Corrosion-resistant nickel-based superalloy, preparation method and application thereof

Abstract

The application relates to a corrosion-resistant nickel-based high-temperature alloy, a preparation method and application thereof, and belongs to the technical field of corrosion-resistant nickel-based alloys. The components are as follows in percentage by mass: Cr: 34-38%, Al: 3.5-5%, Co: 0.5-10%, C: 0.01-0.05%, B: 0.001-0.006%, Zr: 0.02-0.05%, Y: 0.08% or less, La: 0.08% or less, and the balance is Ni. The microstructure comprises equiaxed austenitic alloy grains, dispersedly-distributed spherical a-Cr phases and lamellar structures in a colony-like distribution between the spherical a-Cr phases; the solid solution state hardness is 150-350 HV, the aging state hardness is 380-750 HV, the tensile strength is 1200-2100 MPa, the yield strength is 800-1800 MPa and the like. The application remarkably improves the segregation degree of the alloy by adding Co, reduces the homogenization and hot working difficulty, and can meet the requirements of hot end components serving in complex environments.

Description

Technical Field

[0001] This invention belongs to the field of corrosion-resistant nickel-based alloy technology, and relates to a corrosion-resistant nickel-based high-temperature alloy, its preparation method and its application. Background Technology

[0002] The fuels used in critical equipment such as petroleum refining equipment, thermal power generation equipment, waste-to-energy equipment, gas turbines, and boilers produce highly corrosive combustion ash, causing high-temperature corrosion of critical components. Traditional heat-resistant steels can no longer meet the increasingly demanding performance requirements of these critical components, leading to the gradual adoption of nickel-based superalloys. This is because nickel-based superalloys typically contain a certain amount of chromium (Cr) to ensure good oxidation and corrosion resistance. However, traditional nickel-based alloys generally contain only about 15-25% Cr, and their corrosion resistance and strength are no longer sufficient to meet the current complex and demanding high-temperature, high-corrosion, and high-stress environments. For example, Nimonic 80A and Inconel 625 alloys, widely used in thermal power plants and marine engineering, can no longer meet the current requirements for strength and corrosion resistance.

[0003] Currently, there are some related patented technologies for corrosion-resistant nickel-based alloys, but certain limitations still exist. For example, Chinese invention patent application CN201810457993.3 discloses a "high-cobalt nickel-based high-temperature alloy and its preparation method," which improves the high-temperature mechanical properties of the alloy by adding Co. However, the amount of Cr added in this invention is relatively small, approximately 18%, making it difficult to impart good corrosion resistance to the material and making it unsuitable for complex and harsh high-temperature, high-corrosion, and high-stress environments. Similarly, Chinese invention patent application CN202311737608.8 discloses a "Ni-Cr-Al system nickel-based high-temperature alloy and its preparation method." Although this technology adds a relatively high amount of Cr (30-45%) to the nickel-based alloy, resulting in better corrosion resistance, the lack of Co leads to severe segregation, high brittleness, and poor high-temperature performance. Furthermore, the introduction of Ti significantly degrades the alloy's hot working properties.

[0004] Therefore, we need to design a nickel-based high-temperature alloy with higher strength and better corrosion resistance based on traditional nickel-based alloys to meet the increasingly demanding performance requirements of key components in important equipment such as petroleum refining equipment, thermal power generation equipment, waste-to-energy equipment, gas turbines and boilers, improve their service life, extend overhaul intervals, and reduce economic losses caused by corrosion problems. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a corrosion-resistant nickel-based superalloy and its preparation method. The corrosion-resistant nickel-based superalloy is prepared through a process involving vacuum induction and electroslag double melting, homogenization treatment, forging to prepare billets, solution treatment, and aging treatment. The product exhibits diverse performance characteristics after different heat treatment processes, allowing for tailored adjustments based on component requirements to better adapt to the service environment of the components, which is significantly different from traditional nickel-based superalloys. Furthermore, this superalloy can be applied to hot-end components requiring high strength, corrosion resistance, and wear resistance, such as gas turbine combustor nozzles and fuel control system components, and key components of marine low-speed engine combustors (injector nozzles, exhaust valve stems).

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A corrosion-resistant nickel-based superalloy, a novel high-Cr nickel-based alloy, named TA800, comprises the following components by mass percentage: Cr: 34%~38%, Al: 3.5%~5%, Co: 0.5-10%, C: 0.01-0.05%, B: 0.001-0.006%, Zr: 0.02-0.05%, Y: less than 0.08%, La: less than 0.08%, with the balance being Ni.

[0008] The following details the function and dosage of the main components contained in this invention (all in mass percentage):

[0009] Co: Co mainly exists in Ni-based solid solutions. Through the difference in atomic size between Co and Ni, it causes lattice distortion, increasing the resistance to dislocation movement and thus playing a role in solid solution strengthening, thereby improving the strength and hardness of the alloy. It affects phase stability; Co helps stabilize the γ phase (face-centered cubic structure of Ni-based solid solutions) and inhibits the precipitation of harmful phases. During high-temperature service, it can reduce the aggregation and growth of the γ' phase (intermetallic compound phases such as Ni3(Al,Ti), etc.), maintaining a fine and dispersed distribution of the γ' phase, thereby maintaining the alloy's good high-temperature strength and creep resistance. Regarding its effect on machinability, an appropriate amount of Co can improve the alloy's hot workability, reduce deformation resistance, and increase hot plasticity. Adding Co can significantly improve the degree of segregation, reduce homogenization and hot working difficulty, making the alloy easier to form and reducing machining defects during hot working processes such as forging and rolling. However, if the Co content is too high, harmful σ phases will precipitate, and the work hardening rate of the alloy will increase, which will have an adverse effect on machinability. Therefore, the present invention limits the Co content of the alloy to 0.5-10%.

[0010] Cr: Cr is an indispensable alloying element in nickel-based superalloys. Its main functions are as follows: (1) Solid solution strengthening: Cr in the γ matrix of superalloys causes lattice distortion, generates elastic stress field strengthening, and thus improves the strength of γ solid solution; (2) Precipitation strengthening: In this alloy, Cr mainly exists as lamellar α-Cr phase after appropriate heat treatment. It is one of the important strengthening phases of this alloy, and it can also form a series of Cr-based carbides with C. In this alloy, Cr mainly exists as M 23 C6 type carbide is the main component. This carbide is mainly distributed at the grain boundaries. The uniformly distributed granular discontinuous carbide at the grain boundaries can effectively prevent grain boundary slip and migration, and improve strength. (3) In the nickel-based alloy, after subsequent solid solution and aging heat treatment, it can be uniformly distributed near the grain boundaries with a small size (≤3μm), which is beneficial to the improvement of the alloy's ductility. (4) Antioxidant properties: It can form a Cr2O3 type oxide film, which has good antioxidant properties. The higher the Cr content, the better the antioxidant properties. However, with the increase of Cr content, a eutectic of γ phase and α-Cr phase will be formed in the alloy, which will deteriorate the hot working and service performance. In order to avoid the formation of a eutectic of γ phase and α-Cr phase in the alloy, the Cr content is controlled at 34%~38% in this invention.

[0011] Al: Al is the main element for forming the γ′ phase. It forms the γ' phase (Ni3Al) with Ni, which plays a precipitation strengthening role. One of the most critical roles of adding Al to this alloy is to promote the formation of lamellar structure (strengthening phase), increase the lamellar structure formation rate, and refine the lamellar structure. Too low an Al content will lead to a decrease in the number of strengthening phases, or even the inability to form the key lamellar strengthening phase, thus kinetically inhibiting the formation of strengthening phases. However, excessive Al will lead to the formation of the eutectic phase (γ+αCr), which will deteriorate the hot working and service performance. Therefore, this invention strictly limits the Al content of the alloy to 3.5%~5%.

[0012] C: In nickel-based alloys, carbon (C) primarily affects the mechanical properties of the material through the formation of MC carbides during solidification and the precipitation of M23C6 and M6C during heat treatment. The granular, discontinuous carbides M23C6 precipitated at grain boundaries can inhibit grain boundary slip and crack propagation, improving creep rupture life, ductility, and toughness. Higher C content tends to increase the amount of M23C6 in high-Cr nickel-based alloys. 23 The precipitation of C6 forms large-sized, chain-like carbides and increases the inhomogeneity of M23C6 distribution at grain boundaries, thus deteriorating the mechanical properties of the alloy. Therefore, in this invention, the C content is controlled at 0.01-0.05%.

[0013] B: The addition of trace amounts of boron (B) strengthens grain boundaries, improves carbide morphology, and enhances the creep performance and service life of the alloy. Furthermore, carbides and borides compete with each other; the addition of trace amounts of B can reduce the formation of continuous Cr-based carbides, thus improving carbide morphology. However, excessive addition leads to dense precipitation of borides at grain boundaries, causing grain boundary embrittlement and degrading material performance. Therefore, this invention limits the B content of the alloy to 0.001-0.006%.

[0014] Zr: Zr atoms can segregate to grain boundaries, increasing grain boundary strength, improving carbide morphology and distribution, and inhibiting the formation of secondary carbides M23C6 and M6C, thereby improving the microstructure stability of the alloy under long-term high-temperature heat exposure. Considering factors such as cost, the Zr content in this invention is controlled at 0.02-0.05%.

[0015] Y and La: Adding rare earth elements Y and La can effectively capture free O and S in the alloy, generating stable rare earth oxides or sulfides, thereby reducing the harmful effects of O and S, purifying the alloy, and refining the grain size. However, excessive addition can degrade the alloy's performance. This invention limits the Y and La content of the alloy to below 0.08%.

[0016] The corrosion-resistant nickel-based superalloy has the following microstructure and properties:

[0017] The described nickel-based alloy is a Ni-Co-Cr-Al alloy, belonging to the category of high-Cr high-temperature alloys. Its Cr content far exceeds that of ordinary high-temperature alloys, exceeding 30%, endowing the alloy with excellent corrosion resistance, strength, and hardness. However, high-Cr alloys are often difficult to hot-work, easily leading to cracking and other phenomena. This is due to the severe segregation of Cr elements in high-Cr alloys. Adding Co can significantly improve the degree of segregation, reducing the difficulty of homogenization and hot working. By controlling the solution treatment and aging process, including temperature, time, and cooling method, various special microstructures can be obtained, resulting in different strengths, hardness, and ductility to meet the performance requirements of different components for corrosion-resistant nickel-based alloys. These special microstructures are closely related to the composition and heat treatment process, which is significantly different from traditional nickel-based high-temperature alloys. Details are as follows:

[0018] The microstructure of the nickel-based superalloy mainly includes equiaxed austenitic alloy grains, dispersed spherical α-Cr phases, and lamellar structures distributed in a cluster pattern between the spherical α-Cr phases. Specifically: the grain size of the equiaxed austenitic alloy grains reaches level 7 or above; the average size of the dispersed spherical α-Cr phases is <5μm, and the proportion of spherical α-Cr phases is <16%; the lamellar structure has the following characteristics: the structure of the lamellar structure is composed of α-Cr phase lamellars, γ phase lamellars, and γ' phase; the average spacing between adjacent α-Cr phase lamellars in the lamellar structure is <300nm, wherein the thickness of the α-Cr phase layer is less than that of the γ phase, the thickness of the α-Cr phase layer is <75nm, the average thickness of the γ phase layer is <150nm, the average size of the γ' phase is <75nm, and the lamellar structure is distributed in a cluster pattern between the spherical α-Cr phases, which is defined as lamellar structure clusters (with the same orientation), and the size of the lamellar structure clusters is <10μm. Grain size and lamellar structure endow materials with extremely high strength. Smaller grain size and finer average interlayer spacing result in greater alloy strength. The spherical α-Cr phase acts as a plasticizer; a higher proportion of spherical α-Cr phases improves ductility. However, excessively large grain size will coarsen the lamellar structure, severely reducing ductility. Generally, the grain size should be controlled below 150 μm, preferably below 100 μm. By controlling the aforementioned microstructure and ratios through heat treatment processes, a variety of properties can be obtained.

[0019] Regarding the properties of the nickel-based superalloy, its hardness in the solution-treated state ranges from 150 to 350 HV, and its hardness in the aged state ranges from 380 to 750 HV. The good solution softening effect makes the alloy easy to process into high-precision parts, reducing the processing difficulty. In the aged state, the alloy has high hardness and good red hardness. Its tensile strength ranges from 1200 to 2100 MPa, its yield strength from 800 to 1800 MPa, its elongation from 2 to 30%, and its reduction of area from 5 to 60%. This alloy can possess diverse performance characteristics after different heat treatment processes, and can be tailored to the needs of the parts to better adapt to the service environment of the parts. This is significantly different from traditional nickel-based superalloys.

[0020] A method for preparing a corrosion-resistant nickel-based superalloy includes the following steps:

[0021] Step 1, TA800 alloy smelting:

[0022] High-purity component raw materials are batched according to mass percentage (wt.%), and the batching is processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet.

[0023] The second step is the homogenization treatment of the TA800 alloy:

[0024] Homogenization heat treatment process: Feed the material into the furnace at 700°C, with a heating rate of 2-4°C / min, heat to 1100-1180°C, hold for 16-28 hours, and then remove and air cool.

[0025] The third step, TA800 alloy forging:

[0026] Forging process: The billet is fed into the furnace at 700°C and held for 3-7 hours. Then, the temperature is increased at a rate of 2-4°C / min to 1100-1150°C and held for 4-8 hours before being removed from the furnace for initial forging. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C. Each forging pass requires a reheat holding temperature of 1100-1150°C for at least 40 minutes. The billet is forged in several passes according to this process to obtain forged bars. TA800 alloy billet rolling: For forged bars with a diameter ≥ 50 mm and a length ≥ 2000 mm, hot rolling and drawing of the TA800 alloy is required after initial forging. The specific process includes: entering the furnace at 700°C, heating at a rate of approximately 2.5°C / min, heating to 1130°C, holding at that temperature for 3 hours, and then rolling. Rolling is performed in two passes: the first pass consists of 9-12 passes with a feed of 5 mm per pass (both sides), and the second pass consists of 5-8 passes with a feed of 2 mm per pass (both sides). The specifications of the rolled bar are selected based on the diameter of the exhaust valve forged bar (machined bar). Generally, the diameter allowance is 3-4 mm per side, ultimately yielding a black-skinned forged bar.

[0027] Application of a corrosion-resistant nickel-based superalloy, wherein the corrosion-resistant nickel-based superalloy is a high-strength, high-corrosion-resistant, high-wear-resistant, non-magnetic, and low-density (7.8 g / cm³) superalloy. 3 Nickel-based superalloys can meet the requirements of hot-end components serving in complex environments. They can be applied to components related to gas turbine combustor nozzles and fuel control systems, key components of marine low-speed engine combustors (injector nozzles, exhaust valve stems), or other hot-end components requiring high strength, corrosion resistance, and wear resistance.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) The nickel-based alloy described in this invention is a Ni-Co-Cr-Al alloy, which belongs to the category of high-Cr high-temperature alloys. The Cr content is much higher than that of ordinary high-temperature alloys, exceeding 30%, which endows the alloy material with good corrosion resistance, strength and hardness. However, high-Cr alloys are often difficult to hot work and are prone to cracking. The root cause is that the segregation of elements in high-Cr alloys is more serious. The addition of Co content can significantly improve the degree of segregation of the alloy, reduce the difficulty of homogenization and hot work.

[0030] (2) By controlling the solid solution and aging, including the control of temperature, time and cooling method, the present invention can make the alloy obtain a variety of special microstructures, thereby obtaining different strengths, hardness and ductility to meet the requirements of different components for corrosion-resistant nickel-based alloy performance. The above-mentioned special microstructures are closely related to the composition and heat treatment process, which is significantly different from traditional nickel-based high-temperature alloys. They have diverse performance characteristics and can be tailored to the needs of the components to better adapt to the service environment of the components. Attached Figure Description

[0031] Figure 1 This is a comparison chart of the yield strength of the TA800 alloy obtained in Example 1 and traditional representative corrosion-resistant materials;

[0032] Figure 2 This is a comparison chart of the S and V corrosion resistance of the TA800 alloy obtained in Example 1 and typical corrosion-resistant alloys;

[0033] Figure 3 The image shows the metallographic structure of the TA800 alloy after solution treatment obtained in Example 1.

[0034] Figure 4 The image shows the IPF (Integrated Photoform) of the microstructure of the TA800 alloy after solution treatment obtained in Example 1.

[0035] Figure 5 Metallographic and scanning electron microscope images of the TA800 alloy after solution treatment and aging treatment obtained in Example 1;

[0036] Figure 6 The image shows a transmission electron microscope (TEM) image of the microstructure of the TA800 alloy after solution treatment and aging, obtained in Example 1.

[0037] Figure 7 The results of EBSD grain analysis and precipitate analysis of the TA800 alloy after solution treatment and aging in Example 1 are shown. Figure 7 (a) in the figure represents the EBSD grain analysis. Figure 7 (b) in the figure represents the analysis results of the precipitated phase;

[0038] Figure 8 This is a graph showing the relationship between the hardness of the TA800 alloy obtained in Example 2 and the solution treatment and aging treatment temperatures.

[0039] Figure 9 The results of EBSD grain analysis of the TA800 alloy obtained in Example 3;

[0040] Figure 10 The results of EBSD grain analysis of the TA800 alloy obtained in Example 4;

[0041] Figure 11The results of EBSD grain analysis of the TA800 alloy obtained in Example 5;

[0042] Figure 12 Metallographic images of the as-cast microstructure of the TA800 alloy obtained in Example 6;

[0043] Figure 13 Metallographic photograph of the as-cast microstructure of TA800 alloy obtained in Example 7;

[0044] Figure 14 Metallographic photograph of the as-cast microstructure of TA800 alloy obtained in Example 8;

[0045] Figure 15 Metallographic images of the homogenized TA800 alloy obtained in Comparative Example 1;

[0046] Figure 16 Metallographic photograph of the homogenized TA800 alloy obtained in Example 6;

[0047] Figure 17 Metallographic photograph of the homogenized state of TA800 alloy obtained in Example 7. Detailed Implementation

[0048] The present invention will now be described in further detail with reference to the accompanying drawings and preferred embodiments.

[0049] Example 1

[0050] The TA800 alloy in this embodiment is a high-Cr nickel-based alloy. Specifically, the high-temperature alloy composition, by mass percentage, includes: Cr: 37%, Al: 4.3%, Co: 4%, C: 0.02%, B: 0.004%, Zr: 0.03%, with the balance being Ni. The preparation process of this embodiment includes the following steps:

[0051] Step 1, TA800 alloy smelting:

[0052] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 200mm.

[0053] The second step is the homogenization treatment of the TA800 alloy:

[0054] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 3°C / min, heat up to 1140°C, hold for 24 hours, and then remove and air cool.

[0055] The third step, TA800 alloy forging:

[0056] Forging process: The billet is fed into the furnace at 700°C, held for 7 hours, then heated at a rate of 3°C / min to 1130°C, held for 4 hours, and then removed from the furnace to begin the initial forging process. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a return to the furnace at 1130°C for 50 minutes. Following this process, the billet is forged in three passes, resulting in a forging ratio of 3, yielding the initial billet bar. The billet is then fed into the furnace at 700°C, heated at a rate of 2.5°C / min to 1130°C, held for 3 hours, and then removed from the furnace for rolling. Rolling is performed in two passes: the first pass has 9 passes with a feed rate of 5mm per pass (both sides), and the second pass has 6 passes with a feed rate of 2mm per pass (both sides). The specifications of the rolled bar are selected based on the diameter of the exhaust valve forged bar (machined bar). In this embodiment, the diameter allowance of the rolled bar is 2.5mm on each side, and the final hot-rolled bar has a diameter of 65mm and a length of 2450mm.

[0057] The alloy black forging bar of Example 1 was prepared by the above preparation process. Then, solution treatment and aging heat treatment were performed to evaluate its microstructure and mechanical properties. The TA800 alloy bar was subjected to solution treatment and aging heat treatment. The solution heat treatment regime was 1080°C for 1 hour followed by water cooling. The aging heat treatment temperature was 810°C for 24 hours, followed by air cooling.

[0058] Table 1. Results of mechanical properties and hardness tests

[0059]

[0060] Figure 1 The comparison of room temperature and high temperature yield strength of the alloy of Example 1 with common corrosion-resistant nickel-based alloys shows that the alloy of Example 1 has higher room temperature and high temperature strength compared with common corrosion-resistant nickel-based alloys. Table 1 shows the mechanical properties and hardness data, which shows that Example 1 has excellent comprehensive mechanical properties and hardness level. Figure 2 The comparison of the high-temperature corrosion performance of Example 1 with typical corrosion-resistant alloys 80A and 625 shows that the alloy of Example 1 has less mass loss after corrosion and excellent corrosion resistance. Figure 3 The image shows the metallographic structure of Example 1 after solution treatment (1080°C). It can be seen that many spherical αCr phases with a size of <5μm are diffusely distributed in this state. Figure 4 It can be seen that the grain size of Example 1 is very fine, with a grain size of 13µm, which meets ASTM grade 9.

[0061] Figure 5The images shown are metallographic and scanning electron microscope images of the alloy after solution treatment and aging in Example 1. It can be seen that the microstructure of Example 1 is a composite precipitate of spherical α-Cr phase and lamellar structure. The lamellar structure is distributed in a colony-like pattern in the region between the spherical α-Cr phases. The colonies are oriented similarly to each other. The average interlayer spacing in the lamellar structure is 170 nm. Figure 6 The image shown is a transmission electron microscope (TEM) image of the lamellar structure of the alloy after solution treatment and aging in Example 1. It can be seen that the lamellar structure consists of α-Cr phase lamellars, γ phase lamellars and γ' phase with an average interlayer spacing of 170 nm. The α-Cr phase layer thickness is slightly smaller than that of the γ phase. The average layer thickness of the α-Cr phase is 44 nm, the average layer thickness of the γ phase is 130 nm, and the average size of the γ' phase is 40 nm. Figure 7 The results of EBSD grain analysis and precipitate analysis are shown for the alloy after solution treatment and aging in Example 1. Figure 7 As can be seen from (a) and (b), the lamellar structures with the same orientation are clustered in the region between the spherical α-Cr phases. The average size of the lamellar structure clusters is 2 μm, which is ASTM 15.9 grade. The size and distribution are uniform. The average size of the spherical α-Cr phase is only 1 μm, with a ratio of 13.5%. The solid solution aging structure characteristics endow the alloy material with excellent comprehensive mechanical properties, including high strength, high hardness and good toughness.

[0062] Example 2

[0063] The TA800 alloy in this embodiment is a high-Cr nickel-based alloy. Specifically, the high-temperature alloy composition, by mass percentage, includes: Cr: 37.8%, Al: 4.8%, Co: 3%, C: 0.02%, B: 0.004%, Zr: 0.03%, with the balance being Ni. The preparation process of this embodiment includes the following steps:

[0064] Step 1, TA800 alloy smelting:

[0065] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0066] The second step is the homogenization treatment of the TA800 alloy:

[0067] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 4°C / min, heat up to 1180°C, hold for 16 hours, and then remove and air cool.

[0068] The third step, TA800 alloy forging:

[0069] Forging process: The billet is fed into the furnace at 700°C, held for 5 hours, then heated at a rate of 4°C / min to 1150°C and held for 8 hours before being removed from the furnace for initial forging. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a reheat holding temperature of 1150°C for 45 minutes. Following this process, the billet is forged in three passes, resulting in a forging ratio of 6, producing TA800 alloy forged bars with a diameter of 30mm and a length of 1200mm.

[0070] TA800 alloy forged bars were prepared using the above-described process. Their hardness was then evaluated by different solution treatments and aging heat treatments. The sample size was 12 mm. 12mm The sample was 10 mm thick. Solution heat treatment temperatures were 1050°C, 1100°C, and 1140°C, with a solution treatment time of 1 hour. After water cooling, each solution-treated sample underwent aging heat treatment at different temperatures: 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, and 850°C, for 16 hours. Afterward, it was air-cooled to room temperature. The surface of the sample block was polished with 2000-grit sandpaper, and then hardness testing was performed. The results are as follows: Figure 8 As shown, the alloy hardness increases with increasing solution temperature and decreases with decreasing aging temperature, ranging from 400-750 HV. The table below shows the mechanical properties of the alloy obtained in Example 2 after solution treatment at 1100°C for 1 hour, followed by water cooling, and then aging heat treatment at 830°C and 700°C for 16 hours, respectively, followed by air cooling and room temperature tensile testing. Vickers hardness was also measured for both samples. It can be observed that aging temperature significantly affects the mechanical properties of the alloy; higher aging temperatures result in lower strength and hardness, but significantly improved ductility.

[0071] Table 2. Room temperature mechanical properties and microhardness of Example 2

[0072]

[0073] Examples 3, 4, and 5

[0074] The alloy compositions of Examples 3, 4, and 5, expressed as mass percentages, are shown in Table 3. Example 3 served as a control experiment to investigate the effects of the addition of rare earth elements La and Y.

[0075] Table 3, Alloy composition (wt%)

[0076]

[0077] The preparation process of this Example 3 includes the following steps:

[0078] Step 1, TA800 alloy smelting:

[0079] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0080] The second step is the homogenization treatment of the TA800 alloy:

[0081] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 2°C / min, heat up to 1100°C, hold for 28 hours, and then remove and air cool.

[0082] The third step, TA800 alloy forging:

[0083] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 2°C / min to 1100°C and held for 6 hours before being removed from the furnace for initial forging. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a reheat holding temperature of 1100°C for 40 minutes. Following the above process, the billet is forged in three passes to produce TA800 alloy forged bars with a diameter of 30mm and a length of 1200mm.

[0084] The preparation process of Example 4 includes the following steps:

[0085] Step 1, TA800 alloy smelting:

[0086] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0087] The second step is the homogenization treatment of the TA800 alloy:

[0088] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 2°C / min, heat up to 1100°C, hold for 28 hours, and then remove and air cool.

[0089] The third step, TA800 alloy forging:

[0090] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 2°C / min to 1100°C and held for 6 hours before being removed from the furnace for initial forging. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a reheat holding temperature of 1100°C for 40 minutes. Following the above process, the billet is forged in three passes to produce TA800 alloy forged bars with a diameter of 30mm and a length of 1200mm.

[0091] The preparation process of Example 5 includes the following steps:

[0092] Step 1, TA800 alloy smelting:

[0093] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0094] The second step is the homogenization treatment of the TA800 alloy:

[0095] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 2°C / min, heat up to 1100°C, hold for 28 hours, and then remove and air cool.

[0096] The third step, TA800 alloy forging:

[0097] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 2°C / min to 1100°C and held for 6 hours before being removed from the furnace for initial forging. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a reheat holding temperature of 1100°C for 40 minutes. Following the above process, the billet is forged in three passes to produce TA800 alloy forged bars with a diameter of 30mm and a length of 1200mm.

[0098] Three types of cast billets with identical dimensions were prepared by induction melting combined with electroslag melting. EBSD analysis was performed on the homogenized microstructure. Figure 9 , Figure 10 , Figure 11 The EBSD grain analysis results for Examples 3, 4, and 5 are shown respectively. It can be found that after adding Y and La elements, the grain size of Examples 4 and 5 becomes smaller than that of the alloy in Example 3. The grains are significantly refined, and the as-cast grain size after refinement is less than 50 μm. This can significantly reduce the difficulty of homogenization and forging, and improve the alloy performance.

[0099] Examples 6, 7, and 8

[0100] The TA800 alloy in this embodiment is a high-Cr nickel-based alloy. Specifically, the high-temperature alloy composition, expressed as a percentage by mass, is shown in Table 4 for Comparative Examples 1, 6, 7, and 8.

[0101] Table 4 Alloy composition (wt%)

[0102]

[0103] The preparation process of Example 6 includes the following steps:

[0104] Step 1, TA800 alloy smelting:

[0105] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0106] The second step is the homogenization treatment of the TA800 alloy:

[0107] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 3°C / min, heat up to 1140°C, hold for 24 hours, and then remove and air cool.

[0108] The third step, TA800 alloy forging:

[0109] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 3°C / min to 1140°C, held for 4 hours, and then removed from the furnace to begin the initial forging process. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a return to the furnace at 1140°C for 40 minutes. The billet is forged in three passes according to the above process, resulting in a forged bar with a diameter of 25mm and a length of 1000mm.

[0110] The preparation process of Example 7 includes the following steps:

[0111] Step 1, TA800 alloy smelting:

[0112] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0113] The second step is the homogenization treatment of the TA800 alloy:

[0114] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 3°C / min, heat up to 1140°C, hold for 24 hours, and then remove and air cool.

[0115] The third step, TA800 alloy forging:

[0116] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 3°C / min to 1140°C, held for 4 hours, and then removed from the furnace to begin the initial forging process. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a return to the furnace at 1140°C for 40 minutes. The billet is forged in three passes according to the above process, resulting in a forged bar with a diameter of 25mm and a length of 1000mm.

[0117] The preparation process of Example 8 includes the following steps:

[0118] Step 1, TA800 alloy smelting:

[0119] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0120] The second step is the homogenization treatment of the TA800 alloy:

[0121] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 3°C / min, heat up to 1140°C, hold for 24 hours, and then remove and air cool.

[0122] The third step, TA800 alloy forging:

[0123] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 3°C / min to 1140°C, held for 4 hours, and then removed from the furnace to begin the initial forging process. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a return to the furnace at 1140°C for 40 minutes. The billet is forged in three passes according to the above process, resulting in a forged bar with a diameter of 25mm and a length of 1000mm.

[0124] The preparation process of Comparative Example 1 includes the following steps:

[0125] Step 1, TA800 alloy smelting:

[0126] High-purity component raw materials were batched according to mass percentage (wt.%), and the batching was processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet with a diameter of 80mm.

[0127] The second step is the homogenization treatment of the TA800 alloy:

[0128] Homogenization heat treatment process: feed the material into the furnace at 700°C, heat up at a rate of 3°C / min, heat up to 1140°C, hold for 24 hours, and then remove and air cool.

[0129] The third step, TA800 alloy forging:

[0130] Forging process: The billet is fed into the furnace at 700°C, held for 3 hours, then heated at a rate of 3°C / min to 1140°C, held for 4 hours, and then removed from the furnace to begin the initial forging process. The initial forging method is air hammer free forging with axial elongation. The final forging temperature is not lower than 900°C, with each forging pass requiring a return to the furnace at 1140°C for 40 minutes. The billet is forged in three passes according to the above process, resulting in a forged bar with a diameter of 25mm and a length of 1000mm.

[0131] The alloy compositions of Comparative Examples 1, 6, 7, and 8 are shown in Table 4. The main difference between the four sets of control experiments lies in the amount of Co added. Cast billets were prepared by induction melting combined with electroslag remelting. The as-cast microstructure was first evaluated. Figure 12 , Figure 13 , Figure 14 Metallographic images of the as-cast microstructures of Examples 6, 7, and 8 are shown. It can be seen that the as-cast microstructures are good, with no obvious harmful phases formed, and only some carbides distributed along the grain boundaries. Subsequently, Comparative Example 1, Example 6, and Example 7 were subjected to the same homogenization heat treatment, and metallographic tests were performed on the homogenized samples. The results are as follows: Figure 15 , Figure 16 , Figure 17 As shown in the metallographic photographs of the homogenized microstructures of Comparative Example 1 and Examples 6 and 7, it can be seen that the alloy without added Co still has relatively serious segregation after homogenization heat treatment, which has not been completely eliminated. However, the segregation of the alloys with added 2% Co and 6% Co is basically eliminated after homogenization heat treatment, which is in stark contrast to the alloy without added Co. Therefore, the addition of Co content helps to reduce alloy segregation and reduce the difficulty of homogenization heat treatment.

[0132] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for preparing a corrosion-resistant nickel-based superalloy, characterized in that, The corrosion-resistant nickel-based superalloy comprises, by mass percentage: Cr: 34%~38%, Al: 3.5%~5%, Co: 0.5-10%, C: 0.01-0.05%, B: 0.001-0.006%, Zr: 0.02-0.05%, Y: less than 0.08%, La: less than 0.08%, with the balance being Ni. The alloy comprises the following steps: Step 1, TA800 alloy smelting: High-purity component raw materials are batched according to mass percentage, and the batching is processed by a dual melting method of induction melting and electroslag remelting to obtain TA800 alloy billet; The second step is the homogenization treatment of the TA800 alloy: Homogenization heat treatment process: Feed the material into the furnace at 700°C, heat it to 1100-1180°C, hold it for 16-28 hours, and then remove it and air cool it. The third step, TA800 alloy forging: Forging process: The material is fed into the furnace at 700°C, held for 3-7 hours, then heated to 1100-1150°C and held for 4-8 hours before being removed from the furnace for billet forging to obtain forged bars. Solution treatment and aging heat treatment are performed to evaluate its microstructure and mechanical properties. The solution-treated hardness ranges from 150 to 350 HV, and the aged hardness ranges from 380 to 750 HV. Tensile strength ranges from 1200 to 2100 MPa, yield strength from 800 to 1800 MPa, elongation from 2% to 30%, and reduction of area from 5% to 60%. Its microstructure includes equiaxed austenitic alloy grains, dispersed spherical α-Cr phases, and lamellar structures with colony-like distributions between the spherical α-Cr phases. Specifically: In the third step, the billet forging method is air hammer free forging, axial elongation, and the final forging temperature is not lower than 900°C. The holding temperature for each forging is 1100-1150°C and the holding time is not lower than 40 minutes. The billet is forged several times according to the above process to obtain forged bars. The equiaxed austenitic alloy grains have a grain size of grade 7 or higher; the average size of the dispersed spherical α-Cr phase is <5μm, and the proportion of the spherical α-Cr phase is <16%; The lamellar structure has the following characteristics: the structure of the lamellar structure is composed of α-Cr phase lamellars, γ phase lamellars and γ' phase. The average spacing between adjacent α-Cr phase lamellars in the lamellar structure is <300nm. The thickness of the α-Cr phase layer is less than that of the γ phase, with an α-Cr phase layer thickness of <75nm. The average thickness of the γ phase layer is <150nm. The average size of the γ' phase is <75nm. The lamellar structure is distributed in a cluster pattern in the region between the spherical α-Cr phases, with the same orientation. The size of the lamellar structure clusters is <10μm.

2. The method for preparing a corrosion-resistant nickel-based superalloy according to claim 1, characterized in that, In the second step, the heating rate is 2-4°C / min; in the third step of the forging process, the heating rate is 2-4°C / min.

3. The method for preparing a corrosion-resistant nickel-based superalloy according to claim 1, characterized in that, In the third step, TA800 alloy is rolled into a billet: For forged bars with a diameter ≥ 50 mm and a length ≥ 2000 mm, the TA800 alloy needs to be hot-rolled and drawn after the initial forging. The specific process includes: entering the furnace at 700°C, heating to 1130°C, holding for 3 hours, and then rolling. The rolling is carried out in two passes. The first pass has 9-12 passes with a feed of 5 mm per pass, and the second pass has 5-8 passes with a feed of 2 mm per pass. The diameter allowance of the rolled bar is 3-4 mm on each side, and finally, black-skinned forged bars are obtained.

4. The application of a corrosion-resistant nickel-based superalloy prepared according to any one of claims 1-3, characterized in that, The corrosion-resistant nickel-based superalloy is a high-performance nickel-based superalloy that can meet the requirements of hot-end components serving in complex environments. It is used in gas turbine combustor nozzles and related components of fuel control systems, key components of marine low-speed engine combustors, or other hot-end components requiring high strength, corrosion resistance, and wear resistance.

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