Co-based high-temperature alloy containing hafnium and rhenium and preparation method thereof

Abstract

The invention discloses a Co-based high-temperature alloy containing hafnium and rhenium and a preparation method of the Co-based high-temperature alloy, and belongs to the technical field of high-temperature alloy material processing. 1-3% of a hafnium element and 0.5-1.8% of a rhenium element are added into the Co-based high-temperature alloy, the change of the hafnium element and the rhenium element on a lattice constant and a mismatch degree is taken as an entry point, precipitation strengthening and solid solution strengthening effects are influenced, meanwhile, the size and the form of a gamma'phase are influenced, and a key role is played on a strengthening mechanism of the alloy; the grain size is smaller after deep cold rolling, the nucleation rate of the grain can be increased in the deformation process, the grain of a finished sheet is effectively refined, and the toughness of a workpiece is remarkably improved under the condition that the strength and hardness of the workpiece are not reduced; an asynchronous cold rolling process is adopted, the linear speed of the two sides of a plate during rolling is changed, a complex-phase gamma / gamma'microstructure is broken through strong twisting and rolling deformation of the asynchronous cold-rolled plate, the accumulated strain of a deformation structure is improved, and the comprehensive mechanical property of the high-temperature alloy is improved by promoting refining of the microstructure.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy material processing technology, specifically relating to a Co-based high-temperature alloy containing hafnium and rhenium and its preparation method. Background Technology

[0002] To improve the efficiency of aero-engines, the turbine inlet temperature is constantly increasing, leading to higher service temperatures for key hot-end components like turbine disks. Currently, the widely used turbine disk alloys are γ′-Ni3(Al,Ti) phase-strengthened nickel-based wrought superalloys. However, to improve their high-temperature performance, a large number of alloying elements are added, which drastically reduces the alloy's hot workability, limiting its operating temperature to below 750℃, thus failing to meet the requirements of next-generation turbine disk materials. Novel γ′-Co3(Al,W)-strengthened Co-based superalloys, due to their lower solidification segregation tendency, larger hot workability window, better resistance to hot corrosion, and higher service temperature, are considered the next-generation wrought superalloy for turbine disks and have become a research hotspot in recent years.

[0003] Cobalt-based superalloys possess excellent resistance to hot corrosion, thermal fatigue, and weldability; however, their high-temperature strength is insufficient, primarily due to the lack of a stable γ′ phase at high temperatures, limiting their further application in high-temperature fields. Al, W, Ta, Ti, V, Nb, and Mo are γ′ phase-forming elements, playing a stabilizing role. In novel Co-based superalloys, Ni can broaden the γ′ phase region, while Ta and Ti can significantly improve γ′ stability and dissolution temperature, thereby enhancing the alloy's high-temperature strength. Simultaneously, Ti can suppress the harmful χ-D0 phase. 19 Ni has a tendency to precipitate and a significant weight-reduction effect. Ni can inhibit the precipitation of the brittle and harmful phase B2. The addition of each alloying element reduces the hot working window of the alloy, with Ti and Ta having the greatest impact on the hot working window. Summary of the Invention

[0004] To overcome the aforementioned deficiencies in the existing technology, the present invention aims to provide a Co-based superalloy containing hafnium and rhenium and its preparation method. The invention proposes to add hafnium (Hf) and rhenium (Re) elements to the Co-based superalloy, taking the changes of hafnium and rhenium elements on the lattice constant and mismatch degree as the starting point, to affect the effects of precipitation strengthening and solid solution strengthening, and at the same time affect the size and morphology of the γ′ phase, which plays a key role in the strengthening mechanism of the alloy.

[0005] Hafnium (Hf) has elemental properties similar to Ti, effectively increasing the stable existence temperature of the γ′ phase, even more so than Ta. Rhenium (Re) tends to distribute in the γ phase, causing the lattice mismatch to change in the negative direction, ensuring a significant increase in alloy strength. Furthermore, Re can significantly improve the creep properties of the alloy under high-temperature conditions and effectively slow down the diffusion rate of other elements in the alloy, prolonging the coarsening process of the γ′ phase, increasing the γ / γ′ phase mismatch, and enhancing the creep activation energy of the γ′ phase.

[0006] To achieve the above-mentioned objective, this invention provides a hafnium-rhenium-based Co-based superalloy and its preparation method. The chemical composition of the Co-based superalloy, by mass percentage, is: C: 0.05%–0.15%, Ni: 21.5%–24.5%, Cr: 8.5%–11.0%, Mo: 3.2%–6.4%, Ta: 1.0%–2.5%, Al: 1.2%–2.8%, Ti: 0.4%–0.8%, Si: 0.2%–0.4%, Mn: 0.4%–0.8%, V: 0.2%–0.5%, Hf: 1%–3%, Re: 0.5%–1.8%, B: 0.005%–0.008%, with the balance being Co.

[0007] The preparation method of the hafnium-rhenium-containing Co-based superalloy includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, rapid forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; wherein,

[0008] ① Vacuum induction melting: Materials are prepared according to the chemical composition requirements of the Co-based high-temperature alloy, with a vacuum degree of 0.5~0.6×10⁻⁶. -2 Under Pa conditions, alloy raw materials containing Cr, Co, Ni, Ta, Mo, Si, and V are first added to a medium-frequency induction arc furnace and melted at 1510℃~1540℃. Then, the power is adjusted to a refining temperature of 1450℃~1490℃, and the refining period is held for 70~90 minutes with the vacuum degree controlled at 1~5Pa. After the power is reduced until a film forms on the surface of the melt, alloying materials containing C, Si, Cr, Ta, B, and Hf are added. The mixture is electromagnetically stirred for 4~6 minutes, and argon gas is purged at 3000~5000Pa. The power is then increased to clear the melt, and the temperature of the molten steel is adjusted to a casting temperature of 1450℃~1490℃. Alloy raw materials containing Al, Ti, Mn, and Re are added, and the mixture is electromagnetically stirred for 2~3 minutes before casting to obtain an alloy ingot.

[0009] ② Protective atmosphere electroslag remelting: After the alloy ingot box obtained in step ① has cooled, the riser of the ingot is cut off and its surface is polished. It is used as the electrode for protective atmosphere electroslag remelting. The quaternary slag system is used to go through three stages: the start-up stage, the melting stage and the hot capping stage. An appropriate amount of argon gas is introduced to carry out electroslag remelting to obtain electroslag refined ingot.

[0010] Furthermore, the main components of the quaternary slag system described in step ② are CaF2: 50%–56%, Al2O3: 20%–24%, CaO: 18%–22%, MgO: 4%–6%, with the remainder being unavoidable impurities.

[0011] ③ Homogenization treatment: The electroslag refining ingot is heated from room temperature to 1040℃~1060℃ at a rate of 10~20℃ / min and held for 1.5~2.5h, followed by homogenization treatment at 1140℃~1170℃ for 2~4h.

[0012] ④ Fast forging: The homogenized alloy ingot is forged into a slab at high temperature using a 2000t fast forging machine at 1060℃~1120℃. The deformation amount per pass is 13%~18%, and the total deformation amount is 40%~60%. After the fast forging is completed, it is returned to the furnace for heat preservation.

[0013] ⑤ Hot rolling deformation: After the slab is forged, it is kept at 1200℃~1250℃ for 8~10h and then hot rolled on a hot rolling mill. The initial rolling temperature is 1150℃~1200℃, the final rolling temperature is 850℃~900℃, the total reduction rate is 90%~94%, and when it is rolled to a thickness of 3~3.5mm, it is water cooled to room temperature to obtain hot rolled plate.

[0014] ⑥ Solution treatment: The hot-rolled alloy sheet is solution treated in a muffle furnace at a temperature of 1150℃~1250℃ for 24~36h. The purpose is to obtain a supersaturated solid solution with uniform composition, eliminate compositional segregation and dissolve uneven precipitates in the alloy, provide a uniform microstructure for the next cryogenic asynchronous rolling deformation process, and reduce the deformation resistance during alloy deformation.

[0015] ⑦ Cryogenic asynchronous rolling, including:

[0016] A three-pass cryogenic asynchronous rolling process with a reduction rate of 20%–40% is performed using a four-roll cold rolling mill. The speed ratio is 1.1–1.4. The lower roll is a slow roll with a constant speed, while the upper roll is a fast roll with its speed adjusted according to the speed ratio. The lower roll speed is 0.22–0.33 m / s, and the upper roll speed is 0.24–0.46 m / s. The rolling force is 150–260 kN. Before cryogenic asynchronous rolling, the high-temperature alloy sheet is cooled in liquid nitrogen to a temperature of -160℃ to -120℃. Then, the rolls are turned on and rotated under zero load. The upper and lower work rolls of the mill are cooled using a nitrogen cooling spray gun to achieve a roll surface temperature of -160℃ to -120℃. The high-temperature alloy is then quickly removed for cryogenic asynchronous rolling.

[0017] The first rolling pass has a reduction rate of 20% to 30%, a speed ratio of 1.1 to 1.18, a lower roll speed of 0.22 to 0.25 m / s, an upper roll speed of 0.24 to 0.30 m / s, a rolling force of 150 to 170 kN, and asynchronous rolling to a thickness of 2.1 to 2.8 mm.

[0018] The reduction rate of the second rolling pass is 32% to 40%, the speed ratio is 1.22 to 1.3, the lower roll speed is 0.26 to 0.29 m / s, the upper roll speed is 0.32 to 0.38 m / s, the rolling force is 200 to 260 kN, and the asynchronous rolling is carried out to a thickness of 1.3 to 1.9 mm.

[0019] The reduction rate of the third rolling pass is 20% to 30%, the speed ratio is 1.32 to 1.4, the lower roll speed is 0.30 to 0.33 m / s, the upper roll speed is 0.40 to 0.46 m / s, the rolling force is 160 to 180 kN, and the asynchronous rolling is carried out to a thickness of 0.9 to 1.5 mm.

[0020] After each rolling pass, the rolled piece is returned to the liquid nitrogen tank for heat preservation. This process is repeated until each sheet reaches a thickness of 0.9–1.5 mm.

[0021] ⑧ Heat Treatment: The cryogenically rolled sheet is annealed at 900℃~1000℃ in a vacuum environment of 1~5Pa for 10~20min, followed by water quenching to room temperature; then the alloy sheet is aged at 820℃~920℃ for 8~15h, and then water quenched again to obtain a hafnium-rhenium-based superalloy. The purpose of this step is to allow γ′ particles to disperse in the γ matrix, and to control the size and volume percentage of γ′ particles by changing the aging temperature and time, so that the γ′ nanoparticles do not coarsen significantly after aging, have high high-temperature structural stability, and improve the mechanical properties of the Co-based superalloy.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] ① This invention adds hafnium and rhenium to Co-based superalloys to improve their high-temperature mechanical properties. Compared with existing Co-based superalloys, this alloy, by replacing W with Hf and small amounts of Ti, Mo, and Ta, effectively increases the stable existence temperature of the γ′ phase and reduces the density and cost of the superalloy. It also results in the coherent precipitation of cubic γ′ particles in the γ matrix, and the γ′ nanoparticles do not undergo significant coarsening after long-term aging at 900℃, thus giving this type of alloy excellent high-temperature mechanical properties. Adding Re to distribute it within the γ phase causes the lattice mismatch to change in a negative direction, significantly enhancing the alloy's strength. Simultaneously, it significantly improves the creep performance under high-temperature conditions and effectively slows down the diffusion rate of various elements in the alloy, prolonging the coarsening process of the γ′ phase and increasing the γ / γ′ phase mismatch and the creep activation energy of the γ′ phase. Through alloy composition design, focusing on the changes in elemental effects on lattice constants and mismatch, the effects of precipitation strengthening and solid solution strengthening are influenced, as well as the size and morphology of the γ′ phase, playing a crucial role in the alloy's strengthening mechanism.

[0024] ② After cryogenic rolling, the grain size is smaller, which can increase the nucleation rate of grains during deformation, effectively refine the grains of the finished thin plate, and significantly improve the toughness of the workpiece without reducing its strength and hardness.

[0025] ③ Compared with conventional cryogenic rolled plates, this invention adopts a cryogenic asynchronous rolling process. By changing the linear speed on both sides of the plate during rolling, the intense "rolling" deformation of the cryogenic asynchronous rolled plate causes the microstructure of the multiphase γ / γ′ to break down, increasing the cumulative strain of the deformed structure. This improves the comprehensive mechanical properties of the high-temperature alloy by promoting the refinement of the microstructure. Attached Figure Description

[0026] Figure 1 The image shows the ingot obtained after electroslag melting under a protective atmosphere in Example 1.

[0027] Figure 2 SEM microstructure images of the Co-based superalloys prepared in Examples 1-3 and Comparative Example 1;

[0028] Figure 3 The tensile engineering stress-strain curves of the Co-based superalloys prepared in Examples 1-3 and Comparative Example 1 are shown.

[0029] Figure 4 The high-temperature creep strain-time curves of the Co-based superalloys prepared in Examples 1-3 and Comparative Example 1 are shown. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0031] A method for preparing a Co-based superalloy containing hafnium and rhenium includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, rapid forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; wherein,

[0032] ① Vacuum induction melting: Materials are prepared according to the chemical composition requirements of the Co-based high-temperature alloy, with a vacuum degree of 0.5~0.6×10⁻⁶. -2 Under Pa conditions, alloy raw materials containing Cr, Co, Ni, Ta, Mo, Si, and V are first added to a medium-frequency induction arc furnace and melted at 1510℃~1540℃; then the power is adjusted to a refining temperature of 1450℃~1490℃, and the refining period is held for 70~90min, with the vacuum degree controlled at 1~5Pa; after the power is reduced until a film forms on the surface of the melt, alloying materials containing C, Si, Cr, Ta, B, and Hf are added, and the mixture is electromagnetically stirred for 4~6min. After purging with argon gas at 3000~5000Pa, the power is increased to clear the melt, and the temperature of the molten steel is adjusted to a casting temperature of 1450℃~1490℃. Alloy raw materials containing Al, Ti, Mn, and Re are added, and after electromagnetic stirring for 2~3min, the mixture is cast to obtain an alloy ingot.

[0033] ② Protective atmosphere electroslag remelting: The alloy ingot obtained in step ① is electroslag remelted using argon as a protective atmosphere and a quaternary slag system to obtain an electroslag refined ingot.

[0034] ③ Homogenization treatment: The electroslag refining ingot is heated from room temperature to 1040℃~1060℃ at a rate of 10~20℃ / min and held for 1.5~2.5h, followed by homogenization treatment at 1140℃~1170℃ for 2~4h.

[0035] ④ Rapid forging: The homogenized alloy ingot is rapidly forged into a slab at 1060℃~1120℃, and then returned to the furnace for heat preservation after rapid forging.

[0036] ⑤ Hot rolling deformation: After the slab is forged, it is held at 1200℃~1250℃ for 8~10h and then hot rolled to obtain a hot rolled plate with a thickness of 3~3.5mm.

[0037] ⑥ Solution treatment: The alloy hot-rolled sheet is subjected to solution treatment at a temperature of 1150℃~1250℃ for 24~36h.

[0038] ⑦ Cryogenic asynchronous rolling: Before rolling, the alloy sheet is cooled to -160℃~-120℃ in liquid nitrogen; then, it is rolled in three passes with a reduction rate of 20%~40% using a four-roll cold rolling mill; after each pass, the rolled piece is put back into the liquid nitrogen tank for heat preservation until each sheet reaches 0.9~1.5mm.

[0039] ⑧ Heat treatment: The plate after cryogenic asynchronous rolling is annealed in a vacuum environment (1-5Pa) at 900℃~1000℃ for 10-20 minutes, then water quenched to room temperature; then aged, and then water quenched to obtain a Co-based high-temperature alloy containing hafnium and rhenium.

[0040] The hafnium-rhenium-containing Co-based superalloy prepared by the above method has the following chemical composition by mass percentage: C: 0.05%–0.15%, Ni: 21.5%–24.5%, Cr: 8.5%–11.0%, Mo: 3.2%–6.4%, Ta: 1.0%–2.5%, Al: 1.2%–2.8%, Ti: 0.4%–0.8%, Si: 0.2%–0.4%, Mn: 0.4%–0.8%, V: 0.2%–0.5%, Hf: 1%–3%, Re: 0.5%–1.8%, B: 0.005%–0.008%, with the balance being Co.

[0041] Unless otherwise stated in the following embodiments, all other aspects are the same as those described in the specific embodiments above. The main components of the quaternary slag system in step ② of the embodiment are CaF2: 52.5%, Al2O3: 22%, CaO: 20%, MgO: 5%, with the remainder being impurities.

[0042] Example 1

[0043] A hafnium-rhenium-based Co-based superalloy and its preparation method are disclosed. The chemical composition of the Co-based superalloy, by mass percentage, meets the following requirements: C: 0.05%, Ni: 21.5%, Cr: 8.5%, Mo: 3.2%, Ta: 1.0%, Al: 1.2%, Ti: 0.4%, Si: 0.2%, Mn: 0.4%, V: 0.2%, Hf: 1%, Re: 0.5%, B: 0.005%, with the balance being Co.

[0044] The preparation method of the hafnium-rhenium-containing Co-based superalloy includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, rapid forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; wherein,

[0045] ① Vacuum induction melting: According to the chemical composition requirements of the Co-based high-temperature alloy, Cr, Co plates, Ni plates, Ta blocks, Mo strips, Si and V strips are added to the medium-frequency induction arc furnace, and the vacuum degree of the medium-frequency induction arc furnace is controlled at 0.5 × 10⁻⁶. -2 Pa, melting temperature 1510℃; after the alloy material melts, adjust the power to the refining temperature 1450℃, hold for 70 minutes during the refining period, and control the vacuum degree to 1Pa; reduce the power until a film forms on the surface of the melt, then add carbon electrode, NiB alloy and metal Hf, and stir electromagnetically for 4 minutes; after purging with argon gas at 3000Pa, increase the power to clear the melt, adjust the temperature of the molten steel to the pouring temperature 1450℃, add Al, sponge Ti, metal Mn and metal Re, stir electromagnetically for 2 minutes, and then cast to obtain the alloy ingot.

[0046] ② Protective Atmosphere Electroslag Remelting: After the alloy ingot obtained in step ① has cooled, the riser of the ingot is removed and its surface is polished. This surface is then used as the electrode for protective atmosphere electroslag remelting. A quaternary slag system is used, and the electroslag remelting process proceeds through three stages: start-up, melting, and hot capping. An appropriate amount of argon gas is introduced during the process to obtain a refined electroslag ingot. Example 1: Ingot sample obtained after electroslag remelting under protective atmosphere conditions, such as... Figure 1 As shown, the surface of the ingot sample is smooth, without defects such as slag grooves or sand holes.

[0047] ③ Homogenization treatment: The electroslag refining ingot is heated from room temperature to 1040℃ at a rate of 10℃ / min and held for 2.5h, followed by homogenization treatment at 1140℃ for 4h.

[0048] ④ Fast forging: The homogenized alloy ingot is forged into a slab at 1060℃ using a 2000t fast forging machine. The deformation amount per pass is 13%, and the total deformation amount is 40%. After the fast forging is completed, the slab is returned to the furnace for heat preservation.

[0049] ⑤ Hot rolling deformation: After the slab is forged, it is kept at 1250℃ for 8 hours and then hot rolled on a hot rolling mill. The initial rolling temperature is 1200℃, the final rolling temperature is 900℃, the total reduction rate is 90%, and it is water cooled to room temperature when rolled to a thickness of 3.5mm to obtain hot rolled plate.

[0050] ⑥ Solution treatment: The alloy hot-rolled sheet is solution treated in a muffle furnace at a temperature of 1250℃ for 24 hours.

[0051] ⑦ Cryogenic Asynchronous Rolling: Three passes of cryogenic asynchronous rolling are performed using a four-roll cold rolling mill. The lower roll is a slow roll with a constant speed, while the upper roll is a fast roll with its speed adjusted according to the speed ratio. Before cryogenic asynchronous rolling, the high-temperature alloy plate is cooled in liquid nitrogen to a temperature of -120°C. Then, the rolls are turned on and rotated under zero load. The upper and lower work rolls of the mill are cooled using nitrogen cooling spray guns to achieve a roll surface temperature of -120°C. The high-temperature alloy is then quickly removed for cryogenic asynchronous rolling.

[0052] The first rolling pass has a reduction rate of 20%, a speed ratio of 1.1, a lower roll speed of 0.22 m / s, an upper roll speed of 0.24 m / s, a rolling force of 150 kN, and is asynchronously rolled to a thickness of 2.8 mm.

[0053] The second rolling pass has a reduction rate of 32%, a speed ratio of 1.22, a lower roll speed of 0.26 m / s, an upper roll speed of 0.32 m / s, a rolling force of 200 kN, and is asynchronously rolled to a thickness of 1.9 mm.

[0054] The reduction rate of the third rolling pass is 20%, the speed ratio is 1.32, the lower roll speed is 0.30m / s, the upper roll speed is 0.40m / s, the rolling force is 160kN, and the asynchronous rolling is to a thickness of 1.5mm.

[0055] After each rolling pass, the rolled piece is returned to the liquid nitrogen tank for heat preservation. This process is repeated until each sheet reaches 1.5mm in thickness.

[0056] ⑧ Heat treatment: The plate after cryogenic asynchronous rolling is annealed at 1000℃ and 1Pa vacuum for 10 minutes, and then water quenched to room temperature; then the alloy plate is aged at 920℃ for 8 hours, and then water quenched again to obtain a Co-based high-temperature alloy containing hafnium and rhenium.

[0057] The SEM microstructure of the hafnium-rhenium-containing Co-based superalloy prepared in Example 1 is as follows: Figure 2 As shown in (a), it is composed of a typical multiphase γ / γ′ microstructure, with γ′ nanoparticles coherently precipitated on the γ matrix; Example 1, through specific composition design and the use of deep cryogenic asynchronous rolling and other process steps, by changing the linear speed on both sides of the plate during rolling, utilizes the strong "rolling" deformation of the deep cryogenic asynchronous rolling plate to cause the multiphase γ / γ′ microstructure to break down, increase the cumulative strain of the deformed structure, and improve the comprehensive mechanical properties of the high-temperature alloy by promoting microstructure refinement.

[0058] The tensile engineering stress-strain curve of the hafnium-rhenium-containing Co-based superalloy prepared in Example 1 is shown in the figure. Figure 3As shown, due to the refinement of the microstructure, the strength and plasticity of the high-temperature alloy are significantly increased. The tensile strength, yield strength, and elongation of the hafnium-rhenium-based Co-based high-temperature alloy prepared in Example 1 were measured to be 803 Pa, 588 Pa, and 37.5%, respectively. The tensile strength, yield strength, and elongation of conventional cold-rolled steel sheet were measured to be 786 Pa, 563 Pa, and 30.9%, respectively. Compared with conventional cold-rolled steel sheet, the tensile strength, yield strength, and elongation of the hafnium-rhenium-based Co-based high-temperature alloy prepared in Example 1 were increased by 2.12%, 4.25%, and 17.6%, respectively.

[0059] The high-temperature creep strain-time curve of the Co-based superalloy prepared in Example 1 is shown in the figure. Figure 4 As shown, when the creep stress load is 150 MPa and the temperature is 900 °C, the creep fracture time of the Co-based superalloy containing hafnium and rhenium increases from 40.27 h to 634 h.

[0060] Example 2

[0061] A hafnium-rhenium-based Co-based superalloy and its preparation method are disclosed. The chemical composition of the Co-based superalloy, by mass percentage, meets the following requirements: C: 0.1%, Ni: 22.8%, Cr: 9.8%, Mo: 4.3%, Ta: 1.8%, Al: 2.0%, Ti: 0.6%, Si: 0.3%, Mn: 0.6%, V: 0.35%, Hf: 2%, Re: 1.1%, B: 0.006%, with the balance being Co.

[0062] The preparation method of the hafnium-rhenium-containing Co-based superalloy includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, rapid forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; wherein,

[0063] ① Vacuum induction melting: According to the chemical composition requirements of the Co-based high-temperature alloy, Cr, Co plates, Ni plates, Ta blocks, Mo strips, Si and V strips are added to the medium-frequency induction arc furnace, and the vacuum degree of the medium-frequency induction arc furnace is controlled at 0.55×10⁻⁶. -2 Pa, melting temperature 1520℃; after the alloy material melts, adjust the power to the refining temperature 1470℃, hold for 80 minutes during refining, and control the vacuum degree to 3Pa; reduce the power until a film forms on the surface of the melt, then add carbon electrode, NiB alloy and metal Hf, and stir electromagnetically for 5 minutes; after purging with argon gas at 4000Pa, increase the power to clear the melt, adjust the temperature of the molten steel to the pouring temperature 1470℃, add Al, sponge Ti, metal Mn and metal Re, stir electromagnetically for 2.5 minutes, and then cast to obtain the alloy ingot.

[0064] ② Protective atmosphere electroslag remelting: After the alloy ingot box obtained in step ① has cooled, the riser of the ingot is cut off and its surface is polished to serve as the electrode for protective atmosphere electroslag remelting. The quaternary slag system is used to go through three stages: start-up stage, smelting stage and hot capping stage. An appropriate amount of argon gas is introduced for electroslag remelting to obtain electroslag refined ingot.

[0065] ③ Homogenization treatment: The electroslag refining ingot is heated from room temperature to 1050℃ at a rate of 15℃ / min and held for 2.0h, followed by homogenization treatment at 1155℃ for 3h.

[0066] ④ Fast forging: The homogenized alloy ingot is forged into a slab at 1090℃ using a 2000t fast forging machine. The deformation amount per pass is 16%, and the total deformation amount is 50%. After the fast forging is completed, the slab is returned to the furnace for heat preservation.

[0067] ⑤ Hot rolling deformation: After the slab is forged, it is kept at 1230℃ for 9 hours and then hot rolled on a hot rolling mill. The initial rolling temperature is 1170℃, the final rolling temperature is 870℃, the total reduction rate is 92%, and it is water cooled to room temperature when rolled to a thickness of 3.3mm to obtain hot rolled plate.

[0068] ⑥ Solution treatment: The alloy hot-rolled sheet is solution treated in a muffle furnace at a temperature of 1200℃ for 30 hours.

[0069] ⑦ Cryogenic Asynchronous Rolling: Three passes of cryogenic asynchronous rolling are performed using a four-roll cold rolling mill. The lower roll is a slow roll with a constant speed, while the upper roll is a fast roll with its speed adjusted according to the speed ratio. Before cryogenic asynchronous rolling, the high-temperature alloy plate is cooled in liquid nitrogen to a temperature of -140°C. Then, the rolls are turned on and rotated under zero load. The upper and lower work rolls of the mill are cooled using nitrogen cooling spray guns to achieve a roll surface temperature of -140°C. The high-temperature alloy is then quickly removed for cryogenic asynchronous rolling.

[0070] The first rolling pass has a reduction rate of 25%, a speed ratio of 1.14, a lower roll speed of 0.24 m / s, an upper roll speed of 0.27 m / s, a rolling force of 160 kN, and is asynchronously rolled to a thickness of 2.5 mm.

[0071] The reduction rate of the second rolling pass is 36%, the speed ratio is 1.26, the lower roll speed is 0.28m / s, the upper roll speed is 0.35m / s, the rolling force is 230kN, and the asynchronous rolling is to a thickness of 1.6mm.

[0072] The reduction rate of the third rolling pass is 25%, the speed ratio is 1.36, the lower roll speed is 0.32m / s, the upper roll speed is 0.44m / s, the rolling force is 170kN, and the asynchronous rolling is to a thickness of 1.2mm.

[0073] After each rolling pass, the rolled piece is returned to the liquid nitrogen tank for heat preservation. This process is repeated until each sheet reaches 1.2 mm.

[0074] ⑧ Heat treatment: The cryogenically rolled plate was annealed at 950℃ and 3Pa vacuum for 15 minutes, and then water quenched to room temperature; then the alloy plate was aged at 870℃ for 12 hours, and then water quenched to obtain a Co-based high-temperature alloy containing hafnium and rhenium.

[0075] The SEM microstructure of the hafnium-rhenium-containing Co-based superalloy prepared in Example 2 is as follows: Figure 2 As shown in (b), it consists of a typical multiphase γ / γ′ microstructure, with γ′ nanoparticles coherently precipitated on the γ matrix, and cubically ordered γ′ particles densely and uniformly distributed on the γ matrix. Example 2, through specific composition design and the use of cryogenic asynchronous rolling and other process steps, by changing the linear speed on both sides of the plate during rolling, utilizes the intense "rolling" deformation of the cryogenic asynchronous rolling plate to cause the multiphase γ / γ′ microstructure to break down, increasing the cumulative strain of the deformed structure, and improving the comprehensive mechanical properties of the high-temperature alloy by promoting microstructure refinement.

[0076] The tensile engineering stress-strain curve of the hafnium-rhenium-containing Co-based superalloy obtained in Example 2 is shown in the figure. Figure 3 As shown, due to the refinement of the microstructure, the strength and plasticity of the high-temperature alloy are significantly increased. The tensile strength, yield strength, and elongation of the hafnium-rhenium-based Co-based high-temperature alloy prepared in Example 2 were measured to be 882 Pa, 626 Pa, and 37.9%, respectively. The tensile strength, yield strength, and elongation of conventional cold-rolled steel sheet were measured to be 786 Pa, 563 Pa, and 30.9%, respectively. Compared with conventional cold-rolled steel sheet, the tensile strength, yield strength, and elongation of the hafnium-rhenium-based Co-based high-temperature alloy prepared in Example 2 were increased by 10.88%, 10.06%, and 18.47%, respectively.

[0077] The high-temperature creep strain-time curve of the Co-based superalloy prepared in Example 2 is shown in the figure. Figure 4 As shown, when the creep stress load is 150 MPa and the temperature is 900 °C, the creep fracture time of the Co-based superalloy containing hafnium and rhenium increases from 40.27 h to 682 h.

[0078] Example 3

[0079] A hafnium-rhenium-based Co-based superalloy and its preparation method are disclosed. The chemical composition of the Co-based superalloy, by mass percentage, meets the following requirements: C: 0.15%, Ni: 24.5%, Cr: 11.0%, Mo: 6.4%, Ta: 2.5%, Al: 2.8%, Ti: 0.8%, Si: 0.4%, Mn: 0.8%, V: 0.5%, Hf: 3%, Re: 1.8%, B: 0.008%, with the balance being Co.

[0080] The preparation method of the hafnium-rhenium-containing Co-based superalloy includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, rapid forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; wherein,

[0081] ① Vacuum induction melting: According to the chemical composition requirements of the Co-based high-temperature alloy, Cr, Co plates, Ni plates, Ta blocks, Mo strips, Si and V strips are added to the medium-frequency induction arc furnace, and the vacuum degree of the medium-frequency induction arc furnace is controlled at 0.6×10⁻⁶. -2 Pa, melting temperature 1540℃; after the alloy material melts, adjust the power to the refining temperature 1490℃, hold for 90 minutes during refining, and control the vacuum degree to 5Pa; reduce the power until a film forms on the surface of the melt, then add carbon electrode, NiB alloy and metal Hf, and electromagnetically stir for 6 minutes; after purging with argon gas at 5000Pa, increase the power to clear the melt, adjust the temperature of the molten steel to the pouring temperature 1490℃, add Al, sponge Ti, metal Mn and metal Re, and electromagnetically stir for 3 minutes before casting to obtain the alloy ingot.

[0082] ② Protective atmosphere electroslag remelting: After the alloy ingot box obtained in step ① has cooled, the riser of the ingot is cut off and its surface is polished to serve as the electrode for protective atmosphere electroslag remelting. The quaternary slag system is used to go through three stages: start-up stage, smelting stage and hot capping stage. An appropriate amount of argon gas is introduced for electroslag remelting to obtain electroslag refined ingot.

[0083] ③ Homogenization treatment: The electroslag refining ingot is heated from room temperature to 1060℃ at a rate of 20℃ / min and held for 1.5h, followed by homogenization treatment at 1170℃ for 2h.

[0084] ④ Fast forging: The homogenized alloy ingot is forged into a slab at 1120℃ using a 2000t fast forging machine. The deformation amount per pass is 18%, and the total deformation amount is 60%. After the fast forging is completed, the slab is returned to the furnace for heat preservation.

[0085] ⑤ Hot rolling deformation: After the slab is forged, it is kept at 1200℃ for 10 hours and then hot rolled on a hot rolling mill. The initial rolling temperature is 1150℃, the final rolling temperature is 850℃, the total reduction rate is 94%, and it is water cooled to room temperature when rolled to 3mm thickness to obtain hot rolled plate.

[0086] ⑥ Solution treatment: The alloy hot-rolled sheet is solution treated in a muffle furnace at a temperature of 1150℃ for 36 hours.

[0087] ⑦ Cryogenic Asynchronous Rolling: Three passes of cryogenic asynchronous rolling are performed using a four-roll cold rolling mill. The lower roll is a slow roll with a constant speed, while the upper roll is a fast roll with its speed adjusted according to the speed ratio. Before cryogenic asynchronous rolling, the high-temperature alloy sheet is cooled in liquid nitrogen to a temperature of -160°C. Then, the rolls are turned on and rotated under zero load. The upper and lower work rolls of the mill are cooled using nitrogen cooling spray guns to achieve a roll surface temperature of -160°C. The high-temperature alloy is then quickly removed for cryogenic asynchronous rolling.

[0088] The first rolling pass has a reduction rate of 30%, a speed ratio of 1.18, a lower roll speed of 0.25 m / s, an upper roll speed of 0.30 m / s, a rolling force of 170 kN, and is asynchronously rolled to a thickness of 2.1 mm.

[0089] The second rolling pass has a reduction rate of 40%, a speed ratio of 1.3, a lower roll speed of 0.29 m / s, an upper roll speed of 0.38 m / s, a rolling force of 260 kN, and is asynchronously rolled to a thickness of 1.3 mm.

[0090] The reduction rate of the third rolling pass is 30%, the speed ratio is 1.4, the lower roll speed is 0.33m / s, the upper roll speed is 0.46m / s, the rolling force is 180kN, and the asynchronous rolling is carried out to a thickness of 0.9mm.

[0091] After each rolling pass, the rolled piece is returned to the liquid nitrogen tank for heat preservation. This process is repeated until each sheet reaches 0.9 mm.

[0092] ⑧ Heat treatment: The plate after cryogenic asynchronous rolling is annealed at 900℃ and 5Pa vacuum for 20 minutes, and then water quenched to room temperature; then the alloy plate is aged at 820℃ for 15 hours, and then water quenched to obtain a Co-based high-temperature alloy containing hafnium and rhenium.

[0093] The SEM microstructure of the hafnium-rhenium-containing Co-based superalloy prepared in Example 3 is as follows: Figure 2As shown in (c), it consists of a typical multiphase γ / γ′ microstructure, with γ′ nanoparticles coherently precipitated on the γ matrix. As the velocity ratio increases during cryogenic asynchronous rolling, the shape of the γ′ nanoparticles gradually evolves from an initial cubic shape to a nearly spherical shape and becomes increasingly refined. Example 3, through specific composition design and the use of cryogenic asynchronous rolling and other process steps, changes the linear velocity on both sides of the plate during rolling. The intense "rolling" deformation of the cryogenic asynchronous rolling plate causes the multiphase γ / γ′ microstructure to break down, increasing the cumulative strain of the deformed structure. This promotes the refinement of the microstructure and improves the comprehensive mechanical properties of the high-temperature alloy.

[0094] The tensile engineering stress-strain curve of the hafnium-rhenium-containing Co-based superalloy prepared in Example 3 is shown in the figure. Figure 3 As shown, due to the refinement of the microstructure, the strength and plasticity of the high-temperature alloy are significantly increased. The tensile strength, yield strength, and elongation of the hafnium-rhenium-based Co-based high-temperature alloy prepared in Example 3 were measured to be 907 Pa, 739 Pa, and 40.2%, respectively. The tensile strength, yield strength, and elongation of conventional cold-rolled steel sheet were measured to be 786 Pa, 563 Pa, and 30.9%, respectively. Compared with conventional cold-rolled steel sheet, the tensile strength, yield strength, and elongation of the hafnium-rhenium-based Co-based high-temperature alloy prepared in Example 3 were increased by 13.34%, 23.82%, and 23.13%, respectively.

[0095] The high-temperature creep strain-time curve of the Co-based superalloy prepared in Example 3 is shown in the figure. Figure 4 As shown, when the creep stress load is 150 MPa and the temperature is 900 °C, the creep fracture time of the Co-based superalloy containing hafnium and rhenium increases from 40.27 h to 4122.7 h, and the high-temperature performance is significantly improved.

[0096] Comparative Example 1

[0097] A hafnium-rhenium-based Co-based superalloy and its preparation method are disclosed. The chemical composition of the Co-based superalloy, by mass percentage, meets the following requirements: C: 0.15%, Ni: 24.5%, Cr: 11.0%, Mo: 6.4%, Ta: 2.5%, Al: 2.8%, Ti: 0.8%, Si: 0.4%, Mn: 0.8%, V: 0.5%, Hf: 3%, Re: 1.8%, B: 0.008%, with the balance being Co.

[0098] The preparation method of the hafnium-rhenium-containing Co-based high-temperature alloy includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, fast forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; except for step ⑦ cryogenic asynchronous rolling, which is different from Example 3, the other steps are the same as the preparation method of Example 3.

[0099] The specific process flow of step ⑦ of Comparative Example 1, cryogenic asynchronous rolling, is as follows: three passes of cryogenic rolling are performed using a four-roll cold rolling mill. Before cryogenic asynchronous rolling, the high-temperature alloy plate is placed in liquid nitrogen to cool it to a temperature of -160°C. Then, the rolls are turned on and rotated under zero load. The upper and lower work rolls of the rolling mill are cooled using the mill's nitrogen cooling spray gun to achieve a roll surface temperature of -160°C. The high-temperature alloy is then quickly removed for cryogenic rolling.

[0100] The first rolling pass has a reduction rate of 30%, a roll speed of 0.25 m / s, a rolling force of 170 kN, and is asynchronously rolled to 2.1 mm.

[0101] The second rolling pass has a reduction rate of 40%, a roll speed of 0.29 m / s, a rolling force of 260 kN, and is asynchronously rolled to 1.3 mm.

[0102] The reduction rate of the third rolling pass is 30%, the roll speed is 0.33m / s, the rolling force is 180kN, and it is asynchronously rolled to 0.9mm;

[0103] After each rolling pass, the rolled piece is returned to the liquid nitrogen tank for heat preservation. This process is repeated until each sheet reaches 0.9 mm.

[0104] The SEM microstructure of the hafnium-rhenium-containing Co-based superalloy prepared in Comparative Example 1 is shown in the figure. Figure 2 As shown in (d), the γ′ reinforcing phase is unevenly distributed on the γ matrix, and the γ′ reinforcing phase is relatively coarse with a small volume fraction.

[0105] The tensile stress-strain curve of the hafnium-rhenium-containing Co-based superalloy prepared in Comparative Example 1 is shown in the figure. Figure 3 As shown, the tensile strength, yield strength and elongation of the Co-based superalloy prepared in Comparative Example 1 were tested and found to be 786 Pa, 563 Pa and 30.9%, respectively.

[0106] The high-temperature creep strain-time curve of the Co-based superalloy prepared in Comparative Example 1 is shown in the figure. Figure 4 As shown, when the creep stress load is 150 MPa and the temperature is 900 °C, the creep fracture time of the Co-based superalloy is 40.27 h.

[0107] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A method for preparing a Co-based superalloy containing hafnium and rhenium, characterized in that, The chemical composition of the Co-based superalloy, by mass percentage, is: C: 0.05%–0.15%, Ni: 21.5%–24.5%, Cr: 8.5%–11.0%, Mo: 3.2%–6.4%, Ta: 1.0%–2.5%, Al: 1.2%–2.8%, Ti: 0.4%–0.8%, Si: 0.2%–0.4%, Mn: 0.4%–0.8%, V: 0.2%–0.5%, Hf: 1%–3%, Re: 0.5%–1.8%, B: 0.005%–0.008%, with the balance being Co; The preparation method of the hafnium-rhenium-containing Co-based superalloy includes the following steps: vacuum induction melting, protective atmosphere electroslag melting, homogenization treatment, rapid forging, hot rolling deformation, solution treatment, cryogenic asynchronous rolling, and heat treatment; wherein, ① Vacuum induction melting: Materials are prepared according to the chemical composition requirements of the Co-based high-temperature alloy, with a vacuum degree of 0.5~0.6×10⁻⁶. -2 Under Pa conditions, alloy raw materials containing Cr, Co, Ni, Ta, Mo, Si, and V are first added to a medium-frequency induction arc furnace and melted at 1510℃~1540℃; then the power is adjusted to a refining temperature of 1450℃~1490℃, and the refining period is held for 70~90min, with the vacuum degree controlled at 1~5Pa; after the power is reduced until a film forms on the surface of the melt, alloying materials containing C, Si, Cr, Ta, B, and Hf are added, and the mixture is electromagnetically stirred for 4~6min. After purging with argon gas at 3000~5000Pa, the power is increased to clear the melt, and the temperature of the molten steel is adjusted to a casting temperature of 1450℃~1490℃. Alloy raw materials containing Al, Ti, Mn, and Re are added, and after electromagnetic stirring for 2~3min, the mixture is cast to obtain an alloy ingot. ② Protective atmosphere electroslag remelting: The alloy ingot from step ① is electroslag remelted using argon as a protective atmosphere and a quaternary slag system to obtain an electroslag refined ingot. ③ Homogenization treatment: The electroslag refining ingot is heated from room temperature to 1040℃~1060℃ at a rate of 10~20℃ / min and held for 1.5~2.5h, followed by homogenization treatment at 1140℃~1170℃ for 2~4h. ④ Rapid forging: The homogenized alloy ingot is rapidly forged into a slab at 1060℃~1120℃, and then returned to the furnace for heat preservation after rapid forging. ⑤ Hot rolling deformation: After the slab is forged, it is held at 1200℃~1250℃ for 8~10h and then hot rolled to obtain a hot rolled plate with a thickness of 3~3.5mm. ⑥ Solution treatment: The alloy hot-rolled sheet is subjected to solution treatment at a temperature of 1150℃~1250℃ for 24~36h. ⑦ Cryogenic asynchronous rolling: Before rolling, the alloy sheet is cooled to -160℃~-120℃ in liquid nitrogen; then, it is rolled in three passes with a reduction rate of 20%~40% using a four-roll cold rolling mill; after each pass, the rolled piece is put back into the liquid nitrogen tank for heat preservation until each sheet reaches 0.9~1.5mm. ⑧ Heat treatment: The plate after cryogenic asynchronous rolling is annealed in a vacuum environment of 900℃~1000℃ for 10~20min, then water quenched to room temperature; then aged, and then water quenched to obtain a Co-based high-temperature alloy containing hafnium and rhenium.

2. The method for preparing the Co-based superalloy according to claim 1, characterized in that, Step ② The main components of the quaternary slag system are CaF2: 50%–56%, Al2O3: 20%–24%, CaO: 18%–22%, MgO: 4%–6%, with the remainder being unavoidable impurities.

3. The method for preparing the Co-based superalloy according to claim 1, characterized in that, Step 4: The deformation amount per pass of high-temperature rapid forging is 13% to 18%, and the total deformation amount is 40% to 60%.

4. The method for preparing the Co-based superalloy according to claim 1, characterized in that, Step ⑤ Hot rolling treatment: the initial rolling temperature is 1150℃~1200℃, the final rolling temperature is 850℃~900℃, and the total reduction rate is 90%~94%.

5. The method for preparing the Co-based superalloy according to claim 1, characterized in that, In step ⑦, the speed ratio of cryogenic asynchronous rolling is 1.1 to 1.4, the lower roll speed is 0.22 to 0.33 m / s, the upper roll speed is 0.24 to 0.46 m / s, and the rolling force is 150 to 260 kN.

6. The method for preparing the Co-based superalloy according to claim 1, characterized in that, In step ⑦, the first pass of the three-pass cryogenic asynchronous rolling has a reduction rate of 20% to 30%, a speed ratio of 1.1 to 1.18, a lower roll speed of 0.22 to 0.25 m / s, an upper roll speed of 0.24 to 0.30 m / s, a rolling force of 150 to 170 kN, and is asynchronously rolled to a thickness of 2.1 to 2.8 mm.

7. The method for preparing the Co-based superalloy according to claim 1, characterized in that, In step ⑦, the reduction rate of the second pass in the three-pass cryogenic asynchronous rolling is 32% to 40%, the speed ratio is 1.22 to 1.3, the lower roll speed is 0.26 to 0.29 m / s, the upper roll speed is 0.32 to 0.38 m / s, the rolling force is 200 to 260 kN, and the asynchronous rolling is carried out to a thickness of 1.3 to 1.9 mm.

8. The method for preparing the Co-based superalloy according to claim 1, characterized in that, In step ⑦, the reduction rate of the third pass in the three-pass cryogenic asynchronous rolling is 20% to 30%, the speed ratio is 1.32 to 1.4, the lower roll speed is 0.30 to 0.33 m / s, the upper roll speed is 0.40 to 0.46 m / s, the rolling force is 160 to 180 kN, and the asynchronous rolling is carried out to a thickness of 0.9 to 1.5 mm.

9. The method for preparing the Co-based superalloy according to claim 1, characterized in that, The aging treatment temperature in step ⑧ is 820℃~920℃, and the aging treatment time is 8~15h.

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