Nickel-based high-temperature alloy for large-size high-temperature ultrahigh-pressure reaction kettle

Abstract

The invention relates to a nickel-based high-temperature alloy for a large-size high-temperature ultrahigh-pressure reaction kettle. The nickel-based high-temperature alloy comprises the following components in percentage by weight: less than or equal to 0.06% of C; less than or equal to 0.50% of Si; 0.50% or less of Mn; 1.5 to 2.0 percent of Ti; al < = 1.0%; cr: 14.5 to 17.5%; 2.5 to 3.3 percent of Nb; mo < = 2%; ni: 39.0 to 44%; co < = 1.0%; 0.01 to 0.5 percent of Mg; 0.20% or less of one or more of B and V elements; harmful elements are less than 2%; and the balance of Fe. The alloy has the advantages of high strength, good toughness and plasticity, excellent processability, low element segregation and the like, also has excellent high-temperature mechanical properties and high-temperature durability, can be used for a long time at high temperature and high pressure, can be widely applied to the fields of spaceflight and large gas turbines, especially large-size high-temperature ultrahigh-pressure reaction kettles, and has wide application prospects. And the production of the alloy forge piece for the reaction kettle with the nominal diameter phi of 140-500 mm can be met.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials and relates to a nickel-based high-temperature alloy for large-size high-temperature and ultra-high-pressure reactors. Background Technology

[0002] Gallium nitride (GaN) is the highest-performing third-generation semiconductor material. High-quality and large-size GaN substrates can significantly improve the performance and reliability of GaN devices. Therefore, obtaining high-quality, large-size (≥4 inches) GaN single crystals is a common goal pursued by various synthesis methods. The ammonothermal method is a method for growing crystals from supercritical ammonia under high temperature and ultra-high pressure (500–700℃, 100–600MPa).

[0003] Large-size (nominal diameter ≥ 140 mm) high-temperature and ultra-high-pressure reactors are key equipment for the ammonothermal process to prepare high-quality and large-size gallium nitride substrates. The reactors must withstand long-term exposure to complex operating conditions, including high temperatures (around 650℃), ultra-high pressures (above ~150 MPa), and corrosion from mineralizing agents (such as ammonium fluoride). Simultaneously, during startup, low-temperature (around -30℃) liquid ammonia must be introduced into the reactor. Nickel-based superalloys are the preferred materials for these reactors. Commercial superalloys such as Inconel 718 and Inconel 625, developed by companies like Special Metals and Haynes International, have been reported for use in manufacturing small-diameter high-temperature and ultra-high-pressure reactors (nominal diameter below 60 mm). International research institutions have conducted extensive studies on the high-temperature short-time tensile, creep, fatigue, and other mechanical properties and damage mechanisms of these materials. For example, Inconel 718 alloy can achieve a yield strength of over 800 MPa at 650℃, while also exhibiting good creep resistance and high fracture toughness, making it a commonly used material for small-sized (nominal diameter ≤140 mm) reactors. However, Inconel 718 alloy has a high Nb content, which easily leads to macroscopic segregation during the smelting of large ingots, making it difficult to meet the technical requirements for elemental segregation and processing of large-sized reactor forgings. Inconel 625 alloy has relatively low strength and cannot meet the high strength and toughness requirements of large-sized reactor forgings. To achieve the mass production and commercial application of large-sized gallium nitride single crystals, there is an urgent need to develop a nickel-based superalloy with high strength, good toughness and plasticity, excellent high-temperature performance, excellent processing performance, and low elemental segregation, providing support for the selection and manufacturing of materials for large-sized high-temperature and high-pressure reactors. Summary of the Invention

[0004] The purpose of this invention is to provide a nickel-based superalloy for large-size high-temperature and ultra-high-pressure reactors. This alloy has advantages such as high strength, good toughness and plasticity, excellent processing performance, and low element segregation. At the same time, it has excellent high-temperature mechanical properties and can be widely used in aerospace, large gas turbines, and especially in the field of large-size high-temperature and ultra-high-pressure reactors. It can meet the production requirements of alloy forgings for reactors with nominal diameters of Φ140~Φ500mm.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A nickel-based superalloy for large-size high-temperature and ultra-high-pressure reactors, with the following weight percentages of components: C ≤ 0.06%; Si ≤ 0.50%; Mn ≤ 0.50%; Ti: 1.5–2.0%; Al ≤ 1.0%; Cr: 14.5–17.5%; Nb: 2.5–3.3%; Mo ≤ 2%; Ni: 39.0–44%; Co ≤ 1.0%; Mg: 0.01–0.5%; and one or the sum of B and V. The composition is ≤0.2%; harmful elements <0.2%; balance is Fe. The above components are smelted and remelted. The remelted ingot is homogenized and heat-treated, then heated and held at 850-1180℃ for 2-6 hours to forge into forgings. The forgings are solution treated at 920-1050℃, stabilized at 810-860℃, and then aged at 720-760℃ and 620-650℃ to obtain a nickel-based high-temperature alloy for large-size high-temperature and ultra-high-pressure reactors.

[0007] The weight percentage of each component in the alloy is as follows: C: 0.01–0.05%; Si: 0.20–0.50%; Mn: 0.05–0.50%; Ti: 1.5–2.0%; Al: 0.1–0.8%; Cr: 14.5–17.0%; Nb: 2.5–3.0%; Mo: 0–1.2%; Ni: 39–43.5%; Co ≤ 1.0%; Mg: 0.01–0.5%; one or the sum of B and V: 0.02–0.1%; harmful elements < 0.2%; balance Fe.

[0008] The weight percentage of each component in the alloy is as follows: C: 0.01–0.05%; Si: 0.20–0.40%; Mn: 0.15–0.45%; Ti: 1.5–1.95%; Al: 0.1–0.8%; Cr: 14.5–17.0%; Nb: 2.5–2.9%; Mo: 0.58–1.2%; Ni: 39.5–43.5%; Co ≤ 0.8%; Mg: 0.05–0.2%; one or the sum of B and V: 0.02–0.07%; harmful elements < 0.2%; balance Fe.

[0009] The harmful elements are: Cu, P, S, Pb, Bi, Sb, Sn, As, O, and N.

[0010] The controlled ranges for harmful elements are as follows: Cu≤0.1%, P≤0.02%, S≤0.01%, Pb≤0.005%, Bi≤0.005%; Sb≤0.008%; Sn≤0.005%, As≤0.003%; O≤0.003%, N≤0.005%.

[0011] The method for preparing large-size high-temperature and ultra-high-pressure reactor nickel-based superalloys according to the present invention involves taking each component according to the above-mentioned proportions of nickel-based superalloys for reactors, melting them in an electric arc furnace or induction furnace (including atmospheric pressure induction furnace and vacuum induction furnace), casting them into ingots, and then remelting them. Electroslag remelting, vacuum arc remelting, or a combination of electroslag remelting and vacuum arc remelting can be used to prepare remelted ingots. The remelted ingots undergo homogenization heat treatment to reduce macroscopic segregation and reduce and eliminate the Laves phase. Then, the remelted ingots are heated and held at 850–1180°C for 2–6 hours to forge them into bars, rings, stepped shafts, and other forgings. The forgings are solution treated at 920–1050°C, stabilized at 810–860°C, and then aged at 720–760°C and 620–650°C. After machining and non-destructive testing, the nickel-based superalloy forgings for reactors are obtained upon passing the performance tests.

[0012] The main alloying elements play the following roles:

[0013] Ni: 39.0-44%; as the main alloying element, it is the key to improving the corrosion resistance and high temperature resistance of alloys. When added to nickel-based alloys, it transforms ferrite into a stable austenitic matrix. In addition, nickel can also form γ′ precipitate strengthening phases with elements such as Al, Ti, and Nb to strengthen the alloy.

[0014] Cr: 14.5–17.5%; It is an essential element for improving the alloy's oxidation resistance, hot corrosion resistance, and strength. In addition, Cr can reduce the stacking fault energy of solid solutions and improve high-temperature creep strength. However, too high a Cr content may promote the formation of harmful TCP phases, which will have an adverse effect on the alloy's toughness and plasticity. Therefore, its content should be strictly controlled within the range of 14.5–17.5%.

[0015] Nb: 2.5–3.3%; Nb is an element that stabilizes the γ′ strengthening phase in the alloy and improves the alloy's strength. However, when too much Nb is added, it will lead to the precipitation of harmful phases such as the η phase, σ phase, and Laves phase. At the same time, excessive Nb is prone to alloy segregation, which significantly reduces the stability of the alloy structure. Therefore, its content is strictly controlled at 2.5–3.3%.

[0016] Ti: 1.5–2.0%; Ti mainly forms MC carbides to suppress grain coarsening in the alloy, and also combines with Ni to form Ni3(Ti,Al), producing a significant age-hardening effect. However, when too much Ti is added, it reduces the stability of the γ′ phase at high temperatures and forms the η phase, which reduces the alloy's strength, toughness, plasticity, and long-term high-temperature structural stability. Therefore, its content is strictly controlled at 1.5–2.0%.

[0017] Al ≤ 1.0%; Al combines with Ni to form Ni3(Ti,Al), which has a precipitation strengthening effect on the alloy and is the key to improving the corrosion resistance and high temperature resistance of the material.

[0018] Mo≤2.0%; solid solution strengthening, mostly dissolved in the γ matrix, slows down the high-temperature diffusion rate of Al, Ti and Cr, strengthens the atomic bonding force in the solid solution, and forms stable and fine carbides with carbon elements, improving high-temperature performance and also improving the corrosion resistance of the alloy.

[0019] Both boron (B) and potassium (V) are beneficial for purifying grain boundaries and improving the high-temperature strength of alloys, making them more suitable for use in reactors. Boron significantly improves the durability and creep resistance of high-temperature alloys. However, excessive boron content can reduce alloy strength, so its range must be strictly controlled. The addition of microalloying element potassium (V) can improve segregation in alloy ingots and adjust the morphology, quantity, and distribution of carbides. However, excessive V addition may lead to the formation of the TCP phase, which has an adverse effect on the alloy.

[0020] At least one of B and V is within the above range, but to ensure that the alloy has excellent comprehensive performance, it is better to include both B and V.

[0021] Harmful elements and their control ranges: Cu≤0.1%, P≤0.02%, S≤0.01%, Pb≤0.005%, Bi≤0.005%; Sb≤0.008%; Sn≤0.005%, As≤0.003%; O≤0.003%, N≤0.005%. Excessive levels of these elements will lead to deterioration of properties such as corrosion resistance, oxidation resistance, creep resistance, or fracture toughness, and may even cause difficulties in hot working or segregation; therefore, strict control is necessary.

[0022] The alloy described in this invention, through the design of its elements and proportions, forms a new alloy. Through smelting, the alloy composition is precisely controlled within the optimal range of this invention, while simultaneously minimizing the residue of non-metallic inclusions and harmful impurity elements (O, N, S, P, etc.) to achieve pure smelting, thereby improving processing plasticity and enhancing the overall performance of the material. By controlling the heating temperature, holding time, and deformation amount during hot working, the uniformity of the product's microstructure is ensured, reducing defects and improving production efficiency and yield. Based on precise control of chemical composition and hot working technology, the microstructure of the product is effectively controlled through the regulation of key heat treatment process parameters. For example, when the alloy of this invention is within the alloy proportion range, forging produces forged products with a uniform and fine initial grain structure. Through solution treatment, stabilization, and aging, the precipitation of carbides and strengthening phases (γ′ and γ″ phases) in the alloy is promoted, giving the alloy excellent room temperature strength and toughness as well as high-temperature performance.

[0023] The beneficial effects of the alloy described in this invention are as follows:

[0024] (1) The segregation of Inconel 718 alloy is caused by the Nb- and Mo-rich Laves phase. Compared with Inconel 718 alloy, the alloy of this invention reduces the Nb content, which can reduce the formation of segregation and promote a more uniform distribution of strengthening elements in the alloy. At the same time, reducing or eliminating the Mo element reduces segregation and is beneficial to improving the machinability and machinability of the alloy. Increasing the Ti content ensures the total Nb+Ti content in the alloy, resulting in a reasonable chemical composition, low compositional segregation, and excellent machinability, enabling the smelting of low-segregation large-size steel ingots.

[0025] (2) The alloy described in this invention has comparable comprehensive properties to Inconel 718 alloy. It has high toughness at low temperatures and high strength at high temperatures. The high Ni and Cr content gives the alloy advantages such as high temperature resistance and corrosion resistance, and it can be used reliably for a long time under thermomechanical fatigue, high temperature and high pressure, oxidation and gas corrosion atmosphere.

[0026] (3) The alloy described in this invention can be used to manufacture equipment components requiring high toughness through machining, and is particularly suitable as a material for large-size high-temperature and ultra-high-pressure reactors to achieve the preparation of large-size, high-quality gallium nitride single crystals. This has a significant positive impact on promoting technological progress and industrial development in related industries.

[0027] The applicant's experimental verification:

[0028] (1) The alloy described in this invention has been experimentally verified to have a tensile strength Rm of 1202-1317 MPa and a yield strength Rp of 1202-1317 MPa at room temperature. 0.2With a tensile strength of 1002-1100 MPa and an elongation of A21-24%, it meets the performance requirements of alloy forgings for large-size reactors at room temperature: tensile strength ≥1150 MPa, yield strength ≥900 MPa, and elongation ≥12%.

[0029] (2) The alloy described in this invention has been tested and verified to have an impact energy of 62 to 108 J at a low temperature of -60℃, which meets the performance requirement of ≥60 J for alloy forgings for large-size reactors at -60℃.

[0030] (3) The alloy described in this invention has been tested and verified to have a tensile strength of 987-1039 MPa and a yield strength of 858-912 MPa at a high temperature of 650℃, which meets the performance requirements of alloy forgings for large-size reactors with a tensile strength ≥980 MPa and a yield strength ≥820 MPa at 650℃.

[0031] (4) The alloy described in this invention has been tested and verified to have a cutting speed of 14.13 to 16.64 mm / min and excellent machinability.

[0032] (5) The alloy described in this invention has been tested and verified to have a corrosion rate of 0.046 mm / a in 25% nitric acid at 20°C, which shows that it has excellent corrosion resistance. Detailed Implementation

[0033] Example 1:

[0034] According to the proportions of nickel-based high-temperature alloy described in Table 1, each component was taken, and 2300 kg of new material was melted by vacuum induction melting. The material was then electroslag remelted into Φ600 mm steel ingots (furnace number M220100). The ingots were then upset, drawn, and forged into bars. After solution treatment, aging treatment, and machining, the bars for reactors with a nominal diameter of Φ140 mm were finally obtained.

[0035] Example 2:

[0036] According to the proportions of nickel-based high-temperature alloy described in Table 1, Example 2, each component was taken, and 2600 kg of new material was vacuum induction melted. The material was then vacuum self-consumable remelted into Φ600 mm steel ingots (furnace number R230011). The ingots were forged into Φ600 mm round bars, and then processed into rings through upsetting, drawing, and ring forging. Finally, the ring forgings for reactors with a nominal diameter of Φ140 mm were obtained through solution treatment, aging treatment, and machining.

[0037] Example 3:

[0038] According to the proportions of nickel-based high-temperature alloy described in Table 1, Example 3, each component was taken, and 4600 kg of new material was melted by vacuum induction melting. The material was then electroslag remelted into Φ660 mm steel ingots (furnace number L220104), and then vacuum consumable remelted into Φ760 mm consumable ingots (furnace number IV220069). After upsetting and drawing, the material was forged into a stepped shaft. Finally, after solution treatment, aging treatment, and machining, a stepped shaft forging with a nominal diameter of Φ140 mm for a high-temperature and ultra-high-pressure reactor was obtained.

[0039] Example 4

[0040] According to the proportions of nickel-based high-temperature alloy described in Table 1, Example 4, each component was taken, and 5500 kg of new material was melted by vacuum induction melting. The material was then electroslag remelted into a Φ750 mm steel ingot, and then vacuum self-consumable remelted into a Φ880 mm self-consumable ingot. After upsetting and drawing, the material was forged into a Φ750 mm bar. Finally, after solution treatment, aging treatment, and machining, a nickel-based alloy forging for a high-temperature and ultra-high-pressure reactor with a nominal diameter of φ200 mm was obtained.

[0041] Comparative Example

[0042] According to the proportions of the Inconel 718 alloy in Table 1, each component was taken and 2500 kg of the new material was melted in vacuum induction. The material was then electroslag remelted into Φ400 mm steel ingots, which were then upset, drawn, and forged into Φ160 mm bars. Finally, the forgings for high-temperature and ultra-high-pressure reactors with a nominal diameter of Φ60 mm were obtained through solution treatment, aging treatment, and machining.

[0043] Table 1. Chemical composition (by weight) of the alloys in the examples and comparative examples.

[0044]

[0045] Table 2. Room temperature mechanical properties of alloys from the examples and comparative examples.

[0046]

[0047] The room temperature mechanical properties of the alloys in the examples and comparative examples were tested according to GB / T 228.1. As shown in Table 2, the room temperature tensile strength Rm of the large-sized forgings prepared by the method described in this invention is 1202-1317 MPa, and the yield strength Rp is... 0.2 With a tensile strength of ≥1150MPa, an elongation of A of 21-24%, and a reduction of area Z of 23-54%, it can meet the performance requirements of alloy forgings for large-size reactors under room temperature conditions, which are ≥1150MPa, ≥900MPa, and ≥12%, and can be used for the preparation of large-size reactors.

[0048] Table 3 Low-temperature impact properties of the alloys in the examples and comparative examples.

[0049]

[0050] The low-temperature impact properties of the alloys in the examples and comparative examples were tested according to GB / T 229. As shown in Table 3, the low-temperature impact energy of the large-size forgings prepared by the method described in this invention is 62-888 J at -60℃ (the impact energy varies depending on the specifications of the forged products; smaller specifications and larger forging ratios result in finer grain size, better strength, and better impact performance. Furthermore, differences in product specifications, such as rings and straight bars, as well as forging methods, also lead to significant performance variations). These forgings exhibit excellent low-temperature toughness and meet the performance requirement of ≥60 J impact energy at -60℃ for alloy forgings used in large-size reactors, making them suitable for the fabrication of large-size reactors.

[0051] Table 4. High-temperature mechanical properties of alloys from the examples and comparative examples.

[0052]

[0053] The high-temperature mechanical properties of the alloys in the examples and comparative examples were tested according to GB / T 228.2. As shown in Table 4, the large-size forgings prepared by the method described in this invention have a high-temperature tensile strength of 1008-1039 MPa, a yield strength of 858-912 MPa, an elongation A of 0.5-28.5%, and a reduction of area Z of 30-63% at 650℃. They have excellent high-temperature mechanical properties and can meet the performance requirements of alloy forgings for large-size reactors with a tensile strength ≥980 MPa and a yield strength ≥820 MPa at 650℃. They can be used for the preparation of large-size reactors.

[0054] Table 5. Machining properties of the alloys in the examples and comparative examples.

[0055]

[0056] As shown in Table 5, the cutting speed range of large-size forgings prepared by the method described in this invention can reach 14.13 to 16.64 mm / min. Compared with Inconel 718 alloy, it has excellent machinability, can be cut at higher speeds, and not only has less wear, but also improves machining efficiency.

[0057] Samples of the forgings from the examples were taken and subjected to uniform corrosion rate testing according to GB / T 39534. The corrosion rate of the alloy in 25% nitric acid at 20°C was 0.046 mm / a, which shows excellent corrosion resistance. The high Ni and Cr content also gives the alloy advantages such as high temperature resistance and corrosion resistance.

[0058] This invention is not limited to the above embodiments. The above embodiments and descriptions in the specification are only illustrative of the principles of this invention. Various changes and modifications can be made to this invention without departing from the spirit and scope of this invention, and all of these fall within the scope of protection claimed by this invention.

Claims

1. A nickel-based superalloy for large-size high-temperature and ultra-high-pressure reactors, characterized in that, The weight percentages of each component in this alloy are as follows: C ≤ 0.06%; Si ≤ 0.50%; Mn ≤ 0.50%; Ti: 1.5–2.0%; Al ≤ 1.0%; Cr: 14.5–17.5%; Nb: 2.5–3.3%; Mo ≤ 2%; Ni: 39.0–44%; Co ≤ 1.0%; Mg: 0.01–0.5%; One or the sum of B and V: ≤ 0.2%; Harmful elements <0.2%; balance Fe. The above components are smelted and remelted. The remelted ingot is homogenized and heat-treated, then heated and held at 850-1180℃ for 2-6 hours to forge into forgings. The forgings are solution treated at 920-1050℃, stabilized at 810-860℃, and then aged at 720-760℃ and 620-650℃ to obtain a nickel-based high-temperature alloy for large-size high-temperature and ultra-high-pressure reactors.

2. The alloy according to claim 1, characterized in that, The weight percentage of each component in the alloy is as follows: C: 0.01–0.05%; Si: 0.20–0.50%; Mn: 0.05–0.50%; Ti: 1.5–2.0%. Al: 0.1–0.8%; Cr: 14.5–17.0%; Nb: 2.5–3.0%; Mo: 0–1.2%; Ni: 39–43.5%; Co ≤ 1.0%; Mg: 0.01–0.5%; one or the sum of B and V: 0.02–0.1%; harmful elements < 0.2%; balance Fe.

3. The alloy according to claim 1, characterized in that, The weight percentages of each component in the alloy are as follows: C: 0.01–0.05%; Si: 0.20–0.40%; Mn: 0.15–0.45%; Ti: 1.5–1.95%; Al: 0.1–0.8%; Cr: 14.5–17.0%; Nb: 2.5–2.9%. Mo: 0.58–1.2%; Ni: 39.5–43.5%; Co ≤ 0.8%; Mg: 0.05–0.2%; one or the sum of B and V: 0.02–0.07%; harmful elements < 0.2%; balance Fe.

4. The alloy according to any one of claims 1 to 3, characterized in that: The harmful elements are: Cu, P, S, Pb, Bi, Sb, Sn, As, O, and N.

5. The harmful element according to claim 4, characterized in that: The control range of the harmful elements: Cu≤0.1%, P≤0.02%, S≤0.01%, Pb≤0.005%, Bi≤0.005%; Sb≤0.008%; Sn≤0.005%, As≤0.003%; O≤0.003%, N≤0.005%.

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