Weldable high-temperature corrosion-resistant nickel-based alloy and preparation process thereof

Abstract

The invention relates to the technical field of alloys, in particular to a weldable high-temperature corrosion-resistant nickel-based alloy and a preparation process thereof. The nickel-based alloy comprises Cr, Mo, W, Ti, Al, Nb, Co, B, Zr, La, C, Si, Mn, P, S and the balance Ni and inevitable impurities. The element content meets the following conditions: Al + 0.5 Ti + 0.3 Nb is greater than or equal to 3.35 wt.% and less than or equal to 3.8 wt.%, the volume fraction of the gamma'phase is correspondingly 28-34%, and the electron vacancy number Nv is less than 2.6. According to the preparation process, VIM and PESR duplex smelting, multi-pass forging, solid solution rapid cooling and aging heat treatment are adopted, and the welding process is optimized in a matched mode. The alloy has excellent welding performance while maintaining excellent high-temperature strength and corrosion resistance, and is particularly suitable for high-temperature parts needing to be welded in the fields of aerospace, energy, chemical industry and the like.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, and in particular to a weldable high-temperature corrosion-resistant nickel-based alloy and its preparation process. Background Technology

[0002] Nickel-based superalloys are widely used in key components in aerospace, energy, and chemical industries due to their excellent high-temperature strength, oxidation resistance, and corrosion resistance. With technological advancements in these fields, higher demands are being placed on the overall performance of nickel-based alloys, particularly in balancing high-temperature strength, corrosion resistance, and weldability.

[0003] Currently, traditional high-strength nickel-based alloys are typically designed to achieve higher high-temperature strength by increasing the content of γ′ phase-forming elements such as Al and Ti. However, this often results in an excessively high γ′ phase volume fraction, typically exceeding 35%. While excessive γ′ phase has a positive effect on improving strength, it causes serious problems during welding: on the one hand, high γ′ phase content significantly increases the alloy's susceptibility to strain-aging cracking; on the other hand, under welding thermal cycling, continuous γ′ phase films easily form at grain boundaries, leading to grain boundary embrittlement and increasing the tendency for hot cracking. Existing technologies, although some attempts have been made to improve weldability by adjusting the composition, most rely on simple adjustments to the element content range, failing to fundamentally resolve the inherent contradiction between strength and weldability. For example, simply reducing the Al and Ti content can improve weldability but significantly sacrifices high-temperature strength; and simply controlling the content range of a single element cannot effectively coordinate the synergistic effects of multiple γ′ phase-forming elements.

[0004] Therefore, there is a market demand for a nickel-based alloy that maintains excellent high-temperature strength while significantly improving its weldability, achieving crack-free welding, long-term resistance to high-temperature corrosion, and stable high-temperature strength, so that the alloy can be adapted to high-temperature structural components that require welding processes for manufacturing. Summary of the Invention

[0005] In view of the prominent problem of poor weldability of high-performance nickel-based alloys in the prior art, the present invention aims to provide a weldable high-temperature corrosion-resistant nickel-based alloy and its preparation process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A weldable, high-temperature corrosion-resistant nickel-based alloy, the chemical composition of which, by weight percentage, includes: Cr: 22.0-24.0%, Mo: 2.5-4.0%, W: 1.0-2.0%, Ti: 1.8-2.5%, Al: 1.0-1.5%, Nb: 1.5-3.0%, Co: 5.0-8.0%, B: 0.005-0.02%, Zr: 0.05-0.15%, La: 0.01-0.05%, C: ≤0.03%, Si: ≤0.1%, Mn: ≤0.1%, P: ≤0.005%, S: ≤0.005%, balance Ni.

[0007] Preferred corrosion-resistant core elements: Cr: 22.0-24.0% is key to forming a dense Cr2O3-Al2O3 composite oxide film. When the Cr content is below 22%, the oxide film is discontinuous; above 24%, a brittle σ phase easily precipitates. Mo: 2.5-4.0% and W: 1.0-2.0% synergistically strengthen the alloy through solid solution, significantly improving its corrosion resistance in sulfide and chloride ion media, while also enhancing its high-temperature mechanical properties. Strengthening phase-forming elements: Ti: 1.8-2.5%, Al: 1.0-1.5%, Nb: 1.5-3.0% are the core components of the γ′ phase Ni3 (Al,Ti,Nb), with precise proportioning controlling the volume fraction and morphology of the γ′ phase. Weldability-optimizing element: Co: 5.0-8.0% optimizes the alloy's thermal conductivity and reduces weldability. It addresses temperature gradients and thermal stress while suppressing the precipitation of topologically close-packed (TCP) phases; grain boundary purification elements: B: 0.005-0.02%, Zr: 0.05-0.15%, La: 0.01-0.05%, which work synergistically at grain boundaries; impurity control: C≤0.03%, Si≤0.1%, Mn≤0.1%, P≤0.005%, S≤0.005%, avoiding the formation of brittle carbides, low-melting-point eutectics, and sulfides, thus reducing the risk of welding cracks and intergranular corrosion.

[0008] Preferably, the mass percentage of the alloy's chemical composition must satisfy the relationship 3.35% ≤ Al + 0.5 Ti + 0.3 Nb ≤ 3.8%. For ease of description, this relationship is established based on the difference in contribution efficiency of each element to the formation of the γ′ phase: Al:Ti:Nb ≈ 1.0:0.5:0.3, which can accurately lock the volume fraction of the γ′ phase to 28-34%. This ensures high-temperature strength requirements while avoiding solidification cracks and liquefaction cracks during welding due to excessive γ′ phase, achieving a balance between weldability and high-temperature strength.

[0009] Preferably, the mass ratio of Ti to Al is 1.2-2.0. This ratio can optimize the lattice mismatch of the γ′ phase to be controlled within -0.15 to -0.25%, so that the γ′ phase has a uniform cubic morphology. This avoids the coarsening or morphological distortion of the γ′ phase due to the imbalance of the Ti / Al ratio, thereby improving the high-temperature creep performance and reducing the brittleness of the weld heat-affected zone.

[0010] Preferably, the mass percentage of the grain boundary purification elements satisfies 0.065% ≤ B + Zr + La ≤ 0.22%, and 0.07 ≤ La / Zr ≤ 0.5. 0.065% is the minimum effective amount for synergistic purification by the three elements; below this value, grain boundary impurities S and O cannot be sufficiently removed. 0.22% is the maximum safe amount; above this value, brittle intermetallic compounds or large inclusions are easily formed. 0.07 ≤ La / Zr ≤ 0.5 enables the synergistic effect of La capturing impurities and Zr refining grains. La preferentially combines with S and O to form fine inclusions, while Zr and B synergistically pin grain boundaries, significantly improving grain boundary strength and resistance to welding hot cracking.

[0011] Furthermore, the present invention also provides a preparation process for the above-mentioned weldable high-temperature corrosion-resistant nickel-based alloy, comprising the following steps: (1) Vacuum induction melting Prepare the materials according to the designed composition ratio, and load the metal raw materials other than B, Zr, and La into the magnesium oxide crucible; after evacuating the furnace to a pressure ≤5Pa, fill it with high-purity argon gas to a gauge pressure of -0.05-0MPa; under a protective atmosphere, heat the furnace charge to 1520-1550℃ and hold it for 40-60 minutes, while applying electromagnetic stirring to make the composition uniform and fully refined; before tapping the steel, add nickel-boron, nickel-zirconium, and nickel-lanthanum master alloys to the molten pool to introduce B, Zr, and La elements, and then cast it into a consumable electrode rod; (2) Protective atmosphere electroslag remelting Using the aforementioned consumable electrode rod as the negative electrode, a five-element pre-melted slag system comprising, by mass percentage: CaF2: 46-48%, Al2O3: 19-21%, CaO: 23-25%, MgO: 3-4%, TiO2: 4-5%, was used for smelting under process conditions of remelting current 3200-3800A and voltage 32-36V. Throughout the remelting process, argon gas with a purity ≥99.99% was continuously introduced into the crystallizer as a protective atmosphere, and the melting rate was controlled at 1.0-1.5 kg / min, with a cooling water flow rate of 15-20 L / min, to obtain a dense electroslag ingot. (3) Multi-stage thermomechanical treatment Forging: Heat the electroslag ingot to 1120-1150℃, hold for 2.5-3 hours, and forge in multiple passes, with a total deformation of 55-60%; Intermediate heat treatment: Heat the forging billet to 1050℃, hold for 1.5 hours, and then air cool to room temperature to refine the grains after deformation; Precision forging: Reheat to 1080-1100℃, hold for 1.5-2 hours, then perform precision forging deformation. The final forging temperature is controlled at not less than 900℃. Then air cool to room temperature to obtain an alloy forging with a uniform equiaxed grain structure. (4) Solution treatment and aging heat treatment Solution treatment: Hold the alloy forging at 1180-1200℃ for 2-4 hours, then quench it in water at a rate of not less than 50℃ / s to obtain a supersaturated single-phase solid solution. Aging treatment: The solution-treated workpiece is heated to 780-800℃ and held for 8-12 hours, then air-cooled to room temperature, so that the γ′ strengthening phase is uniformly dispersed and precipitated in a cubic morphology of 200-300nm, thus obtaining the target alloy.

[0012] Preferably, the (1) vacuum induction melting process focuses on precise composition and pure raw materials. Through high-purity control of raw materials, precise addition of intermediate alloys and optimization of process parameters, it effectively reduces the introduction of impurities and element loss, reducing composition segregation from ±0.5% to ±0.3%, and the surface defect rate of the self-consuming electrode rod is ≤0.5%. It solves the pain points of the existing technology, such as loose requirements for raw material purity, uneven element mixing and many electrode rod defects. It lays a solid foundation for the weldability and corrosion resistance of the alloy from the source. Compared with the extensive control of the existing technology, its special feature is that it specifically limits the impurity content of corrosion-resistant and welding-sensitive elements. By precisely matching the melting rhythm, it ensures the uniform distribution of grain boundary purification elements. At the same time, it improves the density of the electrode rod with high-frequency stirring and special gate design, providing high-quality billets for subsequent processes.

[0013] Preferably, the protective atmosphere electroslag remelting process (2) focuses on reducing burn-off, removing inclusions, and homogenizing the microstructure. By narrowing the optimal ratio of the five-element pre-melted slag system to lock the slag system's melting point and viscosity range, and combining precise current and voltage matching, argon positive pressure protection, and internal cooling crystallizer temperature control, the Al / Ti burn-off rate is reduced to ≤8%, the O content in the alloy is ≤8ppm, the S content is ≤0.003%, and the electroslag ingot density is ≥99.9%. This solves the problems of unstable slag system performance, large fluctuations in remelting parameters, and numerous ingot defects in existing technologies, further improving the purity and compositional uniformity of the alloy, reducing welding crack sources, and ensuring uniform distribution of corrosion-resistant elements. Unlike the wide range of parameter limitations in existing technologies, this solution strongly binds the slag system ratio with performance, completely isolates air through positive pressure control, and reduces ingot porosity by combining internal cooling crystallizer and precise melting rate control, achieving dual synergistic optimization of reducing burn-off and removing inclusions.

[0014] Preferably, the (3) multi-stage thermomechanical treatment process revolves around fine grains, density, and homogeneity. It adopts stepped heating, decreasing reduction forging, segmented intermediate heat treatment temperature, and wide anvil precision forging, combined with forced air cooling and an optimal final forging temperature of 920-950℃, to refine the alloy grain size to 15-20μm, with an equiaxed grain ratio ≥95% and a density ≥99.8%. This solves the pain points of existing forging technologies, such as rapid heating, unreasonable reduction, and coarse and uneven grains. It improves the toughness and corrosion resistance of the weld heat-affected zone through precise control of the thermomechanical process. Compared with the extensive forging and natural cooling of existing technologies, its special innovation lies in releasing thermal stress with stepped heating, efficiently breaking the as-cast structure with decreasing reduction, and ensuring uniform grain refinement with wide anvil forging and forced air cooling, thereby achieving isotropic optimization of microstructure and properties.

[0015] Preferably, the solution and aging heat treatment process (4) focuses on precise control of the γ′ phase and grain boundary purification. Through segmented heating solution, high-pressure water quenching and precise aging parameters, the grain boundary carbide dissolution rate is ≥99%, the γ′ phase is in a uniform cubic morphology of 250-280nm, the volume fraction is 30-32%, and the lattice mismatch is controlled at -0.18 to -0.22%. This approach aims to solve the problems of slow solution cooling, ambiguous aging parameters, and uncontrolled γ′ phase morphology in existing technologies, and to achieve a three-in-one optimization of high-temperature strength, weldability, and corrosion resistance. Unlike the wide range of parameter limitations in existing technologies, this solution completely avoids Cr depletion by segmented solution and high-pressure water quenching, and precisely controls the size and morphology of the γ′ phase by narrowing the aging range and slowly heating, effectively improving the structural stability of the alloy during long-term service, while strengthening the bonding force between the corrosion-resistant film and the substrate.

[0016] Preferably, the raw materials meet the following requirements: (1) The raw materials for nickel (Ni), chromium (Cr), molybdenum (Mo), tungsten (W), cobalt (Co), niobium (Nb), aluminum (Al), and titanium (Ti) are all dense metal billets with a purity of not less than 99.9 wt.%, including metal ingots, metal blocks, metal plates, etc., and the content of gaseous impurities in the raw materials meets the following requirements: O≤8ppm, N≤5ppm, H≤2ppm, and the content of harmful impurity elements meets the following requirements: P≤0.003wt.%, S≤0.003wt.%; the surface of the raw materials needs to be sandblasted to remove the oxide scale, and then pickled to remove impurities to ensure that there is no visible oxide layer, oil stains and rust. (2) Boron (B), zirconium (Zr), and lanthanum (La) are all added in the form of nickel-based single master alloys, namely nickel-boron Ni-B, nickel-zirconium Ni-Zr, and nickel-lanthanum Ni-La master alloys. The master alloys need to be purified by vacuum induction remelting. The content of B in the Ni-B master alloy is 16-17 wt.%, the content of Zr in the Ni-Zr master alloy is 15-16 wt.%, and the content of La in the Ni-La master alloy is 17-18 wt.%. The gaseous impurities O in the master alloy are ≤10 ppm and the harmful impurities S are ≤0.005 wt.%. The master alloys are in the form of short rods with a diameter of 10-20 mm or blocks with a diameter of 5-20 mm, which facilitates accurate weighing and rapid melting.

[0017] Preferably, the process further includes subsequent processing steps on the target alloy obtained by the aforementioned process, specifically welding and post-weld treatment: welding is performed using tungsten inert gas welding, and the chemical composition of the welding wire used is matched with that of the alloy to be welded; during welding, argon gas with a purity of ≥99.99% is applied to the weld area and its back side for protection; the welding parameters are controlled as follows: welding speed ≥10mm / s, current 100-130A, voltage 10-12V, heat input ≤12kJ / cm; after welding, the welded component is subjected to stress-relief annealing: held at 650-700℃ for 2-4 hours, then the cooling rate is controlled to be no more than 50℃ / h, and air-cooled after cooling to below 300℃.

[0018] The beneficial effects of this invention are: 1. The alloy of this invention solves the technical dilemma that high strength in traditional nickel-based alloys is inevitably accompanied by low weldability. This invention employs a unique composite control formula of 3.35wt.%≤Al+0.5Ti+0.3Nb≤3.8wt.%. This formula precisely controls the synergistic effect of γ′ phase-forming elements through a weighted approach, accurately controlling the volume fraction of the γ′ strengthening phase within the optimal range of 28-34%. This range ensures that a sufficient number of nanoscale γ′ phases effectively hinder dislocation movement, providing sustained high-temperature strength; while avoiding grain boundary embrittlement and increased sensitivity to weld strain-aging cracks caused by excessive γ′ phase (>35%), thus achieving an optimal balance between strength and weldability.

[0019] 2. The alloy of this invention exhibits excellent resistance to weld hot cracking, and the welded joint maintains a stable microstructure during long-term high-temperature service. This effect stems from the synergistic design of grain boundary purification elements in this invention. The proportions of 0.065%≤B+Zr+La≤0.22% and 0.07≤La / Zr≤0.5 effectively segregate B atoms at grain boundaries, increasing grain boundary cohesion; Zr and B produce a synergistic segregation effect, further stabilizing the grain boundary structure; while La deeply purifies the grain boundaries, forming stable high-melting-point compounds with harmful elements such as S and O, preventing the formation of low-melting-point eutectic films at grain boundaries. The synergistic effect of these three elements reduces the S content at grain boundaries to below 0.001%, fundamentally eliminating the conditions for the initiation of weld hot cracking.

[0020] 3. The alloy of this invention possesses excellent high-temperature corrosion resistance and structural stability. This is because the 22-24% Cr content, combined with the solid solution strengthening of Mo and W, forms a dense and strongly adherent Cr2O3-Al2O3 composite oxide film, significantly improving its resistance to high-temperature oxidation and sulfide corrosion. Simultaneously, the design with an electron vacancy number Nv < 2.6 and the addition of Co element thermodynamically suppress the formation tendency of topologically close-packed phases such as the σ phase and Laves phase, ensuring the stability of the microstructure during long-term high-temperature service.

[0021] 4. The alloy of this invention exhibits stable processing performance and excellent mechanical consistency. Alloy ingots prepared using the VIM and P-ESR dual-process have a compositional uniformity deviation of less than 0.5% and a yield exceeding 95%. The resulting alloy forgings possess a uniform equiaxed grain structure, a room temperature tensile strength of 1350-1420 MPa, an elongation of 25-35%, and performance fluctuations between batches of less than 5%. The protective atmosphere electroslag remelting process, conducted under argon protection, effectively prevents the loss of active elements such as Al and Ti. The optimized five-element slag system ensures excellent desulfurization and inclusion removal effects. Multi-stage thermomechanical treatment, through precise control of deformation and heat treatment regimes, achieves complete dynamic recrystallization, resulting in a uniform and fine equiaxed grain structure. The dual heat treatment of solution and aging precisely regulates the size, distribution, and morphology of the γ′ phase, ensuring uniform and stable performance. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. All component comparison groups, from the first to the third, were prepared using the same optimized preparation process of this invention, while the fourth group used the same optimal components, changing only a single process.

[0023] Example 1: A specific preparation method for a weldable high-temperature corrosion-resistant nickel-based alloy, comprising the following steps: (1) A weldable high-temperature corrosion-resistant nickel-based alloy, the chemical composition of which, by mass percentage, includes: Cr: 23.0%, Mo: 3.5%, W: 1.8%, Ti: 2.32%, Al: 1.50%, Nb: 2.2%, Co: 6.5%, B: 0.012%, Zr: 0.10%, La: 0.03%, C: 0.018%, Si: 0.07%, Mn: 0.07%, P: 0.002%, S: 0.002%, with the balance being Ni and unavoidable impurities. The composition of Al+0.5Ti+0.3Nb is 3.45wt.%, B+Zr+La is 0.142wt.%, and the La / Zr ratio is 0.30. (2) Vacuum induction melting Prepare the materials according to the above composition design and proportion. Put the metal raw materials other than B, Zr, and La into the magnesium oxide crucible; after evacuating the furnace to a pressure ≤5Pa, fill it with high-purity argon gas to a gauge pressure of -0.05-0MPa; under a protective atmosphere, heat the furnace charge to 1520-1550℃ and hold it for 40-60 minutes, while applying electromagnetic stirring to make the composition uniform and fully refined; before tapping the steel, add nickel-boron, nickel-zirconium, and nickel-lanthanum master alloys to the molten pool to introduce B, Zr, and La elements, and then cast it into a consumable electrode rod; (3) Protective atmosphere electroslag remelting Using the aforementioned consumable electrode rod as the negative electrode, a five-element pre-melted slag system comprising, by mass percentage: CaF2: 46-48%, Al2O3: 19-21%, CaO: 23-25%, MgO: 3-4%, TiO2: 4-5%, was used for smelting under process conditions of remelting current 3200-3800A and voltage 32-36V. Throughout the remelting process, argon gas with a purity ≥99.99% was continuously introduced into the crystallizer as a protective atmosphere, and the melting rate was controlled at 1.0-1.5 kg / min, with a cooling water flow rate of 15-20 L / min, to obtain a dense electroslag ingot. (4) Multi-stage thermomechanical treatment Forging: Heat the electroslag ingot to 1120-1150℃, hold for 2.5-3 hours, and forge in multiple passes, with a total deformation of 55-60%; Intermediate heat treatment: Heat the forging billet to 1050℃, hold for 1.5 hours, and then air cool to room temperature to refine the grains after deformation; Precision forging: Reheat to 1080-1100℃, hold for 1.5-2 hours, then perform precision forging deformation. The final forging temperature is controlled at not less than 900℃. Then air cool to room temperature to obtain an alloy forging with a uniform equiaxed grain structure. (5) Solution treatment and aging heat treatment Solution treatment: Hold the alloy forging at 1180-1200℃ for 2-4 hours, then quench it in water at a rate of not less than 50℃ / s to obtain a supersaturated single-phase solid solution. Aging treatment: The solution-treated workpiece is heated to 780-800℃ and held for 8-12 hours, then air-cooled to room temperature, so that the γ′ strengthening phase is uniformly dispersed and precipitated in a cubic morphology of 200-300nm, thus obtaining the target alloy.

[0024] Group 1: The only difference between Examples 2 and 3 and Comparative Examples 1 and 2 and Example 1 is the adjustment of the Ti, Al, and Nb content. All examples use the optimized process of this invention. Specific data are shown in Table 1.

[0025] Table 1. Adjustment of main components in alloy formulations Group 2: The only difference between Examples 4 and 5 and Comparative Examples 3 and 4 and Example 1 is that the total amounts of B, Zr, and La are adjusted, while maintaining La / Zr≈0.3. All examples use the optimized process of this invention, and the specific data are shown in Table 2.

[0026] Table 2. Adjustment of trace element content in alloy formulations (La / Zr unchanged) Group 3: The only difference between Example 6 and Comparative Examples 5 and 6 and Example 1 is that the proportions of B, Zr, and La are adjusted, while maintaining the total amount at approximately 0.142%. All examples use the optimized process of this invention, and the specific data are shown in Table 3.

[0027] Table 3. Adjustment of trace element content in alloy formulations (La / Zr variation) Group 4: Comparative Examples 7, 8, and 9 are set up, which differ from Example 1 only in one process parameter, while the alloy composition is the same. Specific data are shown in Table 4.

[0028] Table 4. Adjustments to the alloying process Performance testing: The above 6 embodiments and 9 comparative examples were subjected to performance tests according to the following national standards to quantify their mechanical properties, high-temperature durability, and weldability: According to GB / T 228.1-2021 and GB / T 4338-2006, tensile tests were conducted at room temperature and 800℃ to obtain tensile strength (Rm) and elongation after fracture (A). According to GB / T 2039-2012, uniaxial tensile creep tests were conducted at 800℃ / 300MPa to obtain creep rupture life (t) and creep ductility. According to HB 5261-1983, variable restraint tests were conducted to measure the critical strain value (ε%). According to GB / T 13303-1991 "Determination of Oxidation Resistance of Steel", an 800℃, 100-hour isothermal oxidation test was conducted, and the high-temperature oxidation resistance of the alloy was evaluated by measuring the weight change per unit area (mg / cm²). According to HB 7235-1995 "Metallic Materials Hot Corrosion Test Method", hot corrosion tests were conducted at 750℃ under salt film conditions of 75% Na2SO4 and 25% NaCl, and the corrosion depth (μm) or weight change per unit area was measured.

[0029] The corresponding results and organizational analysis data are summarized in Tables 5 and 6.

[0030] Table 5. Strength or plasticity of alloys obtained in the examples and comparative examples Table 6. Alloy properties of alloys prepared in the examples and comparative examples Data Analysis: The performance test data of all the above embodiments and comparative examples were analyzed.

[0031] By weighted control of the γ′ phase-forming elements, this invention successfully resolves the contradiction between high strength and high weldability. Data analysis shows that when the alloy composition satisfies the relationship 3.35% ≤ Al + 0.5Ti + 0.3Nb ≤ 3.8%, its room temperature and high temperature strength remain at excellent levels, such as the room temperature strength of 1390 MPa and the 800℃ strength of 860 MPa in Example 1, while the critical welding strain value is as high as 4.5%. The reason for its excellent performance is that the volume fraction of the γ′ strengthening phase is precisely controlled within the ideal range of 28-34%. Conversely, in Comparative Example 1, the composition is below the lower limit, resulting in insufficient γ′ phase and a significant decrease in strength; in Comparative Example 2, the composition exceeds the upper limit, resulting in excessive γ′ phase, grain boundary embrittlement, and a sharp deterioration in weldability. This balance is fundamentally achieved through the dual process of vacuum induction melting and electroslag remelting, which effectively controls the burn-off of active elements such as Al and Ti, ensuring precise composition. As shown in Table 5, all embodiments meeting this composition requirement, such as Examples 1-3, maintained an elongation at room temperature above 25%, demonstrating good toughness under high strength, which is the basis for achieving crack-free welding. The synergistic design of the total amount of grain boundary purifying elements is the core of endowing the alloy with excellent crack resistance and microstructural stability. Experimental data clearly show that the embodiment satisfying the relationship 0.065%≤B+Zr+La≤0.22% exhibits significantly better weld crack sensitivity and creep ductility than the comparative example. The fundamental reason is that within this total amount range, B, Zr, and La elements can synergistically segregate at the grain boundaries. B and Zr jointly pin the grain boundaries and enhance their strength, while La can deeply purify the grain boundaries and form stable compounds with harmful impurities such as S and O. Comparative Example 3 suffers from weak grain boundary purifying and strengthening effects due to insufficient total amount, resulting in poor performance; Comparative Example 4, due to excessive total amount, easily forms brittle phases, impairing ductility. The use of a nickel-based master alloy in the preparation process and the addition of these elements before steelmaking are key to ensuring their uniform distribution and synergistic effect. Performance data shows that Example 1 achieves a high critical strain value while also achieving an excellent creep ductility of 8.0%, far exceeding that of Comparative Example 4. This directly proves that its grain boundaries can maintain toughness and stability under long-term high-temperature loads.

[0032] Optimizing the proportions of grain boundary purifying elements is the decisive factor in achieving their maximum synergistic effect. Data analysis confirms that, while controlling the total amount, further satisfying the ratio of 0.07 ≤ La / Zr ≤ 0.5 can lead to further performance improvements. With similar total amounts, Example 1, with La / Zr = 0.3, exhibits better weldability and corrosion resistance than Comparative Example 5 (La / Zr = 0.6) and Comparative Example 6 (completely La-free). The underlying mechanism is that this ratio ensures an optimal match between the purifying effect of La and the grain boundary strengthening effect of Zr. An excessively high La / Zr ratio leads to excessive La segregation, while a ratio that is too low or zero fails to effectively remove grain boundary impurities. The optimized forging and heat treatment processes employed in this invention provide the kinetic conditions for this microscale synergistic elemental distribution. The oxidation weight gain and hot corrosion depth of Example 1 are significantly lower than those of Comparative Example 6 (La-free), indicating that the optimized La / Zr ratio effectively improves the overall corrosion resistance of the alloy by purifying grain boundaries.

[0033] A comparative analysis of Tables 4 and 5 confirms that the aforementioned supporting preparation process is an indispensable guarantee for achieving the above-mentioned compositional design intent and obtaining the final excellent performance. Using the exact same alloy composition as Example 1, Comparative Examples 7-9 showed a comprehensive decline in strength, plasticity, and weldability due to deviations in only a single process parameter. This is because the excellent comprehensive performance of the alloy of this invention is the result of combining precise compositional design with a precise preparation process. The multi-stage thermomechanical treatment and solution aging regime precisely control the grain size and γ′ phase precipitation behavior, while strict melting protection ensures the purity of the material, thus fully transforming the advantages of compositional design into stable and reliable physical properties.

[0034] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A weldable, high-temperature corrosion-resistant nickel-based alloy, characterized in that, Its chemical composition by mass percentage The composition includes: Cr: 22.0-24.0%, Mo: 2.5-4.0%, W: 1.0-2.0%, Ti: 1.8-2.5%, Al: 1.0-1.5%, Nb: 1.5-3.0%, Co: 5.0-8.0%, B: 0.005-0.02%, Zr: 0.05-0.15%, La: 0.01-0.05%, C: ≤0.03%, Si: ≤0.1%, Mn: ≤0.1%, P: ≤0.005%, S: ≤0.005%, with the balance being Ni.

2. The weldable high-temperature corrosion-resistant nickel-based alloy according to claim 1, characterized in that, The chemical composition of the alloy by mass percentage simultaneously satisfies the following relationship: 3.35%≤Al+0.5Ti+0.3Nb≤3.8%, and the volume fraction of the γ′ phase in the alloy is 28-34%.

3. The weldable high-temperature corrosion-resistant nickel-based alloy according to claim 1, characterized in that, The mass ratio of Ti to Al in the alloy is 1.2-2.0 (Ti / Al).

4. The weldable high-temperature corrosion-resistant nickel-based alloy according to claim 1, characterized in that, The synergistic content of the grain boundary purifying elements in the alloy satisfies the following: 0.065%≤B+Zr+La≤0.22%, and 0.07≤La / Zr≤0.

5.

5. The preparation process of a weldable high-temperature corrosion-resistant nickel-based alloy according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Vacuum induction melting Prepare the materials according to the designed composition ratio, and load the metal raw materials other than B, Zr, and La into the magnesium oxide crucible; after evacuating the furnace to a pressure ≤5Pa, fill it with high-purity argon gas to a gauge pressure of -0.05-0MPa; under a protective atmosphere, heat the furnace charge to 1520-1550℃ and hold it for 40-60 minutes, while applying electromagnetic stirring to make the composition uniform and fully refined; before tapping the steel, add nickel-boron, nickel-zirconium, and nickel-lanthanum master alloys to the molten pool to introduce B, Zr, and La elements, and then cast it into a consumable electrode rod; (2) Protective atmosphere electroslag remelting Using the aforementioned consumable electrode rod as the negative electrode, a five-element pre-melted slag system comprising, by mass percentage: CaF2: 46-48%, Al2O3: 19-21%, CaO: 23-25%, MgO: 3-4%, TiO2: 4-5%, was used for smelting under process conditions of remelting current 3200-3800A and voltage 32-36V. Throughout the remelting process, argon gas with a purity ≥99.99% was continuously introduced into the crystallizer as a protective atmosphere, and the melting rate was controlled at 1.0-1.5 kg / min, with a cooling water flow rate of 15-20 L / min, to obtain a dense electroslag ingot. (3) Multi-stage thermomechanical treatment Forging: Heat the electroslag ingot to 1120-1150℃, hold for 2.5-3 hours, and forge in multiple passes, with a total deformation of 55-60%; Intermediate heat treatment: Heat the forging billet to 1050℃, hold for 1.5 hours, and then air cool to room temperature to refine the grains after deformation; Precision forging: Reheat to 1080-1100℃, hold for 1.5-2 hours, then perform precision forging deformation. The final forging temperature is controlled at not less than 900℃. Then air cool to room temperature to obtain an alloy forging with a uniform equiaxed grain structure. (4) Solution treatment and aging heat treatment Solution treatment: Hold the alloy forging at 1180-1200℃ for 2-4 hours, then quench it in water at a rate of not less than 50℃ / s to obtain a supersaturated single-phase solid solution. Aging treatment: The solution-treated workpiece is heated to 780-800℃ and held for 8-12 hours, then air-cooled to room temperature, so that the γ′ strengthening phase is uniformly dispersed and precipitated in a cubic morphology of 200-300nm, thus obtaining the target alloy.

6. The preparation process of a weldable high-temperature corrosion-resistant nickel-based alloy according to claim 5, characterized in that, The raw materials must meet the following requirements: (1) The raw materials for nickel (Ni), chromium (Cr), molybdenum (Mo), tungsten (W), cobalt (Co), niobium (Nb), aluminum (Al), and titanium (Ti) are all dense metal billets with a purity of not less than 99.9 wt.%, including metal ingots, metal blocks, metal plates, etc., and the content of gaseous impurities in the raw materials meets the following requirements: O≤8ppm, N≤5ppm, H≤2ppm, and the content of harmful impurity elements meets the following requirements: P≤0.003wt.%, S≤0.003wt.%; the surface of the raw materials needs to be sandblasted to remove the oxide scale, and then pickled to remove impurities to ensure that there is no visible oxide layer, oil stains and rust. (2) Boron (B), zirconium (Zr), and lanthanum (La) are all added in the form of nickel-based single master alloys, namely nickel-boron Ni-B, nickel-zirconium Ni-Zr, and nickel-lanthanum Ni-La master alloys, respectively. The master alloys need to be purified by vacuum induction remelting. By mass percentage, the content of B in the Ni-B master alloy is 16-17 wt.%, the content of Zr in the Ni-Zr master alloy is 15-16 wt.%, and the content of La in the Ni-La master alloy is 17-18 wt.%. The gaseous impurities O in the master alloy are ≤10 ppm and the harmful impurities S are ≤0.005 wt.%. The master alloys are in the form of short rods with a diameter of 10-20 mm or blocks with a diameter of 5-20 mm, which facilitates accurate weighing and rapid melting.

7. The preparation process of a weldable high-temperature corrosion-resistant nickel-based alloy according to claim 5, characterized in that, It also includes subsequent processing steps on the target alloy obtained by the process described in claim 5, specifically welding and post-weld treatment: The welding is carried out using tungsten inert gas (TIG) welding, and the chemical composition of the welding wire is matched with the alloy to be welded. During welding, argon gas with a purity of ≥99.99% is applied to the weld area and its back side for protection. The welding parameters are controlled as follows: welding speed ≥10mm / s, current 100-130A, voltage 10-12V, and heat input ≤12kJ / cm. After welding, stress-relief annealing is performed on the welded components: hold at 650-700℃ for 2-4 hours, then control the cooling rate to be no more than 50℃ / h, and air cool after cooling to below 300℃.

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