 2) Heat the annealed bar to 1350~1700℃, keep it warm for 4~5 minutes, and perform two-pass free forging to obtain a forging size of Φ160~165×300~360mm, with a forging height-to-diameter ratio of no more than 3; 3) After free forging, one end of the forging is preformed to form a positioning step and arc transition section that matches the mold cavity; 4) Treat the surface of the machined forging with an anti-oxidation coating, heat it to 1350~1700℃, and use a die for pre-forming forging; 5) After die forging, the forgings are polished, pickled, and annealed. The annealing includes three stages of annealing at 500-600°C for 30 minutes, 800-900°C for 30 minutes, and 1450°C for 90 minutes. The first stage (500-600°C for 30 minutes) is used to release the initial plastic deformation stress generated during forging or punching to avoid stress accumulation and cracking. The second stage (800-900°C for 30 minutes) promotes subgrain structure recovery and microstructure stabilization through medium-temperature holding, thereby improving nucleation uniformity in the area around the hole. The third stage (1450°C for 90 minutes) completes the high-temperature recrystallization process, resulting in grain refinement and complete recovery of the deformed microstructure. At the same time, it improves the high-temperature strength and ductility of the forging, providing a structural foundation for subsequent service. 6) Perform positioning reference processing on the forging before punching, drill a guide hole on the small end face formed by die forging, and chamfer the inner hole at the outlet of the corresponding large end face pre-punching hole; 7) Perform pre-punching with a hole diameter of Φ80~Φ90mm; the punching die used is provided with an R400 arc transition section at the height of H100~120mm; before each punching, heat the forging to 1350~1700℃ and keep it warm for 4~5 minutes; the end position of the punching is left 30~40mm away from the end face of the forging; 8) Grinding, pickling and annealing of forgings after pre-punching; 9) Perform final punching, with the final punching hole diameter being Φ130~Φ155mm. After punching is completed, the forging is pickled, machined, and annealed at 1450℃. An ultrasonic flaw detector is then used for quality inspection, and the defect equivalent is no greater than φ1.2mm.

[0007] Preferably, the heating temperature of the heat straightening process is 800-950° C., and the straightness of the forgings after straightening is controlled to be no greater than 3 mm per piece.

[0008] Preferably, the positioning step has a diameter of 149-149.5 mm and a height of 50-52 mm. The arc transition section has a height of 50-100 mm and an arc radius of R20. The positioning step, installed after free forging, cooperates with the die cavity to limit and position the die, ensuring the coaxial accuracy of the forging during die forging and punching, and preventing structural instability caused by die misalignment or axial expansion.

[0009] Preferably, the guide hole has a diameter of Φ45 ± 0.5 mm. The guide hole, located on the small end face of the forging, serves to guide the punch during punching, preventing tearing and eccentricity at the hole opening. The guide hole is not deep enough to penetrate the forging, and combined with the large end chamfer, it further reduces the risk of stress accumulation in the initial punching area.

[0010] Preferably, the pre-punched hole diameter is Φ80 mm, the final punched hole diameter is Φ135 mm, and the hole expansion rate is controlled to be no more than 50%.

[0011] Preferably, the punching die is provided with an arc transition section with a radius of R400 in the area H100-120 mm in the height direction of the forging.

[0012] Preferably, heating and insulation are performed for 4 to 5 minutes before each punching, and the punching end position is kept at a margin of 30 to 40 mm from the end face of the forging.

[0013] Preferably, a grinding, pickling and three-stage annealing treatment is performed between the pre-punching and the final punching to eliminate the work-hardened structure and residual stress.

[0014] The core innovation of this invention lies in the fact that, based on the physical properties of Nb521 niobium tungsten alloy material, namely "high-temperature strength, low plasticity, and stress sensitivity", a collaborative forging path with multi-level thermal processing control, step-by-step punching and release, and die stress optimization structure is constructed to achieve a high-stability manufacturing process for special-shaped forgings from ingots to finished products.

[0015] Specifically: During the free forging stage, by controlling the height-to-diameter ratio ≤3 and medium-frequency high-temperature forging, the internal deformation of the forging is ensured to be sufficient and the grains are refined, thus reducing the problems of slip accumulation and uneven cross-section deformation. During the punching stage, by setting Φ80-120mm pre-punching holes, controlling the hole expansion rate to ≤50%, and arranging an R400 arc transition section at the H100~120mm position of the punching die, the stress concentration area that is prone to forming annular cracks can be transitionally expanded, effectively reducing local tensile stress; Introducing medium temperature + high temperature annealing in the punching interval, combined with surface grinding and pickling, can eliminate the work hardening, oxidation cracks and latent lattice distortion induced by the first punching, providing a stable plastic foundation for the second punching; In the mold structure design, arc transition and limit control are used to ensure stable punching depth and uniform mold load, further preventing the formation of axial through-hole cracks. The mold is equipped with an R400 arc transition section at the H100-120mm position. This is because this area is subject to concentrated tensile stress during pre-punching and hole expansion, making it a prone location for annular cracks. The arc structure can effectively transfer the stress path, alleviate deformation gradients, and improve mold forming stability and hole integrity. The entire process uses multi-stage temperature control, processing path layering, and mechanical loading rationalization to suppress the formation and expansion of crack sources in niobium tungsten alloy from both the microstructure and macro stress path levels.

[0016] The solution of the present invention is not only suitable for the deformation characteristics of solid solution + dispersion strengthened niobium-based alloys such as Nb521, but can also be extended to other difficult-to-deform high-temperature alloy systems, and has broad engineering application value in aerospace, nuclear power, military industry and other fields.

[0017] Compared with the existing technology, the present invention has significant innovation and practicality in the processing technology of Nb521 niobium tungsten alloy special-shaped forgings. The specific advantages include: Greater stability in the forging process: By controlling the height-to-diameter ratio of the free forging roughing stage to no more than 3 and optimizing the medium-frequency heating temperature range to 1350~1700℃, the forging penetration is significantly improved; at the same time, the number of forging fires and center accumulation deformation are reduced, solving the common problems of center cracks, end folding and middle slip accumulation in the roughing stage.

[0018] Punching crack rate is significantly reduced: A segmented punching strategy is adopted, and an R400 arc transition structure is set in the H100~120mm area of ​​the punching die to effectively alleviate the problem of tensile stress concentration around the hole, prevent annular cracking and axial through-cracks caused by excessive hole expansion rate, and improve the safety and consistency of the punching process.

[0019] Improved tissue uniformity and plasticity: Surface grinding, pickling and multi-stage annealing are performed after each punching process, which can completely eliminate the work hardening layer, thermal cracks and micro-plastic damage caused by punching, making the internal grain structure of the forging more uniform and effectively reducing the risk of crack induction in the final punching process.

[0020] Improvement of yield rate and first-time qualified rate: The present invention arranges annealing and flaw detection processes multiple times before and after forging and before and after punching, supplemented by surface coating and anti-oxidation protection measures, to ensure the stability of the surface and internal quality of the forgings, improve material utilization, dimensional accuracy and batch consistency, greatly increase the first-time inspection pass rate, and is suitable for engineering batch stable production.

[0021] In summary, the present invention solves the key problems commonly faced by Nb521 high-performance niobium-tungsten alloy forgings in the processing of complex special-shaped components, such as high cracking rate, great forming difficulty and low yield rate, by establishing a complete process chain of "high-temperature controllable forging + step-by-step punching and sustained release + die stress optimization + post-punching tissue repair". It has broad engineering application prospects and promotion value. DETAILED DESCRIPTION Example

[0022] This example uses Nb521 niobium tungsten alloy (Nb5W2Mo1Zr0.08C) as raw material and completes a complete 42-step process from raw material mixing to finished product inspection according to the following fixed process parameters: 1) Powder mixing: Take niobium powder, tungsten powder and molybdenum powder and mix them in proportion. Control the oxygen content of the mixed powder to be ≤0.25%. Add carbon powder and press into shape after mixing. Sinter at 1150℃.

[0023] 2) Electron beam melting and assembly: The sintered block is prepared by multiple electron beam furnace melting (≥3 times), welding and bundling, and then assembled with zirconium plate semicircular electrodes.

[0024] 3) Melting and casting: Vacuum electron beam melting + water-cooled copper crucible casting into Φ210×500mm ingots.

[0025] 4) Sawing: Cut the material into the size of Φ200×500mm.

[0026] 5) Chamfer treatment: The extrusion end is processed into a 45°×2mm chamfer to avoid local stress concentration in the mold.

[0027] 6) Homogenization heat treatment: Keep at 1350℃ for 60min to eliminate structural segregation and internal stress.

[0028] 7) Anti-oxidation coating treatment: The ingot is heated to 80°C in a box-type resistance furnace, and a mixture of graphite emulsion, high-temperature glass powder and water glass is sprayed on the surface for surface protection before hot extrusion, mainly for anti-oxidation and lubrication.

[0029] 8) Extrusion heating: medium frequency induction heating to 4 stages (800°C → 1000°C → 1100°C → 1200°C), total heating time 45 minutes, including 2 minutes of holding time at 1200°C.

[0030] 9) Hot extrusion: Extrude the billet into Φ134mm bar.

[0031] 10) Sawing and shrinking the tail: remove the 80mm shrinking section at the tail.

[0032] 11) Hot straightening: Rapid forging and shaping at 800℃, controlling the straightness of the bar to ≤3mm / bar.

[0033] 12) Grinding: Use a bench grinder to grind the entire surface to remove the surface oxide layer and thermal cracks, revealing the original color of the metal.

[0034] 13) Pickling: Use a mixture of HF:HCl:HNO3=1:2:3 for pickling (concentration: HF 40%, HCl 36%, HNO3 68%).

[0035] 14) Annealing: vacuum furnace 1450℃, keep warm for 90min.

[0036] 15) Surface finishing: Manual marking and angle grinder to remove micro cracks, folds and oxide residues.

[0037] 16) NDT: Ultrasonic testing was performed using the CTS-2020 instrument, with a defect equivalent of φ1.2mm and no inclusions or cracks.

[0038] 17) Saw the crack section at the head: L=30mm, and cut off the tail according to the flaw detection line. The whole material is sawed into L=250mm specimens.

[0039] 18) Surface re-coating: Evenly apply Ta1350 high-temperature glass powder, which has high-temperature oxidation resistance and mold adhesion protection functions, helps to reduce mold wear and improve high-temperature stability.

[0040] 19) Medium frequency heating: 80KW induction heating to 1350℃, keep warm for 4 minutes. 20) Free forging roughing: 2-pass forging to Φ160×300mm, with a height-to-diameter ratio of 1.88.

[0041] 21) End pre-processing: Turn one end to Φ149mm × 50mm, arc transition H=50mm, and chamfer the end face.

[0042] 22) Second surface coating: Ta1350 glass powder.

[0043] 23) Medium frequency heating: Heat to 1350℃ and keep warm for 4 minutes.

[0044] 24) Die pre-forming forging: Use closed dies to form the contours of special-shaped forgings.

[0045] 25) Grinding and cleaning: Bench grinder removes thermal cracks and oxide scale after die forging.

[0046] 26) Pickling: Clean with mixed acid of the same proportion.

[0047] 27) Three-stage annealing: Use vacuum annealing furnace to carry out three-stage heat treatment in sequence: Step 1: Keep at 500℃ for 30 minutes to release the initial processing stress; Step 2: Keep at 800℃ for 30 minutes to stabilize the grain nucleation structure; Step 3: Keep at 1450℃ for 90 minutes to complete recrystallization and improve high-temperature mechanical properties.

[0048] 28) Reference hole machining: Using the small end face of the forging as a reference, drill a Φ45mm guide hole. The hole depth does not run through the entire length of the forging. It is used for subsequent punch positioning and punching start guide. At the same time, the punching exit position reserved on the large end face is chamfered to reduce stress concentration and the risk of ring cracking.

[0049] 29) Coating treatment: Re-coat Ta1350 high temperature glass powder.

[0050] 30) Medium frequency heating: Heat to 1350℃ and keep warm for 4 minutes.

[0051] 31) Φ80mm pre-punching: Use a die with an R400 arc transition at H110mm in the height direction for punching, and the bottom of the hole is 30mm from the end face.

[0052] 32) Grinding repair: Use a bench grinder to grind away cracks and a hand-held grinding wheel to trim the hole wall.

[0053] 33) Pickling: Cleaning with the same acid ratio.

[0054] 34) Annealing: The first stage: 500℃×30min; The second stage: 800℃×30min; The third stage: 1450℃×90min; Improve tissue and stress status.

[0055] 35) Re-coating: Re-spray Ta1350 high temperature glass powder.

[0056] 36) Reheating: Heat to 1350℃ and keep warm for 4 minutes.

[0057] 37) Φ135mm final punching: expand the hole to Φ135mm, and leave a 30mm safety margin from the end face at the end position of the punching.

[0058] 38) Pickling: Surface cleaning with mixed acid of the same proportion.

[0059] 39) Finished product machining: Fine-machining of shapes, holes, and chamfers to ensure that the product meets the requirements of the drawings.

[0060] 40) Final annealing: keep at 1450℃ for 90min to release residual stress.

[0061] 41) Final flaw detection: Use CTS-2020 ultrasonic instrument for detection, with a defect equivalent of φ1.2mm. If no defects equivalent to φ1.2mm or larger are found, the internal quality of the forging is judged to be qualified.

[0062] 42) Performance testing and inspection: Conduct full-scale testing on dimensional tolerance, appearance, metallography, hardness, room temperature / high temperature tensile strength, density, etc. Example

[0063] This example uses Nb521 niobium tungsten alloy (Nb5W2Mo1Zr0.08C) as raw material. The process path is the same as that of Example 1, but intermediate values ​​are used for key parameters to verify process stability and product consistency under different process windows: 1) Powder mixing: Mix niobium, tungsten and molybdenum powders, control the oxygen content to 0.20%, add carbon in proportion, press and sinter at 1150℃.

[0064] 2) Electron beam melting: After three EB melting steps, the electrodes are welded and bundled to form zirconium plate semicircular electrodes.

[0065] 3) Melting and casting: vacuum electron beam melting + water-cooled crucible casting into Φ210×500mm ingots.

[0066] 4) Sawing: Sawing according to the size of Φ205×480mm.

[0067] 5) Chamfer: The extruded end is chamfered with R20 arc.

[0068] 6) Homogenization heat treatment: 1400℃ for 90 minutes to eliminate cast stress and structural segregation.

[0069] 7) Coating spraying: Preheat the box-type resistance furnace to 100°C, spray the surface with a mixture of graphite emulsion + high-temperature glass powder + water glass, and apply it evenly by brushing.

[0070] 8) Extrusion heating: The medium frequency heating platform is set to: 800℃→1000℃→1100℃→1250℃, each platform is kept warm for 5~10 minutes, and the total heating time is 20~40 minutes.

[0071] 9) Extrusion: The ingot is extruded into Φ140mm bar.

[0072] 10) Sawing and shrinking the tail: remove 100mm of the tail.

[0073] 11) Heat straightening: 875℃ shaping, straightness ≤ 2mm / root.

[0074] 12) Grinding: Use a bench grinder to remove surface thermal cracks and oxide layers.

[0075] 13) Pickling: Use HF:HCl:HNO3=1:2:3 pickling, concentration: HF 40%, HCl 36%, HNO3 68%.

[0076] 14) Annealing: anneal in a vacuum furnace at 1450°C for 90 minutes.

[0077] 15) Surface finishing: Use an angle grinder to finish fine cracks and surface micro-folds.

[0078] 16) NDT: CTS-2020 ultrasonic instrument detection, defect equivalent φ1.2mm, no cracks or inclusions.

[0079] 17) Sawing crack section: Saw off the front 30mm of the ingot, cut off the tail to 100mm according to the flaw detection marking, and saw it into L=300mm sections.

[0080] 18) Surface re-coating: coating with Ta1350 high temperature glass powder.

[0081] 19) Medium frequency heating: Heat to 1500℃ and keep warm for 5 minutes.

[0082] 20) Free forging roughing: 2-fire roughing forging, controlled to Φ162×330mm, forging height-to-diameter ratio is 2.04.

[0083] 21) End pre-processing: The end size is Φ149.2mm × 51mm, the arc transition H=75mm, and the chamfer is 1×45°.

[0084] 22) Second coating: The surface is coated with high temperature glass powder.

[0085] 23) Heating: Medium frequency heating to 1500℃, keep warm for 5 minutes.

[0086] 24) Die pre-forming forging: Closed die forging is performed to form the external structure.

[0087] 25) Grinding treatment: The bench grinder removes the thermal cracks and peeling layers after forging to reveal the original color of the metal.

[0088] 26) Pickling: Use mixed acid of the same proportion to clean the hole and outer surface; 27) Three-stage annealing treatment: The first stage: 500℃ for 30 minutes; The second stage: 850℃ for 30 minutes; The third stage: keep warm at 1450℃ for 90 minutes.

[0089] 28) Reference drilling and chamfering: Using the small end face of the forging as a reference, drill a Φ45mm guide hole. The hole depth does not run through the entire length of the forging. It is used for subsequent punch positioning and punching start guide. At the same time, the punching exit position reserved on the large end face is chamfered to reduce stress concentration and the risk of ring cracking.

[0090] 29) Surface coating: spray Ta1350 glass powder again.

[0091] 30) Medium frequency heating: Heat to 1500℃ and keep warm for 5 minutes.

[0092] 31) Φ85mm pre-punching: Use a die with an R400 arc transition at the height of H100mm for punching, and control the punching terminal to be 35mm away from the end face of the forging.

[0093] 32) Grinding repair: Grind the inner wall cracks and sharp corners, use manual grinding wheel to deal with fine cracks, and remove the source of stress accumulation.

[0094] 33) Pickling: Use mixed acid with the same ratio.

[0095] 34) Three-stage annealing treatment: The first stage: 500℃×30min; The second stage: 850℃×30min; The third stage: 1450℃×90min.

[0096] 35) Second coating: Ta1350 high temperature glass powder coating.

[0097] 36) Reheating: Medium frequency heating to 1500℃, keep warm for 5 minutes.

[0098] 37) Φ130mm final punching: expand the hole to Φ130mm and maintain a safety margin of 35mm at the end.

[0099] 38) Pickling treatment: Use mixed acid of the same ratio to remove oxide scale and impurities inside and outside the hole.

[0100] 39) Finished product machining: Process end faces, chamfers, and hole finishing according to drawings.

[0101] 40) Final annealing treatment: keep at 1450℃ for 90min to release residual stress.

[0102] 41) Final flaw detection: Use CTS-2020 ultrasonic instrument for detection, with a defect equivalent of φ1.2mm. If no defects equivalent to φ1.2mm or larger are found, the internal quality of the forging is judged to be qualified.

[0103] 42) Performance testing and inspection: Conduct full-scale testing on dimensional tolerance, appearance, metallography, hardness, room temperature / high temperature tensile strength, density, etc. Example

[0104] This embodiment uses Nb521 niobium tungsten alloy (Nb5W2Mo1Zr0.08C) as raw material. Under the premise of maintaining the consistency of the 42-step process flow, the key process parameters are configured with high values ​​to verify the adaptability limit of the process of the present invention.

[0105] 1) Powder mixing: After mixing niobium, tungsten and molybdenum powders, the oxygen content is controlled at 0.25%, carbon is added and pressed into shape, and sintered at 1150℃ to form dense blocks.

[0106] 2) Electron beam melting: The sintered blocks are assembled into zirconium plate semicircular electrodes and purified by electron beam melting four times.

[0107] 3) Melting and casting: Use vacuum EB furnace melting + water-cooled crucible casting to form Φ210×550mm ingots.

[0108] 4) Sawing: Sawing into whole ingots according to the specifications of Φ210×550mm.

[0109] 5) Chamfer: R20 arc chamfer is used, and the arc radius is uniform.

[0110] 6) Homogenization heat treatment: Keep at 1450℃ for 120 minutes to completely eliminate the segregation of cast structure and residual stress.

[0111] 7) Anti-oxidation coating treatment: Preheat the box-type resistance furnace to 120℃ and spray the surface with a mixture of graphite emulsion + high-temperature glass powder + water glass.

[0112] 8) Extrusion heating: Use medium frequency induction heating platform 800→1000→1100→1300℃, keep warm at 1300℃ for 10 minutes, and the total heating time is 45 minutes.

[0113] 9) Hot extrusion: Extruded into Φ145mm rods with smooth surface and uniform structure.

[0114] 10) Sawing and shrinking the tail: Cut off the 120mm shrinking section of the tail to avoid residual deformation area.

[0115] 11) Hot straightening: 950℃ straightening, straightness after shaping ≤2mm / root

[0116] 12) Grinding: Use a bench grinder to finely grind to remove thermal cracks and oxide scale, revealing the original metal color on the surface.

[0117] 13) Pickling: HF:HCl:HNO3 volume ratio 1:2:3, HF concentration 42%, HCl 38%, HNO3 68%, pickling time controlled at 5~8 minutes.

[0118] 14) Annealing: Annealing in a vacuum annealing furnace at 1450°C for 120 minutes until the structure is fully restored.

[0119] 15) Fine-tuning: Scribe and inspect surface defects, remove cracks, folds, and foreign matter residues.

[0120] 16) NDT: CTS-2020 ultrasonic instrument detection, defect equivalent φ1.2mm, no cracks or inclusions.

[0121] 17) Sawing defective sections: remove 30mm of cracked section at the head of the ingot, and cut off 120mm of the tail according to the flaw detection line. The length of the whole material is controlled to 520mm.

[0122] 18) Surface coating: coated with Ta1350 high temperature glass powder to ensure high temperature forging and anti-oxidation.

[0123] 19) Medium frequency heating: 180KW induction heating, temperature rises to 1700℃, keep warm for 5 minutes.

[0124] 20) Free forging roughing: 2-pass forging to Φ165×360mm, height-to-diameter ratio 2.18.

[0125] 21) End machining: Process the end to Φ149.5mm × 52mm, arc transition H=100mm, end face chamfer 2×45°.

[0126] 22) Re-coating: Repeat Ta1350 coating to improve the oxidation resistance of the mold contact surface.

[0127] 23) Mold heating: Medium frequency heating to 1700℃, keep warm for 5 minutes and then perform mold pre-forming forging.

[0128] 24) Die forging: Die forging a complete special-shaped contour, including multiple steps and transition sections.

[0129] 25) Grinding treatment: Grind the entire surface of the die forging to remove the peeling layer, hot spots and micro cracks.

[0130] 26) Pickling: Use mixed acid of the same proportion to clean the hole and outer surface; 27) Three-stage annealing treatment: The first stage: 600℃ for 30 minutes; The second stage: 900℃ for 30 minutes; The third stage: keep warm at 1450℃ for 90 minutes.

[0131] 28) Machining hole reference: Using the small end face of the forging as the reference, drill a Φ45mm guide hole. The hole depth does not run through the entire length of the forging. It is used for subsequent punch positioning and punching start guide. At the same time, the punching exit position reserved on the large end face is chamfered to reduce stress concentration and the risk of ring cracking.

[0132] 29) Re-coating with glass powder: The entire surface is coated with Ta1350 protective layer, and the punching area is especially thickened.

[0133] 30) Heating: Medium frequency heating to 1700℃, keep warm for 5 minutes.

[0134] 31) Φ90mm pre-punching: Use a die with an R400 arc transition at the height of H120mm for punching, and control the punching terminal to be 40mm away from the end face of the forging.

[0135] 32) Grinding and repair after punching: Grind away the cracks and burrs caused by punching, and manually repair the fine cracks on the edges.

[0136] 33) Pickling treatment: Mixed acid treatment with the same ratio to remove deep oxide layer.

[0137] 34) Three-stage annealing treatment: The first stage: 600℃×30min; The second stage: 900℃×30min; The third stage: 1450℃×90min.

[0138] 35) Re-spray: Ta1350 glass powder anti-oxidation layer.

[0139] 36) Reheating: Medium frequency heating to 1700℃, keep warm for 5 minutes.

[0140] 37) Φ135mm final punching: the arc transition of the mold guides the hole expansion, and the punching end leaves a 40mm margin.

[0141] 38) Pickling treatment: Use mixed acid of the same proportion to clean the residue, oil film and oxide layer on the expansion surface.

[0142] 39) Machining: Process end faces, through holes, tolerances and connection structures according to drawings.

[0143] 40) Final annealing: 1450℃ for 90min to release residual stress.

[0144] 41) Final flaw detection: Use CTS-2020 ultrasonic instrument for detection, with a defect equivalent of φ1.2mm. If no defects equivalent to φ1.2mm or larger are found, the internal quality of the forging is judged to be qualified.

[0145] 42) Performance testing and inspection: Conduct full-scale testing on dimensional tolerance, appearance, metallography, hardness, room temperature / high temperature tensile strength, density, etc.

Claims

1. A method for processing a niobium-tungsten alloy forging, wherein the niobium-tungsten alloy is Nb521, characterized in that: The following steps are involved: 1) Taking an extruded bar with a diameter of Φ134-145 mm, the extruded bar is subjected to heat straightening, grinding, pickling and annealing treatment, wherein the annealing temperature is 1450° C. and the holding time is 90-120 minutes; 2) Heat the annealed bar to 1350~1700℃, keep it warm for 4~5 minutes, and perform two-pass free forging to obtain a forging size of Φ160~165×300~360mm, with a forging height-to-diameter ratio of no more than 3; 3) After free forging, one end of the forging is preformed to form a positioning step and arc transition section that matches the mold cavity; 4) Treat the surface of the machined forging with an anti-oxidation coating, heat it to 1350~1700℃, and use a die for pre-forming forging; 5) After die forging, the forging is polished, pickled and annealed, wherein the annealing includes three stages of annealing at 500-600°C for 30 minutes, 800-900°C for 30 minutes and 1450°C for 90 minutes; 6) Perform positioning reference processing on the forging before punching, drill a guide hole on the small end face formed by die forging, and chamfer the inner hole at the outlet of the corresponding large end face pre-punching hole; 7) Perform pre-punching with a hole diameter of Φ80~Φ90mm; the punching die used is provided with an R400 arc transition section at the height of H100~120mm; before each punching, heat the forging to 1350~1700℃ and keep it warm for 4~5 minutes; the end position of the punching is left 30~40mm away from the end face of the forging; 8) Grinding, pickling and annealing of forgings after pre-punching; 9) Perform final punching, with the final punching hole diameter being Φ130~Φ155mm. After punching is completed, the forging is pickled, machined, and annealed at 1450℃. An ultrasonic flaw detector is then used for quality inspection, and the defect equivalent is no greater than φ1.2mm.

2. The method according to claim 1, characterized in that The heating temperature of the heat straightening process is 800-950° C., and the straightness of the forgings after straightening is controlled to be no greater than 3 mm per piece.

3. The method according to claim 1, characterized in that The diameter of the positioning step is 149-149.5 mm, and the height is 50-52 mm. The height of the arc transition section is 50-100 mm, and the arc radius is R20.

4. The method according to claim 1, wherein The diameter of the guide hole is Φ45±0.5mm.

5. The method according to claim 1, wherein The pre-punched hole diameter is Φ80 mm, the final punched hole diameter is Φ135 mm, and the hole expansion rate is controlled to be no more than 50%.

6. The method according to claim 1, characterized in that The punching die is provided with an arc transition section with a radius of R400 in the area H100~120mm in the height direction of the forging.

7. The method according to claim 1, characterized in that Heat and keep warm for 4 to 5 minutes before each punching, and keep a margin of 30 to 40 mm from the end face of the forging at the end of the punching.

8. The method according to claim 1, characterized in that Between the pre-punching and the final punching, a grinding, pickling and three-stage annealing treatment are performed to eliminate the work hardening structure and residual stress.