A high-temperature alloy for ultra-pure ultra-supercritical and a preparation method and application thereof

Abstract

The application discloses a kind of high-temperature alloy for ultra-pure ultra-supercritical and its preparation method and application, belong to metallurgical technical field, to solve the technical problems of the clean, efficient, accurate addition of alloy element difficult to be realized in the method for preparing high-temperature alloy using vacuum induction melting, and secondary oxidation inclusion is easily introduced in the adding process, element burning loss or composition is not uniform.The preparation method of the application comprises the following steps: S1: the alloy raw material is loaded into the vacuum induction furnace, vacuum is extracted and induction heating is started to melt, to form a molten pool;S2: the plasma torch is immersed below the molten pool liquid surface, and induction electromagnetic stirring is applied simultaneously to refine;S3: using the plasma torch, the alloy elements to be added are introduced into the action area of the plasma torch, so that the alloy elements react with the molten pool in the plasma environment or fall into the molten pool, and after final deoxidization and casting, the high-temperature alloy for ultra-pure ultra-supercritical is obtained.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to an ultrapure, ultrasupercritical high-temperature alloy, its preparation method, and its application. Background Technology

[0002] Advances in ultra-supercritical power generation technology have placed near-stringent demands on the purity of high-temperature structural materials. Trace impurities (such as O, N, S, and P) and non-metallic inclusions in alloys are the main causes of crack initiation and propagation, decreased creep performance, and deterioration of corrosion resistance at high temperatures. Vacuum induction melting (VIM), as the first step in the production of such alloys, directly determines the upper limit of quality improvement in subsequent remelting processes and the quality baseline of the final product based on the initial purity achieved.

[0003] Traditional VIM mainly relies on carbon deoxidation under high temperature and vacuum and the volatilization of impurity elements for purification, but its effectiveness is limited by kinetic conditions: the convection inside the molten pool mainly depends on electromagnetic force, which has limited stirring ability for the melt in the lower part of the molten pool and near the crucible wall, resulting in incomplete removal of inclusions by floating; for gaseous elements such as nitrogen and hydrogen, vacuum settling alone is inefficient and time-consuming; in addition, when adding highly reactive elements (such as Al, Ti, and rare earth elements), there is still a risk of reaction with residual oxygen to form inclusions.

[0004] To improve the purity of VIM (Vacuum Induction Melting), existing technologies primarily focus on improvements in raw material pretreatment, smelting process optimization, or ladle refining. For example, Chinese patent CN110408803A discloses a preparation process for nickel-based superalloys with high refractory element content, which controls impurities through multi-step refining, but its kinetic conditions are not fundamentally improved. Chinese patent CN213873755U introduces a top-blown argon gas device and vacuum induction furnace, but this may cause molten pool splashing and secondary oxidation. Plasma metallurgy technology, due to its advantages of high temperature, high energy density, controllable atmosphere, and strong convection, has been applied in the refining of steel and titanium alloys. For instance, patent CN101157992A discloses a method for smelting titanium alloys in a plasma cold hearth furnace. However, there are no reports of systematically integrating non-consumable electrode plasma technology into the VIM process for comprehensive refining throughout the entire process, from raw material pretreatment and assisted smelting to atmosphere alloying, specifically addressing the purity requirements of ultra-supercritical superalloys. Chinese patent application CN117965927A discloses a highly efficient purification smelting method for high-temperature alloy return materials based on hydrogen plasma blowing. This method involves heating in a vacuum induction furnace and using a plasma torch to blow a mixture of argon and hydrogen-rich gas, combined with electromagnetic stirring technology, to remove oxides, nitrides, and other impurities from the return materials, achieving deep purification of the high-temperature alloy. However, this smelting method only adds metal raw materials after refining and sampling to test the composition. This traditional method of directly adding solid materials to the surface or interior of the molten pool can easily introduce secondary inclusions for easily oxidized elements. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide an ultra-pure ultra-supercritical high-temperature alloy, its preparation method and application, in order to solve the technical problems of existing methods for preparing high-temperature alloys using vacuum induction melting, which are difficult to achieve clean, efficient and precise addition of alloying elements, and are prone to introducing secondary oxidation inclusions, element burn-off or uneven composition during the addition process.

[0006] This invention provides a method for preparing ultrapure ultra-supercritical high-temperature alloys. This method innovatively utilizes the multiple effects of plasma by integrating a non-consumable arc plasma torch into a VIM furnace to enhance the entire melting process, ultimately obtaining ultrapure ultra-supercritical high-temperature alloys with extremely low impurity content and extremely high purity.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys, comprising the following steps: S1: The alloy raw material is loaded into a vacuum induction furnace, a vacuum is drawn and induction heating is started to melt it and form a molten pool; S2: Immerse the plasma torch below the surface of the molten pool while applying induction electromagnetic stirring to perform refining; S3: Using a plasma torch, the alloying elements to be added are introduced into the active area of ​​the plasma torch, so that the alloying elements react with the molten pool or fall into the molten pool in the plasma environment. After final deoxidation and casting, an ultra-pure ultra-supercritical high-temperature alloy is obtained.

[0008] In a further preferred embodiment, in step S1, the vacuum is evacuated to ≤1 Pa.

[0009] In a further preferred embodiment, in step S3, the alloying element to be added is introduced into the plasma interaction region using a plasma torch. After the process of the alloying element reacting with the molten pool or falling into the molten pool in the plasma environment is completed, the plasma torch is raised above the molten pool, and a low-power plasma arc is maintained to protect the surface of the molten pool. After final deoxidation and casting, an ultra-pure ultra-supercritical high-temperature alloy is obtained.

[0010] Preferably, the alloying element to be added includes at least one of the following: A) Aluminum and titanium, wherein the mass ratio of aluminum to titanium is 1:0.6; B) Nitrogen or carbon added in gaseous form.

[0011] Preferably, in step S1, after the alloy raw material is loaded into the vacuum induction furnace and before the vacuum is drawn and induction heating is started for melting, the process further includes: scanning the surface of the furnace material in the vacuum induction furnace with the plasma torch, wherein the plasma torch is 100 mm away from the surface of the furnace material, the scanning speed is 10 cm / s, and the scanning time is 10-30 minutes.

[0012] Preferably, in step S1, after loading the alloy raw material into the vacuum induction furnace, a vacuum is drawn and the induction furnace is started; in step S2, the electrode end of the plasma torch is immersed to a depth of 5mm-20mm below the surface of the molten pool and oscillates back and forth at a frequency of 1Hz-5Hz with an oscillation amplitude of 10mm-50mm; the power of the plasma torch is 50kW-200kW; the refining temperature is 1500-1650℃; and the refining time is 20-60 minutes.

[0013] Preferably, in step S1, after the alloy raw material is loaded into the vacuum induction furnace, a vacuum is drawn and the induction furnace is started, the working gas of the plasma torch includes one of high-purity argon, argon-hydrogen mixture and argon-helium mixture, wherein the hydrogen gas fraction in the argon-hydrogen mixture does not exceed 10% and the helium gas fraction in the argon-helium mixture does not exceed 30%.

[0014] Preferably, in step S1, after loading the alloy raw material into the vacuum induction furnace, evacuating the vacuum, and starting the induction furnace, in step S3, the introduction method is as follows: when the alloying element to be added is nitrogen or carbon added in gaseous form, the gas carrying the nitrogen or carbon element is mixed into the working gas of the plasma torch, and reacts with the molten pool after being activated by the plasma arc; the gas carrying the nitrogen or carbon element is mixed into the working gas of the plasma torch to form a mixed gas, and the volume fraction of the gas carrying the nitrogen or carbon element in the mixed gas is 0.3% to 0.8%.

[0015] Preferably, in step S3, the introduction method is as follows: when the alloying elements to be added are aluminum and titanium, they are added through a feeding device that extends into the plasma torch arc zone, so that they fall into the molten pool under the protection of the plasma atmosphere.

[0016] Preferably, in step S1, after the alloy raw material is loaded into the vacuum induction furnace, a vacuum is drawn and the induction furnace is started, and the plasma torch scans the surface of the furnace charge in the vacuum induction furnace in a zigzag path. In a further preferred embodiment, in step S2, the furnace atmosphere and molten pool emission spectrum are monitored online, and plasma parameters or refining time are dynamically adjusted based on the monitoring results. Online monitoring of the furnace atmosphere (e.g., mass spectrometry) and molten pool emission spectrum (e.g., LIBS) allows for real-time acquisition of impurity content such as oxygen and sulfur, as well as alloy element concentrations. Based on this, plasma parameters (e.g., power, gas flow rate) or refining time are dynamically adjusted, thereby achieving closed-loop control of the refining process. Real-time feedback optimizes process parameters, ensuring that the final composition and purity reach the target range, improving process stability and repeatability.

[0017] This invention also provides an ultra-pure ultra-supercritical high-temperature alloy obtained by the aforementioned method, wherein the ultra-pure ultra-supercritical high-temperature alloy has an oxygen content ≤5 ppm, a sulfur content ≤3 ppm, and fewer than 5 inclusions larger than 5 μm per cm. 2 The yields of key alloying elements aluminum and titanium are ≥99%; and the nitrogen content meets one of the following conditions: 1) Nitrogen content ≤ 10 ppm; 2) Nitrogen content is 50-80 ppm 3) Carbon content is 100-180 ppm.

[0018] The present invention also provides an application of the aforementioned ultrapure ultra-supercritical high-temperature alloy in the manufacture of high-temperature components for ultra-supercritical generator sets, aero engines, or gas turbines.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys, solving the problem of alloy element addition through vacuum induction melting and plasma metallurgy. Its core principle lies in: utilizing a vacuum environment to prevent contamination of the alloy molten metal by O2, N2, etc., during refining and alloying; and utilizing induction heating to achieve efficient melting and stirring. Specifically, induction electromagnetic stirring ensures uniform composition and temperature of the molten pool. This invention creatively introduces a plasma torch as the energy source and protective atmosphere source for alloying, thereby achieving deep purification and clean, precise addition of highly reactive elements in stages within a single melting cycle and on the same equipment.

[0020] In step S2, immersing the plasma torch into the molten pool alters the energy and matter transfer process, resulting in multiple synergistic effects: 1) Enhanced thermal convection and stirring: The plasma arc forms a continuous high-temperature heat source and a strong electromagnetic stirring source within the molten pool (the magnetic field generated by the plasma current interacts with the induced magnetic field). Combined with the original induction stirring, this produces a composite convection far stronger than that of traditional VIM. This strong convection makes the composition and temperature highly uniform throughout the molten pool and greatly promotes the collision, aggregation, and flotation speed of inclusions. 2) Enhanced degassing capability: The localized ultra-high temperature of the plasma arc (far exceeding the average temperature of the molten pool) greatly increases the diffusion coefficient and supersaturation of gas in the molten pool, accelerating the diffusion, aggregation, and precipitation of gas atoms. Simultaneously, strong convection rapidly carries bubbles from the deep molten pool to the surface for escape. 3) Deep removal of non-metallic inclusions: Under the action of high-energy plasma, some stable oxide and nitride inclusions can be directly thermally decomposed or reduced through enhanced carbon deoxidation reactions. Experiments show that, especially when using a plasma atmosphere of argon-hydrogen mixture, the strong reducing properties of hydrogen can further reduce oxides. The core innovation of the preparation method of this invention lies in step S3. On the one hand, the high temperature, high energy and controllable atmosphere region generated by the plasma torch provides local protection for the easily oxidized active metal elements in the alloy elements to be added, greatly reducing secondary oxidation and burn-off during the addition process. On the other hand, the high temperature and highly active particles of the plasma can effectively activate the gas molecules in the alloy elements to be added, making them easier to dissociate and react with the molten pool metal, thus solving the problems of low addition efficiency and difficulty in control of the alloy elements to be added.

[0021] Furthermore, the mass ratio of aluminum to titanium is limited to 1:0.6, which corresponds to optimizing the precipitation strengthening effect of the γ' phase (Ni3(Al,Ti)) and improving high-temperature strength. Nitrogen or carbon is added in gaseous form, utilizing the high-temperature dissociation of N2 or hydrocarbon molecules by plasma to generate atomic nitrogen / carbon, significantly improving their solubility and reaction rate in the molten pool. The specific ratio of Al to Ti helps to obtain the ideal strengthening phase composition; the addition of gaseous elements via plasma activation overcomes the problems of low solubility and unstable absorption rate in traditional methods, achieving narrow-range compositional control.

[0022] Furthermore, traditional VIM has limited ability to remove oxide films and adsorbed gases from the surface of raw materials. This invention uses a plasma torch to scan the surface of the furnace charge in a vacuum induction furnace before induction heating melting. The plasma beam generated by the torch has localized ultra-high temperatures of thousands or even tens of thousands of degrees Celsius, which can instantly vaporize or decompose adsorbed impurities such as grease, moisture, and oxides on the surface of the furnace charge, reducing the introduction of impurities from the raw material end and enhancing the purification effect. Simultaneously, the localized high temperature and impact force from the plasma beam help break up slightly sintered agglomerates, making subsequent induction melting more uniform. Scanning parameters (distance 100 mm, speed 10 cm / s, time 10–30 minutes) ensure uniform cleaning of the furnace charge surface and avoid overheating. This step physically "cleans" the furnace charge surface, significantly reducing the total amount of impurities such as oxygen, nitrogen, and hydrogen introduced into the melt from the furnace charge surface.

[0023] Furthermore, by immersing the electrode tip of the plasma torch underwater, the plasma arc is generated directly inside the melt. This increases the refining intensity: the plasma bubbles rising inside the melt can more effectively carry away gaseous impurities and inclusions. It also improves thermal and stirring efficiency: energy is directly transferred to the melt with minimal heat loss, while the arc force generates strong local stirring, which greatly promotes the homogenization of composition and temperature in the molten pool, creating excellent thermodynamic and kinetic conditions for subsequent precise alloying.

[0024] Meanwhile, the plasma torch is immersed to a depth of 5 mm–20 mm, ensuring stable operation within the molten pool and preventing air entrapment. Oscillation at a frequency of 1 Hz–5 Hz and an amplitude of 10 mm–50 mm expands the interaction area between the plasma and the melt, enhancing localized stirring. A power output of 50 kW–200 kW provides sufficient energy to sustain the high-temperature reaction. Refining temperatures of 1500℃–1650℃ and times of 20–60 minutes ensure sufficient diffusion, flotation, or reaction removal of impurities. By optimizing the immersion depth, oscillation, and thermal parameters, the mass and heat transfer efficiency of the refining process is enhanced, promoting the polymerization and flotation of inclusions and the volatilization of harmful elements, further improving purity and uniformity.

[0025] Furthermore, the working gas can be high-purity Ar (inert protection), Ar-H2 (H2≤10%), or Ar-He (He≤30%). H2 dissociates into active hydrogen atoms in the plasma, reacting with oxygen in the molten pool to generate H2O, which then volatilizes, enhancing the deoxidation effect. He has high thermal conductivity, allowing for higher and more concentrated plasma arc temperatures, thus improving energy transfer efficiency. By adjusting the composition of the working gas, deoxidation (hydrogenation) can be specifically enhanced or thermal efficiency improved (helium addition), achieving more flexible and efficient refining control.

[0026] Furthermore, an optimal principle path is provided for nitrogen or carbon added in gaseous form. The alloying elements added in gaseous form are mixed into the working gas of the plasma torch. After passing through the plasma arc, the extremely high temperature and energy of the plasma arc can highly activate or even dissociate the gas molecules into active atoms or ions, which then react with the molten pool surface, achieving extremely uniform and efficient alloying, avoiding inclusions that may be introduced by using solid additives.

[0027] Furthermore, when the alloying element to be added is an easily oxidizable active metal element in aluminum and titanium germanium, it is added through a feeding device that extends into the plasma torch arc zone, so that it falls into the molten pool under the protection of the plasma atmosphere. The easily oxidizable active metal element is rapidly heated and melted when passing through the high temperature and inert plasma arc zone, and falls into the molten pool under the protection of the plasma, which minimizes the reaction with the residual gas in the furnace, improves the yield, and reduces endogenous inclusions.

[0028] In summary, this invention systematically enhances the impurity removal and clean alloying capabilities of the VIM process through three-stage plasma assistance in steps S1-S3, providing a novel process route for obtaining ultra-pure ultra-supercritical high-temperature alloys.

[0029] Furthermore, the zigzag scanning path ensures complete clean coverage of the furnace charge surface.

[0030] This invention also provides an ultra-pure ultra-supercritical high-temperature alloy obtained using the aforementioned method. This alloy exhibits extremely low oxygen (≤5 ppm) and sulfur (≤3 ppm) content, thanks to the deep deoxidation and desulfurization capabilities of plasma refining. The number of large inclusions (>5 μm) is extremely low, resulting from inductive electromagnetic stirring promoting inclusion flotation and removal, as well as clean addition preventing secondary oxidation. The ≥99% yield of aluminum (A) and titanium demonstrates the effectiveness of plasma-protected addition. The flexible control of nitrogen / carbon content (low nitrogen ≤10 ppm or medium nitrogen 50–80 ppm, carbon 100–180 ppm) benefits from precise activation via gas addition. The ultra-pure ultra-supercritical high-temperature alloy of this invention possesses ultra-high purity and controllable microalloying composition, meeting the stringent requirements of ultra-supercritical operating conditions for creep resistance, fatigue resistance, and corrosion resistance.

[0031] This invention also provides the application of high-temperature alloys in the manufacture of high-temperature components for ultra-supercritical generator sets, aero-engines, or gas turbines, which can significantly improve the durability and reliability of components under high-temperature and high-pressure environments and extend their service life. Ultra-high purity reduces the formation of brittle grain boundary phases (such as sulfides and oxides) at high temperatures, improving grain boundary strength; the fine and uniform γ' phase and controllable interstitial element content are beneficial for optimizing creep and fatigue performance. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method for preparing ultrapure, ultrasupercritical high-temperature alloys according to the present invention. Detailed Implementation

[0033] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. 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 the event of any conflict, the definitions in this specification shall prevail.

[0034] 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.

[0035] 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.

[0036] 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.”

[0037] 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.

[0038] 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.

[0039] 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, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0040] Example 1 This embodiment provides a method for preparing a certain type of ultra-supercritical nickel-based high-temperature alloy (target composition includes Cr, Co, W, Mo, Al, Ti, etc.) using the method of this invention. Figure 1 As shown: S1. Equipment Preparation and Loading: A 5-ton vacuum induction furnace with an integrated non-consumable tungsten electrode plasma torch is used. The plasma torch is installed on the furnace cover and can move and rotate in three dimensions. Electrolytic nickel plates, metallic chromium, cobalt blocks, tungsten bars, molybdenum bars, and other main raw materials are loaded into the magnesia crucible according to the target alloy composition (by mass fraction: Ni balance, Cr 18-22%, Co 10-15%, W 5-7%, Mo 3-5%, Al 2.0-3.0%, Ti 1.0-2.0%).

[0041] S2. Plasma Pretreatment: After furnace closure, the vacuum level is evacuated to 0.5 Pa. The plasma torch is started, with high-purity argon as the working gas and the power set to 80 kW. The plasma torch is controlled to scan the furnace charge surface in a zigzag pattern at a scanning speed of 10 cm / s and a distance of approximately 100 mm from the furnace charge surface, for a continuous scanning period of 20 minutes. Mass spectrometry monitoring shows that the partial pressures of H2O, O2, and N2 inside the furnace initially increase sharply, then gradually decrease and stabilize at a low level.

[0042] S3. Induction Melting and Plasma-Assisted Refining: The plasma torch is shut off, and induction heating is initiated to melt all the furnace charge. When the molten pool temperature reaches 1550°C, the plasma torch is restarted (working gas is argon atmosphere, power set to 100 kW), and the tungsten electrode tip is lowered to approximately 10 mm below the molten pool surface. Simultaneously, a medium-frequency current is applied to the induction coil for electromagnetic stirring. Refining is carried out under these conditions, maintaining the refining temperature at 1580°C for 40 minutes. During this time, the plasma torch oscillates horizontally at a frequency of 3 Hz and an amplitude of ±20 mm.

[0043] S4. Adding Aluminum and Titanium to the Plasma Atmosphere: Before the refining process is complete, the plasma working gas is switched to high-purity argon. Using a vibrating feeder installed next to the plasma torch, aluminum and titanium granules are fed into the plasma arc column region at a mass ratio of 1:0.6, according to the alloy composition design target (Al: 2.5 wt%, Ti: 1.5 wt%), and at controllable rates of 3 kg / min and 1.8 kg / min respectively. The aluminum and titanium granules melt instantly upon passing through the arc column at temperatures exceeding 10,000 degrees Celsius and drip into the molten pool. The feeding process lasts approximately 8 minutes.

[0044] S5. Final Deoxidation and Casting: After adding aluminum and titanium granules, adjust the plasma power to 50 kW and raise the plasma torch head to 50 mm above the molten pool to protect the surface of the molten pool. Add nickel-boron alloy and zirconium granules for final deoxidation. After standing for 5 minutes, cast into electrode ingots at 1550℃.

[0045] The horizontal reciprocating oscillation in step S3 above refers to the periodic back-and-forth movement of the plasma torch within a horizontal plane (parallel to the molten pool surface). The ±20 mm amplitude refers to the displacement range of this oscillation motion. Taking the center position within the horizontal plane as the zero point, it moves 20 mm to one side, then reverses direction past the center position and moves 20 mm to the other side. Therefore, the total stroke of one complete oscillation is 40 mm.

[0046] This oscillation, combined with a 3 Hz frequency (i.e., 3 complete cycles per second), aims to make the high-energy beam or heat-affected zone of the plasma torch act more evenly on the molten pool, thereby enhancing the heat transfer, mass transfer, and stirring effects of the refining process and avoiding local overheating or uneven reaction.

[0047] Test results: Analysis of electrode ingot samples showed that O content ≤ 5 ppm, N content ≤ 8 ppm, and S content ≤ 3 ppm. Inclusion analysis using the ASPEX Explorer automated scanning electron microscope revealed that the number density of inclusions larger than 5 μm was less than 5 inclusions / cm³. 2 .

[0048] Example 2 This embodiment provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys. Unlike Embodiment 1, it employs Ar-H2 mixed plasma for deep deoxidation, focusing on exploring the further enhancement of the deoxidation effect using a reducing plasma atmosphere. The specific steps are as follows: S1. Loading and pretreatment: Same as in Example 1.

[0049] S2. Auxiliary Refining: After the furnace charge melts, the plasma working gas is switched to an Ar-5% H2 (volume fraction) mixture, with a power of 120 kW, and then immersed in the molten pool for refining. Other parameters are the same as in Example 1. The introduction of hydrogen enhances the reducing atmosphere, aiming to deeply remove oxidized inclusions.

[0050] S3. Alloying and Casting: Before adding aluminum and titanium particles, the plasma working gas is switched back to high-purity argon to avoid the reaction of hydrogen with the active metals. Subsequent steps are the same as in Example 1.

[0051] Test results: Analysis of the electrode ingot obtained in this embodiment showed that the O content was further reduced to ≤3 ppm and the N content was ≤10 ppm (the slight increase may be related to the introduction of hydrogen). The inclusion number density was comparable to that in Example 1, but smaller oxide inclusion sizes were observed.

[0052] Example 3 This embodiment provides a method for preparing an ultrapure, ultrasupercritical high-temperature alloy, demonstrating the use of plasma to achieve micro-uniform nitriding of the alloy to enhance its strength.

[0053] S1. Loading, pretreatment, melting and preliminary refining: Same as in Example 1, except that pure argon plasma is used during the refining stage.

[0054] S2. Plasma Nitriding: At the end of the refining process, while maintaining the plasma torch in operation, 0.5% by volume of high-purity nitrogen is precisely mixed into the argon working gas and continuously introduced for 15 minutes. The nitrogen is activated in the plasma arc and reacts with the surface of the molten pool to achieve nitriding.

[0055] S3. Adding other elements and casting: After nitriding is completed, switch back to pure argon gas, and then add aluminum and titanium particles and follow the steps in Example 1.

[0056] Test results: Analysis of the electrode ingot samples obtained in this embodiment showed that the N content of the alloy was controllable within the range of 50-80 ppm and was uniformly distributed. The O and S contents were comparable to those in Example 1. The room temperature hardness of the alloy was significantly improved after nitriding.

[0057] Comparative Example 1 This comparative example is a conventional VIM process (without plasma assistance), using the same 5-ton vacuum induction furnace (with plasma function turned off), and melting alloys of the same composition using conventional processes.

[0058] After vacuuming, induction melting is performed directly. Refining relies solely on induction stirring; the refining temperature and time are the same as in Example 1. Aluminum and titanium granules are added through a standard hopper. Casting is completed after final deoxidation.

[0059] Test results: Analysis of the electrode ingots obtained in this comparative example showed that the O content was 15-25 ppm, the N content was 20-35 ppm, and the S content was 8-12 ppm. The number density of inclusions larger than 5 μm was 20-30 inclusions / cm³. 2 .

[0060] Comparative Example 2 This comparative example only involves plasma pretreatment, without auxiliary refining: In this comparative example, step S1 involves the same plasma pretreatment as in Example 1. After pretreatment, the plasma torch is turned off, and subsequent melting, refining (without plasma assistance), alloying, and casting are performed using the same operations as conventional VIM (Comparative Example 1).

[0061] Test results: Analysis of the electrode ingot samples obtained in this comparative example showed that the O content was 10-18 ppm, the N content was 15-25 ppm, and the S content was 5-8 ppm. The inclusion number density was approximately 15 inclusions / cm³. 2 The results showed that pretreatment alone improved purity, but the effect was limited.

[0062] Comparative Example 3 This comparative example only involves plasma-assisted refining, without any pretreatment. Preparation method: S1 does not undergo the plasma pretreatment described in Example 1, and is directly induction melted. After melting, an immersion-assisted refining process is performed using a plasma torch (parameters are the same as in Example 1). Subsequent alloying and casting are the same as in Example 1.

[0063] Test results: Analysis of the electrode ingot samples obtained in this comparative example showed that the O content was 6-10 ppm, the N content was 10-15 ppm, and the S content was 4-6 ppm. The inclusion number density was approximately 8 inclusions / cm³. 2 The results showed that the auxiliary refining effect was significant, but the purity index was still slightly inferior to that of the complete Example 1.

[0064] The detection results of Examples 1-3 and Comparative Examples 1-3 are shown in Table 1 below.

[0065] Table 1

[0066] As can be seen from Table 1 above: 1. The superior effect of the entire process of the present invention: Example 1 (complete three-stage plasma-assisted process) is significantly better than Comparative Example 1 (traditional VIM) in all purity indicators. The oxygen content is reduced by about 70-80%, the sulfur content is reduced by about 70%, and the number of large-size inclusions is reduced by more than 80%, which proves the great advantages of the preparation method of the present invention.

[0067] 2. Analysis of the Contribution of Each Process Step: Comparing Example 1 with Comparative Examples 2 and 3, it can be seen that either the "pretreatment" or "auxiliary refining" step alone can improve purity, but the effect is limited. When the two work synergistically, the effect is superimposed or even multiplied. Pretreatment reduces impurity input from the source, easing the burden on auxiliary refining; auxiliary refining, on the other hand, thoroughly enhances the purification kinetics within the melt. This indicates that the three-stage design of the preparation method of this invention has an inherent synergistic logic.

[0068] 3. Process Scalability and Functionality: Examples 2 and 3 demonstrate the flexibility of the method of the present invention. By changing the plasma atmosphere (Ar-H2), deep deoxidation in the refining stage can be achieved; by introducing an active gas (N2), precise micro-alloying (nitriding) can be achieved. This provides a new approach for preparing ultrapure ultrasupercritical high-temperature alloys with special functions (such as high strength and high corrosion resistance) via a one-step VIM process.

[0069] 4. Benefits to downstream processes: Ultra-pure VIM electrode ingots provide a better quality starting point for subsequent vacuum arc remelting (VAR) or electroslag remelting (ESR), which is expected to further reduce the level of impurities and inclusions in the final product and improve the yield and performance consistency.

[0070] In summary, the purification smelting method for high-temperature alloy return materials provided by this invention, through an innovative three-stage design, effectively overcomes the kinetic limitations of traditional VIM and achieves extreme control over the purity of ultra-supercritical high-temperature alloys, thus possessing significant industrial application value.

[0071] Example 4 This embodiment provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys, specifically including the following steps: S1. Loading and plasma pretreatment: Same as Example 1. However, the plasma torch pretreatment parameters were adjusted: the scanning speed remained at 10 cm / s and the distance was 100 mm, but the scanning time was set to 10 minutes.

[0072] S2. Induction melting and plasma-assisted refining: After the furnace charge melts, plasma-assisted refining is performed. The refining parameters are adjusted as follows: The plasma torch immersion depth is 5 mm.

[0073] The plasma torch oscillates at a frequency of 1 Hz and an amplitude of 10 mm.

[0074] The plasma torch power was set to 50 kW.

[0075] The refining temperature is controlled at 1500℃.

[0076] The refining time is set to 20 minutes.

[0077] In this step, the working gas of the plasma torch is an Ar-30%He mixture. The addition of helium is intended to enhance the thermal conductivity of the plasma arc.

[0078] S3. Alloying and Casting: After refining, the working gas is switched to high-purity argon. The subsequent steps of adding aluminum particles, titanium particles, final deoxidation, and casting are the same as in Example 1.

[0079] Test results: The obtained electrode ingots were pure, with O content ≤ 5 ppm, S content ≤ 3 ppm, and N content ≤ 10 ppm. The recovery rate of key alloying elements was ≥ 98.5%. The results indicate that under the stated parameters, this method can still produce qualified high-temperature alloys, and the use of an argon-helium mixture as the working gas is feasible.

[0080] Example 5 This embodiment provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys, specifically including the following steps: S1. Loading and plasma pretreatment: Same as Example 1. However, the plasma torch pretreatment parameters were adjusted: the scanning speed remained at 10 cm / s, the distance was 100 mm, and the scanning time was set to 30 minutes.

[0081] S2. Induction melting and plasma-assisted refining: After the furnace charge melts, plasma-assisted refining is performed. The refining parameters are adjusted as follows: The plasma torch immersion depth is 20 mm.

[0082] The plasma torch oscillates at a frequency of 5 Hz and an amplitude of 50 mm.

[0083] The plasma torch power was set to 200 kW.

[0084] The refining temperature is controlled at 1650℃.

[0085] The refining time is set to 60 minutes.

[0086] The working gas is high-purity argon.

[0087] S3. Alloying and Casting: Same as Example 1.

[0088] Test results: The obtained electrode ingot has extremely high purity, with O content ≤4 ppm, S content ≤2 ppm, and N content ≤9 ppm. The recovery rate of key alloying elements is ≥99.2%. Long-term, high-power refining helps to further remove impurities.

[0089] Example 6 This embodiment provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys, specifically including the following steps: S1. Charging, pretreatment, melting and preliminary refining: Same as Example 1. Pure argon plasma was used during the refining stage, with the same parameters as in Example 1.

[0090] S2. Plasma carburizing: During the final stage of refining, the plasma torch is kept running. Methane (CH4) gas, at a volume of 0.8%, is precisely mixed into the argon working gas and continuously introduced for 10 minutes. The methane is cracked and activated in the plasma arc, and the resulting active carbon atoms react with the molten pool to achieve carburization.

[0091] S3. Add other elements and casting: After carburizing is completed, switch back to pure argon gas, and then add aluminum and titanium particles and perform subsequent operations as per the steps in Example 1.

[0092] Test results: Analysis of the electrode ingot obtained in this embodiment showed that the carbon content of the alloy was controllable within the range of 100-150 ppm and was uniformly distributed. The O and S contents were comparable to those in Example 1 (O≤5 ppm, S≤3 ppm). The strength of the alloy was improved after carburizing.

[0093] Example 7 This embodiment provides a method for preparing ultrapure, ultrasupercritical high-temperature alloys, specifically including the following steps: S1. Charging, pretreatment, melting and preliminary refining: Same as Example 1. Pure argon plasma was used during the refining period, and the refining parameters were the same as in Example 1.

[0094] S2. Plasma carburizing: During the final stage of refining, the plasma torch is kept running. 0.3% by volume of high-purity acetylene (C2H2) gas is precisely mixed into the argon working gas and continuously introduced for 12 minutes. The acetylene rapidly decomposes in the high-temperature plasma arc, generating highly reactive carbon atoms that react with the molten pool to achieve carburizing.

[0095] S3. Add other elements and casting: After carburizing is completed, switch back to pure argon gas, and then add aluminum and titanium particles and perform subsequent operations as per the steps in Example 1.

[0096] Test results: Analysis of the electrode ingot samples obtained in this embodiment showed that the carbon content of the alloy could be controlled within the range of 100-180 ppm. Due to the high carbon content and strong reactivity of acetylene, effective carburizing could be achieved at a lower concentration and in a shorter time. The oxygen and sulfur content of the alloy was comparable to that of Example 1 (O≤5 ppm, S≤3 ppm). The strength and hardness of the alloy were significantly improved after carburizing.

[0097] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing an ultrapure, ultrasupercritical high-temperature alloy, characterized in that, Includes the following steps: S1: The alloy raw material is loaded into a vacuum induction furnace, a vacuum is drawn and induction heating is started to melt it and form a molten pool; S2: Immerse the plasma torch below the surface of the molten pool while applying induction electromagnetic stirring to perform refining; S3: Using a plasma torch, the alloying elements to be added are introduced into the active area of ​​the plasma torch, so that the alloying elements react with the molten pool or fall into the molten pool in the plasma environment. After final deoxidation and casting, an ultra-pure ultra-supercritical high-temperature alloy is obtained.

2. The method for preparing ultrapure, ultrasupercritical high-temperature alloys according to claim 1, characterized in that, The alloying element to be added includes at least one of the following conditions: A) Aluminum and titanium, wherein the mass ratio of aluminum to titanium is 1:0.6; B) Nitrogen or carbon added in gaseous form.

3. The method for preparing ultrapure ultrasupercritical high-temperature alloys according to claim 1, characterized in that, In step S1, after the alloy raw material is loaded into the vacuum induction furnace and before the vacuum is drawn and induction heating is started for melting, the process further includes: using the plasma torch to scan the surface of the furnace material in the vacuum induction furnace, with the plasma torch 100 mm away from the surface of the furnace material, the scanning speed being 10 cm / s, and the scanning time being 10-30 minutes.

4. The method for preparing ultrapure, ultrasupercritical high-temperature alloys according to claim 1, characterized in that, In step S2, the electrode end of the plasma torch is immersed to a depth of 5mm-20mm below the surface of the molten pool and oscillates back and forth at a frequency of 1Hz-5Hz with an oscillation amplitude of 10mm-50mm. The power of the plasma torch is 50kW-200kW, the refining temperature is 1500-1650℃, and the refining time is 20-60 minutes.

5. The method for preparing ultrapure, ultrasupercritical high-temperature alloys according to claim 1, characterized in that, The working gas of the plasma torch includes one of high-purity argon, an argon-hydrogen mixture, and an argon-helium mixture, wherein the hydrogen component in the argon-hydrogen mixture does not exceed 10%, and the helium component in the argon-helium mixture does not exceed 30%.

6. The method for preparing ultrapure, ultrasupercritical high-temperature alloys according to claim 2, characterized in that, In step S3, the introduction method is as follows: when the alloying element to be added is nitrogen or carbon added in gaseous form, the gas carrying the nitrogen or carbon element is mixed into the working gas of the plasma torch, and reacts with the molten pool after being activated by the plasma arc; the gas carrying the nitrogen or carbon element is mixed into the working gas of the plasma torch to form a mixed gas, and the volume fraction of the gas carrying the nitrogen or carbon element in the mixed gas is 0.3% to 0.8%.

7. The method for preparing ultrapure ultrasupercritical high-temperature alloys according to claim 2, characterized in that, In step S3, the introduction method is as follows: when the alloying elements to be added are aluminum and titanium, they are added through a feeding device that extends into the plasma torch arc zone, so that they fall into the molten pool under the protection of the plasma atmosphere.

8. The method for preparing ultrapure ultrasupercritical high-temperature alloys according to claim 3, characterized in that, The plasma torch scans the surface of the furnace charge in the vacuum induction furnace in a zigzag path.

9. An ultrapure ultra-supercritical high-temperature alloy obtained by the preparation method of any one of claims 1-8, characterized in that, The ultrapure, ultrasupercritical high-temperature alloy has an oxygen content ≤5 ppm and a sulfur content ≤3 ppm; the number of inclusions larger than 5 μm is less than 5 per cm. 2 The yields of aluminum and titanium are ≥99%; and the nitrogen content meets one of the following conditions: 1) Nitrogen content ≤ 10 ppm; 2) Nitrogen content is 50-80 ppm 3) Carbon content is 100-180 ppm.

10. The application of the ultrapure ultra-supercritical high-temperature alloy of claim 9 in the manufacture of high-temperature components for ultra-supercritical generator sets, aero engines, or gas turbines.

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