A method for processing a niobium-tungsten alloy forging

Abstract

The present application relates to a kind of processing methods of niobium-tungsten alloy forgings, belong to high-temperature alloy precision forging technical field.The method includes bar heat treatment, free forging, die preforming, punching and repairing after punching and other steps, especially in the punching process, the die with R400 arc transition section is used, and two sections punching and multiple annealing process are matched, effectively inhibit the generation of ring crack and through crack.Guiding hole and limiting structure are set before punching, which improves the stability of punching, and the hardened area is repaired by grinding, pickling and three-stage annealing after punching.The present application significantly improves the structural integrity, dimensional consistency and high-temperature service reliability of Nb521 alloy forgings, and is suitable for aerospace, military and other high-precision components manufacturing with high requirements for high-temperature resistance and strength stability.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy forging and precision forming technology, and particularly relates to a processing method for niobium-tungsten alloy forgings. Background Technology

[0002] Niobium-tungsten alloys, especially the Nb521 alloy (nominal composition Nb5W2Mo1Zr0.08C) registered with national military standards, are high-temperature, high-specific-strength alloy materials that combine solid solution strengthening and dispersion precipitation strengthening. They have excellent high-temperature strength, high-temperature creep performance, good weldability and plasticity. In addition, their relatively low density makes them of great application value in key structural components such as aerospace propulsion systems and attitude control engines.

[0003] Currently, the forging process of Nb521 alloy still faces many technical challenges. Existing process routes mainly include ingot melting, extrusion forging, heat treatment, free forging, and punching forging, but the following typical problems exist in actual production: If the height-to-diameter ratio is too large during upsetting forging, it can easily cause defects such as uneven deformation, work hardening at the head, slippage and accumulation in the middle, folding, and cracking. The medium-frequency induction heating temperature is too low, the material deformation resistance is high, and the forging final temperature is insufficient, resulting in brittle cracking or incomplete forging of the billet; the punching expansion rate is too high, exceeding the material's ultimate strength, often leading to circumferential cracking and scrapping the entire batch; the mold structure has a design defect of stress concentration, which can easily induce axial cracks at the point where tensile stress overlaps with the sharp angle of the mold; the cumulative deformation and work hardening from multiple punching cycles are severe, and the final punching step is prone to forming transgranular cracks, affecting the quality and pass rate of the finished product.

[0004] In summary, existing Nb521 alloy forging processes suffer from poor stability, difficulty in crack control, low material utilization, and low first-pass yield, severely hindering their mass application and engineering promotion. Therefore, there is an urgent need to propose a novel forming path for irregularly shaped forgings. By adjusting the forging ratio, hole expansion rate, heating / annealing process, and die design, the entire process can be optimized to significantly reduce cracking rate and improve forging quality and production efficiency. Summary of the Invention

[0005] This invention aims to provide a processing method for Nb521 niobium-tungsten alloy irregular forgings, and to provide a matching punching die structure to solve the problems of easy cracking, severe work hardening, low punching accuracy and high product scrap rate of existing Nb521 materials during forging and punching, thereby achieving a significant improvement in product dimensional stability, microstructure uniformity and high-temperature service reliability.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for processing a niobium-tungsten alloy forging, wherein the niobium-tungsten alloy is Nb521 with a nominal composition of Nb5W2Mo1Zr0.08C, includes the following steps: Includes the following steps: 1) Take extruded bars with a diameter of Φ134~145mm, and perform hot straightening, grinding, pickling and annealing on the extruded bars. The annealing temperature is 1450℃ and the holding time is 90~120 minutes. 2) Heat the annealed bar stock to 1350~1700℃, hold for 4~5 minutes, and perform two-stage free forging to obtain forgings with dimensions of Φ160~165×300~360mm and a forging height-to-diameter ratio not greater than 3. 3) After free forging, one end of the forging is pre-formed and machined to form a positioning step and a rounded transition section that fits into the mold cavity; 4) Apply an anti-oxidation coating to the surface of the machined forgings, heat them to 1350~1700℃, and perform pre-forming forging using a die; 5) After die forging, the forging is ground, pickled, and annealed. The annealing includes three stages: 500~600℃×30 minutes, 800~900℃×30 minutes, and 1450℃×90 minutes. The first stage (500~600℃×30 minutes) is used to release the initial plastic deformation stress generated during forging or punching, and to avoid stress accumulation that induces cracks. The second stage (800~900℃×30 minutes) promotes the recovery of subgrain structure and the stabilization of microstructure through medium-temperature holding, and improves the uniformity of nucleation in the peri-hole area. The third stage (1450℃×90 minutes) completes the high-temperature recrystallization process, refines the grains, fully restores the deformed microstructure, and improves the high-temperature strength and ductility of the forging, providing a structural basis for subsequent service. 6) Before punching, the forging is machined to make a positioning reference. A guide hole is drilled on the small end face formed by die forging. The inner hole is chamfered at the pre-punching outlet of the corresponding large end face. 7) Perform pre-punching with a hole diameter of Φ80~Φ90mm; the punching die used has an R400 arc transition section at H100~120mm in the height direction; before each punching, heat the forging to 1350~1700℃ and hold for 4~5 minutes; leave a 30~40mm margin from the end face of the forging at the punching end position. 8) After pre-punching, the forgings are ground, pickled, and annealed; 9) Perform final punching with a hole diameter of Φ130~Φ155mm. After punching, pickle, machine and anneal at 1450℃ for the forging, and use an ultrasonic flaw detector for quality inspection. The defect equivalent is not greater than φ1.2mm.

[0007] Preferably, the heating temperature of the hot straightening process is 800~950℃, and the straightness of the forging after straightening is controlled to be no more than 3mm / piece.

[0008] Preferably, the diameter of the positioning step is 149~149.5mm and the height is 50~52mm, the height of the arc transition section is 50~100mm, and the arc radius is R20. The positioning step, set after free forging, cooperates with the mold cavity to limit and position the mold, ensuring the coaxial accuracy of the forging during die forging and punching, and preventing structural instability caused by mold misalignment or axial deviation leading to hole enlargement.

[0009] Preferably, the diameter of the guide hole is Φ45±0.5mm. The guide hole is located on the small end face of the forging and is used to guide the punch during punching to avoid tearing and eccentricity at the hole opening. The guide hole does not penetrate the forging and, in conjunction with the chamfered structure at the large end, further reduces the risk of stress accumulation in the initial stamping zone.

[0010] Preferably, the pre-punched hole diameter is Φ80mm, the final punched hole diameter is Φ135mm, and the hole expansion rate is controlled to be no more than 50%.

[0011] Preferably, the punching die has an arc transition section with a radius of R400 in the H100~120mm region of the forging height direction.

[0012] Preferably, the workpiece is heated and kept warm for 4-5 minutes before each punching, and the punching end position is left with a margin of 30-40mm from the end face of the forging.

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

[0014] The core innovation of this invention lies in the fact that, based on the physical characteristics of Nb521 niobium-tungsten alloy material, namely "high temperature strength, low plasticity, and stress sensitivity", a collaborative forging path with multi-level hot working control, step-by-step punching slow release, and mold stress optimization structure is constructed to realize a highly stable manufacturing process for irregular forgings from ingots to finished products.

[0015] Specifically: During the free forging stage, by controlling the height-to-diameter ratio to ≤3 and using medium-frequency high-temperature forging, we ensure that the internal deformation of the forging is sufficient and the grains are refined, thereby reducing the problems of slip accumulation and uneven cross-sectional deformation. During the punching stage, by setting Φ80-120mm pre-punching holes, controlling the hole expansion rate to ≤50%, and setting R400 arc transition sections at H100~120mm of the punching die, the stress concentration area that is prone to forming annular cracks can be gradually expanded, effectively reducing local tensile stress. Introducing medium-temperature + high-temperature annealing during the punching interval, combined with surface grinding and pickling, can eliminate work hardening, oxidation cracks and hidden lattice distortion induced by the first punching, providing a stable plastic basis for the second punching. In the mold structure design, the use of arc transition and limit control ensures stable punching depth and uniform mold load, further preventing the generation of axial through cracks. The mold is equipped with an R400 arc transition section at the H100~120mm position because this area is subject to tensile stress concentration during pre-punching and hole expansion, and is a place where annular cracks are prone to occur. The arc structure can effectively transfer stress path, alleviate deformation gradient, and improve mold forming stability and hole integrity. The entire process employs multi-stage temperature control, layered processing paths, and rationalized mechanical loading to suppress the formation and propagation of cracks in niobium-tungsten alloys from both microstructure and macro-stress path perspectives.

[0016] The solution of this invention is not only suitable for the deformation characteristics of solid solution and 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 existing technologies, this invention has significant innovation and practicality in the processing of Nb521 niobium-tungsten alloy irregular forgings, with specific advantages including: The forging process is more stable: By controlling the height-to-diameter ratio to be no greater than 3 during the free forging upsetting stage and optimizing the medium-frequency heating temperature range to 1350~1700℃, the forging penetration was significantly improved. At the same time, the number of forging passes and the central accumulation deformation were reduced, solving common problems in the upsetting stage such as central cracks, end folds, and central slip accumulation.

[0018] The rate of punching cracks was 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 circumferential cracking and axial through cracking caused by excessive hole expansion ratio, and improve the safety and consistency of the punching process.

[0019] Improved tissue uniformity and plasticity: Each punching process includes surface grinding, pickling, and multi-stage annealing, which can completely eliminate the work-hardened layer, hot cracks, and microscopic plastic damage caused by punching, making the internal grain structure of the forging more uniform and effectively reducing the risk of crack induction during the final punching process.

[0020] Improved yield and first pass rate: This invention incorporates multiple annealing and flaw detection processes before and after forging and punching, supplemented by surface coating and anti-oxidation protection measures, to ensure stable surface and internal quality of forgings, improve material utilization, dimensional accuracy and batch consistency, significantly increase first-pass yield, and is suitable for stable mass production in engineering.

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

[0022] This embodiment uses Nb521 niobium-tungsten alloy (Nb5W2Mo1Zr0.08C) as raw material and completes the entire 42-step processing flow from raw material mixing to finished product inspection according to the following fixed process parameters: 1) Powder mixing: Niobium powder, tungsten powder and molybdenum powder are mixed in proportion, and the oxygen content after mixing is controlled to be ≤0.25%. After adding carbon powder and adjusting, the mixture is pressed into shape and sintered at 1150℃.

[0023] 2) Electron beam melting and assembly: The sintered block is melted in an electron beam furnace multiple times (≥3 times), and then welded and bundled before being assembled with the zirconium plate semi-circular electrode.

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

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

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

[0027] 6) Homogenization heat treatment: Hold at 1350℃ for 60 minutes to eliminate 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-stage platform (800℃→1000℃→1100℃→1200℃), total heating time is 45 minutes, of which the holding time at 1200℃ is 2 minutes.

[0030] 9) Hot extrusion: Extruding the billet into Φ134mm bars.

[0031] 10) Sawing and tail reduction: Remove the 80mm tail section.

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

[0033] 12) Grinding: The entire surface of the metal is ground by a bench grinder to remove the oxide layer and hot cracks, revealing the metal's original color.

[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 at 1450℃, hold for 90 minutes.

[0036] 15) Surface finishing: Manual scribing and angle grinder removal of micro-cracks, folds, and oxide residues.

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

[0038] 17) Sawing the head crack section: L=30mm, and cutting off the tail section according to the flaw detection marking, and sawing the whole material into a specimen with L=250mm.

[0039] 18) Surface recoating: Apply Ta1350 high-temperature glass powder evenly by brushing. It has the functions of anti-oxidation at high temperature and mold adhesion protection, which helps to reduce mold wear and improve high-temperature stability.

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

[0041] 21) End pre-machining: Turn one end to Φ149mm × 50mm, with a circular 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 hold for 4 minutes.

[0044] 24) Pre-forming forging using molds: using closed molds to form the outline of irregular forgings.

[0045] 25) Grinding and cleaning: Use a bench grinder to remove hot cracks and oxide scale after forging.

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

[0047] 27) Three-stage annealing: Three stages of heat treatment are performed sequentially using a vacuum annealing furnace. Step 1: Hold at 500℃ for 30 minutes to release initial processing stress; Step 2: Hold at 800℃ for 30 minutes to stabilize the grain nucleation structure; Step 3: Hold at 1450℃ for 90 minutes to complete recrystallization and improve high-temperature mechanical properties.

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

[0049] 29) Coating treatment: Recoat with Ta1350 high-temperature glass powder.

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

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

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

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

[0054] 34) Annealing: First stage: 500℃ × 30min; Second stage: 800℃×30min; Third stage: 1450℃×90min; Improve the organization and stress state.

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

[0056] 36) Reheat: Heat to 1350℃ and hold for 4 minutes.

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

[0058] 38) Pickling: Surface cleaning treatment using mixed acid with the same ratio.

[0059] 39) Finished product machining: finish the shape, openings, and chamfers to make the product meet the requirements of the drawings.

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

[0061] 41) Final flaw detection: Use CTS-2020 ultrasonic instrument to detect defects with an equivalent value of φ1.2mm. If no defects with an equivalent value of φ1.2mm or greater are found, the internal quality of the forging is deemed to be qualified.

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

[0063] This embodiment uses Nb521 niobium-tungsten alloy (Nb5W2Mo1Zr0.08C) as raw material, and the process route is the same as in Example 1, but the key parameters use intermediate values ​​to verify the process stability and product consistency under different process windows: 1) Mixed powder: Niobium, tungsten and molybdenum powders are mixed, the oxygen content is controlled at 0.20%, carbon is added in proportion and then pressed and sintered at 1150℃.

[0064] 2) Electron beam melting: After three EB melting processes, the electrodes are welded and bundled together to form a zirconium plate semi-circular electrode.

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

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

[0067] 5) Chamfer: The extrusion end is treated with an R20 rounded chamfer.

[0068] 6) Homogenization heat treatment: Hold at 1400℃ for 90 minutes to eliminate as-cast stress and microstructure segregation.

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

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

[0071] 9) Extrusion: Extruding the ingot into Φ140mm bars.

[0072] 10) Sawing and tail reduction: Remove 100mm of the tail.

[0073] 11) Hot straightening: 875℃ straightening, straightness ≤2mm / piece.

[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 for pickling, with the following concentrations: HF 40%, HCl 36%, HNO3 68%.

[0076] 14) Annealing: Anneal in a vacuum furnace at 1450℃ and hold for 90 minutes.

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

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

[0079] 17) Sawing the cracked section: Sawing off the front end of the ingot 30mm, cutting off the tail end according to the flaw detection marking line to control 100mm, and sawing it into L=300mm sections.

[0080] 18) Surface recoating: 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 upsetting: Two-stage upsetting forging, controlled to Φ162×330mm, with a forging height-to-diameter ratio of 2.04.

[0083] 21) End pre-processing: The dimensions of the processed end are Φ149.2mm × 51mm, with a rounded transition H=75mm and a chamfer of 1×45°.

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

[0085] 23) Heating: Use medium frequency heating to reach 1500℃ and keep warm for 5 minutes.

[0086] 24) Die preforming forging: Closed die forging is carried out to form the external shape and structure.

[0087] 25) Grinding treatment: Bench grinder removes post-forging hot cracks and spalling layers, revealing the original metal color.

[0088] 26) Pickling: Clean the holes and outer surfaces with a mixed acid of the same ratio; 27) Three-stage annealing process: First stage: Keep warm at 500℃ for 30 minutes; Second stage: Keep warm at 850℃ for 30 minutes; 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 penetrate the entire length of the forging and is used for subsequent punch positioning and punching initiation. At the same time, chamfer the reserved punching exit position on the large end face 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: Punching is performed using a die with an R400 arc transition at H100mm in the height direction, and the distance between the punching end and the end face of the forging is controlled to be 35mm.

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

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

[0095] 34) Three-stage annealing process: First stage: 500℃ × 30min; Second stage: 850℃×30min; Third stage: 1450℃×90min.

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

[0097] 36) Reheat: Heat to 1500℃ using medium frequency and keep warm for 5 minutes.

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

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

[0100] 39) Finished product machining: Machining end faces, chamfers, and smoothing holes according to drawings.

[0101] 40) Final annealing: Hold at 1450℃ for 90 minutes to release residual stress.

[0102] 41) Final flaw detection: Use CTS-2020 ultrasonic instrument to detect defects with an equivalent value of φ1.2mm. If no defects with an equivalent value of φ1.2mm or greater are found, the internal quality of the forging is deemed to be qualified.

[0103] 42) Performance testing and inspection: Conduct full-item testing including dimensional tolerances, 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. While maintaining the consistency of the 42-step process flow, high values ​​are used for key process parameters to verify the adaptability limit of the process of this invention.

[0105] 1) Mixed powder: Niobium, tungsten and molybdenum powders are mixed and the oxygen content is controlled at 0.25%. After carbon adjustment, they are pressed into shape and sintered into dense blocks at 1150℃.

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

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

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

[0109] 5) Chamfer: The chamfer is made of R20 rounded arc with uniform radius.

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

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

[0112] 8) Extrusion heating: Use a medium-frequency induction heating platform with temperatures ranging from 800 to 1000 to 1100 to 1300 degrees Celsius. Maintain the temperature at 1300 degrees Celsius for 10 minutes. The total heating time is 45 minutes.

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

[0114] 10) Sawing and tail reduction: Cut off the 120mm tail reduction section to avoid leaving deformed areas.

[0115] 11) Hot straightening: Straighten at 950℃, and the straightness after shaping is ≤2mm / piece.

[0116] 12) Grinding: Use a bench grinder to finely grind away the heat cracks and oxide scale, revealing the 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: Vacuum annealing furnace annealing, 1450℃, hold for 120 minutes, until the tissue is fully restored.

[0119] 15) Fine finishing: Marking and inspecting surface defects, removing cracks, folds, and foreign matter residue.

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

[0121] 17) Sawing defect section: Remove 30mm of the cracked section at the head of the ingot, and cut off 120mm of the tail according to the flaw detection marking. The length of the whole piece is controlled to 520mm.

[0122] 18) Surface coating: Coated with Ta1350 high-temperature glass powder to ensure oxidation resistance during high-temperature forging.

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

[0124] 20) Free forging roughing: Forging in 2 passes to Φ165×360mm, with a height-to-diameter ratio of 2.18.

[0125] 21) End machining: Machining the end to Φ149.5mm × 52mm, with a rounded transition H=100mm, and a chamfer of 2×45° on the end face.

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

[0127] 23) Die heating: Medium frequency heating to 1700℃, hold for 5 minutes and then perform die pre-forming forging.

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

[0129] 25) Grinding treatment: Grind the entire surface of the forged die to remove the spalling layer, hot spots, and microcracks.

[0130] 26) Pickling: Clean the holes and outer surfaces with a mixed acid of the same ratio; 27) Three-stage annealing process: First stage: Keep warm at 600℃ for 30 minutes; Second stage: Keep warm at 900℃ for 30 minutes; Third stage: Keep warm at 1450℃ for 90 minutes.

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

[0132] 29) Apply glass powder again: Coat the entire surface with a Ta1350 protective layer, with a special thickening in the perforated area.

[0133] 30) Heating: Use medium frequency heating to reach 1700℃ and keep warm for 5 minutes.

[0134] 31) Φ90mm pre-punching: Punching is performed using a die with an R400 arc transition at H120mm in the height direction, and the distance between the punching end and the end face of the forging is controlled to be 40mm.

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

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

[0137] 34) Three-stage annealing process: First stage: 600℃ × 30min; Second stage: 900℃×30min; Third stage: 1450℃×90min.

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

[0139] 36) Reheat: Heat to 1700℃ using medium frequency and keep warm for 5 minutes.

[0140] 37) Φ135mm final punch: The die is rounded to guide the expansion of the hole, and a 40mm edge is left at the end of the punching.

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

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

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

[0144] 41) Final flaw detection: Use CTS-2020 ultrasonic instrument to detect defects with an equivalent value of φ1.2mm. If no defects with an equivalent value of φ1.2mm or greater are found, the internal quality of the forging is deemed to be qualified.

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

Claims

1. A method for processing niobium-tungsten alloy forgings, wherein the niobium-tungsten alloy is Nb521, characterized in that, Includes the following steps: 1) Take extruded bars with a diameter of Φ134~145mm, and perform hot straightening, grinding, pickling and annealing on the extruded bars. The annealing temperature is 1450℃ and the holding time is 90~120 minutes. 2) Heat the annealed bar stock to 1350~1700℃, hold for 4~5 minutes, and perform two-stage free forging to obtain forgings with dimensions of Φ160~165×300~360mm and a forging height-to-diameter ratio not greater than 3. 3) After free forging, one end of the forging is pre-formed and machined to form a positioning step and a rounded transition section that fits into the mold cavity; 4) Apply an anti-oxidation coating to the surface of the machined forgings, heat them to 1350~1700℃, and perform pre-forming forging using a die; 5) After die forging, the forging is ground, pickled and annealed. The annealing includes three stages of annealing: 500~600℃×30 minutes, 800~900℃×30 minutes and 1450℃×90 minutes. 6) Before punching, the forging is machined to make a positioning reference. A guide hole is drilled on the small end face formed by die forging. The inner hole is chamfered at the pre-punching outlet of the corresponding large end face. 7) Perform pre-punching with a hole diameter of Φ80~Φ90mm; the punching die used has an R400 arc transition section at H100~120mm in the height direction; before each punching, heat the forging to 1350~1700℃ and hold for 4~5 minutes; leave a 30~40mm margin from the end face of the forging at the punching end position. 8) After pre-punching, the forgings are ground, pickled, and annealed; 9) Perform final punching with a hole diameter of Φ130~Φ155mm. After punching, pickle, machine, and anneal at 1450℃ for the forging. Use an ultrasonic flaw detector for quality inspection. The ultrasonic defect equivalent should not exceed φ1.2mm.

2. The method according to claim 1, characterized in that, The heating temperature of the hot straightening process is 800~950℃, and the straightness of the forgings after straightening is controlled to be no more than 3mm / piece.

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

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

5. The method according to claim 1, characterized in that, The pre-punched hole diameter is Φ80mm, the final punched hole diameter is Φ135mm, and the hole expansion rate is controlled to not exceed 50%.

6. The method according to claim 1, characterized in that, Between the pre-punching and final punching stages, a grinding, pickling, and three-stage annealing process is performed to eliminate work-hardened structures and residual stress.