Advanced high-temperature alloy for aero-engine, bar, preparation method and application

Abstract

The invention discloses an advanced high-temperature alloy for an aero-engine, which comprises the following chemical components in percentage by weight: 0.04-0.10% of C; 16.0 to 19.0 parts of Cr (chromium); co: 3.0 to 8.0; 2.0 to 5.0 parts of W; 1.0 to 2.5 parts of Nb; 1.0 to 2.0 parts of V; b: less than or equal to 0.010; n: < = 0.01; 6.0 to 10.0 parts of Fe; and the balance of nickel and inevitable impurities. The invention further discloses a bar made of the alloy, a preparation method and application. By optimizing the alloy components and adding a proper amount of alloy elements, the nickel-based alloy with better comprehensive performance and temperature bearing capacity is obtained, the engineering application feasibility of the alloy can be guaranteed, and the application requirement of the commercial aviation field is met.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy preparation technology, specifically to a wrought high-temperature alloy with a service temperature above 815℃, good service performance and batch stability, and its manufacturing method. Background Technology

[0002] High-temperature alloys, especially nickel-based high-temperature alloys, are widely used in hot-section components of aero-engines due to their excellent resistance to oxidation and corrosion, high strength, and superior machinability (weldability). In recent years, with the development of commercial aero-engines in my country, higher requirements have been placed on the service life and stability of high-temperature alloy components. Taking commercial aero-engines as an example, the number of in-flight shutdowns per million flight hours should be less than three, and the time between overhauls (TBO) should be 15,000 to 20,000 flight hours or more. This places even higher demands on the long-term service life and stability of high-temperature alloy materials.

[0003] The combustion chambers and exhaust nozzles of aero-engines operate at high temperatures, are subject to certain levels of gas corrosion and moderate stress, and are often made of solution-strengthened nickel-based alloys. GH536 alloy is one of the most widely used alloys in these hot-end components, with a long-term operating temperature below 900℃ (around 815℃). However, this alloy is smelted using a "medium-frequency furnace + electroslag" process, which makes it difficult to control gaseous elements, easily leading to carbonitride segregation in the microstructure. This results in poor thermoplasticity and significantly affects the uniformity and stability of the forging microstructure. Therefore, developing nickel-based alloys with superior performance and higher stability to meet the material selection requirements of my country's next-generation aero-engines is an urgent issue.

[0004] A novelty search revealed two patents similar to this invention, as shown in Table 1.

[0005] Patent CN108866389A describes a low-cost, high-strength, and corrosion-resistant nickel-based superalloy, the composition of which is shown in Table 1 below. This patent improves the alloy's resistance to oxidation and corrosion by adding Cr and Co, strengthens it through solid solution by adding W and Mo, and strengthens it through age-hardening by precipitating γ′ phases from Al, Ti, and Nb. This alloy has an extremely high degree of alloying (Al+Ti+Nb), with a total content exceeding 7wt%, making it unsuitable for production via casting-forging and limiting its ability to be used in the engineering production of large-size forgings. Therefore, this severely restricts its application in combustion chambers and disc components.

[0006] Patent CN105838925A describes a high-temperature resistant nickel-based oxide alloy, the composition of which is shown in Table 1 below. This patent improves the alloy's high-temperature oxidation resistance by adding Cr and Al elements, but due to the extremely low amount of strengthening elements, the alloy has relatively low strength, especially at high temperatures, which cannot meet the requirements of hot-end components in aero-engines.

[0007] Table 1. Alloy composition (wt%) in the retrieved patents

[0008]

[0009] Therefore, further optimization of the alloy composition is needed to obtain a nickel-based alloy with better overall performance and temperature resistance, in order to ensure the feasibility of the alloy's engineering application and meet the application needs of the commercial aviation field. Summary of the Invention

[0010] Therefore, the technical problem to be solved by this invention is to provide an advanced high-temperature alloy for commercial aero-engines, which has better temperature resistance than GH3536 alloy and can operate at temperatures above 850°C. Another technical problem to be solved by this invention is to provide a method for preparing this alloy. Yet another technical problem to be solved by this invention is to provide applications of this alloy.

[0011] The technical solution of this invention is:

[0012] An advanced high-temperature alloy for aero-engines has the following chemical composition by weight percentage:

[0013] C: 0.04-0.10; Cr: 16.0-19.0; Co: 3.0-8.0; W: 2.0-5.0; Nb: 1.0-2.5; V: 1.0-2.0; B: ≤0.010; N: ≤0.01; Fe: 6.0-10.0; balance is nickel and unavoidable impurities.

[0014] The reasons for selecting this range of chemical composition for the alloy in this invention are as follows:

[0015] C: 0.04-0.10%

[0016] Carbon (C) is an essential element for carbide formation in nickel-based superalloys. A C content below 0.04% results in fewer carbides, which is detrimental to grain refinement and performance, and also hinders deoxidation during vacuum smelting. A C content above 0.10% leads to excessive carbide formation, resulting in excessive inclusions and segregation, causing grain inhomogeneity and deterioration of alloy plasticity.

[0017] Cr: 16.0-19.0%

[0018] The amount of Cr added is determined by two factors: first, to ensure the formation of a single-phase austenitic solid solution; and second, to consider resistance to high-temperature oxidation and corrosion, as Cr is one of the most effective elements for improving alloy oxidation resistance. Taking all factors into account, the Cr content is controlled between 16.0% and 19.0%.

[0019] Co: 3.0-8.0%

[0020] Co can form an austenitic matrix with elements such as Ni and Cr, improving the alloy's thermal strength and structural stability by reducing stacking fault energy and preventing the precipitation of harmful phases. However, excessive addition of Co will increase the alloy's cost. Considering all factors, the Co content in this alloy is controlled between 3.0% and 8.0%.

[0021] W: 2.0-5.0%

[0022] The addition of W is a major highlight of this patent's composition, especially the composite addition of W, Nb, and V. The high content of W, Nb, and V enhances the strength of the alloy matrix. Furthermore, replacing Mo with W, Nb, and V effectively avoids the drawback of Mo forming gaseous oxides at high temperatures, while maintaining the alloy's mechanical properties, thus improving the alloy's resistance to high-temperature oxidation.

[0023] Nb: 1.0-2.0%

[0024] Adding an appropriate amount of Nb can reduce the diffusion rate of other elements in the matrix, thereby improving the high-temperature strength and high-temperature structural stability of the material. However, excessive Nb can easily lead to segregation during smelting, resulting in metallurgical defects such as black spots. The Nb content in this alloy is controlled within the range of 1.0-2.0%.

[0025] V: 1.0-2.0%

[0026] The addition of V is a major highlight of this invention, as V and C can form stable carbides (VC) at high temperatures. Furthermore, the combined addition of W and Nb effectively controls the morphology and size of the alloy, strengthening it while simultaneously controlling grain size, which is beneficial for microstructure stability at high temperatures. However, excessive V leads to increased carbide content, increased segregation bands, and is detrimental to microstructure uniformity. The V content in this alloy is controlled at 1.0-2.0%.

[0027] Studies have shown that the combined addition of W, Nb, and V elements can interact to form complex carbides, resulting in a better strengthening effect. Therefore, the W+Nb+V content is specified to be ≥7.0%. In the composition system of this invention, the combined addition of these three elements has a significant strengthening effect. The main principle is that by adding elements such as W, V, and Nb, carbide structures of MC and M7C3 forms can be formed, which have better high-temperature stability. Through the control of the related technologies of this invention, they can be dispersed in the grain structure to achieve a better strengthening effect.

[0028] N: ≤0.010%

[0029] Excessive nitrogen (N) content in alloys promotes the formation of large-sized, abundant carbonitrides, which negatively impacts the uniformity of the alloy's grain structure and its thermoplasticity. Therefore, it is specifically recommended that the N content be controlled to ≤0.010%.

[0030] Fe: 6.0-10.0%

[0031] The addition of Fe is based on a comprehensive consideration of alloy performance, cost, and production stability. The Fe content in this alloy is controlled within the range of 6.0-10.0%.

[0032] According to the present invention, the advanced high-temperature alloy for aero-engines preferably has a W+Nb+V content ≥7.0.

[0033] According to the present invention, in an advanced high-temperature alloy for aero-engines, preferably, the high-temperature tensile properties of the bar are as follows: at 850°C, σ b For pressures above 250 MPa, σ 0.2 It is above 220MPa and δ5 is above 87%.

[0034] The present invention also provides a method for preparing a bar made of advanced high-temperature alloy for aero-engines, the method comprising vacuum induction smelting → casting electrode → electrode annealing → electroslag remelting → high-temperature homogenization diffusion → forging into a bar → heat treatment.

[0035] The vacuum induction smelting process includes:

[0036] (1) Add Ni, Cr, Co and W as main materials, and add C at the same time. Perform vacuum and high-power smelting, and use CO reaction to degas the steel to ensure that the O and H content in the molten steel is reduced to the control requirements.

[0037] (2) After the main material is completely dissolved, Nb is added for alloying, and the power is controlled at 200-600KW for smelting.

[0038] (3) Take a finished product sample for composition analysis. After the content of the main element meets the index requirements, Ar gas is introduced at a pressure of 9000-11000 Pa. After smelting for 5-10 minutes, the steel is tapped and the electrode is cast.

[0039] In the electroslag remelting process, the surface of the obtained induction electrode is ground clean and the electrode head is smelted downwards with a shrinkage cavity. The melting rate is set at 2.0-5.0 kg / min, and the current is controlled at 4000-6000 A and the power at 100-150 KW (lower limit of control).

[0040] In the heat treatment process, the forged bar stock is heat treated according to the following process:

[0041] Solution treatment: The sample is kept at 1140℃~1180℃ for 2h-4h and then air-cooled after being taken out of the furnace.

[0042] During the electrode grinding process described above, stains, oxide scale, water stains, etc., are not permitted. Steps (1)-(3) of the vacuum induction smelting process described above include the process of “vacuum induction smelting → casting electrode → electrode annealing”. In the electroslag remelting process described above, the lower limit of power control refers to the lower limit not being lower than 100 kW within the range.

[0043] According to a method for preparing bars made of advanced high-temperature alloys for aero-engines, as per the present invention, preferably, the high-temperature homogenization diffusion of the steel ingot before forging is performed by high-temperature diffusion annealing with a holding time of ≥30 hours; during the forging process, the steel ingot is upset once, to a height of 0.4-0.6 times its original height. This increases the forging ratio and improves the uniformity of the steel.

[0044] According to a method for preparing bars made of advanced high-temperature alloys for aero-engines according to the present invention, the high-temperature diffusion annealing with a holding temperature of ≥30h refers to high-temperature diffusion annealing of steel ingots at 1160-1190℃ for ≥30h.

[0045] According to a method for preparing bars made of advanced high-temperature alloys for aero-engines according to the present invention, the vacuum degree and power of the smelting in step (1) are ≤3.0Pa and ≤600Kw respectively.

[0046] This invention also provides the application of the aforementioned advanced high-temperature alloy for aero engines in aero engines.

[0047] The composition design of this invention is mainly based on the following points: 1) Replacing Fe with Co by increasing the Co content and reducing the Fe content. This improves the alloy's resistance to high-temperature oxidation and corrosion, and also enhances the alloy's high-temperature structural stability and heat resistance. 2) Replacing Mo with W, Nb, and V. The combined addition of W, Nb, and V can achieve a stronger solid solution strengthening effect than Mo, and avoids the drawback of Mo forming gaseous oxides at high temperatures, greatly improving the alloy's high-temperature resistance. 3) Controlling the amount of N added can effectively prevent the formation of large-sized carbonitrides, reduce structural segregation, and improve structural uniformity and formability.

[0048] The beneficial effects of this invention are:

[0049] This invention optimizes the alloy composition and adds appropriate amounts of alloying elements to obtain a nickel-based alloy with better overall performance and temperature resistance, thus ensuring the feasibility of the alloy's engineering application and meeting the application needs of the commercial aviation field.

[0050] The alloy bars prepared according to the chemical composition, production process, and heat treatment method provided in this technology, after testing, show performance significantly exceeding that of GH3536 alloy. They exhibit excellent performance at temperatures above 850℃ and are expected to become a potential candidate high-temperature alloy material for hot-end components such as combustion chambers in commercial aero-engines. Detailed Implementation

[0051] The alloy of this invention is smelted in a dual-furnace system of a 1-ton vacuum induction furnace and a 1-ton electroslag furnace. After high-temperature diffusion annealing and billet drawing, it undergoes heat treatment. Detailed embodiments are described below:

[0052] Example 1:

[0053] (1) Vacuum induction furnace smelting process:

[0054] The raw materials are selected from high-purity metals Ni, Cr, Co, and W, and their surfaces are thoroughly cleaned and free of oil. The main elements Ni, Cr, Co, and W are added according to the target composition, with special attention paid to the substitution of Si, Mn, and Cu, and C is added at the upper limit.

[0055] The vacuum is evacuated to below 2.7 Pa, and the power is increased to begin material processing, with the power controlled at 300-600 kW. Once the molten steel surface remains calm and no more bubbles emerge, indicating complete melting, the power is increased to 600-800 kW, and the temperature is raised to 1530℃ for refining. Subsequently, the steel temperature is lowered, and Nb element is added for alloying smelting. A sample of the finished product is analyzed. Once the content of all chemical elements is within the specified range, Ar is introduced at a pressure of 10000 Pa, and the steel is tapped to the casting electrode at a tapping temperature of 1470℃.

[0056] (2) Electroslag remelting process:

[0057] The surface of the induction electrode is ground clean, and the electrode head is smelted downwards with a shrinkage cavity. The melting rate is set at 2.7Kg / min and the control power is 100KW.

[0058] (3) Forging process:

[0059] The steel ingot is heated to 1180℃ and held for more than 40 hours for high-temperature diffusion. Then, the ingot is cooled to 1150℃ for forging, and upsetting is performed once to half the original height to increase the forging ratio. The ingot is then reheated in the furnace to 1150℃ and held for 120 minutes. The initial forging temperature is ≥1100℃, and the final forging temperature is 950℃.

[0060] (4) Heat treatment process:

[0061] The forged bars are heat-treated according to the following process:

[0062] Solution treatment: The sample was kept at 1140℃ for 4 hours, then removed from the furnace and air-cooled; then mechanical property tests were performed.

[0063] Example 2:

[0064] (1) Vacuum induction furnace smelting process:

[0065] The raw materials are selected from high-purity metals Ni, Cr, Co, and W, and their surfaces are thoroughly cleaned and free of oil. The main elements Ni, Cr, Co, and W are added according to the target composition, with special attention paid to the substitution of Si, Mn, and Cu, and C is added at the upper limit.

[0066] The vacuum is evacuated to below 2.7 Pa, and the power is increased to begin material processing, with the power controlled at 300-600 kW. Once the molten steel surface remains calm and no more bubbles emerge, indicating complete melting, the power is increased to 600-800 kW, and the temperature is raised to 1550℃ for refining. Subsequently, the steel temperature is lowered, and Nb element is added for alloying smelting. A sample of the finished product is analyzed. Once the content of all chemical elements is within the specified range, Ar is introduced at a pressure of 10000 Pa, and the steel is tapped to the casting electrode at a tapping temperature of 1480℃.

[0067] (2) Electroslag remelting process:

[0068] The surface of the induction electrode is ground clean, and the electrode head is smelted downwards with a shrinkage cavity. The melting rate is set at 3.2Kg / min and the control power is 150KW.

[0069] (3) Forging process:

[0070] The steel ingot is heated to 1190℃ and held for more than 30 hours for high-temperature diffusion. The ingot is then cooled to 1150℃ for forging, with a single upsetting operation to half its original height to increase the forging ratio. The ingot is then reheated in the furnace at 1120℃ and held for 120 minutes. The initial forging temperature is ≥1080℃, and the final forging temperature is 950℃.

[0071] (4) Heat treatment process:

[0072] The forged bars are heat-treated according to the following process:

[0073] Solution treatment: The sample was kept at 1150℃ for 3 hours, then removed from the furnace and air-cooled; then mechanical property tests were performed.

[0074] Example 3:

[0075] (1) Vacuum induction furnace smelting process:

[0076] The raw materials are selected from high-purity metals Ni, Cr, Co, and W, and their surfaces are thoroughly cleaned and free of oil. The main elements Ni, Cr, Co, and W are added according to the target composition, with special attention paid to the substitution of Si, Mn, and Cu, and C is added at the upper limit.

[0077] The vacuum is evacuated to below 2.7 Pa, and the power is increased to begin material processing, with the power controlled at 300-600 kW. Once the molten steel surface remains calm and no more bubbles emerge, indicating complete melting, the power is increased to 600-800 kW, and the temperature is raised to 1550℃ for refining. Subsequently, the steel temperature is lowered, and Nb element is added for alloying smelting. A sample of the finished product is analyzed. Once the content of all chemical elements is within the specified range, Ar is introduced at a pressure of 10000 Pa, and the steel is tapped to the casting electrode at a tapping temperature of 1460℃.

[0078] (2) Electroslag remelting process:

[0079] The surface of the induction electrode is ground clean, and the electrode head is smelted downwards with a shrinkage cavity. The melting rate is set at 3.8Kg / min and the control power is 200KW.

[0080] (3) Forging process:

[0081] The steel ingot is heated to 1160℃ and held for more than 50 hours for high-temperature diffusion. The ingot is then cooled to 1150℃ for forging, with a single upsetting operation to half its original height to increase the forging ratio. The ingot is then reheated in the furnace at 1110℃ and held for 120 minutes. The initial forging temperature is ≥1070℃, and the final forging temperature is 950℃.

[0082] (4) Heat treatment process:

[0083] The forged bars are heat-treated according to the following process:

[0084] Solution treatment: The sample was kept at 1160℃ for 2 hours, then removed from the furnace and air-cooled; then mechanical property tests were performed.

[0085] Example 4:

[0086] (1) Vacuum induction furnace smelting process:

[0087] The raw materials are selected from high-purity metals Ni, Cr, Co, and W, and their surfaces are thoroughly cleaned and free of oil. The main elements Ni, Cr, Co, and W are added according to the target composition, with special attention paid to the substitution of Si, Mn, and Cu, and C is added at the upper limit.

[0088] The vacuum is evacuated to below 2.7 Pa, and the power is increased to begin material processing, with the power controlled at 300-600 kW. Once the molten steel surface remains calm and no more bubbles emerge, indicating complete melting, the power is increased to 600-800 kW, and the temperature is raised to 1550℃ for refining. Subsequently, the steel temperature is lowered, and elements such as Ti, Al, Nb, and Zr are added for alloying smelting. A sample of the finished product is analyzed. Once the content of all chemical elements is within the specified range, Ar is introduced at a pressure of 10000 Pa, and the steel is tapped to the casting electrode at a tapping temperature of 1470℃.

[0089] (2) Electroslag remelting process:

[0090] The surface of the induction electrode is ground clean, and the electrode head is smelted downwards with a shrinkage cavity. The melting rate is set at 4.0 kg / min and the control power is 150 kW.

[0091] (3) Forging process:

[0092] The steel ingot is heated to 1170℃ and held for more than 40 hours for high-temperature diffusion. The ingot is then cooled to 1150℃ for forging, with a single upsetting operation to half its original height to increase the forging ratio. The ingot is then reheated in the furnace at 1120℃ and held for 120 minutes. The initial forging temperature is ≥1090℃, and the final forging temperature is 950℃.

[0093] (4) Heat treatment process:

[0094] The forged bars are heat-treated according to the following process:

[0095] Solution treatment: The sample was kept at 1180℃ for 2 hours, then removed from the furnace and air-cooled; then mechanical property tests were performed.

[0096] Four heats of alloy were produced using the chemical composition and production method designed according to this invention. The specific compositions of the alloys are shown in Table 2. Samples of the four heats of alloy were taken and mechanical property tests were conducted on each. The results are shown in Tables 3 to 5. Under the control of the above-described process, the performance of the invented alloy is superior to that of GH3526 alloy, and it exhibits excellent mechanical properties above 900℃, making it a promising candidate material for next-generation high-temperature alloys used in combustion chambers.

[0097] Table 2 Chemical composition of the alloy of the present invention, wt%.

[0098]

[0099] Table 3 High-temperature tensile properties of the alloy of the present invention

[0100]

[0101] Table 4 High-Temperature Creep Mechanical Properties of the Alloy of the Present Invention

[0102]

[0103] The successful development of this alloy not only meets the aerospace industry's demand for high-performance nickel-based alloys, but also lays a solid foundation for future research and application of nickel-based high-temperature alloys in my country.

Claims

1. An advanced high-temperature alloy for aero-engines, characterized in that: Its chemical composition by weight percentage is as follows: C: 0.04-0.10; Cr: 16.0-19.0; Co: 3.0-8.0; W: 2.0-5.0; Nb: 1.0-2.5; V：1.0-2.0； B: ≤0.010; N: ≤0.01; Fe: 6.0-10.0; balance is nickel and unavoidable impurities.

2. The advanced high-temperature alloy for aero-engines according to claim 1, characterized in that: The W+Nb+V content is ≥7.

0.

3. The bar stock made of advanced high-temperature alloy for aero-engines as described in claim 1, characterized in that: The high-temperature tensile properties of the bar are as follows: at 850℃, σ b For pressures above 250 MPa, σ 0.2 It is above 220MPa and δ5 is above 87%.

4. The method for preparing a bar made of advanced high-temperature alloy for aero-engines as described in claim 1, characterized in that: The method includes vacuum induction smelting → casting electrode → electrode annealing → electroslag remelting smelting → high-temperature homogenization diffusion → forging into materials → heat treatment. The vacuum induction smelting process includes: (1) Add Ni, Cr, Co and W as main materials, and add C at the same time. Perform vacuum and high-power smelting, and use CO reaction to degas the steel to ensure that the O and H content in the molten steel is reduced to the control requirements. (2) After the main material is completely dissolved, Nb is added for alloying, and the power is controlled at 200-600KW for smelting. (3) Take a finished product sample for composition analysis. After the content of the main element meets the index requirements, Ar gas is introduced at a pressure of 9000-11000 Pa. After smelting for 5-10 minutes, the steel is tapped and the electrode is cast. In the electroslag remelting process, the surface of the obtained induction electrode is ground clean and the electrode head is smelted downwards with a shrinkage cavity. The melting rate is set at 2.0-5.0 kg / min, and the current is controlled at 4000-6000 A and the power at 100-150 KW. In the heat treatment process, the forged bar stock is heat treated according to the following process: Solution treatment: The sample is kept at 1140℃~1180℃ for 2h-4h and then air-cooled after being taken out of the furnace.

5. The method for preparing a bar made of advanced high-temperature alloy for aero-engines according to claim 4, characterized in that: The high-temperature homogenization diffusion of the steel ingot before forging is a high-temperature diffusion annealing with a holding time of ≥30h; during the forging process, the steel ingot is upset once, upsetting to 0.4-0.6 of its original height.

6. The method for preparing a bar made of advanced high-temperature alloy for aero-engines according to claim 5, characterized in that: The high-temperature diffusion annealing with a holding temperature of ≥30h refers to the high-temperature diffusion annealing of steel ingots at 1160-1190℃ for ≥30h.

7. The method for preparing a bar made of advanced high-temperature alloy for aero-engines according to claim 4, characterized in that: The vacuum degree and power of the smelting in step (1) are ≤3.0Pa and ≤600Kw.

8. The application of the advanced high-temperature alloy for aero engines as described in claim 1 in aero engines.

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