Vacuum induction melting-electroslag remelting-vacuum consumable remelting triple melting method for high-purity nickel-based superalloy

Abstract

The invention discloses a vacuum induction melting-electroslag remelting-vacuum consumable remelting triple melting method of a high-purity nickel-based superalloy, which comprises the following steps: carrying out vacuum induction melting on simple substance nickel, simple substance chromium, simple substance cobalt and simple substance molybdenum with the purity of more than or equal to 99.95%, injecting into a mold, and cooling to obtain an alloy electrode bar; adding elemental Ce into the slag body to obtain an optimized slag body, inserting the alloy electrode bar into the optimized slag body for electroslag remelting, electrifying and melting the alloy electrode bar, and purifying and solidifying the slag body to obtain a cast ingot; and the cast ingot serves as a consumable electrode, vacuum consumable remelting is conducted, and the nickel-based high-temperature alloy is prepared. According to the method, the technical problems that in the prior art, the nickel-based superalloy prepared through a duplex process is not enough in component segregation and purity, and the extremely high requirement of a modern aero-engine for the performance of the nickel-based superalloy is difficult to meet are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy smelting technology, and relates to a three-stage smelting method for high-purity nickel-based high-temperature alloys, which involves vacuum induction melting, electroslag remelting, and vacuum consumable remelting. Background Technology

[0002] With the continuous advancement of aviation technology, the requirements for engine performance are becoming increasingly stringent. Achieving higher thrust-to-weight ratios, lower fuel consumption, and longer service life all depend on further improvements in the performance of nickel-based superalloys. The smelting process, as a crucial step in the preparation of nickel-based superalloys, plays a decisive role in the alloy's compositional uniformity, purity, and final properties. Therefore, developing advanced smelting processes to obtain high-quality nickel-based superalloys has become a current research hotspot in the field of aerospace materials.

[0003] However, existing smelting processes still face numerous challenges in meeting the ever-increasing performance requirements of nickel-based superalloys. Currently common single-process smelting methods, such as vacuum induction melting (VIM), while capable of controlling alloy composition to some extent, are significantly inadequate in impurity removal. Impurity elements such as O, N, and S are difficult to completely remove during the smelting process, easily forming inclusions in the alloy. These inclusions become stress concentration sources in the alloy, easily initiating and propagating cracks under high temperature and pressure conditions, thereby reducing the alloy's strength and toughness, and seriously affecting the reliability and service life of critical components of aero-engines.

[0004] Besides VIM, electroslag remelting (ESR) and vacuum arc remelting (VAR) also have their limitations. VAR is less effective at desulfurization and cannot effectively reduce the sulfur content in the alloy, while the presence of sulfur reduces the alloy's hot workability and corrosion resistance. Although ESR has some effect on improving alloy purity, it easily absorbs hydrogen during the melting process, leading to hydrogen enrichment in the alloy. Hydrogen can form hydrogen-induced cracks in the alloy, severely damaging its properties.

[0005] To overcome the shortcomings of single-process smelting, traditional duplex processes have emerged, such as VIM + VAR or VIM + ESR. However, these duplex processes are not without their flaws, still exhibiting issues like compositional segregation and insufficient purity, making it difficult to meet the extremely high performance requirements of modern aero-engines for nickel-based superalloys. Therefore, exploring novel smelting processes has become crucial for driving the development of aero-engine technology. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a three-stage melting method for high-purity nickel-based superalloys, consisting of vacuum induction melting, electroslag remelting, and vacuum arc remelting. This method solves the technical problem that nickel-based superalloys produced by the existing dual-stage process suffer from compositional segregation and insufficient purity, making it difficult to meet the extremely high performance requirements of modern aero-engines for nickel-based superalloys.

[0007] This invention is achieved through the following technical solution: A three-stage melting method for high-purity nickel-based superalloys, comprising vacuum induction melting, electroslag remelting, and vacuum arc remelting, includes the following steps: S1: Vacuum induction melting of elemental nickel, elemental chromium, elemental cobalt and elemental molybdenum with a purity ≥99.95% is performed, and after being injected into a mold and cooled, an alloy electrode rod is obtained. S2: Add elemental Ce to the slag to obtain an optimized slag. Insert the alloy electrode rod into the optimized slag for electroslag remelting. After the alloy electrode rod is energized and melted, it is purified by the slag and solidified to obtain an ingot. S3: Using the ingot as a consumable electrode, vacuum consumable remelting is performed to obtain a nickel-based high-temperature alloy.

[0008] Preferably, the initial sulfur content in the elemental nickel, elemental chromium, elemental cobalt, and elemental molybdenum is ≤50ppm.

[0009] Preferably, during vacuum induction melting, the vacuum degree is ≤0.1Pa, the melting temperature is 1500-1550℃, and the melting time is ≥30min.

[0010] Preferably, during vacuum induction melting, the casting rate is 10-15 kg / min.

[0011] Preferably, the slag comprises CaF2, CaO, Al2O3, and MgO; by mass percentage, the content of CaF2 is 55wt%-65wt%, and the content of MgO is 3wt%-7wt%.

[0012] Preferably, the amount of elemental Ce added is 0.01wt%-0.05wt% of the total mass of the slag.

[0013] Preferably, during electroslag remelting, the current is 12-15kA, the voltage is 25-30V, and the flow rate of cooling water in the crystallizer is 40L / min.

[0014] Preferably, during the vacuum self-consumable remelting process, the vacuum degree is ≤0.01Pa, the melting rate is 3-5kg / min, and the axial solidification gradient is ≥80℃ / cm.

[0015] Preferably, the interval between step S1 and step S2 is ≤24 hours.

[0016] A high-purity nickel-based superalloy is prepared by the above method; the sulfur content of the nickel-based superalloy is ≤10ppm, the oxygen content is ≤5ppm, the macrosegregation grade is ≤ASTM grade 1, and the creep rupture life under 650℃ and 620MPa stress is ≥130 hours.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a three-stage melting method for high-purity nickel-based superalloys, which involves vacuum induction melting, electroslag remelting, and vacuum consumable remelting. At the raw material end, elemental nickel, chromium, cobalt, and molybdenum with a purity of ≥99.95% are selected as initial raw materials to reduce the introduction of impurities from the source, laying the foundation for improving the purity of the alloy. In the vacuum induction melting stage, the vacuum environment isolates air, preventing the oxidation of metal elements and simultaneously achieving full melting and preliminary composition homogenization of the raw materials. This produces alloy electrode rods with relatively uniform composition, reducing the risk of compositional fluctuations in subsequent remelting processes. In the electroslag remelting process, elemental Ce is added to the slag. The strong affinity between Ce and sulfur forms stable sulfide inclusions, which are removed by floating with the slag, achieving deep desulfurization. Simultaneously, the high-temperature slag pool from electroslag remelting further adsorbs oxides, nitrides, and other inclusions in the alloy, significantly reducing the content of gaseous impurities and harmful inclusions, thus solving the problem of insufficient deep purification in the dual-process. Vacuum consumable remelting uses ESR ingots as consumable electrodes, and the vacuum environment further removes residual gases, further improving purity. More importantly, this process effectively suppresses macroscopic segregation of solute elements, compensating for the insufficient compositional uniformity in the dual-process. This invention, through a triple-process, ultimately produces a nickel-based superalloy that achieves a dual improvement in compositional uniformity and purity, meeting the extremely high-performance requirements of modern aero-engines.

[0018] Furthermore, the initial sulfur content in the elemental nickel, elemental chromium, elemental cobalt, and elemental molybdenum is ≤50ppm, which strictly controls the introduction of harmful impurities such as sulfur from the source, reduces the processing load of subsequent desulfurization processes, lays the foundation for achieving low sulfur content in the final alloy, avoids the problem of incomplete desulfurization caused by high initial sulfur, and directly improves the purity of the alloy.

[0019] Furthermore, during vacuum induction melting, the vacuum degree is ≤0.1Pa, the melting temperature is 1500-1550℃, and the melting time is ≥30min. This ensures that the raw materials are fully melted and the composition is homogeneous. The vacuum environment isolates the air to prevent metal oxidation, and the high-temperature, long-time refining promotes the removal of gaseous impurities and low-melting-point impurities by floating to the surface. This not only ensures the uniformity of the electrode rod composition but also initially improves the purity and reduces the composition fluctuations during subsequent remelting.

[0020] Furthermore, during vacuum induction melting, the casting rate is 10-15 kg / min. This casting rate balances fluidity and solidification stability, avoiding defects such as slag entrapment, oxidation, or porosity caused by excessively fast rates, and also preventing compositional segregation caused by excessively slow rates. This ensures that the internal structure of the alloy electrode rod is dense and the composition is uniform, providing high-quality raw materials for subsequent electroslag remelting.

[0021] Furthermore, the slag comprises CaF2, CaO, Al2O3, and MgO; by mass percentage, the content of CaF2 is 55wt%-65wt%, and the content of MgO is 3wt%-7wt%. This ratio optimizes the fluidity and refining ability of the slag, CaF2 ensures the conductivity and high-temperature stability of the slag, and MgO enhances the slag's ability to adsorb oxide inclusions, creating favorable conditions for deep purification of the alloy and removal of impurities, while maintaining the stability of the remelting process.

[0022] Furthermore, the amount of elemental Ce added is 0.01wt%-0.05wt% of the total slag mass. This amount ensures that Ce reacts fully with sulfur to form stable sulfides and is removed with the slag, achieving deep desulfurization. It also avoids rare earth inclusions caused by excessive Ce, precisely balancing the desulfurization effect and alloy purity, thus solving the pain point of insufficient desulfurization efficiency in traditional processes.

[0023] Furthermore, during electroslag remelting, the current is 12-15kA, the voltage is 25-30V, and the cooling water flow rate in the crystallizer is 40L / min. This combination of parameters ensures that the slag body generates stable resistance heat, causing the electrode rod to melt uniformly. The cooling water flow rate of 40L / min ensures efficient cooling of the crystallizer, avoiding ingot cracks or compositional segregation caused by local overheating. At the same time, it promotes the full reaction between the molten droplets and the slag body, improves the purification effect, and obtains ingots with no surface defects and uniform composition.

[0024] Furthermore, in the vacuum self-consumable remelting process, the vacuum degree is ≤0.01Pa, the melting rate is 3-5kg / min, and the axial solidification gradient is ≥80℃ / cm. These parameters guide the directional solidification of the alloy, suppress the macroscopic segregation of solute elements, refine the grain structure, improve the uniformity of alloy composition, enhance the density of the structure, and make up for the deficiency of insufficient segregation suppression in traditional processes.

[0025] Furthermore, the interval between steps S1 and S2 is ≤24 hours, which effectively prevents the alloy electrode rod from being exposed to air and oxidizing, avoids the introduction of additional impurities by the oxide scale, ensures the cleanliness of the electrode rod surface, ensures the melting efficiency and purification effect of the electroslag remelting stage, and avoids component contamination and purity reduction caused by oxidation. Detailed Implementation

[0026] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0028] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0029] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0030] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0031] This invention provides a three-stage melting method for high-purity nickel-based superalloys, consisting of vacuum induction melting, electroslag remelting, and vacuum consumable remelting. This method solves the problems of impurity control and compositional uniformity, achieving oxygen content ≤5ppm, sulfur content ≤10ppm, and macrosegregation level ≤ASTM 1.

[0032] Specifically, the following steps are included: Step S1: Vacuum Induction Melting (VIM) Elemental nickel, chromium, cobalt and molybdenum with a purity ≥ 99.95% were vacuum induction melted, injected into a mold and cooled to obtain alloy electrode rods. In one specific embodiment, elemental nickel, elemental chromium, elemental cobalt, and elemental molybdenum are electrolytic nickel, metallic chromium, cobalt ingots, and molybdenum bars, respectively, and the initial sulfur content in the electrolytic nickel, metallic chromium, cobalt ingots, and molybdenum bars is ≤50ppm.

[0033] During vacuum induction melting, the vacuum degree is ≤0.1Pa, the melting temperature is 1500-1550℃, and the melting time is ≥30min; the diameter of the final electrode rod is 400mm.

[0034] The raw materials used here are high-purity electrolytic nickel, chromium, cobalt, and molybdenum with a purity ≥99.95%. Before feeding, they undergo strict pretreatment: first, ultrasonic cleaning with anhydrous ethanol is used to remove surface oil and dust; then, they are kept at 120℃ in a vacuum drying oven for 2 hours to completely remove adsorbed moisture and gases, preventing defects such as porosity during melting. The pretreated raw materials are weighed and batched according to the preset alloy composition ratio, with the error controlled within ±0.01%.

[0035] The smelting process takes place in a high-frequency vacuum induction furnace. First, the vacuum level inside the furnace is evacuated to ≤0.1 Pa. This vacuum environment effectively isolates air, preventing oxidation of metal elements and avoiding the dissolution of gases such as nitrogen and hydrogen into the alloy. The induction heating system is then activated, raising the temperature to 1500-1550℃ at a rate of 50℃ / min. After the raw materials are completely melted, this temperature is maintained for refining, with the refining time strictly controlled to ≥30min. During the refining stage, electromagnetic stirring rapidly homogenizes the melt composition and simultaneously promotes the full floating of low-melting-point impurities and gases in the melt, which are then removed by the vacuum system.

[0036] After refining, the high-temperature alloy melt is poured steadily into a pre-made graphite mold using a bottom-pouring method. The furnace is kept under vacuum during pouring, and the pouring rate is controlled at 10-15 kg / min to prevent slag entrapment or oxidation caused by excessive melt flow. After the melt cools naturally to 800°C in the mold, the mold is removed to obtain a cylindrical electrode rod with a diameter of 400 mm. The surface of the electrode rod is then preliminarily polished to remove the risers and gates before proceeding to the next process.

[0037] Step S2: Electroslag Remelting (ESR) Elemental Ce is added to the slag to obtain an optimized slag. The alloy electrode rod is then inserted into the optimized slag for electroslag remelting. After the alloy electrode rod is energized and melted, it is purified by the slag and solidified to obtain an ingot. The slag comprises CaF2, CaO, Al2O3, and MgO; by mass percentage, the CaF2 content is 55wt%-65wt%, and the MgO content is 3wt%-7wt%. Preferably, the mass percentage of CaF2, CaO, Al2O3, and MgO is 60:20:15:5, i.e., CaF2:CaO:Al2O3:MgO = 60:20:15:5 (wt%); the amount of Ce added is 0.01wt%-0.05wt% of the total mass of CaF2, CaO, Al2O3, and MgO. Adding rare earth Ce is beneficial for deep desulfurization.

[0038] During electroslag remelting, the current is 12-15kA, the voltage is 25-30V, and the flow rate of cooling water in the crystallizer is 40L / min. Electroslag remelting (ESR), a key process for improving alloy purity and microstructure uniformity, utilizes the resistance heat generated by current passing through molten slag to melt electrodes, achieving secondary refining of the metal. This process uses 400mm diameter alloy electrode rods prepared by vacuum induction melting as raw materials. By precisely controlling the slag system and process parameters, combined with innovative rare earth desulfurization technology, the alloy inclusions and sulfur content are significantly reduced.

[0039] The slag preparation must be strictly carried out according to the following proportions: Analytical grade CaF2, CaO, Al2O3, and MgO are weighed in a mass percentage ratio of 60:20:15:5. Before mixing, each component needs to be calcined in a muffle furnace at 800℃ for 4 hours to remove water of crystallization and volatile impurities, preventing splashing during remelting. After mixing, the mixture is added to a graphite crucible for pre-melting into a homogeneous slag. At the same time, rare earth Ce is added at a ratio of 0.01wt%-0.05wt%, which has a strong affinity for sulfur and can form stable Ce2S3 inclusions, which float with the molten slag to achieve deep desulfurization.

[0040] Before remelting, equipment debugging must be completed: Add the pre-made slag to the copper crystallizer, align the alloy electrode rod vertically with the center of the crystallizer, and ensure good contact between the electrode and the slag pool; check the cooling water system to ensure that the cooling water flow rate of the crystallizer is stable at 40L / min to avoid local overheating and damage to the crystallizer. After starting the power supply, gradually adjust the current to 12-15kA and the voltage to 25-30V to rapidly heat the slag to a molten state.

[0041] During remelting, the electrode tip continuously melts at the high temperature of the slag pool, forming molten metal droplets. As the droplets pass through the slag pool, they are not only further purified but also react fully with the Ce-containing slag to remove sulfur. The cooling water in the crystallizer causes the molten metal to solidify rapidly, forming a uniformly composed and dense ingot. Throughout the process, the stability of the current and voltage, as well as the cooling water temperature, must be monitored. After the electrode rod is completely melted, it is held at that temperature for 30 minutes before the furnace is shut down to ensure that there are no shrinkage cavities inside the ingot, thus preparing it for subsequent vacuum arc remelting.

[0042] Step S3: Vacuum Arsenic Remelting (VAR) Using the ingot as a consumable electrode, vacuum consumable remelting is performed to complete the remelting of the nickel-based high-temperature alloy.

[0043] During the vacuum self-consumable remelting process, the vacuum degree is ≤0.01Pa, the melting rate is 3-5kg / min, and the axial solidification gradient is ≥80℃ / cm, preferably 80-120℃ / cm. The ingot cooling rate is ≤10℃ / h.

[0044] During the vacuum consumable remelting process, a pulsed current is applied between the consumable electrode and the molten pool. The preferred frequency of the pulsed current is 0.5-2Hz. The fluctuation range of the pulsed current is between ±5% and ±15%, that is, the deviation range between the instantaneous value of the pulsed current and the reference value is ±5% to ±15%.

[0045] Vacuum arc remelting (VAR) is a crucial final step in improving the quality of alloy ingots. Through directional solidification and pulsed current control in a vacuum environment, it refines grains and suppresses compositional segregation, laying the microstructural foundation for high-performance alloy materials. This process uses high-quality ingots obtained from electroslag remelting as consumable electrodes, requiring strict control over process connections and parameters to ensure stable performance of the final product.

[0046] To prevent electrode oxidation from affecting purity, the interval between ESR and VAR processes must be strictly controlled within ≤24 hours. Before remelting, the vacuum furnace chamber is evacuated to a high vacuum state of ≤0.01Pa. This environment completely isolates air, preventing high-temperature oxidation of metal elements, and simultaneously removes gaseous impurities generated during the melting process. After starting the equipment, the end of the consumable electrode is melted by arc heating, with the melting rate precisely controlled at 3-5 kg / min to ensure a stable molten pool and uniform composition.

[0047] This process employs a pulsed current with a frequency of 0.5-2Hz. The periodic fluctuations of the current disrupt the stable state of the solid-liquid interface, promoting uniform diffusion of solute elements and effectively suppressing common macroscopic segregation defects in the alloy. Simultaneously, the axial solidification gradient is controlled at ≥80℃ / cm, guiding the molten pool to solidify axially, reducing interdendritic inclusions, and forming a dense columnar crystal structure.

[0048] During the remelting process, the vacuum level, melting rate, and current changes must be monitored in real time to ensure that all parameters remain stable within the set range. Once the consumable electrode has completely melted and the ingot has reached the preset size, heating is stopped and a slow cooling program is initiated.

[0049] To reduce internal stress and prevent cracking, VAR ingots must be cooled to room temperature at a slow rate of ≤10℃ / h. After cooling, the ingot surface is cleaned and quality inspected. Qualified ingots can then be used as billets for subsequent processing of high-end alloy products.

[0050] This invention discloses a three-stage refining method for high-purity nickel-based superalloys, consisting of vacuum induction melting, electroslag remelting, and vacuum arc remelting. This invention imparts superior purity and mechanical properties to the alloy through a three-stage refining process of "vacuum induction melting – electroslag remelting – vacuum arc remelting." The first stage is vacuum induction melting (VIM), using high-purity electrolytic nickel, metallic chromium, cobalt ingots, etc., and melting at a high temperature of 1500-1550℃ in a closed environment with a vacuum degree ≤0.1Pa, while ensuring a refining time of ≥30 minutes. In this stage, electromagnetic stirring is used to homogenize the melt composition, and the vacuum environment effectively isolates air, initially reducing the content of gaseous impurities, ultimately casting a high-quality electrode rod with a diameter of Φ400mm. The second stage, electroslag remelting (ESR), uses VIM electrode rods as raw material, preferably a composite slag system of CaF2:CaO:Al2O3:MgO = 60:20:15:5 (wt%), with the addition of 0.01wt%-0.05wt% rare earth Ce. Under a current of 12-15kA, the slag body generates a resistance-thermal melting electrode, and Ce and sulfur form stable Ce2S3 inclusions that float to the surface with the slag, achieving deep desulfurization and further removing inclusions. In the final stage, vacuum arc remelting (VAR), the ESR ingot is used as the arc electrode, and remelting is performed at a melting rate of 3-5 kg / min under a high vacuum of ≤0.01 Pa, while a pulsed current of 0.5-2 Hz is applied, and the axial solidification gradient is controlled to be ≥80℃ / cm. The pulsed current disrupts the solid-liquid interface equilibrium, suppressing macroscopic segregation, while directional solidification refines the grains. The finished alloy has a sulfur content of ≤10ppm, an oxygen content of ≤5ppm, a macrosegregation grade of ≤ASTM 1, and a high-temperature creep life that is more than 30% higher than that of conventional processes. It is particularly suitable for the preparation of components such as turbine disks and blades for aero-engines under harsh conditions.

[0051] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0052] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0053] Example 1 A three-stage melting method for high-purity nickel-based superalloys, comprising vacuum induction melting, electroslag remelting, and vacuum arc remelting, includes the following steps: The initial stage of the process is vacuum induction melting, using a 5t vacuum induction furnace as the core equipment. Before melting, the furnace chamber is evacuated to 0.08Pa, and then the heating program is started. After the temperature inside the furnace reaches 1520℃ and stabilizes, the alloy is melted at this temperature. At the same time, the refining process is completed by holding the furnace at a high temperature range above 1500℃ for 40 minutes. During this stage, the melt composition is homogenized by electromagnetic stirring, and the vacuum environment effectively isolates air and removes low-boiling-point volatile impurities. After refining, the high-temperature alloy melt is poured smoothly to form an electrode rod with a specification of Φ400mm×1500mm, providing high-quality raw materials for the subsequent remelting process.

[0054] Electrode rods prepared using VIM are used as raw materials in the electroslag remelting process. The core of this stage lies in the customized slag system design and the precise addition of rare earth Ce. The slag is composed of CaF2, CaO, Al2O3, and MgO in specific mass percentages, with CaF2 accounting for 58%, CaO for 22%, Al2O3 for 15%, and MgO for 5%. At the same time, 0.04% elemental Ce is added to the slag system to enhance the desulfurization effect. During the remelting process, the process parameters are strictly controlled, with the current stabilized at 13kA and the voltage adjusted to 28V. Efficient heat exchange is achieved through a stable flow rate of 45L / min of cooling water in the crystallizer, ensuring that the molten pool temperature matches the solidification rate. Finally, a high-quality ingot with a diameter of 500mm and no surface cracks is obtained. The desulfurization mechanism of Ce is particularly significant, as it undergoes a directional reaction with sulfur (reaction formula: Ce + S → CeS precipitation), achieving deep desulfurization of the alloy.

[0055] After a short turnaround time of ≤24h, the ESR ingot is transferred to the vacuum arc remelting process. In this stage, the alloy structure and purity are further optimized through refined parameter control. The vacuum degree of the furnace cavity is increased to 0.008Pa to enhance the removal of gaseous impurities. The melting rate is precisely controlled at 4.2kg / min. At the same time, a pulse current with a frequency of 1.2Hz and a fluctuation amplitude of ±12% is applied. Combined with a high axial solidification gradient of 95℃ / cm achieved by forced cooling, the solidification structure is significantly improved. The introduction of pulse current increases the oscillation depth of the molten pool by 40% and reduces the dendrite spacing to 65% of that of conventional VAR. This effectively breaks the solute enrichment layer at the solid-liquid interface, promotes the uniform diffusion of solute elements, and effectively suppresses macroscopic segregation defects. After remelting, the ingot is cooled to room temperature at a slow cooling rate of 8℃ / h to reduce internal thermal stress and avoid crack formation. Finally, a final ingot with a specification of Φ650mm×2000mm is obtained.

[0056] The triple melting process (VIM+ESR+VAR) for nickel-based superalloys in this invention significantly improves core performance indicators compared to the traditional VIM+VAR process. Firstly, in terms of purity, the measured sulfur content of the alloy prepared by this invention is only 7.2 ppm, a decrease of over 68% compared to the 22.5 ppm of the traditional process; the oxygen content is as low as 3.1 ppm, far superior to the 9.8 ppm of the traditional process. This is attributed to the deep desulfurization of rare earth Ce in the ESR stage and the oxygen control effect of the high vacuum environment in VAR. Regarding microstructure uniformity, the alloy prepared by this invention achieves a macroscopic segregation grade of ASTM 0.5, far exceeding the ASTM 2.5 grade of the traditional process; the γ' phase size uniformity is ≤0.5 μm with a standard deviation of only 0.08, while the γ' phase size in the traditional process reaches 0.8 μm with a standard deviation of 0.25. This demonstrates that the oscillation effect of the pulsed current effectively refines the solidification structure and improves uniformity. Meanwhile, it also demonstrates outstanding performance in high-temperature service. The alloy prepared by this invention achieves a creep rupture life of 102 hours under operating conditions of 750℃ / 550MPa, which is about 50% higher than the 68 hours of the traditional process. Therefore, the triple process, through the synergistic effect of VIM pre-refining, ESR deep purification, and pulsed VAR microstructure regulation, comprehensively optimizes the purity, microstructure uniformity, and high-temperature creep rupture performance of the alloy, providing a better preparation scheme for nickel-based high-temperature alloys for high-end equipment.

[0057] Example 2 This embodiment uses a triple melting process to prepare a high-purity nickel-based superalloy. The specific steps are as follows: S1: Vacuum Induction Melting (VIM) The raw materials selected are elemental nickel, elemental chromium, elemental cobalt, and elemental molybdenum with a purity of 99.96%, and the initial sulfur content of each raw material is 35 ppm. A 5t vacuum induction furnace is used. The furnace chamber is first evacuated to 0.05 Pa, and then the temperature is raised to 1520℃ for melting. After the raw materials are completely melted, the temperature is held above 1500℃ for 35 minutes to complete the refining. The melt is poured into a graphite mold at a pouring rate of 12 kg / min. After cooling, an alloy electrode rod with a diameter of 400 mm × 1500 mm is obtained. The electrode rod has a uniform composition and no obvious porosity defects.

[0058] S2: Electroslag Remelting (ESR). The slag is prepared by mass percentage as follows: CaF2 60wt%, CaO 20wt%, Al2O3 15wt%, MgO 5wt%. Elemental Ce is added to the slag at 0.03wt% of the total slag mass to create an optimized slag. The interval between S1 and S2 is 18 hours. An alloy electrode rod is inserted into the optimized slag, and the ESR parameters are set as follows: current 13.5kA, voltage 27V, and crystallizer cooling water flow rate 40L / min. After the electrode rod melts, it is purified and desulfurized by the slag. After solidification, a Φ500mm ingot is obtained with a smooth, crack-free surface.

[0059] S3: Vacuum Arsenic Remelting (VAR) Using an ESR ingot as the consumable electrode, the vacuum furnace chamber was evacuated to 0.005 Pa, the melting rate was controlled at 4 kg / min, and an axial solidification gradient of 85 °C / cm was applied (achieved through forced cooling). After remelting, the ingot was cooled to room temperature at a rate of 8 °C / h, ultimately yielding a Φ650 mm × 2000 mm nickel-based superalloy ingot.

[0060] Product performance: The alloy has a sulfur content of 8.5 ppm, an oxygen content of 3.8 ppm, a macrosegregation grade of ASTM 0.5, and a creep rupture life of 142 hours under stress at 650℃ / 620MPa.

[0061] Example 3 This embodiment verifies process stability through a combination of boundary parameters. The specific steps are as follows: S1: Vacuum Induction Melting (VIM) The raw materials selected are elemental nickel, elemental chromium, elemental cobalt, and elemental molybdenum with a purity of 99.95%, and the initial sulfur content of each raw material is 50 ppm. A 5t vacuum induction furnace is used. After evacuating to 0.1 Pa, the temperature is raised to 1550℃ and refined by holding at above 1500℃ for 30 minutes. The alloy electrode rod is then cast at a rate of 15 kg / min and cooled to obtain a diameter of 400 mm × 1500 mm.

[0062] S2: Electroslag Remelting (ESR). The slag composition is as follows by mass percentage: CaF 255wt%, CaO 25wt%, Al2O3 15wt%, MgO 5wt%, with 0.05wt% elemental Ce added. The interval between S1 and S2 is 24 hours. The ESR parameters are set as follows: current 15kA, voltage 30V, cooling water flow rate 40L / min. After remelting and solidification, a Φ500mm ingot is obtained.

[0063] S3: Vacuum self-consuming remelting (VAR) The vacuum degree of the furnace cavity is controlled at 0.01Pa, the melting rate is 3kg / min, the axial solidification gradient is 80℃ / cm, and the ingot is cooled to room temperature at a rate of 10℃ / h to finally obtain a nickel-based superalloy ingot with a diameter of 650mm×2000mm.

[0064] Product performance: The alloy was tested and found to have a sulfur content of 10 ppm, an oxygen content of 5 ppm, a macrosegregation grade of ASTM 1, and a creep rupture life of 130 hours under 650℃ / 620MPa stress, meeting the performance indicators.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A three-stage melting method for high-purity nickel-based superalloys, comprising vacuum induction melting, electroslag remelting, and vacuum arc remelting, characterized in that... Includes the following steps: S1: Vacuum induction melting of elemental nickel, elemental chromium, elemental cobalt and elemental molybdenum with a purity ≥99.95% is performed, and after being injected into a mold and cooled, an alloy electrode rod is obtained. S2: Add elemental Ce to the slag to obtain an optimized slag. Insert the alloy electrode rod into the optimized slag for electroslag remelting. After the alloy electrode rod is energized and melted, it is purified by the slag and solidified to obtain an ingot. S3: Using the ingot as a consumable electrode, vacuum consumable remelting is performed to obtain a nickel-based high-temperature alloy.

2. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, The initial sulfur content in the elemental nickel, elemental chromium, elemental cobalt, and elemental molybdenum is ≤50ppm.

3. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, During vacuum induction melting, the vacuum degree is ≤0.1Pa, the melting temperature is 1500-1550℃, and the melting time is ≥30min.

4. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, During vacuum induction melting, the casting rate is 10-15 kg / min.

5. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, The slag comprises CaF2, CaO, Al2O3, and MgO; by mass percentage, the content of CaF2 is 55wt%-65wt%, and the content of MgO is 3wt%-7wt%.

6. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, The amount of elemental Ce added is 0.01wt%-0.05wt% of the total mass of the slag.

7. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, During electroslag remelting, the current is 12-15kA, the voltage is 25-30V, and the flow rate of cooling water in the crystallizer is 40L / min.

8. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, During the vacuum self-consumable remelting process, the vacuum degree is ≤0.01Pa, the melting rate is 3-5kg / min, and the axial solidification gradient is ≥80℃ / cm.

9. The triple melting method for high-purity nickel-based superalloys according to claim 1, characterized in that, The time interval between step S1 and step S2 is ≤24 hours.

10. A high-purity nickel-based superalloy, characterized in that, The nickel-based superalloy is prepared by the method described in any one of claims 1 to 9; the sulfur content is ≤10ppm and the oxygen content is ≤5ppm; the macrosegregation grade is ≤ASTM grade 1; and the creep rupture life under 650℃ and 620MPa stress is ≥130 hours.