A heat treatment process for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy pipes

Abstract

This disclosure provides a microstructure control hot working process for difficult-to-deform nickel-based superalloy tubing, comprising: obtaining a master alloy ingot using a double-melting process with raw materials of standard proportions of each element in the difficult-to-deform nickel-based superalloy; homogenizing and annealing the master alloy ingot to obtain a forged ingot; subjecting the annealed forged ingot to multiple thermomechanical treatments along the axial direction to obtain a fine-grained rod; grinding and cleaning the surface oxide scale of the fine-grained rod, followed by cladding and hot extrusion to obtain a hot-extruded tubing; subjecting the hot-extruded tubing to solution treatment and two-step aging treatment to obtain a heat-treated tubing; and subjecting the heat-treated tubing to oxide scale grinding, sandblasting, fine grinding of the inner surface, and polishing of the outer surface, followed by ultrasonic flaw detection of the finished product. This microstructure control hot working process, combining forged ingot and cladding hot extrusion, effectively improves the microstructure and properties of the alloy tubing, resulting in tubing with fine grains, uniform microstructure, and high thermal strength, meeting the requirements for hot-end components in aerospace equipment.

Description

Technical Field

[0001] This disclosure belongs to the field of high-temperature alloy materials technology, specifically relating to a hot working process for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy pipes. Background Technology

[0002] Tubular components are key parts of high-performance aircraft, widely used in hydraulic, fuel, and environmental control systems in aerospace applications. Their performance directly impacts the airworthiness and safety of the aircraft. These components operate in harsh environments, requiring them to withstand high temperatures, high pressures, and high-frequency vibrations. Their inner walls are also frequently subjected to long-term corrosion from oil and gas media. The continuously increasing performance requirements of aircraft have placed stricter demands on the materials used in critical piping systems. Therefore, using high-temperature-resistant, difficult-to-deform nickel-based superalloys to manufacture high-performance critical piping components for high-temperature service holds great promise.

[0003] These high-temperature alloys exhibit good high-temperature strength and creep life in the 650-750℃ range. However, their high alloying degree and high content of precipitation strengthening phases lead to reduced thermoplasticity, increased deformation resistance, and a narrowed hot working window, making hot working difficult and the microstructure hard to control. High-temperature alloy pipes are often produced by hot extrusion with a cladding process. This process has a greater deformation amount and rate than forging, but it cannot achieve optimal pipe microstructure and properties for the aforementioned high-strength high-temperature alloys. Summary of the Invention

[0004] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a hot working process for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy tubing.

[0005] This disclosure provides a hot working process for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy tubing, the hot working process including: Raw materials were added according to the standard proportions of each element in the difficult-to-deform nickel-based superalloy, and a double melting process was used to obtain the master alloy ingot. The master alloy ingot is subjected to homogenization annealing to obtain ingot forging; The annealed ingot is forged and subjected to multiple thermomechanical treatments along the axial direction to obtain fine-grained rods. After grinding and cleaning the surface oxide scale of the fine-grained rod, it is sequentially subjected to cladding and hot extrusion to obtain hot-extruded pipe. The hot-extruded pipe is subjected to solution treatment and two-step aging treatment to obtain a heat-treated pipe. The heat-treated pipes are subjected to oxide scale removal, sandblasting, fine grinding of the inner surface, and polishing of the outer surface. The finished products are then subjected to ultrasonic flaw detection.

[0006] Optionally, the difficult-to-deform nickel-based superalloy comprises, by weight percentage: Cr: 15.0-17.0%, Co: 13.0-15.0%, W: 3.5-4.5%, Mo: 3.5-4.5%, Ti: 3.5-4.0%, Al: 1.8-2.5%, Fe: 0.5-1.0%, C: 0.025-0.04%, Ni: balance.

[0007] Optionally, the dual-process melting includes vacuum induction melting and vacuum consumable melting.

[0008] Optionally, the high-temperature refining temperature of the vacuum induction melting is 1530-1570℃ and the refining time is 5-10 min, and the low-temperature refining temperature is 1430-1470℃ and the refining time is 5-10 min. The temperature of the casting process in the vacuum self-consumable melting is 1430-1470℃.

[0009] Optionally, the homogenization annealing treatment of the master alloy ingot includes: Hold the master alloy ingot at 1140-1180℃ for 18-24 hours, then raise the temperature to 1180-1230℃ and hold for 10-15 hours.

[0010] Optionally, the step of forging the annealed ingot into a blank by performing multiple thermomechanical treatments along the axial direction includes: The alloy ingot is transformed into a billet by 1 to 3 upsetting and drawing operations using a high-speed forging machine. The billet temperature is 1100 to 1150℃, and the final deformation is 50 to 60%.

[0011] Optionally, the hot extrusion process following grinding and cleaning the surface oxide scale of the fine-grained rod includes: The billet bar is hot extruded and deformed using a hot extrusion press with a die, the extrusion ratio is 8~10:1, glass lubricant is used, and the hot extrusion temperature is 1080~1140℃.

[0012] Optionally, the solution treatment temperature for the hot-extruded pipe is 1100~1140℃, the holding time is 3-5h, and the cooling method is air cooling.

[0013] Optionally, the first aging treatment is carried out at a temperature of 640-660℃ for 23-25 ​​hours, and the cooling method is air cooling; The second step of aging treatment involves a temperature of 750-770℃, a holding time of 15-17 hours, and air cooling.

[0014] This disclosure provides a hot working process for controlling the microstructure of difficult-to-deform nickel-based superalloy tubing, which has the following advantages compared to the prior art: 1. This disclosure achieves defect-free hot forming and microstructure control of difficult-to-deform high-temperature alloy pipes through the control of the entire process, including the purification and smelting of the master alloy for difficult-to-deform high-temperature alloys, high-temperature annealing, multi-pass thermomechanical treatment for billet preparation, and encapsulated hot extrusion forming. By optimizing the microstructure through grain breaking during billet preparation, the deformation resistance of the alloy and the subsequent hot working temperature can be effectively reduced, thereby improving the alloy's formability, hot working efficiency, and finished product quality.

[0015] 2. The billet-filled hot extrusion tube manufacturing process adopted in this disclosure can effectively optimize the microstructure and refine the grains through multi-pass deformation and forming parameter control, and produce fine-grained tubes with uniform microstructure and high purity. Compared with the tube components produced by traditional manufacturing processes, the room temperature and high temperature plasticity are significantly improved. Attached Figure Description

[0016] Figure 1 The flowchart is a hot working process for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy tubing according to a specific embodiment of this disclosure. Figure 2 This is a microstructure diagram of the high-temperature alloy pipe prepared in Example 1 of this disclosure; Figure 3 This is a microstructure diagram of the high-temperature alloy pipe prepared in Example 2 of this disclosure; Figure 4 Microstructure diagram of the high-temperature alloy pipe prepared in Example 3 of this disclosure; Figure 5 This is a microstructure diagram of the high-temperature alloy pipe prepared in Comparative Example 1 of this disclosure. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.

[0018] It should be noted that the difficult-to-deform nickel-based superalloy provided in this embodiment has an austenitic structure, exhibiting excellent high-temperature mechanical properties and structural stability, and demonstrating excellent service performance at operating temperatures of 700-750 °C. Furthermore, due to the high volume fraction of γ′ precipitated strengthening phase in the alloy, its deformation resistance is relatively large, requiring high levels of process control during profile fabrication. Based on this, the following hot working process is proposed in this embodiment.

[0019] As shown in Figure 1, this disclosure provides a hot working process S100 for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy tubing, specifically including the following steps S110~S160: S110, Preparation of Master Alloy Ingots: Raw materials are added according to the standard proportions of each element in difficult-to-deform nickel-based high-temperature alloys, and a double-melting process is adopted. High-temperature refining is carried out during smelting to obtain master alloy ingots with high purity and uniform composition.

[0020] In step S110 above, the difficult-to-deform nickel-based superalloy comprises, by weight percentage: Cr: 15.0-17.0%, Co: 13.0-15.0%, W: 3.5-4.5%, Mo: 3.5-4.5%, Ti: 3.5-4.0%, Al: 1.8-2.5%, Fe: 0.5-1.0%, C: 0.025-0.04%, Ni: balance.

[0021] In step S110 above, the dual-melting process specifically includes a dual-melting process of vacuum induction melting and vacuum consumable melting. Electromagnetic stirring is performed during the melting process. The temperature control range of the alloy liquid in the vacuum induction refining stage is as follows: high temperature refining temperature is 1550±20℃, refining time is 5-10min; low temperature refining temperature is 1450±20℃, refining time is 5-10min; and the temperature control range of the casting process is 1450±20℃.

[0022] S120. Homogenization treatment: The master alloy ingot is subjected to step-by-step homogenization annealing at a temperature above 1140°C to obtain the ingot forging.

[0023] In step S120 above, the homogenization treatment temperature is 1160~1230 ℃, and the homogenization treatment time is greater than 32 h. Preferably, the homogenization annealing treatment specifically includes multiple temperature ranges, for example, holding the ingot at 1140-1180 ℃ for 18-24 h, and then raising the temperature to 1180-1230 ℃ and holding for 10-15 h.

[0024] In a further preferred embodiment, in the multiple temperature segments of the homogenization process, the homogenization temperature of the previous temperature segment is lower than that of the next temperature segment; preferably, the temperature of the first temperature segment is not lower than 1160 ℃ and the holding time is not less than 20h, the temperature of the final temperature segment is not higher than 1230 ℃ and the holding time is not less than 12h; even more preferably, the homogenization process time does not exceed 35h.

[0025] S130, thermomechanical blanking: The annealed ingot is forged and then subjected to multiple thermomechanical treatments along the axial direction to form a blank. The blanking temperature is not lower than 1100℃, and fine-grained rods are obtained after blanking.

[0026] In step S130 above, thermomechanical billeting specifically includes using a fast forging machine to perform 1 to 3 upsetting and drawing transformations on the alloy ingot to form billet bars, with a billeting temperature of 1100 to 1150°C and a final deformation of 50 to 60%.

[0027] In a further preferred embodiment, the billet temperature is not lower than 1120°C, and the deformation firing process is not less than two firings.

[0028] In this embodiment, before hot extrusion, the coarse grains and dendrites in the ingot are pre-broken by upsetting deformation at a high temperature (1100~1150℃) (deformation amount 50~60%), which significantly refines the grains, homogenizes the composition, and reduces the rheological stress of subsequent deformation. This creates better billet microstructure conditions for subsequent encapsulated hot extrusion, broadens the effective hot working window, and fundamentally improves the forming ability and success rate of this type of "difficult-to-deform" alloy.

[0029] S140, Encased Hot Extrusion: After grinding and cleaning the surface oxide scale of the billet, it is encased and then hot extruded to obtain hot extruded pipe.

[0030] In step S140 above, the hot extrusion of the cladding specifically includes using a hot extrusion press to perform hot extrusion deformation of the billet bar with a die, the extrusion ratio being 8~10:1, using glass lubricant, and the hot extrusion temperature being 1080~1140℃.

[0031] In a further preferred embodiment, the extrusion ratio is 10:1, and the extrusion temperature is not higher than 1110°C.

[0032] S150. Heat treatment: The hot-extruded pipe is subjected to solution treatment and two-step aging treatment to obtain heat-treated pipe.

[0033] In step S150 above, the heat treatment specifically includes the following: the hot-extruded pipe needs to undergo solution treatment and aging treatment. The solution treatment temperature is 1100~1140℃, the holding time is 4h, and the pipe is air-cooled. The two-step aging treatment regime is to hold the pipe at 640-660℃ for 23-25h, and the cooling method is air-cooled. The temperature is 750-770℃, the holding time is 15-17h, and the cooling method is air-cooled. The heat treatment heating rate is 10℃ / min.

[0034] In a further preferred embodiment, the solution treatment temperature is 1120°C.

[0035] S160. Surface finishing and ultrasonic testing: After heat treatment, the pipes are cleaned by grinding off the oxide scale, sandblasted, finely ground on the inner surface, and polished on the outer surface. The finished products are then subjected to ultrasonic testing.

[0036] In this embodiment, on the one hand, given that the coarse and uneven grains of the current ingots easily lead to cracks when directly extruded with large deformation, multi-step thermomechanical deformation billeting can break up the coarse grains and refine the microstructure. The deformation resistance of the billet after billeting is reduced, allowing the subsequent hot extrusion temperature to be lowered. On the other hand, traditional direct hot extrusion is unable to obtain a microstructure with fine grains and uniform microstructure, resulting in insufficient mechanical properties of the pipe (especially high-temperature plasticity). To address this, the combination of thermomechanical billeting and encased hot extrusion solves the core contradiction in the preparation of high-performance pipes from nickel-based superalloys with high precipitate phase content (which have difficult deformation characteristics), and is beneficial to improving the microstructure of highly alloyed, difficult-to-deform alloy pipes.

[0037] This embodiment provides a heat treatment process for controlling the microstructure of the aforementioned high-temperature alloy tubular components. By controlling the entire process, including master alloy purification smelting, high-temperature annealing, multi-pass thermomechanical treatment during billet preparation, and encased hot extrusion forming, the problem of difficult forming and poor microstructure uniformity of nickel-based high-temperature alloy tubular components with high precipitate phase content and poor deformation is solved. This improves the efficiency of profile preparation and mechanical properties, producing high-temperature alloy tubular components with uniform microstructure and stable performance, which can be used in components of aircraft and aero-engine hydraulic, fuel, and environmental control systems. The microstructure control heat treatment process, combining billet preparation and encased hot extrusion, effectively improves the microstructure and properties of the alloy tubular components, obtaining tubular components with fine grains, uniform microstructure, and high heat resistance, meeting the requirements of hot-end components in aerospace equipment.

[0038] The following will further illustrate the hot working process for controlling the microstructure of difficult-to-deform nickel-based high-temperature alloy tubing with specific embodiments: It should be noted that in this embodiment, a MEF4A optical microscope was used to observe the microstructure of the prepared high-temperature alloy pipe, and an INSTRON 5582 universal testing machine was used to test the radial tensile properties of the alloy pipe at room temperature and 700℃.

[0039] Example 1 Hot working process for microstructure control of difficult-to-deform nickel-based superalloy tubes includes the following steps: 1) Preparation of master alloy ingot: The alloy raw materials are added to a high-frequency vacuum induction furnace according to the specified ratio. The melting temperature is 1500 ℃ and the vacuum degree is 0.5×10⁻⁶. -2After the raw materials are completely melted, the alloy is refined at 1550 °C for 7 minutes, then cooled to 1450 °C for 7 minutes. An inert gas is introduced, and the molten alloy is poured into ingots, with the pouring temperature controlled within the range of 1450 ± 20 °C. After the vacuum-melted ingot cools, the riser is removed, the oxide scale is cleaned, and it is placed in an electroslag remelting equipment as an electrode. After three remelting steps—arc ignition, flux melting, and capping and feeding—the electroslag remelted refined alloy ingot is obtained. Specifically, the constituent elements in the alloy are formulated according to the weight percentage of the chemical composition of the difficult-to-deform high-temperature alloy described in the claims: Cr: 16%, Co: 15%, W: 4%, Mo: 4%, Ti: 3.7%, Al: 2.3%, Fe: 1%, C: 0.025%, with the balance being Ni.

[0040] 2) Homogenization treatment: The alloy ingot is subjected to the first homogenization treatment at 1180℃ for 24 hours using an electric resistance furnace, followed by the second homogenization treatment at 1230℃ for 12 hours.

[0041] 3) Thermomechanical billet forming: The homogenized ingot is formed into a billet bar by three upsetting and drawing operations using a high-speed forging machine. The billet heating temperature is 1140℃, and the final deformation is 60%.

[0042] 4) Encasing hot extrusion: After the billet is polished, it is encased and then hot extruded into the die using a hot extrusion press. The extrusion ratio is 10:1. Glass lubricant is filled between the encased billet and the die. The hot extrusion temperature is 1090℃. 5) Heat treatment: The alloy tubes after hot extrusion are subjected to solution treatment and two-step aging treatment using a resistance heating tube furnace. The heating rate is 10℃ / min, the solution treatment temperature is 1120℃, the holding time is 4h, and after air cooling, a two-step aging treatment is performed at 650℃ / 24h / air cooling + 760℃ / 16h / air cooling.

[0043] 6) Surface processing and ultrasonic testing: After heat treatment, the pipe is cleaned by grinding off the oxide scale, sandblasted, finely ground on the inner surface, and polished on the outer surface. Then, ultrasonic testing is performed to obtain a difficult-to-deform nickel-based high-temperature alloy pipe.

[0044] The microstructure of the high-temperature alloy pipe prepared in Example 1 is shown in the figure. Figure 2 As shown in Table 1, the axial tensile properties of high-temperature alloy pipes are as follows.

[0045] Example 2 Hot working process for microstructure control of difficult-to-deform nickel-based superalloy tubes includes the following steps: 1) Preparation of master alloy ingot: The alloy raw materials are added to a high-frequency vacuum induction furnace according to the specified ratio. The melting temperature is 1500 ℃ and the vacuum degree is 0.5×10⁻⁶. -2 After the raw materials are completely melted, the alloy is refined at 1550 °C for 7 minutes, then cooled to 1450 °C for 10 minutes. An inert gas is introduced, and the molten alloy is poured into ingots, with the pouring temperature controlled within the range of 1450 ± 20 °C. After the vacuum-melted ingot cools, the riser is removed, the oxide scale is cleaned, and it is placed in an electroslag remelting equipment as an electrode. After three remelting steps—arc ignition, flux melting, and capping and feeding—the electroslag remelted refined alloy ingot is obtained. Specifically, the constituent elements in the alloy are formulated according to the weight percentage of the chemical composition of the difficult-to-deform high-temperature alloy described in the claims: Cr: 16%, Co: 14%, W: 4%, Mo: 4.5%, Ti: 3.7%, Al: 2.5%, Fe: 1%, C: 0.04%, with the balance being Ni.

[0046] 2) Homogenization treatment: The alloy ingot is subjected to the first homogenization treatment at 1180℃ for 24 hours using an electric resistance furnace, followed by the second homogenization treatment at 1230℃ for 12 hours.

[0047] 3) Thermomechanical billet forming: The homogenized ingot is formed into a billet bar by three upsetting and drawing operations using a high-speed forging machine. The billet heating temperature is 1150℃ and the final deformation is 50%.

[0048] 4) Encasing hot extrusion: After the billet is polished, it is encased and then hot extruded into the die using a hot extrusion press. The extrusion ratio is 10:1. Glass lubricant is filled between the encased billet and the die. The hot extrusion temperature is 1100℃. 5) Heat treatment: The alloy tubes after hot extrusion are subjected to solution treatment and two-step aging treatment using a resistance heating tube furnace. The heating rate is 10℃ / min, the solution treatment temperature is 1140℃, the holding time is 4h, and after air cooling, a two-step aging treatment is performed at 650℃ / 24h / air cooling + 760℃ / 16h / air cooling.

[0049] 6) Surface processing and ultrasonic testing: After heat treatment, the pipe is cleaned by grinding off the oxide scale, sandblasted, finely ground on the inner surface, and polished on the outer surface. Then, ultrasonic testing is performed to obtain a difficult-to-deform nickel-based high-temperature alloy pipe.

[0050] The microstructure of the high-temperature alloy pipe prepared in Example 2 is shown in the figure. Figure 3 As shown.

[0051] Example 3 Hot working process for microstructure control of difficult-to-deform nickel-based superalloy tubes includes the following steps: 1) Preparation of master alloy ingot: The alloy raw materials are added to a high-frequency vacuum induction furnace according to the specified ratio. The melting temperature is 1500 ℃ and the vacuum degree is 0.5×10⁻⁶. -2 After the raw materials are completely melted, the alloy is refined at 1550 °C for 7 minutes, then cooled to 1450 °C for 7 minutes. An inert gas is introduced, and the molten alloy is poured into ingots, with the pouring temperature controlled within the range of 1450 ± 20 °C. After the vacuum-melted ingot cools, the riser is removed, the oxide scale is cleaned, and it is placed in an electroslag remelting apparatus as an electrode. After three remelting steps—arc ignition, flux melting, and capping and feeding—the electroslag remelted refined alloy ingot is obtained. Specifically, the constituent elements in the alloy are formulated according to the weight percentage of the chemical composition of the difficult-to-deform high-temperature alloy described in the claims: Cr: 16%, Co: 15%, W: 3.5%, Mo: 4%, Ti: 3.5%, Al: 2%, Fe: 1%, C: 0.03%, with the balance being Ni.

[0052] 2) Homogenization treatment: The alloy ingot is subjected to the first homogenization treatment at 1170℃ for 20h using an electric resistance furnace, followed by the second homogenization treatment at 1200℃ for 15h.

[0053] 3) Thermomechanical billet forming: The homogenized ingot is formed into a billet bar by two upsetting and drawing operations using a high-speed forging machine. The billet heating temperature is 1130℃, and the final deformation is 60%.

[0054] 4) Encasing hot extrusion: After the billet is polished, it is encased and then hot extruded into the die using a hot extrusion press. The extrusion ratio is 10:1. Glass lubricant is filled between the encased billet and the die. The hot extrusion temperature is 1080℃. 5) Heat treatment: The alloy tubes after hot extrusion are subjected to solution treatment and two-step aging treatment using a resistance heating tube furnace. The heating rate is 10℃ / min, the solution treatment temperature is 1100℃, the holding time is 4h, and after air cooling, a two-step aging treatment is performed at 650℃ / 24h / air cooling + 760℃ / 16h / air cooling.

[0055] 6) Surface processing and ultrasonic testing: After heat treatment, the pipe is cleaned by grinding off the oxide scale, sandblasted, finely ground on the inner surface, and polished on the outer surface. Then, ultrasonic testing is performed to obtain a difficult-to-deform nickel-based high-temperature alloy pipe.

[0056] The microstructure of the high-temperature alloy pipe prepared in Example 3 is shown in the figure. Figure 4 As shown.

[0057] Comparative Example 1 The direct hot extrusion process for difficult-to-deform nickel-based superalloy tubes includes the following steps: 1) Preparation of master alloy ingot: The alloy raw materials are added to a high-frequency vacuum induction furnace according to the specified ratio. The melting temperature is 1500 ℃ and the vacuum degree is 0.5×10⁻⁶. -2 After all the raw materials have melted, the alloy is refined at 1550℃ for 7 minutes, then cooled to 1450℃ for 7 minutes. An inert gas is introduced, and the molten alloy is poured into ingots, with the pouring temperature controlled within the range of 1450±20℃. After the vacuum-melted ingot cools, the riser is removed, and the oxide scale is cleaned. It is then placed in an electroslag remelting apparatus as an electrode. After three remelting steps—arc ignition, flux melting, and capping and feeding—the electroslag remelted refined alloy ingot is obtained. Specifically, the constituent elements in the alloy are formulated according to the weight percentage of the chemical composition of the difficult-to-deform high-temperature alloy described in the claims: Cr: 16%, Co: 15%, W: 4%, Mo: 4%, Ti: 3.7%, Al: 2.3%, Fe: 1%, C: 0.025%, with the balance being Ni.

[0058] 2) Homogenization treatment: The alloy ingot is subjected to the first homogenization treatment at 1180℃ for 24 hours using an electric resistance furnace, followed by the second homogenization treatment at 1230℃ for 15 hours.

[0059] 4) Encasing hot extrusion: After the homogenized ingot is surface-polished, it is encased. The encased billet is then hot-extruded and deformed using a hot extrusion press with a die. The extrusion ratio is 5:1. Glass lubricant is filled between the encased billet and the die. The hot extrusion temperature is 1130℃.

[0060] 5) Heat treatment: The alloy tubes after hot extrusion are subjected to solution treatment and two-step aging treatment using a resistance heating tube furnace. The heating rate is 10℃ / min, the solution treatment temperature is 1100℃, the holding time is 4h, and after air cooling, a two-step aging treatment is performed at 650℃ / 24h / air cooling + 760℃ / 16h / air cooling.

[0061] 6) Surface processing and ultrasonic testing: After heat treatment, the pipe is cleaned by grinding off the oxide scale, sandblasted, finely ground on the inner surface, and polished on the outer surface. Then, ultrasonic testing is performed to obtain a difficult-to-deform nickel-based high-temperature alloy pipe.

[0062] The microstructure of the high-temperature alloy pipe prepared in Comparative Example 1 is shown in the figure. Figure 5 As shown in Table 1, the axial tensile properties of high-temperature alloy pipes are as follows.

[0063] Table 1. Room temperature and high temperature tensile properties of difficult-to-deform high-temperature alloy pipes

[0064] In summary, based on the results of Examples 1-3 and Comparative Example 1, the microstructure of the difficult-to-deform high-temperature alloy pipes prepared in the above embodiments of the present invention is a uniform fine-grained deformable structure with an average grain size of less than 10 μm, excellent microstructure uniformity, and grain size difference of less than 1 grade. In contrast, the high-temperature alloy pipes prepared by the traditional casting direct hot extrusion process in Comparative Example 1 have coarser grains and poorer uniformity. This indicates that the preparation process disclosed in this invention can obtain a uniform fine-grained deformable structure, the microstructure control hot working effectively controls the grain size, and the hot working process can effectively reduce the hot working temperature and improve production efficiency. Among them, the high precipitate phase content designed in Example 2 gives the alloy greater deformation resistance. Secondly, as can be seen from the data comparison in Table 1, compared with Comparative Example 1, the elongation at room temperature increased significantly from 18.5% to 25.0%, and the elongation at 700℃ doubled from 7.0% to 15.5%, while maintaining excellent strength levels. Therefore, the process implemented in this invention can effectively achieve stable hot processing preparation and microstructure control, while maintaining high strength and significantly improving the plasticity (especially high-temperature plasticity) of the pipe. This is crucial for aerospace pipes that are subjected to complex stresses, and can effectively avoid brittle fracture. Compared with the direct hot extrusion preparation process used in the comparative example, the microstructure control hot processing method implemented in this invention can effectively refine the deformed microstructure grains and significantly improve the room temperature and high temperature tensile strength and tensile plasticity of the formed pipe.

[0065] In summary, the microstructure control hot working process for difficult-to-deform nickel-based superalloy tubular materials provided by this invention can successfully achieve efficient and stable preparation of high-precipitate-phase-content difficult-to-deform nickel-based superalloy tubular components. The preparation process provided by this invention, through the control of the entire process including master alloy purification smelting, high-temperature annealing, multi-pass thermomechanical treatment for billet preparation, and encapsulated hot extrusion forming, enables defect-free hot working and microstructure control of difficult-to-deform superalloy tubular materials. Simultaneously, the billet preparation + encapsulated hot extrusion effectively optimizes the microstructure and refines the grains, obtaining fine-grained tubular materials with uniform microstructure and good room-temperature and high-temperature strength and plasticity, providing process optimization guidance for the application of materials in hot-end components of aircraft and aero-engines.

[0066] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.

Claims

1. A hot working process for controlling the microstructure of difficult-to-deform nickel-based superalloy pipes, characterized in that, The heat treatment process includes: According to the standard proportion of each element in the difficult-to-deform nickel-based superalloy, the master alloy ingot is obtained by adopting a duplex melting process. The master alloy ingot is subjected to homogenization annealing to obtain ingot forging; The ingot is forged by performing multiple thermomechanical treatments along the axial direction to obtain fine-grained rods. After grinding and cleaning the surface oxide scale of the fine-grained rod, it is sequentially subjected to cladding and hot extrusion to obtain hot-extruded pipe. The hot-extruded pipe is subjected to solution treatment and two-step aging treatment to obtain a heat-treated pipe. The heat-treated pipes are subjected to oxide scale removal, sandblasting, fine grinding of the inner surface, and polishing of the outer surface. The finished products are then subjected to ultrasonic flaw detection.

2. The heat treatment process according to claim 1, characterized in that, By weight percentage, the difficult-to-deform nickel-based superalloy Includes: Cr: 15.0-17.0%, Co: 13.0-15.0%, W: 3.5-4.5%, Mo: 3.5-4.5%, Ti: 3.5-4.0%, Al: 1.8-2.5%, Fe: 0.5-1.0%, C: 0.025-0.04%, Ni: balance.

3. The heat treatment process according to claim 1, characterized in that, The dual-process melting includes vacuum induction melting and vacuum consumable melting.

4. The hot working process according to claim 3, characterized in that, The high-temperature refining temperature for vacuum induction melting is 1530-1570℃, and the refining time is 5-10 min; the low-temperature refining temperature is 1430-1470℃, and the refining time is 5-10 min. The temperature of the casting process in the vacuum self-consumable melting is 1430-1470℃.

5. The hot working process according to claim 1, characterized in that, The homogenization annealing process for the master alloy ingot includes: Hold the master alloy ingot at 1140-1180℃ for 18-24 hours, then raise the temperature to 1180-1230℃ and hold for 10-15 hours.

6. The hot working process according to claim 1, characterized in that, The ingot is forged by performing multiple thermomechanical treatments along the axial direction to open the billet, including: The alloy ingot is transformed into a billet by 1 to 3 upsetting and drawing operations using a high-speed forging machine. The billet temperature is 1100 to 1150℃, and the final deformation is 50 to 60%.

7. The heat treatment process according to claim 1, characterized in that, After grinding and cleaning the surface oxide scale of the fine-grained rods, they undergo hot extrusion processing, including: The billet bar is hot extruded and deformed using a hot extrusion press with a die, the extrusion ratio being (8~10):1, glass lubricant being used, and the hot extrusion temperature being 1080~1140℃.

8. The hot working process according to claim 1, characterized in that, The solution treatment temperature for hot-extruded pipes is 1100~1140℃, the holding time is 3-5h, and the cooling method is air cooling.

9. The heat treatment process according to claim 1, characterized in that, The first step of aging treatment involves holding the temperature at 640-660℃ for 23-25 ​​hours, with air cooling as the cooling method. The second step of aging treatment involves a temperature of 750-770℃, a holding time of 15-17 hours, and air cooling.

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