1400 MPa-grade high-cobalt low-tungsten nickel-based alloy for second-generation high-temperature superconducting baseband and preparation method of 1400 MPa-grade high-cobalt low-tungsten nickel-based alloy

Abstract

The invention relates to a 1400 MPa-grade high-cobalt low-tungsten nickel-based alloy for a second-generation high-temperature superconducting baseband and a preparation method of the 1400 MPa-grade high-cobalt low-tungsten nickel-based alloy, and belongs to the technical field of materials. On the basis of the Hastelloy alloy, the Co element with the optimized content is added, solid solution strengthening and TCP phase precipitation restraining are achieved, and the high plasticity of the nickel-based alloy is guaranteed; by increasing the content of Cr, the oxidation resistance of the material is ensured; and the Mo content is reduced, Mo and W elements are promoted to completely enter a matrix in a solid solution mode, no TCP phase precipitation is achieved in the hot rolling process, cracking caused by a residual second phase in the subsequent cold rolling process is avoided, and therefore the preparation technological process of the material is simplified, and the material manufacturing cost is reduced. By adopting the component control strategy, the simplified preparation technology and the heat treatment technology, the nickel-based alloy with the tensile strength being 1400 MPa or above and the elongation being larger than 21.0% can be obtained after annealing is conducted for 5 min at the temperature of 900 DEG C, and the requirement of a second-generation high-temperature superconducting high-performance metal base band is met.

Description

Technical Field

[0001] The present invention relates to a 1400MPa-grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting base tape and a preparation method thereof, belonging to the field of material technology. Background Art

[0002] Second-generation REBCO high-temperature superconductors, with their advantages of high critical temperature, complete diamagnetism, and high critical current density, have achieved demonstrable applications in power transmission, energy storage, and high-field magnets. They are typically manufactured using a laminated structure consisting of a "metal substrate + buffer layer + superconducting layer + protective layer": On a flexible metal substrate, a buffer layer is first epitaxially grown at 850°C to 900°C using IBAD (ion beam assisted biaxial texture deposition) technology, followed by deposition of a superconducting layer and a protective layer.

[0003] This process places stringent demands on the substrate material—not only must it possess low magnetic properties to match the thermal expansion of the superconducting layer, but it must also maintain excellent mechanical strength at temperatures between 850°C and 900°C after deposition. Currently, commercial Hastelloy C276 is widely used because it can achieve room-temperature tensile strength exceeding 1500 MPa after 50% to 90% cold deformation. However, when deposited at temperatures between 850°C and 900°C, the accumulated energy stored in the large deformation triggers recrystallization, causing the strength to drop below 1100 MPa, making it difficult to meet the strength requirements of the high-strain substrate. Therefore, it cannot meet the current development needs of high-temperature, high-field superconductors, thus limiting the further upgrading of high-temperature superconducting equipment. However, the existing C276 alloy, which significantly adds Mo and W to meet higher strength requirements, suffers from severe solute segregation during casting due to their melting point difference with Ni, resulting in the precipitation of a brittle TCP-structured P phase at the front end of the dendrite arms. To completely dissolve this phase back, the homogenization temperature must be increased from the original 1180°C to approximately 1250°C, which not only increases energy consumption and equipment burden, but also easily reprecipitates coarse TCP phases during subsequent solution or annealing stages, significantly increasing the risk of cold rolling cracking. To address this bottleneck, the present invention introduces and optimizes the Co element, strictly lowering the TCP phase's redissolution temperature and promoting its dissolution, completely eliminating the segregated phase. This simplifies the homogenization and solution processes, reduces manufacturing costs, and significantly improves the safety and yield of cold rolling.

[0004] Patent publication number CN119753431A proposes a 1300 MPa nickel-based alloy for second-generation high-temperature superconducting tape and its preparation method. The alloy's chemical composition, by weight, is as follows: Cr 15.0-17.0%, Mo 15.0-17.0%, W 3.0-4.5%, 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%, N 0.040-0.080%, C <0.002%, P <0.005%, S <0.002%, O <0.002%, with the balance being nickel. The high-nitrogen, boron-free design improves alloy strength to a certain extent, but excessive nitrogen content can lead to grain coarsening and other problems. Relying on N element (0.04-0.08%) to improve the work hardening rate, but not solving the TCP phase problem, the strength after high temperature annealing is only 1300MPa.

[0005] Patent publication number CN119899958A proposes a 1400 MPa nickel-based alloy for second-generation high-temperature superconducting tape and its preparation method. The alloy's chemical composition, by weight, is as follows: Cr 15.0-17.0%, Mo 13.0-15.0%, W 5.5-9.0%, Fe 5.0-7.0%, Mn 0.4-0.6%, Si 0.01-0.05%, V 0.1-0.2%, Co 0-2.5%, 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%, with the balance being nickel. Based on a Ni-Cr-Mo alloy, the alloy adopts a compositional design strategy of increasing W and decreasing Mo, resulting in a Co content of only 0-2.5%, which is unable to suppress the TCP phase. In addition, the presence of B element (0.001-0.01%) and BN inclusions lead to low cold rolling yield.

[0006] Patent publication number CN119685656A proposes a 1500 MPa nickel-based alloy for second-generation high-temperature superconducting tape and its preparation method. The alloy's chemical composition, by weight percentage, is as follows: 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%, with the balance being nickel. Based on Hastelloy alloy, the alloy is enhanced by increasing the W content. While this increases the W content, excessive W content increases alloy cost and easily forms a stable W-rich phase, which affects alloy performance. Without adding Co element, the strength is improved by relying on W content (4.5-9.5%), but high W content leads to an increase in the TCP phase precipitation temperature.

[0007] The applicant's three aforementioned invention patents (publication numbers CN119685656A, CN119753431A, and CN119899958A) all offer targeted improvements based on Hastelloy C276. While these improvements offer a certain degree of tensile strength improvement compared to C276, their alloy composition increases and the manufacturing process becomes more complex, significantly increasing their manufacturing costs. Specifically, the patent for the nitrogen alloy design (publication number CN119753431A) achieves a maximum elongation of only 18.5% after annealing at 900°C for 5 minutes, which falls short of the required elongation of 20% or more.

[0008] In addition, patent publication number CN118398273A proposes a second-generation high-temperature superconducting base tape and its preparation process. The chemical composition of the superconducting base tape, by mass percentage, includes: C: 0.003-0.008%; Mn: 0.3-0.6%; P: 0.003-0.009%; S: 0.00005-0.0001%; ​​Si: 0.01-0.03%; Cr: 14-16%; Mo: 14-16%; V: 0.08-0.2%; Co: 0.5-0.8%; W: 2.5-3.5%; Fe: 4-6%, with the remainder being Ni and other unavoidable impurities. The Co content in the alloy is only 0.5-0.8%, which is unable to effectively suppress TCP phase precipitation, resulting in insufficient tensile strength after high-temperature annealing. In addition, the W content is low (2.5-3.5%), the solid solution strengthening effect is limited, and the Cr and Mo contents are not optimized, resulting in significant strength attenuation after high-temperature recrystallization.

[0009] With the continuous advancement of second-generation high-temperature, high-field superconducting technology, higher requirements are being placed on the baseband materials of key equipment (such as high-field superconducting magnets): not only must they have a higher recrystallization onset temperature to maintain structural stability during large cold deformation and high-temperature preparation, but they must also ensure a tensile strength of no less than 1400 MPa. Currently, the strength of commercial C276 baseband after high-temperature annealing is less than 1100 MPa, which can no longer meet the mechanical performance requirements of the second-generation superconductor baseband. Therefore, there is an urgent need to develop a new nickel-based alloy that can maintain a tensile strength of 1400 MPa and structural stability under high-temperature and large deformation conditions. Summary of the Invention

[0010] The present invention aims to provide a 1400MPa-grade, high-cobalt, low-tungsten nickel-based alloy for second-generation high-temperature superconducting substrates and its preparation method. Based on the traditional Hastelloy C276 alloy, the alloy composition is simplified. A Ni-Cr-W-Mo-Co quinary alloy is formed by the synergistic effect of Co (4-10%) with Cr (16-18%), Mo (14-16%), W (4.5-6.5%), and Ni. This alloy overcomes the technical bias of the existing Co content of nickel-based alloys for high-temperature superconducting substrates, which is ≤2.5%, and significantly reduces TCP phase stability. The alloy utilizes a direct cold rolling process after hot rolling to simplify the process flow and reduce manufacturing costs.

[0011] The technical solution of the present invention is:

[0012] A 1400MPa-grade high-cobalt, low-tungsten nickel-based alloy for second-generation high-temperature superconducting base tape has the following chemical composition, measured by weight: Cr: 16.0-18.0%, Mo: 14.0-16.0%, W: 4.5-6.5%, Co: 4.0-10.0%, C <0.005%, P <0.005%, S <0.002%, O <0.002%, N <0.002%, and the balance is nickel.

[0013] The second generation high temperature superconducting base tape is made of 1400MPa grade high cobalt low tungsten nickel-based alloy, with W: 5.0-6.0%, Co: 7.0-9.0%.

[0014] The second generation high temperature superconducting base tape is made of 1400MPa grade high cobalt low tungsten nickel-based alloy, with C<0.002 and O<0.001.

[0015] The method for preparing the 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for the second-generation high-temperature superconducting base tape comprises the following steps:

[0016] (1) Mixing the chemical components in proportion, and obtaining an ingot through purification smelting and electroslag remelting;

[0017] (2) performing homogenization annealing treatment on the obtained ingot at high temperature;

[0018] (3) Forging the homogenized annealed ingot in the γ single phase region;

[0019] (4) The forged alloy ingot is hot rolled: After being kept at 1100°C to 1250°C for 2 to 4 hours, it is hot rolled at a rolling temperature of 1200°C to 1250°C, with the reduction of each pass controlled at 20 to 30% and the total reduction controlled at 70 to 90%. After hot rolling, it is water-cooled to room temperature;

[0020] (5) Cold rolling directly after hot rolling: cold rolling at room temperature, with a cold rolling deformation of 60-90%;

[0021] (6) After cold rolling, annealing heat treatment is performed at 900°C for 5 minutes.

[0022] In the preparation method of the 1400MPa grade high-cobalt low-tungsten nickel-based alloy for the second-generation high-temperature superconducting base tape, in step (2), the temperature of the homogenization annealing treatment is 1250±20°C, and the temperature is kept for 20h to 30h.

[0023] The preparation method of the 1400MPa grade high-cobalt low-tungsten nickel-based alloy for the second-generation high-temperature superconducting base tape, in step (3), the forging process is: forging temperature 1220-1250°C, forging ratio above 6.0, and air cooling to room temperature after forging.

[0024] The preparation method of the 1400MPa grade high-cobalt low-tungsten nickel-based alloy for the second-generation high-temperature superconducting base tape comprises the following steps: in step (4), the alloy is kept at 1200°C to 1250°C for 2 to 4 hours and then hot rolled.

[0025] The preparation method of the 1400MPa grade high-cobalt low-tungsten nickel-based alloy for the second-generation high-temperature superconducting base tape, in step (5), the cold rolling process is: cold rolling at room temperature, the cold rolling deformation amount is 70-85%.

[0026] The method for preparing a 1400MPa-grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting base tape achieves a tensile strength of more than 1800MPa and an elongation of more than 4.0% after cold rolling; and after annealing at 900°C for 5 minutes, the tensile strength reaches more than 1400MPa and the elongation is more than 21.0%.

[0027] The content ranges of the main elements in the present invention are described as follows:

[0028] Cr: Chromium is a key element in Hastelloy alloy and is the primary factor determining its corrosion resistance. This is because chromium improves the alloy's inherent corrosion resistance and facilitates the formation of a chromium oxide layer. However, when the Cr content is less than 15 wt%, the alloy's required minimum corrosion resistance cannot be achieved. On the other hand, when the Cr content exceeds 17 wt%, chromium-rich intermetallic compounds tend to precipitate, forming chromium-depleted zones around the intermetallic compounds. This not only impairs the material's hot workability and mechanical properties but also deteriorates its resistance to oxidative corrosion. Therefore, to ensure excellent corrosion resistance against most corrosive media in both oxidized and reduced states, the chromium content in the alloy of the present invention is controlled to 16.0 to 18.0 wt%.

[0029] Mo: Molybdenum, like chromium, is a corrosion-resistant element with an ability comparable to that of chromium. The interaction between molybdenum and the corrosive medium will promote the formation of a dense and uniform passivation film on the surface, reducing the possibility of corrosion of the alloy and significantly improving its corrosion resistance. In addition, Mo can enhance the solid solution strengthening effect of nickel-based alloys, improve the strength and service performance of the alloy. However, an excessively high Mo content will suffer varying degrees of oxidation during hot working, deteriorating the processing and performance of the alloy. Therefore, molybdenum with the effect of improving corrosion resistance can be added within a range that does not damage other properties of the material, such as corrosion resistance, hot workability, and weldability. Therefore, the molybdenum content in the alloy of the present invention is controlled to be: 14.0 to 16.0 wt%.

[0030] W: Tungsten plays a similar role to Mo, primarily serving as a solid solution strengthening agent in the alloy system. Since W has a larger atomic radius than Mo, its solid solution strengthening effect is greater than that of Mo. Furthermore, due to W's high melting point, appropriately increasing its content will, to a certain extent, increase the alloy's recrystallization temperature after cold working, which is one of the key points of the present invention. However, excessive W content can cause the alloy to form a relatively stable tungsten-rich and molybdenum-rich μ phase, which cannot be completely eliminated even at very high solution temperatures for extended periods. Therefore, in order to avoid the effects of precipitation on superconducting properties, the W content must be strictly controlled. Therefore, the W content in the alloy of the present invention is controlled to be 4.5 to 6.5 wt%, and further optimized to be 5.0 to 6.0 wt%.

[0031] Co: Cobalt is essentially completely dissolved in the matrix, providing a solid solution strengthening effect without forming carbides. Instead, it forms a synergistic effect with Mo, promoting the precipitation of precipitated phases. Cobalt can inhibit the recovery of dislocation substructures in the microstructure, providing more nucleation sites for subsequent precipitated phases, and promoting precipitation strengthening. Therefore, based on the balancing effect of cobalt on the alloy and its influence on the precipitation effect of the precipitated phase, the cobalt content in the alloy of the present invention is controlled to be: 4.0-10.0wt%, and further optimized to 7.0-9.0wt%.

[0032] C: Carbon in alloys easily forms M with elements such as Cr 23 C6 carbides precipitate, especially during the slow cooling process after solutionization. While these carbides precipitate at the original austenite grain boundaries, pinning dislocations and hindering interfacial motion, effectively enhancing the material's strength through precipitation strengthening, they can also affect the superconducting properties of second-generation superconductors, necessitating strict control of the alloy's carbon content. Therefore, adopting an ultra-low carbon composition design approach, the carbon content in the alloy of the present invention is optimized to: C < 0.005 wt%, and further optimized to C < 0.002 wt%.

[0033] S, P: In the production of nickel-based alloys, phosphorus and sulfur are generally regarded as harmful impurities because they can significantly reduce the overall performance of the alloy. P promotes the segregation of W and Mo to form Laves phase, thereby increasing the cold brittleness of the alloy and reducing the cohesion of the grain boundaries, thereby reducing the toughness and ductility of the material. It also affects the welding performance and makes the welded joints prone to cracking. On the other hand, sulfur increases the tendency of the material to be hot brittle, especially during processing. At the same time, excessive sulfur will also affect the mechanical processing quality of the material and reduce 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 <0.002wt%, P <0.005wt%.

[0034] Oxygen is the primary element responsible for oxide inclusions in alloys. Therefore, to reduce inclusions and maintain material purity, the oxygen content must be minimized. Exceeding a certain limit in a material, particularly when Al is present in the present invention, can lead to the formation of continuous, brittle oxide inclusions. This can cause stress concentration during ribbon processing and lead to ribbon breakage. Therefore, the oxygen content in the present invention alloy is strictly controlled: O < 0.002 wt%, further optimized to O < 0.001 wt%.

[0035] Nitrogen: Nitrogen is a strong austenite-forming element, expanding the austenite phase and shrinking the ferrite phase, thus inhibiting the formation of high-temperature ferrite. While nitrogen can increase the cold work hardening rate and improve the strength of the alloy after cold working, the addition of a certain amount of boron to the present invention requires strict control of the nitrogen content in the present material to prevent the formation of BN inclusions. Therefore, the nitrogen content in the present alloy is strictly controlled: N < 0.002 wt%.

[0036] The innovative design ideas of the present invention are as follows:

[0037] 1. Innovative composition design concept: By adding a certain optimized content of Co to the Hastelloy alloy composition system, on the one hand, Co inhibits the precipitation of TCP phase, laying the foundation for the simplification of subsequent preparation process flow; on the other hand, Co plays a role in solid solution strengthening. After a certain amount of cold rolling deformation, the tensile strength of the nickel-based alloy exceeds 1800 MPa. Finally, Co is used to provide nucleation points to promote the dispersed precipitation of precipitates. After annealing at 900°C for 5 minutes, although the nickel-based alloy matrix undergoes recrystallization, the tensile strength is still greater than 1400 MPa. Moreover, the precipitates are small in size and dispersed. The elongation of the material is greater than 21%, and the strength and plasticity are much higher than those of the current commercial Hastelloy alloy (tensile strength of approximately 1100 MPa).

[0038] 2. Simplified alloy composition system: Based on the Ni-Cr-Mo Hastelloy alloy, the present invention simplifies and optimizes the alloy composition system and content. After adding the Co element content, only four key elements, Cr, Mo, and W, are retained. The Cr, Mo, and W element contents are optimized to 16.0-18.0%, 14.0-16.0%, and 4.5-6.5%, respectively, ensuring the matching of the oxidation resistance and strength of the nickel-based alloy. In addition, due to the optimization of the Mo and W contents, the stability of the TCP phase is significantly reduced, and its precipitation temperature is reduced from the original 1240°C to 1078°C. This simplification and optimization of the alloy composition system ensures that the solid-solution elements of the nickel-based alloy can be completely dissolved back into the matrix before cold working, reducing the risk of cold working cracking.

[0039] The present invention forms a five-element alloy system by optimizing the synergistic effect of Co (4.0-10.0%), Cr (16.0-18.0%), Mo (14.0-16.0%), W (4.5-6.5%) and Ni matrix, and its effects are as follows:

[0040] (1) Synergistic effect of Co and W: Co significantly reduces the precipitation temperature of TCP phase (such as μ phase and P phase) (from 1240℃ of traditional alloy to 1078℃), promotes its complete dissolution during homogenization annealing (1250±20℃), and avoids the risk of cracking caused by brittle phase during cold rolling. Co element can improve the toughness of the alloy, so that the alloy can better absorb energy when subjected to external force, reducing the occurrence of brittle fracture. The atomic radius of W element is large. While playing a role in solid solution strengthening in the alloy, it can also hinder the growth of grains at high temperature and increase the recrystallization temperature of the alloy. Co+W synergistic solid solution strengthening, Co and W jointly improve the interatomic bonding strength of the nickel matrix, and the tensile strength after cold rolling is ≥1800MPa, which is significantly higher than that of traditional C276 alloy. Co inhibits the recovery of dislocation substructure, and the high melting point of W hinders dynamic recrystallization, synergistically improving the cold work hardening rate.

[0041] (2) Optimization of Mo / W ratio: Synergistic solid solution strengthening of Mo (14-16%) and W (4.5-6.5%) balances the difference in atomic radius (W atoms are larger), reduces lattice distortion stress, and suppresses Mo / W-rich segregation.

[0042] (3) The addition of Cr, Mo, and W can refine the grains, while Co can help maintain the smallness and uniformity of the grains to a certain extent. Fine grains can increase the number of dislocation sources and make the dislocations more evenly distributed, thereby improving the plastic deformation ability of the alloy.

[0043] (4) Elements such as Co, Cr, Mo, and W form solid solutions in the nickel matrix. Since the atomic radius of these elements is different from that of nickel, lattice distortion will occur in the crystal lattice, increasing the resistance to dislocation movement, thereby improving the strength of the alloy. Among them, the solid solution strengthening effect of Co is significant, which can effectively improve the yield strength and tensile strength of the alloy.

[0044] Therefore, forming a Ni-Cr-W-Mo-Co quinary alloy system in the alloy can enable the alloy to maintain a good match between plasticity and toughness while having high strength.

[0045] 3. Simplified processing and preparation technology achieves low cost: The innovative composition design and simplified alloy system of the present invention ensure that no second phase such as TCP is precipitated during the hot rolling process. The nickel-based alloy can be directly cold-processed after hot rolling without the need for high-temperature solution treatment. This not only simplifies the process flow, but also significantly shortens the production cycle, reduces energy consumption and equipment investment costs. The most critical thing is that the simplified preparation process can make the microstructure after hot working inherited, retaining fine grains (about 15μm), providing a large number of recrystallization nucleation sites for annealing after cold rolling, promoting complete recrystallization, and avoiding the formation of a heterogeneous structure mixed with deformation bands and recrystallized grains. Therefore, the smaller grain size and dispersed precipitation strengthening of the precipitated phase after annealing of the nickel-based alloy largely compensate for the loss of strength after recrystallization. This is the main reason why its tensile strength remains above 1400MPa and its elongation is greater than 21%, which is better than the currently commercial Hastelloy alloy, reflecting the superiority of the simplified process and achieving low cost.

[0046] In addition, in the hot rolling process of the present invention, the design of holding the temperature at 1100°C to 1250°C for 2 to 4 hours before rolling has the following key effects:

[0047] (1) Promote complete solid solution of alloy elements and eliminate segregation and brittle phase

[0048] Dissolving TCP phase: High temperature insulation allows elements such as Mo and W that are prone to forming brittle TCP phases (such as μ phase and P phase) to fully dissolve in the nickel matrix, avoiding the risk of cracking caused by undissolved brittle phases during rolling.

[0049] Homogenized structure: Eliminate dendritic segregation in the cast state, ensure uniform distribution of elements such as Cr, Mo, and Co, and improve the overall performance consistency of the material.

[0050] (2) Reduce rolling resistance and improve processability

[0051] Softening the matrix: The yield strength of the material is significantly reduced at high temperatures, allowing a larger single-pass reduction (20-30%), achieving efficient rolling (total reduction of 70-90%), while reducing the risk of rolling cracks.

[0052] (3) Simplify the process flow and avoid subsequent solution treatment

[0053] By keeping the elements fully dissolved in the solution, direct water cooling after hot rolling can suppress the precipitation phase, eliminating the solution treatment step required in traditional processes, shortening the production cycle and reducing energy consumption.

[0054] (4) Synergistic cold rolling and annealing process to achieve high strength-high plasticity matching

[0055] After the cold rolling deformation reaches 60-90%, the tensile strength is ≥1800MPa; after annealing at 900℃ for 5min, the fine grains promote uniform recrystallization and the precipitated phase is dispersed, and the final tensile strength is ≥1400MPa and the elongation is >21%.

[0056] Therefore, the present invention maintains the temperature at 1100°C to 1250°C for 2 to 4 hours before hot rolling, which can achieve the triple effects of element solid solution control + grain refinement + process simplification, breaking through the limitation of traditional nickel-based alloys requiring multiple steps of solid solution treatment, and realizing the necessary link of "solution-free direct cold rolling" process innovation.

[0057] The advantages and beneficial effects of the present invention are:

[0058] 1. Based on the simplified Hastelloy C276 alloy, the present invention achieves complete dissolution of the second phase formed during the casting process into the matrix through optimized matching of subsequent preparation and heat treatment systems. At the same time, by adding 4.0-10.0wt% of the alloying element Co, the unique solid solution strengthening effect of Co is fully utilized to improve the strength of the cold-rolled material. In addition, the Co element is used to enhance the nucleation effect of the precipitate phase, forming a finer and more dispersed precipitate phase after annealing, thereby improving the precipitation strengthening effect and obtaining a 1400MPa-level superconducting base tape material.

[0059] 2. By optimizing the alloy composition, this invention allows the secondary phase formed during hot rolling to completely dissolve into the matrix at high temperatures, completely eliminating the traditional solution treatment required to eliminate the coarse phases precipitated during hot rolling cooling. This allows for direct cold rolling, significantly simplifying the process while also effectively reducing production costs, shortening production cycles, and significantly improving processing efficiency.

[0060] 3. This invention provides a 1400MPa nickel-based alloy for second-generation high-temperature superconducting substrates and a key preparation process. Using the technical solutions provided by this invention, high-purity, high-strength nickel-based superalloys can be stably obtained. This material can better support the rapid development of my country's high-temperature, high-field superconducting industry and promote equipment upgrades. It also provides new insights into the development and application of high-strength nickel-based alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a metallographic structure picture of Example 1 under cast conditions.

[0062] Figure 2 This is a scanning microstructure image of Example 2 after water cooling after hot rolling.

[0063] Figure 3 This is the electron backscatter diffraction (EBSD) image of Example 3 after annealing at 900°C for 5 minutes and air cooling.

[0064] Figure 4 This is a scanning microstructure image of Example 4 after annealing at 900°C for 5 minutes and air cooling.

[0065] Figure 5 This is a scanning electron microscope (SEM) image of Example 5 after annealing at 900°C for 5 minutes and air cooling.

[0066] Figure 6 This is the SEM microstructure image of the as-cast alloy in Comparative Example 2 after solution treatment at 1100°C for 2 hours and water cooling.

[0067] Figure 7 This is the metallographic structure of the traditional Hastelloy alloy after hot rolling and water cooling in Comparative Example 4. DETAILED DESCRIPTION

[0068] In specific implementation, the present invention simplifies the alloy system based on the traditional material Hastelloy, while optimizing the addition of 4.0-10.0wt% Co to achieve solid solution strengthening and inhibit TCP phase precipitation, thereby ensuring the strong plasticity of the nickel-based alloy. By increasing the Cr content to 16.0-18.0wt%, the material's oxidation resistance is guaranteed; and by reducing the Mo content to 14.0-16.0wt%, the Mo and W elements are completely dissolved into the matrix. Combined with an optimized hot working and heat treatment system, the present invention achieves, for the first time, no precipitation of TCP phases such as μ-phase and P-phase after hot rolling, thus avoiding cracking caused by residual second phases during the subsequent cold rolling process. This completely eliminates the solid solution treatment required in traditional processes to eliminate coarse phases precipitated during hot rolling cooling, thereby simplifying the material preparation process and reducing material manufacturing costs. In addition, the solid solution strengthening effect of Co in the nickel-based alloy and the precipitation strengthening effect after annealing are fully utilized. By adopting the above-mentioned composition control strategy, simplified preparation process and heat treatment process, the tensile strength of the material of the present invention reaches above 1800 MPa and the elongation is greater than 4% after cold rolling; after annealing at 900°C for 5 minutes, the tensile strength reaches above 1400 MPa and the elongation is greater than 21.0%, meeting the requirements of high-performance metal substrates for second-generation high-temperature superconductors.

[0069] The preparation process of the 1400 MPa grade nickel-based alloy for the second-generation high-temperature superconducting substrate of the present invention is: batching → smelting → casting → homogenization → forging → hot rolling → cold working. Examples 1 to 5 are all prepared using the following method, and the specific steps are as follows:

[0070] (1) Mixing the chemical components in proportion, smelting and electroslag remelting to obtain an ingot;

[0071] (2) The homogenization annealing temperature is 1250±20°C (1250°C, 1270°C, 1230°C, 1242°C, and 1258°C for Examples 1 to 5, respectively), and the temperature is kept for 20 to 30 hours (20 hours, 30 hours, 25 hours, 22 hours, and 28 hours for Examples 1 to 5, respectively), and then air-cooled to room temperature;

[0072] (3) Forging the homogenized annealed ingot in the austenite single phase region: the forging temperature is 1220°C to 1250°C (1220°C, 1250°C, 1236°C, 1226°C, and 1245°C for Examples 1 to 5, respectively), the forging ratio is greater than 6.0 (6.8, 12.5, 9.5, 14.0, and 8.6 for Examples 1 to 5, respectively), and air cooling to room temperature after forging;

[0073] (4) The forged alloy ingot is hot rolled: the rolling temperature is 1200°C to 1250°C (1200°C, 1250°C, 1226°C, 1212°C, and 1240°C in Examples 1 to 5, respectively), and the temperature is kept for 2 to 4 hours (3 hours, 2 hours, 4 hours, 2.5 hours, and 3.5 hours in Examples 1 to 5, respectively). The rolling reduction per pass is controlled to be 20 to 30% (20.1%, 30.0%, 25.1%, 22.1%, and 27.4% in Examples 1 to 5, respectively), and the total rolling reduction is controlled to be 60 to 90% (70%, 90%, 80%, 67%, and 84% in Examples 1 to 5, respectively). After hot rolling, the alloy ingot is water-cooled to room temperature.

[0074] (5) Cold rolling is performed directly after hot rolling: the cold rolling deformation amount is 70.0-85.0% (Examples 1-5 are 78.3%, 82.1%, 73.11%, 81.15%, and 84.1%, respectively).

[0075] The present invention is further described in detail below through the accompanying drawings, embodiments and comparative examples.

[0076] Example 1

[0077] In this embodiment, the chemical composition of the 1400 MPa grade nickel-based alloy for the second-generation high-temperature superconducting base tape is as follows, by weight percentage: Cr: 16.79%, Mo: 15.90%, W: 5.90%, Co: 4.53%, C: 11 ppm, S: 15 ppm, O: 8 ppm, P: 48 ppm, N: 16 ppm, and the balance is nickel.

[0078] Example 2

[0079] In this embodiment, the chemical composition of the 1400 MPa grade nickel-based alloy for the second-generation high-temperature superconducting base tape is as follows, by weight percentage: Cr: 16.78%, Mo: 15.78%, W: 5.96%, Co: 4.15%, C: 18 ppm, S: 17 ppm, O: 9 ppm, P: 45 ppm, N: 15 ppm, and the balance is nickel.

[0080] Example 3

[0081] In this embodiment, the chemical composition of the 1400 MPa grade nickel-based alloy for the second-generation high-temperature superconducting base tape is, by weight percentage, Cr: 16.85%, Mo: 15.10%, W: 5.99%, Co: 8.97%, C: 16 ppm, S: 15 ppm, O: 7 ppm, P: 41 ppm, N: 11 ppm, and the balance is nickel.

[0082] Example 4

[0083] In this embodiment, the chemical composition of the 1400 MPa grade nickel-based alloy for the second-generation high-temperature superconducting base tape is, by weight percentage, Cr: 16.90%, Mo: 15.47%, W: 4.85%, Co: 5.46%, C: 16 ppm, S: 13 ppm, O: 11 ppm, P: 39 ppm, N: 17 ppm, and the balance is nickel.

[0084] Example 5

[0085] In this embodiment, the chemical composition of the 1400 MPa grade nickel-based alloy for the second-generation high-temperature superconducting base tape is, by weight percentage, Cr: 16.35%, Mo: 15.07%, W: 5.95%, Co: 7.89%, C: 19 ppm, S: 14 ppm, O: 10 ppm, P: 44 ppm, N: 14 ppm, and the balance is nickel.

[0086] Comparative Example 1

[0087] In this comparative example, no Co was added to the nickel-based alloy for the second-generation high-temperature superconducting tape. The remaining chemical composition, by weight percentage, was: Cr: 16.36%, Mo: 15.99%, W: 5.46%, C: 13 ppm, S: 14 ppm, O: 8 ppm, P: 46 ppm, N: 14 ppm, with the balance being nickel. The homogenization, forging, hot rolling, and cold working processes were identical to those in Example 1.

[0088] Comparative Example 2

[0089] In this comparative example, the nickel-based alloy for second-generation high-temperature superconducting tape contains 12.02% Co by weight. Other chemical compositions are similar to those in Example 2: 16.82% Cr, 15.75% Mo, 5.91% W, 12.02% Co, 19 ppm C, 18 ppm S, 8 ppm O, 43 ppm P, 16 ppm N, with the balance being nickel. The homogenization, forging, hot rolling, and cold working processes are identical to those in Example 2.

[0090] Comparative Example 3

[0091] In this comparative example, the chemical composition, homogenization treatment, forging process, and hot rolling process of the nickel-based alloy for the second-generation high-temperature superconducting substrate are exactly the same as those in Example 3, calculated by weight percentage. After hot rolling, a solid solution treatment (1250°C, 2h) is introduced, and then the same cold working process as in Example 3 is carried out.

[0092] Comparative Example 4

[0093] In this comparative example, the chemical composition of the conventional Hastelloy alloy, by weight percentage, is: Cr: 15.12%, Mo: 16.97%, W: 2.92%, Fe: 5.11%, Mn: 0.45%, Si: 0.034%, V: 0.14%, Co: 0.31%, Al: 0.12%, B: 12 ​​ppm, C: 11 ppm, P: 48 ppm, S: 12 ppm, O: 8 ppm, N: 14 ppm, with the balance being nickel. The homogenization, forging, and hot rolling processes are identical to those of Example 3.

[0094] Table 1 Mechanical properties of the plates after cold rolling of the embodiment and comparative example

[0095]

[0096]

[0097] As shown in Table 1, the present invention utilizes a simplified Hastelloy C276 alloy, innovatively adding an optimized Co content and optimizing the heat treatment process to ensure complete Co solutionization into the nickel-based alloy matrix after hot rolling. With a cold rolling reduction of 70% to 85% deformation, a novel nickel-based alloy with excellent strength-ductility matching is achieved, with a tensile strength exceeding 1800 MPa and an elongation exceeding 21%. Comparative Example 1, in which no Co is added, exhibits an annealed tensile strength of 1214 MPa, lower than the mechanical properties of the present invention. Comparative Example 2, with a Co content of 12.02%, falls outside the Co composition control range of the present invention. Compared to Example 2, the presence of large, undissolved TCP phases in the alloy after hot rolling results in lower mechanical properties, with an elongation of only 1.0%. Comparative Example 3, which undergoes solution treatment using conventional heat treatment followed by cold rolling and annealing, exhibits a tensile strength of 1220 MPa and an elongation of 12.3%, significantly lower than the mechanical properties of the present invention. In Comparative Example 4, a large amount of precipitation phases are formed near the grain boundaries of Hastelloy C276 after hot rolling, which increases the risk of cold rolling cracking.

[0098] like Figure 1 As shown in FIG. 1 , the metallographic structure of Example 1 under as-cast conditions is shown. As can be seen from the figure, there is a chain-like second phase with a size of 20 to 30 μm in the as-cast structure, which is mainly a second phase rich in Mo and W elements.

[0099] like Figure 2 As shown in FIG2 , the scanning structure of Example 2 after water cooling after hot rolling can be seen from the figure that the structure has been completely recrystallized after hot rolling. At the same time, no precipitate phase is precipitated around the recrystallization, and the alloy elements are completely dissolved into the matrix, which provides favorable conditions for subsequent direct cold rolling.

[0100] like Figure 3 As shown in FIG. 3 , the EBSD image of the alloy of Example 3 after annealing at 900° C. for 5 minutes and air cooling to room temperature is shown. As can be seen from the figure, after annealing at 900° C. for 5 minutes, the structure is completely recrystallized and the grain size is 5 to 10 μm.

[0101] like Figure 4 As shown in FIG. 4 , the scanning microstructure of the alloy of Example 4 after annealing at 900° C. for 5 minutes and air cooling to room temperature is shown. As can be seen from the figure, a large amount of precipitated phases precipitate around the recrystallized grains after annealing, thereby improving the precipitation strengthening effect.

[0102] like Figure 5 As shown in FIG5 , the SEM microstructure of the alloy of Example 5 after annealing at 900° C. for 5 min and air cooling to room temperature is shown. As can be seen from the figure, due to the simplification of alloy elements and the reasonable addition of Co, the TCP phase no longer precipitates, which is conducive to direct cold rolling after hot rolling, reducing processing steps and saving ingredients.

[0103] like Figure 6 As shown in FIG, the SEM image of the as-cast alloy in Comparative Example 2 after solution treatment at 1100°C for 2h and water cooling, it can be seen from the figure that a large amount of precipitate phases are formed in the alloy, which shows that a high Co content is conducive to increasing the precipitation temperature of the TCP phase. The phenomenon of recrystallization and precipitation during hot rolling cannot be avoided. High-temperature solution treatment must be carried out according to the traditional process before cold rolling can be carried out.

[0104] like Figure 7 As shown in FIG4, the metallographic structure of the conventional Hastelloy alloy after hot rolling and water cooling in Comparative Example 4, it can be seen from the figure that a large amount of TCP phase is formed in the structure after hot rolling, and cold rolling cannot be directly performed.

[0105] The mechanical property test results of Examples 1 to 5 above demonstrate that the present invention utilizes a direct cold rolling process after hot rolling to shorten the process flow and reduce processing and manufacturing costs. Furthermore, the simultaneous addition of Co promotes the precipitation of precipitated phases after annealing, reduces their size, and increases their dispersion, thereby achieving enhanced precipitation strengthening. By simplifying the alloying elements and adding an optimized Co content based on the commercial Hastelloy C276 alloy, combined with subsequent optimized homogenization treatment, hot working, and innovative processing techniques, a 1400MPa-grade nickel-based alloy for second-generation high-temperature superconductors can be achieved, achieving a tensile strength exceeding 1800MPa and an elongation exceeding 4.0%. After annealing at 900°C for 5 minutes, the tensile strength reaches over 1400MPa and the elongation exceeds 21.0%. This alloy exhibits excellent strength and ductility, meeting the requirements for high-strength metal substrates for second-generation high-temperature superconductors.

[0106] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A 1400MPa grade high cobalt low tungsten nickel-based alloy for second-generation high-temperature superconducting base tape, characterized in that: Calculated in weight percentage, its chemical composition is: Cr: 16.0-18.0%, Mo: 14.0-16.0%, W: 4.5-6.5%, Co: 4.0-10.0%, C<0.005%, P<0.005, S<0.002%, O<0.002%, N<0.002%, and the balance is nickel.

2. The 1400MPa grade high cobalt and low tungsten nickel-based alloy for the second generation high temperature superconducting tape according to claim 1, characterized in that: W: 5.0~6.0%, Co: 7.0~9.0%.

3. The 1400MPa grade high cobalt and low tungsten nickel-based alloy for the second generation high temperature superconducting tape according to claim 1, characterized in that: C<0.002, O<0.

001.

4. A method for preparing a 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting tape according to any one of claims 1 to 3, characterized in that: The steps include: (1) Mixing the chemical components in proportion, and obtaining an ingot through purification smelting and electroslag remelting; (2) performing homogenization annealing treatment on the obtained ingot at high temperature; (3) Forging the homogenized annealed ingot in the γ single phase region; (4) The forged alloy ingot is hot rolled: After being kept at 1100°C to 1250°C for 2 to 4 hours, it is hot rolled at a rolling temperature of 1200°C to 1250°C, with the reduction of each pass controlled at 20 to 30% and the total reduction controlled at 70 to 90%. After hot rolling, it is water-cooled to room temperature; (5) Cold rolling directly after hot rolling: cold rolling at room temperature, with a cold rolling deformation of 60-90%; (6) After cold rolling, annealing heat treatment is performed at 900°C for 5 minutes.

5. The method for preparing a 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting tape according to claim 4, characterized in that: In step (2), the temperature of the homogenization annealing treatment is 1250±20°C, and the temperature is kept for 20h to 30h.

6. The method for preparing a 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting tape according to claim 4, characterized in that: In step (3), the forging process is as follows: forging temperature 1220-1250°C, forging ratio above 6.0, and air cooling to room temperature after forging.

7. The method for preparing a 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting tape according to claim 4, characterized in that: In step (4), the steel is kept at 1200°C to 1250°C for 2 to 4 hours and then hot rolled.

8. The method for preparing a 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting tape according to claim 4, characterized in that: In step (5), the cold rolling process is: cold rolling is performed at room temperature, and the cold rolling deformation is 70 to 85%.

9. The method for preparing a 1400MPa grade high-cobalt, low-tungsten nickel-based alloy for a second-generation high-temperature superconducting tape according to claim 4, characterized in that: After cold rolling, the tensile strength of the nickel-based alloy reaches more than 1800 MPa and the elongation is greater than 4.0%. After annealing at 900° C. for 5 minutes, the tensile strength reaches more than 1400 MPa and the elongation is greater than 21.0%.

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