1600MPa-grade high-strength nickel-based alloy for second-generation high-temperature superconducting baseband and preparation method of 1600MPa-grade high-strength nickel-based alloy

Abstract

The invention relates to a 1600MPa-grade high-strength nickel-based alloy for a second-generation high-temperature superconducting baseband and a preparation method of the 1600MPa-grade high-strength nickel-based alloy, and belongs to the technical field of materials. The nickel-based alloy is prepared from the following chemical components in percentage by weight: 15.0 to 17.0 percent of Cr, 15.0 to 17.0 percent of Mo, 0 to 10.0 percent of Ta, 0.2 to 6.0 percent of Re, 3.0 to 5.0 percent of W, 4.0 to 7.0 percent of Fe, 0.5 to 2.5 percent of Co, 0.3 to 0.7 percent of Mn, 0.01 to 0.05 percent of Si, 0.1 to 0.2 percent of V, 0.1 to 0.2 percent of Al, 0.001 to 0.01 percent of B, Clt and the balance of Ni. 0.005%, Plt; 0.005%, Slt; 0.002%, Olt; 0.002%, Nlt; 0.002%, and the balance being nickel. On the basis of Hastelloy, Ta and Re elements are creatively added, follow-up optimized homogenization treatment, hot working, heat treatment processes and cold working processes are matched, after the nickel-based alloy is annealed for 5 min at the temperature of 900 DEG C, the nickel-based alloy with the yield strength being 1500 MPa or above, the tensile strength being 1600 MPa or above and the ductility being 3.0% or above can be obtained, and the nickel-based alloy has good high-temperature oxidation resistance.

Description

Technical Field

[0001] The present invention relates to a 1600 MPa grade high-strength nickel-based alloy for a second-generation high-temperature superconducting baseband and a preparation method thereof, belonging to the technical field of materials. Background Art

[0002] Since the discovery of the second-generation superconductor of rare-earth barium copper oxide (REBCO, RE is a rare-earth element), it has attracted extensive international attention. The second-generation high-temperature superconductor has advantages such as a relatively high transition temperature, perfect diamagnetism, high critical current density, and high frozen magnetic field, and has achieved demonstration applications in many fields such as electric power, energy, and magnets. The most critical superconducting layer in REBCO is an oxide material with poor ductility. Since its thickness is generally less than 4 μm, it is also called a coated superconductor.

[0003] The realization of the superconducting properties of REBCO requires other multifunctional coatings for protection. Usually, a superconducting layer needs to be epitaxially grown on a flexible metal baseband. The basis of the REBCO superconductor is the metal baseband, and the buffer layer, superconducting layer, and protective layer are all built on the metal baseband. Therefore, the comprehensive properties of the metal baseband determine the quality of the superconducting properties of REBCO. The ion beam-assisted biaxial texture deposition technology (IBAD) has no specific requirements for the orientation and properties of the metal baseband. The ion energy and beam current can be independently adjusted, and the process is flexible and controllable. It is one of the commonly used methods for commercially preparing the REBCO superconducting layer at present. The IBAD technology has certain requirements for the temperature and atmosphere environment during the preparation of the buffer layer, superconducting layer, and protective layer. The optimal preparation process parameters for the superconducting layer are 850°C to 900°C. Therefore, it is required that the metal baseband has good mechanical properties, non-magnetic or weakly magnetic, a thermal expansion coefficient corresponding to the superconducting layer, good high-temperature tissue stability, and excellent oxidation resistance, etc. At present, the commercially mature Hastelloy C276 has excellent comprehensive properties and is a baseband material widely used in the IBAD technology. The tensile strength of Hastelloy C276 can be above 1500 MPa after 50% to 90% cold deformation. However, due to the deformation storage energy accumulated by the large cold deformation, it is prone to recrystallization when heated to 850°C to 900°C, resulting in its tensile strength being lower than 1100 MPa, and it cannot solve the contradiction between large deformation and recrystallization strength of the material. Therefore, it cannot meet the development needs of current high-temperature and high-field superconductivity, thus restricting the further upgrading of high-temperature superconducting equipment.

[0004] In addition, the applicant's Chinese invention patent (application number 202411589006.7) proposes a 1500 MPa grade nickel-based alloy for the second-generation high-temperature superconducting baseband and its preparation method. In terms of weight percentage, its chemical composition is: Cr: 15.0 - 17.0%, Mo: 15.0 - 17.0%, W: 4.5 - 9.5%, Fe: 5.0 - 7.0%, Mn: 0.3 - 0.7%, Si: 0.01 - 0.05%, V: 0.1 - 0.2%, Co: 0.1 - 0.5%, Al: 0.1 - 0.2%, B: 0.001 - 0.01%, C < 0.005%, P < 0.005%, S < 0.002%, O < 0.002%, N < 0.002%, and the balance is nickel. The core component design lies in further increasing the content of W element in its matrix on the basis of C276. Although the tensile strength of the 1500 MPa grade nickel-based alloy for the high-temperature superconducting baseband reaches more than 1500 MPa, it is 100 MPa lower than the tensile strength of the material of the present invention. In addition, due to the increase in the content of W, more stable W-rich P phase and μ phase are formed in the material of the present invention, and the homogenization and solution treatment temperatures are relatively high, resulting in an increase in the difficulty of its processing and preparation. The applicant also applied for two Chinese invention patents (application numbers 202411672542.3 and 202411881969.4), and developed nickel-based alloys for the second-generation superconducting baseband with grades of 1300 MPa and 1400 MPa respectively by adopting the composition design ideas of "N alloying" and "replacing Mo with W". The tensile strengths of these two invention patents after annealing are 300 MPa and 200 MPa lower than that of the material of the present invention respectively, showing a certain gap.

[0005] With the development of the second-generation high-temperature and high-field superconductivity, higher requirements are put forward for the operating parameters of key equipment such as high-field superconducting magnets prepared therefrom, requiring that the metal baseband has a higher recrystallization temperature, can maintain the stability of its structure during the high-temperature preparation process of the superconductor with a large cold deformation amount, and the tensile strength reaches more than 1600 MPa. At present, the tensile strength of the commercially available Hastelloy C276 metal baseband is reduced to less than 1100 MPa due to recrystallization, which cannot meet the development requirements of the current second-generation high-temperature superconducting metal baseband. Therefore, in order to update and replace superconducting equipment, it is extremely urgent to develop a 1600 MPa grade nickel-based alloy for the second-generation high-temperature superconductivity. Summary of the Invention

[0006] The object of the present invention is to provide a 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband and its preparation method. Based on Hastelloy C276, an innovative composition design concept of Re+Ta solid solution strengthening is adopted. By adding optimized contents of Re and Ta elements, the composite solid solution strengthening of Re and Ta is realized for the first time in wrought superalloys. Utilizing the characteristics of Re to reduce the atomic migration rate and Ta with a high melting point, the recrystallization temperature after cold rolling of the material is further increased, thereby ensuring its high strength after annealing. Pure refining is adopted to strictly control the content of O element in the alloy and avoid the formation of large-size inclusions. The content of carbon element is controlled, and heat treatment processes of homogenization annealing and solution rapid cooling are adopted to avoid the precipitation of carbides and TCP phases. Finally, by cold deformation, a nickel-based alloy with a yield strength reaching above 1550 MPa, a tensile strength reaching above 1650 MPa, and an elongation rate reaching above 2.0% can be obtained; after annealing at 900 °C for 5 min, the yield strength reaches above 1500 MPa, the tensile strength reaches above 1600 MPa, and the elongation rate reaches above 4.0%, and it has good high-temperature oxidation resistance.

[0007] The technical solution of the present invention is as follows:

[0008] A 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, by weight percentage, its chemical composition is: Cr: 15.0 - 17.0%, Mo: 15.0 - 17.0%, Ta: 0.5 - 6.5%, Re: 0.2 - 6.0%, W: 3.0 - 5.0%, Fe: 4.0 - 7.0%, Co: 0.5 - 2.5%, Mn: 0.3 - 0.7%, Si: 0.01 - 0.05%, V: 0.1 - 0.2%, Al: 0.1 - 0.2%, B: 0.001 - 0.01%, C < 0.005%, P < 0.005%, S < 0.002%, O < 0.002%, N < 0.002%, and the balance is nickel.

[0009] For the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, preferably, Ta: 1.0 - 4.0%, Re: 0.5 - 2.5%, Re+Ta: 3.0 - 5.0%.

[0010] For the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, preferably, B: 0.001 - 0.003%.

[0011] For the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, preferably, C < 0.002%, O < 0.001%.

[0012] The preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband includes the following steps:

[0013] (1) Mix each chemical component proportionally, and obtain an ingot through pure purification smelting and electroslag remelting;

[0014] (2) Anneal the obtained ingot at a high temperature for homogenization. The temperature of the homogenization annealing treatment is 1250 ± 10 °C. After holding for 25 h to 40 h, air cool it to room temperature;

[0015] (3) Forge the ingot after homogenization annealing in the austenite single-phase region. The forging process is as follows: the forging temperature is 1230 - 1250 °C, the forging ratio is above 7.0, and water cool it to room temperature after forging;

[0016] (4) Perform hot rolling on the forged alloy ingot: the rolling temperature is 1230 °C - 1250 °C, the reduction per pass of rolling is controlled at 15 - 20%, the total reduction is controlled at 60 - 80%, and water cool it to room temperature after hot rolling;

[0017] (5) Perform solution heat treatment after hot rolling. The solution heat treatment process is as follows: hold at 1220 °C - 1240 °C for 2 - 6 h and then water quench to room temperature;

[0018] (6) Perform cold deformation after solution heat treatment. The cold deformation process is as follows: perform cold deformation at room temperature, and the cold deformation amount is 60 - 80%.

[0019] For the preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, after cold deformation, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength reaches above 1550 MPa, the tensile strength reaches above 1650 MPa, and the elongation reaches above 2.0%.

[0020] For the preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, preferably, after cold deformation, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength is 1560 - 1600 MPa, the tensile strength is 1650 - 1700 MPa, and the elongation is 2.0 - 4.0%.

[0021] For the preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband, after annealing at 900 °C for 5 min, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength reaches above 1500 MPa, the tensile strength reaches above 1600 MPa, the elongation reaches above 4.0%, and it has good high-temperature oxidation resistance.

[0022] The preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband. Preferably, after annealing at 900 °C for 5 min, the room-temperature performance indexes of the nickel-based alloy are as follows: the yield strength is 1500 - 1550 MPa, the tensile strength is 1610 - 1660 MPa, and the elongation is 4.0 - 7.0%.

[0023] The preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband. After oxidizing at 900 °C for 150 h, an oxide layer with a thickness of 3 - 5 μm is formed on the surface of the nickel-based alloy, and the thickness of the oxide layer is uniform.

[0024] The content ranges of the main elements in the present invention are described as follows:

[0025] Cr: Chromium is an important element of Hastelloy and is the primary element determining the corrosion resistance of Hastelloy. This is because chromium improves the corrosion resistance of the alloy itself and makes it easy to form a chromium oxide layer on the material. However, when the Cr content is less than 15 wt%, the minimum corrosion resistance required for the alloy cannot be obtained. On the other hand, when the Cr content exceeds 17 wt%, chromium-rich intermetallic compounds are likely to precipitate, forming a chromium-depleted zone around the intermetallic compounds, which not only damages the hot working performance and mechanical properties of the material but also deteriorates the oxidation and corrosion resistance of the material. Therefore, to ensure that the material has excellent corrosion resistance to most corrosive media in both the oxidized and reduced states, the chromium content in the alloy of the present invention is controlled to be: 15.0 - 17.0 wt%.

[0026] Mo: Like chromium, molybdenum is a corrosion-resistant element with a corrosion resistance equivalent to that of chromium. The interaction between molybdenum and the corrosive medium promotes the formation of a dense and uniform passivation film on the surface, reducing the possibility of the alloy being corroded and significantly improving its corrosion resistance. In addition, Mo can enhance the solid solution strengthening effect of the nickel-based alloy, improving the strength and service performance of the alloy. However, too high a Mo content will be oxidized to varying degrees during the hot working process, deteriorating the processing performance and service performance of the alloy. Therefore, molybdenum elements with the effect of improving corrosion resistance can be added within the range that does not damage other properties such as the corrosion resistance, hot workability, and weldability of the material. Therefore, the molybdenum content in the alloy of the present invention is controlled to be: 15.0 - 17.0 wt%.

[0027] W: The role of tungsten is similar to that of molybdenum. It mainly plays a role in solid solution strengthening in the alloy system. Since the atomic radius of tungsten is larger than that of molybdenum, the solid solution strengthening effect is greater than that of molybdenum. Moreover, due to the high melting point of tungsten, appropriately increasing its content will, to a certain extent, increase the recrystallization temperature of the alloy after cold working, which is also one of the keys of this invention. However, too much tungsten will cause the alloy to form a relatively stable μ phase rich in nickel and molybdenum, which cannot be completely eliminated even when held at a very high solid solution temperature for a long time. In order to avoid the influence of the precipitated phase on the superconducting properties, the content of tungsten needs to be strictly controlled. Therefore, the content of tungsten in the alloy of this invention is controlled to be 3.0 - 5.0 wt%.

[0028] Re + Ta: Rhenium and tantalum are important solid solution strengthening elements in nickel-based alloys. Especially, rhenium reduces the atomic migration rate in the new generation of cast single crystal alloys and plays a crucial role in the stability of the single crystal alloy microstructure at high temperatures. In addition, since the atomic radii of rhenium and tantalum are significantly larger than those of other alloy elements, the solid solution strengthening effect is good, which can greatly improve the matrix strength of nickel-based alloys. However, when the contents of rhenium and tantalum are too low, the solid solution strengthening is limited, and it is difficult to meet the requirements for strength improvement; while higher contents of rhenium and tantalum will cause the matrix to generate large and stable TCP phases, which require a relatively high temperature to be completely eliminated, deteriorating the plasticity of the material. At the same time, the alloy preparation cost will increase significantly. Through calculation and design optimization, on the premise of ensuring the stable and controllable precipitation of the precipitated phase, the contents of tantalum and rhenium elements in this invention are respectively optimized and controlled to be 0.5 - 6.5% and 0.2 - 6.0%. Further optimized control is: Ta: 1.0 - 4.0%, Re: 0.5 - 2.5%, and the content of Re + Ta is controlled within 3.0 - 5.0%.

[0029] Fe: The addition of iron is mainly to control the cost of the alloy system. Since nickel and iron can be infinitely soluble, the addition of iron replaces the atomic positions of nickel, causing lattice distortion and playing a role in solid solution strengthening to a certain extent. Excessive addition of iron will form Laves phases with Mo and W in the matrix, thus deteriorating the material properties. Therefore, the content of iron in the alloy of this invention is controlled to be: 4.0 - 7.0 wt%.

[0030] Co: Cobalt is basically completely dissolved in the matrix, playing a role in solid solution strengthening and not forming carbides. More importantly, it forms a synergistic effect with Mo, promoting the precipitation of the precipitated phase. Cobalt can inhibit the recovery of dislocation substructures in the microstructure, providing more nucleation sites for the subsequent precipitated phase and promoting the precipitation strengthening effect. Therefore, according to the balance effect of cobalt on the alloy and its influence on the precipitation effect of the precipitated phase, the content of cobalt in the alloy of this invention is controlled to be: 0.5 - 2.5 wt%.

[0031] Mn: Manganese can enhance the strength and toughness of the alloy through the solid solution strengthening mechanism. Mn replaces nickel atoms therein, generating distortion, thus hindering the movement of dislocations and increasing the yield and tensile strength of the material. At the same time, it can significantly reduce the martensite formation temperature M S point, ensuring the stability of the austenite structure of the alloy. When the Mn content is added too high, it is easy to form MnS inclusions with S in the alloy, and the increase in the volume fraction of inclusions reduces the impact toughness of the alloy. Therefore, the content of manganese in the alloy of the present invention is controlled to be: 0.3 - 0.7 wt%.

[0032] Si: The silicon element plays several key roles: First, as a deoxidizer, silicon helps to remove oxygen in the smelting liquid, reacts with oxygen to form silicon oxides, thereby improving the purity and overall quality of the alloy. Second, silicon enhances the strength and hardness of the alloy through the solid solution strengthening mechanism. However, the content of silicon needs to be controlled because too high a silicon content may affect the welding performance of the alloy. Therefore, the silicon content in the present invention is controlled to be: 0.01 - 0.05 wt%.

[0033] V: Vanadium is a strong carbide-forming element, which easily forms precipitation phases with carbon and nitrogen in the alloy and pins dislocations. V can play a role in fixing carbon elements and preventing the diffusion of alloying elements such as Cr from the matrix into the carbides, resulting in ripening, thereby improving the mechanical strength of the alloy. When the vanadium content is too low, it is not easy to fully form fine carbides and cannot play the role of pinning dislocations, while when the content is too high, the alloy becomes brittle. Therefore, the content of vanadium in the alloy of the present invention is controlled to be: 0.1 - 0.2 wt%.

[0034] Al: Aluminum is an element for forming the γ′ strengthening phase of intermetallic compounds and is an important element for enhancing the strength of the alloy. At the same time, the Al content is also an important indicator of the high-temperature oxidation resistance of the material. There is a short-term high-temperature process in the preparation process of the REBCO superconducting layer, which puts higher requirements on the oxidation resistance of the material of the present invention. Therefore, the content of Al in the alloy of the present invention is optimized and controlled to be: 0.1 - 0.2 wt%.

[0035] B: Trace amounts of boron can greatly improve the mechanical properties of the alloy. Boron is a basic grain boundary strengthening element in polycrystalline superalloys. Boron can segregate at the grain boundaries, causing an increase in the grain boundary bonding force, improving the fracture strength, consuming or reducing the massive precipitation phases precipitated at the grain boundaries, reducing the content of harmful elements such as S at the grain boundaries through site competition, and improving the slip and dislocation climb at the grain boundaries to prevent crack generation. Moreover, it can form borides with metals to strengthen the grain boundaries. Therefore, the boron content in the alloy of the present invention is controlled to be 0.001 - 0.01 wt%, and further optimized to be: 0.001 - 0.003 wt%.

[0036] C: Carbon in the alloy is easy to form M with elements such as Cr 23The carbide of C6 will precipitate especially during the slow cooling process after solution treatment. Although the carbide precipitates at the grain boundary interface of the original austenite, it can pin dislocations and hinder the movement of the interface, playing a role in precipitation strengthening and effectively improving the strength of the material. However, the precipitation of these carbide precipitates will affect the superconducting properties of the second-generation superconductors, and it is necessary to strictly control the carbon content in the alloy. Therefore, adopting the design idea of ultra-low carbon composition, the content of C in the alloy of the present invention is optimized and controlled as: C < 0.005 wt%, and further optimized to C < 0.002 wt%.

[0037] S, P: In the production of nickel-based alloys, phosphorus and sulfur are usually regarded as harmful impurities because they will significantly reduce the overall properties of the alloy. P will promote the segregation of W and Mo to form Laves phase, thereby increasing the cold brittleness of the alloy, reducing the cohesion of the grain boundary, thus reducing the ductility and plasticity of the material, and at the same time, it will also affect the welding performance, resulting in cracks in the welded joint. On the other hand, sulfur will increase the tendency of thermal brittleness of the material, especially during the processing, and excessive sulfur will also affect the machining quality of the material, reducing the strength and toughness of the material. Therefore, the content of sulfur and phosphorus in the alloy of the present invention is strictly controlled: S < 0.002 wt%, P < 0.005 wt%.

[0038] O: Oxygen is the main element that generates oxide inclusions in the alloy. In order to reduce the inclusions in the alloy and ensure the purification of the material, it is necessary to minimize the oxygen content. When the oxygen content in the material exceeds a certain limit, especially when the material of the present invention contains a certain content of Al, it will lead to the formation of continuous brittle oxide inclusions in the alloy, and stress concentration will occur during the thin strip processing, resulting in the occurrence of strip breakage accidents. Therefore, the content of oxygen in the alloy of the present invention is strictly controlled: O < 0.002 wt%, and further optimized to O < 0.001 wt%.

[0039] N: Nitrogen is a strong austenite-forming element, which expands the austenite phase region and shrinks the ferrite phase region, and can inhibit the formation of high-temperature ferrite. Although nitrogen can increase the cold work hardening rate and improve the strength index of the alloy after cold working, due to the addition of a certain content of B element in the present invention, in order to avoid the formation of BN inclusions, it is necessary to strictly control the content of N element in the material of the present invention. Therefore, the content of nitrogen in the alloy of the present invention is strictly controlled: N < 0.002 wt%.

[0040] There are four innovative design ideas in the present invention, which are described as follows:

[0041] 1) Innovative alloy composition design concept: Based on Hastelloy, the present invention innovatively adopts the composition design concept of Re+Ta composite strengthening. By adding optimized contents of Re and Ta elements, controlling the total amount of Re+Ta alloying elements, and using optimized hot working processes and heat treatment systems, while no precipitation phase precipitates, the Re and Ta elements are completely dissolved into the alloy matrix, giving play to the solution strengthening effect of Re and Ta elements in Hastelloy, and realizing the Re and Ta composite solution strengthening in wrought nickel-based alloys for the first time. By adopting the above technical solution, a second-generation high-temperature superconducting baseband material with a strength level of 1600 MPa can be stably obtained after annealing at 900 °C for 5 minutes, and the tensile strength index is superior to the currently commercial Hastelloy C276.

[0042] 2) Optimization of hot working and heat treatment systems: The alloy of the present invention contains 15-17 wt% of Mo element and 3.0-5.0 wt% of W element. On the basis of this composition, optimized contents of Re+Ta elements are added. Although the total amount is controlled between 3.0-5.0%, it will still promote the formation of more stable μ and P phases in the matrix. Therefore, it is necessary to match optimized hot working and heat treatment systems to solve the contradiction between the higher temperature required for complete re-solution of the matrix precipitation phase and the lower temperature required to avoid abnormal grain growth. The material of the present invention combines homogenization + hot working process with large deformation at high temperature + solution treatment at high temperature, and adopts optimized process parameters such as temperature and deformation amount. On the premise of ensuring the grain size, the goal of no precipitation phase in the matrix is achieved, thus ensuring that the innovative composition design concept of Re+Ta composite strengthening is realized in wrought superalloys for the first time.

[0043] 3) Purification smelting technology: The purification smelting technology is adopted to strictly control the contents of harmful elements such as P, S, O and N in the alloy that are likely to form inclusions. The O content is controlled below 10 ppm, and the P and S contents are controlled below 50 and 20 ppm respectively, reducing the formation of inclusions in the alloy and laying a good foundation for the subsequent preparation of superconducting base materials with a thickness of 20-50 μm.

[0044] In summary, based on Hastelloy, the present invention innovatively adds Ta and Re elements, matches optimized heat treatment processes to ensure that Ta and Re are completely dissolved into the matrix, combines cold deformation to improve the strength of the matrix; controls the C content, controls the precipitation of carbides, and ensures complete dissolution into the matrix during homogenization treatment; adopts a purification smelting process, reduces the oxygen content in the alloy, reduces the inclusion content, and ensures the high purity of the material.

[0045] The advantages and beneficial effects of the present invention are:

[0046] 1. Based on Hastelloy C276, the present invention adopts the compositional design concept of Re+Ta composite strengthening. By adding optimized contents of Re and Ta elements, controlling the total content of Re+Ta, and matching the subsequent optimized hot working process and heat treatment system, the complete solid solution of Re and Ta elements is achieved, giving full play to the role of Re element in reducing the atomic migration rate and Ta element in solid solution strengthening, increasing the recrystallization temperature after cold deformation of the material, ensuring the tissue stability of the material, and thus obtaining a high strength of 1600 MPa after high-temperature annealing, meeting the urgent need for high strength in the second-generation high-temperature superconducting baseband.

[0047] 2. The present invention adopts a purification smelting technology to greatly reduce the content of O in the material of the present invention. On this basis, the contents of P, S, and N elements in the material are further reduced, ensuring that the inclusion content of the material of the present invention is controlled at an extremely low level, and superconducting baseband materials with a thickness of 20 - 50 μm can be stably prepared, meeting the requirements of the second-generation high-temperature and high-field superconducting equipment for materials.

[0048] 3. The present invention provides a 1600 MPa nickel-based alloy for the second-generation high-temperature superconducting baseband and a key preparation process. By adopting the technical solution provided by the present invention, a nickel-based superalloy with high purity and high strength can be stably obtained. The material of the present invention can better support the rapid development of China's high-temperature and high-field superconducting industry and promote the upgrading of industry equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the forged metallographic structure of Example 1.

[0050] Figure 2 Schematic diagram of the solution-treated metallographic structure of Example 2.

[0051] Figure 3 Cross-sectional morphology of Example 1 after oxidation in air at 900°C for 100 h.

[0052] Figure 4 Schematic diagram of the forged metallographic structure of Comparative Example 1.

[0053] Figure 5 Schematic diagram of the solution-treated metallographic structure of Comparative Example 2.

[0054] Figure 6 Cross-sectional morphology of Comparative Example 1 after oxidation in air at 900°C for 100 h. DETAILED DESCRIPTION OF THE INVENTION

[0055] In the specific implementation process, based on the traditional material C276, the present invention first adopts the composition design idea of Re+Ta composite strengthening. By combining computational simulation and orthogonal composition design, the optimal combination of Re and Ta and the alloy total amount control strategy are obtained, and the subsequent optimized hot working and heat treatment systems are matched. For the first time, Re+Ta is completely dissolved in the matrix of the deformed nickel-based alloy, giving full play to the solution strengthening effect of Re and Ta in the nickel-based alloy, especially the role of the Re element in reducing the atomic migration rate in the alloy, increasing the recrystallization temperature of the nickel-based alloy after cold deformation, and thus ensuring the tensile strength of the material of the present invention after annealing. In addition, the composite addition of Re+Ta significantly improves the bonding force between the surface oxide layer and the matrix, further enhancing the high-temperature oxidation performance of the material of the present invention. The material with the above new composition design idea has a yield strength of more than 1550 MPa, a tensile strength of more than 1650 MPa, and an elongation of more than 2.0% after cold deformation; after annealing at 900 °C for 5 minutes, the yield strength is more than 1500 MPa, the tensile strength is more than 1600 MPa, and the elongation is more than 4.0%.

[0056] The following examples and drawings will further illustrate the present invention, but do not limit the present invention thereby. The nickel-based alloys in the examples and the nickel-based alloys in the comparative examples are processed into standard plate-shaped tensile specimens after purification smelting, hot working and heat treatment for mechanical property testing. The high-temperature oxidation performance of the material of the present invention is tested in accordance with GB / T 13303—"Method for Determining Oxidation Resistance of Steels".

[0057] The preparation process of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband of the present invention is: batching → melting → casting and forming → homogenization treatment → forging and hot working → heat treatment → cold working. Examples 1 to 5 are all prepared by the following method, and the specific steps are as follows:

[0058] (1) Mix each chemical component in proportion and obtain an ingot by adopting purification smelting technology;

[0059] (2) The temperature of the homogenization annealing treatment is 1250 ± 10 °C (Examples 1 to 5 are 1250 °C, 1260 °C, 1240 °C, 1245 °C, and 1255 °C respectively), and after holding for 25 h to 40 h (Examples 1 to 5 are 25 h, 45 h, 32 h, 28 h, and 36 h respectively), it is air-cooled to room temperature;

[0060] (3) Forge the homogenized and annealed ingot in the austenite single-phase region: the forging temperature is 1230°C to 1250°C (1230°C, 1249°C, 1240°C, 1235°C, 1244°C for Examples 1 to 5 respectively), the forging ratio is greater than 7.0 (7.5, 13.5, 10.0, 12.0, 10.5 for Examples 1 to 5 respectively), and water-cool to room temperature after forging;

[0061] (4) Hot-roll the forged alloy ingot: the rolling temperature is 1230°C to 1250°C (1230°C, 1250°C, 1240°C, 1235°C, 1245°C for Examples 1 to 5 respectively), the reduction per pass of rolling is controlled at 15 - 20% (15%, 20%, 17%, 18%, 19% for Examples 1 to 5 respectively), the total reduction is controlled at 60 - 80% (60%, 80%, 70%, 75%, 65% for Examples 1 to 5 respectively), and water-cool to room temperature after hot-rolling;

[0062] (5) Perform solution heat treatment after hot-rolling: the solution temperature is 1220°C to 1240°C (1220°C, 1240°C, 1230°C, 1225°C, 1235°C for Examples 1 to 5 respectively), the holding time is 2.0 h to 6.0 h (4.0 h, 6.0 h, 2.0 h, 5.0 h, 3.0 h for Examples 1 to 5 respectively), and water-cool to room temperature after holding;

[0063] (6) Perform cold deformation at room temperature after solution heat treatment: the cold deformation amount is 60 - 80% (70%, 60%, 80%, 65%, 75% for Examples 1 to 5 respectively).

[0064] Next, the present invention will be further elaborated in detail through the drawings, examples and comparative examples.

[0065] Example 1

[0066] In this example, by weight percentage, the chemical composition of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband is: Cr: 16.01%, Mo: 16.05%, Ta: 2.51%, Re: 1.50%, W: 4.02%, Fe: 5.52%, Co: 1.52%, Mn: 0.49%, Si: 0.03%, V: 0.15%, Al: 0.16%, B: 16 ppm, C: 11 ppm, S: 12 ppm, O: 6 ppm, P: 32 ppm, N: 11 ppm, and the balance is nickel.

[0067] Example 2

[0068] In this embodiment, by weight percentage, the chemical composition of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband is: Cr: 16.98%, Mo: 16.99%, Ta: 3.52%, Re: 1.47%, W: 3.01%, Fe: 4.05%, Co: 2.48%, Mn: 0.68%, Si: 0.05%, V: 0.20%, Al: 0.20%, B: 26 ppm, C: 12 ppm, S: 14 ppm, O: 5 ppm, P: 36 ppm, N: 14 ppm, and the balance is nickel.

[0069] Example 3

[0070] In this embodiment, by weight percentage, the chemical composition of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband is: Cr: 15.04%, Mo: 15.11%, Ta: 2.49%, Re: 0.54%, W: 4.96%, Fe: 6.89%, Co: 0.52%, Mn: 0.36%, Si: 0.01%, V: 0.11%, Al: 0.10%, B: 11 ppm, C: 10 ppm, S: 16 ppm, O: 9 ppm, P: 44 ppm, N: 18 ppm, and the balance is nickel.

[0071] Example 4

[0072] In this embodiment, by weight percentage, the chemical composition of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband is: Cr: 16.49%, Mo: 16.51%, Ta: 2.01%, Re: 2.48%, W: 3.49%, Fe: 4.87%, Co: 2.03%, Mn: 0.61%, Si: 0.04%, V: 0.18%, Al: 0.16%, B: 25 ppm, C: 14 ppm, S: 18 ppm, O: 8 ppm, P: 40 ppm, N: 15 ppm, and the balance is nickel.

[0073] Example 5

[0074] In this embodiment, by weight percentage, the chemical composition of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband is: Cr: 15.56%, Mo: 15.49%, Ta: 1.56%, Re: 1.98%, W: 4.57%, Fe: 6.25%, Co: 1.04%, Mn: 0.38%, Si: 0.025%, V: 0.13%, Al: 0.12%, B: 20 ppm, C: 13 ppm, S: 15 ppm, O: 7 ppm, P: 35 ppm, N: 16 ppm, and the balance is nickel.

[0075] Comparative Example 1

[0076] In this comparative example, by weight percentage, the chemical composition of the nickel-based alloy is as follows: Cr: 16.03%, Mo: 16.02%, Ta: 2.54%, Re: 1.51%, W: 4.05%, Fe: 5.48%, Co: 1.50%, Mn: 0.48%, Si: 0.02%, V: 0.13%, Al: 0.17%, B: 18 ppm, C: 12 ppm, S: 13 ppm, O: 7 ppm, P: 31 ppm, N: 14 ppm, and the balance is nickel. The chemical composition of the nickel-based alloy in this comparative example is similar to that in Example 1. The main difference is that the Ta and Re elements are not added, and the other homogenization treatment, forging process, hot rolling process, solution treatment, and cold working process are exactly the same as those in Example 1.

[0077] Comparative Example 2

[0078] In this comparative example, by weight percentage, the chemical composition of the nickel-based alloy is as follows: Cr: 16.95%, Mo: 16.97%, Ta: 8.02%, Re: 7.01%, W: 3.02%, Fe: 4.03%, Co: 2.46%, Mn: 0.67%, Si: 0.06%, V: 0.19%, Al: 0.21%, B: 25 ppm, C: 13 ppm, S: 15 ppm, O: 6 ppm, P: 34 ppm, N: 16 ppm, and the balance is nickel. The chemical composition of the nickel-based alloy in this comparative example is similar to that in Example 2. The main difference is that the content of Ta element is 8.02% and the content of Re element is 7.01%, and the content of Re + Ta is as high as 15.03%. The other homogenization treatment, forging process, hot rolling process, solution treatment, and cold working process are exactly the same as those in Example 2.

[0079] Table 1 Mechanical properties of the cold-rolled sheets in the examples and comparative examples

[0080] Serial number <![CDATA[Yield strength Rp 0.2 , MPa]]> Tensile strength Rm, MPa Elongation A, % Example 1 1580 1682 3.0 Example 2 1599 1698 2.2 Example 3 1557 1658 4.0 Example 4 1588 1690 2.5 Example 5 1568 1670 3.6 Comparative example 1 1225 1515 5.6 Comparative example 2 1641 1712 0.4

[0081] As can be seen from Table 1, based on the traditional material Hastelloy C276, the present invention innovatively adopts the Re+Ta composite solid solution strengthening method. By adding optimized contents of Re and Ta elements, controlling the total content of Re+Ta, and matching the optimized hot working process and heat treatment system, it is ensured that the added Re and Ta are completely dissolved into the matrix. Finally, through cold deformation with a certain deformation amount, a nickel-based alloy with a yield strength above 1557 MPa, a tensile strength above 1658 MPa, and an elongation above 2.0% can be obtained. In Comparative Example 1, no Re and Ta elements were added. By comparing with Example 1, it was found that the yield strength of the comparative example reached 1225 MPa and the tensile strength reached 1515 MPa, which were lower than the performance indexes of the materials of the present invention. In Comparative Example 2, the Ta element content was 8.02%, the Re element content was 7.01%, and the Re+Ta content was as high as 15.03%, all exceeding the control range of the Re and Ta element contents of the present invention. By comparing with Example 2, it was found that due to the presence of relatively large second phases rich in Re and Ta in the nickel-based alloy matrix, the yield strength reached 1641 MPa and the tensile strength reached 1712 MPa, and the strength indexes met the strength index requirements of the present invention, but the elongation was only 0.4%, lower than the performance indexes of the materials of the present invention.

[0082] Table 2 Mechanical properties of the cold-rolled sheets of the examples and comparative examples after annealing at 900 °C for 5 min and air cooling

[0083] Serial number <![CDATA[Yield strength Rp 0.2 , MPa]]> Tensile strength Rm, MPa Elongation A, % Example 1 1526 1635 5.0 Example 2 1548 1652 4.2 Example 3 1505 1611 6.8 Example 4 1536 1644 4.5 Example 5 1516 1625 5.6 Comparative example 1 1045 1234 10.5 Comparative example 2 1634 1668 0.6

[0084] As can be seen from Table 2, after annealing at 900 °C for 5 min, the yield strength of the materials of the present invention is above 1505 MPa, the tensile strength is above 1611 MPa, and the elongation is above 4.2%. After holding at 900 °C for 5 min, no recrystallization occurred in the cold-rolled nickel-based alloy matrix of the present invention, and only a certain degree of dynamic recovery occurred. Therefore, the tensile strength of the materials of the present invention still remained above 1600 MPa. In Comparative Example 1, no Re and Ta elements were added, and recrystallization occurred in the material. Its yield strength reached 1045 MPa and the tensile strength was only 1234 MPa, and the strength indexes did not meet the index requirements of the materials of the present invention. The yield strength of Comparative Example 2 was as high as 1634 MPa, and the tensile strength was only 1668 Pa. Although the strength indexes met the requirements, the elongation was only 0.6%, far lower than 4.0%, and far from meeting the plasticity index requirements of the materials of the present invention.

[0085] Such as Figure 1As shown, the metallographic structure of Example 1 after air cooling after hot forging with large deformation at 1230°C. It can be seen from the figure that after one heat treatment, the dendrites of the original as-cast structure are broken. During the homogenization at 1250°C for 25 h and the holding stage before forging, all the Re and Ta elements in the nickel-based alloy matrix are redissolved into the nickel-based alloy matrix. After forging and cooling, no recrystallization occurs in the material of the present invention.

[0086] As Figure 2 shown, the SEM structure of Example 2 after solution treatment at 1240°C for 4 h. It can be seen from the figure that after homogenization treatment, hot forging with large deformation, hot rolling and solution treatment, the Re and Ta elements in Example 2 are completely dissolved into the matrix, and there is no second phase rich in Re and Ta at the grain boundaries.

[0087] As Figure 3 shown, the cross-sectional morphology of the oxide layer of Example 1 after cold deformation by 70% and oxidation in air at 900°C for 150 h. It can be seen from the figure that after oxidation at 900°C for 150 h, an oxide layer with a thickness of 3 - 5 μm is formed on the surface. The thickness of the oxide layer is uniform, and the combined addition of Re and Ta improves the oxidation resistance of the material of the present invention.

[0088] As Figure 4 shown, the scanning structure of Comparative Example 1 after air cooling after hot forging with large deformation at 1230°C. It can be seen from the figure that since Re and Ta elements are not added in Comparative Example 1, after one heat treatment of forging, the matrix undergoes complete recrystallization, and the recrystallization volume fraction is as high as more than 85%, resulting in lower yield strength and tensile strength of Comparative Example 1.

[0089] As Figure 5 shown, the SEM structure of Comparative Example 2 after solution treatment at 1240°C for 4 h. It can be seen from the figure that since the Ta element content in Comparative Example 2 is 8.02%, the Re element content is 7.01%, and the Re + Ta content is as high as 15.03%, all higher than the composition range required by the present invention. After solution treatment at 1240°C for 4 h, there are still a large number of micron-sized second phases rich in Re and Ta in the matrix. The large particle second phases existing in the base band will affect its superconducting properties and deteriorate its mechanical properties, which is the main reason for the low plasticity index of Comparative Example 2.

[0090] As Figure 6 shown, the cross-sectional morphology of the oxide layer of Comparative Example 1 after cold deformation by 70% and oxidation in air at 900°C for 150 h. It can be seen from the figure that after oxidation at 900°C for 150 h, Comparative Example 1 without the addition of Re and Ta undergoes uneven oxidation, and the thickness of the oxide layer is uneven, with an average thickness of the oxide layer reaching 10 μm.

[0091] The mechanical property test results of the above Examples 1 to 5 show that on the basis of commercial Hastelloy C276, the present invention innovatively adopts Re+Ta composite strengthening. By adopting the technical solution of the embodiment of the present invention, the content of Ta element is optimized to be between 1.5% and 4.0%, the content of Re element is optimized to be between 0.5% and 2.5%, the total content of Re+Ta is controlled at 3.0% to 5.0%, and the contents of Mo, W, and Fe are optimized to be 15.0% to 17.0%, 3.0% to 5.0%, and 4.0% to 7.0% respectively. By matching the subsequent optimized homogenization treatment, hot working, heat treatment process and cold working process, a nickel-based alloy with a yield strength of more than 1557 MPa, a tensile strength of more than 1658 MPa, and an elongation of more than 2.2% can be obtained; after annealing at 900°C for 5 minutes, the yield strength and tensile strength of the material of the present invention reach more than 1505 MPa and 1611 MPa respectively, and the elongation reaches more than 4.2%. After oxidation at 900°C for 150 hours, the thickness of the oxide layer is significantly lower than that of Comparative Example 1, and it has excellent high-temperature oxidation resistance.

[0092] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it accordingly, and cannot be used to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A 1600 MPa grade high-strength nickel-based alloy for second-generation high-temperature superconducting baseband, characterized in that, By weight percentage, its chemical composition is: Cr: 15.0 - 17.0%, Mo: 15.0 - 17.0%, Ta: 0.5 - 6.5%, Re: 0.2 - 6.0%, W: 3.0 - 5.0%, Fe: 4.0 - 7.0%, Co: 0.5 - 2.5%, Mn: 0.3 - 0.7%, Si: 0.01 - 0.05%, V: 0.1 - 0.2%, Al: 0.1 - 0.2%, B: 0.001 - 0.01%, C < 0.005%, P < 0.005%, S < 0.002%, O < 0.002%, N < 0.002%, and the balance is nickel.

2. The 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 1, characterized in that, Preferably, Ta: 1.0 - 4.0%, Re: 0.5 - 2.5%, Re + Ta: 3.0 - 5.0%.

3. The 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 1, characterized in that, Preferably, B: 0.001 - 0.003%.

4. The 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 1, wherein Preferably, C < 0.002%, O < 0.001%.

5. A method for preparing a 1600 MPa grade high-strength nickel-based alloy for a second-generation high-temperature superconducting baseband according to any one of claims 1 to 4, characterized in that, It includes the following steps: (1) Mix each chemical component in proportion, and obtain an ingot through purification smelting and electroslag remelting; (2) Anneal the obtained ingot at high temperature for homogenization. The temperature of the homogenization annealing treatment is 1250 ± 10 °C, and after holding for 25 h - 40 h, it is air-cooled to room temperature; (3) Forge the ingot after homogenization annealing in the austenite single-phase region. The forging process is: the forging temperature is 1230 - 1250 °C, the forging ratio is above 7.0, and after forging, it is water-cooled to room temperature; (4) Perform hot rolling on the forged alloy ingot: the rolling temperature is 1230 °C - 1250 °C, the reduction per pass of rolling is controlled at 15 - 20%, the total reduction is controlled at 60 - 80%, and after hot rolling, it is water-cooled to room temperature; (5) Perform solution heat treatment after hot rolling. The solution heat treatment process is: hold at 1220 °C - 1240 °C for 2 - 6 h and then water-quench to room temperature; (6) Perform cold deformation after solution heat treatment. The cold deformation process is: perform cold deformation at room temperature, and the cold deformation amount is 60 - 80%.

6. The preparation method of a 1600 MPa grade high-strength nickel-based alloy for a second-generation high-temperature superconducting baseband according to claim 5, characterized in that, After cold deformation, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength reaches above 1550 MPa, the tensile strength reaches above 1650 MPa, and the elongation reaches above 2.0%.

7. The preparation method of the 1600MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 6, characterized in that, Preferably, after cold deformation, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength is 1560 - 1600 MPa, the tensile strength is 1650 - 1700 MPa, and the elongation is 2.0 - 4.0%.

8. The preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 5, characterized in that, After annealing at 900 °C for 5 min, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength reaches above 1500 MPa, the tensile strength reaches above 1600 MPa, the elongation reaches above 4.0%, and it has good high-temperature oxidation resistance.

9. The preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 8, characterized in that, Preferably, after annealing at 900 °C for 5 min, the room temperature performance indexes of the nickel-based alloy are as follows: the yield strength is 1500 - 1550 MPa, the tensile strength is 1610 - 1660 MPa, and the elongation is 4.0 - 7.0%.

10. The preparation method of the 1600 MPa grade high-strength nickel-based alloy for the second-generation high-temperature superconducting baseband according to claim 5, characterized in that, After oxidizing at 900 °C for 150 h, an oxide layer of 3 - 5 μm is formed on the surface of the nickel-based alloy, and the thickness of the oxide layer is uniform.

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